Prady, On Tue, 20 Jan 2009, Pradyumna Sampath wrote: > Hi Robert, Jurgen, > > On Tue, Jan 20, 2009 at 1:19 PM, Robert Schwebel > <r.schwebel@xxxxxxxxxxxxxx> wrote: > > > > Can you reproduce these long latencies with cyclictest, or does it only > > happen with your code? > > > > A few months ago, I had hit some really long latencies when ptpd (1588 > time synch) was trying to synchronize from 1970 to the current time. > After the time change we could observe some really long latencies. > Maybe, your device might also be > > Here is the post I made about it. > http://marc.info/?l=linux-rt-users&m=122111918015981&w=4 Fix for the kernel warning is below. The warning is a false positive caused by the huge time jump. You said that your application is showing weird behaviour after the time was set. Is your application using CLOCK_REALTIME ABSTIME timers ? We have had bug reports in the past where people run into problems with code like that: while (1) { clock_nanosleep(CLOCK_REALTIME, TIMER_ABSTIME, &next, NULL); ... next += interval; } If the clock is set into the future then the above loop will try to catch up for quite a while until next is past now. Using CLOCK_REALTIME/ABSTIME timers needs to be aware of the fact that CLOCK_REALTIME can be set and handle such a case gracefully. Thanks, tglx --- Subject: hrtimer: prevent negative expiry value after clock_was_set() From: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Date: Sun, 25 Jan 2009 11:31:36 +0100 Impact: prevent false positive WARN_ON() in clockevents_program_event() clock_was_set() changes the base->offset of CLOCK_REALTIME and enforces the reprogramming of the clockevent device to expire timers which are based on CLOCK_REALTIME. If the clock change is large enough then the subtraction of the timer expiry value and base->offset can become negative which triggers the warning in clockevents_program_event(). Check the subtraction result and set a negative value to 0. Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx> --- kernel/hrtimer.c | 7 +++++++ 1 file changed, 7 insertions(+) Index: linux-2.6-rt/kernel/hrtimer.c =================================================================== --- linux-2.6-rt.orig/kernel/hrtimer.c +++ linux-2.6-rt/kernel/hrtimer.c @@ -405,6 +405,13 @@ static void hrtimer_force_reprogram(stru continue; timer = rb_entry(base->first, struct hrtimer, node); expires = ktime_sub(timer->expires, base->offset); + /* + * clock_was_set has changed base->offset, so the + * result might be negative. Fix it up to prevent a + * false positive in clockevents_program_event() + */ + if (expires.tv64 < 0) + expires.tv64 = 0; if (expires.tv64 < cpu_base->expires_next.tv64) cpu_base->expires_next = expires; } -- To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
