linux-kernel - Re: [PATCH 20/41] perf tools: Let a user specify a PMU event without any config terms

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Message-ID: <5400CB13.4040004@intel.com>
Date:	Fri, 29 Aug 2014 21:48:51 +0300
From:	Adrian Hunter <adrian.hunter@...el.com>
To:	Jiri Olsa <jolsa@...hat.com>
CC:	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	linux-kernel@...r.kernel.org, David Ahern <dsahern@...il.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Namhyung Kim <namhyung@...il.com>,
	Paul Mackerras <paulus@...ba.org>,
	Stephane Eranian <eranian@...gle.com>
Subject: Re: [PATCH 20/41] perf tools: Let a user specify a PMU event without
 any config terms

On 16/07/2014 9:22 p.m., Jiri Olsa wrote:
> On Wed, Jul 16, 2014 at 06:04:44PM +0300, Adrian Hunter wrote:
>> On 16/07/2014 5:25 p.m., Jiri Olsa wrote:
>>> On Mon, Jul 14, 2014 at 01:02:44PM +0300, Adrian Hunter wrote:
>>>> This enables a PMU event to be specified in the form:
>>>>
>>>> 	pmu//
>>>>
>>>> which is effectively the same as:
>>>>
>>>> 	pmu/config=0/
>>>>
>>>> This patch is a precursor to defining
>>>> default config for a PMU.
>>>
>>> I understand the need for default config, but could you please elaborate
>>> why do we want to parse 'pmu//' as an event string string?
>>
>> Currently the parser requires the slashes to identify a PMU event
>> as opposed to a hardware or other kind of event.
>
> right, so why do we want to parse 'pmu//' as an event string? ;-)

I am not sure what you mean.  Here I am using 'pmu' as a placeholder
for a real PMU name.  So actual event strings are 'intel_bts//' or
'intel_pt//' or 'intel_pt/tsc=0,noretcomp=1/'

The parser uses various tricks to decide what kind of event the event
name actually is e.g. colons indicate a tracepoint.

If you are asking why the parser isn't smart enough to know the event
name is a PMU name, I guess it is either to keep the namespaces separate,
or because it was easier to program it that way.
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