From: Maxime Coquelin <maxime.coquelin@redhat.com>
Date: Thu, 7 Jun 2018 14:38:26 +0000 (+0200)
Subject: vhost: use SMP memory barrier before kicking guest
X-Git-Url: http://git.droids-corp.org/?a=commitdiff_plain;h=63b113afa51f223325642705685d3f1004cfdcaa;p=dpdk.git

vhost: use SMP memory barrier before kicking guest

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>
Reviewed-by: Tiwei Bie <tiwei.bie@intel.com>
---

diff --git a/lib/librte_vhost/vhost.h b/lib/librte_vhost/vhost.h
index 588b7cf9a7..528e01c8f9 100644
--- a/lib/librte_vhost/vhost.h
+++ b/lib/librte_vhost/vhost.h
@@ -593,7 +593,7 @@ 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)) {