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Message-ID: <48E0F7B9.3040301@nortel.com>
Date: Mon, 29 Sep 2008 09:43:53 -0600
From: "Chris Friesen" <cfriesen@nortel.com>
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To: Ingo Molnar <mingo@elte.hu>
CC: Peter Zijlstra <a.p.zijlstra@chello.nl>, linux-kernel@vger.kernel.org,
       Steven Rostedt <rostedt@goodmis.org>
Subject: Re: unpredictability in scheduler test results -- still present
References: <48D2DA0D.4060300@nortel.com> <48DA5A84.8030704@nortel.com> <48DACF55.3070209@nortel.com> <20080927200433.GC28937@elte.hu>
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Ingo Molnar wrote:
> * Chris Friesen <cfriesen@nortel.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.

Chris