Patchwork cpuidle: Measure idle state durations with monotonic clock

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Submitter Julius Werner
Date Nov. 13, 2012, 9:52 p.m.
Message ID <1352843563-16392-1-git-send-email-jwerner@chromium.org>
Download mbox | patch
Permalink /patch/198803/
State Not Applicable
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Comments

Julius Werner - Nov. 13, 2012, 9:52 p.m.
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 use the monotonic
clock for their measurements instead. 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>
---
 arch/powerpc/platforms/pseries/processor_idle.c |    4 ++--
 drivers/acpi/processor_idle.c                   |   12 ++++++------
 drivers/cpuidle/cpuidle.c                       |    3 +--
 drivers/idle/intel_idle.c                       |   13 ++++---------
 4 files changed, 13 insertions(+), 19 deletions(-)
Deepthi Dharwar - Nov. 14, 2012, 9:06 a.m.
On 11/14/2012 03:22 AM, Julius Werner wrote:
> 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 use the monotonic
> clock for their measurements instead. It also removes the erroneous
> cast, making sure that negative residency values are applied correctly
> even though they should not appear anymore.

Currently tegra/cpuidle uses ktime_get(). Good to have it for all
the other arch idle residency time logging too.
Tested patch on pseries.

Reviewed-by: Deepthi Dharwar <deepthi@linux.vnet.ibm.com>

Cheers,
Deepthi

> 
> Signed-off-by: Julius Werner <jwerner@chromium.org>
> ---
>  arch/powerpc/platforms/pseries/processor_idle.c |    4 ++--
>  drivers/acpi/processor_idle.c                   |   12 ++++++------
>  drivers/cpuidle/cpuidle.c                       |    3 +--
>  drivers/idle/intel_idle.c                       |   13 ++++---------
>  4 files changed, 13 insertions(+), 19 deletions(-)
> 
> diff --git a/arch/powerpc/platforms/pseries/processor_idle.c b/arch/powerpc/platforms/pseries/processor_idle.c
> index 45d00e5..4d806b4 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,
> diff --git a/drivers/acpi/processor_idle.c b/drivers/acpi/processor_idle.c
> index e8086c7..8c98d73 100644
> --- a/drivers/acpi/processor_idle.c
> +++ b/drivers/acpi/processor_idle.c
> @@ -751,9 +751,9 @@ static int acpi_idle_enter_c1(struct cpuidle_device *dev,
> 
> 
>  	lapic_timer_state_broadcast(pr, cx, 1);
> -	kt1 = ktime_get_real();
> +	kt1 = ktime_get();
>  	acpi_idle_do_entry(cx);
> -	kt2 = ktime_get_real();
> +	kt2 = ktime_get();
>  	idle_time =  ktime_to_us(ktime_sub(kt2, kt1));
> 
>  	/* Update device last_residency*/
> @@ -843,11 +843,11 @@ static int acpi_idle_enter_simple(struct cpuidle_device *dev,
>  	if (cx->type == ACPI_STATE_C3)
>  		ACPI_FLUSH_CPU_CACHE();
> 
> -	kt1 = ktime_get_real();
> +	kt1 = ktime_get();
>  	/* Tell the scheduler that we are going deep-idle: */
>  	sched_clock_idle_sleep_event();
>  	acpi_idle_do_entry(cx);
> -	kt2 = ktime_get_real();
> +	kt2 = ktime_get();
>  	idle_time_ns = ktime_to_ns(ktime_sub(kt2, kt1));
>  	idle_time = idle_time_ns;
