linux-kernel - Re: [PATCH 1/2] perf tools: add event modifier to request exclusive PMU access

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Date:	Fri, 19 Oct 2012 17:58:52 +0200
From:	Stephane Eranian <eranian@...gle.com>
To:	Jiri Olsa <jolsa@...hat.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	LKML <linux-kernel@...r.kernel.org>,
	"mingo@...e.hu" <mingo@...e.hu>,
	"ak@...ux.intel.com" <ak@...ux.intel.com>,
	Arnaldo Carvalho de Melo <acme@...hat.com>
Subject: Re: [PATCH 1/2] perf tools: add event modifier to request exclusive
 PMU access

On Fri, Oct 19, 2012 at 5:53 PM, Jiri Olsa <jolsa@...hat.com> wrote:
> On Fri, Oct 19, 2012 at 05:47:11PM +0200, Stephane Eranian wrote:
>> On Fri, Oct 19, 2012 at 5:23 PM, Jiri Olsa <jolsa@...hat.com> wrote:
>> > On Fri, Oct 19, 2012 at 05:17:57PM +0200, Stephane Eranian wrote:
>> >> On Fri, Oct 19, 2012 at 5:13 PM, Peter Zijlstra <peterz@...radead.org> wrote:
>> >> > On Fri, 2012-10-19 at 16:52 +0200, Stephane Eranian wrote:
>> >> >> -modifier_event [ukhpGH]{1,8}
>> >> >> +modifier_event [ukhpGHx]{1,8}
>> >> >
>> >> > wouldn't the max modifier sting length grow by adding another possible
>> >> > modifier?
>> >>
>> >> That's what I thought too, but then I don't understand why it was at
>> >> eight before and not
>> >> seven: One instance of each letter, + a second for pp (precise=2). Or
>> >> am I missing
>> >> something here?
>> >
>> > hm, I think I assumed for some reason that 'ppp' is valid as well
>> >
>> If that's the case, then yes, I need to bump that number to 9.
>
> found my source ;)
>
> include/linux/perf_event.h:
> ...
>
>            /*
>             * precise_ip:
>             *
>             *  0 - SAMPLE_IP can have arbitrary skid
>             *  1 - SAMPLE_IP must have constant skid
>             *  2 - SAMPLE_IP requested to have 0 skid
>             *  3 - SAMPLE_IP must have 0 skid
>             *
>             *  See also PERF_RECORD_MISC_EXACT_IP
>             */
>            precise_ip     :  2, /* skid constraint       */
> ...
>
Ok, nobody supports 3 today, but that's fine. I can change that value to 9 then.
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