linux-kernel - Re: [Bug #12650] Strange load average and ksoftirqd behavior with 2.6.29-rc2-git1

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Message-ID: <20090215103445.GA2335@localhost.localdomain>
Date:	Sun, 15 Feb 2009 11:34:45 +0100
From:	Damien Wyart <damien.wyart@...e.fr>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	"Rafael J. Wysocki" <rjw@...k.pl>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Kernel Testers List <kernel-testers@...r.kernel.org>
Subject: Re: [Bug #12650] Strange load average and ksoftirqd behavior with
	2.6.29-rc2-git1

* Ingo Molnar <mingo@...e.hu> [2009-02-15 11:13]:
> Note that if the box you test this on is multi-core or HT, then interpreting
> traces is easier if there's just a single CPU to look at. In that case i'd 
> suggest to reproduce with just a single core, by turning the second one off:

>    echo 0 > /sys/devices/system/cpu/cpu1/online

> Or, if the problem only occurs with two cpus, restrict tracing to CPU#1:

>    echo 2 > /debug/tracing/tracing_cpumask 

The box I test on is HT, so I tried the first suggestion and it made the
problem much less visible (but not completely absent).

So I used "echo 1 > /sys/devices/system/cpu/cpu1/online" to go back to
HT mode and then it made the problem much more visible on CPU#1:
ksoftirqd/1 is running a lot and ksoftirqd/0 is almost normal. The load
average is about 0.80 and the total running time for ksoftirqd/1 is
almost one minute (and I booted on rc5 ten minutes ago)!

So I followed the tracing steps in the tutorial (with the 1 sec sleep),
which gave me this:
http://damien.wyart.free.fr/trace_2.6.29-rc5_ksoftirqd_prob.txt.gz

As I will be away until tomorrow, I did this on vanilla rc5 to get
something out today, and if tip is really needed, I will work on it
tomorrow. But maybe this vanilla trace will be helpful to you...

Do not hesitate to ask for further tests or info.

-- 
Damien
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