On Fri, Nov 04, 2016 at 09:09:22AM +0100, Maxime Coquelin wrote:
>
>
> On 11/04/2016 03:00 AM, Yuanhan Liu wrote:
> >On Thu, Nov 03, 2016 at 09:36:52PM +0100, Maxime Coquelin wrote:
> >>Hi Yuanhan,
> >>
> >>On 11/03/2016 05:09 PM, Yuanhan Liu wrote:
> >>>This reverts commit 9a0615af7746 ("virtio: fix restart"); conflict is
> >>>manually addressed.
> >>>
> >>>Kyle reported an issue with above commit
> >>>
> >>> qemu-kvm: Guest moved used index from 5 to 1
> >>>
> >>>with following steps,
> >>>
> >>> 1) Start my virtio interfaces
> >>> 2) Send some traffic into/out of the interfaces
> >>> 3) Stop the interfaces
> >>> 4) Start the interfaces
> >>> 5) Send some more traffic
> >>>
> >>>And here are some quotes from Kyle's analysis,
> >>>
> >>> Prior to the patch, if an interface were stopped then started, without
> >>> restarting the application, the queues would be left as-is, because
> >>> hw->started would be set to 1. Now, calling stop sets hw->started to 0,
> >>> which means the next call to start will "touch the queues". This is the
> >>> unintended side-effect that causes the problem.
> >>
> >>Maybe a good idea to explain what is the problem the revert aims to fix.
> >
> >It aims to fix the issue, by "not touching the queues" on restart.
> >
> >>It does not seem to be clearly stated in the commit message.
> >
> >I was thinking the quote from Kyle is enough. How about following supplement:
> >
> > We should not touch the queues once the init is done, otherwise, the
> > vring state of virtio PMD driver and vhost-user would be inconsistent,
> > leading some issue like above.
> >
> > Thus this patch is reverted.
> >
> >Better now?
> Yes, this is much clearer from my PoV.
Fixed, and series applied to dpdk-next-virtio.
Thanks for the review!
--yliu
