linux-kernel - Re: High CPU load when machine is idle (related to PROBLEM: Unusually high load average when idle in 2.6.35, 2.6.35.1 and later)

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Message-ID: <87bp56eoya.fsf@free.fr>
Date:	Tue, 30 Nov 2010 17:49:49 +0100
From:	Damien Wyart <damien.wyart@...e.fr>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	tmhikaru@...il.com, Venkatesh Pallipadi <venki@...gle.com>,
	Chase Douglas <chase.douglas@...onical.com>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org, Kyle McMartin <kyle@...artin.ca>
Subject: Re: High CPU load when machine is idle (related to PROBLEM: Unusually high load average when idle in 2.6.35, 2.6.35.1 and later)

* Peter Zijlstra <peterz@...radead.org> [101129 12:38]:
> > Doesn't give wrong numbers like initial bug and tentative patches, but
> > feels a bit too slow when numbers go up and down. Correct values are
> > reached when waiting long enough, but it feels slow.

> > As I've tested many combinations, maybe this is an impression because
> > I do not remember about "normal" delays for the load to rise and fall,
> > but this still feels slow.

> You can test this by either booting with nohz=off, or builting with
> CONFIG_NO_HZ=n and then comparing the result, something like

> make O=defconfig clean; while sleep 10; do uptime >> load.log; done &
> make -j32 O=defconfig; kill %1

> And comparing the curves between the NO_HZ and !NO_HZ kernels.

In fact, timings were very similar between the two configurations, so
I guess my feelings were wrong... They were also similar with the next
version of the patch.

-- 
Damien Wyart
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