On Friday 30 April 2010 11:08:14 Ingo Molnar wrote:
>
> * Thomas Renninger <trenn@xxxxxxx> wrote:
>
> > + trace_power_start(POWER_CSTATE, 1, smp_processor_id());
> > + trace_power_start(POWER_CSTATE, (ax>>4)+1, smp_processor_id());
> > + trace_power_start(POWER_CSTATE, 1, smp_processor_id());
> > + trace_power_start(POWER_CSTATE, 0, smp_processor_id());
> > + trace_power_frequency(POWER_PSTATE, freqs->new, freqs->cpu);
> > + trace_power_end(smp_processor_id());
>
> Extending power tracing to all cpufreq modules is obviously a good thing.
>
> But why is trace_power_start() adding a CPU ID argument? CPU ids are already
> available and can be sampled via PERF_SAMPLE_CPU if needed. AFAICS only
> power_frequency needs a new 'target_cpu_id' field.
Currently the C-states get triggered on the machine you are running on.
But you can have C-state dependencies (ACPI spec at least defines this
the same way as done for P-states, not sure whether this exists in
reality already, Linux does not evaluate them yet).
The same way we run into trouble with P-states (SW_ALL, SW_ANY, HW).
Not sure how this will/could show up in reality in HW or implementation, but
as these dependencies are already defined in spec, it sounds like a good idea
to pass the CPU through the POWER_CSTATE events as well.
Compare with chapter 8.4.2.2 _CSD (C-State Dependency)
of an ACPI spec 3.0 or newer.
There are also other architectures starting to use processor sleep states.
So this is not actually used (smp_processor_id() is the same as already
tracked by trace event internally), but to make the interface more robust
for the future. Changes in the trace_power layout later may hurt.
> > diff --git a/tools/perf/builtin-timechart.c b/tools/perf/builtin-timechart.c
> > index 0d4d8ff..7809bef 100644
> > --- a/tools/perf/builtin-timechart.c
> > +++ b/tools/perf/builtin-timechart.c
>
> Timechart is maintained by Arjan so we need an ack from him as well. I've seen
> some back and forth in the discussions - what's the technical resolution of
> that?
>
> (Also, there's some whitespace noise in the patch.)
Oops. Tell me if you like to push it and I send a checkpatch cleaned up version.
Sorry about that.
Thomas
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