Re: [dpdk-dev] [PATCH] vhost: use SMP memory barrier before kicking guest

[Tiwei Bie <tiwei.bie@intel.com>]

On Thu, Jun 07, 2018 at 04:38:26PM +0200, Maxime Coquelin wrote:
> 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
> 

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