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

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Date:	Tue, 03 Aug 2010 11:05:59 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Pekka Enberg <penberg@...helsinki.fi>
Cc:	Damien Wyart <damien.wyart@...e.fr>,
	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
Subject: Re: kmemleak, cpu usage jump out of nowhere

On Thu, 2010-07-15 at 23:52 +0300, Pekka Enberg wrote:
> On Thu, Jul 15, 2010 at 11:00 PM, Damien Wyart <damien.wyart@...e.fr> wrote:
> >> > 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?
> >
> > * Pekka Enberg <penberg@...helsinki.fi> [2010-07-15 22:50]:
> >> 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."
> >
> > Not sure I will have enough time in the coming days (doing that remotely
> > is fishy since ssh access is almost stuck when the problem occurs); if
> > Zeno can and would like to do it, maybe this could be done faster.
> >
> > As the scheduler is now very well instrumented (many debugging features
> > are available), reproducing the bug on a test platform (it happens quite
> > quickly for me) might also give some hints. So testers, if you have
> > time, please test 2.6.35-rc5 with CONFIG_NO_BOOTMEM on a Core i7 and see
> > if you can reproduce the problem!
> 
> Yeah, there's "perf sched" tool available for that:
> 
>   http://lwn.net/Articles/353295/
> 
> The only problem is that we'd need a scheduler hacker to decipher the
> report and all of them seem to be missing at the moment (probably at
> OLS). Anyway, like I said, git bisect will probably speed up the
> debugging process, that's all.

Vacation.. but now I'm back ;-)

Even something simple as: perf top -r 1 (make sure you're root in order
to run with real-time prios) could give a clue as to what is consuming
all your cpu-time.

Or did the issue get sorted already?
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