svm: more fifo refactor/cleanup

Change-Id: Ie76c69641c8598164d0d00fd498018037258fd86
Signed-off-by: Florin Coras <fcoras@cisco.com>

12 files changed, 959 insertions, 715 deletions

diff --git a/src/plugins/http_static/static_server.c b/src/plugins/http_static/static_server.c
index ac07f6f5534..860e03997bd 100644
--- a/src/plugins/http_static/static_server.c
+++ b/src/plugins/http_static/static_server.c
@@ -379,7 +379,7 @@ static_send_data (http_session_t * hs, u8 * data, u32 length, u32 offset)
     {
       int actual_transfer;
 
-      actual_transfer = svm_fifo_enqueue_nowait
+      actual_transfer = svm_fifo_enqueue
 	(hs->tx_fifo, bytes_to_send, data + offset);
 
       /* Made any progress? */
diff --git a/src/plugins/quic/quic.c b/src/plugins/quic/quic.c
index 5ff962d8102..e2c2514858c 100644
--- a/src/plugins/quic/quic.c
+++ b/src/plugins/quic/quic.c
@@ -138,9 +138,9 @@ quic_send_datagram (session_t * udp_session, quicly_datagram_t * packet)
       clib_memcpy (&hdr.rmt_ip.ip6, &sa6->sin6_addr, 16);
     }
 
-  rv = svm_fifo_enqueue_nowait (f, sizeof (hdr), (u8 *) & hdr);
+  rv = svm_fifo_enqueue (f, sizeof (hdr), (u8 *) & hdr);
   ASSERT (rv == sizeof (hdr));
-  if (svm_fifo_enqueue_nowait (f, len, packet->data.base) != len)
+  if (svm_fifo_enqueue (f, len, packet->data.base) != len)
     return 1;
   return 0;
 }
@@ -242,7 +242,7 @@ quic_on_receive (quicly_stream_t * stream, size_t off, const void *src,
     to_enqueue = len;
   // TODO what happens to the excess bytes?
 
-  svm_fifo_enqueue_nowait (rx_fifo, to_enqueue, src);
+  svm_fifo_enqueue (rx_fifo, to_enqueue, src);
 
   // Notify app
   app_wrk = app_worker_get_if_valid (stream_session->app_wrk_index);
diff --git a/src/plugins/tlsmbedtls/tls_mbedtls.c b/src/plugins/tlsmbedtls/tls_mbedtls.c
index c54d17cd121..294f7126c87 100644
--- a/src/plugins/tlsmbedtls/tls_mbedtls.c
+++ b/src/plugins/tlsmbedtls/tls_mbedtls.c
@@ -167,7 +167,7 @@ tls_net_send (void *ctx_indexp, const unsigned char *buf, size_t len)
   ctx_index = pointer_to_uword (ctx_indexp);
   ctx = mbedtls_ctx_get (ctx_index);
   tls_session = session_get_from_handle (ctx->tls_session_handle);
-  rv = svm_fifo_enqueue_nowait (tls_session->tx_fifo, len, buf);
+  rv = svm_fifo_enqueue (tls_session->tx_fifo, len, buf);
   if (rv < 0)
     return MBEDTLS_ERR_SSL_WANT_WRITE;
   tls_add_vpp_q_tx_evt (tls_session);
@@ -185,7 +185,7 @@ tls_net_recv (void *ctx_indexp, unsigned char *buf, size_t len)
   ctx_index = pointer_to_uword (ctx_indexp);
   ctx = mbedtls_ctx_get (ctx_index);
   tls_session = session_get_from_handle (ctx->tls_session_handle);
-  rv = svm_fifo_dequeue_nowait (tls_session->rx_fifo, len, buf);
+  rv = svm_fifo_dequeue (tls_session->rx_fifo, len, buf);
   return (rv < 0) ? 0 : rv;
 }
 
@@ -516,8 +516,8 @@ mbedtls_ctx_read (tls_ctx_t * ctx, session_t * tls_session)
       return 0;
     }
 
-  enq = svm_fifo_enqueue_nowait (app_session->rx_fifo, read,
-				 mm->rx_bufs[thread_index]);
+  enq = svm_fifo_enqueue (app_session->rx_fifo, read,
+			  mm->rx_bufs[thread_index]);
   ASSERT (enq == read);
   vec_reset_length (mm->rx_bufs[thread_index]);
 
diff --git a/src/plugins/unittest/svm_fifo_test.c b/src/plugins/unittest/svm_fifo_test.c
index 9e834a1a056..99f0e5044d6 100644
--- a/src/plugins/unittest/svm_fifo_test.c
+++ b/src/plugins/unittest/svm_fifo_test.c
@@ -214,7 +214,7 @@ sfifo_test_fifo1 (vlib_main_t * vm, unformat_input_t * input)
   /*
    * Enqueue an initial (un-dequeued) chunk
    */
-  rv = svm_fifo_enqueue_nowait (f, sizeof (u32), (u8 *) test_data);
+  rv = svm_fifo_enqueue (f, sizeof (u32), (u8 *) test_data);
   SFIFO_TEST ((rv == sizeof (u32)), "enqueued %d", rv);
   SFIFO_TEST ((f->tail == 4), "fifo tail %u", f->tail);
 
@@ -228,7 +228,7 @@ sfifo_test_fifo1 (vlib_main_t * vm, unformat_input_t * input)
       data = (u8 *) (test_data + (2 * i + 1));
       if (i == 0)
 	{
-	  rv = svm_fifo_enqueue_nowait (f, sizeof (u32), data);
+	  rv = svm_fifo_enqueue (f, sizeof (u32), data);
 	  rv = rv > 0 ? 0 : rv;
 	}
       else
@@ -247,8 +247,8 @@ sfifo_test_fifo1 (vlib_main_t * vm, unformat_input_t * input)
     vlib_cli_output (vm, "fifo after odd segs: %U", format_svm_fifo, f, 1);
 
   SFIFO_TEST ((f->tail == 8), "fifo tail %u", f->tail);
-  SFIFO_TEST ((svm_fifo_number_ooo_segments (f) == 2),
-	      "number of ooo segments %u", svm_fifo_number_ooo_segments (f));
+  SFIFO_TEST ((svm_fifo_n_ooo_segments (f) == 2),
+	      "number of ooo segments %u", svm_fifo_n_ooo_segments (f));
 
   /*
    * Try adding a completely overlapped segment
@@ -265,8 +265,8 @@ sfifo_test_fifo1 (vlib_main_t * vm, unformat_input_t * input)
   if (verbose)
     vlib_cli_output (vm, "fifo after overlap seg: %U", format_svm_fifo, f, 1);
 
-  SFIFO_TEST ((svm_fifo_number_ooo_segments (f) == 2),
-	      "number of ooo segments %u", svm_fifo_number_ooo_segments (f));
+  SFIFO_TEST ((svm_fifo_n_ooo_segments (f) == 2),
+	      "number of ooo segments %u", svm_fifo_n_ooo_segments (f));
 
   /*
    * Make sure format functions are not buggy
@@ -295,8 +295,8 @@ sfifo_test_fifo1 (vlib_main_t * vm, unformat_input_t * input)
   if (verbose)
     vlib_cli_output (vm, "fifo before missing link: %U", format_svm_fifo, f,
 		     1);
-  SFIFO_TEST ((svm_fifo_number_ooo_segments (f) == 1),
-	      "number of ooo segments %u", svm_fifo_number_ooo_segments (f));
+  SFIFO_TEST ((svm_fifo_n_ooo_segments (f) == 1),
+	      "number of ooo segments %u", svm_fifo_n_ooo_segments (f));
   ooo_seg = svm_fifo_first_ooo_segment (f);
   SFIFO_TEST ((ooo_seg->start == 12),
 	      "first ooo seg position %u", ooo_seg->start);
@@ -306,20 +306,20 @@ sfifo_test_fifo1 (vlib_main_t * vm, unformat_input_t * input)
   /*
    * Enqueue the missing u32
    */
-  rv = svm_fifo_enqueue_nowait (f, sizeof (u32), (u8 *) (test_data + 2));
+  rv = svm_fifo_enqueue (f, sizeof (u32), (u8 *) (test_data + 2));
   if (verbose)
     vlib_cli_output (vm, "fifo after missing link: %U", format_svm_fifo, f,
 		     1);
   SFIFO_TEST ((rv == 20), "bytes to be enqueued %u", rv);
-  SFIFO_TEST ((svm_fifo_number_ooo_segments (f) == 0),
-	      "number of ooo segments %u", svm_fifo_number_ooo_segments (f));
+  SFIFO_TEST ((svm_fifo_n_ooo_segments (f) == 0),
+	      "number of ooo segments %u", svm_fifo_n_ooo_segments (f));
 
   /*
    * Collect results
    */
   for (i = 0; i < 7; i++)
     {
-      rv = svm_fifo_dequeue_nowait (f, sizeof (u32), (u8 *) & data_word);
+      rv = svm_fifo_dequeue (f, sizeof (u32), (u8 *) & data_word);
       if (rv != sizeof (u32))
 	{
 	  clib_warning ("bytes dequeues %u", rv);
@@ -356,14 +356,14 @@ sfifo_test_fifo1 (vlib_main_t * vm, unformat_input_t * input)
 
   rv = svm_fifo_enqueue_with_offset (f, 8 - f->tail, 21, data);
   SFIFO_TEST ((rv == 0), "ooo enqueued %u", rv);
-  SFIFO_TEST ((svm_fifo_number_ooo_segments (f) == 1),
-	      "number of ooo segments %u", svm_fifo_number_ooo_segments (f));
+  SFIFO_TEST ((svm_fifo_n_ooo_segments (f) == 1),
+	      "number of ooo segments %u", svm_fifo_n_ooo_segments (f));
 
   /* add missing data to be able to dequeue something */
-  rv = svm_fifo_enqueue_nowait (f, 4, data);
+  rv = svm_fifo_enqueue (f, 4, data);
   SFIFO_TEST ((rv == 32), "enqueued %u", rv);
-  SFIFO_TEST ((svm_fifo_number_ooo_segments (f) == 0),
-	      "number of ooo segments %u", svm_fifo_number_ooo_segments (f));
+  SFIFO_TEST ((svm_fifo_n_ooo_segments (f) == 0),
+	      "number of ooo segments %u", svm_fifo_n_ooo_segments (f));
 
   vec_validate (data_buf, vec_len (test_data));
   svm_fifo_peek (f, 0, 4, data_buf);
@@ -398,13 +398,13 @@ sfifo_test_fifo1 (vlib_main_t * vm, unformat_input_t * input)
   if (verbose)
     vlib_cli_output (vm, "fifo after enqueue: %U", format_svm_fifo, f, 1);
 
-  rv = svm_fifo_enqueue_nowait (f, 29, data);
+  rv = svm_fifo_enqueue (f, 29, data);
   if (verbose)
     vlib_cli_output (vm, "fifo after enqueueing 29: %U", format_svm_fifo, f,
 		     1);
   SFIFO_TEST ((rv == 32), "ooo enqueued %u", rv);
-  SFIFO_TEST ((svm_fifo_number_ooo_segments (f) == 0),
-	      "number of ooo segments %u", svm_fifo_number_ooo_segments (f));
+  SFIFO_TEST ((svm_fifo_n_ooo_segments (f) == 0),
+	      "number of ooo segments %u", svm_fifo_n_ooo_segments (f));
 
   vec_validate (data_buf, vec_len (data));
   svm_fifo_peek (f, 0, vec_len (data), data_buf);
@@ -459,8 +459,8 @@ sfifo_test_fifo2 (vlib_main_t * vm)
     }
 
   /* Expected result: one big fat chunk at offset 4 */
-  SFIFO_TEST ((svm_fifo_number_ooo_segments (f) == 1),
-	      "number of ooo segments %u", svm_fifo_number_ooo_segments (f));
+  SFIFO_TEST ((svm_fifo_n_ooo_segments (f) == 1),
+	      "number of ooo segments %u", svm_fifo_n_ooo_segments (f));
   ooo_seg = svm_fifo_first_ooo_segment (f);
   SFIFO_TEST ((ooo_seg->start == 4),
 	      "first ooo seg position %u", ooo_seg->start);
@@ -468,7 +468,7 @@ sfifo_test_fifo2 (vlib_main_t * vm)
 	      "first ooo seg length %u", ooo_seg->length);
 
   data64 = 0;
-  rv = svm_fifo_enqueue_nowait (f, sizeof (u32), (u8 *) & data64);
+  rv = svm_fifo_enqueue (f, sizeof (u32), (u8 *) & data64);
   SFIFO_TEST ((rv == 3000), "bytes to be enqueued %u", rv);
 
   svm_fifo_free (f);
@@ -493,8 +493,8 @@ sfifo_test_fifo2 (vlib_main_t * vm)
     }
 
   /* Expecting the same result: one big fat chunk at offset 4 */
-  SFIFO_TEST ((svm_fifo_number_ooo_segments (f) == 1),
-	      "number of ooo segments %u", svm_fifo_number_ooo_segments (f));
+  SFIFO_TEST ((svm_fifo_n_ooo_segments (f) == 1),
+	      "number of ooo segments %u", svm_fifo_n_ooo_segments (f));
   ooo_seg = svm_fifo_first_ooo_segment (f);
   SFIFO_TEST ((ooo_seg->start == 4),
 	      "first ooo seg position %u", ooo_seg->start);
@@ -502,7 +502,7 @@ sfifo_test_fifo2 (vlib_main_t * vm)
 	      "first ooo seg length %u", ooo_seg->length);
 
   data64 = 0;
-  rv = svm_fifo_enqueue_nowait (f, sizeof (u32), (u8 *) & data64);
+  rv = svm_fifo_enqueue (f, sizeof (u32), (u8 *) & data64);
 
   SFIFO_TEST ((rv == 3000), "bytes to be enqueued %u", rv);
 
@@ -665,7 +665,7 @@ sfifo_test_fifo3 (vlib_main_t * vm, unformat_input_t * input)
 
