linux-kernel - Re: [PATCH] correct inconsistent ntp interval/tick

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Message-ID: <Pine.LNX.4.64.0801290439480.17507@scrub.home>
Date:	Tue, 29 Jan 2008 05:02:21 +0100 (CET)
From:	Roman Zippel <zippel@...ux-m68k.org>
To:	john stultz <johnstul@...ibm.com>
cc:	lkml <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCH] correct inconsistent ntp interval/tick_length usage

Hi,

On Mon, 28 Jan 2008, john stultz wrote:

> Regardless, current_tick_length() really is the base interval we're
> using in the error accumulation loop, so it seems the cleanest interface
> to use (just to avoid redundancy at least) when establishing the
> clocksource's interval length. Or do you not agree?

I see, what you need to use in timex.h for !CONFIG_NO_HZ is:

#define NTP_INTERVAL_LENGTH ((s64)LATCH * NSEC_PER_SEC) / (s64)CLOCK_TICK_RATE)

this calculates the base length of a clock tick in nsec.

current_tick_length() would only work during boot. If you switch clocks 
later, it would include random adjustments specific to the old clock.

bye, Roman
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