linux-kernel - Re: RTC subsystem and fractions of seconds

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Message-ID: <Pine.LNX.4.64.0701070108001.1428@blonde.wat.veritas.com>
Date:	Sun, 7 Jan 2007 01:11:43 +0000 (GMT)
From:	Hugh Dickins <hugh@...itas.com>
To:	David Brownell <david-b@...bell.net>
cc:	Matt Mackall <mpm@...enic.com>,
	Philippe De Muyter <phdm@...qel.be>,
	Linux Kernel list <linux-kernel@...r.kernel.org>
Subject: Re: RTC subsystem and fractions of seconds

On Sat, 6 Jan 2007, David Brownell wrote:
> On Saturday 06 January 2007 3:26 pm, Philippe De Muyter wrote:
> 
> > The way it is done currently 
> > in drivers/rtc/hctosys.c is 0.5 sec off.  We could obtain a much better
> > precision by looping there until the next change (next second for old clocks,
> > next 0.01 second for m41t81, maybe even better for other ones).
> 
> Hmm ... "looping" fights against "quickly"; as would "wait for next
> update IRQ" (on RTCs that support that).  But it would improve precision,
> at least in the sense of having the system clock and that RTC spending
> less time with the lowest "seconds" digit disagreeing.
> 
> This is something you could write a patch for, n'est-ce pas?

If you're thinking of going that way, it'd be courteous to CC Matt,
who devoted some effort to removing just that loop in 2.6.17 ;)

Hugh
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