linux-kernel - Re: kmemleak, cpu usage jump out of nowhere

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Date:	Thu, 15 Jul 2010 22:50:02 +0300
From:	Pekka Enberg <penberg@...helsinki.fi>
To:	Damien Wyart <damien.wyart@...e.fr>
Cc:	Zeno Davatz <zdavatz@...il.com>,
	Catalin Marinas <catalin.marinas@....com>,
	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>, x86@...nel.org,
	mingo@...e.hu, yinghai@...nel.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: kmemleak, cpu usage jump out of nowhere

On Thu, Jul 15, 2010 at 10:16 PM, Damien Wyart <damien.wyart@...e.fr> wrote:
>> > > I also did not have anymore hangs and random bad moods of my CPUs
>> > > that all of a sudden grab 100% of all 8 cores of my CPU power across
>> > > my machine since I disabled
>> > > CONFIG_NO_BOOTMEM:
>
>> * Pekka Enberg <penberg@...helsinki.fi> [2010-07-15 18:54]:
>> > Interesting. Damien, does disabling CONFIG_NO_BOOTMEM fix you problem too?
>
>> I will test in the coming hours, and report back tomorrow... Just
>> recompiled 2.6.35-rc5-git1 with this option disabled.
>
> For now, I can't reproduce the problem with CONFIG_NO_BOOTMEM disabled ;
> with the option and rc5 the problem was happening quite quickly after
> boot and normal use of the machine. So it seems I can confirme what Zeno
> has seen and I hope this will give a hint to debug the problem. I guess
> this has not been reported that much because many testers might not have
> enabled CONFIG_NO_BOOTMEM... Maybe the scheduler folks could test their
> benchmark with a kernel having this option enabled?

To be honest, the bug is bit odd. It's related to boot-time memory
allocator changes but yet it seems to manifest itself as a scheduling
problem. So if you have some spare time and want to speed up the
debugging process, please test v2.6.34 and v2.6.35-rc1 with
CONFIG_NO_BOOTMEM and if former is good and latter is bad, try to see
if you can identify the offending commit with "git bisect."

                         Pekka
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