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

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Date:   Wed, 29 May 2019 10:42:10 -0400
From:   "Liang, Kan" <kan.liang@...ux.intel.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     acme@...nel.org, mingo@...hat.com, linux-kernel@...r.kernel.org,
        tglx@...utronix.de, jolsa@...nel.org, eranian@...gle.com,
        alexander.shishkin@...ux.intel.com, ak@...ux.intel.com
Subject: Re: [PATCH 4/9] perf/x86/intel: Support hardware TopDown metrics



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@...ux.intel.com 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