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

From: Shirley Ma <mashirle@us.ibm.com>
To: Jason Wang <jasowang@redhat.com>
Cc: "Michael S. Tsirkin" <mst@redhat.com>,
	eric.dumazet@gmail.com, netdev@vger.kernel.org,
	linux-kernel@vger.kernel.org, ebiederm@xmission.com,
	davem@davemloft.net
Subject: Re: [V2 PATCH 9/9] vhost: zerocopy: poll vq in zerocopy callback
Date: Thu, 17 May 2012 08:34:22 -0700	[thread overview]
Message-ID: <1337268862.10741.58.camel@oc3660625478.ibm.com> (raw)
In-Reply-To: <4FB4677A.8020402@redhat.com>

On Thu, 2012-05-17 at 10:50 +0800, Jason Wang wrote:
> The problem is we may stop the tx queue when there no enough capacity
> to 
> place packets, at this moment  we depends on the tx interrupt to 
> re-enable the tx queue. So if we didn't poll the vhost during
> callback, 
> guest may lose the tx interrupt to re-enable the tx queue which could 
> stall the whole tx queue. 

VHOST_MAX_PEND should handle the capacity. 

Hasn't the above situation been handled in handle_tx() code?:
...
                        if (unlikely(num_pends > VHOST_MAX_PEND)) {
                                tx_poll_start(net, sock);
                                set_bit(SOCK_ASYNC_NOSPACE, &sock->flags);
                                break;
                        }
...

Thanks
Shirley