linux-kernel - RE: Large increase in context switch rate

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Message-ID: <0E902970173AF84089673FA54B7FE78A32906C@lonpexch01.citrite.net>
Date:	Thu, 17 Jul 2008 17:04:20 +0100
From:	"Alex Nixon (Intern)" <Alex.Nixon@...citrix.com>
To:	"Jeremy Fitzhardinge" <jeremy@...p.org>
Cc:	"Peter Zijlstra" <peterz@...radead.org>,
	"Ingo Molnar" <mingo@...e.hu>,
	"Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>,
	"Ian Campbell" <Ian.Campbell@...citrix.com>
Subject: RE: Large increase in context switch rate

I'm talking about total number of context switches - kernbench gets it
from

time -f "%c" make -j 4

Dividing through it gives me a rate of around 250/sec (vs Peters 3000),
but I've set CONFIG_HZ=100 (vs Peters 1000), so they don't wildly
conflict.

Well spotted :-)

- Alex


-----Original Message-----
From: Jeremy Fitzhardinge [mailto:jeremy@...p.org] 
Sent: 17 July 2008 16:45
To: Alex Nixon (Intern)
Cc: Peter Zijlstra; Ingo Molnar; Linux Kernel Mailing List; Ian Campbell
Subject: Re: Large increase in context switch rate

Alex Nixon (Intern) wrote:
> Yeah I've checked - the number of context switches seems to be around
> 60k regardless of whether CONFIG_PARAVIRT is switched on, and
regardless
> of whether it's running in domu or native (-j4 on dual core)
>   

OK, just to be sure we're talking about the same thing, is kernbench 
displaying the context switch *rate*, or the total number of context 
switches during the build?

Peter is looking at vmstat, which is showing cs/sec.

    J
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