diff options
Diffstat (limited to 'drivers/cpuidle/coupled.c')
| -rw-r--r-- | drivers/cpuidle/coupled.c | 678 |
1 files changed, 678 insertions, 0 deletions
diff --git a/drivers/cpuidle/coupled.c b/drivers/cpuidle/coupled.c new file mode 100644 index 00000000000..aab6bba8dae --- /dev/null +++ b/drivers/cpuidle/coupled.c @@ -0,0 +1,678 @@ +/* + * coupled.c - helper functions to enter the same idle state on multiple cpus + * + * Copyright (c) 2011 Google, Inc. + * + * Author: Colin Cross <ccross@android.com> + * + * This program is free software; you can redistribute it and/or modify + * it under the terms of the GNU General Public License as published by + * the Free Software Foundation; either version 2 of the License, or + * (at your option) any later version. + * + * This program is distributed in the hope that it will be useful, but WITHOUT + * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or + * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for + * more details. + */ + +#include <linux/kernel.h> +#include <linux/cpu.h> +#include <linux/cpuidle.h> +#include <linux/mutex.h> +#include <linux/sched.h> +#include <linux/slab.h> +#include <linux/spinlock.h> + +#include "cpuidle.h" + +/** + * DOC: Coupled cpuidle states + * + * On some ARM SMP SoCs (OMAP4460, Tegra 2, and probably more), the + * cpus cannot be independently powered down, either due to + * sequencing restrictions (on Tegra 2, cpu 0 must be the last to + * power down), or due to HW bugs (on OMAP4460, a cpu powering up + * will corrupt the gic state unless the other cpu runs a work + * around). Each cpu has a power state that it can enter without + * coordinating with the other cpu (usually Wait For Interrupt, or + * WFI), and one or more "coupled" power states that affect blocks + * shared between the cpus (L2 cache, interrupt controller, and + * sometimes the whole SoC). Entering a coupled power state must + * be tightly controlled on both cpus. + * + * This file implements a solution, where each cpu will wait in the + * WFI state until all cpus are ready to enter a coupled state, at + * which point the coupled state function will be called on all + * cpus at approximately the same time. + * + * Once all cpus are ready to enter idle, they are woken by an smp + * cross call. At this point, there is a chance that one of the + * cpus will find work to do, and choose not to enter idle. A + * final pass is needed to guarantee that all cpus will call the + * power state enter function at the same time. During this pass, + * each cpu will increment the ready counter, and continue once the + * ready counter matches the number of online coupled cpus. If any + * cpu exits idle, the other cpus will decrement their counter and + * retry. + * + * requested_state stores the deepest coupled idle state each cpu + * is ready for. It is assumed that the states are indexed from + * shallowest (highest power, lowest exit latency) to deepest + * (lowest power, highest exit latency). The requested_state + * variable is not locked. It is only written from the cpu that + * it stores (or by the on/offlining cpu if that cpu is offline), + * and only read after all the cpus are ready for the coupled idle + * state are are no longer updating it. + * + * Three atomic counters are used. alive_count tracks the number + * of cpus in the coupled set that are currently or soon will be + * online. waiting_count tracks the number of cpus that are in + * the waiting loop, in the ready loop, or in the coupled idle state. + * ready_count tracks the number of cpus that are in the ready loop + * or in the coupled idle state. + * + * To use coupled cpuidle states, a cpuidle driver must: + * + * Set struct cpuidle_device.coupled_cpus to the mask of all + * coupled cpus, usually the same as cpu_possible_mask if all cpus + * are part of the same cluster. The coupled_cpus mask must be + * set in the struct