linux-kernel - Re: [PATCH v3 3/6] ARCv2: perf: Support sampling events using overflow interrupts

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Message-ID: <1440599752.15478.49.camel@synopsys.com>
Date:	Wed, 26 Aug 2015 14:35:52 +0000
From:	Alexey Brodkin <Alexey.Brodkin@...opsys.com>
To:	"peterz@...radead.org" <peterz@...radead.org>
CC:	"linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Vineet.Gupta1@...opsys.com" <Vineet.Gupta1@...opsys.com>,
	"arc-linux-dev@...opsys.com" <arc-linux-dev@...opsys.com>,
	"arnd@...db.de" <arnd@...db.de>,
	"acme@...nel.org" <acme@...nel.org>
Subject: Re: [PATCH v3 3/6] ARCv2: perf: Support sampling events using
 overflow interrupts

Hi Peter,

On Wed, 2015-08-26 at 16:32 +0200, Peter Zijlstra wrote:
> On Wed, Aug 26, 2015 at 01:21:08PM +0000, Alexey Brodkin wrote:
> > Hi Peter,
> > 
> > On Wed, 2015-08-26 at 15:12 +0200, Peter Zijlstra wrote:
> > > On Mon, Aug 24, 2015 at 05:20:20PM +0300, Alexey Brodkin wrote:
> > > > @@ -295,6 +317,16 @@ 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));
> > > > +	}
> > > > +
> > > 
> > > pmu::add should call pmu::start when PERF_EF_START, without that it
> > > should not start the counter, only schedule it.
> > > 
> > > (although currently all pmu::add() calls will have EF_START set)
> > 
> > And that's what we do, don't we?
> > ----------------------->8-----------------------
> > 	if (flags & PERF_EF_START)
> > 		arc_pmu_start(event, PERF_EF_RELOAD);
> > ----------------------->8-----------------------
> > 
> 
> D'uh indeed! I read that above as enabling it, while what it really does
> it simply program the interrupt thresholds.

That's ok.
So do I need to do anything now or both your initial comments today are no longer valid?

-Alexey--
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