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, 2 insertions, 2 deletions

diff --git a/src/tests/vnet/session/tcp_echo.c b/src/tests/vnet/session/tcp_echo.c
index d76e9395a75..99b6765cdf5 100644
--- a/src/tests/vnet/session/tcp_echo.c
+++ b/src/tests/vnet/session/tcp_echo.c
@@ -507,7 +507,7 @@ recv_data_chunk (echo_main_t * em, echo_session_t * s, u8 * rx_buf)
 {
   int n_to_read, n_read;
 
-  n_to_read = svm_fifo_max_dequeue (s->rx_fifo);
+  n_to_read = svm_fifo_max_dequeue_cons (s->rx_fifo);
   if (!n_to_read)
     return;
 
@@ -1063,7 +1063,7 @@ server_handle_rx (echo_main_t * em, session_event_t * e)
    * message queue */
   svm_fifo_unset_event (s->rx_fifo);
 
-  max_dequeue = svm_fifo_max_dequeue (s->rx_fifo);
+  max_dequeue = svm_fifo_max_dequeue_cons (s->rx_fifo);
   if (PREDICT_FALSE (!max_dequeue))
     return;