cpuidle_device for each cpu. + * + * Set struct cpuidle_device.safe_state to a state that is not a + * coupled state. This is usually WFI. + * + * Set CPUIDLE_FLAG_COUPLED in struct cpuidle_state.flags for each + * state that affects multiple cpus. + * + * Provide a struct cpuidle_state.enter function for each state + * that affects multiple cpus. This function is guaranteed to be + * called on all cpus at approximately the same time. The driver + * should ensure that the cpus all abort together if any cpu tries + * to abort once the function is called. The function should return + * with interrupts still disabled. + */ + +/** + * struct cpuidle_coupled - data for set of cpus that share a coupled idle state + * @coupled_cpus: mask of cpus that are part of the coupled set + * @requested_state: array of requested states for cpus in the coupled set + * @ready_waiting_counts: combined count of cpus in ready or waiting loops + * @online_count: count of cpus that are online + * @refcnt: reference count of cpuidle devices that are using this struct + * @prevent: flag to prevent coupled idle while a cpu is hotplugging + */ +struct cpuidle_coupled { + cpumask_t coupled_cpus; + int requested_state[NR_CPUS]; + atomic_t ready_waiting_counts; + int online_count; + int refcnt; + int prevent; +}; + +#define WAITING_BITS 16 +#define MAX_WAITING_CPUS (1 << WAITING_BITS) +#define WAITING_MASK (MAX_WAITING_CPUS - 1) +#define READY_MASK (~WAITING_MASK) + +#define CPUIDLE_COUPLED_NOT_IDLE (-1) + +static DEFINE_MUTEX(cpuidle_coupled_lock); +static DEFINE_PER_CPU(struct call_single_data, cpuidle_coupled_poke_cb); + +/* + * The cpuidle_coupled_poked_mask mask is used to avoid calling + * __smp_call_function_single with the per cpu call_single_data struct already + * in use. This prevents a deadlock where two cpus are waiting for each others + * call_single_data struct to be available + */ +static cpumask_t cpuidle_coupled_poked_mask; + +/** + * cpuidle_state_is_coupled - check if a state is part of a coupled set + * @dev: struct cpuidle_device for the current cpu + * @drv: struct cpuidle_driver for the platform + * @state: index of the target state in drv->states + * + * Returns true if the target state is coupled with cpus besides this one + */ +bool cpuidle_state_is_coupled(struct cpuidle_device *dev, + struct cpuidle_driver *drv, int state) +{ + return drv->states[state].flags & CPUIDLE_FLAG_COUPLED; +} + +/** + * cpuidle_coupled_set_ready - mark a cpu as ready + * @coupled: the struct coupled that contains the current cpu + */ +static inline void cpuidle_coupled_set_ready(struct cpuidle_coupled *coupled) +{ + atomic_add(MAX_WAITING_CPUS, &coupled->ready_waiting_counts); +} + +/** + * cpuidle_coupled_set_not_ready - mark a cpu as not ready + * @coupled: the struct coupled that contains the current cpu + * + * Decrements the ready counter, unless the ready (and thus the waiting) counter + * is equal to the number of online cpus. Prevents a race where one cpu + * decrements the waiting counter and then re-increments it just before another + * cpu has decremented its ready counter, leading to the ready counter going + * down from the number of online cpus without going through the coupled idle + * state. + * + * Returns 0 if the counter was decremented successfully, -EINVAL if the ready + * counter was equal to the number of online cpus. + */ +static +inline int cpuidle_coupled_set_not_ready(struct cpuidle_coupled *coupled) +{ + int all; + int ret; + + all = coupled->online_count || (coupled->online_count << WAITING_BITS); + ret = atomic_add_unless(&coupled->ready_waiting_counts, + -MAX_WAITING_CPUS, all); + + return ret ? 