linux-kernel - Re: [PATCH 3/3] perf/x86: Add CAP_NO

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Date:   Tue, 21 Nov 2023 10:59:06 -0500
From:   "Liang, Kan" <kan.liang@...ux.intel.com>
To:     Namhyung Kim <namhyung@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>
Cc:     Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Ian Rogers <irogers@...gle.com>,
        Mingwei Zhang <mizhang@...gle.com>
Subject: Re: [PATCH 3/3] perf/x86: Add CAP_NO_INTERRUPT for uncore PMUs



On 2023-11-20 5:19 p.m., Namhyung Kim wrote:
> It doesn't support sampling in uncore PMU events.  While it's
> technically possible to generate interrupts, let's treat it as if it
> has no interrupt in order to skip the freq adjust/unthrottling logic
> in the timer handler which is only meaningful to sampling events.
> 
> Also remove the sampling event check because it'd be done in the general
> code in the perf_event_open syscall.
> 
> Signed-off-by: Namhyung Kim <namhyung@...nel.org>
> ---
>  arch/x86/events/intel/uncore.c | 11 ++++++-----
>  1 file changed, 6 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/x86/events/intel/uncore.c b/arch/x86/events/intel/uncore.c
> index 69043e02e8a7..f7e6228bd1b1 100644
> --- a/arch/x86/events/intel/uncore.c
> +++ b/arch/x86/events/intel/uncore.c
> @@ -744,10 +744,6 @@ static int uncore_pmu_event_init(struct perf_event *event)
>  	if (pmu->func_id < 0)
>  		return -ENOENT;
>  
> -	/* Sampling not supported yet */
> -	if (hwc->sample_period)
> -		return -EINVAL;
> -
>  	/*
>  	 * Place all uncore events for a particular physical package
>  	 * onto a single cpu
> @@ -919,7 +915,12 @@ static int uncore_pmu_register(struct intel_uncore_pmu *pmu)
>  			.stop		= uncore_pmu_event_stop,
>  			.read		= uncore_pmu_event_read,
>  			.module		= THIS_MODULE,
> -			.capabilities	= PERF_PMU_CAP_NO_EXCLUDE,
> +			/*
> +			 * It doesn't allow sampling for uncore events, let's
> +			 * treat the PMU has no interrupts to skip them in the
> +			 * perf_adjust_freq_unthr_context().
> +			 */
> +			.capabilities	= PERF_PMU_CAP_NO_EXCLUDE | PERF_PMU_CAP_NO_INTERRUPT,
>  			.attr_update	= pmu->type->attr_update,
>  		};


There is a special customized uncore PMU which needs the flag as well.

diff --git a/arch/x86/events/intel/uncore_snb.c
b/arch/x86/events/intel/uncore_snb.c
index 7fd4334e12a1..46a63e291975 100644
--- a/arch/x86/events/intel/uncore_snb.c
+++ b/arch/x86/events/intel/uncore_snb.c
@@ -1013,7 +1013,7 @@ static struct pmu snb_uncore_imc_pmu = {
        .start          = uncore_pmu_event_start,
        .stop           = uncore_pmu_event_stop,
        .read           = uncore_pmu_event_read,
-       .capabilities   = PERF_PMU_CAP_NO_EXCLUDE,
+       .capabilities   = PERF_PMU_CAP_NO_EXCLUDE |
PERF_PMU_CAP_NO_INTERRUPT,
 };

 static struct intel_uncore_ops snb_uncore_imc_ops = {


Thanks,
Kan
>  	} else {