linux-kernel - Re: Is it a workqueue related issue in 2.6.37 (Was: Re: [libvirt] blkio cgroup [solved])

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Date:	Thu, 24 Feb 2011 15:31:05 +0100
From:	Tejun Heo <tj@...nel.org>
To:	Vivek Goyal <vgoyal@...hat.com>
Cc:	linux kernel mailing list <linux-kernel@...r.kernel.org>,
	libvir-list@...hat.com, Dominik Klein <dk@...telegence.net>
Subject: Re: Is it a workqueue related issue in 2.6.37 (Was: Re: [libvirt]
 blkio cgroup [solved])

Hello,

On Thu, Feb 24, 2011 at 09:23:03AM -0500, Vivek Goyal wrote:
> On Thu, Feb 24, 2011 at 10:18:00AM +0100, Dominik Klein wrote:
> 
> Hi Dominik,
> 
> Thanks for the tests and reports. I checked the latest logs also and
> I see that cfq has scheduled a work but that work never gets scheduled.
> I never see the trace message which says cfq_kick_queue().
> 
> I am ccing it to lkml and tejun to see if he has any suggestions.
> 
> Tejun,
> 
> I will give you some details about what we have discussed so far.
> 
> Dominik is trying blkio throttling feature and trying to throttle some
> virtual machines. He is using 2.6.37 kernels and once he launches 3
> virtual machines he notices that system is kind of frozen. After running
> some traces we noticed that CFQ has requests but it is not dispatching
> these to devices any more.
> 
> This problem does not show up with deadline scheduler and also goes away
> with 2.6.38-rc6 kernels.

Hmmm...  Maybe the following commit?

commit 7576958a9d5a4a677ad7dd40901cdbb6c1110c98
Author: Tejun Heo <tj@...nel.org>
Date:   Mon Feb 14 14:04:46 2011 +0100

    workqueue: wake up a worker when a rescuer is leaving a gcwq

    After executing the matching works, a rescuer leaves the gcwq
    whether there are more pending works or not.  This may decrease
    the concurrency level to zero and stall execution until a new work
    item is queued on the gcwq.

    Make rescuer wake up a regular worker when it leaves a gcwq if
    there are more works to execute, so that execution isn't stalled.

    Signed-off-by: Tejun Heo <tj@...nel.org>
    Reported-by: Ray Jui <rjui@...adcom.com>
    Cc: stable@...nel.org

-- 
tejun
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