0 : -EINVAL; +} + +/** + * cpuidle_coupled_no_cpus_ready - check if no cpus in a coupled set are ready + * @coupled: the struct coupled that contains the current cpu + * + * Returns true if all of the cpus in a coupled set are out of the ready loop. + */ +static inline int cpuidle_coupled_no_cpus_ready(struct cpuidle_coupled *coupled) +{ + int r = atomic_read(&coupled->ready_waiting_counts) >> WAITING_BITS; + return r == 0; +} + +/** + * cpuidle_coupled_cpus_ready - check if all cpus in a coupled set are ready + * @coupled: the struct coupled that contains the current cpu + * + * Returns true if all cpus coupled to this target state are in the ready loop + */ +static inline bool cpuidle_coupled_cpus_ready(struct cpuidle_coupled *coupled) +{ + int r = atomic_read(&coupled->ready_waiting_counts) >> WAITING_BITS; + return r == coupled->online_count; +} + +/** + * cpuidle_coupled_cpus_waiting - check if all cpus in a coupled set are waiting + * @coupled: the struct coupled that contains the current cpu + * + * Returns true if all cpus coupled to this target state are in the wait loop + */ +static inline bool cpuidle_coupled_cpus_waiting(struct cpuidle_coupled *coupled) +{ + int w = atomic_read(&coupled->ready_waiting_counts) & WAITING_MASK; + return w == coupled->online_count; +} + +/** + * cpuidle_coupled_no_cpus_waiting - check if no cpus in coupled set are waiting + * @coupled: the struct coupled that contains the current cpu + * + * Returns true if all of the cpus in a coupled set are out of the waiting loop. + */ +static inline int cpuidle_coupled_no_cpus_waiting(struct cpuidle_coupled *coupled) +{ + int w = atomic_read(&coupled->ready_waiting_counts) & WAITING_MASK; + return w == 0; +} + +/** + * cpuidle_coupled_get_state - determine the deepest idle state + * @dev: struct cpuidle_device for this cpu + * @coupled: the struct coupled that contains the current cpu + * + * Returns the deepest idle state that all coupled cpus can enter + */ +static inline int cpuidle_coupled_get_state(struct cpuidle_device *dev, + struct cpuidle_coupled *coupled) +{ + int i; + int state = INT_MAX; + + /* + * Read barrier ensures that read of requested_state is ordered after + * reads of ready_count. Matches the write barriers + * cpuidle_set_state_waiting. + */ + smp_rmb(); + + for_each_cpu_mask(i, coupled->coupled_cpus) + if (cpu_online(i) && coupled->requested_state[i] < state) + state = coupled->requested_state[i]; + + return state; +} + +static void cpuidle_coupled_poked(void *info) +{ + int cpu = (unsigned long)info; + cpumask_clear_cpu(cpu, &cpuidle_coupled_poked_mask); +} + +/** + * cpuidle_coupled_poke - wake up a cpu that may be waiting + * @cpu: target cpu + * + * Ensures that the target cpu exits it's waiting idle state (if it is in it) + * and will see updates to waiting_count before it re-enters it's waiting idle + * state. + * + * If cpuidle_coupled_poked_mask is already set for the target cpu, that cpu + * either has or will soon have a pending IPI that will wake it out of idle, + * or it is currently processing the IPI and is not in idle. + */ +static void cpuidle_coupled_poke(int cpu) +{ + struct call_single_data *csd = &per_cpu(cpuidle_coupled_poke_cb, cpu); + + if (!cpumask_test_and_set_cpu(cpu, &cpuidle_coupled_poked_mask)) + __smp_call_function_single(cpu, csd, 0); +} + +/** + * cpuidle_coupled_poke_others - wake up all other cpus that may be waiting + * @dev: struct cpuidle_device for this cpu + * @coupled: the struct coupled that contains the current cpu + * + * Calls cpuidle_coupled_poke on all other online cpus. + */ +static void cpuidle_coupled_poke_others(int this_cpu, + struct cpuidle_coupled *coupled) +{ + int cpu; + + for_each_cpu_mask(cpu, coupled->coupled_cpus) + if (cpu != this_cpu && cpu_online(cpu)) + cpuidle_coupled_poke(cpu); +} + +/** + * cpuidle_coupled_set_waiting - mark this cpu as in the wait loop + * @dev: struct cpuidle_device for this cpu + * @coupled: the struct coupled that contains the current cpu + * @next_state: the index in drv->states of the requested state for this cpu + * + * Updates the requested idle state for the specified cpuidle device, + * poking