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cpuset子系统与cpu亲缘性设置sched_setaffinity

目前cpu亲缘性设置有两种方式:

  1. 通过sched_setaffinity()函数将进程绑定到某些cpu上运行
  2. 讲进程加入到cpuset控制组,通过修改cpuset.cpus参数来实现亲缘性设置

但是有一点需要注意的是,通过sched_setaffinity设置的cpu_mask不允许超出cpuset.cpus的范围,超出部分是无效的。

举例,进程A所在的cpuset控制组cpuset.cpus参数值是0,1,2,3,4,但是进程运行期间调用sched_setaffinity()修改cpu_mask为0,1,2,4,7。因为7并不在cpuset.cpus范围里,所以内核会把7忽略掉,最终进程只能在0,1,2,4这几个CPU上运行。

// linux-3.10.82/kernel/sched/core.c

long sched_setaffinity(pid_t pid, const struct cpumask *in_mask)
{
	cpumask_var_t cpus_allowed, new_mask;
	struct task_struct *p;
	int retval;

	get_online_cpus();
	rcu_read_lock();

	p = find_process_by_pid(pid);
	if (!p) {
		rcu_read_unlock();
		put_online_cpus();
		return -ESRCH;
	}

	/* Prevent p going away */
	get_task_struct(p);
	rcu_read_unlock();

	if (p->flags & PF_NO_SETAFFINITY) {
		retval = -EINVAL;
		goto out_put_task;
	}
	if (!alloc_cpumask_var(&cpus_allowed, GFP_KERNEL)) {
		retval = -ENOMEM;
		goto out_put_task;
	}
	if (!alloc_cpumask_var(&new_mask, GFP_KERNEL)) {
		retval = -ENOMEM;
		goto out_free_cpus_allowed;
	}
	retval = -EPERM;
	if (!check_same_owner(p)) {
		rcu_read_lock();
		if (!ns_capable(__task_cred(p)->user_ns, CAP_SYS_NICE)) {
			rcu_read_unlock();
			goto out_unlock;
		}
		rcu_read_unlock();
	}

	retval = security_task_setscheduler(p);
	if (retval)
		goto out_unlock;

	cpuset_cpus_allowed(p, cpus_allowed);
	cpumask_and(new_mask, in_mask, cpus_allowed);
again:
	retval = set_cpus_allowed_ptr(p, new_mask);

	if (!retval) {
		cpuset_cpus_allowed(p, cpus_allowed);
		if (!cpumask_subset(new_mask, cpus_allowed)) {
			/*
			 * We must have raced with a concurrent cpuset
			 * update. Just reset the cpus_allowed to the
			 * cpuset's cpus_allowed
			 */
			cpumask_copy(new_mask, cpus_allowed);
			goto again;
		}
	}
out_unlock:
	free_cpumask_var(new_mask);
out_free_cpus_allowed:
	free_cpumask_var(cpus_allowed);
out_put_task:
	put_task_struct(p);
	put_online_cpus();
	return retval;
}

如上所见,当调用sched_setaffinity系统调用时,内核会将in_mask与cpuset_cpus_allowed做一次与操作

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