linux-kernel - Re: ksoftirqd problem

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Date:	Wed, 30 Dec 2009 22:15:57 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Nico <segfault2@...mail.com>
Cc:	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: ksoftirqd problem

On Sun, Dec 13, 2009 at 08:05:29PM +0100, Nico wrote:
> 
> Hi,
> 
> I recently switched to kernel 2.6.32 (self configured/compiled) and I've noticed an odd behavior on one of my servers. I run a bittorrent tracker on one of my servers and when using kernel 2.6.32, every now and then ksoftirqd will jump up to 20% of my CPU for almost a minute. The tracker has a total peers amount of ~45000 peers (if it matters) and this behavior seems to only happen under kernel 2.6.32. Switching back to kernel 2.6.31.1 on the server, ksoftirdq does not behave that way.
> 
> Any thoughts?
> 
> PS: please CC me as I'm not subscribed to the list
> 
> Thanks :)


Hi,

I wonder if this problem still happens in 2.6.33-rc2.

A trace of softirqs during the issue would be helpful
to determine which softirq is the culprit:

mount -t debugfs /debug

echo 1 > /debug/tracing/events/irq/softirq_entry/enable
# wait a bit 
echo 0 > /debug/tracing/events/irq/softirq_entry/enable

cat trace

Thanks.

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