netdev - Re: [PATCH 6/6] vhost_net: don't poll on -EFAULT

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Message-ID: <4F8CE305.9090100@redhat.com>
Date:	Tue, 17 Apr 2012 11:27:01 +0800
From:	Jason Wang <jasowang@...hat.com>
To:	"Michael S. Tsirkin" <mst@...hat.com>
CC:	netdev@...r.kernel.org, xma@...ibm.com, davem@...emloft.net,
	linux-kernel@...r.kernel.org, ebiederm@...ssion.com
Subject: Re: [PATCH 6/6] vhost_net: don't poll on -EFAULT

On 04/16/2012 09:39 PM, Michael S. Tsirkin wrote:
> On Mon, Apr 16, 2012 at 04:28:10PM +0800, Jason Wang wrote:
>> >  On 04/16/2012 03:16 PM, Michael S. Tsirkin wrote:
>>> >  >On Mon, Apr 16, 2012 at 02:08:33PM +0800, Jason Wang wrote:
>>>> >  >>Currently, we restart tx polling unconditionally when sendmsg()
>>>> >  >>fails. This would cause unnecessary wakeups of vhost wokers as it's
>>>> >  >>only needed when the socket send buffer were exceeded.
>>> >  >Why is this a problem?
>> >  
>> >  This issue is when guest driver is able to hit the -EFAULT, vhost
>> >  discard the the descriptor and restart the polling. This would wake
>> >  vhost thread and repeat the loop again which waste cpu.
> Does same thing happen if we get an error from copy from user?
>

Right, so do you think it makes sense that we only restart polling on 
-EAGAIN or -ENOBUFS?
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