linux-kernel - Re: [patch 02/14] remove clocksource inline functions

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Date:	Thu, 13 Aug 2009 15:14:34 -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 02/14] remove clocksource inline functions

On Thu, 2009-08-13 at 17:40 +0200, Martin Schwidefsky wrote:
> plain text document attachment (clocksource-inline.diff)
> From: Martin Schwidefsky <schwidefsky@...ibm.com>
> 
> The three inline functions clocksource_read, clocksource_enable
> and clocksource_disable are simple wrappers of an indirect call
> plus the copy from and to the mult_orig value. The functions
> are exclusively used by the timekeeping code which has intimate
> knowledge of the clocksource anyway. Therefore remove the inline
> functions. No functional change.
> 
> Cc: Ingo Molnar <mingo@...e.hu>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Daniel Walker <dwalker@...o99.com>
> Acked-by: John Stultz <johnstul@...ibm.com>
> Signed-off-by: Martin Schwidefsky <schwidefsky@...ibm.com>
> ---
>  include/linux/clocksource.h |   58
> --------------------------------------------
>  kernel/time/timekeeping.c   |   42 +++++++++++++++++++++----------
>  2 files changed, 28 insertions(+), 72 deletions(-)
> 
> Index: linux-2.6/kernel/time/timekeeping.c
> ===================================================================
> --- linux-2.6.orig/kernel/time/timekeeping.c
> +++ linux-2.6/kernel/time/timekeeping.c
[snip]
> @@ -477,8 +492,7 @@ static int timekeeping_resume(struct sys
>  	}
>  	update_xtime_cache(0);
>  	/* re-base the last cycle value */
> -	clock->cycle_last = 0;
> -	clock->cycle_last = clocksource_read(clock);
> +	clock->cycle_last = clock->read(clock);

Minor bug here, the clearing of cycle_last has a side-effect of making
sure the TSC doesn't trip over its own cycle_last checking in the read()
function. This is part of the uglyness of the TSC pulling this internal
timeekping state to avoid minor inconsistencies, but until we find a
better way, we have to live with it.

So you'll need to preserve the cycle_last = 0 line.

thanks
-john




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