linux-kernel - Re: [patch 11/14] timekeeper read clock helper functions

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Date:	Thu, 13 Aug 2009 16:30:18 -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: [patch 11/14] timekeeper read clock helper functions

On Thu, 2009-08-13 at 17:40 +0200, Martin Schwidefsky wrote:
> plain text document attachment (timekeeper-helper.diff)
> From: Martin Schwidefsky <schwidefsky@...ibm.com>
> 
> Add timekeeper_read_clock_ntp and timekeeper_read_clock_raw and use
> them for getnstimeofday, ktime_get, ktime_get_ts and getrawmonotonic.
> 
> 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>
> ---
>  kernel/time/timekeeping.c |   91 +++++++++++++++++++---------------------------
>  1 file changed, 38 insertions(+), 53 deletions(-)
> 
> Index: linux-2.6/kernel/time/timekeeping.c
> ===================================================================
> --- linux-2.6.orig/kernel/time/timekeeping.c
> +++ linux-2.6/kernel/time/timekeeping.c
> @@ -95,6 +95,40 @@ static void timekeeper_setup_internals(s
>  	timekeeper.mult = clock->mult;
>  }
> 
> +/* Timekeeper helper functions. */
> +static inline s64 timekeeping_get_ns(void)
> +{
> +	cycle_t cycle_now, cycle_delta;
> +	struct clocksource *clock;
> +
> +	/* read clocksource: */
> +	clock = timekeeper.clock;
> +	cycle_now = clock->read(clock);
> +
> +	/* calculate the delta since the last update_wall_time: */
> +	cycle_delta = (cycle_now - clock->cycle_last) & clock->mask;
> +
> +	/* return delta convert to nanoseconds using ntp adjusted mult. */
> +	return clocksource_cyc2ns(cycle_delta, timekeeper.mult,
> +				  timekeeper.shift);
> +}

Again, not a huge issue, but if we kept the read() out of this function
and instead passed the cycle_now value in as a argument, we could also
use this function in  timekeeping_forward_now()


thanks
-john


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