>  	do_div(idle_time, NSEC_PER_USEC);
> @@ -934,7 +934,7 @@ static int acpi_idle_enter_bm(struct cpuidle_device *dev,
>  	 */
>  	lapic_timer_state_broadcast(pr, cx, 1);
> 
> -	kt1 = ktime_get_real();
> +	kt1 = ktime_get();
>  	/*
>  	 * disable bus master
>  	 * bm_check implies we need ARB_DIS
> @@ -965,7 +965,7 @@ static int acpi_idle_enter_bm(struct cpuidle_device *dev,
>  		c3_cpu_count--;
>  		raw_spin_unlock(&c3_lock);
>  	}
> -	kt2 = ktime_get_real();
> +	kt2 = ktime_get();
>  	idle_time_ns = ktime_to_ns(ktime_sub(kt2, kt1));
>  	idle_time = idle_time_ns;
>  	do_div(idle_time, NSEC_PER_USEC);
> diff --git a/drivers/cpuidle/cpuidle.c b/drivers/cpuidle/cpuidle.c
> index 7f15b85..1536edd 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;
> diff --git a/drivers/idle/intel_idle.c b/drivers/idle/intel_idle.c
> index b0f6b4c..6329a97 100644
> --- a/drivers/idle/intel_idle.c
> +++ b/drivers/idle/intel_idle.c
> @@ -56,7 +56,7 @@
>  #include <linux/kernel.h>
>  #include <linux/cpuidle.h>
>  #include <linux/clockchips.h>
> -#include <linux/hrtimer.h>	/* ktime_get_real() */
> +#include <linux/hrtimer.h>	/* ktime_get() */
>  #include <trace/events/power.h>
>  #include <linux/sched.h>
>  #include <linux/notifier.h>
> @@ -281,8 +281,7 @@ static int intel_idle(struct cpuidle_device *dev,
>  	struct cpuidle_state_usage *state_usage = &dev->states_usage[index];
>  	unsigned long eax = (unsigned long)cpuidle_get_statedata(state_usage);
>  	unsigned int cstate;
> -	ktime_t kt_before, kt_after;
> -	s64 usec_delta;
> +	ktime_t kt_before;
>  	int cpu = smp_processor_id();
> 
>  	cstate = (((eax) >> MWAIT_SUBSTATE_SIZE) & MWAIT_CSTATE_MASK) + 1;
> @@ -297,7 +296,7 @@ static int intel_idle(struct cpuidle_device *dev,
>  	if (!(lapic_timer_reliable_states & (1 << (cstate))))
>  		clockevents_notify(CLOCK_EVT_NOTIFY_BROADCAST_ENTER, &cpu);
> 
> -	kt_before = ktime_get_real();
> +	kt_before = ktime_get();
> 
>  	stop_critical_timings();
>  	if (!need_resched()) {
> @@ -310,17 +309,13 @@ static int intel_idle(struct cpuidle_device *dev,
> 
>  	start_critical_timings();
> 
> -	kt_after = ktime_get_real();
> -	usec_delta = ktime_to_us(ktime_sub(kt_after, kt_before));
> +	dev->last_residency = ktime_to_us(ktime_sub(ktime_get(), kt_before));
> 
>  	local_irq_enable();
> 
>  	if (!(lapic_timer_reliable_states & (1 << (cstate))))
>  		clockevents_notify(CLOCK_EVT_NOTIFY_BROADCAST_EXIT, &cpu);
> 
> -	/* Update cpuidle counters */
> -	dev->last_residency = (int)usec_delta;
> -
>  	return index;
>  }
>
Daniel Lezcano - Nov. 14, 2012, 10:57 a.m.
On 11/14/2012 10:06 AM, Deepthi Dharwar wrote:
> On 11/14/2012 03:22 AM, Julius Werner wrote:
>> 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 use the monotonic
>> clock for their measurements instead. It also removes the erroneous
>> cast, making sure that negative residency values are applied correctly
>> even though they should not appear anymore.
> 
> Currently tegra/cpuidle uses ktime_get(). Good to have it for all
> the other arch idle residency time logging too.

