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370 lines
11 KiB
370 lines
11 KiB
// SPDX-License-Identifier: GPL-2.0 |
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/* |
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* Copyright 2018 Linaro Limited |
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* |
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* Author: Daniel Lezcano <[email protected]> |
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* |
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* The idle injection framework provides a way to force CPUs to enter idle |
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* states for a specified fraction of time over a specified period. |
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* |
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* It relies on the smpboot kthreads feature providing common code for CPU |
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* hotplug and thread [un]parking. |
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* |
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* All of the kthreads used for idle injection are created at init time. |
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* |
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* Next, the users of the the idle injection framework provide a cpumask via |
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* its register function. The kthreads will be synchronized with respect to |
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* this cpumask. |
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* |
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* The idle + run duration is specified via separate helpers and that allows |
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* idle injection to be started. |
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* |
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* The idle injection kthreads will call play_idle_precise() with the idle |
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* duration and max allowed latency specified as per the above. |
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* |
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* After all of them have been woken up, a timer is set to start the next idle |
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* injection cycle. |
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* |
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* The timer interrupt handler will wake up the idle injection kthreads for |
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* all of the CPUs in the cpumask provided by the user. |
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* |
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* Idle injection is stopped synchronously and no leftover idle injection |
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* kthread activity after its completion is guaranteed. |
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* |
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* It is up to the user of this framework to provide a lock for higher-level |
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* synchronization to prevent race conditions like starting idle injection |
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* while unregistering from the framework. |
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*/ |
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#define pr_fmt(fmt) "ii_dev: " fmt |
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#include <linux/cpu.h> |
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#include <linux/hrtimer.h> |
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#include <linux/kthread.h> |
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#include <linux/sched.h> |
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#include <linux/slab.h> |
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#include <linux/smpboot.h> |
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#include <linux/idle_inject.h> |
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#include <uapi/linux/sched/types.h> |
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/** |
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* struct idle_inject_thread - task on/off switch structure |
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* @tsk: task injecting the idle cycles |
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* @should_run: whether or not to run the task (for the smpboot kthread API) |
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*/ |
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struct idle_inject_thread { |
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struct task_struct *tsk; |
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int should_run; |
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}; |
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/** |
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* struct idle_inject_device - idle injection data |
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* @timer: idle injection period timer |
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* @idle_duration_us: duration of CPU idle time to inject |
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* @run_duration_us: duration of CPU run time to allow |
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* @latency_us: max allowed latency |
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* @cpumask: mask of CPUs affected by idle injection |
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*/ |
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struct idle_inject_device { |
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struct hrtimer timer; |
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unsigned int idle_duration_us; |
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unsigned int run_duration_us; |
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unsigned int latency_us; |
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unsigned long cpumask[]; |
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}; |
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static DEFINE_PER_CPU(struct idle_inject_thread, idle_inject_thread); |
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static DEFINE_PER_CPU(struct idle_inject_device *, idle_inject_device); |
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/** |
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* idle_inject_wakeup - Wake up idle injection threads |
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* @ii_dev: target idle injection device |
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* |
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* Every idle injection task associated with the given idle injection device |
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* and running on an online CPU will be woken up. |
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*/ |
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static void idle_inject_wakeup(struct idle_inject_device *ii_dev) |
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{ |
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struct idle_inject_thread *iit; |
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unsigned int cpu; |
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for_each_cpu_and(cpu, to_cpumask(ii_dev->cpumask), cpu_online_mask) { |
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iit = per_cpu_ptr(&idle_inject_thread, cpu); |
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iit->should_run = 1; |
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wake_up_process(iit->tsk); |
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} |
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} |
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/** |
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* idle_inject_timer_fn - idle injection timer function |
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* @timer: idle injection hrtimer |
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* |
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* This function is called when the idle injection timer expires. It wakes up |
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* idle injection tasks associated with the timer and they, in turn, invoke |
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* play_idle_precise() to inject a specified amount of CPU idle time. |
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* |
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* Return: HRTIMER_RESTART. |
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*/ |
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static enum hrtimer_restart idle_inject_timer_fn(struct hrtimer *timer) |
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{ |
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unsigned int duration_us; |
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struct idle_inject_device *ii_dev = |
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container_of(timer, struct idle_inject_device, timer); |
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duration_us = READ_ONCE(ii_dev->run_duration_us); |
