Re: [PATCH] cpuidle/idle: move idle traces to cpuidle_enter_state

[Peter Zijlstra <peterz@infradead.org>]

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On Mon, Jul 14, 2014 at 09:47:46PM +0200, Rafael J. Wysocki wrote:
> On Saturday, July 05, 2014 05:45:24 PM Daniel Lezcano wrote:
> > On 07/02/2014 11:30 AM, Sandeep Tripathy wrote:
> > >   idle_exit event is the first event after a core exits
> > > idle state. 

This

> > > So this should be traced before local irq
> > > is ebabled. 

does not follow, interrupt state does not correlate to events or not.

> > > Likewise idle_entry is the last event before
> > > a core enters idle state. This will ease visualising the
> > > cpu idle state from kernel traces.
> > >
> > > Signed-off-by: Sandeep Tripathy <sandeep.tripathy@linaro.org>
> > 
> > Acked-by: Daniel Lezcano <daniel.lezcano@linaro.org>
> 
> I'm going to take this for 3.17.
> 
> Peter, will there be any problems with it if I take it?

don't think so, if there's anything, I'll fix it up.

> > > ---
> > >   drivers/cpuidle/cpuidle.c | 3 +++
> > >   kernel/sched/idle.c       | 4 ----
> > >   2 files changed, 3 insertions(+), 4 deletions(-)
> > >
> > > diff --git a/drivers/cpuidle/cpuidle.c b/drivers/cpuidle/cpuidle.c
> > > index 8236746..97680d0 100644
> > > --- a/drivers/cpuidle/cpuidle.c
> > > +++ b/drivers/cpuidle/cpuidle.c
> > > @@ -99,12 +99,15 @@ int cpuidle_enter_state(struct cpuidle_device *dev, struct cpuidle_driver *drv,
> > >   	ktime_t time_start, time_end;
> > >   	s64 diff;
> > >
> > > +	trace_cpu_idle_rcuidle(index, dev->cpu);
> > >   	time_start = ktime_get();
> > >
> > >   	entered_state = target_state->enter(dev, drv, index);
> > >
> > >   	time_end = ktime_get();
> > >
> > > +	trace_cpu_idle_rcuidle(PWR_EVENT_EXIT, dev->cpu);

If someone were to instrument ktime_get() the changelog is obviously
fail. Now I appreciate that instrumenting the timing infrastructure
might be challenging .. :-)

And I suppose the 'assumption' is that the target_state->enter()
function does not entail 'tracing' ? Is it made sure that these
functions do not generate __mcount or other function tracer stubs etc. ?

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