linux-kernel - Re: performance "regression" in cfq compared to anticipatory, deadline and noop

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Date:	Tue, 13 May 2008 14:58:53 +0200
From:	Matthew <jackdachef@...il.com>
To:	"Jens Axboe" <jens.axboe@...cle.com>
Cc:	"Kasper Sandberg" <lkml@...anurb.dk>,
	"Daniel J Blueman" <daniel.blueman@...il.com>,
	"Linux Kernel" <linux-kernel@...r.kernel.org>
Subject: Re: performance "regression" in cfq compared to anticipatory, deadline and noop

On Tue, May 13, 2008 at 2:20 PM, Jens Axboe <jens.axboe@...cle.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]

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 ?

Thanks

Mat
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