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

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Date:	Fri, 14 Aug 2009 13:12:54 +0200
From:	Martin Schwidefsky <schwidefsky@...ibm.com>
To:	john stultz <johnstul@...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, 13 Aug 2009 16:30:18 -0700
john stultz <johnstul@...ibm.com> wrote:

> On Thu, 2009-08-13 at 17:40 +0200, Martin Schwidefsky wrote:
> > 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()

I actually tested how the code would look like if I do that. Didn't like
the result. The thing is that timekeeping_get_ns is a helper that is
supposed to reduce the number of lines you need in the caller. If you
push clock->read(clock) call back into the caller it doesn't help much ..

-- 
blue skies,
   Martin.

"Reality continues to ruin my life." - Calvin.

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