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

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Message-Id: <20061220202621.8e147b1d.akpm@osdl.org>
Date:	Wed, 20 Dec 2006 20:26:21 -0800
From:	Andrew Morton <akpm@...l.org>
To:	john stultz <johnstul@...ibm.com>
Cc:	Roman Zippel <zippel@...ux-m68k.org>, Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC] HZ free ntp

On Tue, 19 Dec 2006 17:54:18 -0800
john stultz <johnstul@...ibm.com> wrote:

> On Tue, 2006-12-19 at 17:32 -0800, john stultz wrote:
> > On Wed, 2006-12-13 at 21:40 +0100, Roman Zippel wrote:
> > > On Wed, 13 Dec 2006, john stultz wrote:
> > > > > You don't have to introduce anything new, it's tick_length that changes
> > > > > and HZ that becomes a variable in this function.
> > > >
> > > > So, forgive me for rehashing this, but it seems we're cross talking
> > > > again. The context here is the dynticks code. Where HZ doesn't change,
> > > > but we get interrupts at much reduced rates.
> > > 
> > > I know and all you have to change in the ntp and some related code is to
> > > replace HZ there with a variable, thus make it changable, so you can
> > > increase the update interval (i.e. it becomes 1s/hz instead of 1s/HZ).
> > 
> > Untested patch below. Does this vibe better with you are suggesting?
> 
> And here would be the follow on patch (again *untested*) for
> CONFIG_NO_HZ slowing the time accumulation down to once per second.

I'm still awaiting a final-looking version of this patch, fyi.

I don't understand whether this is a theoretical might-happen thing,
or if NTP problems have actually been observed in the field?

Either way, I'm sure the final changelog will clear that up ;)
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