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

Rafael J. Wysocki
2012-11-27T19:07:43Z

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.

Applied to the linux-next branch of the linux-pm.git tree.

Thanks,
Rafael

> Signed-off-by: Julius Werner <jwerner@chromium.org>
> ---
> 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.