diff options
| author | Julius Werner <jwerner@chromium.org> | 2012-11-27 14:17:58 +0100 |
|---|---|---|
| committer | Rafael J. Wysocki <rafael.j.wysocki@intel.com> | 2012-11-27 14:17:58 +0100 |
| commit | a474a515497ef3566cfc17a2cab3d54d6d50ff1c (patch) | |
| tree | 377b53565f728dfee5604ae0c8c6879d38a2a3ec /arch/powerpc/platforms | |
| parent | a093b93ee0e08cd73a07848752bc09ecea68cb13 (diff) | |
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 <jwerner@chromium.org>
Reviewed-by: Preeti U Murthy <preeti@linux.vnet.ibm.com>
Tested-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Acked-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Acked-by: Len Brown <len.brown@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Diffstat (limited to 'arch/powerpc/platforms')
| -rw-r--r-- | arch/powerpc/platforms/pseries/processor_idle.c | 4 |
1 files changed, 2 insertions, 2 deletions
diff --git a/arch/powerpc/platforms/pseries/processor_idle.c b/arch/powerpc/platforms/pseries/processor_idle.c index 45d00e5fe14d..4d806b419606 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, |