Messages in this thread | | | Date | Fri, 31 Jul 2009 10:27:08 +0200 | From | Martin Schwidefsky <> | Subject | Re: [RFC][patch 10/12] move NTP adjusted clock multiplier to struct timekeeper |
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On Fri, 31 Jul 2009 01:12:59 -0700 john stultz <johnstul@us.ibm.com> wrote:
> On Fri, 2009-07-31 at 09:52 +0200, Martin Schwidefsky wrote: > > On Thu, 30 Jul 2009 15:04:48 -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-mult.diff) > > > > From: Martin Schwidefsky <schwidefsky@de.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@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> > > > > --- > > > > 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]. > > > > True the NTP code does not adjust the shift value. But mult and shift > > build a pair, no? I think it is more readable if we use timekeeper.mult > > and timekeeper.shift instead of timekeeper.mult and clock->shift. > > And the xtime_shift does not need to be the same value as the clock > > shift - at least in theory. It is just a shift to increase precision. > > Therefore I would like to use the xtime_shift and ntp_error_shift values > > exclusively as the shifts for the respective xtime_nsec and ntp_error > > values. Makes sense ? > > But can't we drop the xtime_shift if we have the clocksource shift kept > internally? Unless I'm missing something more subtle in your patches, > they should be the same at all times.
They are the same. Perhaps a good comment in the timekeeper struct is good enough. Then the patch that introduces the shift values would add timekeeper.shift, timekeeper.xtime_shift is dropped, and the patch that add the timekeeper.mult would just use the timekeeper.shift as it is.
-- blue skies, Martin.
"Reality continues to ruin my life." - Calvin.
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