Re: TSC marked unstable on suspend and resume

[john stultz <johnstul@us.ibm.com>]

On Wed, 2009-04-29 at 18:25 -0500, David Fries wrote:
> On Wed, Apr 29, 2009 at 09:45:40AM -0700, john stultz wrote:
> > On Fri, Feb 20, 2009 at 7:39 PM, David Fries <david@fries.net> wrote:
> > > I'm getting TSC marked as unsable on hibernate to disk with
> > > 2.6.29-rc3. ?The last kernel I ran 2.6.24.4 ran 300+ days without a
> > > problem and does not loose TSC on hibernate.
> > >
> > > I'm hibernating with `echo disk > /sys/power/state`.
> > > These look like the relavant messages,
> > >
> > > CPU 0 irqstacks, hard=c0379000 soft=c0378000
> > > PID hash table entries: 1024 (order: 10, 4096 bytes)
> > > Fast TSC calibration using PIT
> > > Detected 300.705 MHz processor.
> > > Calibrating delay loop (skipped), value calculated using timer frequency.. 601.41 BogoMIPS (lpj=300705)
> > > hibernate to disk,
> > > Restarting tasks ... done.
> > > Clocksource tsc unstable (delta = 499883531 ns)
> > 
> > Hmm. Seems like the clocksource watchdog is having some problem
> > handling state around hibernate.

Yea. This seems to be the case here. There's watchdog code and variables
to handle resume properly, but there isn't a corresponding suspend hook,
so the resume path doesn't actually change anything.

Here's a patch you can try, I only had time to compile test it today, so
its untested. Hopefully I didn't miss anything obvious.

Thomas, I suspect you intended to have something like the following?

Signed-off-by: John Stultz <johnstul@us.ibm.com>

diff --git a/include/linux/clocksource.h b/include/linux/clocksource.h
index 5a40d14..450431f 100644
--- a/include/linux/clocksource.h
+++ b/include/linux/clocksource.h
@@ -360,6 +360,7 @@ extern void clocksource_touch_watchdog(void);
 extern struct clocksource* clocksource_get_next(void);
 extern void clocksource_change_rating(struct clocksource *cs, int rating);
 extern void clocksource_resume(void);
+extern void clocksource_suspend(void);
 
 #ifdef CONFIG_GENERIC_TIME_VSYSCALL
 extern void update_vsyscall(struct timespec *ts, struct clocksource *c);
diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c
index ecfd7b5..3dbe55f 100644
--- a/kernel/time/clocksource.c
+++ b/kernel/time/clocksource.c
@@ -236,6 +236,11 @@ static void clocksource_resume_watchdog(void)
 	set_bit(0, &watchdog_resumed);
 }
 
+static void clocksource_suspend_watchdog(void)
+{
+	set_bit(1, &watchdog_resumed);
+}
+
 static void clocksource_check_watchdog(struct clocksource *cs)
 {
 	struct clocksource *cse;
@@ -278,6 +283,7 @@ static void clocksource_check_watchdog(struct clocksource *cs)
 	}
 	spin_unlock_irqrestore(&watchdog_lock, flags);
 }
+
 #else
 static void clocksource_check_watchdog(struct clocksource *cs)
 {
@@ -286,6 +292,7 @@ static void clocksource_check_watchdog(struct clocksource *cs)
 }
 
 static inline void clocksource_resume_watchdog(void) { }
+static inline void clocksource_suspend_watchdog(void) { }
 #endif
 
 /**
@@ -321,6 +328,18 @@ void clocksource_touch_watchdog(void)
 }
 
 /**
+ * clocksource_suspend - suspend the clocksource(s)
+ */
+void clocksource_suspend(void)
+{
+	unsigned long flags;
+
+	spin_lock_irqsave(&clocksource_lock, flags);
+	clocksource_suspend_watchdog();
+	spin_unlock_irqrestore(&clocksource_lock, flags);
+}
+
+/**
  * clocksource_get_next - Returns the selected clocksource
  *
  */
diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index 687dff4..e39e3d3 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -368,6 +368,7 @@ static int timekeeping_suspend(struct sys_device *dev, pm_message_t state)
 
 	clockevents_notify(CLOCK_EVT_NOTIFY_SUSPEND, NULL);
 
+	clocksource_suspend();
 	return 0;
 }