[dpdk-dev] [PATCH 1/8] net/virtio: revert "virtio: fix restart"
maxime.coquelin at redhat.com
Fri Nov 4 09:09:22 CET 2016
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.
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