   /* Add the first segment in order for non random data */
   if (!randomize)
-    svm_fifo_enqueue_nowait (f, generate[0].len, (u8 *) data_pattern);
+    svm_fifo_enqueue (f, generate[0].len, (u8 *) data_pattern);
 
   /*
    * Expected result: one big fat chunk at offset 1 if randomize == 1
@@ -683,7 +683,7 @@ sfifo_test_fifo3 (vlib_main_t * vm, unformat_input_t * input)
       u32 bytes_to_enq = 1;
       if (in_seq_all)
 	bytes_to_enq = total_size;
-      rv = svm_fifo_enqueue_nowait (f, bytes_to_enq, data_pattern + 0);
+      rv = svm_fifo_enqueue (f, bytes_to_enq, data_pattern + 0);
 
       if (verbose)
 	vlib_cli_output (vm, "in-order enqueue returned %d", rv);
@@ -694,7 +694,7 @@ sfifo_test_fifo3 (vlib_main_t * vm, unformat_input_t * input)
     }
 
   SFIFO_TEST ((svm_fifo_has_ooo_data (f) == 0), "number of ooo segments %u",
-	      svm_fifo_number_ooo_segments (f));
+	      svm_fifo_n_ooo_segments (f));
 
   /*
    * Test if peeked data is the same as original data
@@ -717,7 +717,7 @@ sfifo_test_fifo3 (vlib_main_t * vm, unformat_input_t * input)
     }
   else
     {
-      svm_fifo_dequeue_nowait (f, vec_len (data_pattern), data_buf);
+      svm_fifo_dequeue (f, vec_len (data_pattern), data_buf);
       if (compare_data
 	  (data_buf, data_pattern, 0, vec_len (data_pattern), &j))
 	{
@@ -787,11 +787,11 @@ sfifo_test_fifo4 (vlib_main_t * vm, unformat_input_t * input)
 	}
     }
 
-  svm_fifo_enqueue_nowait (f, sizeof (u8), &test_data[0]);
+  svm_fifo_enqueue (f, sizeof (u8), &test_data[0]);
 
   vec_validate (data_buf, vec_len (test_data));
 
-  svm_fifo_dequeue_nowait (f, vec_len (test_data), data_buf);
+  svm_fifo_dequeue (f, vec_len (test_data), data_buf);
   rv = compare_data (data_buf, test_data, 0, vec_len (test_data), &j);
   if (rv)
     vlib_cli_output (vm, "[%d] dequeued %u expected %u", j, data_buf[j],
@@ -853,8 +853,8 @@ sfifo_test_fifo5 (vlib_main_t * vm, unformat_input_t * input)
   svm_fifo_enqueue_with_offset (f, 100, 100, &test_data[100]);
   svm_fifo_enqueue_with_offset (f, 300, 100, &test_data[300]);
 
-  SFIFO_TEST ((svm_fifo_number_ooo_segments (f) == 2),
-	      "number of ooo segments %u", svm_fifo_number_ooo_segments (f));
+  SFIFO_TEST ((svm_fifo_n_ooo_segments (f) == 2),
+	      "number of ooo segments %u", svm_fifo_n_ooo_segments (f));
   SFIFO_TEST ((f->ooos_newest == 1), "newest %u", f->ooos_newest);
   if (verbose)
     vlib_cli_output (vm, "fifo after [100, 200] and [300, 400] : %U",
@@ -868,8 +868,8 @@ sfifo_test_fifo5 (vlib_main_t * vm, unformat_input_t * input)
   if (verbose)
     vlib_cli_output (vm, "fifo after [225, 275] : %U",
 		     format_svm_fifo, f, 2 /* verbose */ );
-  SFIFO_TEST ((svm_fifo_number_ooo_segments (f) == 3),
-	      "number of ooo segments %u", svm_fifo_number_ooo_segments (f));
+  SFIFO_TEST ((svm_fifo_n_ooo_segments (f) == 3),
+	      "number of ooo segments %u", svm_fifo_n_ooo_segments (f));
   ooo_seg = svm_fifo_first_ooo_segment (f);
   SFIFO_TEST ((ooo_seg->start == fifo_pos (f, 100 + offset)),
 	      "first seg start %u expected %u", ooo_seg->start,
@@ -896,8 +896,8 @@ sfifo_test_fifo5 (vlib_main_t * vm, unformat_input_t * input)
   if (verbose)
     vlib_cli_output (vm, "fifo after [190, 310] : %U",
 		     format_svm_fifo, f, 1 /* verbose */ );
-  SFIFO_TEST ((svm_fifo_number_ooo_segments (f) == 1),
-	      "number of ooo segments %u", svm_fifo_number_ooo_segments (f));
+  SFIFO_TEST ((svm_fifo_n_ooo_segments (f) == 1),
+	      "number of ooo segments %u", svm_fifo_n_ooo_segments (f));
   ooo_seg = svm_fifo_first_ooo_segment (f);
   SFIFO_TEST ((ooo_seg->start == fifo_pos (f, offset + 100)),
 	      "first seg start %u expected %u",
@@ -908,15 +908,15 @@ sfifo_test_fifo5 (vlib_main_t * vm, unformat_input_t * input)
   /*
    * Add [0, 150]
    */
-  rv = svm_fifo_enqueue_nowait (f, 150, test_data);
+  rv = svm_fifo_enqueue (f, 150, test_data);
 
   if (verbose)
     vlib_cli_output (vm, "fifo after [0 150] : %U", format_svm_fifo, f,
 		     2 /* verbose */ );
 
   SFIFO_TEST ((rv == 400), "managed to enqueue %u expected %u", rv, 400);
-  SFIFO_TEST ((svm_fifo_number_ooo_segments (f) == 0),
-	      "number of ooo segments %u", svm_fifo_number_ooo_segments (f));
+  SFIFO_TEST ((svm_fifo_n_ooo_segments (f) == 0),
+	      "number of ooo segments %u", svm_fifo_n_ooo_segments (f));
 
   vec_validate (data_buf, 399);
   svm_fifo_peek (f, 0, 400, data_buf);
@@ -934,8 +934,8 @@ sfifo_test_fifo5 (vlib_main_t * vm, unformat_input_t * input)
 
   svm_fifo_enqueue_with_offset (f, 100, 100, &test_data[100]);
   svm_fifo_enqueue_with_offset (f, 50, 200, &test_data[50]);
-  SFIFO_TEST ((svm_fifo_number_ooo_segments (f) == 1),
-	      "number of ooo segments %u", svm_fifo_number_ooo_segments (f));
+  SFIFO_TEST ((svm_fifo_n_ooo_segments (f) == 1),
+	      "number of ooo segments %u", svm_fifo_n_ooo_segments (f));
   ooo_seg = svm_fifo_first_ooo_segment (f);
   SFIFO_TEST ((ooo_seg->start == 50), "first seg start %u expected %u",
 	      ooo_seg->start, 50);
@@ -984,20 +984,20 @@ sfifo_test_fifo6 (vlib_main_t * vm, unformat_input_t * input)
   /*
    * |0|---[start]--(len5)-->|0|--(len6)-->[end]---|0|
    */
-  rv = ooo_segment_distance_to_tail (f, ~0 - 5, 5);
+  rv = f_distance_from (f, ~0 - 5, 5);
   SFIFO_TEST (rv == 11, "distance to tail should be %u is %u", 11, rv);
 
-  rv = ooo_segment_distance_from_tail (f, ~0 - 5, 5);
+  rv = f_distance_to (f, ~0 - 5, 5);
   SFIFO_TEST (rv == f->size - 11, "distance from tail should be %u is %u",
 	      f->size - 11, rv);
 
   /*
    * |0|---[end]--(len5)-->|0|--(len6)-->[start]---|0|
    */
-  rv = ooo_segment_distance_from_tail (f, 5, ~0 - 5);
+  rv = f_distance_to (f, 5, ~0 - 5);
   SFIFO_TEST (rv == 11, "distance from tail should be %u is %u", 11, rv);
 
-  rv = ooo_segment_distance_to_tail (f, 5, ~0 - 5);
+  rv = f_distance_from (f, 5, ~0 - 5);
   SFIFO_TEST (rv == f->size - 11, "distance to tail should be %u is %u",
 	      f->size - 11, rv);
 
@@ -1006,15 +1006,15 @@ sfifo_test_fifo6 (vlib_main_t * vm, unformat_input_t * input)
    */
   svm_fifo_init_pointers (f, ~0, ~0);
   svm_fifo_enqueue_with_offset (f, 10, 10, &test_data[10]);
-  SFIFO_TEST ((svm_fifo_number_ooo_segments (f) == 1),
-	      "number of ooo segments %u", svm_fifo_number_ooo_segments (f));
+  SFIFO_TEST ((svm_fifo_n_ooo_segments (f) == 1),
+	      "number of ooo segments %u", svm_fifo_n_ooo_segments (f));
   ooo_seg = svm_fifo_first_ooo_segment (f);
   rv = ooo_segment_offset_prod (f, ooo_seg);
   SFIFO_TEST (rv == 10, "offset should be %u is %u", 10, rv);
 
-  svm_fifo_enqueue_nowait (f, 10, test_data);
-  SFIFO_TEST ((svm_fifo_number_ooo_segments (f) == 0),
-	      "number of ooo segments %u", svm_fifo_number_ooo_segments (f));
+  svm_fifo_enqueue (f, 10, test_data);
+  SFIFO_TEST ((svm_fifo_n_ooo_segments (f) == 0),
+	      "number of ooo segments %u", svm_fifo_n_ooo_segments (f));
   SFIFO_TEST (f->ooos_list_head == OOO_SEGMENT_INVALID_INDEX,
 	      "there should be no ooo seg");
 
@@ -1023,7 +1023,7 @@ sfifo_test_fifo6 (vlib_main_t * vm, unformat_input_t * input)
     SFIFO_TEST (0, "[%d] dequeued %u expected %u", j, data_buf[j],
 		test_data[j]);
 
-  svm_fifo_dequeue_nowait (f, 20, data_buf);
+  svm_fifo_dequeue (f, 20, data_buf);
   if (compare_data (data_buf, test_data, 0, 20, (u32 *) & j))
     SFIFO_TEST (0, "[%d] dequeued %u expected %u", j, data_buf[j],
 		test_data[j]);
@@ -1033,14 +1033,14 @@ sfifo_test_fifo6 (vlib_main_t * vm, unformat_input_t * input)
    */
   svm_fifo_init_pointers (f, ~0 - 10, ~0 - 10);
   svm_fifo_enqueue_with_offset (f, 5, 15, &test_data[5]);
-  svm_fifo_enqueue_nowait (f, 12, test_data);
+  svm_fifo_enqueue (f, 12, test_data);
 
-  SFIFO_TEST ((svm_fifo_number_ooo_segments (f) == 0),
-	      "number of ooo segments %u", svm_fifo_number_ooo_segments (f));
+  SFIFO_TEST ((svm_fifo_n_ooo_segments (f) == 0),
+	      "number of ooo segments %u", svm_fifo_n_ooo_segments (f));
   SFIFO_TEST (f->ooos_list_head == OOO_SEGMENT_INVALID_INDEX,
 	      "there should be no ooo seg");
 
-  svm_fifo_dequeue_nowait (f, 20, data_buf);
+  svm_fifo_dequeue (f, 20, data_buf);
   if (compare_data (data_buf, test_data, 0, 20, (u32 *) & j))
     SFIFO_TEST (0, "[%d] dequeued %u expected %u", j, data_buf[j],
 		test_data[j]);
@@ -1097,23 +1097,23 @@ sfifo_test_fifo7 (vlib_main_t * vm, unformat_input_t * input)
       for (j = n_test_bytes - 1; j > 0; j -= 2)
 	{
 	  svm_fifo_enqueue_with_offset (f, j, 1, &test_data[j]);
-	  rv = svm_fifo_number_ooo_segments (f);
+	  rv = svm_fifo_n_ooo_segments (f);
 	  if (rv != (n_test_bytes - j) / 2 + 1)
 	    SFIFO_TEST (0, "number of ooo segments expected %u is %u",
 			(n_test_bytes - j) / 2 + 1, rv);
 	}
 
       svm_fifo_enqueue_with_offset (f, 1, n_test_bytes - 1, &test_data[1]);
-      rv = svm_fifo_number_ooo_segments (f);
+      rv = svm_fifo_n_ooo_segments (f);
       if (rv != 1)
 	SFIFO_TEST (0, "number of ooo segments %u", rv);
 
-      svm_fifo_enqueue_nowait (f, 1, test_data);
-      rv = svm_fifo_number_ooo_segments (f);
+      svm_fifo_enqueue (f, 1, test_data);
+      rv = svm_fifo_n_ooo_segments (f);
       if (rv != 0)
 	SFIFO_TEST (0, "number of ooo segments %u", rv);
 
-      svm_fifo_dequeue_nowait (f, n_test_bytes, data_buf);
+      svm_fifo_dequeue (f, n_test_bytes, data_buf);
       if (compare_data (data_buf, test_data, 0, n_test_bytes, (u32 *) & j))
 	SFIFO_TEST (0, "[%d] dequeued %u expected %u", j, data_buf[j],
 		    test_data[j]);
@@ -1171,11 +1171,11 @@ sfifo_test_fifo_large (vlib_main_t * vm, unformat_input_t * input)
   for (i = 0; i < n_iterations; i++)
     {
       svm_fifo_enqueue_with_offset (f, half, half, &test_data[half]);
-      svm_fifo_enqueue_nowait (f, half, test_data);
-      rv = svm_fifo_number_ooo_segments (f);
+      svm_fifo_enqueue (f, half, test_data);
+      rv = svm_fifo_n_ooo_segments (f);
       if (rv != 0)
 	SFIFO_TEST (0, "number of ooo segments %u", rv);
-      svm_fifo_dequeue_nowait (f, n_bytes_per_iter, data_buf);
+      svm_fifo_dequeue (f, n_bytes_per_iter, data_buf);
       if (compare_data (data_buf, test_data, 0, n_bytes_per_iter,
 			(u32 *) & j))
 	SFIFO_TEST (0, "[%d][%d] dequeued %u expected %u", i, j, data_buf[j],
@@ -1247,7 +1247,7 @@ sfifo_test_fifo_grow (vlib_main_t * vm, unformat_input_t * input)
    * Unwrap fifo
    */
   vec_validate (data_buf, 200);
-  svm_fifo_dequeue_nowait (f, 201, data_buf);
+  svm_fifo_dequeue (f, 201, data_buf);
 
