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    SubjectRe: [RFC][patch 11/12] timekeeper read clock helper functions
    On Thu, 30 Jul 2009 14:39:54 -0700
    john stultz <johnstul@us.ibm.com> wrote:

    > On Wed, 2009-07-29 at 15:41 +0200, Martin Schwidefsky wrote:
    > > plain text document attachment (timekeeper-helper.diff)
    > > From: Martin Schwidefsky <schwidefsky@de.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@elte.hu>
    > > Cc: Thomas Gleixner <tglx@linutronix.de>
    > > Cc: john stultz <johnstul@us.ibm.com>
    > > Cc: Daniel Walker <dwalker@fifo99.com>
    > > Signed-off-by: Martin Schwidefsky <schwidefsky@de.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
    > > @@ -84,6 +84,40 @@ static void timekeeper_setup_internals(s
    > > timekeeper.shift = clock->shift;
    > > }
    > >
    > > +/* Timekeeper helper functions. */
    > > +static inline s64 timekeeper_read_clock_ntp(void)
    > > +{
    > > + cycle_t cycle_now, cycle_delta;
    > > + struct clocksource *clock;
    > > +
    > > + /* read clocksource: */
    > > + clock = timekeeper.clock;
    > > + cycle_now = clock->read(clock);
    > > +
    >
    > I know it seems nice to have it here, but I think these helpers would be
    > more reusable in other contexts if they took the cycle_now value as an
    > argument. Also I'd drop the ntp bit, just to avoid confusing it with
    > some ntp specific function. So:
    >
    > timekeeping_get_ns(cycle_t now);
    > timekeeping_get_ns_raw(cycle_t now);
    >
    > That way in some situations we don't have to make two accesses to the
    > hardware if we want to get both values at the same point.
    >
    > Seem reasonable?

    The new names are fine but if we pull out the ->read call to the
    caller we again have a rather strange mix. The caller gets the cycle
    value using some clock, the helper uses the value of the timekeeper
    clock or the timerkeeper mult/shift. I would like to keep the ->read
    call in the helper. Is there a situation where we need both
    calculations for the same cycles value? There is none in the current
    code as far as I can see.

    --
    blue skies,
    Martin.

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



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