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

[Rafael J. Wysocki]

On Wednesday, November 14, 2012 05:56:30 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 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@xxxxxxxxxxxx>

Len, I need your ACK on intel_idle change in this patch if you agree with it.

Thanks,
Rafael


> ---
>  arch/powerpc/platforms/pseries/processor_idle.c |    4 +-
>  drivers/acpi/processor_idle.c                   |   57 +---------------------
>  drivers/cpuidle/cpuidle.c                       |    3 +-
>  drivers/idle/intel_idle.c                       |   14 +-----
>  4 files changed, 7 insertions(+), 71 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..f1a5da4 100644
> --- a/drivers/acpi/processor_idle.c
> +++ b/drivers/acpi/processor_idle.c
> @@ -735,31 +735,18 @@ static inline void acpi_idle_do_entry(struct acpi_processor_cx *cx)
>  static int acpi_idle_enter_c1(struct cpuidle_device *dev,
>  		struct cpuidle_driver *drv, int index)
>  {
> -	ktime_t  kt1, kt2;
> -	s64 idle_time;
>  	struct acpi_processor *pr;
>  	struct cpuidle_state_usage *state_usage = &dev->states_usage[index];
>  	struct acpi_processor_cx *cx = cpuidle_get_statedata(state_usage);
>  
>  	pr = __this_cpu_read(processors);
> -	dev->last_residency = 0;
>  
>  	if (unlikely(!pr))
>  		return -EINVAL;
>  
> -	local_irq_disable();
> -
> -
>  	lapic_timer_state_broadcast(pr, cx, 1);
> -	kt1 = ktime_get_real();
>  	acpi_idle_do_entry(cx);
> -	kt2 = ktime_get_real();
> -	idle_time =  ktime_to_us(ktime_sub(kt2, kt1));
> -
> -	/* Update device last_residency*/
> -	dev->last_residency = (int)idle_time;
>  
> -	local_irq_enable();
>  	lapic_timer_state_broadcast(pr, cx, 0);
>  
>  	return index;
> @@ -806,19 +793,12 @@ static int acpi_idle_enter_simple(struct cpuidle_device *dev,
>  	struct acpi_processor *pr;
>  	struct cpuidle_state_usage *state_usage = &dev->states_usage[index];
>  	struct acpi_processor_cx *cx = cpuidle_get_statedata(state_usage);
> -	ktime_t  kt1, kt2;
> -	s64 idle_time_ns;
> -	s64 idle_time;
>  
>  	pr = __this_cpu_read(processors);
> -	dev->last_residency = 0;
>  
>  	if (unlikely(!pr))
>  		return -EINVAL;
>  
> -	local_irq_disable();
> -
> -
>  	if (cx->entry_method != ACPI_CSTATE_FFH) {
>  		current_thread_info()->status &= ~TS_POLLING;
>  		/*
> @@ -829,7 +809,6 @@ static int acpi_idle_enter_simple(struct cpuidle_device *dev,
>  
>  		if (unlikely(need_resched())) {
>  			current_thread_info()->status |= TS_POLLING;
> -			local_irq_enable();
>  			return -EINVAL;
>  		}
>  	}
> @@ -843,22 +822,12 @@ static int acpi_idle_enter_simple(struct cpuidle_device *dev,
>  	if (cx->type == ACPI_STATE_C3)
>  		ACPI_FLUSH_CPU_CACHE();
>  
> -	kt1 = ktime_get_real();
>  	/* Tell the scheduler that we are going deep-idle: */
>  	sched_clock_idle_sleep_event();
>  	acpi_idle_do_entry(cx);
> -	kt2 = ktime_get_real();
> -	idle_time_ns = ktime_to_ns(ktime_sub(kt2, kt1));
> -	idle_time = idle_time_ns;
> -	do_div(idle_time, NSEC_PER_USEC);
>  
> -	/* Update device last_residency*/
> -	dev->last_residency = (int)idle_time;
> +	sched_clock_idle_wakeup_event(0);
>  
> -	/* Tell the scheduler how much we idled: */
> -	sched_clock_idle_wakeup_event(idle_time_ns);
> -
> -	local_irq_enable();
>  	if (cx->entry_method != ACPI_CSTATE_FFH)
>  		current_thread_info()->status |= TS_POLLING;
>  
> @@ -883,13 +852,8 @@ static int acpi_idle_enter_bm(struct cpuidle_device *dev,
