linux-kernel - Re: [PATCH 2/4] perf_event: add PERF_COUNT_HW_REF_CPU

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Date:	Mon, 12 Dec 2011 13:57:37 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Stephane Eranian <eranian@...gle.com>
Cc:	linux-kernel@...r.kernel.org, mingo@...e.hu, acme@...radead.org,
	robert.richter@....com, ming.m.lin@...el.com, andi@...stfloor.org,
	asharma@...com
Subject: Re: [PATCH 2/4] perf_event: add PERF_COUNT_HW_REF_CPU_CYCLES
 generic PMU event

On Sun, 2011-12-11 at 00:28 +0100, Stephane Eranian wrote:
> This event counts the number of reference core cpu cycles.
> Reference means that the event increments at a constant rate which
> is not subject to core CPU frequency adjustments. The event may
> not count when the processor is in halted (low power) state.
> As such, it may not be equivalent to wall clock time. However,
> when the processor is not halted state, the event keeps
> a constant correlation with wall clock time.
> 
> Signed-off-by: Stephane Eranian <eranian@...gle.com>
> ---
>  include/linux/perf_event.h |    1 +
>  1 files changed, 1 insertions(+), 0 deletions(-)
> 
> diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
> index 564769c..0885561 100644
> --- a/include/linux/perf_event.h
> +++ b/include/linux/perf_event.h
> @@ -54,6 +54,7 @@ enum perf_hw_id {
>  	PERF_COUNT_HW_BUS_CYCLES		= 6,
>  	PERF_COUNT_HW_STALLED_CYCLES_FRONTEND	= 7,
>  	PERF_COUNT_HW_STALLED_CYCLES_BACKEND	= 8,
> +	PERF_COUNT_HW_REF_CPU_CYCLES		= 9,
>  
>  	PERF_COUNT_HW_MAX,			/* non-ABI */
>  };

Does it make sense to add this to the 'generic' events? Are other archs
going to use this?

That is, I already queued patch 1, I'm just wondering if the generic bit
makes sense, Even BUS_CYCLES seems to be a questionable 'generic' event,
but that's history and we can't fix it.
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