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 09:52:13 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     kan.liang@...ux.intel.com
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 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?