>  	struct acpi_processor *pr;
>  	struct cpuidle_state_usage *state_usage = &dev->states_usage[index];
>  	struct acpi_processor_cx *cx = cpuidle_get_statedata(state_usage);
> -	ktime_t  kt1, kt2;
> -	s64 idle_time_ns;
> -	s64 idle_time;
> -
>  
>  	pr = __this_cpu_read(processors);
> -	dev->last_residency = 0;
>  
>  	if (unlikely(!pr))
>  		return -EINVAL;
> @@ -899,16 +863,11 @@ static int acpi_idle_enter_bm(struct cpuidle_device *dev,
>  			return drv->states[drv->safe_state_index].enter(dev,
>  						drv, drv->safe_state_index);
>  		} else {
> -			local_irq_disable();
>  			acpi_safe_halt();
> -			local_irq_enable();
>  			return -EBUSY;
>  		}
>  	}
>  
> -	local_irq_disable();
> -
> -
>  	if (cx->entry_method != ACPI_CSTATE_FFH) {
>  		current_thread_info()->status &= ~TS_POLLING;
>  		/*
> @@ -919,7 +878,6 @@ static int acpi_idle_enter_bm(struct cpuidle_device *dev,
>  
>  		if (unlikely(need_resched())) {
>  			current_thread_info()->status |= TS_POLLING;
> -			local_irq_enable();
>  			return -EINVAL;
>  		}
>  	}
> @@ -934,7 +892,6 @@ static int acpi_idle_enter_bm(struct cpuidle_device *dev,
>  	 */
>  	lapic_timer_state_broadcast(pr, cx, 1);
>  
> -	kt1 = ktime_get_real();
>  	/*
>  	 * disable bus master
>  	 * bm_check implies we need ARB_DIS
> @@ -965,18 +922,9 @@ static int acpi_idle_enter_bm(struct cpuidle_device *dev,
>  		c3_cpu_count--;
>  		raw_spin_unlock(&c3_lock);
>  	}
> -	kt2 = ktime_get_real();
> -	idle_time_ns = ktime_to_ns(ktime_sub(kt2, kt1));
> -	idle_time = idle_time_ns;
> -	do_div(idle_time, NSEC_PER_USEC);
> -
> -	/* Update device last_residency*/
> -	dev->last_residency = (int)idle_time;
>  
> -	/* Tell the scheduler how much we idled: */
> -	sched_clock_idle_wakeup_event(idle_time_ns);
> +	sched_clock_idle_wakeup_event(0);
>  
> -	local_irq_enable();
>  	if (cx->entry_method != ACPI_CSTATE_FFH)
>  		current_thread_info()->status |= TS_POLLING;
>  
> @@ -987,6 +935,7 @@ static int acpi_idle_enter_bm(struct cpuidle_device *dev,
>  struct cpuidle_driver acpi_idle_driver = {
>  	.name =		"acpi_idle",
>  	.owner =	THIS_MODULE,
> +	.en_core_tk_irqen = 1,
>  };
>  
>  /**
> 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..c49c04d 100644
> --- a/drivers/idle/intel_idle.c
> +++ b/drivers/idle/intel_idle.c
> @@ -56,7 +56,6 @@
>  #include <linux/kernel.h>
>  #include <linux/cpuidle.h>
>  #include <linux/clockchips.h>
> -#include <linux/hrtimer.h>	/* ktime_get_real() */
>  #include <trace/events/power.h>
>  #include <linux/sched.h>
>  #include <linux/notifier.h>
> @@ -72,6 +71,7 @@
>  static struct cpuidle_driver intel_idle_driver = {
>  	.name = "intel_idle",
>  	.owner = THIS_MODULE,
> +	.en_core_tk_irqen = 1,
>  };
>  /* intel_idle.max_cstate=0 disables driver */
>  static int max_cstate = MWAIT_MAX_NUM_CSTATES - 1;
> @@ -281,8 +281,6 @@ 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;
>  	int cpu = smp_processor_id();
>  
>  	cstate = (((eax) >> MWAIT_SUBSTATE_SIZE) & MWAIT_CSTATE_MASK) + 1;
> @@ -297,8 +295,6 @@ 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();
> -
>  	stop_critical_timings();
>  	if (!need_resched()) {
>  
> @@ -310,17 +306,9 @@ 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));
> -
> -	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;
>  }
>  
> 
-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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