   SFIFO_TEST (f->end_chunk == c, "tail chunk should be updated");
   SFIFO_TEST (f->size == fifo_size + 200, "size expected %u is %u",
@@ -1288,7 +1288,7 @@ sfifo_test_fifo_grow (vlib_main_t * vm, unformat_input_t * input)
   SFIFO_TEST (f->size == fifo_size + 200, "size expected %u is %u",
 	      fifo_size + 200, f->size);
 
-  svm_fifo_dequeue_nowait (f, 201, data_buf);
+  svm_fifo_dequeue (f, 201, data_buf);
 
   SFIFO_TEST (f->size == fifo_size + 200 + 10 * 100, "size expected %u is %u",
 	      fifo_size + 200 + 10 * 100, f->size);
@@ -1312,11 +1312,11 @@ sfifo_test_fifo_grow (vlib_main_t * vm, unformat_input_t * input)
   SFIFO_TEST (f->tail_chunk->start_byte == 201, "start byte expected %u is "
 	      "%u", 201, f->tail_chunk->start_byte);
 
-  svm_fifo_enqueue_nowait (f, 200, test_data);
+  svm_fifo_enqueue (f, 200, test_data);
   SFIFO_TEST (f->tail_chunk->start_byte == 401, "start byte expected %u is "
 	      "%u", 401, f->tail_chunk->start_byte);
 
-  svm_fifo_dequeue_nowait (f, 200, data_buf);
+  svm_fifo_dequeue (f, 200, data_buf);
   SFIFO_TEST (f->head_chunk->start_byte == 401, "start byte expected %u is "
 	      "%u", 401, f->head_chunk->start_byte);
 
@@ -1326,7 +1326,7 @@ sfifo_test_fifo_grow (vlib_main_t * vm, unformat_input_t * input)
   svm_fifo_init_pointers (f, f->nitems / 2, f->nitems / 2);
   for (i = 0; i < test_n_bytes; i++)
     {
-      rv = svm_fifo_enqueue_nowait (f, sizeof (u8), &test_data[i]);
+      rv = svm_fifo_enqueue (f, sizeof (u8), &test_data[i]);
       if (rv < 0)
 	{
 	  clib_warning ("enqueue returned %d", rv);
@@ -1338,7 +1338,7 @@ sfifo_test_fifo_grow (vlib_main_t * vm, unformat_input_t * input)
 	      "is %u", test_n_bytes, svm_fifo_max_dequeue (f));
 
   for (i = 0; i < test_n_bytes; i++)
-    svm_fifo_dequeue_nowait (f, 1, &data_buf[i]);
+    svm_fifo_dequeue (f, 1, &data_buf[i]);
 
   rv = compare_data (data_buf, test_data, 0, vec_len (test_data),
 		     (u32 *) & j);
@@ -1352,7 +1352,7 @@ sfifo_test_fifo_grow (vlib_main_t * vm, unformat_input_t * input)
    */
   for (i = 0; i <= n_enqs; i++)
     {
-      rv = svm_fifo_enqueue_nowait (f, enq_bytes, test_data + i * enq_bytes);
+      rv = svm_fifo_enqueue (f, enq_bytes, test_data + i * enq_bytes);
       if (rv < 0)
 	{
 	  clib_warning ("enqueue returned %d", rv);
@@ -1364,7 +1364,7 @@ sfifo_test_fifo_grow (vlib_main_t * vm, unformat_input_t * input)
 	      "is %u", test_n_bytes, svm_fifo_max_dequeue (f));
 
   for (i = 0; i <= n_deqs; i++)
-    svm_fifo_dequeue_nowait (f, deq_bytes, data_buf + i * deq_bytes);
+    svm_fifo_dequeue (f, deq_bytes, data_buf + i * deq_bytes);
 
   rv = compare_data (data_buf, test_data, 0, vec_len (test_data),
 		     (u32 *) & j);
@@ -1391,11 +1391,11 @@ sfifo_test_fifo_grow (vlib_main_t * vm, unformat_input_t * input)
   SFIFO_TEST (svm_fifo_max_dequeue (f) == 0, "max deq expected %u is %u",
 	      0, svm_fifo_max_dequeue (f));
 
-  svm_fifo_enqueue_nowait (f, sizeof (u8), &test_data[0]);
+  svm_fifo_enqueue (f, sizeof (u8), &test_data[0]);
 
   memset (data_buf, 0, vec_len (data_buf));
   for (i = 0; i <= n_deqs; i++)
-    svm_fifo_dequeue_nowait (f, deq_bytes, data_buf + i * deq_bytes);
+    svm_fifo_dequeue (f, deq_bytes, data_buf + i * deq_bytes);
 
   rv = compare_data (data_buf, test_data, 0, vec_len (test_data),
 		     (u32 *) & j);
@@ -1423,11 +1423,11 @@ sfifo_test_fifo_grow (vlib_main_t * vm, unformat_input_t * input)
 	}
     }
 
-  svm_fifo_enqueue_nowait (f, enq_bytes, &test_data[0]);
+  svm_fifo_enqueue (f, enq_bytes, &test_data[0]);
 
   memset (data_buf, 0, vec_len (data_buf));
   for (i = 0; i <= n_deqs; i++)
-    svm_fifo_dequeue_nowait (f, deq_bytes, data_buf + i * deq_bytes);
+    svm_fifo_dequeue (f, deq_bytes, data_buf + i * deq_bytes);
 
   rv = compare_data (data_buf, test_data, 0, vec_len (test_data),
 		     (u32 *) & j);
@@ -1520,16 +1520,16 @@ sfifo_test_fifo_segment_hello_world (int verbose)
   vec_validate (retrieved_data, vec_len (test_data) - 1);
 
   while (svm_fifo_max_enqueue (f) >= vec_len (test_data))
-    svm_fifo_enqueue_nowait (f, vec_len (test_data), test_data);
+    svm_fifo_enqueue (f, vec_len (test_data), test_data);
 
   while (svm_fifo_max_dequeue (f) >= vec_len (test_data))
-    svm_fifo_dequeue_nowait (f, vec_len (retrieved_data), retrieved_data);
+    svm_fifo_dequeue (f, vec_len (retrieved_data), retrieved_data);
 
   while (svm_fifo_max_enqueue (f) >= vec_len (test_data))
-    svm_fifo_enqueue_nowait (f, vec_len (test_data), test_data);
+    svm_fifo_enqueue (f, vec_len (test_data), test_data);
 
   while (svm_fifo_max_dequeue (f) >= vec_len (test_data))
-    svm_fifo_dequeue_nowait (f, vec_len (retrieved_data), retrieved_data);
+    svm_fifo_dequeue (f, vec_len (retrieved_data), retrieved_data);
 
   SFIFO_TEST (!memcmp (retrieved_data, test_data, vec_len (test_data)),
 	      "data should be identical");
@@ -1657,7 +1657,7 @@ sfifo_test_fifo_segment_slave (int verbose)
 
   for (i = 0; i < 1000; i++)
     {
-      svm_fifo_dequeue_nowait (f, vec_len (retrieved_data), retrieved_data);
+      svm_fifo_dequeue (f, vec_len (retrieved_data), retrieved_data);
       if (memcmp (retrieved_data, test_data, vec_len (retrieved_data)))
 	{
 	  result = (u32 *) f->head_chunk->data;
@@ -1711,7 +1711,7 @@ sfifo_test_fifo_segment_master_slave (int verbose)
   usleep (200e3);
 
   for (i = 0; i < 1000; i++)
-    svm_fifo_enqueue_nowait (f, vec_len (test_data), test_data);
+    svm_fifo_enqueue (f, vec_len (test_data), test_data);
 
   /* Wait for slave */
   i = 0;
diff --git a/src/svm/svm_fifo.c b/src/svm/svm_fifo.c
index 4c84fce4c01..3512c72d9f1 100644
--- a/src/svm/svm_fifo.c
+++ b/src/svm/svm_fifo.c
@@ -101,29 +101,25 @@ svm_fifo_copy_from_chunk (svm_fifo_t * f, svm_fifo_chunk_t * c, u32 head_idx,
 static inline u8
 position_lt (svm_fifo_t * f, u32 a, u32 b, u32 tail)
 {
-  return (ooo_segment_distance_from_tail (f, a, tail)
-	  < ooo_segment_distance_from_tail (f, b, tail));
+  return (f_distance_to (f, a, tail) < f_distance_to (f, b, tail));
 }
 
 static inline u8
 position_leq (svm_fifo_t * f, u32 a, u32 b, u32 tail)
 {
-  return (ooo_segment_distance_from_tail (f, a, tail)
-	  <= ooo_segment_distance_from_tail (f, b, tail));
+  return (f_distance_to (f, a, tail) <= f_distance_to (f, b, tail));
 }
 
 static inline u8
 position_gt (svm_fifo_t * f, u32 a, u32 b, u32 tail)
 {
-  return (ooo_segment_distance_from_tail (f, a, tail)
-	  > ooo_segment_distance_from_tail (f, b, tail));
+  return (f_distance_to (f, a, tail) > f_distance_to (f, b, tail));
 }
 
 static inline u32
-position_diff (svm_fifo_t * f, u32 posa, u32 posb, u32 tail)
+position_diff (svm_fifo_t * f, u32 a, u32 b, u32 tail)
 {
-  return ooo_segment_distance_from_tail (f, posa, tail)
-    - ooo_segment_distance_from_tail (f, posb, tail);
+  return f_distance_to (f, a, tail) - f_distance_to (f, b, tail);
 }
 
 static inline u32
@@ -132,151 +128,250 @@ ooo_segment_end_pos (svm_fifo_t * f, ooo_segment_t * s)
   return s->start + s->length;
 }
 
-u8 *
-format_ooo_segment (u8 * s, va_list * args)
+void
+svm_fifo_free_ooo_data (svm_fifo_t * f)
 {
-  svm_fifo_t *f = va_arg (*args, svm_fifo_t *);
-  ooo_segment_t *seg = va_arg (*args, ooo_segment_t *);
-  u32 normalized_start = (seg->start + f->nitems - f->tail) % f->size;
-  s = format (s, "[%u, %u], len %u, next %d, prev %d", normalized_start,
-	      (normalized_start + seg->length) % f->size, seg->length,
-	      seg->next, seg->prev);
+  pool_free (f->ooo_segments);
+}
+
+static inline ooo_segment_t *
+ooo_segment_get_prev (svm_fifo_t * f, ooo_segment_t * s)
+{
+  if (s->prev == OOO_SEGMENT_INVALID_INDEX)
+    return 0;
+  return pool_elt_at_index (f->ooo_segments, s->prev);
+}
+
+static inline ooo_segment_t *
+ooo_segment_next (svm_fifo_t * f, ooo_segment_t * s)
+{
+  if (s->next == OOO_SEGMENT_INVALID_INDEX)
+    return 0;
+  return pool_elt_at_index (f->ooo_segments, s->next);
+}
+
+static inline ooo_segment_t *
+ooo_segment_alloc (svm_fifo_t * f, u32 start, u32 length)
+{
+  ooo_segment_t *s;
+
+  pool_get (f->ooo_segments, s);
+
+  s->start = start;
+  s->length = length;
+  s->prev = s->next = OOO_SEGMENT_INVALID_INDEX;
+
   return s;
 }
 
-u8 *
-svm_fifo_dump_trace (u8 * s, svm_fifo_t * f)
+static inline void
+ooo_segment_free (svm_fifo_t * f, u32 index)
 {
-#if SVM_FIFO_TRACE
-  svm_fifo_trace_elem_t *seg = 0;
-  int i = 0;
+  ooo_segment_t *cur, *prev = 0, *next = 0;
+  cur = pool_elt_at_index (f->ooo_segments, index);
 
-  if (f->trace)
+  if (cur->next != OOO_SEGMENT_INVALID_INDEX)
     {
-      vec_foreach (seg, f->trace)
-      {
-	s = format (s, "{%u, %u, %u}, ", seg->offset, seg->len, seg->action);
-	i++;
-	if (i % 5 == 0)
-	  s = format (s, "\n");
-      }
-      s = format (s, "\n");
+      next = pool_elt_at_index (f->ooo_segments, cur->next);
+      next->prev = cur->prev;
     }
-  return s;
-#else
-  return 0;
-#endif
+
+  if (cur->prev != OOO_SEGMENT_INVALID_INDEX)
+    {
+      prev = pool_elt_at_index (f->ooo_segments, cur->prev);
+      prev->next = cur->next;
+    }
+  else
+    {
+      f->ooos_list_head = cur->next;
+    }
+
+  pool_put (f->ooo_segments, cur);
 }
 
-u8 *
-svm_fifo_replay (u8 * s, svm_fifo_t * f, u8 no_read, u8 verbose)
+/**
+ * Add segment to fifo's out-of-order segment list. Takes care of merging
+ * adjacent segments and removing overlapping ones.
+ */
+static void
+ooo_segment_add (svm_fifo_t * f, u32 offset, u32 head, u32 tail, u32 length)
 {
-  int i, trace_len;
-  u8 *data = 0;
-  svm_fifo_trace_elem_t *trace;
-  u32 offset;
-  svm_fifo_t *dummy_fifo;
+  ooo_segment_t *s, *new_s, *prev, *next, *it;
+  u32 new_index, s_end_pos, s_index;
+  u32 offset_pos, offset_end_pos;
 
-  if (!f)
-    return s;
+  ASSERT (offset + length <= f_distance_to (f, head, tail) || head == tail);
 
-#if SVM_FIFO_TRACE
-  trace = f->trace;
-  trace_len = vec_len (trace);
-#else
-  trace = 0;
-  trace_len = 0;
-#endif
+  offset_pos = tail + offset;
+  offset_end_pos = tail + offset + length;
 
