linux/drivers/cpuidle/cpuidle.c
Daniel Lezcano 442bf3aaf5 sched: Let the scheduler see CPU idle states
When the cpu enters idle, it stores the cpuidle state pointer in its
struct rq instance which in turn could be used to make a better decision
when balancing tasks.

As soon as the cpu exits its idle state, the struct rq reference is
cleared.

There are a couple of situations where the idle state pointer could be changed
while it is being consulted:

1. For x86/acpi with dynamic c-states, when a laptop switches from battery
   to AC that could result on removing the deeper idle state. The acpi driver
   triggers:
	'acpi_processor_cst_has_changed'
		'cpuidle_pause_and_lock'
			'cpuidle_uninstall_idle_handler'
				'kick_all_cpus_sync'.

All cpus will exit their idle state and the pointed object will be set to
NULL.

2. The cpuidle driver is unloaded. Logically that could happen but not
in practice because the drivers are always compiled in and 95% of them are
not coded to unregister themselves.  In any case, the unloading code must
call 'cpuidle_unregister_device', that calls 'cpuidle_pause_and_lock'
leading to 'kick_all_cpus_sync' as mentioned above.

A race can happen if we use the pointer and then one of these two scenarios
occurs at the same moment.

In order to be safe, the idle state pointer stored in the rq must be
used inside a rcu_read_lock section where we are protected with the
'rcu_barrier' in the 'cpuidle_uninstall_idle_handler' function. The
idle_get_state() and idle_put_state() accessors should be used to that
effect.

Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Signed-off-by: Nicolas Pitre <nico@linaro.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>
Cc: linux-pm@vger.kernel.org
Cc: linaro-kernel@lists.linaro.org
Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/n/tip-@git.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2014-09-24 14:46:58 +02:00

