linux-kernel - RE: [RFC PATCH 13/22 -v2] handle accurate time keeping over longdelays

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Date:	Thu, 10 Jan 2008 13:33:09 -0800
From:	"Luck, Tony" <tony.luck@...el.com>
To:	"john stultz" <johnstul@...ibm.com>, <bob.picco@...com>
Cc:	"Steven Rostedt" <rostedt@...dmis.org>,
	"LKML" <linux-kernel@...r.kernel.org>,
	"Ingo Molnar" <mingo@...e.hu>,
	"Linus Torvalds" <torvalds@...ux-foundation.org>,
	"Andrew Morton" <akpm@...ux-foundation.org>,
	"Peter Zijlstra" <a.p.zijlstra@...llo.nl>,
	"Christoph Hellwig" <hch@...radead.org>,
	"Mathieu Desnoyers" <mathieu.desnoyers@...ymtl.ca>,
	"Gregory Haskins" <ghaskins@...ell.com>,
	"Arnaldo Carvalho de Melo" <acme@...stprotocols.net>,
	"Thomas Gleixner" <tglx@...utronix.de>,
	"Tim Bird" <tim.bird@...sony.com>,
	"Sam Ravnborg" <sam@...nborg.org>,
	"Frank Ch. Eigler" <fche@...hat.com>,
	"Steven Rostedt" <srostedt@...hat.com>
Subject: RE: [RFC PATCH 13/22 -v2] handle accurate time keeping over longdelays

> If you noticed in my email, the fix for ppc was a bit easier, as it has
> only a 64bit counter that is quite unlikely to wrap twice between calls
> to update_wall_time().

"quite unlikely" ...

Hmmm just how fast are you driving the clocks on your ppc?  Even at 100GHz
It is almost SIX YEARS between wrap-arounds of a 64-bit counter.
Perhaps you could just have a cron job that forces a call to update_wall_time()
every January 1st, rather than add extra code overhead to a hot path :-) ?

But I agree that narrower counters are a problem.

-Tony
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