-  dummy_fifo = svm_fifo_create (f->size);
-  clib_memset (f->head_chunk->data, 0xFF, f->nitems);
-  vec_validate (data, f->nitems);
-  for (i = 0; i < vec_len (data); i++)
-    data[i] = i;
+  f->ooos_newest = OOO_SEGMENT_INVALID_INDEX;
 
-  for (i = 0; i < trace_len; i++)
+  if (f->ooos_list_head == OOO_SEGMENT_INVALID_INDEX)
     {
-      offset = trace[i].offset;
-      if (trace[i].action == 1)
-	{
-	  if (verbose)
-	    s = format (s, "adding [%u, %u]:", trace[i].offset,
-			(trace[i].offset + trace[i].len) % dummy_fifo->size);
-	  svm_fifo_enqueue_with_offset (dummy_fifo, trace[i].offset,
-					trace[i].len, &data[offset]);
-	}
-      else if (trace[i].action == 2)
+      s = ooo_segment_alloc (f, offset_pos, length);
+      f->ooos_list_head = s - f->ooo_segments;
+      f->ooos_newest = f->ooos_list_head;
+      return;
+    }
+
+  /* Find first segment that starts after new segment */
+  s = pool_elt_at_index (f->ooo_segments, f->ooos_list_head);
+  while (s->next != OOO_SEGMENT_INVALID_INDEX
+	 && position_lt (f, s->start, offset_pos, tail))
+    s = pool_elt_at_index (f->ooo_segments, s->next);
+
+  /* If we have a previous and we overlap it, use it as starting point */
+  prev = ooo_segment_get_prev (f, s);
+  if (prev
+      && position_leq (f, offset_pos, ooo_segment_end_pos (f, prev), tail))
+    {
+      s = prev;
+      s_end_pos = ooo_segment_end_pos (f, s);
+
+      /* Since we have previous, offset start position cannot be smaller
+       * than prev->start. Check tail */
+      ASSERT (position_lt (f, s->start, offset_pos, tail));
+      goto check_tail;
+    }
+
+  s_index = s - f->ooo_segments;
+  s_end_pos = ooo_segment_end_pos (f, s);
+
+  /* No overlap, add before current segment */
+  if (position_lt (f, offset_end_pos, s->start, tail))
+    {
+      new_s = ooo_segment_alloc (f, offset_pos, length);
+      new_index = new_s - f->ooo_segments;
+
+      /* Pool might've moved, get segment again */
+      s = pool_elt_at_index (f->ooo_segments, s_index);
+      if (s->prev != OOO_SEGMENT_INVALID_INDEX)
 	{
-	  if (verbose)
-	    s = format (s, "adding [%u, %u]:", 0, trace[i].len);
-	  svm_fifo_enqueue_nowait (dummy_fifo, trace[i].len, &data[offset]);
+	  new_s->prev = s->prev;
+	  prev = pool_elt_at_index (f->ooo_segments, new_s->prev);
+	  prev->next = new_index;
 	}
-      else if (!no_read)
+      else
 	{
-	  if (verbose)
-	    s = format (s, "read: %u", trace[i].len);
-	  svm_fifo_dequeue_drop (dummy_fifo, trace[i].len);
+	  /* New head */
+	  f->ooos_list_head = new_index;
 	}
-      if (verbose)
-	s = format (s, "%U", format_svm_fifo, dummy_fifo, 1);
+
+      new_s->next = s_index;
+      s->prev = new_index;
+      f->ooos_newest = new_index;
+      return;
     }
+  /* No overlap, add after current segment */
+  else if (position_gt (f, offset_pos, s_end_pos, tail))
+    {
+      new_s = ooo_segment_alloc (f, offset_pos, length);
+      new_index = new_s - f->ooo_segments;
 
-  s = format (s, "result: %U", format_svm_fifo, dummy_fifo, 1);
+      /* Pool might've moved, get segment again */
+      s = pool_elt_at_index (f->ooo_segments, s_index);
 
-  return s;
-}
+      /* Needs to be last */
+      ASSERT (s->next == OOO_SEGMENT_INVALID_INDEX);
 
-u8 *
-format_ooo_list (u8 * s, va_list * args)
-{
-  svm_fifo_t *f = va_arg (*args, svm_fifo_t *);
-  u32 indent = va_arg (*args, u32);
-  u32 ooo_segment_index = f->ooos_list_head;
-  ooo_segment_t *seg;
+      new_s->prev = s_index;
+      s->next = new_index;
+      f->ooos_newest = new_index;
 
-  while (ooo_segment_index != OOO_SEGMENT_INVALID_INDEX)
+      return;
+    }
+
+  /*
+   * Merge needed
+   */
+
+  /* Merge at head */
+  if (position_lt (f, offset_pos, s->start, tail))
     {
-      seg = pool_elt_at_index (f->ooo_segments, ooo_segment_index);
-      s = format (s, "%U%U\n", format_white_space, indent, format_ooo_segment,
-		  f, seg);
-      ooo_segment_index = seg->next;
+      s->start = offset_pos;
+      s->length = position_diff (f, s_end_pos, s->start, tail);
+      f->ooos_newest = s - f->ooo_segments;
     }
 
-  return s;
+check_tail:
+
+  /* Overlapping tail */
+  if (position_gt (f, offset_end_pos, s_end_pos, tail))
+    {
+      s->length = position_diff (f, offset_end_pos, s->start, tail);
+
+      /* Remove the completely overlapped segments in the tail */
+      it = ooo_segment_next (f, s);
+      while (it && position_leq (f, ooo_segment_end_pos (f, it),
+				 offset_end_pos, tail))
+	{
+	  next = ooo_segment_next (f, it);
+	  ooo_segment_free (f, it - f->ooo_segments);
+	  it = next;
+	}
+
+      /* If partial overlap with last, merge */
+      if (it && position_leq (f, it->start, offset_end_pos, tail))
+	{
+	  s->length = position_diff (f, ooo_segment_end_pos (f, it),
+				     s->start, tail);
+	  ooo_segment_free (f, it - f->ooo_segments);
+	}
+      f->ooos_newest = s - f->ooo_segments;
+    }
 }
 
-u8 *
-format_svm_fifo (u8 * s, va_list * args)
+/**
+ * Removes segments that can now be enqueued because the fifo's tail has
+ * advanced. Returns the number of bytes added to tail.
+ */
+static int
+ooo_segment_try_collect (svm_fifo_t * f, u32 n_bytes_enqueued, u32 * tail)
 {
-  svm_fifo_t *f = va_arg (*args, svm_fifo_t *);
-  int verbose = va_arg (*args, int);
-  u32 indent;
+  u32 s_index, bytes = 0;
+  ooo_segment_t *s;
+  i32 diff;
 
-  if (!s)
-    return s;
+  s = pool_elt_at_index (f->ooo_segments, f->ooos_list_head);
+  diff = f_distance_from (f, s->start, *tail);
 
-  indent = format_get_indent (s);
-  s = format (s, "cursize %u nitems %u has_event %d\n",
-	      svm_fifo_max_dequeue (f), f->nitems, f->has_event);
-  s = format (s, "%Uhead %u tail %u segment manager %u\n", format_white_space,
-	      indent, (f->head % f->size), (f->tail % f->size),
-	      f->segment_manager);
+  ASSERT (diff != n_bytes_enqueued);
 
-  if (verbose > 1)
-    s = format (s, "%Uvpp session %d thread %d app session %d thread %d\n",
-		format_white_space, indent, f->master_session_index,
-		f->master_thread_index, f->client_session_index,
-		f->client_thread_index);
+  if (diff > n_bytes_enqueued)
+    return 0;
 
-  if (verbose)
+  /* If last tail update overlaps one/multiple ooo segments, remove them */
+  while (0 <= diff && diff < n_bytes_enqueued)
     {
-      s = format (s, "%Uooo pool %d active elts newest %u\n",
-		  format_white_space, indent, pool_elts (f->ooo_segments),
-		  f->ooos_newest);
-      if (svm_fifo_has_ooo_data (f))
-	s = format (s, " %U", format_ooo_list, f, indent, verbose);
+      s_index = s - f->ooo_segments;
+
+      /* Segment end is beyond the tail. Advance tail and remove segment */
+      if (s->length > diff)
+	{
+	  bytes = s->length - diff;
+	  *tail = *tail + bytes;
+	  ooo_segment_free (f, s_index);
+	  break;
+	}
+
+      /* If we have next go on */
+      if (s->next != OOO_SEGMENT_INVALID_INDEX)
+	{
+	  s = pool_elt_at_index (f->ooo_segments, s->next);
+	  diff = f_distance_from (f, s->start, *tail);
+	  ooo_segment_free (f, s_index);
+	}
+      /* End of search */
+      else
+	{
+	  ooo_segment_free (f, s_index);
+	  break;
+	}
     }
-  return s;
+
+  ASSERT (bytes <= f->nitems);
+  return bytes;
 }
 
 void
@@ -289,7 +384,6 @@ svm_fifo_init (svm_fifo_t * f, u32 size)
    */
   f->nitems = f->size - 1;
   f->ooos_list_head = OOO_SEGMENT_INVALID_INDEX;
-  f->ct_session_index = SVM_FIFO_INVALID_SESSION_INDEX;
   f->segment_index = SVM_FIFO_INVALID_INDEX;
   f->refcnt = 1;
   f->default_chunk.start_byte = 0;
@@ -465,16 +559,11 @@ svm_fifo_find_chunk (svm_fifo_t * f, u32 pos)
 		return c;
 	      return 0;
 	    }
-	  /* Hit tnil as a right child. Check if this is the one, otherwise
-	   * search for successor */
+	  /* Hit tnil as a right child. Check if this is the one */
 	  c = uword_to_pointer (prev->opaque, svm_fifo_chunk_t *);
 	  if (svm_fifo_chunk_includes_pos (c, pos))
 	    return c;
 
-	  cur = rb_tree_successor (rt, prev);
-	  c = uword_to_pointer (cur->opaque, svm_fifo_chunk_t *);
-	  if (svm_fifo_chunk_includes_pos (c, pos))
-	    return c;
 	  return 0;
 	}
     }
@@ -491,12 +580,6 @@ svm_fifo_free_chunk_lookup (svm_fifo_t * f)
 }
 
 void
-svm_fifo_free_ooo_data (svm_fifo_t * f)
-{
-  pool_free (f->ooo_segments);
-}
-
-void
 svm_fifo_free (svm_fifo_t * f)
 {
   ASSERT (f->refcnt > 0);
@@ -509,234 +592,8 @@ svm_fifo_free (svm_fifo_t * f)
     }
 }
 
