Created attachment 21774
Test patch against heavy io bug

I have made an bisection and got these two patches. Reverting these patches improves the desktop responsiveness on my notebook enormous. I have tested it on a 2.6.28 non smp kernel (my heavy io testing installation) during four concurrent read and write operations, while working with two VMs. It's only a Core2 @2.4GHz system. I can even start new application during heavy io.

I have added the patch, which I have applied to my test installation. Use it with care, as I am not a kernel developer and does not know the dependencies in the cfq scheduler. 

I have reverted theses two patches:

07db59bd6b0f279c31044cba6787344f63be87ea is first bad commit
commit 07db59bd6b0f279c31044cba6787344f63be87ea
Author: Linus Torvalds <email address hidden>
Date:   Fri Apr 27 09:10:47 2007 -0700

    Change default dirty-writeback limits

    Do this really early in the 2.6.22-rc series, so that we'll get
    feedback.  And don't change by half measures.  Just cut the default
    dirty limit to a quarter of what it was, and see if anybody even
    notices.

    Signed-off-by: Linus Torvalds <email address hidden>

:040000 040000 b63eb9faf5b9a42a1cdad901a5f18d6cceb7fdf6 2b8b4117ca34077cb0b817c77595aa6c9e34253a M      mm

a993800655ee516b6f6a6fc4c2ee13fedfb0590b is first bad commit
commit a993800655ee516b6f6a6fc4c2ee13fedfb0590b
Author: Jens Axboe <email address hidden>
Date:   Fri Apr 20 08:55:52 2007 +0200

    cfq-iosched: fix sequential write regression
    
    We have a 10-15% performance regression for sequential writes on TCQ/NCQ
    enabled drives in 2.6.21-rcX after the CFQ update went in.  It has been
    reported by Valerie Clement <email address hidden> and the Intel
    testing folks.  The regression is because of CFQ's now more aggressive
    queue control, limiting the depth available to the device.
    
    This patches fixes that regression by allowing a greater depth when only
    one queue is busy.  It has been tested to not impact sync-vs-async
    workloads too much - we still do a lot better than 2.6.20.
    
    Signed-off-by: Jens Axboe <email address hidden>
    Signed-off-by: Linus Torvalds <email address hidden>

:040000 040000 07c48a6930ce62d36540b6650e3ea0563bd7ec59 95fc11105fe3339c90c4e7bebb66a820f7084601 M      block


Here the fsync result on my machine:

**************************************************************************
Without patch
Linux balrog 2.6.28 #2 Mon Mar 23 11:19:13 CET 2009 x86_64 GNU/Linux

fsync time: 7.8282
fsync time: 17.3598
fsync time: 24.0352
fsync time: 19.7307
fsync time: 21.9559
fsync time: 21.0571
5000+0 Datensätze ein
5000+0 Datensätze aus
5242880000 Bytes (5,2 GB) kopiert, 129,286 s, 40,6 MB/s
fsync time: 21.8491
fsync time: 0.0430
fsync time: 0.0448
fsync time: 0.0451
fsync time: 0.0451
fsync time: 0.0451
fsync time: 0.0452



**************************************************************************
With patch
Linux balrog 2.6.28 #5 Fri Jun 5 22:23:54 CEST 2009 x86_64 GNU/Linux

fsync time: 2.8409
fsync time: 2.3345
fsync time: 2.8423
fsync time: 0.0851
fsync time: 1.2497
fsync time: 0.9981
fsync time: 0.9494
fsync time: 2.7094
fsync time: 2.9753
fsync time: 2.8886
fsync time: 2.9894
fsync time: 1.2673
fsync time: 2.6728
fsync time: 1.3408
5000+0 Datensätze ein
5000+0 Datensätze aus
5242880000 Bytes (5,2 GB) kopiert, 117,388 s, 44,7 MB/s
fsync time: 85.1461
fsync time: 23.5310
fsync time: 0.0317
fsync time: 0.0337
fsync time: 0.0338
fsync time: 0.0338