[dpdk-dev] [memnic PATCH v2 4/7] pmd: use compiler barrier

[Hiroshi Shimamoto]

From: Hiroshi Shimamoto <h-shimam...@ct.jp.nec.com>

x86 can keep store ordering with standard operations.

Using memory barrier is much expensive in main packet processing loop.
Removing this improves xmit/recv packet performance.

We can see performance improvements with memnic-tester.
Using Xeon E5-2697 v2 @ 2.70GHz, 4 vCPU.
 size |  before  |  after
   64 | 4.18Mpps | 4.59Mpps
  128 | 3.85Mpps | 4.87Mpps
  256 | 4.01Mpps | 4.72Mpps
  512 | 3.52Mpps | 4.41Mpps
 1024 | 3.18Mpps | 3.64Mpps
 1280 | 2.86Mpps | 3.15Mpps
 1518 | 2.59Mpps | 2.87Mpps

Note: we have to take care if we use non-temporal cache.

Signed-off-by: Hiroshi Shimamoto <h-shimamoto at ct.jp.nec.com>
Reviewed-by: Hayato Momma <h-momma at ce.jp.nec.com>
---
 pmd/pmd_memnic.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/pmd/pmd_memnic.c b/pmd/pmd_memnic.c
index 872f3c4..0783440 100644
--- a/pmd/pmd_memnic.c
+++ b/pmd/pmd_memnic.c
@@ -316,7 +316,7 @@ static uint16_t memnic_recv_pkts(void *rx_queue,
                bytes += p->len;

 drop:
-               rte_mb();
+               rte_compiler_barrier();
                p->status = MEMNIC_PKT_ST_FREE;

                if (++idx >= MEMNIC_NR_PACKET)
@@ -403,7 +403,7 @@ retry:
                pkts++;
                bytes += pkt_len;

-               rte_mb();
+               rte_compiler_barrier();
                p->status = MEMNIC_PKT_ST_FILLED;

                rte_pktmbuf_free(tx_pkts[nr]);
-- 
1.8.3.1