avf: Handle chain buffer in TX properly

For chain buffer, need to traverse b->next_buffer to transmit all buffers
in the chain. Only set EOP at the last descriptor in the chain to signal
this is a chain descriptor.

Introduce slow path to handle ring wrap. This is needed because chain
buffer may consist of multiple pieces and it may span from near the end of
the ring to the beginning of the ring.

Type: fix
Ticket: VPP-1843

Signed-off-by: Steven Luong <sluong@cisco.com>
Change-Id: Id7c872f3e39e09f3566aa63f3cdba8f40736d508
(cherry picked from commit f7ab7b2d9bc0f42c1e766d22d49dd0dc4f28abb6)

2 files changed, 140 insertions, 7 deletions

diff --git a/src/plugins/avf/avf.h b/src/plugins/avf/avf.h
index 1ddae6671b0..356d6904641 100644
--- a/src/plugins/avf/avf.h
+++ b/src/plugins/avf/avf.h
@@ -327,7 +327,8 @@ typedef struct
 } avf_input_trace_t;
 
 #define foreach_avf_tx_func_error	       \
-_(NO_FREE_SLOTS, "no free tx slots")
+  _(SEGMENT_SIZE_EXCEEDED, "segment size exceeded")	\
+  _(NO_FREE_SLOTS, "no free tx slots")
 
 typedef enum
 {
diff --git a/src/plugins/avf/output.c b/src/plugins/avf/output.c
index 1e38377e844..6c43885569e 100644
--- a/src/plugins/avf/output.c
+++ b/src/plugins/avf/output.c
@@ -31,8 +31,8 @@ avf_tx_desc_get_dtyp (avf_tx_desc_t * d)
 }
 
 static_always_inline u16
-avf_tx_enqueue (vlib_main_t * vm, avf_txq_t * txq, u32 * buffers,
-		u32 n_packets, int use_va_dma)
+avf_tx_enqueue (vlib_main_t * vm, vlib_node_runtime_t * node, avf_txq_t * txq,
+		u32 * buffers, u32 n_packets, int use_va_dma)
 {
   u16 next = txq->next;
   u64 bits = AVF_TXD_CMD_EOP | AVF_TXD_CMD_RSV;
@@ -41,6 +41,8 @@ avf_tx_enqueue (vlib_main_t * vm, avf_txq_t * txq, u32 * buffers,
   u16 mask = txq->size - 1;
   vlib_buffer_t *b[4];
   avf_tx_desc_t *d = txq->descs + next;
+  u16 n_desc_needed;
+  vlib_buffer_t *b0;
 
   /* avoid ring wrap */
   n_desc_left = txq->size - clib_max (txq->next, txq->n_enqueued + 8);
@@ -48,6 +50,7 @@ avf_tx_enqueue (vlib_main_t * vm, avf_txq_t * txq, u32 * buffers,
   if (n_desc_left == 0)
     return 0;
 
+  /* Fast path, no ring wrap */
   while (n_packets_left && n_desc_left)
     {
       u32 or_flags;
@@ -103,6 +106,57 @@ avf_tx_enqueue (vlib_main_t * vm, avf_txq_t * txq, u32 * buffers,
       txq->bufs[next] = buffers[0];
       b[0] = vlib_get_buffer (vm, buffers[0]);
 
+      /* Deal with chain buffer if present */
+      if (b[0]->flags & VLIB_BUFFER_NEXT_PRESENT)
+	{
+	  n_desc_needed = 1;
+	  b0 = b[0];
+
+	  /* Wish there were a buffer count for chain buffer */
+	  while (b0->flags & VLIB_BUFFER_NEXT_PRESENT)
+	    {
+	      b0 = vlib_get_buffer (vm, b0->next_buffer);
+	      n_desc_needed++;
+	    }
+
+	  /* spec says data descriptor is limited to 8 segments */
+	  if (PREDICT_FALSE (n_desc_needed > 8))
+	    {
+	      vlib_buffer_free_one (vm, buffers[0]);
+	      vlib_error_count (vm, node->node_index,
+				AVF_TX_ERROR_SEGMENT_SIZE_EXCEEDED, 1);
+	      n_packets_left -= 1;
+	      buffers += 1;
+	      continue;
+	    }
+
+	  if (PREDICT_FALSE (n_desc_left < n_desc_needed))
+	    /*
+	     * Slow path may be able to to deal with this since it can handle
+	     * ring wrap
+	     */
+	    break;
+
+	  while (b[0]->flags & VLIB_BUFFER_NEXT_PRESENT)
+	    {
+	      if (use_va_dma)
+		d[0].qword[0] = vlib_buffer_get_current_va (b[0]);
+	      else
+		d[0].qword[0] = vlib_buffer_get_current_pa (vm, b[0]);
+
+	      d[0].qword[1] = (((u64) b[0]->current_length) << 34) |
+		AVF_TXD_CMD_RSV;
+
+	      next += 1;
+	      n_desc += 1;
+	      n_desc_left -= 1;
+	      d += 1;
+
+	      txq->bufs[next] = b[0]->next_buffer;
+	      b[0] = vlib_get_buffer (vm, b[0]->next_buffer);
+	    }
+	}
+
       if (use_va_dma)
 	d[0].qword[0] = vlib_buffer_get_current_va (b[0]);
       else
@@ -118,6 +172,84 @@ avf_tx_enqueue (vlib_main_t * vm, avf_txq_t * txq, u32 * buffers,
       d += 1;
     }
 