all coupled cpus out of idle if necessary to let them see the new + * state. + */ +static void cpuidle_coupled_set_waiting(int cpu, + struct cpuidle_coupled *coupled, int next_state) +{ + int w; + + coupled->requested_state[cpu] = next_state; + + /* + * If this is the last cpu to enter the waiting state, poke + * all the other cpus out of their waiting state so they can + * enter a deeper state. This can race with one of the cpus + * exiting the waiting state due to an interrupt and + * decrementing waiting_count, see comment below. + * + * The atomic_inc_return provides a write barrier to order the write + * to requested_state with the later write that increments ready_count. + */ + w = atomic_inc_return(&coupled->ready_waiting_counts) & WAITING_MASK; + if (w == coupled->online_count) + cpuidle_coupled_poke_others(cpu, coupled); +} + +/** + * cpuidle_coupled_set_not_waiting - mark this cpu as leaving the wait loop + * @dev: struct cpuidle_device for this cpu + * @coupled: the struct coupled that contains the current cpu + * + * Removes the requested idle state for the specified cpuidle device. + */ +static void cpuidle_coupled_set_not_waiting(int cpu, + struct cpuidle_coupled *coupled) +{ + /* + * Decrementing waiting count can race with incrementing it in + * cpuidle_coupled_set_waiting, but that's OK. Worst case, some + * cpus will increment ready_count and then spin until they + * notice that this cpu has cleared it's requested_state. + */ + atomic_dec(&coupled->ready_waiting_counts); + + coupled->requested_state[cpu] = CPUIDLE_COUPLED_NOT_IDLE; +} + +/** + * cpuidle_coupled_set_done - mark this cpu as leaving the ready loop + * @cpu: the current cpu + * @coupled: the struct coupled that contains the current cpu + * + * Marks this cpu as no longer in the ready and waiting loops. Decrements + * the waiting count first to prevent another cpu looping back in and seeing + * this cpu as waiting just before it exits idle. + */ +static void cpuidle_coupled_set_done(int cpu, struct cpuidle_coupled *coupled) +{ + cpuidle_coupled_set_not_waiting(cpu, coupled); + atomic_sub(MAX_WAITING_CPUS, &coupled->ready_waiting_counts); +} + +/** + * cpuidle_coupled_clear_pokes - spin until the poke interrupt is processed + * @cpu - this cpu + * + * Turns on interrupts and spins until any outstanding poke interrupts have + * been processed and the poke bit has been cleared. + * + * Other interrupts may also be processed while interrupts are enabled, so + * need_resched() must be tested after turning interrupts off again to make sure + * the interrupt didn't schedule work that should take the cpu out of idle. + * + * Returns 0 if need_resched was false, -EINTR if need_resched was true. + */ +static int cpuidle_coupled_clear_pokes(int cpu) +{ + local_irq_enable(); + while (cpumask_test_cpu(cpu, &cpuidle_coupled_poked_mask)) + cpu_relax(); + local_irq_disable(); + + return need_resched() ? -EINTR : 0; +} + +/** + * cpuidle_enter_state_coupled - attempt to enter a state with coupled cpus + * @dev: struct cpuidle_device for the current cpu + * @drv: struct cpuidle_driver for the platform + * @next_state: index of the requested state in drv->states + * + * Coordinate with coupled cpus to enter the target state. This is a two + * stage process. In the first stage, the cpus are operating independently, + * and may call into cpuidle_enter_state_coupled at completely different times. + * To save as much power as possible, the first cpus to call this function will + * go to an intermediate state (the cpuidle_device's safe state), and wait for + * all the other cpus to call this function. Once all coupled cpus are idle, + * the second stage will start. Each coupled cpu will spin until all cpus have + * guaranteed that they will call the target_state. + * + * This function must be called with interrupts disabled. It may enable + * interrupts while preparing for