linux-kernel - Re: [RESEND PATCH V3 2/8] perf/x86/intel: Basic support for metrics counters

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Date:   Wed, 28 Aug 2019 09:59:02 -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: [RESEND PATCH V3 2/8] perf/x86/intel: Basic support for metrics
 counters



On 8/28/2019 3:52 AM, Peter Zijlstra wrote:
> On Mon, Aug 26, 2019 at 07:47:34AM -0700, kan.liang@...ux.intel.com wrote:
> 
>> diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
>> index 81b005e4c7d9..54534ff00940 100644
>> --- a/arch/x86/events/core.c
>> +++ b/arch/x86/events/core.c
>> @@ -1033,18 +1033,30 @@ static inline void x86_assign_hw_event(struct perf_event *event,
>>   				struct cpu_hw_events *cpuc, int i)
>>   {
>>   	struct hw_perf_event *hwc = &event->hw;
>> +	int reg_idx;
>>   
>>   	hwc->idx = cpuc->assign[i];
>>   	hwc->last_cpu = smp_processor_id();
>>   	hwc->last_tag = ++cpuc->tags[i];
>>   
>> +	/*
>> +	 * Metrics counters use different indexes in the scheduler
>> +	 * versus the hardware.
>> +	 *
>> +	 * Map metrics to fixed counter 3 (which is the base count),
>> +	 * but the update event callback reads the extra metric register
>> +	 * and converts to the right metric.
>> +	 */
>> +	reg_idx = get_reg_idx(hwc->idx);
>> +
>>   	if (hwc->idx == INTEL_PMC_IDX_FIXED_BTS) {
>>   		hwc->config_base = 0;
>>   		hwc->event_base	= 0;
>>   	} else if (hwc->idx >= INTEL_PMC_IDX_FIXED) {
>>   		hwc->config_base = MSR_ARCH_PERFMON_FIXED_CTR_CTRL;
>> -		hwc->event_base = MSR_ARCH_PERFMON_FIXED_CTR0 + (hwc->idx - INTEL_PMC_IDX_FIXED);
>> -		hwc->event_base_rdpmc = (hwc->idx - INTEL_PMC_IDX_FIXED) | 1<<30;
>> +		hwc->event_base = MSR_ARCH_PERFMON_FIXED_CTR0 +
>> +				  (reg_idx - INTEL_PMC_IDX_FIXED);
>> +		hwc->event_base_rdpmc = (reg_idx - INTEL_PMC_IDX_FIXED) | 1<<30;
>>   	} else {
>>   		hwc->config_base = x86_pmu_config_addr(hwc->idx);
>>   		hwc->event_base  = x86_pmu_event_addr(hwc->idx);
> 
> That reg_idx is a pointless unconditional branch; better to write it
> like:
> 
> static inline void x86_assign_hw_event(struct perf_event *event,
> 				struct cpu_hw_events *cpuc, int i)
> {
> 	struct hw_perf_event *hwc = &event->hw;
> 	int idx;
> 
> 	idx = hwc->idx = cpuc->assign[i];
> 	hwc->last_cpu = smp_processor_id();
> 	hwc->last_tag = ++cpuc->tags[i];
> 
> 	switch (hwc->idx) {
> 	case INTEL_PMC_IDX_FIXED_BTS:
> 		hwc->config_base = 0;
> 		hwc->event_base	= 0;
> 		break;
> 
> 	case INTEL_PMC_IDX_FIXED_METRIC_BASE ... INTEL_PMC_IDX_FIXED_METRIC_BASE+3:
> 		/* All METRIC events are mapped onto the fixed SLOTS counter */
> 		idx = INTEL_PMC_IDX_FIXED_SLOTS;
> 
> 	case INTEL_PMC_IDX_FIXED ... INTEL_PMC_IDX_FIXED_METRIC_BASE-1:
> 		hwc->config_base = MSR_ARCH_PERFMON_FIXED_CTR_CTRL;
> 		hwc->event_base = MSR_ARCH_PERFMON_FIXED_CTR0 +
> 				  (idx - INTEL_PMC_IDX_FIXED);
> 		hwc->event_base_rdpmc = (idx - INTEL_PMC_IDX_FIXED) | 1<<30;
> 		break;
> 
> 	default:
> 		hwc->config_base = x86_pmu_config_addr(hwc->idx);
> 		hwc->event_base = x86_pmu_event_addr(hwc->idx);
> 		hwc->event_base_rdpmc = x86_pmu_rdpmc_index(hwc->idx);
> 		break;
> 	}
> }
> 
> On that; wth does this to the RDPMC userspace support!? Does that even
> work with these counters?
> 

The event_base_rdpmc is only for kernel usage now.
But it seems we can update x86_pmu_event_idx() to use it as well.

Thanks,
Kan