linux-kernel - Re: Scheduler on C2D CPU and latest 2.6.27 kernel

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Message-ID: <48FDB7E7.4090007@redhat.com>
Date:	Tue, 21 Oct 2008 07:07:19 -0400
From:	Chris Snook <csnook@...hat.com>
To:	Zdenek Kabelac <zdenek.kabelac@...il.com>
CC:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <pzijlstr@...hat.com>
Subject: Re: Scheduler on C2D CPU and latest 2.6.27 kernel

Zdenek Kabelac wrote:
> Hi
> 
> Recently I'm noticing bad behavior of the CPU scheduler on my T61 (2GB, C2D)
> 
> It looks like Linux concentrates all running tasks on one CPU and the
> second cpu is sleeping.
> 
> With recent changes to DRI - glxgears went up to 840FPS but also takes
> 100% (with Xorg) and when I run 'while :; do true; done' loop in
> parallel frame rate drops to 300FPS.
> 
> But as I have C2D CPU I would expect that there should be no such
> dramatic slowdown.
> 
> Xosview shows that only one CPU is fully loaded.
> 
> Here are my .config scheduler options:
> 
> CONFIG_HAVE_UNSTABLE_SCHED_CLOCK=y
> # CONFIG_GROUP_SCHED is not set
> CONFIG_IOSCHED_NOOP=y
> CONFIG_IOSCHED_AS=y
> CONFIG_IOSCHED_DEADLINE=y
> CONFIG_IOSCHED_CFQ=y
> CONFIG_DEFAULT_IOSCHED="cfq"
> CONFIG_SCHED_SMT=y
> # CONFIG_SCHED_MC is not set
> CONFIG_SCHED_HRTICK=y
> # CONFIG_NET_SCHED is not set
> CONFIG_USB_EHCI_TT_NEWSCHED=y
> CONFIG_SCHED_DEBUG=y
> CONFIG_SCHEDSTATS=y
> CONFIG_SCHED_TRACER=y
> 
> 
> Am I missing something?

You're running a loop that does nothing except create new tasks that have no 
scheduling history, and then disappear before the scheduler can migrate them.

Try running 'openssl speed' to chew up CPU.  I promise you the scheduler will 
behave very nicely.

-- Chris
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