Subject: 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
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	 <20120516151444.GC9934@redhat.com>
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Date: Thu, 17 May 2012 08:34:22 -0700
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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

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