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Re: possible fsync02() xfs slowness regression on power7

To: Dave Chinner <david@xxxxxxxxxxxxx>
Subject: Re: possible fsync02() xfs slowness regression on power7
From: CAI Qian <caiqian@xxxxxxxxxx>
Date: Fri, 1 Mar 2013 04:20:18 -0500 (EST)
Cc: xfs@xxxxxxxxxxx, Steve Best <sbest@xxxxxxxxxx>
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <20130228115410.GN5551@dastard>

----- ååéä -----
> åää: "Dave Chinner" <david@xxxxxxxxxxxxx>
> æää: "CAI Qian" <caiqian@xxxxxxxxxx>
> æé: xfs@xxxxxxxxxxx, "Steve Best" <sbest@xxxxxxxxxx>
> åéæé: ææå, 2013å 2 æ 28æ äå 7:54:10
> äé: Re: possible fsync02() xfs slowness regression on power7
> 
> On Thu, Feb 28, 2013 at 04:28:35AM -0500, CAI Qian wrote:
> > This LTP test starting to fail using the latest upstream kernel on
> > one of the power7
> > systems here, http://tinyurl.com/bngwouj
> > 
> > # ./fsync02
> > fsync02     1  TFAIL  :  fsync took too long: 252.000000 seconds;
> > max_block: 214
> > 
> > When it is working, the test is almost returned immediately. The
> > bisecting so far
> > indicated that one or a few of the following could be culprits.
> > 
> > # git log --pretty=oneline
> > 498f7f505dc79934c878c7667840c50c64f232fc..b199c8a4ba11879df87daad496ceee41fdc6aa82
> 
> They are all patches committed more than 2 years ago, and none of
> them are platform specific. This sounds more like a machine specific
> issue than a platform specific problem (i.e. lots of RAM, slow,
> slow disk).
> 
> In future when reporting a bug, please tell use hardware you are
> using as per:
> 
> http://xfs.org/index.php/XFS_FAQ#Q:_What_information_should_I_include_when_reporting_a_problem.3F
> 
> Given that this is a sparse file test that repeatedly extends the
> file, this is the likely culprit:
> 
> > 055388a3188f56676c21e92962fc366ac8b5cb72 xfs: dynamic speculative
> > EOF preallocation
Yes, you are right, just confirmed it. Nice catch!
> 
> And this commit in 3.9-rc1:
> 
> a1e16c2 xfs: limit speculative prealloc size on sparse files
Just back-ported it and running at the moment and will let you know. Thanks 
Dave.
> 
> should fix the problem. Please confirm these commits are the cause
> and the fix respectively....
> 
> Cheers,
> 
> Dave.
> --
> Dave Chinner
> david@xxxxxxxxxxxxx
> 

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