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authorMartin Schwidefsky <schwidefsky@de.ibm.com>2009-08-14 15:47:20 +0200
committerThomas Gleixner <tglx@linutronix.de>2009-08-15 10:55:45 +0200
commit1be396794897f80bfc8774719ba60309a9e3d374 (patch)
treef0e11ffe7b7cc2cf58129cf3ea1c543de0da9898 /kernel/time/timekeeping.c
parenta0f7d48bfb95a4c5172a2756dbc4b82afc8e9ae4 (diff)
timekeeping: Move reset of cycle_last for tsc clocksource to tsc
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 after a resume. The reason is that the TSC read function uses cycle_last to detect backwards going TSCs. In the resume case cycle_last contains the TSC value from the last update before the suspend. On resume the TSC starts counting from 0 again and would trip over the cycle_last comparison. This is subtle and surprising. Move the reset to a resume function in the tsc code. Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com> Acked-by: Thomas Gleixner <tglx@linutronix.de> Acked-by: John Stultz <johnstul@us.ibm.com> Cc: Daniel Walker <dwalker@fifo99.com> LKML-Reference: <20090814134808.142191175@de.ibm.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Diffstat (limited to 'kernel/time/timekeeping.c')
-rw-r--r--kernel/time/timekeeping.c1
1 files changed, 0 insertions, 1 deletions
diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index 016a2591d719..b5673016089f 100644
--- a/kernel/time/timekeeping.c
+++ b/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;