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sched: Add p->pi_lock to task_rq_lock()

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In order to be able to call set_task_cpu() while either holding
p->pi_lock or task_rq(p)->lock we need to hold both locks in order to
stabilize task_rq().

This makes task_rq_lock() acquire both locks, and have
__task_rq_lock() validate that p->pi_lock is held. This increases the
locking overhead for most scheduler syscalls but allows reduction of
rq->lock contention for some scheduler hot paths (ttwu).

Reviewed-by: Frank Rowand <frank.rowand@am.sony.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Nick Piggin <npiggin@kernel.dk>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Link: http://lkml.kernel.org/r/20110405152729.232781355@chello.nl
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Peter Zijlstra 2011-04-05 17:23:51 +02:00 committed by Ingo Molnar
parent 2acca55ed9
commit 0122ec5b02
1 changed files with 47 additions and 56 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

103
kernel/sched.c
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@ -599,7 +599,7 @@ static inline int cpu_of(struct rq *rq)
* Return the group to which this tasks belongs.
*
* We use task_subsys_state_check() and extend the RCU verification
* with lockdep_is_held(&task_rq(p)->lock) because cpu_cgroup_attach()
* with lockdep_is_held(&p->pi_lock) because cpu_cgroup_attach()
* holds that lock for each task it moves into the cgroup. Therefore
* by holding that lock, we pin the task to the current cgroup.
*/
@ -609,7 +609,7 @@ static inline struct task_group *task_group(struct task_struct *p)
struct cgroup_subsys_state *css;
css = task_subsys_state_check(p, cpu_cgroup_subsys_id,
lockdep_is_held(&task_rq(p)->lock));
lockdep_is_held(&p->pi_lock));
tg = container_of(css, struct task_group, css);
return autogroup_task_group(p, tg);
@ -924,23 +924,15 @@ static inline void finish_lock_switch(struct rq *rq, struct task_struct *prev)
#endif /* __ARCH_WANT_UNLOCKED_CTXSW */
/*
* Check whether the task is waking, we use this to synchronize ->cpus_allowed
* against ttwu().
*/
static inline int task_is_waking(struct task_struct *p)
{
return unlikely(p->state == TASK_WAKING);
}
/*
* __task_rq_lock - lock the runqueue a given task resides on.
* Must be called interrupts disabled.
* __task_rq_lock - lock the rq @p resides on.
*/
static inline struct rq *__task_rq_lock(struct task_struct *p)
__acquires(rq->lock)
{
struct rq *rq;
lockdep_assert_held(&p->pi_lock);
for (;;) {
rq = task_rq(p);
raw_spin_lock(&rq->lock);
@ -951,22 +943,22 @@ static inline struct rq *__task_rq_lock(struct task_struct *p)
}
/*
* task_rq_lock - lock the runqueue a given task resides on and disable
* interrupts. Note the ordering: we can safely lookup the task_rq without
* explicitly disabling preemption.
* task_rq_lock - lock p->pi_lock and lock the rq @p resides on.
*/
static struct rq *task_rq_lock(struct task_struct *p, unsigned long *flags)
__acquires(p->pi_lock)
__acquires(rq->lock)
{
struct rq *rq;
for (;;) {
local_irq_save(*flags);
raw_spin_lock_irqsave(&p->pi_lock, *flags);
rq = task_rq(p);
raw_spin_lock(&rq->lock);
if (likely(rq == task_rq(p)))
return rq;
raw_spin_unlock_irqrestore(&rq->lock, *flags);
raw_spin_unlock(&rq->lock);
raw_spin_unlock_irqrestore(&p->pi_lock, *flags);
}
}
@ -976,10 +968,13 @@ static void __task_rq_unlock(struct rq *rq)
raw_spin_unlock(&rq->lock);
}
static inline void task_rq_unlock(struct rq *rq, unsigned long *flags)
static inline void
task_rq_unlock(struct rq *rq, struct task_struct *p, unsigned long *flags)
__releases(rq->lock)
__releases(p->pi_lock)
{
raw_spin_unlock_irqrestore(&rq->lock, *flags);
raw_spin_unlock(&rq->lock);
raw_spin_unlock_irqrestore(&p->pi_lock, *flags);
}
/*
@ -2175,6 +2170,11 @@ void set_task_cpu(struct task_struct *p, unsigned int new_cpu)
*/
WARN_ON_ONCE(p->state != TASK_RUNNING && p->state != TASK_WAKING &&
