linux-kernel - Re: [PATCH 2/2] perf/x86/intel: Add Tremont core PMU support

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Date:   Wed, 10 Apr 2019 09:58:40 -0400
From:   "Liang, Kan" <kan.liang@...ux.intel.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     mingo@...hat.com, linux-kernel@...r.kernel.org, tglx@...utronix.de,
        acme@...nel.org, jolsa@...nel.org, eranian@...gle.com,
        alexander.shishkin@...ux.intel.com, ak@...ux.intel.com
Subject: Re: [PATCH 2/2] perf/x86/intel: Add Tremont core PMU support



On 4/10/2019 3:51 AM, Peter Zijlstra wrote:
> On Tue, Apr 09, 2019 at 06:10:00PM -0700, kan.liang@...ux.intel.com wrote:
> 
>> The generic purpose counter 0 and fixed counter 0 have less skid.
>> Force :ppp events on generic purpose counter 0.
>> Force instruction:ppp always on fixed counter 0.
> 
>> +static struct event_constraint *
>> +tnt_get_event_constraints(struct cpu_hw_events *cpuc, int idx,
>> +			  struct perf_event *event)
>> +{
>> +	struct event_constraint *c;
>> +
>> +	/*
>> +	 * :ppp means to do reduced skid PEBS,
>> +	 * which is available at PMC0 and fixed counter 0.
>> +	 */
>> +	if (event->attr.precise_ip == 3) {
>> +		/* Force instruction:ppp in Fixed counter 0 */
>> +		if (event->hw.config == X86_CONFIG(.event=0xc0))
>> +			return &fixed_counter0_constraint;
>> +
>> +		return &counter0_constraint;
> 
> I'm confused, 0xc0 is the architectural 'instructions' event, surely we
> can program that on pmc0 too?
> 
> Did we want a fixed0_counter0_constraint for that?
> 

Yes, I will send out V2 shortly to fix it.

Thanks,
Kan