linux-kernel - Re: [RFC][patch 10/12] move NTP adjusted clock multiplier to struct timekeeper

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Date:	Thu, 30 Jul 2009 15:04:48 -0700
From:	john stultz <johnstul@...ibm.com>
To:	Martin Schwidefsky <schwidefsky@...ibm.com>
Cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Daniel Walker <dwalker@...o99.com>
Subject: Re: [RFC][patch 10/12] move NTP adjusted clock multiplier to
 struct timekeeper

On Wed, 2009-07-29 at 15:41 +0200, Martin Schwidefsky wrote:
> plain text document attachment (timekeeper-mult.diff)
> From: Martin Schwidefsky <schwidefsky@...ibm.com>
> 
> The clocksource structure has two multipliers, the unmodified multiplier
> clock->mult_orig and the NTP corrected multiplier clock->mult. The NTP
> multiplier is misplaced in the struct clocksource, this is private
> information of the timekeeping code. Add the mult field to the struct
> timekeeper to contain the NTP corrected value, keep the unmodifed
> multiplier in clock->mult and remove clock->mult_orig. For consistency
> add the shift value associated with the NTP corrected mult value to
> struct timekeeper as well.
> 
> Cc: Ingo Molnar <mingo@...e.hu>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: john stultz <johnstul@...ibm.com>
> Cc: Daniel Walker <dwalker@...o99.com>
> Signed-off-by: Martin Schwidefsky <schwidefsky@...ibm.com>
> ---
>  arch/arm/plat-omap/common.c |    2 +-
>  include/linux/clocksource.h |    4 +---
>  kernel/time/timekeeping.c   |   43 +++++++++++++++++++++++++------------------
>  3 files changed, 27 insertions(+), 22 deletions(-)
> 
> Index: linux-2.6/include/linux/clocksource.h
> ===================================================================
> --- linux-2.6.orig/include/linux/clocksource.h
> +++ linux-2.6/include/linux/clocksource.h
> @@ -149,8 +149,7 @@ extern u64 timecounter_cyc2time(struct t
>   * @disable:		optional function to disable the clocksource
>   * @mask:		bitmask for two's complement
>   *			subtraction of non 64 bit counters
> - * @mult:		cycle to nanosecond multiplier (adjusted by NTP)
> - * @mult_orig:		cycle to nanosecond multiplier (unadjusted by NTP)
> + * @mult:		cycle to nanosecond multiplier
>   * @shift:		cycle to nanosecond divisor (power of two)
>   * @flags:		flags describing special properties
>   * @vread:		vsyscall based read
> @@ -168,7 +167,6 @@ struct clocksource {
>  	void (*disable)(struct clocksource *cs);
>  	cycle_t mask;
>  	u32 mult;
> -	u32 mult_orig;
>  	u32 shift;
>  	unsigned long flags;
>  	cycle_t (*vread)(void);
> Index: linux-2.6/kernel/time/timekeeping.c
> ===================================================================
> --- linux-2.6.orig/kernel/time/timekeeping.c
> +++ linux-2.6/kernel/time/timekeeping.c
> @@ -29,6 +29,8 @@ struct timekeeper {
>  	s64	ntp_error;
>  	int	xtime_shift;
>  	int	ntp_error_shift;
> +	u32	mult;			/* NTP adjusted clock multiplier */
> +	u32	shift;			/* NTP adjusted clock shift */

I'm a little confused here. NTP doesn't adjust the shift value. This
seems redundant with the xtime_shift value introduced in [patch 9/12].

thanks
-john


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