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cpuidle: Measure idle state durations with monotonic clock
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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>
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Julius Werner authored and Rafael J. Wysocki committed Nov 27, 2012
1 parent a093b93 commit a474a51
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Showing 4 changed files with 7 additions and 71 deletions.
4 changes: 2 additions & 2 deletions arch/powerpc/platforms/pseries/processor_idle.c
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Original file line number Diff line number Diff line change
Expand Up @@ -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
Expand All @@ -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,
Expand Down
57 changes: 3 additions & 54 deletions drivers/acpi/processor_idle.c
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Original file line number Diff line number Diff line change
Expand Up @@ -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;
Expand Down Expand Up @@ -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;
/*
Expand All @@ -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;
}
}
Expand All @@ -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;

Expand All @@ -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;
Expand All @@ -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;
/*
Expand All @@ -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;
}
}
Expand All @@ -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
Expand Down Expand Up @@ -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;

Expand All @@ -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,
};

/**
Expand Down
3 changes: 1 addition & 2 deletions drivers/cpuidle/cpuidle.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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;
Expand Down
14 changes: 1 addition & 13 deletions drivers/idle/intel_idle.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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>
Expand All @@ -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;
Expand Down Expand Up @@ -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;
Expand All @@ -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()) {

Expand All @@ -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;
}

Expand Down

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