Re: [PATCH net-next 8/8] vhost-net: reduce vq polling on tx zerocopy

Vlad Yasevich
2012-10-30T15:47:55Z

On 10/29/2012 11:49 AM, Michael S. Tsirkin wrote:
> It seems that to avoid deadlocks it is enough to poll vq before
> we are going to use the last buffer. This should be faster than
> c70aa540c7a9f67add11ad3161096fb95233aa2e.
>
> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> ---
> drivers/vhost/net.c | 12 ++++++++++--
> 1 file changed, 10 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
> index 8e9de79..3967f82 100644
> --- a/drivers/vhost/net.c
> +++ b/drivers/vhost/net.c
> @@ -197,8 +197,16 @@ static void vhost_zerocopy_callback(struct ubuf_info *ubuf, int status)
> {
> struct vhost_ubuf_ref *ubufs = ubuf->ctx;
> struct vhost_virtqueue *vq = ubufs->vq;
> -
> - vhost_poll_queue(&vq->poll);
> + int cnt = atomic_read(&ubufs->kref.refcount);
> +
> + /*
> + * Trigger polling thread if guest stopped submitting new buffers:
> + * in this case, the refcount after decrement will eventually reach 1
> + * so here it is 2.
> + * We also trigger polling periodically after each 16 packets.
> + */
> + if (cnt <= 2 || !(cnt % 16))

Why 16? Does it make sense to make it configurable?

-vlad

> + vhost_poll_queue(&vq->poll);
> /* set len to mark this desc buffers done DMA */
> vq->heads[ubuf->desc].len = status ?
> VHOST_DMA_FAILED_LEN : VHOST_DMA_DONE_LEN;
>