linux-kernel - Re: [RFC][PATCH 8/8] perf: Rework the PMU methods

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Date:	Fri, 18 Jun 2010 09:15:38 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	paulus <paulus@...ba.org>,
	stephane eranian <eranian@...glemail.com>,
	Robert Richter <robert.richter@....com>,
	Will Deacon <will.deacon@....com>,
	Paul Mundt <lethal@...ux-sh.org>,
	Cyrill Gorcunov <gorcunov@...il.com>,
	Lin Ming <ming.m.lin@...el.com>,
	Yanmin <yanmin_zhang@...ux.intel.com>,
	Deng-Cheng Zhu <dengcheng.zhu@...il.com>,
	David Miller <davem@...emloft.net>,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC][PATCH 8/8] perf: Rework the PMU methods

On Fri, 2010-06-18 at 06:21 +0200, Frederic Weisbecker wrote:
> On Wed, Jun 16, 2010 at 06:00:35PM +0200, Peter Zijlstra wrote:
> > -static void x86_pmu_stop(struct perf_event *event)
> > +static void x86_pmu_stop(struct perf_event *event, int flags)
> >  {
> > -	struct cpu_hw_events *cpuc = &__get_cpu_var(cpu_hw_events);
> > -	struct hw_perf_event *hwc = &event->hw;
> > -	int idx = hwc->idx;
> > -
> >  	if (!__test_and_clear_bit(idx, cpuc->active_mask))
> > -		return;
> 
> 
> 
> Do you still need active_mask now that you have HES_STOPPED?

there still were some users, but yeah, we cuold probably clean that up,
bit since the patch is large enough as is, I didn't attempt that.

> > +static void perf_swevent_start(struct perf_event *event, int flags)
> > +{
> > +	event->hw.state = 0;
> > +}
> > +
> > +static void perf_swevent_stop(struct perf_event *event, int flags)
> >  {
> > +	event->hw.state = 1;
> >  }
> 
> 
> So, instead of doing this and add yet another check in the fast path,
> what about just playing with the hlist insertion and deletion?

I wanted to avoid too much trickery, first make a simple one work, then
try something fancy.

> It would be nice to have a PERF_EF_STOP as well in ->del, so that
> each pmu don't need to maintain an internal state.

You have to track it since we can stop the thing outselves without the
caller knowing.

> >  }
> >  #endif
> > @@ -4591,12 +4582,12 @@ static void perf_swevent_start_hrtimer(s
> >  	if (hwc->sample_period) {
> >  		u64 period;
> >  
> > -		if (hwc->remaining) {
> > -			if (hwc->remaining < 0)
> > +		if (hwc->period_left) {
> > +			if (hwc->period_left < 0)
> >  				period = 10000;
> >  			else
> > -				period = hwc->remaining;
> > -			hwc->remaining = 0;
> > +				period = hwc->period_left;
> > +			hwc->period_left = 0;
> 
> 
> 
> If remaining can be replaced by period_left, it should probably be done
> in another patch.

true.
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