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SubjectRe: PATCH] ftrace: Add a C/P state tracer to help power optimization
On Mon, 06 Oct 2008 22:46:09 +0200
Andi Kleen <andi@firstfloor.org> wrote:
> >
> > + trace_power_mark(&it, POWER_PSTATE, next_perf_state);
>
> Wouldn't that be better higher up in the cpufreq system? It would
> seem bad to duplicate that in all low level cpufreq modules.

the problem is that higher up the actual P state isn't known.

>
> Also I suspect some higher level format would be good here too.
> Just put the frequency in?

the link between P states and frequency is... rather lose.
Especially with Turbo Mode it no longer is really relevant to list
frequencies.

> > + ret = trace_seq_printf(s, "[%5ld.%09ld]
> > CSTATE: Going to C%i on cpu %i for %ld.%09ld\n",
> > + stamp.tv_sec,
> > + stamp.tv_nsec,
> > + it->state, iter->cpu,
> > + duration.tv_sec,
> > + duration.tv_nsec);
> > + if (it->type == POWER_PSTATE)
> > + ret = trace_seq_printf(s, "[%5ld.%09ld]
> > PSTATE: Going to P%i on cpu %i\n",
> > + stamp.tv_sec,
> > + stamp.tv_nsec,
> > + it->state, iter->cpu);
>
> I suspect a less verbose output format would be better.
why?
It's fine as it is, and it's actually human readable as well.

>
> > +{
> > + if (!trace_power_enabled)
> > + return;
> > +
> > + memset(it, 0, sizeof(struct power_trace));
>
> The memset seems redundant.

it's free and it initializes the datastructure cleanly; and only when
the tracer is in use.

>

> Hmm, that does a unconditional wake_up() in idle. Doesn't this cause
> a loop on UP?
>
> idle -> wakeup -> idle -> wakeup -> ... etc.
>
> Am I missing something?

yes you're missing something ;-)
this code is called when going out of idle, not when going into idle.


--
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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