Patch below fixes the problem we were seeing (negative delta calculated in tick_do_update_jiffies64).
Thanks again Thomas! On Wed, Sep 12, 2007 at 12:36:34AM +0200, Thomas Gleixner wrote: > Timekeeping resume adjusts xtime by adding the slept time in seconds and > resets the reference value of the clock source (clock->cycle_last). > clock->cycle last is used to calculate the delta between the last xtime > update and the readout of the clock source in __get_nsec_offset(). xtime > plus the offset is the current time. The resume code ignores the delta > which had already elapsed between the last xtime update and the actual > time of suspend. If the suspend time is short, then we can see time > going backwards on resume. > > Suspend: > offs_s = clock->read() - clock->cycle_last; > now = xtime + offs_s; > timekeeping_suspend_time = read_rtc(); > > Resume: > sleep_time = read_rtc() - timekeeping_suspend_time; > xtime.tv_sec += sleep_time; > clock->cycle_last = clock->read(); > offs_r = clock->read() - clock->cycle_last; > now = xtime + offs_r; > > if sleep_time_seconds == 0 and offs_r < offs_s, then time goes > backwards. > > Fix this by storing the offset from the last xtime update and add it to > xtime during resume, when we reset clock->cycle_last: > > sleep_time = read_rtc() - timekeeping_suspend_time; > xtime.tv_sec += sleep_time; > xtime += offs_s; /* Fixup xtime offset at suspend time */ > clock->cycle_last = clock->read(); > offs_r = clock->read() - clock->cycle_last; > now = xtime + offs_r; > > Thanks to Marcelo for tracking this down on the OLPC and providing the > necessary details to analyze the root cause. > > Signed-off-by: Thomas Gleixner <[EMAIL PROTECTED]> > > --- a/kernel/time/timekeeping.c > +++ b/kernel/time/timekeeping.c > @@ -280,6 +280,8 @@ void __init timekeeping_init(void) > static int timekeeping_suspended; > /* time in seconds when suspend began */ > static unsigned long timekeeping_suspend_time; > +/* xtime offset when we went into suspend */ > +static s64 timekeeping_suspend_offset; > > /** > * timekeeping_resume - Resumes the generic timekeeping subsystem. > @@ -305,6 +307,8 @@ static int timekeeping_resume(struct sys_device *dev) > wall_to_monotonic.tv_sec -= sleep_length; > total_sleep_time += sleep_length; > } > + /* Make sure that we have the correct xtime reference */ > + timespec_add_ns(&xtime, timekeeping_suspend_offset); > /* re-base the last cycle value */ > clock->cycle_last = clocksource_read(clock); > clock->error = 0; > @@ -326,6 +330,8 @@ static int timekeeping_suspend(struct sys_device *dev, > pm_message_t state) > unsigned long flags; > > write_seqlock_irqsave(&xtime_lock, flags); > timekeeping_suspended = 1; > + /* Get the current xtime offset */ > + timekeeping_suspend_offset = __get_nsec_offset(); > timekeeping_suspend_time = read_persistent_clock(); > write_sequnlock_irqrestore(&xtime_lock, flags); > - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
