linux-kernel - Re: ext3 IO latency measurements (was: Linux 2.6.29)

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Message-Id: <20090326073851.fcee79dd.akpm@linux-foundation.org>
Date:	Thu, 26 Mar 2009 07:38:51 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Jan Kara <jack@...e.cz>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Theodore Tso <tytso@....edu>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Arjan van de Ven <arjan@...radead.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Nick Piggin <npiggin@...e.de>,
	Jens Axboe <jens.axboe@...cle.com>,
	David Rees <drees76@...il.com>, Jesper Krogh <jesper@...gh.cc>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Roland McGrath <roland@...hat.com>
Subject: Re: ext3 IO latency measurements (was: Linux 2.6.29)

On Thu, 26 Mar 2009 10:06:30 +0100 Ingo Molnar <mingo@...e.hu> wrote:

> And it's not just sys_fsync(). The script i wrote tests file read 
> latencies. I have created 1000 files with the same size (all copies 
> of kernel/sched.c ;-), and tested their cache-cold plain-cat 
> performance via:
> 
>   for ((i=0;i<1000;i++)); do
>     printf "file #%4d, plain reading it took: " $i
>     /usr/bin/time -f "%e seconds."  cat $i >/dev/null
>   done
> 
> I.e. plain, supposedly high-prio reads. The result is very common 
> hickups in read latencies:
> 
> file # 579 (253560 bytes), reading it took: 0.08 seconds.
> file # 580 (253560 bytes), reading it took: 0.05 seconds.
> file # 581 (253560 bytes), reading it took: 0.01 seconds.
> file # 582 (253560 bytes), reading it took: 0.01 seconds.
> file # 583 (253560 bytes), reading it took: 4.61 seconds.
> file # 584 (253560 bytes), reading it took: 1.29 seconds.
> file # 585 (253560 bytes), reading it took: 3.01 seconds.
> file # 586 (253560 bytes), reading it took: 7.74 seconds.
> file # 587 (253560 bytes), reading it took: 3.22 seconds.
> file # 588 (253560 bytes), reading it took: 0.05 seconds.
> file # 589 (253560 bytes), reading it took: 0.36 seconds.
> file # 590 (253560 bytes), reading it took: 7.39 seconds.
> file # 591 (253560 bytes), reading it took: 7.58 seconds.
> file # 592 (253560 bytes), reading it took: 7.90 seconds.
> file # 593 (253560 bytes), reading it took: 8.78 seconds.
> file # 594 (253560 bytes), reading it took: 8.01 seconds.
> file # 595 (253560 bytes), reading it took: 7.47 seconds.
> file # 596 (253560 bytes), reading it took: 11.52 seconds.
> file # 597 (253560 bytes), reading it took: 10.33 seconds.
> file # 598 (253560 bytes), reading it took: 8.56 seconds.
> file # 599 (253560 bytes), reading it took: 7.58 seconds.

(gets deja-vu feelings)

http://lkml.org/lkml/2003/2/21/10

Maybe you should be running a 2.5.61 kernel.
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