linux-kernel - Re: [PATCH v4 1/3] perf: Use monotonic clock as a source for timestamps

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Message-ID: <1417100750.4371.1.camel@arm.com>
Date:	Thu, 27 Nov 2014 15:05:50 +0000
From:	Pawel Moll <pawel.moll@....com>
To:	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>
Cc:	Richard Cochran <richardcochran@...il.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Paul Mackerras <paulus@...ba.org>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	John Stultz <john.stultz@...aro.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>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-api@...r.kernel.org" <linux-api@...r.kernel.org>
Subject: Re: [PATCH v4 1/3] perf: Use monotonic clock as a source for
 timestamps

On Thu, 2014-11-06 at 16:51 +0000, Pawel Moll wrote:
> Until now, perf framework never defined the meaning of the timestamps
> captured as PERF_SAMPLE_TIME sample type. The values were obtaining
> from local (sched) clock, which is unavailable in userspace. This made
> it impossible to correlate perf data with any other events. Other
> tracing solutions have the source configurable (ftrace) or just share
> a common time domain between kernel and userspace (LTTng).
> 
> Follow the trend by using monotonic clock, which is readily available
> as POSIX CLOCK_MONOTONIC.
> 
> Also add a sysctl "perf_sample_time_clk_id" attribute which can be used
> by the user to obtain the clk_id to be used with POSIX clock API (eg.
> clock_gettime()) to obtain a time value comparable with perf samples.
> 
> Old behaviour can be restored by using "perf_use_local_clock" kernel
> parameter.
> 
> Signed-off-by: Pawel Moll <pawel.moll@....com>

It's been 3 weeks without any negative feedback (no feedback at all, but
I take the optimistic view :-)...

How about queuing at least this patch alone for the incoming merge
window? Or at least getting it into -next, with the view at 3.20?

Pawel

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