588 lines
13 KiB
C

/*
* cpuidle.c - core cpuidle infrastructure
*
* (C) 2006-2007 Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
* Shaohua Li <shaohua.li@intel.com>
* Adam Belay <abelay@novell.com>
*
* This code is licenced under the GPL.
*/
#include <linux/clockchips.h>
#include <linux/kernel.h>
#include <linux/mutex.h>
#include <linux/sched.h>
#include <linux/notifier.h>
#include <linux/pm_qos.h>
#include <linux/cpu.h>
#include <linux/cpuidle.h>
#include <linux/ktime.h>
#include <linux/hrtimer.h>
#include <linux/module.h>
#include <trace/events/power.h>
#include "cpuidle.h"
DEFINE_PER_CPU(struct cpuidle_device *, cpuidle_devices);
DEFINE_PER_CPU(struct cpuidle_device, cpuidle_dev);
DEFINE_MUTEX(cpuidle_lock);
LIST_HEAD(cpuidle_detected_devices);
static int enabled_devices;
static int off __read_mostly;
static int initialized __read_mostly;
static bool use_deepest_state __read_mostly;
int cpuidle_disabled(void)
{
return off;
}
void disable_cpuidle(void)
{
off = 1;
}
/**
* cpuidle_play_dead - cpu off-lining
*
* Returns in case of an error or no driver
*/
int cpuidle_play_dead(void)
{
struct cpuidle_device *dev = __this_cpu_read(cpuidle_devices);
struct cpuidle_driver *drv = cpuidle_get_cpu_driver(dev);
int i;
if (!drv)
return -ENODEV;
/* Find lowest-power state that supports long-term idle */
for (i = drv->state_count - 1; i >= CPUIDLE_DRIVER_STATE_START; i--)
if (drv->states[i].enter_dead)
return drv->states[i].enter_dead(dev, i);
return -ENODEV;
}
/**
* cpuidle_use_deepest_state - Enable/disable the "deepest idle" mode.
* @enable: Whether enable or disable the feature.
*
* If the "deepest idle" mode is enabled, cpuidle will ignore the governor and
* always use the state with the greatest exit latency (out of the states that
* are not disabled).
*
* This function can only be called after cpuidle_pause() to avoid races.
*/
void cpuidle_use_deepest_state(bool enable)
{
use_deepest_state = enable;
}
/**
* cpuidle_find_deepest_state - Find the state of the greatest exit latency.
* @drv: cpuidle driver for a given CPU.
* @dev: cpuidle device for a given CPU.
*/
static int cpuidle_find_deepest_state(struct cpuidle_driver *drv,
struct cpuidle_device *dev)
{
unsigned int latency_req = 0;
int i, ret = CPUIDLE_DRIVER_STATE_START - 1;
for (i = CPUIDLE_DRIVER_STATE_START; i < drv->state_count; i++) {
struct cpuidle_state *s = &drv->states[i];
struct cpuidle_state_usage *su = &dev->states_usage[i];
if (s->disabled || su->disable || s->exit_latency <= latency_req)
continue;
latency_req = s->exit_latency;
ret = i;
}
return ret;
}
/**
* cpuidle_enter_state - enter the state and update stats
* @dev: cpuidle device for this cpu
* @drv: cpuidle driver for this cpu
* @next_state: index into drv->states of the state to enter
*/
int cpuidle_enter_state(struct cpuidle_device *dev, struct cpuidle_driver *drv,
int index)
{
int entered_state;
struct cpuidle_state *target_state = &drv->states[index];
ktime_t time_start, time_end;
s64 diff;
trace_cpu_idle_rcuidle(index, dev->cpu);
time_start = ktime_get();
entered_state = target_state->enter(dev, drv, index);
time_end = ktime_get();
trace_cpu_idle_rcuidle(PWR_EVENT_EXIT, dev->cpu);
if (!cpuidle_state_is_coupled(dev, drv, entered_state))
local_irq_enable();
diff = ktime_to_us(ktime_sub(time_end, time_start));
if (diff > INT_MAX)
diff = INT_MAX;
dev->last_residency = (int) diff;
if (entered_state >= 0) {
/* Update cpuidle counters */
/* This can be moved to within driver enter routine
* but that results in multiple copies of same code.
*/
dev->states_usage[entered_state].time += dev->last_residency;
dev->states_usage[entered_state].usage++;
} else {
dev->last_residency = 0;
}
return entered_state;
}
/**
* cpuidle_select - ask the cpuidle framework to choose an idle state
*
* @drv: the cpuidle driver
* @dev: the cpuidle device
*
* Returns the index of the idle state.
*/
int cpuidle_select(struct cpuidle_driver *drv, struct cpuidle_device *dev)
{
if (off || !initialized)
return -ENODEV;
if (!drv || !dev || !dev->enabled)
return -EBUSY;
if (unlikely(use_deepest_state))
return cpuidle_find_deepest_state(drv, dev);
return cpuidle_curr_governor->select(drv, dev);
}
/**
* cpuidle_enter - enter into the specified idle state
