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

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Message-ID: <aApkwfEUCJcc9PXn@gmail.com>
Date: Thu, 24 Apr 2025 18:20:17 +0200
From: Ingo Molnar <mingo@...nel.org>
To: Luo Gengkun <luogengkun@...weicloud.com>
Cc: peterz@...radead.org, 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,
	kan.liang@...ux.intel.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


* Luo Gengkun <luogengkun@...weicloud.com> 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>
> ---
>  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) {

Hm, so how come it works here, on an affected x86 system:

$ perf stat -- sleep 1

 Performance counter stats for 'sleep 1':

              0.64 msec task-clock:u                     #    0.001 CPUs utilized             
                 0      context-switches:u               #    0.000 /sec                      
                 0      cpu-migrations:u                 #    0.000 /sec                      
                73      page-faults:u                    #  114.063 K/sec                     
           325,849      instructions:u                   #    0.56  insn per cycle            
                                                  #    0.88  stalled cycles per insn   
           580,323      cycles:u                         #    0.907 GHz                       
           286,348      stalled-cycles-frontend:u        #   49.34% frontend cycles idle      
            72,623      branches:u                       #  113.474 M/sec                     
             4,713      branch-misses:u                  #    6.49% of all branches           


?

Thanks,

	Ingo