svm_fifo rework to avoid contention on cursize

Problems Addressed:
- Contention of cursize by producer and consumer.
- Reduce the no of modulo operations.

Changes:
- Synchronization between producer and consumer changed from cursize
  to head and tail indexes
  Implications: reduces the usable size of fifo by 1.
- Using weaker memory ordering C++11 atomics to access head and tail
  based on producer and consumer role.
- Head and tail indexes are unsigned 32 bit integers. Additions and
  subtraction on them are implicit 32 bit Modulo operation.
- Adding weaker memory ordering variants of max_enq, max_deq, is_empty
  and is_full Using them appropriately in all places.

Perfomance improvement (iperf3 via Hoststack):

iperf3 Server: Marvell ThunderX2(AArch64) - iperf3 Client: Skylake(x86)
   ~6%(256 rxd/txd) - ~11%(2048 rxd/txd)

Change-Id: I1d484e000e437430fdd5a819657d1c6b62443018
Signed-off-by: Sirshak Das <sirshak.das@arm.com>
Reviewed-by: Honnappa Nagarahalli <honnappa.nagarahalli@arm.com>

1 files changed, 5 insertions, 5 deletions

diff --git a/src/vcl/vcl_private.c b/src/vcl/vcl_private.c
index a572fd4d540..3e82becfc93 100644
--- a/src/vcl/vcl_private.c
+++ b/src/vcl/vcl_private.c
@@ -346,9 +346,9 @@ vcl_session_read_ready (vcl_session_t * session)
     return clib_fifo_elts (session->accept_evts_fifo);
 
   if (vcl_session_is_ct (session))
-    return svm_fifo_max_dequeue (session->ct_rx_fifo);
+    return svm_fifo_max_dequeue_cons (session->ct_rx_fifo);
 
-  return svm_fifo_max_dequeue (session->rx_fifo);
+  return svm_fifo_max_dequeue_cons (session->rx_fifo);
 }
 
 int
@@ -365,7 +365,7 @@ vcl_session_write_ready (vcl_session_t * session)
   if (PREDICT_FALSE (session->session_state & STATE_LISTEN))
     {
       if (session->tx_fifo)
-	return svm_fifo_max_enqueue (session->tx_fifo);
+	return svm_fifo_max_enqueue_prod (session->tx_fifo);
       else
 	return VPPCOM_EBADFD;
     }
@@ -383,9 +383,9 @@ vcl_session_write_ready (vcl_session_t * session)
     }
 
   if (vcl_session_is_ct (session))
-    return svm_fifo_max_enqueue (session->ct_tx_fifo);
+    return svm_fifo_max_enqueue_prod (session->ct_tx_fifo);
 
-  return svm_fifo_max_enqueue (session->tx_fifo);
+  return svm_fifo_max_enqueue_prod (session->tx_fifo);
 }
 
 /*