linux-kernel - Re: [PATCH 3/9] perf/x86/intel: Support overflows on SLOTS

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Date:   Tue, 28 May 2019 14:20:29 +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: [PATCH 3/9] perf/x86/intel: Support overflows on SLOTS

On Tue, May 21, 2019 at 02:40:49PM -0700, kan.liang@...ux.intel.com wrote:
> From: Andi Kleen <ak@...ux.intel.com>
> 
> The internal counters used for the metrics can overflow. If this happens
> an overflow is triggered on the SLOTS fixed counter. Add special code
> that resets all the slave metric counters in this case.

The SDM also talked about a OVF_PERF_METRICS overflow bit. Which seems
to suggest something else.

> Signed-off-by: Andi Kleen <ak@...ux.intel.com>
> Signed-off-by: Kan Liang <kan.liang@...ux.intel.com>
> ---
>  arch/x86/events/intel/core.c | 23 +++++++++++++++++++++++
>  1 file changed, 23 insertions(+)
> 
> diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c
> index 75ed91a36413..a66dc761f09d 100644
> --- a/arch/x86/events/intel/core.c
> +++ b/arch/x86/events/intel/core.c
> @@ -2279,12 +2279,35 @@ static void intel_pmu_add_event(struct perf_event *event)
>  		intel_pmu_lbr_add(event);
>  }
>  
> +/* When SLOTS overflowed update all the active topdown-* events */
> +static void intel_pmu_update_metrics(struct perf_event *event)
> +{
> +	struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
> +	int idx;
> +	u64 slots_events;
> +
> +	slots_events = *(u64 *)cpuc->enabled_events & INTEL_PMC_MSK_ANY_SLOTS;
> +
> +	for_each_set_bit(idx, (unsigned long *)&slots_events, 64) {

	for (idx = INTEL_PMC_IDX_TD_RETIRING;
	     idx <= INTEL_PMC_IDX_TD_BE_BOUND; idx++)

perhaps?

> +		struct perf_event *ev = cpuc->events[idx];
> +
> +		if (ev == event)
> +			continue;
> +		x86_perf_event_update(event);

		if (ev != event)
			x86_perf_event_update(event)
> +	}
> +}
> +
>  /*
>   * Save and restart an expired event. Called by NMI contexts,
>   * so it has to be careful about preempting normal event ops:
>   */
>  int intel_pmu_save_and_restart(struct perf_event *event)
>  {
> +	struct hw_perf_event *hwc = &event->hw;
> +
> +	if (unlikely(hwc->reg_idx == INTEL_PMC_IDX_FIXED_SLOTS))
> +		intel_pmu_update_metrics(event);
> +
>  	x86_perf_event_update(event);
>  	/*
>  	 * For a checkpointed counter always reset back to 0.  This
> -- 
> 2.14.5
>