Messages in this thread | | | Date | Wed, 9 Jan 2008 19:25:00 -0500 (EST) | From | Steven Rostedt <> | Subject | Re: [RFC PATCH 13/22 -v2] handle accurate time keeping over long delays |
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On Wed, 9 Jan 2008, john stultz wrote: > > Index: linux-compile-i386.git/kernel/time/timekeeping.c > > =================================================================== > > --- linux-compile-i386.git.orig/kernel/time/timekeeping.c 2008-01-09 14:07:34.000000000 -0500 > > +++ linux-compile-i386.git/kernel/time/timekeeping.c 2008-01-09 15:17:31.000000000 -0500 > > @@ -448,27 +449,29 @@ static void clocksource_adjust(s64 offse > > */ > > void update_wall_time(void) > > { > > - cycle_t offset; > > + cycle_t cycle_now, offset; > > > > /* Make sure we're fully resumed: */ > > if (unlikely(timekeeping_suspended)) > > return; > > > > #ifdef CONFIG_GENERIC_TIME > > - offset = (clocksource_read(clock) - clock->cycle_last) & clock->mask; > > + cycle_now = clocksource_read(clock); > > #else > > - offset = clock->cycle_interval; > > + cycle_now = clock->cycle_last + clock->cycle_interval; > > #endif > > + offset = (cycle_now - clock->cycle_last) & clock->mask; > > It seems this offset addition was to merge against the colliding > xtime_cache changes in mainline. However, I don't think its quite right, > and might be causing incorrect time() or vtime() results if NO_HZ is > enabled.
Yeah, this had a bit of clashes in its life in the RT kernel.
> > > + clocksource_accumulate(clock, cycle_now); > > + > > clock->xtime_nsec += (s64)xtime.tv_nsec << clock->shift; > > > > /* normally this loop will run just once, however in the > > * case of lost or late ticks, it will accumulate correctly. > > */ > > - while (offset >= clock->cycle_interval) { > > + while (clock->cycle_accumulated >= clock->cycle_interval) { > > /* accumulate one interval */ > > clock->xtime_nsec += clock->xtime_interval; > > - clock->cycle_last += clock->cycle_interval; > > - offset -= clock->cycle_interval; > > + clock->cycle_accumulated -= clock->cycle_interval; > > > > if (clock->xtime_nsec >= (u64)NSEC_PER_SEC << clock->shift) { > > clock->xtime_nsec -= (u64)NSEC_PER_SEC << clock->shift; > > @@ -482,7 +485,7 @@ void update_wall_time(void) > > } > > > > /* correct the clock when NTP error is too big */ > > - clocksource_adjust(offset); > > + clocksource_adjust(clock->cycle_accumulated); > > > I suspect the following is needed, but haven't been able to test it yet.
Thanks, I'll pull it in and start testing it.
-- Steve
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