linux-kernel - Re: mmotm 2009-04-10-02-21 uploaded

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Date:	Mon, 13 Apr 2009 19:18:53 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Valdis.Kletnieks@...edu, Mike Travis <travis@....com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	mm-commits@...r.kernel.org, Rusty Russell <rusty@...tcorp.com.au>,
	Dave Jones <davej@...hat.com>
Subject: Re: mmotm 2009-04-10-02-21 uploaded - forkbombed by work_for_cpu


* Linus Torvalds <torvalds@...ux-foundation.org> wrote:

> So I do think Andrew's commit is broken and we should think about 
> it a bit more, but I also think that Valdis' problem comes from 
> acpi-cpufreq just being damn stupid. Doing a 
> smp_call_function_single() to read two MSR's is going to be a 
> _lot_ more efficient than doing that crazy work_on_cpu() for that.
> 
> So the _real_ problem came through the commits like
> 
>     cpufreq: use work_on_cpu in acpi-cpufreq.c for drv_read and drv_write
>     cpumask: use work_on_cpu in acpi-cpufreq.c for read_measured_perf_ctrs
> 
> that were meant to reduce stack usage with big cpu masks. And 
> sure, the _old_ way of doing it was also stupid (it rescheduled 
> the process to the other CPU by using cpus_allowed()).
> 
> Mike, Ingo?

I think Andrew has a stack of fixes queued up, one of which should 
solve this problem too - which Mike tested - as the commit from 
Andrew has caused another regression as well.

There's no sha1 - the patch is in this thread on lkml:

  sysbench(oltp)+mysql 10% regression with 2.6.30-rc1

| From: Andrew Morton <akpm@...ux-foundation.org>
|
| Atttempting to rid us of the problematic work_on_cpu().  Just use
| smp_call_fuction_single() here.
|
| This repairs a 10% sysbench(oltp)+mysql regression which Mike 
| reported,

	Ingo
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