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

Alexey Kopytov
2004-05-21T21:13:40Z

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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