Messages in this thread |  | | | Subject | Re: [RFC][patch 09/12] add xtime_shift and ntp_error_shift to struct timekeeper | | From | john stultz <> | | Date | Thu, 30 Jul 2009 15:15:23 -0700 |
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On Wed, 2009-07-29 at 15:41 +0200, Martin Schwidefsky wrote: > plain text document attachment (timekeeper-shift.diff) > From: Martin Schwidefsky <schwidefsky@de.ibm.com> > > The xtime_nsec value in the timekeeper structure is shifted by a few > bits to improve precision. This happens to be the same value as the > clock->shift. To improve readability add xtime_shift to the timekeeper > and use it instead of the clock->shift. Likewise add ntp_error_shift > and replace all (NTP_SCALE_SHIFT - clock->shift) expressions. > > 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 | 33 ++++++++++++++++++--------------- > 1 file changed, 18 insertions(+), 15 deletions(-) > > Index: linux-2.6/kernel/time/timekeeping.c > =================================================================== > --- linux-2.6.orig/kernel/time/timekeeping.c > +++ linux-2.6/kernel/time/timekeeping.c > @@ -27,6 +27,8 @@ struct timekeeper { > u32 raw_interval; > u64 xtime_nsec; > s64 ntp_error; > + int xtime_shift; > + int ntp_error_shift; > };
I suspect ntp_error_shift is one of the lease intuitive values in the timekeeper structure. They all probably need nice comments explaining what they store, but especially this one.
Something like:
struct clocksource *clock; /* current clocksource used for timekeeping*/ cycle_t cycle_interval; /* fixed chunk of cycles used in accumulation */ u64 xtime_interval; /* number clock shifted nsecs accumulated per cycle_interval */ u32 raw_interval; /* raw nsecs accumulated per cycle_interval */ u64 xtime_nsec; /* clock shifted nsecs remainder not stored in xtime.tv_nsec */ s64 ntp_error; /* Difference between accumulated time and NTP time in ntp shifted nsecs */ int xtime_shift; /* The shift value of the current clocksource */ int ntp_error_shift; /* Shift conversion between clock shifted nsecs and ntp shifted nsecs */
Other then that this patch looks ok, but will need rigorous testing, as its very complicated and difficult to understand code thats being changed.
thanks -john
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