lkml.org 
[lkml]   [2009]   [Jul]   [31]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [RFC][patch 10/12] move NTP adjusted clock multiplier to struct timekeeper
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 ?

--
blue skies,
Martin.

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



\
 
 \ /
  Last update: 2009-07-31 09:55    [from the cache]
©2003-2014 Jasper Spaans. Advertise on this site