linux-kernel - Re: [patch 54/55] timekeeping: Provide fast and NMI safe access to CLOCK_MONOTONIC[

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Message-ID: <alpine.DEB.2.10.1407141615130.24854@nanos>
Date:	Mon, 14 Jul 2014 16:15:35 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
cc:	Peter Zijlstra <peterz@...radead.org>,
	LKML <linux-kernel@...r.kernel.org>,
	John Stultz <john.stultz@...aro.org>,
	Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [patch 54/55] timekeeping: Provide fast and NMI safe access to
 CLOCK_MONOTONIC[_RAW]

On Mon, 14 Jul 2014, Mathieu Desnoyers wrote:

> ----- Original Message -----
> > From: "Peter Zijlstra" <peterz@...radead.org>
> > To: "Thomas Gleixner" <tglx@...utronix.de>
> > Cc: "LKML" <linux-kernel@...r.kernel.org>, "John Stultz" <john.stultz@...aro.org>, "Steven Rostedt"
> > <rostedt@...dmis.org>, "Mathieu Desnoyers" <mathieu.desnoyers@...icios.com>
> > Sent: Monday, July 14, 2014 5:47:50 AM
> > Subject: Re: [patch 54/55] timekeeping: Provide fast and NMI safe access to CLOCK_MONOTONIC[_RAW]
> > 
> > On Fri, Jul 11, 2014 at 01:45:19PM -0000, Thomas Gleixner wrote:
> > > +static struct tk_fast tk_fast_raw  ____cacheline_aligned;
> > > +static struct tk_fast tk_fast_mono ____cacheline_aligned;
> > 
> > Question to the 'trace maniacs'; why do you lot need access to mono_raw?
> > 
> > I would much prefer to limit choice here.
> 
> For LTTng, which I guess qualifies as bring part of the aforementioned
> trace maniacs group, we only need the "tk_fast_mono" clock. We don't
> need mono_raw.
> 
> We can then correlate with user-space traces by using tk_fast_mono in
> kernel-space and using CLOCK_MONOTONIC in userspace.

I'm happy to ditch the raw one ...
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