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, 14 deletions

diff --git a/src/vnet/session/application_worker.c b/src/vnet/session/application_worker.c
index a8edad3edbb..dd1088e2cbb 100644
--- a/src/vnet/session/application_worker.c
+++ b/src/vnet/session/application_worker.c
@@ -369,21 +369,12 @@ app_worker_own_session (app_worker_t * app_wrk, session_t * s)
   if (app_worker_alloc_session_fifos (sm, s))
     return -1;
 
-  if (!svm_fifo_is_empty (rxf))
-    {
-      clib_memcpy_fast (s->rx_fifo->data, rxf->data, rxf->nitems);
-      s->rx_fifo->head = rxf->head;
-      s->rx_fifo->tail = rxf->tail;
-      s->rx_fifo->cursize = rxf->cursize;
-    }
+  if (!svm_fifo_is_empty_cons (rxf))
+    svm_fifo_clone (s->rx_fifo, rxf);
+
+  if (!svm_fifo_is_empty_cons (txf))
+    svm_fifo_clone (s->tx_fifo, txf);
 
-  if (!svm_fifo_is_empty (txf))
-    {
-      clib_memcpy_fast (s->tx_fifo->data, txf->data, txf->nitems);
-      s->tx_fifo->head = txf->head;
-      s->tx_fifo->tail = txf->tail;
-      s->tx_fifo->cursize = txf->cursize;
-    }
 
   segment_manager_dealloc_fifos (rxf, txf);