linux-kernel - Re: clock_gettime

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Date:	Mon, 9 Sep 2013 10:47:01 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	John Stultz <john.stultz@...aro.org>, Arun Sharma <asharma@...com>,
	LKML <linux-kernel@...r.kernel.org>,
	Kumar Sundararajan <kumar@...com>
Subject: Re: clock_gettime_ns

On Wed, Sep 4, 2013 at 6:22 PM, H. Peter Anvin <hpa@...or.com> wrote:
> I think it would be crazy encoding UTC with a non-POSIX scheme.

The whole point is to find a good way to return the time that solves
the problems with the POSIX scheme.  Some of the problems, as I see
them, are:

 - Performance: seconds + nanoseconds is expensive to compute and
expensive to use.
 - Leap seconds, part 1: Times like 23:59:60.1 are not representable.
 - Leap seconds, part 2: The limited leap-second support that already
exists (via the NTP APIs) is so obscure that it's frequently broken.
 - Offsets between clocks can't be read without using complicated
calls like adjtimex.

I think that coming up with something that's both non-POSIX and
half-arsed is a bad idea, but doing something that's non-POSIX and
well thought-through could be valuable.

--Andy
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