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

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Date:   Tue, 14 Jun 2022 15:08:15 -0700
From:   Namhyung Kim <namhyung@...nel.org>
To:     Yajun Deng <yajun.deng@...ux.dev>
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

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.

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
>