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Date: Fri, 18 May 2012 08:29:34 -0700 From: Shirley Ma <mashirle@...ibm.com> To: Jason Wang <jasowang@...hat.com> Cc: "Michael S. Tsirkin" <mst@...hat.com>, eric.dumazet@...il.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 Fri, 2012-05-18 at 17:58 +0800, Jason Wang wrote: > On 05/17/2012 11:34 PM, Shirley Ma wrote: > > 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 > > It may not help in because: > > - tx polling depends on skb_orphan() which is often called by device > driver when it place the packet into the queue of the devices instead > of when the packets were sent. So it was too early for vhost to be > notified. Then do you think it's better to replace with vhost_poll_queue here instead? > - it only works when the pending DMAs exceeds VHOST_MAX_PEND, it's > highly possible that guest needs to be notified when the pending > packets > isn't so much. In which situation the guest needs to be notified when there is no TX besides buffers run out? > So this piece of code may not help and could be removed and we need > to > poll the virt-queue during zerocopy callback ( through it could be > further optimized but may not be easy). Thanks Shirley -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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