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>
This commit is contained in:
parent
a0f7d48bfb
commit
1be3967948
|
@ -744,10 +744,16 @@ static cycle_t __vsyscall_fn vread_tsc(void)
|
|||
}
|
||||
#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 |
|
||||
|
|
|
@ -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;
|
||||
|
|
Loading…
Reference in New Issue