linux-kernel - Re: [RFC 1/2] perf/core: Enable sched

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Date:   Thu, 5 Nov 2020 09:47:54 -0500
From:   "Liang, Kan" <kan.liang@...ux.intel.com>
To:     Namhyung Kim <namhyung@...nel.org>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>,
        Ingo Molnar <mingo@...nel.org>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Jiri Olsa <jolsa@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Stephane Eranian <eranian@...gle.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Ian Rogers <irogers@...gle.com>, Gabriel Marin <gmx@...gle.com>
Subject: Re: [RFC 1/2] perf/core: Enable sched_task callbacks if PMU has it



On 11/2/2020 9:52 AM, Namhyung Kim wrote:
> If an event associated with a PMU which has a sched_task callback,
> it should be called regardless of cpu/task context.  For example,


I don't think it's necessary. We should call it when we have to. 
Otherwise, it just waste cycles.
Shouldn't the patch 2 be enough?

Thanks,
Kan

> a per-cpu event might enable large PEBS buffers so it needs to flush
> the buffer whenever task scheduling happens. >
> The underlying PMU may or may not require this for the given event,
> but it will be handled in the pmu::sched_task() callback anyway.
> 
> Signed-off-by: Namhyung Kim <namhyung@...nel.org>
> ---
>   kernel/events/core.c | 4 ++++
>   1 file changed, 4 insertions(+)
> 
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index b458ed3dc81b..aaa0155c4142 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -4696,6 +4696,8 @@ static void unaccount_event(struct perf_event *event)
>   		dec = true;
>   	if (has_branch_stack(event))
>   		dec = true;
> +	if (event->pmu->sched_task)
> +		dec = true;
>   	if (event->attr.ksymbol)
>   		atomic_dec(&nr_ksymbol_events);
>   	if (event->attr.bpf_event)
> @@ -11225,6 +11227,8 @@ static void account_event(struct perf_event *event)
>   		inc = true;
>   	if (is_cgroup_event(event))
>   		inc = true;
> +	if (event->pmu->sched_task)
> +		inc = true;
>   	if (event->attr.ksymbol)
>   		atomic_inc(&nr_ksymbol_events);
>   	if (event->attr.bpf_event)
>