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

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Message-ID: <1154261133.13906.1405341566164.JavaMail.zimbra@efficios.com>
Date:	Mon, 14 Jul 2014 12:39:26 +0000 (UTC)
From:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	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]

----- 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.

Thanks,

Mathieu

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com
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