From a474a515497ef3566cfc17a2cab3d54d6d50ff1c Mon Sep 17 00:00:00 2001 From: Julius Werner Date: Tue, 27 Nov 2012 14:17:58 +0100 Subject: cpuidle: Measure idle state durations with monotonic clock Many cpuidle drivers measure their time spent in an idle state by reading the wallclock time before and after idling and calculating the difference. This leads to erroneous results when the wallclock time gets updated by another processor in the meantime, adding that clock adjustment to the idle state's time counter. If the clock adjustment was negative, the result is even worse due to an erroneous cast from int to unsigned long long of the last_residency variable. The negative 32 bit integer will zero-extend and result in a forward time jump of roughly four billion milliseconds or 1.3 hours on the idle state residency counter. This patch changes all affected cpuidle drivers to either use the monotonic clock for their measurements or make use of the generic time measurement wrapper in cpuidle.c, which was already working correctly. Some superfluous CLIs/STIs in the ACPI code are removed (interrupts should always already be disabled before entering the idle function, and not get reenabled until the generic wrapper has performed its second measurement). It also removes the erroneous cast, making sure that negative residency values are applied correctly even though they should not appear anymore. Signed-off-by: Julius Werner Reviewed-by: Preeti U Murthy Tested-by: Daniel Lezcano Acked-by: Daniel Lezcano Acked-by: Len Brown Signed-off-by: Rafael J. Wysocki --- arch/powerpc/platforms/pseries/processor_idle.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) (limited to 'arch/powerpc/platforms') diff --git a/arch/powerpc/platforms/pseries/processor_idle.c b/arch/powerpc/platforms/pseries/processor_idle.c index 45d00e5fe14..4d806b41960 100644 --- a/arch/powerpc/platforms/pseries/processor_idle.c +++ b/arch/powerpc/platforms/pseries/processor_idle.c @@ -36,7 +36,7 @@ static struct cpuidle_state *cpuidle_state_table; static inline void idle_loop_prolog(unsigned long *in_purr, ktime_t *kt_before) { - *kt_before = ktime_get_real(); + *kt_before = ktime_get(); *in_purr = mfspr(SPRN_PURR); /* * Indicate to the HV that we are idle. Now would be @@ -50,7 +50,7 @@ static inline s64 idle_loop_epilog(unsigned long in_purr, ktime_t kt_before) get_lppaca()->wait_state_cycles += mfspr(SPRN_PURR) - in_purr; get_lppaca()->idle = 0; - return ktime_to_us(ktime_sub(ktime_get_real(), kt_before)); + return ktime_to_us(ktime_sub(ktime_get(), kt_before)); } static int snooze_loop(struct cpuidle_device *dev, -- cgit v1.2.3-70-g09d2