linux-kernel - Re: [PATCH v4 3/3] perf: Sample additional clock value

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Date:	Mon, 5 Jan 2015 11:17:39 -0800
From:	John Stultz <john.stultz@...aro.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Pawel Moll <pawel.moll@....com>,
	Richard Cochran <richardcochran@...il.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ingo Molnar <mingo@...hat.com>,
	Paul Mackerras <paulus@...ba.org>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Christopher Covington <cov@...eaurora.org>,
	Namhyung Kim <namhyung@...nel.org>,
	David Ahern <dsahern@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Tomeu Vizoso <tomeu@...euvizoso.net>,
	lkml <linux-kernel@...r.kernel.org>,
	Linux API <linux-api@...r.kernel.org>
Subject: Re: [PATCH v4 3/3] perf: Sample additional clock value

On Mon, Jan 5, 2015 at 5:45 AM, Peter Zijlstra <peterz@...radead.org> wrote:
> On Thu, Nov 06, 2014 at 04:51:58PM +0000, Pawel Moll wrote:
>> Currently three clocks are implemented: CLOCK_REALITME = 0,
>> CLOCK_MONOTONIC = 1 and CLOCK_MONOTONIC_RAW = 2. The clock field is
>> 5 bits wide to allow for future extension to custom, non-POSIX clock
>> sources(MAX_CLOCK for those is 16, see include/uapi/linux/time.h) like
>> ARM CoreSight (hardware trace) timestamp generator.
>
>> @@ -304,7 +305,16 @@ struct perf_event_attr {
>>                               mmap2          :  1, /* include mmap with inode data     */
>>                               comm_exec      :  1, /* flag comm events that are due to an exec */
>>                               uevents        :  1, /* allow uevents into the buffer */
>> -                             __reserved_1   : 38;
>> +
>> +                             /*
>> +                              * clock: one of the POSIX clock IDs:
>> +                              *
>> +                              * 0 - CLOCK_REALTIME
>> +                              * 1 - CLOCK_MONOTONIC
>> +                              * 4 - CLOCK_MONOTONIC_RAW
>> +                              */
>> +                             clock          :  5, /* clock type */
>> +                             __reserved_1   : 33;
>>
>>       union {
>>               __u32           wakeup_events;    /* wakeup every n events */
>
> This would put a constraint on actually changing MAX_CLOCKS, are the
> time people OK with that? Thomas, John?

Yea, I'd not want to enshrine MAX_CLOCKS if we can avoid it. We're
getting a bit close to it these days.

thanks
-john
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