Re: [PATCH RFC v5 net-next 2/6] virtio_ring: try to disable event index callbacks in virtqueue_disable_cb()

From: Rusty Russell <rusty@rustcorp.com.au>
To: Jason Wang <jasowang@redhat.com>,
	netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
	virtualization@lists.linux-foundation.org, mst@redhat.com
Cc: pagupta@redhat.com
Subject: Re: [PATCH RFC v5 net-next 2/6] virtio_ring: try to disable event index callbacks in virtqueue_disable_cb()
Date: Tue, 10 Feb 2015 11:37:38 +1030	[thread overview]
Message-ID: <8761bay3ol.fsf@rustcorp.com.au> (raw)
In-Reply-To: <1423471165-34243-3-git-send-email-jasowang@redhat.com>

Jason Wang <jasowang@redhat.com> writes:
> Currently, we do nothing to prevent the callbacks in
> virtqueue_disable_cb() when event index is used. This may cause
> spurious interrupts which may damage the performance. This patch tries
> to publish avail event as the used even to prevent the callbacks.
>
> Signed-off-by: Jason Wang <jasowang@redhat.com>

Acked-by: Rusty Russell <rusty@rustcorp.com.au>

> ---
>  drivers/virtio/virtio_ring.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> index 545fed5..e9ffbfb 100644
> --- a/drivers/virtio/virtio_ring.c
> +++ b/drivers/virtio/virtio_ring.c
> @@ -539,6 +539,8 @@ void virtqueue_disable_cb(struct virtqueue *_vq)
>  	struct vring_virtqueue *vq = to_vvq(_vq);
>  
>  	vq->vring.avail->flags |= cpu_to_virtio16(_vq->vdev, VRING_AVAIL_F_NO_INTERRUPT);
> +	vring_used_event(&vq->vring) = cpu_to_virtio16(_vq->vdev,
> +						       vq->vring.avail->idx);
>  }
>  EXPORT_SYMBOL_GPL(virtqueue_disable_cb);
>  
> -- 
> 1.8.3.1
>
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