linux-kernel - Re: PATCH] ftrace: Add a C/P state tracer to help power optimization

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Message-ID: <20081006142131.37104893@infradead.org>
Date:	Mon, 6 Oct 2008 14:21:31 -0700
From:	Arjan van de Ven <arjan@...radead.org>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	Andi Kleen <andi@...stfloor.org>, linux-kernel@...r.kernel.org,
	Steven Rostedt <rostedt@...dmis.org>, mingo@...e.hu,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>, lenb@...nel.org
Subject: Re: PATCH] ftrace: Add a C/P state tracer to help power
 optimization

> > the link between P states and frequency is... rather lose.
> > Especially with Turbo Mode it no longer is really relevant to list
> > frequencies.
> 
> It would probably be less confusing for everyone if the higher level
> cpufreq layers reported the correct frequency for turbo mode too.
> I haven't checked how complicated this would be.

it's impossible until after the fact; you don't know which frequencies
you got until you check back later.


> Ok.
> 
> That means that when a CPU is idle forever there won't be any output?

correct; it'll wait until it stops being idle before telling  you how
long it was idle.

if it really bothers you we could do a dummy broadcast ipi on shutting
down the tracer.. in practice it's not a problem.
(we wake up all cpus all the time)



-- 
Arjan van de Ven 	Intel Open Source Technology Centre
For development, discussion and tips for power savings, 
visit http://www.lesswatts.org
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