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

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Date:	Fri, 25 Feb 2011 12:46:16 +0100
From:	Dominik Klein <dk@...telegence.net>
To:	Tejun Heo <tj@...nel.org>
CC:	Vivek Goyal <vgoyal@...hat.com>,
	linux kernel mailing list <linux-kernel@...r.kernel.org>,
	libvir-list@...hat.com
Subject: Re: Is it a workqueue related issue in 2.6.37 (Was: Re: [libvirt]
 blkio cgroup [solved])

Hi

>> This was taken with 2.6.37 plus the patch you mentioned on a Dell R815
>> with 2 12 core AMD Opteron 6174 CPUs. If you need any more information,
>> please let me know.
> 
> Hmmm... well, I have no idea what you were trying to do 

Long story short: I have a couple of virtual machines. Some of them have
blkio throttle configured, some don't. To simulate whether the
throttling works, I start
dd if=/dev/zero of=testfile bs=1M count=1500
in each guest simultaneously.

The result is that from that point, no i/o is happening any more. You
see the result in the trace.

With 2.6.37 (also tried .1 and .2) it does not work but end up like I
documented. With 2.6.38-rc1, it does work. With deadline scheduler, it
also works in 2.6.37.

I am in bisect run 2 currently to find the changeset that fixed it.

Will let you know as soon as I do.

Regards
Dominik

ps. I am by no means a kernel hacker and none of the rest of your email
made any sense to me. Sorry.

> but here are
> some info which might be helpful.
> 
> * queue_work happens when the work item is queued.
> 
> * activate_work happens when the work item becomes eligible for
>   execution.  e.g. If the workqueue's @max_active is limited and
>   maximum number of work items are already in flight, a new item will
>   only get activated after one of the in flight ones retires.
> 
> * execute_start marks the actual starting of execution.
> 
> * execute_end marks the end of execution.
> 
> So, I would look for the matching work function and then try to follow
> what happens to it after being scheduled and if it doesn't get
> executed what's going on with the target workqueue.
> 
> Thanks.
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