357 lines
10 KiB
C
357 lines
10 KiB
C
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// 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 <daniel.lezcano@linaro.org>
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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() with the idle duration
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* 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 <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_ms: duration of CPU idle time to inject
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* @run_duration_ms: duration of CPU run time to allow
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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_ms;
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unsigned int run_duration_ms;
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unsigned long int cpumask[0];
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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() 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_ms;
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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_ms = READ_ONCE(ii_dev->run_duration_ms);
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duration_ms += READ_ONCE(ii_dev->idle_duration_ms);
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idle_inject_wakeup(ii_dev);
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hrtimer_forward_now(timer, ms_to_ktime(duration_ms));
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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() to inject a specified amount of CPU idle
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* 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(READ_ONCE(ii_dev->idle_duration_ms));
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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_ms: CPU run time to allow in milliseconds
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* @idle_duration_ms: CPU idle time to inject in milliseconds
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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_ms,
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unsigned int idle_duration_ms)
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{
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if (run_duration_ms && idle_duration_ms) {
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WRITE_ONCE(ii_dev->run_duration_ms, run_duration_ms);
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WRITE_ONCE(ii_dev->idle_duration_ms, idle_duration_ms);
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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_ms: memory location to store the current CPU run time
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* @idle_duration_ms: 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_ms,
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unsigned int *idle_duration_ms)
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{
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*run_duration_ms = READ_ONCE(ii_dev->run_duration_ms);
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*idle_duration_ms = READ_ONCE(ii_dev->idle_duration_ms);
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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_ms = READ_ONCE(ii_dev->idle_duration_ms);
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unsigned int run_duration_ms = READ_ONCE(ii_dev->run_duration_ms);
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if (!idle_duration_ms || !run_duration_ms)
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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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ms_to_ktime(idle_duration_ms + run_duration_ms),
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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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struct sched_param param = { .sched_priority = MAX_USER_RT_PRIO / 2 };
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sched_setscheduler(current, SCHED_FIFO, ¶m);
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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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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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