-always_inline ooo_segment_t *
-ooo_segment_new (svm_fifo_t * f, u32 start, u32 length)
-{
-  ooo_segment_t *s;
-
-  pool_get (f->ooo_segments, s);
-
-  s->start = start;
-  s->length = length;
-
-  s->prev = s->next = OOO_SEGMENT_INVALID_INDEX;
-
-  return s;
-}
-
-always_inline void
-ooo_segment_del (svm_fifo_t * f, u32 index)
-{
-  ooo_segment_t *cur, *prev = 0, *next = 0;
-  cur = pool_elt_at_index (f->ooo_segments, index);
-
-  if (cur->next != OOO_SEGMENT_INVALID_INDEX)
-    {
-      next = pool_elt_at_index (f->ooo_segments, cur->next);
-      next->prev = cur->prev;
-    }
-
-  if (cur->prev != OOO_SEGMENT_INVALID_INDEX)
-    {
-      prev = pool_elt_at_index (f->ooo_segments, cur->prev);
-      prev->next = cur->next;
-    }
-  else
-    {
-      f->ooos_list_head = cur->next;
-    }
-
-  pool_put (f->ooo_segments, cur);
-}
-
-/**
- * Add segment to fifo's out-of-order segment list. Takes care of merging
- * adjacent segments and removing overlapping ones.
- */
-static void
-ooo_segment_add (svm_fifo_t * f, u32 offset, u32 head, u32 tail, u32 length)
-{
-  ooo_segment_t *s, *new_s, *prev, *next, *it;
-  u32 new_index, s_end_pos, s_index;
-  u32 offset_pos, offset_end_pos;
-
-  ASSERT (offset + length <= ooo_segment_distance_from_tail (f, head, tail)
-	  || head == tail);
-
-  offset_pos = tail + offset;
-  offset_end_pos = tail + offset + length;
-
-  f->ooos_newest = OOO_SEGMENT_INVALID_INDEX;
-
-  if (f->ooos_list_head == OOO_SEGMENT_INVALID_INDEX)
-    {
-      s = ooo_segment_new (f, offset_pos, length);
-      f->ooos_list_head = s - f->ooo_segments;
-      f->ooos_newest = f->ooos_list_head;
-      return;
-    }
-
-  /* Find first segment that starts after new segment */
-  s = pool_elt_at_index (f->ooo_segments, f->ooos_list_head);
-  while (s->next != OOO_SEGMENT_INVALID_INDEX
-	 && position_lt (f, s->start, offset_pos, tail))
-    s = pool_elt_at_index (f->ooo_segments, s->next);
-
-  /* If we have a previous and we overlap it, use it as starting point */
-  prev = ooo_segment_get_prev (f, s);
-  if (prev
-      && position_leq (f, offset_pos, ooo_segment_end_pos (f, prev), tail))
-    {
-      s = prev;
-      s_end_pos = ooo_segment_end_pos (f, s);
-
-      /* Since we have previous, offset start position cannot be smaller
-       * than prev->start. Check tail */
-      ASSERT (position_lt (f, s->start, offset_pos, tail));
-      goto check_tail;
-    }
-
-  s_index = s - f->ooo_segments;
-  s_end_pos = ooo_segment_end_pos (f, s);
-
-  /* No overlap, add before current segment */
-  if (position_lt (f, offset_end_pos, s->start, tail))
-    {
-      new_s = ooo_segment_new (f, offset_pos, length);
-      new_index = new_s - f->ooo_segments;
-
-      /* Pool might've moved, get segment again */
-      s = pool_elt_at_index (f->ooo_segments, s_index);
-      if (s->prev != OOO_SEGMENT_INVALID_INDEX)
-	{
-	  new_s->prev = s->prev;
-	  prev = pool_elt_at_index (f->ooo_segments, new_s->prev);
-	  prev->next = new_index;
-	}
-      else
-	{
-	  /* New head */
-	  f->ooos_list_head = new_index;
-	}
-
-      new_s->next = s_index;
-      s->prev = new_index;
-      f->ooos_newest = new_index;
-      return;
-    }
-  /* No overlap, add after current segment */
-  else if (position_gt (f, offset_pos, s_end_pos, tail))
-    {
-      new_s = ooo_segment_new (f, offset_pos, length);
-      new_index = new_s - f->ooo_segments;
-
-      /* Pool might've moved, get segment again */
-      s = pool_elt_at_index (f->ooo_segments, s_index);
-
-      /* Needs to be last */
-      ASSERT (s->next == OOO_SEGMENT_INVALID_INDEX);
-
-      new_s->prev = s_index;
-      s->next = new_index;
-      f->ooos_newest = new_index;
-
-      return;
-    }
-
-  /*
-   * Merge needed
-   */
-
-  /* Merge at head */
-  if (position_lt (f, offset_pos, s->start, tail))
-    {
-      s->start = offset_pos;
-      s->length = position_diff (f, s_end_pos, s->start, tail);
-      f->ooos_newest = s - f->ooo_segments;
-    }
-
-check_tail:
-
-  /* Overlapping tail */
-  if (position_gt (f, offset_end_pos, s_end_pos, tail))
-    {
-      s->length = position_diff (f, offset_end_pos, s->start, tail);
-
-      /* Remove the completely overlapped segments in the tail */
-      it = ooo_segment_next (f, s);
-      while (it && position_leq (f, ooo_segment_end_pos (f, it),
-				 offset_end_pos, tail))
-	{
-	  next = ooo_segment_next (f, it);
-	  ooo_segment_del (f, it - f->ooo_segments);
-	  it = next;
-	}
-
-      /* If partial overlap with last, merge */
-      if (it && position_leq (f, it->start, offset_end_pos, tail))
-	{
-	  s->length = position_diff (f, ooo_segment_end_pos (f, it),
-				     s->start, tail);
-	  ooo_segment_del (f, it - f->ooo_segments);
-	}
-      f->ooos_newest = s - f->ooo_segments;
-    }
-}
-
-/**
- * Removes segments that can now be enqueued because the fifo's tail has
- * advanced. Returns the number of bytes added to tail.
- */
-static int
-ooo_segment_try_collect (svm_fifo_t * f, u32 n_bytes_enqueued, u32 * tail)
-{
-  ooo_segment_t *s;
-  u32 index, bytes = 0;
-  i32 diff;
-
-  s = pool_elt_at_index (f->ooo_segments, f->ooos_list_head);
-  diff = ooo_segment_distance_to_tail (f, s->start, *tail);
-
-  ASSERT (diff != n_bytes_enqueued);
-
-  if (diff > n_bytes_enqueued)
-    return 0;
-
-  /* If last tail update overlaps one/multiple ooo segments, remove them */
-  while (0 <= diff && diff < n_bytes_enqueued)
-    {
-      index = s - f->ooo_segments;
-
-      /* Segment end is beyond the tail. Advance tail and remove segment */
-      if (s->length > diff)
-	{
-	  bytes = s->length - diff;
-	  *tail = *tail + bytes;
-	  ooo_segment_del (f, index);
-	  break;
-	}
-
-      /* If we have next go on */
-      if (s->next != OOO_SEGMENT_INVALID_INDEX)
-	{
-	  s = pool_elt_at_index (f->ooo_segments, s->next);
-	  diff = ooo_segment_distance_to_tail (f, s->start, *tail);
-	  ooo_segment_del (f, index);
-	}
-      /* End of search */
-      else
-	{
-	  ooo_segment_del (f, index);
-	  break;
-	}
-    }
-
-  ASSERT (bytes <= f->nitems);
-  return bytes;
-}
-
 void
-svm_fifo_overwrite_head (svm_fifo_t * f, u8 * data, u32 len)
+svm_fifo_overwrite_head (svm_fifo_t * f, u8 * src, u32 len)
 {
   u32 n_chunk;
   u32 head, tail, head_idx;
@@ -750,16 +607,16 @@ svm_fifo_overwrite_head (svm_fifo_t * f, u8 * data, u32 len)
   head_idx -= c->start_byte;
   n_chunk = c->length - head_idx;
   if (len <= n_chunk)
-    clib_memcpy_fast (&c->data[head_idx], data, len);
+    clib_memcpy_fast (&c->data[head_idx], src, len);
   else
     {
-      clib_memcpy_fast (&c->data[head_idx], data, n_chunk);
-      clib_memcpy_fast (&c->next->data[0], data + n_chunk, len - n_chunk);
+      clib_memcpy_fast (&c->data[head_idx], src, n_chunk);
+      clib_memcpy_fast (&c->next->data[0], src + n_chunk, len - n_chunk);
     }
 }
 
 int
-svm_fifo_enqueue_nowait (svm_fifo_t * f, u32 len, const u8 * src)
+svm_fifo_enqueue (svm_fifo_t * f, u32 len, const u8 * src)
 {
   u32 tail, head, free_count;
 
@@ -771,16 +628,15 @@ svm_fifo_enqueue_nowait (svm_fifo_t * f, u32 len, const u8 * src)
   f->ooos_newest = OOO_SEGMENT_INVALID_INDEX;
 
   if (PREDICT_FALSE (free_count == 0))
-    return SVM_FIFO_FULL;
+    return SVM_FIFO_EFULL;
 
   /* number of bytes we're going to copy */
   len = clib_min (free_count, len);
-
   svm_fifo_copy_to_chunk (f, f->tail_chunk, tail % f->size, src, len,
 			  &f->tail_chunk);
   tail += len;
 
-  svm_fifo_trace_add (f, head, n_total, 2);
+  svm_fifo_trace_add (f, head, len, 2);
 
   /* collect out-of-order segments */
   if (PREDICT_FALSE (f->ooos_list_head != OOO_SEGMENT_INVALID_INDEX))
@@ -811,14 +667,11 @@ svm_fifo_enqueue_with_offset (svm_fifo_t * f, u32 offset, u32 len, u8 * src)
 
   /* will this request fit? */
   if ((len + offset) > free_count)
-    return -1;
+    return SVM_FIFO_EFULL;
 
   f->ooos_newest = OOO_SEGMENT_INVALID_INDEX;
-
   svm_fifo_trace_add (f, offset, len, 1);
-
   ooo_segment_add (f, offset, head, tail, len);
-
   tail_idx = (tail % f->size + offset) % f->size;
 
   if (!svm_fifo_chunk_includes_pos (f->ooo_enq, tail_idx))
@@ -830,7 +683,7 @@ svm_fifo_enqueue_with_offset (svm_fifo_t * f, u32 offset, u32 len, u8 * src)
 }
 
 int
-svm_fifo_dequeue_nowait (svm_fifo_t * f, u32 len, u8 * dst)
+svm_fifo_dequeue (svm_fifo_t * f, u32 len, u8 * dst)
 {
   u32 tail, head, cursize;
 
@@ -840,10 +693,9 @@ svm_fifo_dequeue_nowait (svm_fifo_t * f, u32 len, u8 * dst)
   cursize = f_cursize (f, head, tail);
 
   if (PREDICT_FALSE (cursize == 0))
-    return -2;			/* nothing in the fifo */
+    return SVM_FIFO_EEMPTY;
 
   len = clib_min (cursize, len);
-
   svm_fifo_copy_from_chunk (f, f->head_chunk, head % f->size, dst, len,
 			    &f->head_chunk);
   head += len;
@@ -868,7 +720,7 @@ svm_fifo_peek (svm_fifo_t * f, u32 offset, u32 len, u8 * dst)
   cursize = f_cursize (f, head, tail);
 
   if (PREDICT_FALSE (cursize < offset))
-    return -2;			/* nothing in the fifo */
+    return SVM_FIFO_EEMPTY;
 
   len = clib_min (cursize - offset, len);
   head_idx = (head % f->size + offset) % f->size;
@@ -880,28 +732,25 @@ svm_fifo_peek (svm_fifo_t * f, u32 offset, u32 len, u8 * dst)
 }
 
 int
-svm_fifo_dequeue_drop (svm_fifo_t * f, u32 max_bytes)
+svm_fifo_dequeue_drop (svm_fifo_t * f, u32 len)
 {
-  u32 total_drop_bytes;
-  u32 tail, head, cursize;
+  u32 total_drop_bytes, tail, head, cursize;
 
   f_load_head_tail_cons (f, &head, &tail);
 
-  /* number of bytes we're going to drop */
+  /* number of bytes available */
   cursize = f_cursize (f, head, tail);
-
   if (PREDICT_FALSE (cursize == 0))
-    return -2;			/* nothing in the fifo */
+    return SVM_FIFO_EEMPTY;
 
   svm_fifo_trace_add (f, tail, total_drop_bytes, 3);
 
   /* number of bytes we're going to drop */
-  total_drop_bytes = (cursize < max_bytes) ? cursize : max_bytes;
+  total_drop_bytes = clib_min (cursize, len);
 
   /* move head */
   head += total_drop_bytes;
 
-  ASSERT (cursize >= total_drop_bytes);
   /* store-rel: consumer owned index (paired with load-acq in producer) */
   clib_atomic_store_rel_n (&f->head, head);
 
@@ -928,7 +777,7 @@ svm_fifo_segments (svm_fifo_t * f, svm_fifo_seg_t * fs)
   cursize = f_cursize (f, head, tail);
 
   if (PREDICT_FALSE (cursize == 0))
-    return -2;			/* nothing in the fifo */
+    return SVM_FIFO_EEMPTY;
 
   head_idx = head % f->size;
 
@@ -964,7 +813,13 @@ svm_fifo_segments_free (svm_fifo_t * f, svm_fifo_seg_t * fs)
   clib_atomic_store_rel_n (&f->head, head);
 }
 
-/* Assumption: no prod and cons are accessing either dest or src fifo */
+/**
+ * Clones fifo
+ *
+ * Assumptions:
+ * - no prod and cons are accessing either dest or src fifo
+ * - fifo is not multi chunk
+ */
 void
 svm_fifo_clone (svm_fifo_t * df, svm_fifo_t * sf)
 {
@@ -977,7 +832,7 @@ svm_fifo_clone (svm_fifo_t * df, svm_fifo_t * sf)
 }
 
 u32
-svm_fifo_number_ooo_segments (svm_fifo_t * f)
+svm_fifo_n_ooo_segments (svm_fifo_t * f)
 {
   return pool_elts (f->ooo_segments);
 }
@@ -1031,6 +886,153 @@ svm_fifo_del_subscriber (svm_fifo_t * f, u8 subscriber)
     }
 }
 
+u8 *
+format_ooo_segment (u8 * s, va_list * args)
+{
+  svm_fifo_t *f = va_arg (*args, svm_fifo_t *);
+  ooo_segment_t *seg = va_arg (*args, ooo_segment_t *);
+  u32 normalized_start = (seg->start + f->nitems - f->tail) % f->size;
+  s = format (s, "[%u, %u], len %u, next %d, prev %d", normalized_start,
+	      (normalized_start + seg->length) % f->size, seg->length,
+	      seg->next, seg->prev);
+  return s;
+}
+
+u8 *
+svm_fifo_dump_trace (u8 * s, svm_fifo_t * f)
+{
+#if SVM_FIFO_TRACE
+  svm_fifo_trace_elem_t *seg = 0;
+  int i = 0;
+
+  if (f->trace)
+    {
+      vec_foreach (seg, f->trace)
+      {
+	s = format (s, "{%u, %u, %u}, ", seg->offset, seg->len, seg->action);
+	i++;
+	if (i % 5 == 0)
+	  s = format (s, "\n");
+      }
+      s = format (s, "\n");
+    }
+  return s;
+#else
+  return 0;
+#endif
+}
+
+u8 *
+svm_fifo_replay (u8 * s, svm_fifo_t * f, u8 no_read, u8 verbose)
+{
+  int i, trace_len;
+  u8 *data = 0;
+  svm_fifo_trace_elem_t *trace;
+  u32 offset;
+  svm_fifo_t *dummy_fifo;
+
+  if (!f)
+    return s;
+
+#if SVM_FIFO_TRACE
+  trace = f->trace;
+  trace_len = vec_len (trace);
+#else
+  trace = 0;
+  trace_len = 0;
+#endif
+
+  dummy_fifo = svm_fifo_create (f->size);
+  clib_memset (f->head_chunk->data, 0xFF, f->nitems);
+  vec_validate (data, f->nitems);
+  for (i = 0; i < vec_len (data); i++)
+    data[i] = i;
+
+  for (i = 0; i < trace_len; i++)
+    {
+      offset = trace[i].offset;
+      if (trace[i].action == 1)
+	{
+	  if (verbose)
+	    s = format (s, "adding [%u, %u]:", trace[i].offset,
+			(trace[i].offset + trace[i].len) % dummy_fifo->size);
+	  svm_fifo_enqueue_with_offset (dummy_fifo, trace[i].offset,
+					trace[i].len, &data[offset]);
+	}
+      else if (trace[i].action == 2)
+	{
+	  if (verbose)
+	    s = format (s, "adding [%u, %u]:", 0, trace[i].len);
+	  svm_fifo_enqueue (dummy_fifo, trace[i].len, &data[offset]);
+	}
+      else if (!no_read)
+	{
+	  if (verbose)
+	    s = format (s, "read: %u", trace[i].len);
+	  svm_fifo_dequeue_drop (dummy_fifo, trace[i].len);
+	}
+      if (verbose)
+	s = format (s, "%U", format_svm_fifo, dummy_fifo, 1);
+    }
+
+  s = format (s, "result: %U", format_svm_fifo, dummy_fifo, 1);
+
+  return s;
+}
+
+u8 *
+format_ooo_list (u8 * s, va_list * args)
+{
+  svm_fifo_t *f = va_arg (*args, svm_fifo_t *);
+  u32 indent = va_arg (*args, u32);
+  u32 ooo_segment_index = f->ooos_list_head;
+  ooo_segment_t *seg;
+
+  while (ooo_segment_index != OOO_SEGMENT_INVALID_INDEX)
+    {
+      seg = pool_elt_at_index (f->ooo_segments, ooo_segment_index);
+      s = format (s, "%U%U\n", format_white_space, indent, format_ooo_segment,
+		  f, seg);
+      ooo_segment_index = seg->next;
+    }
+
+  return s;
+}
+
+u8 *
+format_svm_fifo (u8 * s, va_list * args)
+{
+  svm_fifo_t *f = va_arg (*args, svm_fifo_t *);
+  int verbose = va_arg (*args, int);
+  u32 indent;
+
+  if (!s)
+    return s;
+
+  indent = format_get_indent (s);
+  s = format (s, "cursize %u nitems %u has_event %d\n",
+	      svm_fifo_max_dequeue (f), f->nitems, f->has_event);
+  s = format (s, "%Uhead %u tail %u segment manager %u\n", format_white_space,
+	      indent, (f->head % f->size), (f->tail % f->size),
+	      f->segment_manager);
+
+  if (verbose > 1)
+    s = format (s, "%Uvpp session %d thread %d app session %d thread %d\n",
+		format_white_space, indent, f->master_session_index,
+		f->master_thread_index, f->client_session_index,
+		f->client_thread_index);
+
+  if (verbose)
+    {
+      s = format (s, "%Uooo pool %d active elts newest %u\n",
+		  format_white_space, indent, pool_elts (f->ooo_segments),
+		  f->ooos_newest);
+      if (svm_fifo_has_ooo_data (f))
+	s = format (s, " %U", format_ooo_list, f, indent, verbose);
+    }
+  return s;
+}
+
 #endif
 /*
  * fd.io coding-style-patch-verification: ON
diff --git a/src/svm/svm_fifo.h b/src/svm/svm_fifo.h
index c9370955dfb..96ca3ee01c6 100644
--- a/src/svm/svm_fifo.h
+++ b/src/svm/svm_fifo.h
@@ -30,7 +30,6 @@ typedef struct
 {
   u32 next;	/**< Next linked-list element pool index */
   u32 prev;	/**< Previous linked-list element pool index */
-
   u32 start;	/**< Start of segment, normalized*/
   u32 length;	/**< Length of segment */
 } ooo_segment_t;
@@ -41,12 +40,12 @@ typedef struct
 #define SVM_FIFO_INVALID_INDEX		((u32)~0)
 #define SVM_FIFO_MAX_EVT_SUBSCRIBERS	7
 
