linux-kernel - Re: [PATCH] perf/core: fix perf_event_mux_interval

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Message-ID: <f1cdd17717cef7ec33af096e104db03c@linux.dev>
Date:   Wed, 15 Jun 2022 01:29:55 +0000
From:   "Yajun Deng" <yajun.deng@...ux.dev>
To:     "Namhyung Kim" <namhyung@...nel.org>
Cc:     "Peter Zijlstra" <peterz@...radead.org>,
        "Ingo Molnar" <mingo@...hat.com>,
        "Arnaldo Carvalho de Melo" <acme@...nel.org>,
        "Mark Rutland" <mark.rutland@....com>,
        "Alexander Shishkin" <alexander.shishkin@...ux.intel.com>,
        "Jiri Olsa" <jolsa@...nel.org>,
        "Stephane Eranian" <eranian@...gle.com>,
        "linux-perf-users" <linux-perf-users@...r.kernel.org>,
        "linux-kernel" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] perf/core: fix perf_event_mux_interval_ms when set
 zero

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

> Hello,
> 
> On Tue, Jun 14, 2022 at 3:38 AM Yajun Deng <yajun.deng@...ux.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@...ux.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