linux-kernel - Re: Linux 2.6.29

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Message-ID: <x49myaxjrsb.fsf@segfault.boston.devel.redhat.com>
Date:	Fri, 03 Apr 2009 18:28:36 -0400
From:	Jeff Moyer <jmoyer@...hat.com>
To:	lsorense@...lub.uwaterloo.ca (Lennart Sorensen)
Cc:	Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	torvalds@...ux-foundation.org, tytso@....edu, drees76@...il.com,
	jesper@...gh.cc, linux-kernel@...r.kernel.org,
	jens.axboe@...cle.com
Subject: Re: Linux 2.6.29

lsorense@...lub.uwaterloo.ca (Lennart Sorensen) writes:

> On Thu, Apr 02, 2009 at 03:00:44AM +0200, Ingo Molnar wrote:
>> I'll test this (and the other suggestions) once i'm out of the merge 
>> window.
>> 
>> I probably wont test that though ;-)
>> 
>> Going back to v2.6.14 to do pre-mutex-merge performance tests was 
>> already quite a challenge on modern hardware.
>
> Well after a day of running my mythtv box with anticipatiry rather than
> the default cfq scheduler, it certainly looks a lot better.  I haven't
> seen any slowdowns, the disk activity light isn't on solidly (it just
> flashes every couple of seconds instead), and it doesn't even mind
> me lanuching bittornado on multiple torrents at the same time as two
> recordings are taking place and some commercial flagging is taking place.
> With cfq this would usually make the system unusable (and a Q6600 with
> 6GB ram should never be unresponsive in my opinion).
>
> So so far I would rank anticipatory at about 1000x better than cfq for
> my work load.  It sure acts a lot more like it used to back in 2.6.18
> times.

Hi, Lennart,

Could you try one more test, please?  Switch back to CFQ and set
/sys/block/sdX/queue/iosched/slice_idle to 0?

I'm not sure how the applications you are running write to disk, but if
they interleave I/O between processes, this could help.  I'm not too
confident that this will make a difference, though, since CFQ changed to
time-slice based instead of quantum based before 2.6.18.  Still, it
would be another data point if you have the time.

Thanks in advance!

-Jeff
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