linux-kernel - Re: [patch] CFS scheduler, -v8

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Message-ID: <20070510130954.GC4052@ucw.cz>
Date:	Thu, 10 May 2007 13:09:55 +0000
From:	Pavel Machek <pavel@....cz>
To:	Peter Williams <pwil3058@...pond.net.au>
Cc:	Esben Nielsen <nielsen.esben@...glemail.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Con Kolivas <kernel@...ivas.org>,
	Nick Piggin <npiggin@...e.de>, Mike Galbraith <efault@....de>,
	Arjan van de Ven <arjan@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>, caglar@...dus.org.tr,
	Willy Tarreau <w@....eu>,
	Gene Heskett <gene.heskett@...il.com>, Mark Lord <lkml@....ca>,
	Zach Carter <linux@...hcarter.com>,
	buddabrod <buddabrod@...il.com>
Subject: Re: [patch] CFS scheduler, -v8

Hi!

> >>You say there is "no danger of overflow", and I mostly 
> >>agree that once
> >>we're talking about 64-bit values, the overflow issue 
> >>simply doesn't
> >>exist, and furthermore the difference between 63 and 
> >>64 bits is not really
> >>relevant, so there's no major reason to actively avoid 
> >>signed entries.
> >>
> >>So in that sense, it all sounds perfectly sane. And 
> >>I'm definitely not
> >>sure your "292 years after bootup" worry is really 
> >>worth even considering.
> >>
> >
> >I would hate to tell mission control for Mankind's 
> >first mission to another
> >star to reboot every 200 years because "there is no 
> >need to worry about it."
> >
> >As a matter of principle an OS should never need a 
> >reboot (with exception for upgrading). If you say you 
> >have to reboot every 200 years, why not every 100? 
> >Every 50? .... Every 45 days (you know what I am 
> >referring to :-) ?
> 
> There's always going to be an upper limit on the 
> representation of time. At least until we figure out 
>  how to implement infinity properly.

There's also upper limit on life time of this universe. 1000 bits is
certainly enough  to represent that in u-seconds.

Also notice that current cpus were not designed to work 300 years.
When we have hw designed for 50 years+, we can start to worry.

							Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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