Actually it is used by all arm cpuidle drivers through the wrapper
"cpuidle_wrap_enter" and the en_core_tk_irqen flag.

> Tested patch on pseries.
> 
> Reviewed-by: Deepthi Dharwar <deepthi@linux.vnet.ibm.com>
> 
> Cheers,
> Deepthi
> 
>>
>> Signed-off-by: Julius Werner <jwerner@chromium.org>
>> ---
>>  arch/powerpc/platforms/pseries/processor_idle.c |    4 ++--
>>  drivers/acpi/processor_idle.c                   |   12 ++++++------
>>  drivers/cpuidle/cpuidle.c                       |    3 +--
>>  drivers/idle/intel_idle.c                       |   13 ++++---------
>>  4 files changed, 13 insertions(+), 19 deletions(-)
>>
>> diff --git a/arch/powerpc/platforms/pseries/processor_idle.c b/arch/powerpc/platforms/pseries/processor_idle.c
>> index 45d00e5..4d806b4 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,
>> diff --git a/drivers/acpi/processor_idle.c b/drivers/acpi/processor_idle.c
>> index e8086c7..8c98d73 100644
>> --- a/drivers/acpi/processor_idle.c
>> +++ b/drivers/acpi/processor_idle.c
>> @@ -751,9 +751,9 @@ static int acpi_idle_enter_c1(struct cpuidle_device *dev,
>>
>>
>>  	lapic_timer_state_broadcast(pr, cx, 1);
>> -	kt1 = ktime_get_real();
>> +	kt1 = ktime_get();
>>  	acpi_idle_do_entry(cx);
>> -	kt2 = ktime_get_real();
>> +	kt2 = ktime_get();
>>  	idle_time =  ktime_to_us(ktime_sub(kt2, kt1));
>>
>>  	/* Update device last_residency*/
>> @@ -843,11 +843,11 @@ static int acpi_idle_enter_simple(struct cpuidle_device *dev,
>>  	if (cx->type == ACPI_STATE_C3)
>>  		ACPI_FLUSH_CPU_CACHE();
>>
>> -	kt1 = ktime_get_real();
>> +	kt1 = ktime_get();
>>  	/* Tell the scheduler that we are going deep-idle: */
>>  	sched_clock_idle_sleep_event();
>>  	acpi_idle_do_entry(cx);
>> -	kt2 = ktime_get_real();
>> +	kt2 = ktime_get();
>>  	idle_time_ns = ktime_to_ns(ktime_sub(kt2, kt1));
>>  	idle_time = idle_time_ns;
>>  	do_div(idle_time, NSEC_PER_USEC);
>> @@ -934,7 +934,7 @@ static int acpi_idle_enter_bm(struct cpuidle_device *dev,
>>  	 */
>>  	lapic_timer_state_broadcast(pr, cx, 1);
>>
>> -	kt1 = ktime_get_real();
>> +	kt1 = ktime_get();
>>  	/*
>>  	 * disable bus master
>>  	 * bm_check implies we need ARB_DIS
>> @@ -965,7 +965,7 @@ static int acpi_idle_enter_bm(struct cpuidle_device *dev,
>>  		c3_cpu_count--;
>>  		raw_spin_unlock(&c3_lock);
>>  	}
>> -	kt2 = ktime_get_real();
>> +	kt2 = ktime_get();
>>  	idle_time_ns = ktime_to_ns(ktime_sub(kt2, kt1));
>>  	idle_time = idle_time_ns;
>>  	do_div(idle_time, NSEC_PER_USEC);
>> diff --git a/drivers/cpuidle/cpuidle.c b/drivers/cpuidle/cpuidle.c
>> index 7f15b85..1536edd 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;
>> diff --git a/drivers/idle/intel_idle.c b/drivers/idle/intel_idle.c
>> index b0f6b4c..6329a97 100644
>> --- a/drivers/idle/intel_idle.c
>> +++ b/drivers/idle/intel_idle.c
>> @@ -56,7 +56,7 @@
>>  #include <linux/kernel.h>
>>  #include <linux/cpuidle.h>
>>  #include <linux/clockchips.h>
>> -#include <linux/hrtimer.h>	/* ktime_get_real() */
>> +#include <linux/hrtimer.h>	/* ktime_get() */
>>  #include <trace/events/power.h>
>>  #include <linux/sched.h>
>>  #include <linux/notifier.h>
>> @@ -281,8 +281,7 @@ static int intel_idle(struct cpuidle_device *dev,
>>  	struct cpuidle_state_usage *state_usage = &dev->states_usage[index];
>>  	unsigned long eax = (unsigned long)cpuidle_get_statedata(state_usage);
>>  	unsigned int cstate;
>> -	ktime_t kt_before, kt_after;
>> -	s64 usec_delta;
