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authorJulius Werner <jwerner@chromium.org>2012-11-27 14:17:58 +0100
committerRafael J. Wysocki <rafael.j.wysocki@intel.com>2012-11-27 14:17:58 +0100
commita474a515497ef3566cfc17a2cab3d54d6d50ff1c (patch)
tree377b53565f728dfee5604ae0c8c6879d38a2a3ec /drivers/cpuidle/cpuidle.c
parenta093b93ee0e08cd73a07848752bc09ecea68cb13 (diff)
downloadlinux-linaro-stable-a474a515497ef3566cfc17a2cab3d54d6d50ff1c.tar.gz
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 'drivers/cpuidle/cpuidle.c')
-rw-r--r--drivers/cpuidle/cpuidle.c3
1 files changed, 1 insertions, 2 deletions
diff --git a/drivers/cpuidle/cpuidle.c b/drivers/cpuidle/cpuidle.c
index 711dd83fd3ba..8df53dd8dbe1 100644
--- a/drivers/cpuidle/cpuidle.c
+++ b/drivers/cpuidle/cpuidle.c
@@ -109,8 +109,7 @@ int cpuidle_enter_state(struct cpuidle_device *dev, struct cpuidle_driver *drv,
/* This can be moved to within driver enter routine
* but that results in multiple copies of same code.
*/
- dev->states_usage[entered_state].time +=
- (unsigned long long)dev->last_residency;
+ dev->states_usage[entered_state].time += dev->last_residency;
dev->states_usage[entered_state].usage++;
} else {
dev->last_residency = 0;