Re: [RFC 1/2] perf/core: Enable sched_task callbacks if PMU has it

[Liang, Kan]

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@xxxxxxxxxx>
> ---
>   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)