linux-kernel - RE: fsync occasionally very slow

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Message-ID: <000c01c74180$dfe71070$6600a8c0@charm>
Date:	Fri, 26 Jan 2007 14:33:36 -0500
From:	"Matthew Kirk" <mkirk01@....com>
To:	"'Andrew Morton'" <akpm@...l.org>
Cc:	<linux-kernel@...r.kernel.org>
Subject: RE: fsync occasionally very slow

Sorry, this will show my ignorance...  my system is lacking
/proc/sysrq-trigger.  I can find how to build a kernel with the magic sysrq
key (CONFIG_MAGIC_SYSRQ=y), and have done so, but I still don't have
/proc/sysrq-* and cannot seem to find how to build in sysrq functionality
itself - assuming that's what's missing.  Presumably it's something in
.config I'm just not seeing?

Thanks again!

Matt

-----Original Message-----
From: Andrew Morton [mailto:akpm@...l.org] 
Sent: Friday, January 26, 2007 6:17 AM
To: Matthew Kirk
Cc: linux-kernel@...r.kernel.org
Subject: Re: fsync occasionally very slow

On Fri, 26 Jan 2007 05:37:38 -0500
"Matthew Kirk" <mkirk01@....com> wrote:

> I am working on an application that fsync(2) files and directories as
> needed.    I’m seeing intermittent stalls on fsync that can last many
> seconds.

Please generate an all-task backtrace during the stall via:

dmesg -n 8
<wait for a stall>
echo t > /prov/sysrq-trigger
dmesg -s 1000000 > foo

and send foo.

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