[PATCH -rt] disconnect warp check from hrtimers

[PATCH -rt] disconnect warp check from hrtimers

[Daniel Walker]

These calls were getting inconsistent wrt. the xtime_lock. The xtime_lock should
be held when doing the warp check update, and interrupts should be off.

In some places the warp update was getting called twice, once under the xtime_lock
then again right outside the xtime_lock.

Signed-Off-By: Daniel Walker <dwalker@mvista.com>

---
 include/linux/hrtimer.h |    2 +-
 kernel/hrtimer.c        |    2 --
 kernel/time/ntp.c       |    2 ++
 kernel/timer.c          |    1 +
 4 files changed, 4 insertions(+), 3 deletions(-)

Index: linux-2.6.19/include/linux/hrtimer.h
===================================================================
--- linux-2.6.19.orig/include/linux/hrtimer.h
+++ linux-2.6.19/include/linux/hrtimer.h
@@ -262,7 +262,7 @@ static inline ktime_t hrtimer_cb_get_tim
  * is expired in the next softirq when the clock was advanced.
  * (we still call the warp-check debugging code)
  */
-static inline void clock_was_set(void) { warp_check_clock_was_changed(); }
+static inline void clock_was_set(void) { }
 static inline void hrtimer_clock_notify(void) { }
 
 /*
Index: linux-2.6.19/kernel/hrtimer.c
===================================================================
--- linux-2.6.19.orig/kernel/hrtimer.c
+++ linux-2.6.19/kernel/hrtimer.c
@@ -452,8 +452,6 @@ static void retrigger_next_event(void *a
  */
 void clock_was_set(void)
 {
-	warp_check_clock_was_changed();
-
 	/* Retrigger the CPU local events everywhere */
 	on_each_cpu(retrigger_next_event, NULL, 0, 1);
 }
Index: linux-2.6.19/kernel/time/ntp.c
===================================================================
--- linux-2.6.19.orig/kernel/time/ntp.c
+++ linux-2.6.19/kernel/time/ntp.c
@@ -116,6 +116,7 @@ void second_overflow(void)
 			 */
 			time_interpolator_update(-NSEC_PER_SEC);
 			time_state = TIME_OOP;
+			warp_check_clock_was_changed();
 			clock_was_set();
 			printk(KERN_NOTICE "Clock: inserting leap second "
 					"23:59:60 UTC\n");
@@ -131,6 +132,7 @@ void second_overflow(void)
 			 */
 			time_interpolator_update(NSEC_PER_SEC);
 			time_state = TIME_WAIT;
+			warp_check_clock_was_changed();
 			clock_was_set();
 			printk(KERN_NOTICE "Clock: deleting leap second "
 					"23:59:59 UTC\n");
Index: linux-2.6.19/kernel/timer.c
===================================================================
--- linux-2.6.19.orig/kernel/timer.c
+++ linux-2.6.19/kernel/timer.c
@@ -1162,6 +1162,7 @@ static int timekeeping_resume(struct sys
 	clock->cycle_last = clocksource_read(clock);
 	clock->error = 0;
 	timekeeping_suspended = 0;
+	warp_check_clock_was_changed();
 	write_sequnlock_irqrestore(&xtime_lock, flags);
 
 	hrtimer_notify_resume();
--

Re: [PATCH -rt] disconnect warp check from hrtimers

[Ingo Molnar]

* Daniel Walker <dwalker@mvista.com> wrote:

> These calls were getting inconsistent wrt. the xtime_lock. The 
> xtime_lock should be held when doing the warp check update, and 
> interrupts should be off.

thanks, applied. Does this solve some warnings that you saw trigger?

	Ingo

Re: [PATCH -rt] disconnect warp check from hrtimers

[Daniel Walker]

On Wed, 2006-12-27 at 18:39 +0100, Ingo Molnar wrote:
> * Daniel Walker <dwalker@mvista.com> wrote:
> 
> > These calls were getting inconsistent wrt. the xtime_lock. The 
> > xtime_lock should be held when doing the warp check update, and 
> > interrupts should be off.
> 
> thanks, applied. Does this solve some warnings that you saw trigger?

I saw some unexplained time warping while using the source at this url,

http://www.atnf.csiro.au/people/rgooch/benchmarks/linux-scheduler.html

it was on an older 2.6.18 based -rt .. The system would print the time
warp warning, then hang .. I applied something similar to the patch I
just sent, and the time warp warning was gone but the system still hung.

New -rt version don't hang, and I don't see the warning .. However, I
suspect the time warp warning was a side effect of the hang..

The system hang was resolved by changing the irq threads to all prio
50 ..

Daniel

Re: [PATCH -rt] disconnect warp check from hrtimers

[Daniel Walker]

On Wed, 2006-12-27 at 09:53 -0800, Daniel Walker wrote:

> The system hang was resolved by changing the irq threads to all prio
> 50 ..

Guess I was wrong about this.. The hang was resolved, but I's not sure
how yet ..

Daniel

Re: [PATCH -rt] disconnect warp check from hrtimers

[Daniel Walker]

On Wed, 2006-12-27 at 10:04 -0800, Daniel Walker wrote:
> On Wed, 2006-12-27 at 09:53 -0800, Daniel Walker wrote:
> 
> > The system hang was resolved by changing the irq threads to all prio
> > 50 ..
> 
> Guess I was wrong about this.. The hang was resolved, but I's not sure
> how yet ..

Looks like it was the irq thread priority _and_ the softirq prio needed
to be raised. softirq was at SCHED_FIFO 1 which caused the hang (or
that's how it looks).

Daniel