Re: [PATCH 4/9] perf/x86/intel: Support hardware TopDown metrics

[Liang, Kan]

On 5/29/2019 3:54 AM, Peter Zijlstra wrote:
> On Tue, May 28, 2019 at 02:24:38PM -0400, Liang, Kan wrote:
> > On 5/28/2019 9:43 AM, Peter Zijlstra wrote:
> > > On Tue, May 21, 2019 at 02:40:50PM -0700, kan.liang@xxxxxxxxxxxxxxx wrote:
> > > > @@ -3287,6 +3304,13 @@ static int core_pmu_hw_config(struct perf_event *event)
> > > >    	return intel_pmu_bts_config(event);
> > > >    }
> > > > +#define EVENT_CODE(e)	(e->attr.config & INTEL_ARCH_EVENT_MASK)
> > > > +#define is_slots_event(e)	(EVENT_CODE(e) == 0x0400)
> > > > +#define is_perf_metrics_event(e)				\
> > > > +		(((EVENT_CODE(e) & 0xff) == 0xff) &&		\
> > > > +		 (EVENT_CODE(e) >= 0x01ff) &&			\
> > > > +		 (EVENT_CODE(e) <= 0x04ff))
> > > > +
> > >
> > > That is horrific.. (e & INTEL_ARCH_EVENT_MASK) & 0xff is just daft,
> > > that should be: (e & ARCH_PERFMON_EVENTSEL_EVENT).
> > >
> > > Also, we already have fake events for event=0, see FIXED2, why are we
> > > now using event=0xff ?
> >
> > I think event=0 is for genuine fixed events. Metrics events are fake events.
> > I didn't find FIXED2 in the code. Could you please share more hints?
>
> cd09c0c40a97 ("perf events: Enable raw event support for Intel unhalted_reference_cycles event")
>
> We used the fake event=0x00, umask=0x03 for CPU_CLK_UNHALTED.REF_TSC,
> because that was not available as a generic event, *until now* it seems.
> I see ICL actually has it as a generic event, which means we need to fix
> up the constraint mask for that differently.

There is no change for REF_TSC on ICL.

> But note that for all previous uarchs this event did not in fact exist.
>
> It appears the TOPDOWN.SLOTS thing, which is available in in FIXED3 is
> event=0x00, umask=0x04, is indeed a generic event too.

The SLOTS do have a generic event, TOPDOWN.SLOTS_P, event=0xA4, umask=0x1.

I think we need a fix as below for ICL, so the SLOT event can be 
extended to generic event.
-	FIXED_EVENT_CONSTRAINT(0x0400, 3),	/* SLOTS */
+	FIXED_EVENT_CONSTRAINT(0x01a4, 3),	/* TOPDOWN.SLOTS */

I will send a separate patch for it.

Thanks,
Kan