RE: [PATCH v2 4/8] ARCv2: perf: Support sampling events using overflow interrupts

[Alexey Brodkin]

Hi Peter,

> -----Original Message-----
> From: Peter Zijlstra [mailto:peterz@xxxxxxxxxxxxx]
> Sent: 19 августа 2015 г. 1:12
> To: Alexey Brodkin
> Cc: linux-arch@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; Vineet.Gupta1@xxxxxxxxxxxx; arc-linux-dev@xxxxxxxxxxxx;
> arnd@xxxxxxxx; Arnaldo Carvalho de Melo
> Subject: Re: [PATCH v2 4/8] ARCv2: perf: Support sampling events using overflow interrupts
> 
> On Wed, Aug 05, 2015 at 06:13:30PM +0300, Alexey Brodkin wrote:
> > @@ -319,6 +336,20 @@ static int arc_pmu_add(struct perf_event *event, int flags)
> >  	}
> >
> >  	write_aux_reg(ARC_REG_PCT_INDEX, idx);
> > +
> > +	arc_pmu->act_counter[idx] = event;
> > +
> > +	if (is_sampling_event(event)) {
> > +		/* Mimic full counter overflow as other arches do */
> > +		write_aux_reg(ARC_REG_PCT_INT_CNTL, (u32)arc_pmu->max_period);
> > +		write_aux_reg(ARC_REG_PCT_INT_CNTH,
> > +			      (arc_pmu->max_period >> 32));
> > +
> > +		/* Enable interrupt for this counter */
> > +		write_aux_reg(ARC_REG_PCT_INT_CTRL,
> > +			      read_aux_reg(ARC_REG_PCT_INT_CTRL) | (1 << idx));
> > +	}
> 
> *confused* pmu::add should only start on flags & PERF_EF_START, and then
> we start with hwc->sample_period, not the max_period.

Did you mean here that we should enable interrupts in arc_pmu_start() but not
in arc_pmu_add()?

-Alexey
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