[PATCH] ARM: perf: limit sample_period to half max_period in non-sampling mode

[Will Deacon]

On Mon, Feb 20, 2012 at 12:39:11PM +0000, Ming Lei wrote:
> On Mon, Feb 20, 2012 at 8:07 PM, Will Deacon <will.deacon at arm.com> wrote:
> > diff --git a/arch/arm/kernel/perf_event.c b/arch/arm/kernel/perf_event.c
> > index 5bb91bf..56173ae 100644
> > --- a/arch/arm/kernel/perf_event.c
> > +++ b/arch/arm/kernel/perf_event.c
> > @@ -180,7 +180,7 @@ armpmu_event_set_period(struct perf_event *event,
> >  u64
> >  armpmu_event_update(struct perf_event *event,
> >                    struct hw_perf_event *hwc,
> > -                   int idx, int overflow)
> > +                   int idx)
> >  {
> >        struct arm_pmu *armpmu = to_arm_pmu(event->pmu);
> >        u64 delta, prev_raw_count, new_raw_count;
> > @@ -193,13 +193,7 @@ again:
> >                             new_raw_count) != prev_raw_count)
> >                goto again;
> >
> > -       new_raw_count &= armpmu->max_period;
> > -       prev_raw_count &= armpmu->max_period;
> > -
> > -       if (overflow)
> > -               delta = armpmu->max_period - prev_raw_count + new_raw_count + 1;
> > -       else
> > -               delta = new_raw_count - prev_raw_count;
> > +       delta = (new_raw_count - prev_raw_count) & armpmu->max_period;
> 
> Please add
> 
>            Signed-off-by: Ming Lei <ming.lei at canonical.com>

Sure, didn't want to add anything more than a CC until I was sure you were
happy with it.

On the plus side, the warnings from Stephane's IRQ throttling code have been
fixed in -rc4 by f39d47ff ("perf: Fix double start/stop in
x86_pmu_start()").

So the ball should be back in the OMAP court now as far as enabling perf on
Panda.

Will