[patch 03/15] reset of cycle_last for tsc clocksource

[Martin Schwidefsky]

From: Martin Schwidefsky <schwidefsky@xxxxxxxxxx>

change_clocksource resets the cycle_last value to zero then sets
it to a value read from the clocksource. The reset to zero is
required only for the TSC clocksource to make the read_tsc function
work. This is subtle and surprising. Move the reset to a resume
function in the tsc code.

Cc: Ingo Molnar <mingo@xxxxxxx>
Cc: Daniel Walker <dwalker@xxxxxxxxxx>
Cc: John Stultz <johnstul@xxxxxxxxxx>
Acked-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Martin Schwidefsky <schwidefsky@xxxxxxxxxx>
---
 arch/x86/kernel/tsc.c     |    6 ++++++
 kernel/time/timekeeping.c |    1 -
 2 files changed, 6 insertions(+), 1 deletion(-)

Index: linux-2.6/arch/x86/kernel/tsc.c
===================================================================
--- linux-2.6.orig/arch/x86/kernel/tsc.c
+++ linux-2.6/arch/x86/kernel/tsc.c
@@ -744,10 +744,16 @@ static cycle_t __vsyscall_fn vread_tsc(v
 }
 #endif
 
+static void resume_tsc(void)
+{
+	clocksource_tsc.cycle_last = 0;
+}
+
 static struct clocksource clocksource_tsc = {
 	.name                   = "tsc",
 	.rating                 = 300,
 	.read                   = read_tsc,
+	.resume			= resume_tsc,
 	.mask                   = CLOCKSOURCE_MASK(64),
 	.shift                  = 22,
 	.flags                  = CLOCK_SOURCE_IS_CONTINUOUS |
Index: linux-2.6/kernel/time/timekeeping.c
===================================================================
--- linux-2.6.orig/kernel/time/timekeeping.c
+++ linux-2.6/kernel/time/timekeeping.c
@@ -295,7 +295,6 @@ static void change_clocksource(void)
 	if (old->disable)
 		old->disable(old);
 
-	clock->cycle_last = 0;
 	clock->cycle_last = clock->read(clock);
 	clock->error = 0;
 	clock->xtime_nsec = 0;

-- 
blue skies,
   Martin.

"Reality continues to ruin my life." - Calvin.

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