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Date: Thu, 2 Sep 2010 15:06:48 +0100
Message-ID: <AANLkTimjuyHMkVPrjpPAe2sMwCAVnQjDigQkHmV4ZhAc@mail.gmail.com>
Subject: Re: I/O scheduler deadlocks on Xen virtual block devices
From: Doug Neal <dneallkml@gmail.com>
To: Jeff Moyer <jmoyer@redhat.com>, linux-kernel@vger.kernel.org
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>>>
>>> Did you try these different I/O schedulers in the domU or on the dom0?
>>> Does switching I/O schedulers in either place make the problem go away
>>> when it happens?
>>>
>>
>> In the domU, and the bug was present in all cases. The dom0 was using
>> cfq. I'll run the tests again using each scheduler in the dom0 with
>> domU set to noop and report back.
>
> While I think this is an interesting test, you need only test one I/O
> scheduler in the dom0.  Also, I think you misunderstood the second
> question.  I'd like to know if switching I/O schedulers while the system
> is in this bad state helps get I/O going again.
>
Jeff,

Issue confirmed in the following cases:

dom0:domU
noop:noop
noop:deadline
noop:anticipatory
cfq:noop
cfq:deadline
cfq:anticipatory
cfq:cfq

I try switching schedulers in the domU during the lockup, the echo x >
/sys/block/xvda/queue/scheduler command also hangs. In the dom0, no
effect.

Cheers,

Doug