idle, and it will always return with + * interrupts enabled. + */ +int cpuidle_enter_state_coupled(struct cpuidle_device *dev, + struct cpuidle_driver *drv, int next_state) +{ + int entered_state = -1; + struct cpuidle_coupled *coupled = dev->coupled; + + if (!coupled) + return -EINVAL; + + while (coupled->prevent) { + if (cpuidle_coupled_clear_pokes(dev->cpu)) { + local_irq_enable(); + return entered_state; + } + entered_state = cpuidle_enter_state(dev, drv, + dev->safe_state_index); + } + + /* Read barrier ensures online_count is read after prevent is cleared */ + smp_rmb(); + + cpuidle_coupled_set_waiting(dev->cpu, coupled, next_state); + +retry: + /* + * Wait for all coupled cpus to be idle, using the deepest state + * allowed for a single cpu. + */ + while (!cpuidle_coupled_cpus_waiting(coupled)) { + if (cpuidle_coupled_clear_pokes(dev->cpu)) { + cpuidle_coupled_set_not_waiting(dev->cpu, coupled); + goto out; + } + + if (coupled->prevent) { + cpuidle_coupled_set_not_waiting(dev->cpu, coupled); + goto out; + } + + entered_state = cpuidle_enter_state(dev, drv, + dev->safe_state_index); + } + + if (cpuidle_coupled_clear_pokes(dev->cpu)) { + cpuidle_coupled_set_not_waiting(dev->cpu, coupled); + goto out; + } + + /* + * All coupled cpus are probably idle. There is a small chance that + * one of the other cpus just became active. Increment the ready count, + * and spin until all coupled cpus have incremented the counter. Once a + * cpu has incremented the ready counter, it cannot abort idle and must + * spin until either all cpus have incremented the ready counter, or + * another cpu leaves idle and decrements the waiting counter. + */ + + cpuidle_coupled_set_ready(coupled); + while (!cpuidle_coupled_cpus_ready(coupled)) { + /* Check if any other cpus bailed out of idle. */ + if (!cpuidle_coupled_cpus_waiting(coupled)) + if (!cpuidle_coupled_set_not_ready(coupled)) + goto retry; + + cpu_relax(); + } + + /* all cpus have acked the coupled state */ + next_state = cpuidle_coupled_get_state(dev, coupled); + + entered_state = cpuidle_enter_state(dev, drv, next_state); + + cpuidle_coupled_set_done(dev->cpu, coupled); + +out: + /* + * Normal cpuidle states are expected to return with irqs enabled. + * That leads to an inefficiency where a cpu receiving an interrupt + * that brings it out of idle will process that interrupt before + * exiting the idle enter function and decrementing ready_count. All + * other cpus will need to spin waiting for the cpu that is processing + * the interrupt. If the driver returns with interrupts disabled, + * all other cpus will loop back into the safe idle state instead of + * spinning, saving power. + * + * Calling local_irq_enable here allows coupled states to return with + * interrupts disabled, but won't cause problems for drivers that + * exit with interrupts enabled. + */ + local_irq_enable(); + + /* + * Wait until all coupled cpus have exited idle. There is no risk that + * a cpu exits and re-enters the ready state because this cpu has + * already decremented its waiting_count. + */ + while (!cpuidle_coupled_no_cpus_ready(coupled)) + cpu_relax(); + + return entered_state; +} + +static void cpuidle_coupled_update_online_cpus(struct cpuidle_coupled *coupled) +{ + cpumask_t cpus; + cpumask_and(&cpus, cpu_online_mask, &coupled->coupled_cpus); + coupled->online_count = cpumask_weight(&cpus); +} + +/** + * cpuidle_coupled_register_device - register a coupled cpuidle device + * @dev: struct cpuidle_device for the current cpu + * + * Called from cpuidle_register_device to handle coupled idle init. Finds the + * cpuidle_coupled struct for this set of coupled cpus, or creates one if none + * exists yet. + */ +int cpuidle_coupled_register_device(struct cpuidle_device *dev) +{ + int cpu; + struct cpuidle_device *other_dev; + struct call_single_data *csd; + struct cpuidle_coupled *coupled; + + if (cpumask_empty(&dev->coupled_cpus)) + return 