linux-kernel - Re: [PATCH V2 04/13] perf/core: output multiplexing overhead

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Date:   Tue, 6 Dec 2016 12:23:30 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     kan.liang@...el.com
Cc:     mingo@...hat.com, acme@...nel.org, linux-kernel@...r.kernel.org,
        alexander.shishkin@...ux.intel.com, tglx@...utronix.de,
        namhyung@...nel.org, jolsa@...nel.org, adrian.hunter@...el.com,
        wangnan0@...wei.com, mark.rutland@....com, andi@...stfloor.org
Subject: Re: [PATCH V2 04/13] perf/core: output multiplexing overhead

On Fri, Dec 02, 2016 at 04:19:12PM -0500, kan.liang@...el.com wrote:
> From: Kan Liang <kan.liang@...el.com>
> 
> Multiplexing overhead is one of the key overhead when the number of
> events is more than available counters.
> 
> The multiplexing overhead PERF_CORE_MUX_OVERHEAD is a common overhead
> type.
> 

> diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
> index fe7b1fb..355086f 100644
> --- a/include/uapi/linux/perf_event.h
> +++ b/include/uapi/linux/perf_event.h
> @@ -999,6 +999,7 @@ struct perf_branch_entry {
>   */
>  enum perf_record_overhead_type {
>  	PERF_CORE_OVERHEAD	 = 0,
> +	PERF_CORE_MUX_OVERHEAD	 = 0,

'0' already had a name ?!

>  
>  	PERF_PMU_OVERHEAD	 = 20,
>  	PERF_PMU_SAMPLE_OVERHEAD = 20,

Same here I suppose, why are there two with the same name?

> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index 306bc92..025a19d 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -1830,6 +1830,9 @@ event_sched_out(struct perf_event *event,
>  	if (event->attr.exclusive || !cpuctx->active_oncpu)
>  		cpuctx->exclusive = 0;
>  
> +	if (log_overhead && cpuctx->mux_overhead.nr)
> +		perf_log_overhead(event, PERF_CORE_MUX_OVERHEAD, &cpuctx->mux_overhead);
> +

This isn't mentioned in the Changelog. Why is it here?

>  	perf_pmu_enable(event->pmu);
>  }
>