linux-kernel - Re: Costly Context Switches

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Date:	Sun, 12 Dec 2010 20:07:07 +0100
From:	Andres Freund <andres@...razel.de>
To:	Ralf Hildebrandt <Ralf.Hildebrandt@...rite.de>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: Costly Context Switches

On Sunday 12 December 2010 16:11:12 Ralf Hildebrandt wrote:
> I recently made a parallel installation of dovecot-2.0 on my mailbox
> server, which is running dovecot-1.2 without any problems whatsoever.
> 
> Using dovecot-2.0 on the same hardware, same kernel, with the same users
> and same mailboxes and usage behaviour results in an immense increase in
> the load numbers.
> 
> Switching back to 1.2 results in a immediate decrease of the load back
> to "normal" numbers.
> 
> This is mainly due to a 10-20 fold increase of the number of context
> switches. The same problem has been reported independently by Cor
> Bosman of XS4All, on different hardware (64bit instead of 32bit, real
> hardware instead of virtual hardware).
> 
> So, now the kernel related question: How can I find out WHY the
> context switches are happening? Are there any "in kernel" statistics I
> could look at?
"strace" or "perf trace syscall-counts" would be a good start.

Andres
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