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Re: xfs, 2.6.27=>.32 sync write 10 times slowdown [was: xfs, aacraid 2.6

To: Dave Chinner <david@xxxxxxxxxxxxx>
Subject: Re: xfs, 2.6.27=>.32 sync write 10 times slowdown [was: xfs, aacraid 2.6.27 => 2.6.32 results in 6 times slowdown]
From: Michael Tokarev <mjt@xxxxxxxxxx>
Date: Thu, 10 Jun 2010 09:59:18 +0400
Cc: Linux-kernel <linux-kernel@xxxxxxxxxxxxxxx>, xfs@xxxxxxxxxxx
In-reply-to: <20100610004701.GN7869@dastard>
Organization: Telecom Service, JSC
References: <4C0E13A7.20402@xxxxxxxxxxxxxxxx> <20100608122919.GC7869@dastard> <4C0EA938.9000104@xxxxxxxxxxxxxxxx> <20100608231845.GG7869@dastard> <4C0F3819.4000409@xxxxxxxxxxxxxxxx> <20100609074741.GJ7869@dastard> <4C0FE779.8010603@xxxxxxxxxxxxxxxx> <20100610004701.GN7869@dastard>
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10.06.2010 04:47, Dave Chinner wrote:
On Wed, Jun 09, 2010 at 11:11:53PM +0400, Michael Tokarev wrote:
09.06.2010 11:47, Dave Chinner wrote:
On Wed, Jun 09, 2010 at 10:43:37AM +0400, Michael Tokarev wrote:
09.06.2010 03:18, Dave Chinner wrote:
On Wed, Jun 09, 2010 at 12:34:00AM +0400, Michael Tokarev wrote:
[]
Simple test doing random reads or writes of 4k blocks in a 1Gb
file located on an xfs filesystem, Mb/sec:

                      sync  direct
              read   write   write
2.6.27 xfs   1.17    3.69    3.80
2.6.32 xfs   1.26    0.52    5.10
                     ^^^^
2.6.32 ext3  1.19    4.91    5.02

Out of curiousity, what does 2.6.34 get on this workload?

2.6.34 works quite well:
      2.6.34 xfs    1.14   4.75    5.00

Ok, so we are looking at a fixed regression, then. What stable
version of 2.6.32 are you testing? A large number of XFS fixes went
into 2.6.32.12 (IIRC, it might have been .13), so maybe the problem
is fixed there. Alternatively, can you use 2.6.34 rather than
2.6.32, or bisect the regression down to a specific set of fixes so
we can consider whether a backport is worth the effort?

I tried 2.6.32.15.  A few previous versions too, but all recent
testing were with 2.6.32.15.  So no, the fix is not in 2.6.32.y
yet, since .15 is the latest currently.

Too bad it'd be very difficult for me to do any bisection, -- users
are not comfortable at all already due to all my experiments, --
f.e. their reports that are collecting for whole night stopped
working completely since a few days ago (because every night I'm
rebooting the machine).

Yes it'd be nice to have this fixed in 2.6.32.y.  And I promise I'll
try to find time for bisection (but not promise the tries will be
successful... ;).  Definitely worth a try anyway.

Thank you!

/mjt

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