-enum svm_fifo_tx_ntf_
+typedef enum svm_fifo_tx_ntf_
 {
   SVM_FIFO_NO_TX_NOTIF = 0,
   SVM_FIFO_WANT_TX_NOTIF = 1,
   SVM_FIFO_WANT_TX_NOTIF_IF_FULL = 2,
-};
+} svm_fifo_tx_ntf_t;
 
 typedef struct
 {
@@ -57,10 +56,10 @@ typedef struct
 
 typedef struct svm_fifo_chunk_
 {
-  u32 start_byte;
-  u32 length;
-  struct svm_fifo_chunk_ *next;
-  u8 data[0];
+  u32 start_byte;		/**< chunk start byte */
+  u32 length;			/**< length of chunk in bytes */
+  struct svm_fifo_chunk_ *next;	/**< pointer to next chunk in linked-lists */
+  u8 data[0];			/**< start of chunk data */
 } svm_fifo_chunk_t;
 
 typedef enum svm_fifo_flag_
@@ -73,8 +72,8 @@ typedef enum svm_fifo_flag_
 typedef struct _svm_fifo
 {
   CLIB_CACHE_LINE_ALIGN_MARK (shared_first);
-  u32 size;			/**< size of the fifo */
-  u32 nitems;			/**< usable size(size-1) */
+  u32 size;			/**< size of the fifo in bytes */
+  u32 nitems;			/**< usable size (size-1) */
   u8 flags;			/**< fifo flags */
   svm_fifo_chunk_t *start_chunk;/**< first chunk in fifo chunk list */
   svm_fifo_chunk_t *end_chunk;	/**< end chunk in fifo chunk list */
@@ -83,14 +82,12 @@ typedef struct _svm_fifo
 
     CLIB_CACHE_LINE_ALIGN_MARK (shared_second);
   volatile u32 has_event;	/**< non-zero if deq event exists */
-
-  u32 master_session_index;
-  u32 client_session_index;
-  u8 master_thread_index;
-  u8 client_thread_index;
-  u32 segment_manager;
-  u32 segment_index;
-  u32 ct_session_index;		/**< Local session index for vpp */
+  u32 master_session_index;	/**< session layer session index */
+  u32 client_session_index;	/**< app session index */
+  u8 master_thread_index;	/**< session layer thread index */
+  u8 client_thread_index;	/**< app worker index */
+  u32 segment_manager;		/**< session layer segment manager index */
+  u32 segment_index;		/**< segment index in segment manager */
   u32 freelist_index;		/**< aka log2(allocated_size) - const. */
   i8 refcnt;			/**< reference count  */
   struct _svm_fifo *next;	/**< next in freelist/active chain */
@@ -110,7 +107,7 @@ typedef struct _svm_fifo
   svm_fifo_chunk_t *ooo_enq;	/**< last chunk used for ooo enqueue */
   ooo_segment_t *ooo_segments;	/**< Pool of ooo segments */
   u32 ooos_newest;		/**< Last segment to have been updated */
-  volatile u8 n_subscribers;
+  volatile u8 n_subscribers;	/**< Number of subscribers for io events */
   u8 subscribers[SVM_FIFO_MAX_EVT_SUBSCRIBERS];
 
 #if SVM_FIFO_TRACE
@@ -122,7 +119,8 @@ typedef struct _svm_fifo
 
 typedef enum
 {
-  SVM_FIFO_FULL = -2,
+  SVM_FIFO_EFULL = -2,
+  SVM_FIFO_EEMPTY = -3,
 } svm_fifo_err_t;
 
 typedef struct svm_fifo_seg_
@@ -147,7 +145,11 @@ typedef struct svm_fifo_seg_
 u8 *svm_fifo_dump_trace (u8 * s, svm_fifo_t * f);
 u8 *svm_fifo_replay (u8 * s, svm_fifo_t * f, u8 no_read, u8 verbose);
 
-/* internal function */
+/**
+ * Load head and tail optimized for consumer
+ *
+ * Internal function.
+ */
 static inline void
 f_load_head_tail_cons (svm_fifo_t * f, u32 * head, u32 * tail)
 {
@@ -157,7 +159,10 @@ f_load_head_tail_cons (svm_fifo_t * f, u32 * head, u32 * tail)
   *tail = clib_atomic_load_acq_n (&f->tail);
 }
 
-/* internal function */
+/** Load head and tail optimized for producer
+ *
+ * Internal function
+ */
 static inline void
 f_load_head_tail_prod (svm_fifo_t * f, u32 * head, u32 * tail)
 {
@@ -167,8 +172,10 @@ f_load_head_tail_prod (svm_fifo_t * f, u32 * head, u32 * tail)
   *head = clib_atomic_load_acq_n (&f->head);
 }
 
-/* producer consumer role independent */
-/* internal function */
+/* Load head and tail independent of producer/consumer role
+ *
+ * Internal function.
+ */
 static inline void
 f_load_head_tail_all_acq (svm_fifo_t * f, u32 * head, u32 * tail)
 {
@@ -178,21 +185,247 @@ f_load_head_tail_all_acq (svm_fifo_t * f, u32 * head, u32 * tail)
   *head = clib_atomic_load_acq_n (&f->head);
 }
 
-/* internal function */
+/**
+ * Fifo free bytes, i.e., number of free bytes
+ *
+ * Internal function
+ */
 static inline u32
 f_free_count (svm_fifo_t * f, u32 head, u32 tail)
 {
   return (f->nitems + head - tail);
 }
 
-/* internal function */
+/**
+ * Fifo current size, i.e., number of bytes enqueued
+ *
+ * Internal function.
+ */
 static inline u32
 f_cursize (svm_fifo_t * f, u32 head, u32 tail)
 {
   return (f->nitems - f_free_count (f, head, tail));
 }
 
-/* used by consumer */
+/**
+ * Distance to a from b, i.e., a - b in the fifo
+ *
+ * Internal function.
+ */
+static inline u32
+f_distance_to (svm_fifo_t * f, u32 a, u32 b)
+{
+  return ((f->size + a - b) % f->size);
+}
+
+/**
+ * Distance from a to b, i.e., b - a in the fifo
+ *
+ * Internal function.
+ */
+static inline u32
+f_distance_from (svm_fifo_t * f, u32 a, u32 b)
+{
+  return ((f->size + b - a) % f->size);
+}
+
+/**
+ * Create fifo of requested size
+ *
+ * Allocates fifo on current heap.
+ *
+ * @param size		data size in bytes for fifo to be allocated. Will be
+ * 			rounded to the next highest power-of-two value.
+ * @return 		pointer to new fifo
+ */
+svm_fifo_t *svm_fifo_create (u32 size);
+/**
+ * Initialize fifo
+ *
+ * @param size		size for fifo
+ */
+void svm_fifo_init (svm_fifo_t * f, u32 size);
+/**
+ * Allocate a fifo chunk on heap
+ *
+ * If the chunk is allocated on a fifo segment, this should be called
+ * with the segment's heap pushed.
+ *
+ * @param size	chunk size in bytes. Will be rounded to the next highest
+ * 		power-of-two
+ * @return	new chunk or 0 if alloc failed
+ */
+svm_fifo_chunk_t *svm_fifo_chunk_alloc (u32 size);
+/**
+ * Grow fifo size by adding chunk to chunk list
+ *
+ * If fifos are allocated on a segment, this should be called with
+ * the segment's heap pushed.
+ *
+ * @param f	fifo to be extended
+ * @param c 	chunk or linked list of chunks to be added
+ */
+void svm_fifo_add_chunk (svm_fifo_t * f, svm_fifo_chunk_t * c);
+/**
+ * Free fifo and associated state
+ *
+ * @param f	fifo
+ */
+void svm_fifo_free (svm_fifo_t * f);
+/**
+ * Cleanup fifo chunk lookup rb tree
+ *
+ * The rb tree is allocated in segment heap so this should be called
+ * with it pushed.
+ *
+ * @param f 	fifo to cleanup
+ */
+void svm_fifo_free_chunk_lookup (svm_fifo_t * f);
+/**
+ * Cleanup fifo ooo data
+ *
+ * The ooo data is allocated in producer process memory. The fifo
+ * segment heap should not be pushed.
+ *
+ * @param f	fifo to cleanup
+ */
+void svm_fifo_free_ooo_data (svm_fifo_t * f);
+/**
+ * Init fifo head and tail
+ *
+ * @param f	fifo
+ * @param head	head value that will be matched to a chunk
+ * @param tail	tail value that will be matched to a chunk
+ */
+void svm_fifo_init_pointers (svm_fifo_t * f, u32 head, u32 tail);
+/**
+ * Clone fifo
+ *
+ * Clones single/default chunk fifo. It does not work for fifos with
+ * multiple chunks.
+ */
+void svm_fifo_clone (svm_fifo_t * df, svm_fifo_t * sf);
+/**
+ * Enqueue data to fifo
+ *
+ * Data is enqueued and tail pointer is updated atomically. If the new data
+ * enqueued partly overlaps or "touches" an out-of-order segment, said segment
+ * is "consumed" and the number of bytes returned is appropriately updated.
+ *
+ * @param f	fifo
+ * @param len	length of data to copy
+ * @param src	buffer from where to copy the data
+ * @return	number of contiguous bytes that can be consumed or error
+ */
+int svm_fifo_enqueue (svm_fifo_t * f, u32 len, const u8 * src);
+/**
+ * Enqueue data to fifo with offset
+ *
+ * Data is enqueued without updating tail pointer. Instead, an out-of-order
+ * list of segments is generated and maintained. Fifo takes care of coalescing
+ * contiguous or overlapping segments.
+ *
+ * @param f		fifo
+ * @param offset	offset at which to copy the data
+ * @param len		len of data to copy
+ * @param src		buffer from where to copy the data
+ * @return		0 if enqueue was successful, error otherwise
+ */
+int svm_fifo_enqueue_with_offset (svm_fifo_t * f, u32 offset, u32 len,
+				  u8 * src);
+/**
+ * Overwrite fifo head with new data
+ *
+ * This should be typically used by dgram transport protocols that need
+ * to update the dgram header after dequeueing a chunk of data. It assumes
+ * that the dgram header is at most spread over two chunks.
+ *
+ * @param f		fifo
+ * @param src		src of new data
+ * @param len		length of new data
+ */
+void svm_fifo_overwrite_head (svm_fifo_t * f, u8 * src, u32 len);
+/**
+ * Dequeue data from fifo
+ *
+ * Data is dequeued to consumer provided buffer and head is atomically
+ * updated.
+ *
+ * @param f		fifo
+ * @param len		length of data to dequeue
+ * @param dst		buffer to where to dequeue the data
+ * @return		number of bytes dequeued or error
+ */
+int svm_fifo_dequeue (svm_fifo_t * f, u32 len, u8 * dst);
+/**
+ * Peek data from fifo
+ *
+ * Data is copied from requested offset into provided dst buffer. Head is
+ * not updated.
+ *
+ * @param f		fifo
+ * @param offset	offset from which to copy the data
+ * @param len		length of data to copy
+ * @param dst		buffer to where to dequeue the data
+ * @return		number of bytes peeked
+ */
+int svm_fifo_peek (svm_fifo_t * f, u32 offset, u32 len, u8 * dst);
+/**
+ * Dequeue and drop bytes from fifo
+ *
+ * Advances fifo head by requested amount of bytes.
+ *
+ * @param f		fifo
+ * @param len		number of bytes to drop
+ * @return		number of bytes dropped
+ */
+int svm_fifo_dequeue_drop (svm_fifo_t * f, u32 len);
+/**
+ * Dequeue and drop all bytes from fifo
+ *
+ * Advances head to tail position.
+ *
+ * @param f		fifo
+ */
+void svm_fifo_dequeue_drop_all (svm_fifo_t * f);
+int svm_fifo_segments (svm_fifo_t * f, svm_fifo_seg_t * fs);
+void svm_fifo_segments_free (svm_fifo_t * f, svm_fifo_seg_t * fs);
+/**
+ * Add io events subscriber to list
+ *
+ * @param f	fifo
+ * @param sub	subscriber opaque index (typically app worker index)
+ */
+void svm_fifo_add_subscriber (svm_fifo_t * f, u8 sub);
+/**
+ * Remove io events subscriber form list
+ *
+ * @param f	fifo
+ * @param sub	subscriber index to be removed
+ */
+void svm_fifo_del_subscriber (svm_fifo_t * f, u8 subscriber);
+/**
+ * Number of out-of-order segments for fifo
+ *
+ * @param f	fifo
+ * @return	number of out of order segments
+ */
+u32 svm_fifo_n_ooo_segments (svm_fifo_t * f);
+/*
+ * First out-of-order segment for fifo
+ *
+ * @param f	fifo
+ * @return	first out-of-order segment for fifo
+ */
+ooo_segment_t *svm_fifo_first_ooo_segment (svm_fifo_t * f);
+format_function_t format_svm_fifo;
+
+/**
+ * Fifo max bytes to dequeue optimized for consumer
+ *
+ * @param f	fifo
+ * @return	max number of bytes that can be dequeued
+ */
 static inline u32
 svm_fifo_max_dequeue_cons (svm_fifo_t * f)
 {
@@ -201,7 +434,12 @@ svm_fifo_max_dequeue_cons (svm_fifo_t * f)
   return f_cursize (f, head, tail);
 }
 
