Re: [PATCH v2 3/5] arm_pmu: Add support for 64bit event counters

[Suzuki K Poulose]

On 06/06/2018 05:48 PM, Mark Rutland wrote:
> On Tue, May 29, 2018 at 11:55:54AM +0100, Suzuki K Poulose wrote:
> > Each PMU has a set of 32bit event counters. But in some
> > special cases, the events could be counted using counters
> > which are effectively 64bit wide.
> >
> > e.g, Arm V8 PMUv3 has a 64 bit cycle counter which can count
> > only the CPU cycles. Also, the PMU can chain the event counters
> > to effectively count as a 64bit counter.
> >
> > Add support for tracking the events that uses 64bit counters.
> > This only affects the periods set for each counter in the core
> > driver.
> >
> > Cc: Mark Rutland <mark.rutland@xxxxxxx>
> > Cc: Will Deacon <will.deacon@xxxxxxx>
> > Signed-off-by: Suzuki K Poulose <suzuki.poulose@xxxxxxx>
> > ---
> > Changes since v1:
> >   - Rename ARMPMU_EVT_LONG => ARMPMU_EVT_64BIT
> > ---
> >   drivers/perf/arm_pmu.c       | 14 ++++++++------
> >   include/linux/perf/arm_pmu.h |  6 ++++++
> >   2 files changed, 14 insertions(+), 6 deletions(-)
> >
> > diff --git a/drivers/perf/arm_pmu.c b/drivers/perf/arm_pmu.c
> > index 8962d26..ff858e6 100644
> > --- a/drivers/perf/arm_pmu.c
> > +++ b/drivers/perf/arm_pmu.c
> > @@ -28,9 +28,10 @@
> >   static DEFINE_PER_CPU(struct arm_pmu *, cpu_armpmu);
> >   static DEFINE_PER_CPU(int, cpu_irq);
> >   
> > -static inline u64 arm_pmu_max_period(void)
> > +static inline u64 arm_pmu_event_max_period(struct perf_event *event)
> >   {
> > -	return (1ULL << 32) - 1;
> > +	return (event->hw.flags & ARMPMU_EVT_64BIT) ?
> > +		~0ULL : (1ULL << 32) - 1;
> >   }
>
> Could we please have:
>
> static inline u64 arm_pmu_event_max_period(struct perf_event *event)
> {
> 	if (event->hw.flags & ARMPMU_EVT_64BIT)
> 		return GENMASK_ULL(63, 0);
> 	else
> 		return GENMASK_ULL(31, 0);
> }
>
> ... since that's obviously balanced, with both values generated in the
> same way.

Sure, will do

Suzuki