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duration_us += READ_ONCE(ii_dev->idle_duration_us); |
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idle_inject_wakeup(ii_dev); |
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hrtimer_forward_now(timer, ns_to_ktime(duration_us * NSEC_PER_USEC)); |
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return HRTIMER_RESTART; |
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} |
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/** |
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* idle_inject_fn - idle injection work function |
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* @cpu: the CPU owning the task |
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* |
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* This function calls play_idle_precise() to inject a specified amount of CPU |
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* idle time. |
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*/ |
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static void idle_inject_fn(unsigned int cpu) |
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{ |
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struct idle_inject_device *ii_dev; |
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struct idle_inject_thread *iit; |
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ii_dev = per_cpu(idle_inject_device, cpu); |
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iit = per_cpu_ptr(&idle_inject_thread, cpu); |
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/* |
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* Let the smpboot main loop know that the task should not run again. |
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*/ |
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iit->should_run = 0; |
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play_idle_precise(READ_ONCE(ii_dev->idle_duration_us) * NSEC_PER_USEC, |
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READ_ONCE(ii_dev->latency_us) * NSEC_PER_USEC); |
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} |
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/** |
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* idle_inject_set_duration - idle and run duration update helper |
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* @run_duration_us: CPU run time to allow in microseconds |
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* @idle_duration_us: CPU idle time to inject in microseconds |
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*/ |
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void idle_inject_set_duration(struct idle_inject_device *ii_dev, |
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unsigned int run_duration_us, |
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unsigned int idle_duration_us) |
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{ |
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if (run_duration_us && idle_duration_us) { |
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WRITE_ONCE(ii_dev->run_duration_us, run_duration_us); |
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WRITE_ONCE(ii_dev->idle_duration_us, idle_duration_us); |
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} |
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} |
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/** |
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* idle_inject_get_duration - idle and run duration retrieval helper |
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* @run_duration_us: memory location to store the current CPU run time |
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* @idle_duration_us: memory location to store the current CPU idle time |
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*/ |
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void idle_inject_get_duration(struct idle_inject_device *ii_dev, |
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unsigned int *run_duration_us, |
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unsigned int *idle_duration_us) |
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{ |
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*run_duration_us = READ_ONCE(ii_dev->run_duration_us); |
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*idle_duration_us = READ_ONCE(ii_dev->idle_duration_us); |
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} |
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/** |
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* idle_inject_set_latency - set the maximum latency allowed |
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* @latency_us: set the latency requirement for the idle state |
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*/ |
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void idle_inject_set_latency(struct idle_inject_device *ii_dev, |
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unsigned int latency_us) |
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{ |
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WRITE_ONCE(ii_dev->latency_us, latency_us); |
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} |
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/** |
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* idle_inject_start - start idle injections |
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* @ii_dev: idle injection control device structure |
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* |
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* The function starts idle injection by first waking up all of the idle |
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* injection kthreads associated with @ii_dev to let them inject CPU idle time |
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* sets up a timer to start the next idle injection period. |
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* |
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* Return: -EINVAL if the CPU idle or CPU run time is not set or 0 on success. |
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*/ |
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int idle_inject_start(struct idle_inject_device *ii_dev) |
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{ |
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unsigned int idle_duration_us = READ_ONCE(ii_dev->idle_duration_us); |
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unsigned int run_duration_us = READ_ONCE(ii_dev->run_duration_us); |
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if (!idle_duration_us || !run_duration_us) |
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return -EINVAL; |
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pr_debug("Starting injecting idle cycles on CPUs '%*pbl'\n", |
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cpumask_pr_args(to_cpumask(ii_dev->cpumask))); |
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idle_inject_wakeup(ii_dev); |
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hrtimer_start(&ii_dev->timer, |
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ns_to_ktime((idle_duration_us + run_duration_us) * |
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NSEC_PER_USEC), |
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HRTIMER_MODE_REL); |
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return 0; |
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} |
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/** |
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* idle_inject_stop - stops idle injections |
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* @ii_dev: idle injection control device structure |
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* |
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* The function stops idle injection and waits for the threads to finish work. |
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* If CPU idle time is being injected when this function runs, then it will |
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* wait until the end of the cycle. |
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* |
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* When it returns, there is no more idle injection kthread activity. The |
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* kthreads are scheduled out and the periodic timer is off. |
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*/ |
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void idle_inject_stop(struct idle_inject_device *ii_dev) |
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{ |
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struct idle_inject_thread *iit; |
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unsigned int cpu; |
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pr_debug("Stopping idle injection on CPUs '%*pbl'\n", |
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cpumask_pr_args(to_cpumask(ii_dev->cpumask))); |
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hrtimer_cancel(&ii_dev->timer); |
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/* |
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* Stopping idle injection requires all of the idle injection kthreads |
