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 588b7cf..528e01c 100644 (file)
--- 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)) {