netdev - Re: [PATCH net-next 1/4] bpf: add helper bpf_perf_read_counter

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Date:   Fri, 1 Sep 2017 22:41:09 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Yonghong Song <yhs@...com>
Cc:     rostedt@...dmis.org, ast@...com, daniel@...earbox.net,
        netdev@...r.kernel.org, kernel-team@...com
Subject: Re: [PATCH net-next 1/4] bpf: add helper bpf_perf_read_counter_time
 for perf event array map

On Fri, Sep 01, 2017 at 09:53:54AM -0700, Yonghong Song wrote:
> diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
> index b14095b..7fd5e94 100644
> --- a/include/linux/perf_event.h
> +++ b/include/linux/perf_event.h
> @@ -901,6 +901,8 @@ extern void perf_pmu_migrate_context(struct pmu *pmu,
>  int perf_event_read_local(struct perf_event *event, u64 *value);
>  extern u64 perf_event_read_value(struct perf_event *event,
>  				 u64 *enabled, u64 *running);
> +extern void calc_timer_values(struct perf_event *event, u64 *now,
> +         u64 *enabled, u64 *running);
>  
>  

> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index 8c01572..ef5c7fb 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -4883,7 +4883,7 @@ static int perf_event_index(struct perf_event *event)
>  	return event->pmu->event_idx(event);
>  }
>  
> -static void calc_timer_values(struct perf_event *event,
> +void calc_timer_values(struct perf_event *event,
>  				u64 *now,
>  				u64 *enabled,
>  				u64 *running)

Yeah, not going to happen...

Why not do the obvious thing and extend perf_event_read_local() to
optionally return the enabled/running times?