+  /* Slow path to support ring wrap */
+  if (PREDICT_FALSE (n_packets_left))
+    {
+      txq->n_enqueued += n_desc;
+
+      n_desc = 0;
+      d = txq->descs + (next & mask);
+
+      /* +8 to be consistent with fast path */
+      n_desc_left = txq->size - (txq->n_enqueued + 8);
+
+      while (n_packets_left && n_desc_left)
+	{
+	  txq->bufs[next & mask] = buffers[0];
+	  b[0] = vlib_get_buffer (vm, buffers[0]);
+
+	  /* Deal with chain buffer if present */
+	  if (b[0]->flags & VLIB_BUFFER_NEXT_PRESENT)
+	    {
+	      n_desc_needed = 1;
+	      b0 = b[0];
+
+	      while (b0->flags & VLIB_BUFFER_NEXT_PRESENT)
+		{
+		  b0 = vlib_get_buffer (vm, b0->next_buffer);
+		  n_desc_needed++;
+		}
+
+	      /* Spec says data descriptor is limited to 8 segments */
+	      if (PREDICT_FALSE (n_desc_needed > 8))
+		{
+		  vlib_buffer_free_one (vm, buffers[0]);
+		  vlib_error_count (vm, node->node_index,
+				    AVF_TX_ERROR_SEGMENT_SIZE_EXCEEDED, 1);
+		  n_packets_left -= 1;
+		  buffers += 1;
+		  continue;
+		}
+
+	      if (PREDICT_FALSE (n_desc_left < n_desc_needed))
+		break;
+
+	      while (b[0]->flags & VLIB_BUFFER_NEXT_PRESENT)
+		{
+		  if (use_va_dma)
+		    d[0].qword[0] = vlib_buffer_get_current_va (b[0]);
+		  else
+		    d[0].qword[0] = vlib_buffer_get_current_pa (vm, b[0]);
+
+		  d[0].qword[1] = (((u64) b[0]->current_length) << 34) |
+		    AVF_TXD_CMD_RSV;
+
+		  next += 1;
+		  n_desc += 1;
+		  n_desc_left -= 1;
+		  d = txq->descs + (next & mask);
+
+		  txq->bufs[next & mask] = b[0]->next_buffer;
+		  b[0] = vlib_get_buffer (vm, b[0]->next_buffer);
+		}
+	    }
+
+	  if (use_va_dma)
+	    d[0].qword[0] = vlib_buffer_get_current_va (b[0]);
+	  else
+	    d[0].qword[0] = vlib_buffer_get_current_pa (vm, b[0]);
+
+	  d[0].qword[1] = (((u64) b[0]->current_length) << 34) | bits;
+
+	  next += 1;
+	  n_desc += 1;
+	  buffers += 1;
+	  n_packets_left -= 1;
+	  n_desc_left -= 1;
+	  d = txq->descs + (next & mask);
+	}
+    }
+
   if ((slot = clib_ring_enq (txq->rs_slots)))
     {
       u16 rs_slot = slot[0] = (next - 1) & mask;
@@ -177,15 +309,15 @@ retry:
 	  n_free = (complete_slot + 1 - first) & mask;
 
 	  txq->n_enqueued -= n_free;
-	  vlib_buffer_free_from_ring (vm, txq->bufs, first, txq->size,
-				      n_free);
+	  vlib_buffer_free_from_ring_no_next (vm, txq->bufs, first, txq->size,
+					      n_free);
 	}
     }
 
   if (ad->flags & AVF_DEVICE_F_VA_DMA)
-    n_enq = avf_tx_enqueue (vm, txq, buffers, n_left, 1);
+    n_enq = avf_tx_enqueue (vm, node, txq, buffers, n_left, 1);
   else
-    n_enq = avf_tx_enqueue (vm, txq, buffers, n_left, 0);
+    n_enq = avf_tx_enqueue (vm, node, txq, buffers, n_left, 0);
 
   n_left -= n_enq;