Messages in this thread | | | Date | Tue, 17 Apr 2012 14:30:27 +0800 | From | Jason Wang <> | Subject | Re: [PATCH 6/6] vhost_net: don't poll on -EFAULT |
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On 04/17/2012 02:07 PM, Michael S. Tsirkin wrote: > On Tue, Apr 17, 2012 at 01:54:55PM +0800, Jason Wang wrote: >> 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. > Yes but do you have a test that makes guest hit EFAULT or EINVAL?
Looks like we can do this by supplying an invalid hdr_len in vnet header as tap does the check for this. > -- > To unsubscribe from this list: send the line "unsubscribe netdev" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html
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