Messages in this thread | | | Date | Tue, 17 Apr 2012 13:54:55 +0800 | From | Jason Wang <> | Subject | Re: [PATCH 6/6] vhost_net: don't poll on -EFAULT |
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On 04/17/2012 12:57 PM, Michael S. Tsirkin wrote: > 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? >
Not very hard, w/o this patch, we can see almost 100% cpu utilization for vhost thread if guest hit EFAULT or EINVAL. With this patch, the cpu utilization should be very low I think.
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