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

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Message-Id: <1167766932.3141.10.camel@localhost>
Date:	Tue, 02 Jan 2007 11:42:12 -0800
From:	john stultz <johnstul@...ibm.com>
To:	Roman Zippel <zippel@...ux-m68k.org>
Cc:	Ingo Molnar <mingo@...e.hu>, Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...l.org>, linux-kernel@...r.kernel.org
Subject: Re: [RFC] HZ free ntp

On Mon, 2007-01-01 at 17:27 +0100, Roman Zippel wrote:
> On Wednesday 20 December 2006 02:32, john stultz wrote:
> 
> > > 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?
> 
> Yes, thanks.
> tick_nsec doesn't require special treatment, in the middle term it's obsolete
> anyway, it could be replaced with (current_tick_length() >>
> TICK_LENGTH_SHIFT) and current_tick_length() being inlined.

If NTP_INTERVAL_FREQ is different then HZ, then tick_nsec still has a
different meaning then (current_tick_length() >> TICK_LENGTH_SHIFT).
So since tick_nsec is still used in quite a few places, so I'm hesitant
to pull it.

> NTP_INTERVAL_FREQ could be a real variable (so it can be initialized at
> runtime), it's already gone from all important paths.

Wait, so you're suggesting NTP_INTERVAL_FREQ be a dynamic variable
instead of a constant? Curious, could you give a bit more detail on why?

> In the short term I'd prefered a clock would store its frequency instead of
> using NTP_INTERVAL_LENGTH in clocksource_calculate_interval(), so it doesn't
> has to be derived there.

I don't follow this at all. clocksources do store their own frequency
(via mult/shift). Could you explain?

thanks
-john

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