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Commit 674311d5 authored by Nick Piggin's avatar Nick Piggin Committed by Linus Torvalds
Browse files

[PATCH] sched: RCU domains 



One of the problems with the multilevel balance-on-fork/exec is that it needs
to jump through hoops to satisfy sched-domain's locking semantics (that is,
you may traverse your own domain when not preemptable, and you may traverse
others' domains when holding their runqueue lock).

balance-on-exec had to potentially migrate between more than one CPU before
finding a final CPU to migrate to, and balance-on-fork needed to potentially
take multiple runqueue locks.

So bite the bullet and make sched-domains go completely RCU.  This actually
simplifies the code quite a bit.

From: Ingo Molnar <mingo@elte.hu>

schedstats RCU fix, and a nice comment on for_each_domain, from Ingo.

Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
Signed-off-by: default avatarNick Piggin <nickpiggin@yahoo.com.au>
Acked-by: default avatarIngo Molnar <mingo@elte.hu>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent 3dbd5342

kernel/sched.c

+15 −45
Original line number Diff line number Diff line
@@ -260,8 +260,15 @@ struct runqueue { 


static DEFINE_PER_CPU(struct runqueue, runqueues);



/*

 * The domain tree (rq->sd) is protected by RCU's quiescent state transition.

 * See update_sched_domains: synchronize_kernel for details.

 *

 * The domain tree of any CPU may only be accessed from within

 * preempt-disabled sections.

 */

#define for_each_domain(cpu, domain) \

	for (domain = cpu_rq(cpu)->sd; domain; domain = domain->parent)

for (domain = rcu_dereference(cpu_rq(cpu)->sd); domain; domain = domain->parent)



#define cpu_rq(cpu)		(&per_cpu(runqueues, (cpu)))

#define this_rq()		(&__get_cpu_var(runqueues))
@@ -395,6 +402,7 @@ static int show_schedstat(struct seq_file *seq, void *v) 


#ifdef CONFIG_SMP

		/* domain-specific stats */

		preempt_disable();

		for_each_domain(cpu, sd) {

			enum idle_type itype;

			char mask_str[NR_CPUS];
@@ -419,6 +427,7 @@ static int show_schedstat(struct seq_file *seq, void *v) 
			    sd->sbf_cnt, sd->sbf_balanced, sd->sbf_pushed,

			    sd->ttwu_wake_remote, sd->ttwu_move_affine, sd->ttwu_move_balance);

		}

		preempt_enable();

#endif

	}

	return 0;
@@ -824,22 +833,12 @@ inline int task_curr(const task_t *p) 
}



#ifdef CONFIG_SMP

enum request_type {

	REQ_MOVE_TASK,

	REQ_SET_DOMAIN,

};



typedef struct {

	struct list_head list;

	enum request_type type;



	/* For REQ_MOVE_TASK */

	task_t *task;

	int dest_cpu;



	/* For REQ_SET_DOMAIN */

	struct sched_domain *sd;



	struct completion done;

} migration_req_t;
@@ -861,7 +860,6 @@ static int migrate_task(task_t *p, int dest_cpu, migration_req_t *req) 
	}



	init_completion(&req->done);

	req->type = REQ_MOVE_TASK;

	req->task = p;

	req->dest_cpu = dest_cpu;

	list_add(&req->list, &rq->migration_queue);
@@ -4378,17 +4376,9 @@ static int migration_thread(void * data) 
		req = list_entry(head->next, migration_req_t, list);

		list_del_init(head->next);



		if (req->type == REQ_MOVE_TASK) {

		spin_unlock(&rq->lock);

		__migrate_task(req->task, cpu, req->dest_cpu);

		local_irq_enable();

		} else if (req->type == REQ_SET_DOMAIN) {

			rq->sd = req->sd;

			spin_unlock_irq(&rq->lock);

		} else {

			spin_unlock_irq(&rq->lock);

			WARN_ON(1);

		}



		complete(&req->done);

	}
@@ -4619,7 +4609,6 @@ static int migration_call(struct notifier_block *nfb, unsigned long action, 
			migration_req_t *req;

			req = list_entry(rq->migration_queue.next,

					 migration_req_t, list);

			BUG_ON(req->type != REQ_MOVE_TASK);

			list_del_init(&req->list);

			complete(&req->done);

		}
@@ -4800,10 +4789,7 @@ static int __devinit sd_parent_degenerate(struct sched_domain *sd, 
 */

void __devinit cpu_attach_domain(struct sched_domain *sd, int cpu)

{

	migration_req_t req;

	unsigned long flags;

	runqueue_t *rq = cpu_rq(cpu);

	int local = 1;

	struct sched_domain *tmp;



	/* Remove the sched domains which do not contribute to scheduling. */
@@ -4820,24 +4806,7 @@ void __devinit cpu_attach_domain(struct sched_domain *sd, int cpu) 


	sched_domain_debug(sd, cpu);



	spin_lock_irqsave(&rq->lock, flags);



	if (cpu == smp_processor_id() || !cpu_online(cpu)) {

		rq->sd = sd;

	} else {

		init_completion(&req.done);

		req.type = REQ_SET_DOMAIN;

		req.sd = sd;

		list_add(&req.list, &rq->migration_queue);

		local = 0;

	}



	spin_unlock_irqrestore(&rq->lock, flags);



	if (!local) {

		wake_up_process(rq->migration_thread);

		wait_for_completion(&req.done);

	}

	rcu_assign_pointer(rq->sd, sd);

}



/* cpus with isolated domains */
@@ -5112,6 +5081,7 @@ static int update_sched_domains(struct notifier_block *nfb, 
	case CPU_DOWN_PREPARE:

		for_each_online_cpu(i)

			cpu_attach_domain(NULL, i);

		synchronize_kernel();

		arch_destroy_sched_domains();

		return NOTIFY_OK;