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

["Liang, Kan" <kan.liang@linux.intel.com>]

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@huaweicloud.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@linux.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)