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

[Michael S. Tsirkin]

On Tue, Apr 17, 2012 at 11:27:01AM +0800, Jason Wang wrote:
> 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?

Sounds OK. BTW how do you test this?

-- 
MST
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