linux-kernel - RE: [PATCH V6 5/8] perf/x86/intel/uncore: add infrastructure for free running counter

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Date:   Mon, 19 Mar 2018 13:00:09 +0000
From:   "Liang, Kan" <kan.liang@...el.com>
To:     'Peter Zijlstra' <peterz@...radead.org>
CC:     "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "acme@...nel.org" <acme@...nel.org>,
        "eranian@...gle.com" <eranian@...gle.com>,
        "ak@...ux.intel.com" <ak@...ux.intel.com>
Subject: RE: [PATCH V6 5/8] perf/x86/intel/uncore: add infrastructure for
 free running counter

> On Thu, Jan 25, 2018 at 12:13:45PM -0800, kan.liang@...el.com wrote:
> > @@ -512,6 +538,17 @@ static int uncore_pmu_event_add(struct
> perf_event *event, int flags)
> >  	if (!box)
> >  		return -ENODEV;
> >
> > +	/*
> > +	 * The free funning counter is assigned in event_init().
> > +	 * The free running counter event and free running counter
> > +	 * are 1:1 mapped. It doesn't need to be tracked in event_list.
> > +	 */
> > +	if (uncore_pmc_freerunning(hwc->idx)) {
> > +		if (flags & PERF_EF_START)
> > +			uncore_pmu_event_start(event, 0);
> > +		return 0;
> > +	}
> > +
> >  	ret = n = uncore_collect_events(box, event, false);
> >  	if (ret < 0)
> >  		return ret;
> 
> This will result in some (probably) unexpected scheduling artifacts.
> Probably the only way to really cure that is to have the free running
> counters in their own PMU and not share with the GP counters of this
> box.

I'm not quite sure what the unexpected scheduling artifacts could be.
But, yes, I can move all the free running counters to new PMU for SKX
and later platforms.

Thanks,
Kan