linux-kernel - Re: [RFC PATCH] Add timer-source of walltime for ftrace

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Message-ID: <alpine.DEB.2.00.0908181454090.727@gandalf.stny.rr.com>
Date:	Tue, 18 Aug 2009 14:58:38 -0400 (EDT)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
cc:	Zhaolei <zhaolei@...fujitsu.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...e.hu>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH] Add timer-source of walltime for ftrace


On Wed, 19 Aug 2009, KOSAKI Motohiro wrote:

> > +u64 notrace trace_clock_walltime(void)
> > +{
> > +	u32 remainder;
> > +	return base_walltime.tv_sec + div_u64_rem(
> > +			trace_clock() + base_walltime.tv_nsec,
> > +			NSEC_PER_SEC, &remainder);
> > +}
> 
> Why do we need calculate walltime at ring-buffer recordng phase?
> IOW, Why can't we calculate this at displaing time?

Right! We should have something like this:

	return (u64)base_walltime.tv_sec * NSEC_PER_SEC +
		trace_clock() + base_walltime.tv_nsec;

And then we could divide it out later.

And then we could even show more fields in the output and not limit 
ourselves to seconds.

-- Steve

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