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

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Date:	Tue, 28 Oct 2008 11:04:03 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Arjan van de Ven <arjan@...radead.org>
Cc:	"Frank Ch. Eigler" <fche@...hat.com>, linux-kernel@...r.kernel.org,
	Steven Rostedt <rostedt@...dmis.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>, lenb@...nel.org
Subject: Re: PATCH] ftrace: Add a C/P state tracer to help power
	optimization


* Arjan van de Ven <arjan@...radead.org> wrote:

> On Mon, 27 Oct 2008 15:47:30 -0400
> fche@...hat.com (Frank Ch. Eigler) wrote:
> 
> > 
> > Arjan van de Ven <arjan@...radead.org> writes:
> > 
> > > [...]
> > > --- a/arch/x86/kernel/cpu/cpufreq/acpi-cpufreq.c
> > > +++ b/arch/x86/kernel/cpu/cpufreq/acpi-cpufreq.c
> > > [...]
> > > @@ -427,6 +429,8 @@ static int acpi_cpufreq_target(struct
> > > cpufreq_policy *policy, }
> > >  	}
> > >  
> > > +	trace_power_mark(&it, POWER_PSTATE, next_perf_state);
> > > +
> > >  	switch (data->cpu_feature) {
> > >  	case SYSTEM_INTEL_MSR_CAPABLE:
> > >  		cmd.type = SYSTEM_INTEL_MSR_CAPABLE;
> > > [...]
> > 
> > Is there some reason that this doesn't use tracepoints instead
> > of such a single-backend hook?
> 
> because it's a ton simpler this way? do simple things simpe and all 
> that....

correct.

	Ingo
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