linux-kernel - Re: [PATCH] trace power_frequency events on the correct cpu (for Intel x86 CPUs)

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Date:	Tue, 16 Mar 2010 10:57:05 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Robert Sch?ne <robert.schoene@...dresden.de>
Cc:	Thomas Renninger <trenn@...e.de>,
	Arjan van de Ven <arjan@...ux.intel.com>,
	Dave Jones <davej@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	cpufreq <cpufreq@...r.kernel.org>, x86@...nel.org
Subject: Re: [PATCH] trace power_frequency events on the correct cpu  (for
 Intel x86 CPUs)


* Robert Sch?ne <robert.schoene@...dresden.de> wrote:

> Am Montag, den 15.03.2010, 11:51 +0100 schrieb Thomas Renninger:
> > On Friday 12 March 2010 16:41:46 Robert Sch??ne wrote:
> > > Am Freitag, den 12.03.2010, 06:52 -0800 schrieb Arjan van de Ven:
> > > > On 3/12/2010 5:17, Robert Sch??ne wrote:
> > > > > This patch fixes the following behaviour:
> > > > > Currently, the power_frequency event is reported for the cpu (core) which initiated the frequency change.
> > > > > It should be reported for the cpu that actually changes its frequency.
> > > > >
> > > > > Example: when using
> > > > >   taskset -c 0 echo<new_frequency>  >  /sys/devices/system/cpu/cpu1/cpufreq/scaling_setspeed
> > > > > cpu 0 is traced, instead of cpu 1
> > > > >
> > > > > Signed of by Robert Schoene<robert.schoene@...dresden.de>
> > > > >
> > > > >
> > > > > diff --git a/arch/x86/kernel/cpu/cpufreq/acpi-cpufreq.c b/arch/x86/kernel/cpu/cpufreq/acpi-cpufreq.c
> > > > > index 1b1920f..0a47f10 100644
> > > > > --- a/arch/x86/kernel/cpu/cpufreq/acpi-cpufreq.c
> > > > > +++ b/arch/x86/kernel/cpu/cpufreq/acpi-cpufreq.c
> > > > > @@ -174,6 +174,7 @@ static void do_drv_write(void *_cmd)
> > > > >
> > > > >          switch (cmd->type) {
> > > > >          case SYSTEM_INTEL_MSR_CAPABLE:
> > > > > +               trace_power_frequency(POWER_PSTATE, cmd->val);
> > > > >                  rdmsr(cmd->addr.msr.reg, lo, hi);
> > > > >                  lo = (lo&  ~INTEL_MSR_RANGE) | (cmd->val&  INTEL_MSR_RANGE);
> > > > >                  wrmsr(cmd->addr.msr.reg, lo, hi);
> > > > > @@ -363,7 +364,6 @@ static int acpi_cpufreq_target(struct cpufreq_policy *policy,
> > > > >                  }
> > > > >          }
> > > > >
> > > > > -       trace_power_frequency(POWER_PSTATE, data->freq_table[next_state].frequency);
> > > > >
> > > > >          switch (data->cpu_feature) {
> > > > >          case SYSTEM_INTEL_MSR_CAPABLE:
> > > > >
> > > > >
> > > > 
> > > > are you sure this is right?
> > > > it's moving something from outside a switch statement to inside only one prong of a switch statement...
> You are right, it should be in all cases, which execute a frequency change.
> > > 
> > > I'm pretty sure, since I'm moving it from function acpi_cpufreq_target(...) to do_drv_write(...)
> > What exactly is the argument you are pretty sure this is correct?
> > 
> > I expect Arjan is right.
> > You now only trace MSR based and not IO based frequency switching.
> > 
> > I don't know the tracing stuff, but it seems the cpu that executes
> > trace_power_frequency shows up in the statistics as the one on which the
> > frequency change happened which currently is wrong and you try to fix this?
> Yes
> > 
> > What exactly is the reason you do not add
> > trace_power_frequency(..);
> > also in the
> > SYSTEM_IO_CAPABLE:
> > branch in do_drv_write()?
> I don't know system io capable systems and what they are doing, so I ignored it to prevent reporting wrong "frequencies". 
> > 
> >     Thomas
> > 
> > 
> > 
> >    Thomas
>
> I stand corrected and appended the new patch (with an additional trace 
> command for io capable systems) Robert

Please send a changelogged version with everyone Cc:-ed once the dust settles 
and the acks are in.

Thanks,

	Ingo
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