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Message-ID: <20120417045736.GA31278@redhat.com> Date: Tue, 17 Apr 2012 07:57:37 +0300 From: "Michael S. Tsirkin" <mst@...hat.com> To: Jason Wang <jasowang@...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 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 -- 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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