Subject: Re: [PATCH] cpuidle: Measure idle state durations with monotonic clock

From: Deepthi Dharwar <[email-masked]>
Date: Wed, 14 Nov 2012 14:36:41 +0530

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 <[email-masked]>

Cheers,
Deepthi

> 
> Signed-off-by: Julius Werner <[email-masked]>
> ---
>  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;
>  }
>