linux-kernel - Re: [RFC] HZ free ntp

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Message-ID: <20061213095132.GA22280@elte.hu>
Date:	Wed, 13 Dec 2006 10:51:33 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	john stultz <johnstul@...ibm.com>
Cc:	Roman Zippel <zippel@...ux-m68k.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...l.org>, linux-kernel@...r.kernel.org
Subject: Re: [RFC] HZ free ntp


* john stultz <johnstul@...ibm.com> wrote:

> On Wed, 2006-12-06 at 15:33 +0100, Roman Zippel wrote:
> > On Wed, 6 Dec 2006, Ingo Molnar wrote:
> > > i disagree with you and it's pretty low-impact anyway. There's still
> > > quite many HZ/tick assumptions all around the time code (NTP being one
> > > example), we'll deal with those via other patches.
> > 
> > Why do you pick on the NTP code? That's actually one of the places where
> > assumptions about HZ are largely gone. NTP state is updated incrementally
> > and this won't change, but the update frequency can now be easily
> > disconnected from HZ.
> 
> Hey Roman,
> 	Here's my rough first attempt at doing so. I'd not call it easy, but
> maybe you have some suggestions for a simpler way?
> 
> Basically INTERVAL_LENGTH_NSEC defines the NTP interval length that 
> the time code will use to accumulate with. In this patch I've pushed 
> it out to a full second, but it could be set via config 
> (NSEC_PER_SEC/HZ for regular systems, something larger for systems 
> using dynticks).

cool! I'll give this one a go in -rt, combined with the exponential 
second-overflow patch. (that one is now algorithmically safe, right?)

	Ingo
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