Re: Random file I/O regressions in 2.6 [patch+results]

[Alexey Kopytov <alexeyk@mysql.com>]

On Friday 21 May 2004 01:59, Andrew Morton wrote:
>The patches in Linus's tree improve sysbench significantly here.  It's a
>256MB 2-way with IDE disks, writeback caching enabled:
>
>sysbench --num-threads=16 --test=fileio --file-total-size=2G
> --file-test-mode=rndrw run
>
>2.4.27-pre2, ext2:
>
>	Time spent for test:  61.0240s
>		0.06s user 6.03s system 4% cpu 2:05.95 total
>	Time spent for test:  60.8456s
>		0.11s user 5.49s system 4% cpu 2:04.94 total
>
>2.6.6-bk, AS, ext2:
>
>	Time spent for test:  62.5316s
>		0.05s user 5.27s system 4% cpu 2:01.28 total
>	Time spent for test:  62.7401s
>		0.04s user 5.17s system 4% cpu 2:00.50 total

I ran the tests with a configuration as close to yours as possible. Here are 
the results for mem=256M, 2G total file size (ext3):

2.4.25:
       Time spent for test:  79.4146s
                0.20user 16.08system 3:20.29elapsed 8%CPU
       Time spent for test:  78.9797s
                0.11user 15.84system 3:19.76elapsed 7%CPU 

2.6.6-bk, AS:
       Time spent for test:  81.2208s
                0.13user 17.97system 3:13.30elapsed 9%CPU
       Time spent for test:  82.5538s
                0.14user 18.00system 3:14.88elapsed 9%CPU

This correlates very well your results. But when I returned back to my 
original configuration (mem=640M, 3G total file size), I got the following:

2.4.25:
       Time spent for test:  77.5377s

2.6.6-bk, AS:
       Time spent for test:  83.1929s

It seems like the smaller file size just hides the regression, but I have to 
run some more tests to ensure this.
  

>I don't know why you're still seeing significant discrepancies.
>
>What sort of disk+controller system are you using?  If scsi, what is the
>tag queue depth set to?  Is writeback caching enabled on the disk?

It's IDE disk without TCQ support with writeback caching enabled.

-- 
Alexey Kopytov, Software Developer
MySQL AB, www.mysql.com

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