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SubjectRe: Patch for tracing c states (power_end) on x86
Robert Schöne wrote:
> Hi,
>

Please don't top posting. :)

> I tried to pass 0 in "my" sleep routine "static void mwait_idle(void)"
> Which led to the following behaviour:
> The event was reported on /sys/kernel/debug/tracing, but still not
> for sys_perf_open.

The event was not reported by sys_perf_open()? Could you be more
elaborate on this? Because I don't get you here.

> As 1 had been the argument which led to a working tracing, I assumed,
> that the argument should be the same as the 2nd arg of the last
> power_start event.
> Since this argument had been 1 in my case, it worked for me. However, 0
> did not.
>
> Bye Robert
>
>
>
> Am Mittwoch, den 24.02.2010, 16:36 +0800 schrieb Li Zefan:
>> Robert Schöne wrote:
>>> Hello,
>>>
>>> Since noone replied to my last mail (Febr. 15th, 11:42), describing the
>>> way to fix the missing c-state tracing, here's a patch.
>>> Maybe its easier that way.
>>>
>>> (I used the perf-fixes-for-linus git tree to obtain a
>>> more-then-up-to-date version)
>>>
>>> Bye Robert
>>>
>>>
>>> diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
>>> index 02d6780..b1cfb88 100644
>>> --- a/arch/x86/kernel/process.c
>>> +++ b/arch/x86/kernel/process.c
>>> @@ -384,6 +384,7 @@ void default_idle(void)
>>> else
>>> local_irq_enable();
>>> current_thread_info()->status |= TS_POLLING;
>>> + trace_power_end(1);
>>> } else {
>>> local_irq_enable();
>>> /* loop is done by the caller */
>>> @@ -451,6 +452,7 @@ void mwait_idle_with_hints(unsigned long ax,
>>> unsigned long cx)
>>> if (!need_resched())
>>> __mwait(ax, cx);
>>> }
>>> + trace_power_end((ax>>4)+1);
>> The only argument of trace_power_end() is a dummy, so you can just
>> pass 0 or 1 to the trace hook, actually better pass 0 to be
>> consistent with other parts.
>>
>> The dummy argument can't be eliminated, because the macros that
>> automatically generates racing code have some limitations, and
>> seems it's not so easy to get over.
>>
>>> }
>>>
>>> /* Default MONITOR/MWAIT with no hints, used for default C1 state */
>>> @@ -467,6 +469,7 @@ static void mwait_idle(void)
>>> __sti_mwait(0, 0);
>>> else
>>> local_irq_enable();
>>> + trace_power_end(1);
>>> } else
>>> local_irq_enable();
>>> }
>>>
>>>
>> --
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>> Please read the FAQ at http://www.tux.org/lkml/
>>
> ------------------------- Mail from Febr. 15th --------------------
> Hi,
> I have a question regarding the event "power/power_end".
> For the standard linux kernel (2.6.32.8), it's just not reported -
> neither for the /sys/kernel/debug/tracing nor for the sys_perf_open
> approach.
>
> System:
> Intel Core 2 Quad,
> Kernel 2.6.32.8,
> for sys_perf_open:always using sampling counters,
> (Kernel 2.6.33-rcX should show the same behavior)
>
> After finding "my" c-state procedure in arch/x86/kernel/process.c
> (which was "static void mwait_idle(void)" btw), I added a
> trace_power_end call on the correct line:
> ...
> else
> local_irq_enable();
> } else
> ...
> ->
> ...
> else
> local_irq_enable();
> trace_power_end(0);
> } else
> ...
> Now the event was reported on /sys/kernel/debug/tracing, but still not
> for sys_perf_open.
>
> Then I had the idea, that trace_power_end's argument should be the same
> as the 2nd argument of the previous power_start.
>
> That worked.
>
> However, things to be done are: add trace_power_end's to some
> process.c's procedures.
>
>
> Bye Robert
>
> -------------------------End of Mail of Febr. 15th --------------------
>
>
>
>
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