标签：kernel stopper thread work stop migration cpu
migration/* kernel thread用途
console:/proc/13 # ps -Af |grep migration root 13 2 0 02:29:43 ? 00:00:00 [migration/0] root 16 2 0 02:29:43 ? 00:00:00 [migration/1] root 21 2 0 02:29:43 ? 00:00:00 [migration/2] root 26 2 0 02:29:43 ? 00:00:00 [migration/3]
内核线程migration/*是一个工作线程，可以将工作发给它让它执行，将工作发给它有两种API，如下，这个两个API的差异是一个会等这个work function调用完成，它有一个完成量（completion），可以理解为同步方式；而另外一个是不等它完成，queue到migration/*线程的work queue并wake它就会返回，可以理解为异步方式。这两个API会根据其cpu参数找到这个cpu的per cpu变量struct cpu_stopper，然后将此work加到此cpu_stopper变量的works链表上
这两个API参数含义：
cpu: 表示这个work你要给与这个cpu绑定的migration thread去处理
fn: work function，work所做的事情；
arg：传给fn的参数，即fn(arg):
int stop_one_cpu(unsigned int cpu, cpu_stop_fn_t fn, void *arg);
bool stop_one_cpu_nowait(unsigned int cpu, cpu_stop_fn_t fn, void *arg,
struct cpu_stop_work *work_buf);
至于migration/*线程是怎么创建的以及有什么特性描述如下：
它是和cpu core绑定的，每个cpu core都会有这样一个线程，另外这些kernel thread sched class是stop_sched_class，sched policy是SCHED_FIFO(RT)，priority是99，是RT priority里最低的优先级。在cpu_stop_threads.cpu_stop_create函数里设置此thread的sched class、policy、priority：
kernel/sched/core.c
void sched_set_stop_task(int cpu, struct task_struct *stop)
{
struct sched_param param = { .sched_priority = MAX_RT_PRIO - 1 };
struct task_struct *old_stop = cpu_rq(cpu)->stop;
if (stop) {
/*
* Make it appear like a SCHED_FIFO task, its something
* userspace knows about and won't get confused about.
*
* Also, it will make PI more or less work without too
* much confusion -- but then, stop work should not
* rely on PI working anyway.
*/
sched_setscheduler_nocheck(stop, SCHED_FIFO, ¶m);
stop->sched_class = &stop_sched_class;
}
cpu_rq(cpu)->stop = stop;
if (old_stop) {
/*
* Reset it back to a normal scheduling class so that
* it can die in pieces.
*/
old_stop->sched_class = &rt_sched_class;
}
}
4.19/kernel/stop_machine.c
static void cpu_stop_create(unsigned int cpu)
{
sched_set_stop_task(cpu, per_cpu(cpu_stopper.thread, cpu));
}
static struct smp_hotplug_thread cpu_stop_threads = {
.store = &cpu_stopper.thread,
.thread_should_run = cpu_stop_should_run,
.thread_fn = cpu_stopper_thread,
.thread_comm = "migration/%u",
.create = cpu_stop_create,
.park = cpu_stop_park,
.selfparking = true,
};
static int __init cpu_stop_init(void)
{
unsigned int cpu;
for_each_possible_cpu(cpu) {
struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
raw_spin_lock_init(&stopper->lock);
INIT_LIST_HEAD(&stopper->works);
}
BUG_ON(smpboot_register_percpu_thread(&cpu_stop_threads));
stop_machine_unpark(raw_smp_processor_id());
stop_machine_initialized = true;
return 0;
}
early_initcall(cpu_stop_init);
使用stop_one_cpu()或者stop_one_cpu_nowait()将work发给目标migration线程并wake它后，migration线程将会wakeup执行cpu_stopper_thread()，从works链表中取出work，并执行其work function：
static void cpu_stopper_thread(unsigned int cpu)
{
struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
struct cpu_stop_work *work;
repeat:
work = NULL;
raw_spin_lock_irq(&stopper->lock);
if (!list_empty(&stopper->works)) {
work = list_first_entry(&stopper->works,
struct cpu_stop_work, list);
list_del_init(&work->list);
}
raw_spin_unlock_irq(&stopper->lock);
if (work) {
cpu_stop_fn_t fn = work->fn;
void *arg = work->arg;
struct cpu_stop_done *done = work->done;
int ret;
/* cpu stop callbacks must not sleep, make in_atomic() == T */
preempt_count_inc();
ret = fn(arg);
if (done) {
if (ret)
done->ret = ret;
cpu_stop_signal_done(done);
}
preempt_count_dec();
WARN_ONCE(preempt_count(),
"cpu_stop: %pf(%p) leaked preempt count\n", fn, arg);
goto repeat;
}
}
标签：kernel,stopper,thread,work,stop,migration,cpu 来源： https://www.cnblogs.com/aspirs/p/15705964.html
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