>> +	ktime_t kt_before;
>>  	int cpu = smp_processor_id();
>>
>>  	cstate = (((eax) >> MWAIT_SUBSTATE_SIZE) & MWAIT_CSTATE_MASK) + 1;
>> @@ -297,7 +296,7 @@ static int intel_idle(struct cpuidle_device *dev,
>>  	if (!(lapic_timer_reliable_states & (1 << (cstate))))
>>  		clockevents_notify(CLOCK_EVT_NOTIFY_BROADCAST_ENTER, &cpu);
>>
>> -	kt_before = ktime_get_real();
>> +	kt_before = ktime_get();
>>
>>  	stop_critical_timings();
>>  	if (!need_resched()) {
>> @@ -310,17 +309,13 @@ static int intel_idle(struct cpuidle_device *dev,
>>
>>  	start_critical_timings();
>>
>> -	kt_after = ktime_get_real();
>> -	usec_delta = ktime_to_us(ktime_sub(kt_after, kt_before));
>> +	dev->last_residency = ktime_to_us(ktime_sub(ktime_get(), kt_before));
>>
>>  	local_irq_enable();
>>
>>  	if (!(lapic_timer_reliable_states & (1 << (cstate))))
>>  		clockevents_notify(CLOCK_EVT_NOTIFY_BROADCAST_EXIT, &cpu);
>>
>> -	/* Update cpuidle counters */
>> -	dev->last_residency = (int)usec_delta;
>> -
>>  	return index;
>>  }
>>
>
Daniel Lezcano - Nov. 14, 2012, 11:05 a.m.
On 11/13/2012 10:52 PM, Julius Werner wrote:
> 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 use the monotonic
> clock for their measurements instead. 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>
> ---
>  arch/powerpc/platforms/pseries/processor_idle.c |    4 ++--
>  drivers/acpi/processor_idle.c                   |   12 ++++++------
>  drivers/cpuidle/cpuidle.c                       |    3 +--
>  drivers/idle/intel_idle.c                       |   13 ++++---------
>  4 files changed, 13 insertions(+), 19 deletions(-)
> 
> diff --git a/arch/powerpc/platforms/pseries/processor_idle.c b/arch/powerpc/platforms/pseries/processor_idle.c
> index 45d00e5..4d806b4 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,
> diff --git a/drivers/acpi/processor_idle.c b/drivers/acpi/processor_idle.c
> index e8086c7..8c98d73 100644
> --- a/drivers/acpi/processor_idle.c
> +++ b/drivers/acpi/processor_idle.c
> @@ -751,9 +751,9 @@ static int acpi_idle_enter_c1(struct cpuidle_device *dev,
>  
>  
>  	lapic_timer_state_broadcast(pr, cx, 1);
> -	kt1 = ktime_get_real();
> +	kt1 = ktime_get();
>  	acpi_idle_do_entry(cx);
> -	kt2 = ktime_get_real();
> +	kt2 = ktime_get();
>  	idle_time =  ktime_to_us(ktime_sub(kt2, kt1));
>  
>  	/* Update device last_residency*/
> @@ -843,11 +843,11 @@ static int acpi_idle_enter_simple(struct cpuidle_device *dev,
>  	if (cx->type == ACPI_STATE_C3)
>  		ACPI_FLUSH_CPU_CACHE();
>  
> -	kt1 = ktime_get_real();
> +	kt1 = ktime_get();
>  	/* Tell the scheduler that we are going deep-idle: */
>  	sched_clock_idle_sleep_event();
>  	acpi_idle_do_entry(cx);
> -	kt2 = ktime_get_real();
> +	kt2 = ktime_get();
>  	idle_time_ns = ktime_to_ns(ktime_sub(kt2, kt1));
>  	idle_time = idle_time_ns;
>  	do_div(idle_time, NSEC_PER_USEC);
> @@ -934,7 +934,7 @@ static int acpi_idle_enter_bm(struct cpuidle_device *dev,
>  	 */
>  	lapic_timer_state_broadcast(pr, cx, 1);
>  
> -	kt1 = ktime_get_real();
> +	kt1 = ktime_get();
>  	/*
>  	 * disable bus master
>  	 * bm_check implies we need ARB_DIS
> @@ -965,7 +965,7 @@ static int acpi_idle_enter_bm(struct cpuidle_device *dev,
>  		c3_cpu_count--;
>  		raw_spin_unlock(&c3_lock);
>  	}
> -	kt2 = ktime_get_real();
> +	kt2 = ktime_get();
>  	idle_time_ns = ktime_to_ns(ktime_sub(kt2, kt1));
>  	idle_time = idle_time_ns;
>  	do_div(idle_time, NSEC_PER_USEC);


