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

Andrew Morton
2004-05-21T23:58:02Z

Alexey Kopytov <alexeyk@mysql.com> wrote:
>
> Ram Pai wrote:
>
> >Attached the cleaned up patch and the performance results of the patch.
> >
> >Overall Observation:
> > 1.Small improvement with iozone with the patch, and overall
> > much better performance than 2.4
> > 2.Small/neglegible improvement with DSS workload.
> > 3.Negligible impact with sysbench, but results worser than
> > 2.4 kernels
>
> Ram, can you clarify the status of this patch please?

Everything we have is now in Linus's tree. And in 2.6.6-mm4.

> I ran the same sysbench test on my hardware with patched 2.6.6 and got
> 122.2348s execution time, i.e. almost the same results as in the original
> tests. Is this patch an intermediate step to improve the sysbench workload on
> 2.6, or it just addresses another problem?

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, CFQ, ext2:

Time spent for test: 85.6614s
0.05s user 5.66s system 3% cpu 2:26.75 total
Time spent for test: 85.2090s
0.06s user 5.32s system 3% cpu 2:24.75 total

2.6.6-bk, CFQ, ext2:

Time spent for test: 66.7717s
0.04s user 5.54s system 4% cpu 2:06.19 total
Time spent for test: 67.5666s
0.04s user 5.10s system 4% cpu 2:06.72 total

2.6.6, as, ext2:

Time spent for test: 83.8358s
0.07s user 5.89s system 4% cpu 2:22.92 total
Time spent for test: 83.8068s
0.06s user 5.34s system 3% cpu 2:21.33 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

2.6.6, deadline, ext2:

Time spent for test: 103.0084s
0.06s user 5.76s system 3% cpu 2:40.74 total
Time spent for test: 101.9648s
0.07s user 5.35s system 3% cpu 2:38.83 total

2.6.6-bk, deadline, ext2:

Time spent for test: 63.3405s
0.03s user 5.49s system 4% cpu 2:01.05 total
Time spent for test: 63.5288s
0.03s user 5.05s system 4% cpu 2:00.78 total

There's still something wrong here. 2.6.6-bk+deadline is pretty equivalent
to 2.4 from an IO scheduler point of view in this test. Yet it's a couple
of percent slower.

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?