linux-kernel - Re: [PATCH V2 03/13] perf/x86: output sampling overhead

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Message-ID: <20161206112013.GJ3124@twins.programming.kicks-ass.net>
Date:   Tue, 6 Dec 2016 12:20:13 +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 03/13] perf/x86: output sampling overhead

On Fri, Dec 02, 2016 at 04:19:11PM -0500, kan.liang@...el.com wrote:
> From: Kan Liang <kan.liang@...el.com>
> 
> On x86, NMI handler is the most important part which brings overhead
> for sampling. Adding a pmu specific overhead type
> PERF_PMU_SAMPLE_OVERHEAD for it.
> 
> For other architectures which may don't have NMI, the overhead type can
> be reused.
> 
> Signed-off-by: Kan Liang <kan.liang@...el.com>
> ---
>  arch/x86/events/core.c          | 17 ++++++++++++++++-
>  arch/x86/events/perf_event.h    |  2 ++
>  include/uapi/linux/perf_event.h |  1 +
>  3 files changed, 19 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
> index 9d4bf3a..de40f96 100644
> --- a/arch/x86/events/core.c
> +++ b/arch/x86/events/core.c
> @@ -1397,6 +1397,9 @@ static void x86_pmu_del(struct perf_event *event, int flags)
>  
>  	perf_event_update_userpage(event);
>  
> +	if ((flags & PERF_EF_LOG) && cpuc->nmi_overhead.nr)
> +		perf_log_overhead(event, PERF_PMU_SAMPLE_OVERHEAD, &cpuc->nmi_overhead);
> +
>  do_del:
>  	if (x86_pmu.del) {
>  		/*

That's not at all mentioned in the changelog, and it clearly isn't
nmi_overhead.