linux-kernel - Re: unpredictability in scheduler test results -- still present

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Date:	Tue, 30 Sep 2008 13:12:17 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Chris Friesen <cfriesen@...tel.com>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	linux-kernel@...r.kernel.org, Steven Rostedt <rostedt@...dmis.org>
Subject: Re: unpredictability in scheduler test results -- still present


* Chris Friesen <cfriesen@...tel.com> wrote:

> Ingo Molnar wrote:
>> * Chris Friesen <cfriesen@...tel.com> wrote:
>
>>> It turns out that disabling CONFIG_DYNAMIC_FTRACE makes the load  
>>> balancing problem go away and causes all cpus to be used.
>>>
>>> With this option enabled, the problem seems to be present as far back 
>>> as 2.6.27-rc2.  (2.6.27-rc1 doesn't compile on my machine, and 2.6.26 
>>> doesn't have ftrace).
>>>
>>> I have no idea why turning on dynamic ftrace would affect load  
>>> balancing behaviour, but it's very repeatable.  The very first test  
>>> run after booting works fine, and all successive runs fail to balance 
>>> properly.
>
>> OTOH, what does 'truning on dftrace' exactly mean? Just enabling it in  
>> the .config, or also activating it via /debug/tracing/current_tracer?
>
> Just enabling it in the .config is enough to trigger the behaviour 
> change.  I'm not explicitly activating any traces.

ok, that would be a clear ftrace bug i guess?

	Ingo
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