linux-kernel - Re: Dynticks Causing High Context Switch Rate in ksoftirqd

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Message-Id: <20071127212805.31f0de96.akpm@linux-foundation.org>
Date:	Tue, 27 Nov 2007 21:28:05 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Robert Hancock <hancockr@...w.ca>
Cc:	bdupree@...hfinesse.com, linux-kernel@...r.kernel.org
Subject: Re: Dynticks Causing High Context Switch Rate in ksoftirqd

On Mon, 26 Nov 2007 22:36:17 -0600 Robert Hancock <hancockr@...w.ca> wrote:

> bdupree@...hfinesse.com wrote:
> > Question: Why is ksoftirqd eating about 5 to 10 percent of my CPU on an idle
> > system? The problem occurs if I config the kernel with tickless
> > support (i.e. CONFIG_TICK_ONESHOT=y).  (Thanks to "oprofile" for putting me
> > onto this.)
> > 
> > I have noted this same problem on kernel versions: 2.6.23.1, 2.6.23.8 and
> > 2.6.23.9
> > 
> > **************************************************************************
> > *** Output from "vmstat -n 1 10" -- Note very high context switch rate ***
> > *** This is on a idle machine!                                         ***
> > **************************************************************************
> > 
> > procs -----------memory---------- ---swap-- -----io---- --system--
> > ----cpu----
> >  r  b   swpd   free   buff  cache   si   so    bi    bo   in    cs us sy
> > id wa
> >  0  0      0 1925556   4768 116104    0    0   124     2    6  7538  1  2
> > 96  1
> >  0  0      0 1925556   4768 116104    0    0     0     0    2 147329  0  1
> > 99  0
> 
> What did oprofile show? It should be able to narrow down what 
> function(s) are responsible for the CPU usage..

Sigh.  I just asked a similar thing.   Let's look at the mail headers:



Message-ID: <41877.67.173.156.207.1196130992.squirrel@....techfinesse.net>
...
From: bdupree@...hfinesse.com


From: Robert Hancock <hancockr@...w.ca>
...
In-reply-to: <fa.c70Wy8WHP3DOaDydQ2D94+Xxx/8@....uio.no>


Please fix your email client so as to not break threading?
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