Re: [PATCH v5 05/11] arm-cci PMU: Delay counter writes to pmu_enable

[Suzuki K. Poulose]

On 04/01/16 19:24, Mark Rutland wrote:
> On Mon, Jan 04, 2016 at 11:54:44AM +0000, Suzuki K. Poulose wrote:
> > Delay setting the event periods for enabled events to pmu::pmu_enable().
> > We mark the event.hw->state PERF_HES_ARCH for the events that we know
> > have their counts recorded and have been started.
>
> Please add a comment to the code stating exactly what PERF_HES_ARCH
> means for the CCI PMU driver, so it's easy to find.

Sure.

> > +void cci_pmu_update_counters(struct cci_pmu *cci_pmu)
> > +{
> > +	int i;
> > +	unsigned long mask[BITS_TO_LONGS(cci_pmu->num_cntrs)];
>
> I think this can be:
>
> 	DECLARE_BITMAP(mask, cci_pmu->num_cntrs);
>
> > +
> > +	memset(mask, 0, BITS_TO_LONGS(cci_pmu->num_cntrs) * sizeof(unsigned long));
>
> Likewise:
>
> 	bitmap_zero(mask, cci_pmu->num_cntrs);

OK

> > +		if (!cci_pmu->hw_events.events[i]) {
> > +			WARN_ON(1);
> > +			continue;
> > +		}
> > +
>
> 		if (WARN_ON(!cci_pmu->hw_events.events[i]))
> 			continue;

OK
 
> > @@ -980,8 +1015,11 @@ static void cci_pmu_start(struct perf_event *event, int pmu_flags)
> >   	/* Configure the counter unless you are counting a fixed event */
> >   	if (!pmu_fixed_hw_idx(cci_pmu, idx))
> >   		pmu_set_event(cci_pmu, idx, hwc->config_base);
> > -
> > -	pmu_event_set_period(event);
> > +	/*
> > +	 * Mark this counter, so that we can program the
> > +	 * counter with the event_period. see cci_pmu_enable()
> > +	 */
> > +	hwc->state = PERF_HES_ARCH;
>
> Why couldn't we have kept pmu_event_set_period here, and have that set
> prev_count and PERF_HES_ARCH?
>
> Then we'd be able to do the same betching for overflow too.

The pmu is not disabled while we are in overflow irq handler. Hence there may
not be a pmu_enable() which would set the period for the counter which
overflowed, if defer the write in that case. Is that assumption wrong ?

Cheers
Suzuki
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