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

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Date:	Wed, 21 Jan 2015 19:48:04 +0000
From:	Pawel Moll <pawel.moll@....com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	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>,
	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 Wed, 2015-01-21 at 15:52 +0000, Pawel Moll wrote:
> On Mon, 2015-01-05 at 13:00 +0000, Peter Zijlstra wrote:
> > On Thu, Nov 06, 2014 at 04:51:56PM +0000, Pawel Moll wrote:
> > >  Documentation/kernel-parameters.txt |  9 +++++++++
> > >  kernel/events/core.c                | 37 +++++++++++++++++++++++++++++++++++++
> > >  2 files changed, 46 insertions(+)
> > 
> > > diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
> > > index 4c81a86..8ead8d8 100644
> > > --- a/Documentation/kernel-parameters.txt
> > > +++ b/Documentation/kernel-parameters.txt
> > 
> > > @@ -2763,6 +2764,14 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
> > >  			allocator.  This parameter is primarily	for debugging
> > >  			and performance comparison.
> > >  
> > > +	perf_use_local_clock
> > > +			[PERF]
> > > +			Use local_clock() as a source for perf timestamps
> > > +			generation. This was be the default behaviour and
> > > +			this parameter can be used to maintain backward
> > > +			compatibility or on older hardware with expensive
> > > +			monotonic clock source.
> > > +
> > >  	pf.		[PARIDE]
> > >  			See Documentation/blockdev/paride.txt.
> > 
> > So I'm always terminally confused on the naming of kernel parameters,
> > sometimes things are modules (even when they're not actually =m capable)
> > and get a module::foo naming or so and sometimes they're not.
> 
> I guess you mean module.foo?
> 
> > So we want to use the module naming thing or not?
> 
> Honestly, I don't mind either way. For one thing ftrace doesn't bother
> and just uses __setup() as well.

There's one more thing to this - as far as I remember, the module name
is actually derived from the compilation unit name (at some level of
Kbuild). I may be wrong (will have to double check), but a module
parameter defined in kernel/events/core.c may be called something like
"core.parameter" ;-).

Pawel

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