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
......@@ -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);
}
spin_unlock(&rq->lock);
__migrate_task(req->task, cpu, req->dest_cpu);
local_irq_enable();
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;
......
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