linux-kernel - Re: [RFC 0/2] ABI for clock_gettime

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Date:	Mon, 12 Dec 2011 19:43:02 -0800
From:	john stultz <johnstul@...ibm.com>
To:	Richard Cochran <richardcochran@...il.com>
Cc:	Andy Lutomirski <luto@...capital.net>,
	linux-kernel@...r.kernel.org, Kumar Sundararajan <kumar@...com>,
	Arun Sharma <asharma@...com>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [RFC 0/2] ABI for clock_gettime_ns

On Tue, 2011-12-13 at 04:24 +0100, Richard Cochran wrote:
> On Mon, Dec 12, 2011 at 05:26:36PM -0800, Andy Lutomirski wrote:
> > On x86-64, clock_gettime is so fast that the overhead converting to and
> > from nanoseconds is non-negligible.  clock_gettime_ns is a different
> > interface that is potentially faster.  If people like the ABI, I'll
> > implement an optimized version.
> 
> I am not so interested in performance optimizations, but do I think
> offering time in nanoseconds is attractive from an application point
> of view. The timespec is impractical for everyone.
> 
> While you are at it with new syscalls, why not make a clean break from
> POSIX and fix the uglies?
> 
> - New name, to distance ourselves from POSIX (clock_ns_get?)
> - Family of calls, with set/get
> - Sub nanosecond field
> - TAI time base (or according to parameter?)

Having a CLOCK_TAI would be interesting across the board. We already
keep a TAI offset in the ntp code. However, I'm not sure if ntp actually
sets it these days.

thanks
-john

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