possible fsync02() xfs slowness regression on power7

[Dave Chinner]

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

And this commit in 3.9-rc1:

a1e16c2 xfs: limit speculative prealloc size on sparse files

should fix the problem. Please confirm these commits are the cause
and the fix respectively....

Cheers,

Dave.
-- 
Dave Chinner
david at fromorbit.com