linux-kernel - Re: [PATCH] perf/x86: Fix open counting event error

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Message-ID: <7bafc0c9-0f72-44ba-a242-51918e32808a@linux.intel.com>
Date: Wed, 23 Apr 2025 09:51:11 -0400
From: "Liang, Kan" <kan.liang@...ux.intel.com>
To: Luo Gengkun <luogengkun@...weicloud.com>, peterz@...radead.org
Cc: mingo@...hat.com, acme@...nel.org, namhyung@...nel.org,
 mark.rutland@....com, alexander.shishkin@...ux.intel.com, jolsa@...nel.org,
 irogers@...gle.com, adrian.hunter@...el.com, tglx@...utronix.de,
 bp@...en8.de, dave.hansen@...ux.intel.com, x86@...nel.org, hpa@...or.com,
 ravi.bangoria@....com, linux-perf-users@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH] perf/x86: Fix open counting event error



On 2025-04-23 2:47 a.m., Luo Gengkun wrote:
> Perf doesn't work at perf stat for hardware events:
> 
>  $perf stat -- sleep 1
>  Performance counter stats for 'sleep 1':
>              16.44 msec task-clock                       #    0.016 CPUs utilized
>                  2      context-switches                 #  121.691 /sec
>                  0      cpu-migrations                   #    0.000 /sec
>                 54      page-faults                      #    3.286 K/sec
>    <not supported>	cycles
>    <not supported>	instructions
>    <not supported>	branches
>    <not supported>	branch-misses
> 
> The reason is that the check in x86_pmu_hw_config for sampling event is
> unexpectedly applied to the counting event.
> 
> Fixes: 88ec7eedbbd2 ("perf/x86: Fix low freqency setting issue")
> Signed-off-by: Luo Gengkun <luogengkun@...weicloud.com>

Yes, it should only be applied for the sampling event. The
event->attr.freq is always 0 in the counting mode.

Reviewed-by: Kan Liang <kan.liang@...ux.intel.com>

Thanks,
Kan> ---
>  arch/x86/events/core.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
> index 6866cc5acb0b..3a4f031d2f44 100644
> --- a/arch/x86/events/core.c
> +++ b/arch/x86/events/core.c
> @@ -629,7 +629,7 @@ int x86_pmu_hw_config(struct perf_event *event)
>  	if (event->attr.type == event->pmu->type)
>  		event->hw.config |= x86_pmu_get_event_config(event);
>  
> -	if (!event->attr.freq && x86_pmu.limit_period) {
> +	if (is_sampling_event(event) && !event->attr.freq && x86_pmu.limit_period) {
>  		s64 left = event->attr.sample_period;
>  		x86_pmu.limit_period(event, &left);
>  		if (left > event->attr.sample_period)