-/* used by producer*/
+/**
+ * Fifo max bytes to dequeue optimized for producer
+ *
+ * @param f	fifo
+ * @return	max number of bytes that can be dequeued
+ */
 static inline u32
 svm_fifo_max_dequeue_prod (svm_fifo_t * f)
 {
@@ -210,9 +448,12 @@ svm_fifo_max_dequeue_prod (svm_fifo_t * f)
   return f_cursize (f, head, tail);
 }
 
-/* use producer or consumer specific functions for perfomance.
- * svm_fifo_max_dequeue_cons (svm_fifo_t *f)
- * svm_fifo_max_dequeue_prod (svm_fifo_t *f)
+/**
+ * Fifo max bytes to dequeue
+ *
+ * Note: use producer or consumer specific functions for performance:
+ * @ref svm_fifo_max_dequeue_cons (svm_fifo_t *f)
+ * @ref svm_fifo_max_dequeue_prod (svm_fifo_t *f)
  */
 static inline u32
 svm_fifo_max_dequeue (svm_fifo_t * f)
@@ -222,15 +463,22 @@ svm_fifo_max_dequeue (svm_fifo_t * f)
   return f_cursize (f, head, tail);
 }
 
-/* used by producer */
+/**
+ * Check if fifo is full optimized for producer
+ *
+ * @param f	fifo
+ * @return	1 if fifo is full 0 otherwise
+ */
 static inline int
 svm_fifo_is_full_prod (svm_fifo_t * f)
 {
   return (svm_fifo_max_dequeue_prod (f) == f->nitems);
 }
 
-/* use producer or consumer specific functions for perfomance.
- * svm_fifo_is_full_prod (svm_fifo_t * f)
+/* Check if fifo is full.
+ *
+ * Note: use producer or consumer specific functions for performance.
+ * @ref svm_fifo_is_full_prod (svm_fifo_t * f)
  * add cons version if needed
  */
 static inline int
@@ -239,23 +487,36 @@ svm_fifo_is_full (svm_fifo_t * f)
   return (svm_fifo_max_dequeue (f) == f->nitems);
 }
 
-/* used by consumer */
+/**
+ * Check if fifo is empty optimized for consumer
+ *
+ * @param f 	fifo
+ * @return	1 if fifo is empty 0 otherwise
+ */
 static inline int
 svm_fifo_is_empty_cons (svm_fifo_t * f)
 {
   return (svm_fifo_max_dequeue_cons (f) == 0);
 }
 
-/* used by producer */
+/**
+ * Check if fifo is empty optimized for producer
+ *
+ * @param f	fifo
+ * @return	1 if fifo is empty 0 otherwise
+ */
 static inline int
 svm_fifo_is_empty_prod (svm_fifo_t * f)
 {
   return (svm_fifo_max_dequeue_prod (f) == 0);
 }
 
-/* use producer or consumer specific functions for perfomance.
- * svm_fifo_is_empty_cons (svm_fifo_t * f)
- * svm_fifo_is_empty_prod (svm_fifo_t * f)
+/**
+ * Check if fifo is empty
+ *
+ * Note: use producer or consumer specific functions for perfomance.
+ * @ref svm_fifo_is_empty_cons (svm_fifo_t * f)
+ * @ref svm_fifo_is_empty_prod (svm_fifo_t * f)
  */
 static inline int
 svm_fifo_is_empty (svm_fifo_t * f)
@@ -263,6 +524,12 @@ svm_fifo_is_empty (svm_fifo_t * f)
   return (svm_fifo_max_dequeue (f) == 0);
 }
 
+/**
+ * Check if fifo is wrapped
+ *
+ * @param f	fifo
+ * @return 	1 if 'normalized' head is ahead of tail
+ */
 static inline u8
 svm_fifo_is_wrapped (svm_fifo_t * f)
 {
@@ -271,7 +538,14 @@ svm_fifo_is_wrapped (svm_fifo_t * f)
   return head % f->size > tail % f->size;
 }
 
-/* used by producer*/
+/**
+ * Maximum number of bytes that can be enqueued into fifo
+ *
+ * Optimized for producer
+ *
+ * @param f	fifo
+ * @return	max number of bytes that can be enqueued into fifo
+ */
 static inline u32
 svm_fifo_max_enqueue_prod (svm_fifo_t * f)
 {
@@ -280,8 +554,10 @@ svm_fifo_max_enqueue_prod (svm_fifo_t * f)
   return f_free_count (f, head, tail);
 }
 
-/* use producer or consumer specfic functions for perfomance.
- * svm_fifo_max_enqueue_prod (svm_fifo_t *f)
+/* Maximum number of bytes that can be enqueued into fifo
+ *
+ * Note: use producer or consumer specific functions for performance.
+ * @ref svm_fifo_max_enqueue_prod (svm_fifo_t *f)
  * add consumer specific version if needed.
  */
 static inline u32
@@ -292,111 +568,10 @@ svm_fifo_max_enqueue (svm_fifo_t * f)
   return f_free_count (f, head, tail);
 }
 
-static inline int
-svm_fifo_has_event (svm_fifo_t * f)
-{
-  return f->has_event;
-}
-
-static inline u8
-svm_fifo_has_ooo_data (svm_fifo_t * f)
-{
-  return f->ooos_list_head != OOO_SEGMENT_INVALID_INDEX;
-}
-
-/**
- * Sets fifo event flag.
- *
- * Also acts as a release ordering.
- *
- * @return 1 if flag was not set.
- */
-always_inline u8
-svm_fifo_set_event (svm_fifo_t * f)
-{
-  /* return __sync_lock_test_and_set (&f->has_event, 1) == 0;
-     return __sync_bool_compare_and_swap (&f->has_event, 0, 1); */
-  return !clib_atomic_swap_rel_n (&f->has_event, 1);
-}
-
-/**
- * Unsets fifo event flag.
- *
- * Also acts as an acquire barrier.
- */
-always_inline void
-svm_fifo_unset_event (svm_fifo_t * f)
-{
-  clib_atomic_swap_acq_n (&f->has_event, 0);
-}
-
-svm_fifo_t *svm_fifo_create (u32 data_size_in_bytes);
-void svm_fifo_init (svm_fifo_t * f, u32 size);
-
-/**
- * Allocate a fifo chunk on heap
- *
- * If the chunk is allocated on a fifo segment, this should be called
- * with the segment's heap pushed.
- *
- * @param size	chunk size in bytes. Will be rounded to the next highest
- * 		power-of-two
- * @return	new chunk or 0 if alloc failed
- */
-svm_fifo_chunk_t *svm_fifo_chunk_alloc (u32 size);
-
-/**
- * Grow fifo size by adding chunk to chunk list
- *
- * If fifos are allocated on a segment, this should be called with
- * the segment's heap pushed.
- *
- * @param f	fifo to be extended
- * @param c 	chunk or linked list of chunks to be added
- */
-void svm_fifo_add_chunk (svm_fifo_t * f, svm_fifo_chunk_t * c);
-void svm_fifo_free (svm_fifo_t * f);
-/**
- * Cleanup fifo chunk lookup rb tree
- *
- * The rb tree is allocated in segment heap so this should be called
- * with it pushed.
- *
- * @param f 	fifo to cleanup
- */
-void svm_fifo_free_chunk_lookup (svm_fifo_t * f);
-/**
- * Cleanup fifo ooo data
- *
- * The ooo data is allocated in producer process memory. The fifo
- * segment heap should not be pushed.
- *
- * @param f	fifo to cleanup
- */
-void svm_fifo_free_ooo_data (svm_fifo_t * f);
-
-int svm_fifo_enqueue_nowait (svm_fifo_t * f, u32 max_bytes,
-			     const u8 * copy_from_here);
-int svm_fifo_enqueue_with_offset (svm_fifo_t * f, u32 offset,
-				  u32 required_bytes, u8 * copy_from_here);
-int svm_fifo_dequeue_nowait (svm_fifo_t * f, u32 max_bytes, u8 * copy_here);
-
-int svm_fifo_peek (svm_fifo_t * f, u32 offset, u32 max_bytes, u8 * copy_here);
-int svm_fifo_dequeue_drop (svm_fifo_t * f, u32 max_bytes);
-void svm_fifo_dequeue_drop_all (svm_fifo_t * f);
-int svm_fifo_segments (svm_fifo_t * f, svm_fifo_seg_t * fs);
-void svm_fifo_segments_free (svm_fifo_t * f, svm_fifo_seg_t * fs);
-void svm_fifo_init_pointers (svm_fifo_t * f, u32 head, u32 tail);
-void svm_fifo_clone (svm_fifo_t * df, svm_fifo_t * sf);
-void svm_fifo_overwrite_head (svm_fifo_t * f, u8 * data, u32 len);
-void svm_fifo_add_subscriber (svm_fifo_t * f, u8 subscriber);
-void svm_fifo_del_subscriber (svm_fifo_t * f, u8 subscriber);
-format_function_t format_svm_fifo;
-
 /**
  * Max contiguous chunk of data that can be read
  */
-always_inline u32
+static inline u32
 svm_fifo_max_read_chunk (svm_fifo_t * f)
 {
   u32 head, tail;
@@ -410,7 +585,7 @@ svm_fifo_max_read_chunk (svm_fifo_t * f)
 /**
  * Max contiguous chunk of data that can be written
  */
-always_inline u32
+static inline u32
 svm_fifo_max_write_chunk (svm_fifo_t * f)
 {
   u32 head, tail;
@@ -425,19 +600,22 @@ svm_fifo_max_write_chunk (svm_fifo_t * f)
  * Advance tail pointer
  *
  * Useful for moving tail pointer after external enqueue.
+ *
+ * @param f		fifo
+ * @param len		number of bytes to add to tail
  */
-always_inline void
-svm_fifo_enqueue_nocopy (svm_fifo_t * f, u32 bytes)
+static inline void
+svm_fifo_enqueue_nocopy (svm_fifo_t * f, u32 len)
 {
-  ASSERT (bytes <= svm_fifo_max_enqueue_prod (f));
+  ASSERT (len <= svm_fifo_max_enqueue_prod (f));
   /* load-relaxed: producer owned index */
   u32 tail = f->tail;
-  tail += bytes;
+  tail += len;
   /* store-rel: producer owned index (paired with load-acq in consumer) */
   clib_atomic_store_rel_n (&f->tail, tail);
 }
 
-always_inline u8 *
+static inline u8 *
 svm_fifo_head (svm_fifo_t * f)
 {
   /* load-relaxed: consumer owned index */
@@ -445,7 +623,7 @@ svm_fifo_head (svm_fifo_t * f)
 	  + ((f->head % f->size) - f->head_chunk->start_byte));
 }
 
-always_inline u8 *
+static inline u8 *
 svm_fifo_tail (svm_fifo_t * f)
 {
   /* load-relaxed: producer owned index */
@@ -453,18 +631,132 @@ svm_fifo_tail (svm_fifo_t * f)
 	  + ((f->tail % f->size) - f->tail_chunk->start_byte));
 }
 
+static inline u8
+svm_fifo_n_subscribers (svm_fifo_t * f)
+{
+  return f->n_subscribers;
+}
+
+/**
+ * Check if fifo has out-of-order data
+ *
+ * @param f	fifo
+ * @return	1 if fifo has ooo data, 0 otherwise
+ */
+static inline u8
+svm_fifo_has_ooo_data (svm_fifo_t * f)
+{
+  return f->ooos_list_head != OOO_SEGMENT_INVALID_INDEX;
+}
+
+static inline ooo_segment_t *
+svm_fifo_newest_ooo_segment (svm_fifo_t * f)
+{
+  if (f->ooos_newest == OOO_SEGMENT_INVALID_INDEX)
+    return 0;
+  return pool_elt_at_index (f->ooo_segments, f->ooos_newest);
+}
+
+static inline void
+svm_fifo_newest_ooo_segment_reset (svm_fifo_t * f)
+{
+  f->ooos_newest = OOO_SEGMENT_INVALID_INDEX;
+}
+
+static inline u32
+ooo_segment_offset_prod (svm_fifo_t * f, ooo_segment_t * s)
+{
+  u32 tail;
+  /* load-relaxed: producer owned index */
+  tail = f->tail;
+
+  return f_distance_to (f, s->start, tail);
+}
+
+static inline u32
+ooo_segment_length (svm_fifo_t * f, ooo_segment_t * s)
+{
+  return s->length;
+}
+
+/**
+ * Check if fifo has io event
+ *
+ * @param f	fifo
+ * @return	1 if fifo has event, 0 otherwise
+ */
+static inline int
+svm_fifo_has_event (svm_fifo_t * f)
+{
+  return f->has_event;
+}
+
+/**
+ * Set fifo event flag.
+ *
+ * Forces release semantics.
+ *
+ * @param f	fifo
+ * @return 	1 if flag was not set, 0 otherwise
+ */
+always_inline u8
+svm_fifo_set_event (svm_fifo_t * f)
+{
+  return !clib_atomic_swap_rel_n (&f->has_event, 1);
+}
+
+/**
+ * Unset fifo event flag.
+ *
+ * Forces acquire semantics
+ *
+ * @param f	fifo
+ */
+always_inline void
+svm_fifo_unset_event (svm_fifo_t * f)
+{
+  clib_atomic_swap_acq_n (&f->has_event, 0);
+}
+
+/**
+ * Set specific want tx notification flag
+ *
+ * For list of flags see @ref svm_fifo_tx_ntf_t
+ *
+ * @param f		fifo
+ * @param ntf_type	type of notification requested
+ */
 static inline void
 svm_fifo_add_want_tx_ntf (svm_fifo_t * f, u8 ntf_type)
 {
   f->want_tx_ntf |= ntf_type;
 }
 
