linux-kernel - Re: [PATCH V2 5/6] vhost_net: poll vhost queue after marking DMA is done

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Message-ID: <20140212160117.GA25440@redhat.com>
Date:	Wed, 12 Feb 2014 18:01:17 +0200
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Qin Chuanyu <qinchuanyu@...wei.com>
Cc:	Jason Wang <jasowang@...hat.com>,
	virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [PATCH V2 5/6] vhost_net: poll vhost queue after marking DMA is
 done

On Wed, Feb 12, 2014 at 03:38:18PM +0800, Qin Chuanyu wrote:
> another question is that vhost_zerocopy_callback is called by kfree_skb,
> it may called in different thread context.
> vhost_poll_queue is called decided by ubufs->kref.refcount, this may
> cause there isn't any thread call  vhost_poll_queue, but at least
> one is needed. and this cause network break.
> We could repeat it by using 8 netperf thread in guest to xmit tcp to
> its host.

Thanks a lot for the report, will send the patch soon.

> 
> I think if using atomic_read to decide while do vhost_poll_queue or not,
> at least a spink_lock is needed.

No, nothing so drastic.
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