linux-kernel - Re: [V2 PATCH 9/9] vhost: zerocopy: poll vq in zerocopy callback

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Message-ID: <1337100630.8220.4.camel@oc3660625478.ibm.com>
Date:	Tue, 15 May 2012 09:50:30 -0700
From:	Shirley Ma <mashirle@...ibm.com>
To:	Jason Wang <jasowang@...hat.com>
Cc:	eric.dumazet@...il.com, mst@...hat.com, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, ebiederm@...ssion.com,
	davem@...emloft.net
Subject: Re: [V2 PATCH 9/9] vhost: zerocopy: poll vq in zerocopy callback

On Wed, 2012-05-02 at 11:42 +0800, Jason Wang wrote:
> We add used and signal guest in worker thread but did not poll the
> virtqueue
> during the zero copy callback. This may lead the missing of adding and
> signalling during zerocopy. Solve this by polling the virtqueue and
> let it
> wakeup the worker during callback.
> 
> Signed-off-by: Jason Wang <jasowang@...hat.com>
> ---
>  drivers/vhost/vhost.c |    1 +
>  1 files changed, 1 insertions(+), 0 deletions(-)
> 
> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> index 947f00d..7b75fdf 100644
> --- a/drivers/vhost/vhost.c
> +++ b/drivers/vhost/vhost.c
> @@ -1604,6 +1604,7 @@ void vhost_zerocopy_callback(void *arg)
>         struct vhost_ubuf_ref *ubufs = ubuf->arg;
>         struct vhost_virtqueue *vq = ubufs->vq;
> 
> +       vhost_poll_queue(&vq->poll);
>         /* set len = 1 to mark this desc buffers done DMA */
>         vq->heads[ubuf->desc].len = VHOST_DMA_DONE_LEN;
>         kref_put(&ubufs->kref, vhost_zerocopy_done_signal);

Doing so, we might have redundant vhost_poll_queue(). Do you know in
which scenario there might be missing of adding and signaling during
zerocopy?

Thanks
Shirley

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