[PATCH] vhost: use SMP memory barrier before kicking guest

From: Maxime Coquelin <maxime.coquelin@redhat.com>
To: zhihong.wang@intel.com, tiwei.bie@intel.com, dev@dpdk.org
Cc: Maxime Coquelin <maxime.coquelin@redhat.com>
Subject: [PATCH] vhost: use SMP memory barrier before kicking guest
Date: Thu,  7 Jun 2018 16:38:26 +0200	[thread overview]
Message-ID: <20180607143826.23647-1-maxime.coquelin@redhat.com> (raw)

vhost_vring_call() used rte_mb(), which translates into
mfence instruction on x86.

This patch changes to use rte_smp_mb(), which changed recently
to translate into a locked ADD instruction for performance
reason.

The measured gain is up to 3% with the testpmd benchmarks.

Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>
---
 lib/librte_vhost/vhost.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/librte_vhost/vhost.h b/lib/librte_vhost/vhost.h
index 58c425a5c..1bc99ed3c 100644
--- a/lib/librte_vhost/vhost.h
+++ b/lib/librte_vhost/vhost.h
@@ -591,7 +591,7 @@ static __rte_always_inline void
 vhost_vring_call(struct virtio_net *dev, struct vhost_virtqueue *vq)
 {
 	/* Flush used->idx update before we read avail->flags. */
-	rte_mb();
+	rte_smp_mb();
 
 	/* Don't kick guest if we don't reach index specified by guest. */
 	if (dev->features & (1ULL << VIRTIO_RING_F_EVENT_IDX)) {
-- 
2.14.3
