linux-kernel - Re: How how latent should non-preemptive scheduling be?

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Date:	Tue, 23 Sep 2008 13:53:23 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Sitsofe Wheeler <sitsofe@...oo.com>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Arjan van de Ven <arjan@...radead.org>,
	linux-kernel@...r.kernel.org, Steven Rostedt <rostedt@...dmis.org>
Subject: Re: How how latent should non-preemptive scheduling be?

* Sitsofe Wheeler <sitsofe@...oo.com> wrote:

> Ingo Molnar wrote:
>> well, since they went away after you enabled CONFIG_PREEMPT=y, they are 
>> definitely in-kernel latencies, not any external SMM latencies.
>>
>> I.e. they are inherently fixable. Could you enable:
>>
>>   CONFIG_DYNAMIC_FTRACE=y
>>   CONFIG_FTRACE_MCOUNT_RECORD=y
>>
>> that should make the traces a lot more verbose - every kernel function  
>> executed in the latency path will be logged. That way we'll be able to  
>> say which one takes that long.
>
> I do not appear to have the CONFIG_FTRACE_MCOUNT_RECORD option in 
> 2.6.27rc7. Is it an option that is only in -tip ?

yeah - it's a new ftrace feature queued up for v2.6.28.

	Ingo
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