linux-kernel - Re: CFQ: async queue blocks the whole system

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Date:	Fri, 10 Jun 2011 18:00:37 +0800
From:	Tao Ma <tm@....ma>
To:	Vivek Goyal <vgoyal@...hat.com>
CC:	linux-kernel@...r.kernel.org, Jens Axboe <axboe@...nel.dk>
Subject: Re: CFQ: async queue blocks the whole system

On 06/10/2011 05:14 PM, Vivek Goyal wrote:
> On Fri, Jun 10, 2011 at 01:48:37PM +0800, Tao Ma wrote:
> 
> [..]
>>>> btw, reverting the patch doesn't work. I can still get the livelock.
> 
> What test exactly you are running. I am primarily interested in whether
> you still get the hung task timeout warning where a writer is waiting on
> get_request_wait() for more than 120 secods or not.
> 
> Livelock might be a different problem and for which Christoph provided
> a patch for XFS.
> 
>>>
>>> Can you give following patch a try and see if it helps. On my system this
>>> does allow CFQ to dispatch some writes once in a while.
>> Sorry, this patch doesn't work in my test.
> 
> Can you give me backtrace of say 15 seconds each with and without patch.
> I think now we must be dispatching some writes, that's a different thing
> that writer still sleeps more than 120 seconds because there are  way
> too many readers.
> 
> May be we need to look into show workload tree scheduling takes place and
> tweak that logic a bit.
OK, our test cases can be downloaded for free. ;)
svn co http://code.taobao.org/svn/dirbench/trunk/meta_test/press/set_vs_get
Modify run.sh to be fit for your need. Normally within 10 mins, you will
get the livelock. We have a SAS disk with 15000 RPMs.

btw, you have to mount the volume on /test since the test program are
not that clever. :)

Regards,
Tao
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