lkml.org 
[lkml]   [2012]   [Apr]   [17]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [PATCH 6/6] vhost_net: don't poll on -EFAULT
    On Tue, Apr 17, 2012 at 02:30:27PM +0800, Jason Wang wrote:
    > 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.

    Ah so you patched qemu to do this? Cool. Can you post the patch for testing pls?

    > >--
    > >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


    \
     
     \ /
      Last update: 2012-04-17 12:21    [W:0.023 / U:1.092 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site