*
* @drv: the cpuidle driver tied with the cpu
* @dev: the cpuidle device
* @index: the index in the idle state table
*
* Returns the index in the idle state, < 0 in case of error.
* The error code depends on the backend driver
*/
int cpuidle_enter(struct cpuidle_driver *drv, struct cpuidle_device *dev,
int index)
{
if (cpuidle_state_is_coupled(dev, drv, index))
return cpuidle_enter_state_coupled(dev, drv, index);
return cpuidle_enter_state(dev, drv, index);
}
/**
* cpuidle_reflect - tell the underlying governor what was the state
* we were in
*
* @dev : the cpuidle device
* @index: the index in the idle state table
*
*/
void cpuidle_reflect(struct cpuidle_device *dev, int index)
{
if (cpuidle_curr_governor->reflect && !unlikely(use_deepest_state))
cpuidle_curr_governor->reflect(dev, index);
}
/**
* cpuidle_install_idle_handler - installs the cpuidle idle loop handler
*/
void cpuidle_install_idle_handler(void)
{
if (enabled_devices) {
/* Make sure all changes finished before we switch to new idle */
smp_wmb();
initialized = 1;
}
}
/**
* cpuidle_uninstall_idle_handler - uninstalls the cpuidle idle loop handler
*/
void cpuidle_uninstall_idle_handler(void)
{
if (enabled_devices) {
initialized = 0;
wake_up_all_idle_cpus();
}
/*
* Make sure external observers (such as the scheduler)
* are done looking at pointed idle states.
*/
synchronize_rcu();
}
/**
* cpuidle_pause_and_lock - temporarily disables CPUIDLE
*/
void cpuidle_pause_and_lock(void)
{
mutex_lock(&cpuidle_lock);
cpuidle_uninstall_idle_handler();
}
EXPORT_SYMBOL_GPL(cpuidle_pause_and_lock);
/**
* cpuidle_resume_and_unlock - resumes CPUIDLE operation
*/
void cpuidle_resume_and_unlock(void)
{
cpuidle_install_idle_handler();
mutex_unlock(&cpuidle_lock);
}
EXPORT_SYMBOL_GPL(cpuidle_resume_and_unlock);
/* Currently used in suspend/resume path to suspend cpuidle */
void cpuidle_pause(void)
{
mutex_lock(&cpuidle_lock);
cpuidle_uninstall_idle_handler();
mutex_unlock(&cpuidle_lock);
}
/* Currently used in suspend/resume path to resume cpuidle */
void cpuidle_resume(void)
{
mutex_lock(&cpuidle_lock);
cpuidle_install_idle_handler();
mutex_unlock(&cpuidle_lock);
}
/**
* cpuidle_enable_device - enables idle PM for a CPU
* @dev: the CPU
*
* This function must be called between cpuidle_pause_and_lock and
* cpuidle_resume_and_unlock when used externally.
*/
int cpuidle_enable_device(struct cpuidle_device *dev)
{
int ret;
struct cpuidle_driver *drv;
if (!dev)
return -EINVAL;
if (dev->enabled)
return 0;
drv = cpuidle_get_cpu_driver(dev);
if (!drv || !cpuidle_curr_governor)
return -EIO;
if (!dev->registered)
return -EINVAL;
if (!dev->state_count)
dev->state_count = drv->state_count;
ret = cpuidle_add_device_sysfs(dev);
if (ret)
return ret;
if (cpuidle_curr_governor->enable &&
(ret = cpuidle_curr_governor->enable(drv, dev)))
goto fail_sysfs;
smp_wmb();
dev->enabled = 1;
enabled_devices++;
return 0;
fail_sysfs:
cpuidle_remove_device_sysfs(dev);
return ret;
}
EXPORT_SYMBOL_GPL(cpuidle_enable_device);
/**
* cpuidle_disable_device - disables idle PM for a CPU
* @dev: the CPU
*
* This function must be called between cpuidle_pause_and_lock and
* cpuidle_resume_and_unlock when used externally.
*/
void cpuidle_disable_device(struct cpuidle_device *dev)
{
struct cpuidle_driver *drv = cpuidle_get_cpu_driver(dev);
if (!dev || !dev->enabled)
return;
if (!drv || !cpuidle_curr_governor)
return;
dev->enabled = 0;
if (cpuidle_curr_governor->disable)
cpuidle_curr_governor->disable(drv, dev);
cpuidle_remove_device_sysfs(dev);
enabled_devices--;
}
EXPORT_SYMBOL_GPL(cpuidle_disable_device);
static void __cpuidle_unregister_device(struct cpuidle_device *dev)
{
struct cpuidle_driver *drv = cpuidle_get_cpu_driver(dev);
list_del(&dev->device_list);
per_cpu(cpuidle_devices, dev->cpu) = NULL;
module_put(drv->owner);
}
static void __cpuidle_device_init(struct cpuidle_device *dev)
{
memset(dev->states_usage, 0, sizeof(dev->states_usage));
dev->last_residency = 0;
}
/**
* __cpuidle_register_device - internal register function called before register
* and enable routines
* @dev: the cpu
*
* cpuidle_lock mutex must be held before this is called
*/
static int __cpuidle_register_device(struct cpuidle_device *dev)
{
int ret;
