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SubjectRE: [PATCH v2 4/8] ARCv2: perf: Support sampling events using overflow interrupts
Date
Hi Peter,

> -----Original Message-----
> From: Peter Zijlstra [mailto:peterz@infradead.org]
> Sent: 19 августа 2015 г. 1:12
> To: Alexey Brodkin
> Cc: linux-arch@vger.kernel.org; linux-kernel@vger.kernel.org; Vineet.Gupta1@synopsys.com; arc-linux-dev@synopsys.com;
> arnd@arndb.de; 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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