+/**
+ * Clear specific want tx notification flag
+ *
+ * For list of flags see @ref svm_fifo_tx_ntf_t
+ *
+ * @param f 		fifo
+ * @param ntf_type	type of notification to be cleared
+ */
 static inline void
 svm_fifo_del_want_tx_ntf (svm_fifo_t * f, u8 ntf_type)
 {
   f->want_tx_ntf &= ~ntf_type;
 }
 
+/**
+ * Clear the want tx notification flag and set has tx notification
+ *
+ * Should be used after enqueuing a tx event. This clears the
+ * SVM_FIFO_WANT_TX_NOTIF flag but it does not clear
+ * SVM_FIFO_WANT_TX_NOTIF_IF_FULL. If the latter was set, has_tx_ntf is
+ * set to avoid enqueueing tx events for for all dequeue operations until
+ * it is manually cleared.
+ *
+ * @param f	fifo
+ */
 static inline void
 svm_fifo_clear_tx_ntf (svm_fifo_t * f)
 {
@@ -473,12 +765,31 @@ svm_fifo_clear_tx_ntf (svm_fifo_t * f)
   svm_fifo_del_want_tx_ntf (f, SVM_FIFO_WANT_TX_NOTIF);
 }
 
+/**
+ * Clear has tx notification flag
+ *
+ * The fifo generates only one event per SVM_FIFO_WANT_TX_NOTIF_IF_FULL
+ * request and sets has_tx_ntf. To received new events the flag must be
+ * cleared using this function.
+ *
+ * @param f	fifo
+ */
 static inline void
 svm_fifo_reset_tx_ntf (svm_fifo_t * f)
 {
   f->has_tx_ntf = 0;
 }
 
+/**
+ * Check if fifo needs tx notification
+ *
+ * Determines based on tx notification request flags and state of the fifo if
+ * a tx io event should be generated.
+ *
+ * @param f		fifo
+ * @param n_last_deq	number of bytes last dequeued
+ * @return		1 if tx io event should be generated, 0 otherwise
+ */
 static inline u8
 svm_fifo_needs_tx_ntf (svm_fifo_t * f, u32 n_last_deq)
 {
@@ -501,73 +812,6 @@ svm_fifo_needs_tx_ntf (svm_fifo_t * f, u32 n_last_deq)
   return 0;
 }
 
-always_inline u8
-svm_fifo_n_subscribers (svm_fifo_t * f)
-{
-  return f->n_subscribers;
-}
-
-u32 svm_fifo_number_ooo_segments (svm_fifo_t * f);
-ooo_segment_t *svm_fifo_first_ooo_segment (svm_fifo_t * f);
-
-always_inline ooo_segment_t *
-svm_fifo_newest_ooo_segment (svm_fifo_t * f)
-{
-  if (f->ooos_newest == OOO_SEGMENT_INVALID_INDEX)
-    return 0;
-  return pool_elt_at_index (f->ooo_segments, f->ooos_newest);
-}
-
-always_inline void
-svm_fifo_newest_ooo_segment_reset (svm_fifo_t * f)
-{
-  f->ooos_newest = OOO_SEGMENT_INVALID_INDEX;
-}
-
-always_inline u32
-ooo_segment_distance_from_tail (svm_fifo_t * f, u32 pos, u32 tail)
-{
-  return ((f->size + pos - tail) % f->size);
-}
-
-always_inline u32
-ooo_segment_distance_to_tail (svm_fifo_t * f, u32 pos, u32 tail)
-{
-  return ((f->size + tail - pos) % f->size);
-}
-
-always_inline u32
-ooo_segment_offset_prod (svm_fifo_t * f, ooo_segment_t * s)
-{
-  u32 tail;
-  /* load-relaxed: producer owned index */
-  tail = f->tail;
-
-  return ooo_segment_distance_from_tail (f, s->start, tail);
-}
-
-always_inline u32
-ooo_segment_length (svm_fifo_t * f, ooo_segment_t * s)
-{
-  return s->length;
-}
-
-always_inline ooo_segment_t *
-ooo_segment_get_prev (svm_fifo_t * f, ooo_segment_t * s)
-{
-  if (s->prev == OOO_SEGMENT_INVALID_INDEX)
-    return 0;
-  return pool_elt_at_index (f->ooo_segments, s->prev);
-}
-
-always_inline ooo_segment_t *
-ooo_segment_next (svm_fifo_t * f, ooo_segment_t * s)
-{
-  if (s->next == OOO_SEGMENT_INVALID_INDEX)
-    return 0;
-  return pool_elt_at_index (f->ooo_segments, s->next);
-}
-
 #endif /* __included_ssvm_fifo_h__ */
 
 /*
diff --git a/src/tests/vnet/session/udp_echo.c b/src/tests/vnet/session/udp_echo.c
index f1ecca8e926..3a70d3964c6 100644
--- a/src/tests/vnet/session/udp_echo.c
+++ b/src/tests/vnet/session/udp_echo.c
@@ -447,10 +447,9 @@ cut_through_thread_fn (void *arg)
 	{
 	  /* We read from the tx fifo and write to the rx fifo */
 	  if (utm->have_return || do_dequeue)
-	    actual_transfer = svm_fifo_dequeue_nowait (rx_fifo,
-						       vec_len
-						       (my_copy_buffer),
-						       my_copy_buffer);
+	    actual_transfer = svm_fifo_dequeue (rx_fifo,
+						vec_len (my_copy_buffer),
+						my_copy_buffer);
 	  else
 	    {
 	      /* We don't do anything with the data, drop it */
@@ -467,8 +466,8 @@ cut_through_thread_fn (void *arg)
 	  buffer_offset = 0;
 	  while (actual_transfer > 0)
 	    {
-	      rv = svm_fifo_enqueue_nowait (tx_fifo, actual_transfer,
-					    my_copy_buffer + buffer_offset);
+	      rv = svm_fifo_enqueue (tx_fifo, actual_transfer,
+				     my_copy_buffer + buffer_offset);
 	      if (rv > 0)
 		{
 		  actual_transfer -= rv;
diff --git a/src/vnet/session-apps/echo_client.c b/src/vnet/session-apps/echo_client.c
index 8366c56aa6b..bcb2edf3792 100644
--- a/src/vnet/session-apps/echo_client.c
+++ b/src/vnet/session-apps/echo_client.c
@@ -97,7 +97,7 @@ send_data_chunk (echo_client_main_t * ecm, eclient_session_t * s)
 	  clib_memcpy_fast (&hdr.lcl_ip, &at->lcl_ip,
 			    sizeof (ip46_address_t));
 	  hdr.lcl_port = at->lcl_port;
-	  svm_fifo_enqueue_nowait (f, sizeof (hdr), (u8 *) & hdr);
+	  svm_fifo_enqueue (f, sizeof (hdr), (u8 *) & hdr);
 	  svm_fifo_enqueue_nocopy (f, rv);
 	  session_send_io_evt_to_thread_custom (&f->master_session_index,
 						s->thread_index,
diff --git a/src/vnet/session-apps/http_server.c b/src/vnet/session-apps/http_server.c
index c7e06bfbb2d..ace3c75ebb8 100644
--- a/src/vnet/session-apps/http_server.c
+++ b/src/vnet/session-apps/http_server.c
@@ -310,7 +310,7 @@ send_data (http_session_t * hs, u8 * data)
     {
       int actual_transfer;
 
-      actual_transfer = svm_fifo_enqueue_nowait
+      actual_transfer = svm_fifo_enqueue
 	(hs->tx_fifo, bytes_to_send, data + offset);
 
       /* Made any progress? */
diff --git a/src/vnet/session/application_interface.h b/src/vnet/session/application_interface.h
index aa1a3f30877..234813e5814 100644
--- a/src/vnet/session/application_interface.h
+++ b/src/vnet/session/application_interface.h
@@ -469,10 +469,10 @@ app_send_dgram_raw (svm_fifo_t * f, app_session_transport_t * at,
   hdr.rmt_port = at->rmt_port;
   clib_memcpy_fast (&hdr.lcl_ip, &at->lcl_ip, sizeof (ip46_address_t));
   hdr.lcl_port = at->lcl_port;
-  rv = svm_fifo_enqueue_nowait (f, sizeof (hdr), (u8 *) & hdr);
+  rv = svm_fifo_enqueue (f, sizeof (hdr), (u8 *) & hdr);
   ASSERT (rv == sizeof (hdr));
 
-  rv = svm_fifo_enqueue_nowait (f, actual_write, data);
+  rv = svm_fifo_enqueue (f, actual_write, data);
   if (do_evt)
     {
       if (rv > 0 && svm_fifo_set_event (f))
@@ -497,7 +497,7 @@ app_send_stream_raw (svm_fifo_t * f, svm_msg_q_t * vpp_evt_q, u8 * data,
 {
   int rv;
 
-  rv = svm_fifo_enqueue_nowait (f, len, data);
+  rv = svm_fifo_enqueue (f, len, data);
   if (do_evt)
     {
       if (rv > 0 && svm_fifo_set_event (f))
@@ -572,7 +572,7 @@ app_recv_stream_raw (svm_fifo_t * f, u8 * buf, u32 len, u8 clear_evt, u8 peek)
   if (peek)
     return svm_fifo_peek (f, 0, len, buf);
 
-  return svm_fifo_dequeue_nowait (f, len, buf);
+  return svm_fifo_dequeue (f, len, buf);
 }
 
 always_inline int
diff --git a/src/vnet/session/session.c b/src/vnet/session/session.c
index aaf252be257..75f7baf7318 100644
--- a/src/vnet/session/session.c
+++ b/src/vnet/session/session.c
@@ -296,7 +296,7 @@ session_enqueue_chain_tail (session_t * s, vlib_buffer_t * b,
 	continue;
       if (is_in_order)
 	{
-	  rv = svm_fifo_enqueue_nowait (s->rx_fifo, len, data);
+	  rv = svm_fifo_enqueue (s->rx_fifo, len, data);
 	  if (rv == len)
 	    {
 	      written += rv;
@@ -363,9 +363,9 @@ session_enqueue_stream_connection (transport_connection_t * tc,
 
   if (is_in_order)
     {
-      enqueued = svm_fifo_enqueue_nowait (s->rx_fifo,
-					  b->current_length,
-					  vlib_buffer_get_current (b));
+      enqueued = svm_fifo_enqueue (s->rx_fifo,
+				   b->current_length,
+				   vlib_buffer_get_current (b));
       if (PREDICT_FALSE ((b->flags & VLIB_BUFFER_NEXT_PRESENT)
 			 && enqueued >= 0))
 	{
@@ -414,10 +414,9 @@ session_enqueue_dgram_connection (session_t * s,
   ASSERT (svm_fifo_max_enqueue_prod (s->rx_fifo)
 	  >= b->current_length + sizeof (*hdr));
 
-  svm_fifo_enqueue_nowait (s->rx_fifo, sizeof (session_dgram_hdr_t),
-			   (u8 *) hdr);
-  enqueued = svm_fifo_enqueue_nowait (s->rx_fifo, b->current_length,
-				      vlib_buffer_get_current (b));
+  svm_fifo_enqueue (s->rx_fifo, sizeof (session_dgram_hdr_t), (u8 *) hdr);
+  enqueued = svm_fifo_enqueue (s->rx_fifo, b->current_length,
+			       vlib_buffer_get_current (b));
   if (PREDICT_FALSE ((b->flags & VLIB_BUFFER_NEXT_PRESENT) && enqueued >= 0))
     {
       in_order_off = enqueued > b->current_length ? enqueued : 0;
diff --git a/src/vnet/session/session_node.c b/src/vnet/session/session_node.c
index 605fd584e2d..1a04658cb41 100644
--- a/src/vnet/session/session_node.c
+++ b/src/vnet/session/session_node.c
@@ -414,8 +414,8 @@ session_tx_fifo_chain_tail (vlib_main_t * vm, session_tx_context_t * ctx,
 		}
 	    }
 	  else
-	    n_bytes_read = svm_fifo_dequeue_nowait (ctx->s->tx_fifo,
-						    len_to_deq, data);
+	    n_bytes_read = svm_fifo_dequeue (ctx->s->tx_fifo,
+					     len_to_deq, data);
 	}
       ASSERT (n_bytes_read == len_to_deq);
       chain_b->current_length = n_bytes_read;
@@ -494,8 +494,8 @@ session_tx_fill_buffer (vlib_main_t * vm, session_tx_context_t * ctx,
 	}
       else
 	{
-	  n_bytes_read = svm_fifo_dequeue_nowait (ctx->s->tx_fifo,
-						  len_to_deq, data0);
+	  n_bytes_read = svm_fifo_dequeue (ctx->s->tx_fifo,
+					   len_to_deq, data0);
 	  ASSERT (n_bytes_read > 0);
 	}
     }