struct cpuidle_driver *drv = cpuidle_get_cpu_driver(dev);
if (!try_module_get(drv->owner))
return -EINVAL;
per_cpu(cpuidle_devices, dev->cpu) = dev;
list_add(&dev->device_list, &cpuidle_detected_devices);
ret = cpuidle_coupled_register_device(dev);
if (ret)
__cpuidle_unregister_device(dev);
else
dev->registered = 1;
return ret;
}
/**
* cpuidle_register_device - registers a CPU's idle PM feature
* @dev: the cpu
*/
int cpuidle_register_device(struct cpuidle_device *dev)
{
int ret = -EBUSY;
if (!dev)
return -EINVAL;
mutex_lock(&cpuidle_lock);
if (dev->registered)
goto out_unlock;
__cpuidle_device_init(dev);
ret = __cpuidle_register_device(dev);
if (ret)
goto out_unlock;
ret = cpuidle_add_sysfs(dev);
if (ret)
goto out_unregister;
ret = cpuidle_enable_device(dev);
if (ret)
goto out_sysfs;
cpuidle_install_idle_handler();
out_unlock:
mutex_unlock(&cpuidle_lock);
return ret;
out_sysfs:
cpuidle_remove_sysfs(dev);
out_unregister:
__cpuidle_unregister_device(dev);
goto out_unlock;
}
EXPORT_SYMBOL_GPL(cpuidle_register_device);
/**
* cpuidle_unregister_device - unregisters a CPU's idle PM feature
* @dev: the cpu
*/
void cpuidle_unregister_device(struct cpuidle_device *dev)
{
if (!dev || dev->registered == 0)
return;
cpuidle_pause_and_lock();
cpuidle_disable_device(dev);
cpuidle_remove_sysfs(dev);
__cpuidle_unregister_device(dev);
cpuidle_coupled_unregister_device(dev);
cpuidle_resume_and_unlock();
}
EXPORT_SYMBOL_GPL(cpuidle_unregister_device);
/**
* cpuidle_unregister: unregister a driver and the devices. This function
* can be used only if the driver has been previously registered through
* the cpuidle_register function.
*
* @drv: a valid pointer to a struct cpuidle_driver
*/
void cpuidle_unregister(struct cpuidle_driver *drv)
{
int cpu;
struct cpuidle_device *device;
for_each_cpu(cpu, drv->cpumask) {
device = &per_cpu(cpuidle_dev, cpu);
cpuidle_unregister_device(device);
}
cpuidle_unregister_driver(drv);
}
EXPORT_SYMBOL_GPL(cpuidle_unregister);
/**
* cpuidle_register: registers the driver and the cpu devices with the
* coupled_cpus passed as parameter. This function is used for all common
* initialization pattern there are in the arch specific drivers. The
* devices is globally defined in this file.
*
* @drv : a valid pointer to a struct cpuidle_driver
* @coupled_cpus: a cpumask for the coupled states
*
* Returns 0 on success, < 0 otherwise
*/
int cpuidle_register(struct cpuidle_driver *drv,
const struct cpumask *const coupled_cpus)
{
int ret, cpu;
struct cpuidle_device *device;
ret = cpuidle_register_driver(drv);
if (ret) {
pr_err("failed to register cpuidle driver\n");
return ret;
}
for_each_cpu(cpu, drv->cpumask) {
device = &per_cpu(cpuidle_dev, cpu);
device->cpu = cpu;
#ifdef CONFIG_ARCH_NEEDS_CPU_IDLE_COUPLED
/*
* On multiplatform for ARM, the coupled idle states could be
* enabled in the kernel even if the cpuidle driver does not
* use it. Note, coupled_cpus is a struct copy.
*/
if (coupled_cpus)
device->coupled_cpus = *coupled_cpus;
#endif
ret = cpuidle_register_device(device);
if (!ret)
continue;
pr_err("Failed to register cpuidle device for cpu%d\n", cpu);
cpuidle_unregister(drv);
break;
}
return ret;
}
EXPORT_SYMBOL_GPL(cpuidle_register);
#ifdef CONFIG_SMP
/*
* This function gets called when a part of the kernel has a new latency
* requirement. This means we need to get all processors out of their C-state,
* and then recalculate a new suitable C-state. Just do a cross-cpu IPI; that
* wakes them all right up.
*/
static int cpuidle_latency_notify(struct notifier_block *b,
unsigned long l, void *v)
{
wake_up_all_idle_cpus();
return NOTIFY_OK;
}
static struct notifier_block cpuidle_latency_notifier = {
.notifier_call = cpuidle_latency_notify,
};
static inline void latency_notifier_init(struct notifier_block *n)
{
pm_qos_add_notifier(PM_QOS_CPU_DMA_LATENCY, n);
}
#else /* CONFIG_SMP */
#define latency_notifier_init(x) do { } while (0)
#endif /* CONFIG_SMP */
/**
* cpuidle_init - core initializer
*/
static int __init cpuidle_init(void)
{
int ret;
if (cpuidle_disabled())
return -ENODEV;
ret = cpuidle_add_interface(cpu_subsys.dev_root);
if (ret)
return ret;
latency_notifier_init(&cpuidle_latency_notifier);
return 0;
}
module_param(off, int, 0444);
core_initcall(cpuidle_init);