linux-kernel - Re: [PATCH v2 0/3] perf,x86: add Intel RAPL PMU support

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Date:	Thu, 17 Oct 2013 22:09:48 +0200
From:	Stephane Eranian <eranian@...gle.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Ingo Molnar <mingo@...nel.org>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Borislav Petkov <bp@...en8.de>,
	LKML <linux-kernel@...r.kernel.org>,
	"mingo@...e.hu" <mingo@...e.hu>,
	"ak@...ux.intel.com" <ak@...ux.intel.com>,
	Jiri Olsa <jolsa@...hat.com>,
	"Yan, Zheng" <zheng.z.yan@...el.com>
Subject: Re: [PATCH v2 0/3] perf,x86: add Intel RAPL PMU support

Peter,

On Thu, Oct 17, 2013 at 11:07 AM, Peter Zijlstra <peterz@...radead.org> wrote:
> On Thu, Oct 17, 2013 at 10:14:20AM +0200, Ingo Molnar wrote:
>> > > I.e. you would be encoding the counter unit as the suffix, might as well
>> > > call it "power/cores.joules" and use the dot as the separator for the
>> > > unit, but would be just a compact form to encode the counter->unit
>> > > table.
>> >
>> > May be easier to add a sysfs entry with the unit to display.
>>
>> Yes - with no entry meaning a raw 'count' or such.
>
> The downside to such a sysfs entry will be the scope. It would either be
> pmu wide (unwieldy for many PMUs) or be only per listed event; and we
> really don't want exhaustive event lists in the kernel.
>
Why not put in the events subdir:

/sys/devices/power/events/energy-cores
/sys/devices/power/events/energy-cores.unit
/sys/devices/power/events/energy-cores.scaling
$ cat energy-core.unit
Joules
$ cat energy-core.scaling
0.00000000023

Perf could easily lookup those files and if they are not present it will print
the event as it does today. If present, then it will print the unit and apply
the scaling factor to the raw cont (already scaled for multiplexing).

Borislav, the scaling factor cannot be hardcoded into perf because it
can change for processor to processor.
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