lkml.org 
[lkml]   [2009]   [Aug]   [14]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
Subject[patch 03/15] reset of cycle_last for tsc clocksource
From: Martin Schwidefsky <schwidefsky@de.ibm.com>

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@elte.hu>
Cc: Daniel Walker <dwalker@fifo99.com>
Cc: John Stultz <johnstul@us.ibm.com>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
---
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.



\
 
 \ /
  Last update: 2009-08-14 15:57    [from the cache]
©2003-2011 Jasper Spaans