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SubjectRe: performance "regression" in cfq compared to anticipatory, deadline and noop
On Tue, May 13 2008, Matthew wrote:
> On Tue, May 13, 2008 at 2:20 PM, Jens Axboe <jens.axboe@oracle.com> wrote:
> >
> > On Sun, May 11 2008, Kasper Sandberg wrote:
> > > On Sun, 2008-05-11 at 14:14 +0100, Daniel J Blueman wrote:
> > > > I've been experiencing this for a while also; an almost 50% regression
> > > > is seen for single-process reads (ie sync) if slice_idle is 1ms or
> > > > more (eg default of 8) [1], which seems phenomenal.
> > > >
> > > > Jens, is this the expected price to pay for optimal busy-spindle
> > > > scheduling, a design issue, bug or am I missing something totally?
> > > >
> > > > Thanks,
> > > > Daniel
> [snip]
> ...
> [snip]
> > >
> > > Thisd would appear to be quite a considerable performance difference.
> >
> > Indeed, that is of course a bug. The initial mail here mentions this as
> > a regression - which kernel was the last that worked ok?
> >
> > If someone would send me a blktrace of such a slow run, that would be
> > nice. Basically just do a blktrace /dev/sda (or whatever device) while
> > doing the hdparm, preferably storing output files on a difference
> > device. Then send the raw sda.blktrace.* files to me. Thanks!
> >
> > --
> > Jens Axboe
> >
> >
>
> Hi Jens,
>
> I called this a "regression" since I wasn't sure if this is a real bug
> or just something introduced recently, I just started to use cfq as
> main io-scheduler so I can't tell ...
>
> testing 2.6.17 unfortunately is somewhat impossible for me (reiser4;
> too new hardware - problems with jmicron)
>
> google "says" that it seemingly already existed since at least 2.6.18
> (Ubuntu DapperDrake) [see:
> http://ubuntuforums.org/showpost.php?p=1484633&postcount=12]

Funky :/

> well - back to topic:
>
> for a blktrace one need to enable CONFIG_BLK_DEV_IO_TRACE , right ?
> blktrace can be obtained from your git-repo ?

Yes on both accounts, or just grab a blktrace snapshot from:

http://brick.kernel.dk/snaps/blktrace-git-latest.tar.gz

if you don't use git.

--
Jens Axboe



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