Maybe you can remove all these computations and set the flag
en_core_tk_irqen for the driver ? That will be handled by the cpuidle
framework, no ?

Same comment for the intel_idle driver.

Thanks
  -- Daniel
Julius Werner - Nov. 14, 2012, 5:15 p.m.
> Maybe you can remove all these computations and set the flag
> en_core_tk_irqen for the driver ? That will be handled by the cpuidle
> framework, no ?
>
> Same comment for the intel_idle driver.

Yeah, I thought about that, too. I was a little too afraid of touching
the sched_clock_idle_wakeup_event() parameter that is tied to the
measurement, but it seems to have been vestigial for some time now and
other drivers also just set it 0. I will whip up another version of
the patch (won't change the PPC further though, if this version works
I would just leave it at that... thanks for testing, Deepthi).

Patch

diff --git a/arch/powerpc/platforms/pseries/processor_idle.c b/arch/powerpc/platforms/pseries/processor_idle.c
index 45d00e5..4d806b4 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,
diff --git a/drivers/acpi/processor_idle.c b/drivers/acpi/processor_idle.c
index e8086c7..8c98d73 100644
--- a/drivers/acpi/processor_idle.c
+++ b/drivers/acpi/processor_idle.c
@@ -751,9 +751,9 @@  static int acpi_idle_enter_c1(struct cpuidle_device *dev,
 
 
 	lapic_timer_state_broadcast(pr, cx, 1);
-	kt1 = ktime_get_real();
+	kt1 = ktime_get();
 	acpi_idle_do_entry(cx);
-	kt2 = ktime_get_real();
+	kt2 = ktime_get();
 	idle_time =  ktime_to_us(ktime_sub(kt2, kt1));
 
 	/* Update device last_residency*/
@@ -843,11 +843,11 @@  static int acpi_idle_enter_simple(struct cpuidle_device *dev,
 	if (cx->type == ACPI_STATE_C3)
 		ACPI_FLUSH_CPU_CACHE();
 
-	kt1 = ktime_get_real();
+	kt1 = ktime_get();
 	/* Tell the scheduler that we are going deep-idle: */
 	sched_clock_idle_sleep_event();
 	acpi_idle_do_entry(cx);
-	kt2 = ktime_get_real();
+	kt2 = ktime_get();
 	idle_time_ns = ktime_to_ns(ktime_sub(kt2, kt1));
 	idle_time = idle_time_ns;
 	do_div(idle_time, NSEC_PER_USEC);
@@ -934,7 +934,7 @@  static int acpi_idle_enter_bm(struct cpuidle_device *dev,
 	 */
 	lapic_timer_state_broadcast(pr, cx, 1);
 
-	kt1 = ktime_get_real();
+	kt1 = ktime_get();
 	/*
 	 * disable bus master
 	 * bm_check implies we need ARB_DIS
@@ -965,7 +965,7 @@  static int acpi_idle_enter_bm(struct cpuidle_device *dev,
 		c3_cpu_count--;
 		raw_spin_unlock(&c3_lock);
 	}
-	kt2 = ktime_get_real();
+	kt2 = ktime_get();
 	idle_time_ns = ktime_to_ns(ktime_sub(kt2, kt1));
 	idle_time = idle_time_ns;
 	do_div(idle_time, NSEC_PER_USEC);
diff --git a/drivers/cpuidle/cpuidle.c b/drivers/cpuidle/cpuidle.c
index 7f15b85..1536edd 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;
diff --git a/drivers/idle/intel_idle.c b/drivers/idle/intel_idle.c
index b0f6b4c..6329a97 100644
--- a/drivers/idle/intel_idle.c
+++ b/drivers/idle/intel_idle.c
@@ -56,7 +56,7 @@ 
 #include <linux/kernel.h>
 #include <linux/cpuidle.h>
 #include <linux/clockchips.h>
-#include <linux/hrtimer.h>	/* ktime_get_real() */
+#include <linux/hrtimer.h>	/* ktime_get() */
 #include <trace/events/power.h>
 #include <linux/sched.h>
 #include <linux/notifier.h>
@@ -281,8 +281,7 @@  static int intel_idle(struct cpuidle_device *dev,
 	struct cpuidle_state_usage *state_usage = &dev->states_usage[index];
 	unsigned long eax = (unsigned long)cpuidle_get_statedata(state_usage);
 	unsigned int cstate;
-	ktime_t kt_before, kt_after;
-	s64 usec_delta;
+	ktime_t kt_before;
 	int cpu = smp_processor_id();
 
 	cstate = (((eax) >> MWAIT_SUBSTATE_SIZE) & MWAIT_CSTATE_MASK) + 1;
@@ -297,7 +296,7 @@  static int intel_idle(struct cpuidle_device *dev,
 	if (!(lapic_timer_reliable_states & (1 << (cstate))))
 		clockevents_notify(CLOCK_EVT_NOTIFY_BROADCAST_ENTER, &cpu);
 
-	kt_before = ktime_get_real();
+	kt_before = ktime_get();
 
 	stop_critical_timings();
 	if (!need_resched()) {
@@ -310,17 +309,13 @@  static int intel_idle(struct cpuidle_device *dev,
 
 	start_critical_timings();
 
-	kt_after = ktime_get_real();
-	usec_delta = ktime_to_us(ktime_sub(kt_after, kt_before));
+	dev->last_residency = ktime_to_us(ktime_sub(ktime_get(), kt_before));
 
 	local_irq_enable();
 
 	if (!(lapic_timer_reliable_states & (1 << (cstate))))
 		clockevents_notify(CLOCK_EVT_NOTIFY_BROADCAST_EXIT, &cpu);
 
-	/* Update cpuidle counters */
-	dev->last_residency = (int)usec_delta;
-
 	return index;
 }