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* associated with the given cpumask to be parked and stay that way, so |
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* prevent CPUs from going online at this point. Any CPUs going online |
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* after the loop below will be covered by clearing the should_run flag |
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* that will cause the smpboot main loop to schedule them out. |
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*/ |
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cpu_hotplug_disable(); |
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/* |
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* Iterate over all (online + offline) CPUs here in case one of them |
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* goes offline with the should_run flag set so as to prevent its idle |
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* injection kthread from running when the CPU goes online again after |
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* the ii_dev has been freed. |
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*/ |
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for_each_cpu(cpu, to_cpumask(ii_dev->cpumask)) { |
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iit = per_cpu_ptr(&idle_inject_thread, cpu); |
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iit->should_run = 0; |
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wait_task_inactive(iit->tsk, 0); |
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} |
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cpu_hotplug_enable(); |
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} |
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/** |
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* idle_inject_setup - prepare the current task for idle injection |
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* @cpu: not used |
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* |
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* Called once, this function is in charge of setting the current task's |
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* scheduler parameters to make it an RT task. |
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*/ |
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static void idle_inject_setup(unsigned int cpu) |
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{ |
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sched_set_fifo(current); |
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} |
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/** |
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* idle_inject_should_run - function helper for the smpboot API |
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* @cpu: CPU the kthread is running on |
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* |
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* Return: whether or not the thread can run. |
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*/ |
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static int idle_inject_should_run(unsigned int cpu) |
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{ |
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struct idle_inject_thread *iit = |
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per_cpu_ptr(&idle_inject_thread, cpu); |
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return iit->should_run; |
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} |
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/** |
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* idle_inject_register - initialize idle injection on a set of CPUs |
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* @cpumask: CPUs to be affected by idle injection |
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* |
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* This function creates an idle injection control device structure for the |
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* given set of CPUs and initializes the timer associated with it. It does not |
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* start any injection cycles. |
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* |
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* Return: NULL if memory allocation fails, idle injection control device |
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* pointer on success. |
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*/ |
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struct idle_inject_device *idle_inject_register(struct cpumask *cpumask) |
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{ |
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struct idle_inject_device *ii_dev; |
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int cpu, cpu_rb; |
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ii_dev = kzalloc(sizeof(*ii_dev) + cpumask_size(), GFP_KERNEL); |
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if (!ii_dev) |
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return NULL; |
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cpumask_copy(to_cpumask(ii_dev->cpumask), cpumask); |
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hrtimer_init(&ii_dev->timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL); |
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ii_dev->timer.function = idle_inject_timer_fn; |
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ii_dev->latency_us = UINT_MAX; |
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for_each_cpu(cpu, to_cpumask(ii_dev->cpumask)) { |
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if (per_cpu(idle_inject_device, cpu)) { |
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pr_err("cpu%d is already registered\n", cpu); |
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goto out_rollback; |
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} |
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per_cpu(idle_inject_device, cpu) = ii_dev; |
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} |
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return ii_dev; |
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out_rollback: |
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for_each_cpu(cpu_rb, to_cpumask(ii_dev->cpumask)) { |
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if (cpu == cpu_rb) |
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break; |
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per_cpu(idle_inject_device, cpu_rb) = NULL; |
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} |
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kfree(ii_dev); |
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return NULL; |
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} |
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/** |
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* idle_inject_unregister - unregister idle injection control device |
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* @ii_dev: idle injection control device to unregister |
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* |
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* The function stops idle injection for the given control device, |
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* unregisters its kthreads and frees memory allocated when that device was |
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* created. |
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*/ |
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void idle_inject_unregister(struct idle_inject_device *ii_dev) |
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{ |
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unsigned int cpu; |
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idle_inject_stop(ii_dev); |
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for_each_cpu(cpu, to_cpumask(ii_dev->cpumask)) |
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per_cpu(idle_inject_device, cpu) = NULL; |
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kfree(ii_dev); |
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} |
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static struct smp_hotplug_thread idle_inject_threads = { |
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.store = &idle_inject_thread.tsk, |
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.setup = idle_inject_setup, |
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.thread_fn = idle_inject_fn, |
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.thread_comm = "idle_inject/%u", |
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.thread_should_run = idle_inject_should_run, |
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}; |
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static int __init idle_inject_init(void) |
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{ |
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return smpboot_register_percpu_thread(&idle_inject_threads); |
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} |
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early_initcall(idle_inject_init);
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