linux-ext4 - Ext4 performance regression: Post 2.6.30

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Date:	Sun, 28 Mar 2010 23:25:35 -0700
From:	Keith Mannthey <kmannth@...ibm.com>
To:	linux-ext4 <linux-ext4@...r.kernel.org>
Subject: Ext4 performance regression:  Post 2.6.30

After 2.6.30 I am seeing large performance regressions on a raid setup.
I am working to publish a larger amount of data but I wanted to get some
quick data out about what I am seeing. 

The test (FFSB test suite) I am running is basically random direct io
writes.  The below data is from 128 threads all doing these random
writes. 1 and 32 thread results are not as drastically bad but 2.6.30
has the strongest results.  

  Under a mailserver workload I see similar performance impacts at this
same kernel change point.  I hope to publish better data soon.  Several
other workload types do not show this performance regression. 

2.6.30:

Total Results
===============
             Op Name   Transactions	 Trans/sec	% Trans	    % Op Weight
Throughput
             =======   ============	 =========	=======	    ===========
==========
               write :      9015040	  29561.46	100.000%		100.000%
115MB/sec
-
29561.46 Transactions per Second

Any kernel past 2.6.30.  This is from 2.6.31-rc1:

Total Results
===============
             Op Name   Transactions	 Trans/sec	% Trans	    % Op Weight
Throughput
             =======   ============	 =========	=======	    ===========
==========
               write :      3185920	  10120.50	100.000%		100.000%
39.5MB/sec
-
10120.50 Transactions per Second

Nothing is sticking out in oprofile data with this workload. 

I am in the middle of a kernel git bisect that should be done in another
day or so. 

Thanks,
  Keith Mannthey 

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