On Sat, 23 Jun 2007 04:59:06 +0200 Carlo Wood <[email protected]> wrote:
> On Fri, Jun 22, 2007 at 10:31:32PM -0300, Henrique de Moraes Holschuh wrote:
> > for i in /sys/block/sd*/queue/scheduler ; do echo -n "scheduler for $i was:" ; cat $i ; echo anticipatory > $i ; done
> >
> > Should show you the scheduler for all libata/scsi discs, and switch to
> > anticipatory. It probably works for hd* as well, but I don't have any
> > around to test.
> >
> > I had ridiculous md raid performance (on resync) using cfq at least once.
> > Unfortunately I never bothered trying to track it down, and I didn't check
> > the throughput after the resync was done either. Also, I don't recall the
> > kernel version, but it was either 2.6.18 or 2.6.20.
>
> Just one kernel version? The problem here is in every
> kernel revision after 551c012d7eea3dc5ec063c7ff9c718d39e77634f
>
> 2.6.20-rc2,rc3,rc4,rc5,rc6,rc7 ... 2.6.20 ... 2.6.21 ... 2.6.22-rc5
>
> noop:
> Timing buffered disk reads: 254 MB in 3.00 seconds = 84.66 MB/sec
>
> anticipatory:
> Timing buffered disk reads: 252 MB in 3.02 seconds = 83.43 MB/sec
>
> deadline:
> Timing buffered disk reads: 258 MB in 3.02 seconds = 85.41 MB/sec
>
> cfq:
> Timing buffered disk reads: 194 MB in 3.03 seconds = 64.06 MB/sec
>
> The normal value is cfq. So, all other schedulars are somewhat faster,
> but still far from the correct 165 MB/s.
>
Please see http://bugzilla.kernel.org/show_bug.cgi?id=8636
In that report a pretty large slowdown with CFQ has been identified.
Jens has plunked a patch in there (Comment #50) and then ran away on
vacation.
If someone can test that patch and demonstrate its goodness, I'll
queue it up, thanks.
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