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, 3 insertions, 3 deletions

diff --git a/src/vnet/session/session.c b/src/vnet/session/session.c
index 90248b64401..58ec1c01369 100644
--- a/src/vnet/session/session.c
+++ b/src/vnet/session/session.c
@@ -411,7 +411,7 @@ session_enqueue_dgram_connection (session_t * s,
 {
   int enqueued = 0, rv, in_order_off;
 
-  ASSERT (svm_fifo_max_enqueue (s->rx_fifo)
+  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),
@@ -508,7 +508,7 @@ session_enqueue_notify_inline (session_t * s)
   /* *INDENT-OFF* */
   SESSION_EVT_DBG(SESSION_EVT_ENQ, s, ({
       ed->data[0] = SESSION_IO_EVT_RX;
-      ed->data[1] = svm_fifo_max_dequeue (s->rx_fifo);
+      ed->data[1] = svm_fifo_max_dequeue_prod (s->rx_fifo);
   }));
   /* *INDENT-ON* */
 
@@ -1112,7 +1112,7 @@ session_transport_close (session_t * s)
    * point, either after sending everything or after a timeout, call delete
    * notify. This will finally lead to the complete cleanup of the session.
    */
-  if (svm_fifo_max_dequeue (s->tx_fifo))
+  if (svm_fifo_max_dequeue_cons (s->tx_fifo))
     s->session_state = SESSION_STATE_CLOSED_WAITING;
   else
     s->session_state = SESSION_STATE_CLOSED;