How does Linux kernel migrate the process among multiple cores?

问题

Context:

Process-1 is executing on core-0. Core-1 is idle.

Now, process-1 uses sched_setaffinity() to change its CPU affinity as core-1.

Question:

Which kernel function(s) migrate the process-1 to execute on core-1?

回答1:

Here is the call sequence starting from the sched_setaffinity system call entry point in the kernel:

1. sys_sched_setaffinity.
2. sched_setaffinity.
3. __set_cpus_allowed_ptr.

In the last function, there are two cases as shown in the code at line 1101:

if (task_running(rq, p) || p->state == TASK_WAKING) {
    // ...
    stop_one_cpu(cpu_of(rq), migration_cpu_stop, &arg);
    // ...
} else if (task_on_rq_queued(p)) {
    rq = move_queued_task(rq, &rf, p, dest_cpu);
}

If the task to be migrated is currently running or waking up, then it is migrated by calling stop_one_cpu, which calls the following functions in order:

1. migration_cpu_stop.
2. __migrate_task.
3. move_queued_task.

The last function, move_queued_task, is the one that actually moves the task from the current runqueue to the target runqueue. Note that this is the same function that is called from the other branch of __set_cpus_allowed_ptr. That branch handles the case where the task is in any of the other states.

来源：https://stackoverflow.com/questions/49707124/how-does-linux-kernel-migrate-the-process-among-multiple-cores