Re: [PATCH] perf/core: fix perf_event_mux_interval_ms when set zero

["Yajun Deng" <yajun.deng@linux.dev>]

June 15, 2022 6:08 AM, "Namhyung Kim" <namhyung@kernel.org> wrote:

> Hello,
> 
> On Tue, Jun 14, 2022 at 3:38 AM Yajun Deng <yajun.deng@linux.dev> wrote:
> 
>> The perf_event_mux_interval_ms is set to zero or one by default.
> 
> I see that __perf_mux_hrtimer_init() sets it to PERF_CPU_HRTIMER
> if it's less than 1.
> 
Yes, pmu->hrtimer_interval_ms was set to PERF_CPU_HRTIMER, but perf_event_mux_interval_ms didn't.
We can execute 'cat /sys/devices/intel_pt/perf_event_mux_interval_ms' see that.

> Thanks,
> Namhyung
> 
>> It can't change back when someone changes it from zero to another
>> value.
>> 
>> Make perf_event_mux_interval_ms to PERF_CPU_HRTIMER when set zero.
>> 
>> Fixes: 62b856397927 ("perf: Add sysfs entry to adjust multiplexing interval per PMU")
>> Signed-off-by: Yajun Deng <yajun.deng@linux.dev>
>> ---
>> kernel/events/core.c | 5 ++++-
>> 1 file changed, 4 insertions(+), 1 deletion(-)
>> 
>> diff --git a/kernel/events/core.c b/kernel/events/core.c
>> index 61ad10862c21..73c8c7462bbf 100644
>> --- a/kernel/events/core.c
>> +++ b/kernel/events/core.c
>> @@ -10954,9 +10954,12 @@ perf_event_mux_interval_ms_store(struct device *dev,
>> if (ret)
>> return ret;
>> 
>> - if (timer < 1)
>> + if (timer < 0)
>> return -EINVAL;
>> 
>> + if (timer < 1)
>> + timer = PERF_CPU_HRTIMER;
>> +
>> /* same value, noting to do */
>> if (timer == pmu->hrtimer_interval_ms)
>> return count;
>> --
>> 2.25.1