0; + + for_each_cpu_mask(cpu, dev->coupled_cpus) { + other_dev = per_cpu(cpuidle_devices, cpu); + if (other_dev && other_dev->coupled) { + coupled = other_dev->coupled; + goto have_coupled; + } + } + + /* No existing coupled info found, create a new one */ + coupled = kzalloc(sizeof(struct cpuidle_coupled), GFP_KERNEL); + if (!coupled) + return -ENOMEM; + + coupled->coupled_cpus = dev->coupled_cpus; + +have_coupled: + dev->coupled = coupled; + if (WARN_ON(!cpumask_equal(&dev->coupled_cpus, &coupled->coupled_cpus))) + coupled->prevent++; + + cpuidle_coupled_update_online_cpus(coupled); + + coupled->refcnt++; + + csd = &per_cpu(cpuidle_coupled_poke_cb, dev->cpu); + csd->func = cpuidle_coupled_poked; + csd->info = (void *)(unsigned long)dev->cpu; + + return 0; +} + +/** + * cpuidle_coupled_unregister_device - unregister a coupled cpuidle device + * @dev: struct cpuidle_device for the current cpu + * + * Called from cpuidle_unregister_device to tear down coupled idle. Removes the + * cpu from the coupled idle set, and frees the cpuidle_coupled_info struct if + * this was the last cpu in the set. + */ +void cpuidle_coupled_unregister_device(struct cpuidle_device *dev) +{ + struct cpuidle_coupled *coupled = dev->coupled; + + if (cpumask_empty(&dev->coupled_cpus)) + return; + + if (--coupled->refcnt) + kfree(coupled); + dev->coupled = NULL; +} + +/** + * cpuidle_coupled_prevent_idle - prevent cpus from entering a coupled state + * @coupled: the struct coupled that contains the cpu that is changing state + * + * Disables coupled cpuidle on a coupled set of cpus. Used to ensure that + * cpu_online_mask doesn't change while cpus are coordinating coupled idle. + */ +static void cpuidle_coupled_prevent_idle(struct cpuidle_coupled *coupled) +{ + int cpu = get_cpu(); + + /* Force all cpus out of the waiting loop. */ + coupled->prevent++; + cpuidle_coupled_poke_others(cpu, coupled); + put_cpu(); + while (!cpuidle_coupled_no_cpus_waiting(coupled)) + cpu_relax(); +} + +/** + * cpuidle_coupled_allow_idle - allows cpus to enter a coupled state + * @coupled: the struct coupled that contains the cpu that is changing state + * + * Enables coupled cpuidle on a coupled set of cpus. Used to ensure that + * cpu_online_mask doesn't change while cpus are coordinating coupled idle. + */ +static void cpuidle_coupled_allow_idle(struct cpuidle_coupled *coupled) +{ + int cpu = get_cpu(); + + /* + * Write barrier ensures readers see the new online_count when they + * see prevent == 0. + */ + smp_wmb(); + coupled->prevent--; + /* Force cpus out of the prevent loop. */ + cpuidle_coupled_poke_others(cpu, coupled); + put_cpu(); +} + +/** + * cpuidle_coupled_cpu_notify - notifier called during hotplug transitions + * @nb: notifier block + * @action: hotplug transition + * @hcpu: target cpu number + * + * Called when a cpu is brought on or offline using hotplug. Updates the + * coupled cpu set appropriately + */ +static int cpuidle_coupled_cpu_notify(struct notifier_block *nb, + unsigned long action, void *hcpu) +{ + int cpu = (unsigned long)hcpu; + struct cpuidle_device *dev; + + mutex_lock(&cpuidle_lock); + + dev = per_cpu(cpuidle_devices, cpu); + if (!dev->coupled) + goto out; + + switch (action & ~CPU_TASKS_FROZEN) { + case CPU_UP_PREPARE: + case CPU_DOWN_PREPARE: + cpuidle_coupled_prevent_idle(dev->coupled); + break; + case CPU_ONLINE: + case CPU_DEAD: + cpuidle_coupled_update_online_cpus(dev->coupled); + /* Fall through */ + case CPU_UP_CANCELED: + case CPU_DOWN_FAILED: + cpuidle_coupled_allow_idle(dev->coupled); + break; + } + +out: + mutex_unlock(&cpuidle_lock); + return NOTIFY_OK; +} + +static struct notifier_block cpuidle_coupled_cpu_notifier = { + .notifier_call = cpuidle_coupled_cpu_notify, +}; + +static int __init cpuidle_coupled_init(void) +{ + return register_cpu_notifier(&cpuidle_coupled_cpu_notifier); +} +core_initcall(cpuidle_coupled_init); |