On Wed, 2009-03-11 at 17:30 -0700, john stultz wrote: > On Wed, 2009-03-11 at 17:03 +0100, Frans Pop wrote: > > OK, I think I've gotten a lot further now. > > > > On Wednesday 11 March 2009, john stultz wrote: > > > Also the negative conditional you add doesn't really make sense either, > > > as we expect the xtime.tv_nsec << clock->shift to be larger then > > > clock->xtime_nsec, as we've rounded it up by one. We then accumulate > > > the negative difference between them into clock->error. > > > > I'm not at all fluent in casts, bit shifting and stuff, so it took a > > while for the quarter to drop. But AFAICT what you're saying here is > > exactly the problem. > > > > Indeed you do round xtime.tv_nsec up, so when you do > > clock->xtime_nsec -= (s64)xtime.tv_nsec << clock->shift; > > or > > clock->xtime_nsec = clock->xtime_nsec - ((s64)xtime.tv_nsec << clock->shift); > > the second argument is always going to be bigger than the first, so you > > always end up with a negative value. > > > > > Hmm.. Does the following explicit casting help? > > > > Even with the cast you're just papering over the issue that we're moving a > > negative value into a field that is defined as unsigned: > > include/linux/clocksource.h: u64 xtime_nsec; > > Probably agreed here, xtime_nsec probably should be converted to a s64 > as negative values are possible. > > > However, Its unclear to me if my patch worked or not? > Did you try it alone? For a cleaner version, could you try the following, against 2.6.29-git with no other modification? thanks -john xtime_nsec is expected at times to be negative. Instead of trying to handle all the shifting properly via casts, define it as a s64 instead of a u64. NOT FOR INCLUSION Signed-off-by: John Stultz <johnstul@xxxxxxxxxx> diff --git a/include/linux/clocksource.h b/include/linux/clocksource.h index f88d32f..e217000 100644 --- a/include/linux/clocksource.h +++ b/include/linux/clocksource.h @@ -86,7 +86,7 @@ struct clocksource { * more than one cache line. */ cycle_t cycle_last ____cacheline_aligned_in_smp; - u64 xtime_nsec; + s64 xtime_nsec; s64 error; struct timespec raw_time; diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c index 900f1b6..387be3c 100644 --- a/kernel/time/timekeeping.c +++ b/kernel/time/timekeeping.c @@ -546,7 +546,7 @@ void update_wall_time(void) /* store full nanoseconds into xtime after rounding it up and * add the remainder to the error difference. */ - xtime.tv_nsec = ((s64)clock->xtime_nsec >> clock->shift) + 1; + xtime.tv_nsec = (clock->xtime_nsec >> clock->shift) + 1; clock->xtime_nsec -= (s64)xtime.tv_nsec << clock->shift; clock->error += clock->xtime_nsec << (NTP_SCALE_SHIFT - clock->shift); -- To unsubscribe from this list: send the line "unsubscribe linux-s390" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html