linux-kernel - Re: [PATCH V2 2/2] perf/x86/intel: Add Tremont core PMU support

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Date:   Thu, 11 Apr 2019 09:30:10 -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 V2 2/2] perf/x86/intel: Add Tremont core PMU support



On 4/11/2019 5:06 AM, Peter Zijlstra wrote:
> On Wed, Apr 10, 2019 at 11:57:09AM -0700, kan.liang@...ux.intel.com wrote:
>> +static struct event_constraint *
>> +tnt_get_event_constraints(struct cpu_hw_events *cpuc, int idx,
>> +			  struct perf_event *event)
> 
> That 'tnt' still cracks me up, I keep seeing explosions.
>

Boom!

>> +{
>> +	struct event_constraint *c;
>> +
>> +	/*
>> +	 * :ppp means to do reduced skid PEBS,
>> +	 * which is available on PMC0 and fixed counter 0.
>> +	 */
>> +	if (event->attr.precise_ip == 3) {
>> +		/* Force instruction:ppp on PMC0 and Fixed counter 0 */
>> +		if (EVENT_CONFIG(event->hw.config) == X86_CONFIG(.event=0xc0))
>> +			return &fixed0_counter0_constraint;
>> +
>> +		return &counter0_constraint;
>> +	}
>> +
>> +	c = intel_get_event_constraints(cpuc, idx, event);
>> +
>> +	return c;
>> +}
> 
> I changed that like so:
> 
> --- a/arch/x86/events/intel/core.c
> +++ b/arch/x86/events/intel/core.c
> @@ -3508,7 +3508,7 @@ tnt_get_event_constraints(struct cpu_hw_
>   	 */
>   	if (event->attr.precise_ip == 3) {
>   		/* Force instruction:ppp on PMC0 and Fixed counter 0 */
> -		if (EVENT_CONFIG(event->hw.config) == X86_CONFIG(.event=0xc0))
> +		if (constraint_match(&fixed_counter0_constraint, event->hw.config))

Should be
	if (constraint_match(&fixed0_counter0_constraint, event->hw.config))
>   			return &fixed0_counter0_constraint;
>   
>   		return &counter0_constraint;
> 
> 
> And maybe we should do:
> 
> 	s/fixed_counter0_constraint/fixed0_constraint/'
>

Yes, definitely. It has already caused confusions. :)

Thanks,
Kan

> Those two constraints only differ by a single character, that's bad for
> reading comprehension.
> 
> In fact, I just did that too.
>