linux-kernel - Re: [PATCH] time: Improve documentation of timekeeeping

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Message-ID: <20111028060534.GB1957@netboy.at.omicron.at>
Date:	Fri, 28 Oct 2011 08:05:35 +0200
From:	Richard Cochran <richardcochran@...il.com>
To:	John Stultz <john.stultz@...aro.org>
Cc:	LKML <linux-kernel@...r.kernel.org>, Chen Jie <chenj@...ote.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] time: Improve documentation of timekeeeping_adjust()

On Thu, Oct 27, 2011 at 06:12:42PM -0700, John Stultz wrote:
> diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
> index a5846a8..de8737e 100644
> --- a/kernel/time/timekeeping.c
> +++ b/kernel/time/timekeeping.c
> @@ -802,14 +802,44 @@ static void timekeeping_adjust(s64 offset)
>  	s64 error, interval = timekeeper.cycle_interval;
>  	int adj;
>  
> +	/*
> +	 * The point of this is to check if the error is greater then half
> +	 * an interval.
> +	 *
> +	 * First we shift it down from NTP_SHIFT to clocksource->shifted nsecs.
> +	 *
> +	 * Note we subtract one in the shift, so that error is really error*2.
> +	 * This "saves" dividing(shifting) intererval twice, but keeps the
> +	 * (error > interval) comparision as still measuring if error is
> +	 * larger then half an interval.
> +	 *
> +	 * Note: It does not "save" on aggrivation when reading the code.

... or on "aggravation" either :)

Thanks,
Richard
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