!(task_thread_info(p)->preempt_count & PREEMPT_ACTIVE));
#ifdef CONFIG_LOCKDEP
WARN_ON_ONCE(debug_locks && !(lockdep_is_held(&p->pi_lock) ||
lockdep_is_held(&task_rq(p)->lock)));
#endif
#endif
trace_sched_migrate_task(p, new_cpu);
@ -2270,7 +2270,7 @@ unsigned long wait_task_inactive(struct task_struct *p, long match_state)
ncsw = 0;
if (!match_state || p->state == match_state)
ncsw = p->nvcsw | LONG_MIN; /* sets MSB */
task_rq_unlock(rq, &flags);
task_rq_unlock(rq, p, &flags);
/*
* If it changed from the expected state, bail out now.
@ -2652,6 +2652,7 @@ static void __sched_fork(struct task_struct *p)
*/
void sched_fork(struct task_struct *p, int clone_flags)
{
unsigned long flags;
int cpu = get_cpu();
__sched_fork(p);
@ -2702,9 +2703,9 @@ void sched_fork(struct task_struct *p, int clone_flags)
*
* Silence PROVE_RCU.
*/
rcu_read_lock();
raw_spin_lock_irqsave(&p->pi_lock, flags);
set_task_cpu(p, cpu);
rcu_read_unlock();
raw_spin_unlock_irqrestore(&p->pi_lock, flags);
#if defined(CONFIG_SCHEDSTATS) || defined(CONFIG_TASK_DELAY_ACCT)
if (likely(sched_info_on()))
@ -2753,7 +2754,7 @@ void wake_up_new_task(struct task_struct *p, unsigned long clone_flags)
set_task_cpu(p, cpu);
p->state = TASK_RUNNING;
task_rq_unlock(rq, &flags);
task_rq_unlock(rq, p, &flags);
#endif
rq = task_rq_lock(p, &flags);
@ -2765,7 +2766,7 @@ void wake_up_new_task(struct task_struct *p, unsigned long clone_flags)
if (p->sched_class->task_woken)
p->sched_class->task_woken(rq, p);
#endif
task_rq_unlock(rq, &flags);
task_rq_unlock(rq, p, &flags);
put_cpu();
}
@ -3490,12 +3491,12 @@ void sched_exec(void)
likely(cpu_active(dest_cpu)) && need_migrate_task(p)) {
struct migration_arg arg = { p, dest_cpu };
task_rq_unlock(rq, &flags);
task_rq_unlock(rq, p, &flags);
stop_one_cpu(cpu_of(rq), migration_cpu_stop, &arg);
return;
}
unlock:
task_rq_unlock(rq, &flags);
task_rq_unlock(rq, p, &flags);
}
#endif
@ -3532,7 +3533,7 @@ unsigned long long task_delta_exec(struct task_struct *p)
rq = task_rq_lock(p, &flags);
ns = do_task_delta_exec(p, rq);
task_rq_unlock(rq, &flags);
task_rq_unlock(rq, p, &flags);
return ns;
}
@ -3550,7 +3551,7 @@ unsigned long long task_sched_runtime(struct task_struct *p)
rq = task_rq_lock(p, &flags);
ns = p->se.sum_exec_runtime + do_task_delta_exec(p, rq);
task_rq_unlock(rq, &flags);
task_rq_unlock(rq, p, &flags);
return ns;
}
@ -3574,7 +3575,7 @@ unsigned long long thread_group_sched_runtime(struct task_struct *p)
rq = task_rq_lock(p, &flags);
thread_group_cputime(p, &totals);
ns = totals.sum_exec_runtime + do_task_delta_exec(p, rq);
task_rq_unlock(rq, &flags);
task_rq_unlock(rq, p, &flags);
return ns;
}
@ -4693,16 +4694,13 @@ EXPORT_SYMBOL(sleep_on_timeout);
*/
void rt_mutex_setprio(struct task_struct *p, int prio)
{
unsigned long flags;
int oldprio, on_rq, running;
struct rq *rq;
const struct sched_class *prev_class;
BUG_ON(prio < 0 || prio > MAX_PRIO);
lockdep_assert_held(&p->pi_lock);
rq = task_rq_lock(p, &flags);
rq = __task_rq_lock(p);
trace_sched_pi_setprio(p, prio);
oldprio = p->prio;
@ -4727,7 +4725,7 @@ void rt_mutex_setprio(struct task_struct *p, int prio)
enqueue_task(rq, p, oldprio < prio ? ENQUEUE_HEAD : 0);
check_class_changed(rq, p, prev_class, oldprio);
task_rq_unlock(rq, &flags);
__task_rq_unlock(rq);
}
#endif
@ -4775,7 +4773,7 @@ void set_user_nice(struct task_struct *p, long nice)
resched_task(rq->curr);
}
out_unlock:
task_rq_unlock(rq, &flags);
task_rq_unlock(rq, p, &flags);
}
EXPORT_SYMBOL(set_user_nice);
@ -5003,20 +5001,17 @@ recheck:
/*
* make sure no PI-waiters arrive (or leave) while we are
* changing the priority of the task:
*/
raw_spin_lock_irqsave(&p->pi_lock, flags);
/*
*
* To be able to change p->policy safely, the appropriate
* runqueue lock must be held.
*/
rq = __task_rq_lock(p);
rq = task_rq_lock(p, &flags);
/*
* Changing the policy of the stop threads its a very bad idea
*/
if (p == rq->stop) {
__task_rq_unlock(rq);
raw_spin_unlock_irqrestore(&p->pi_lock, flags);
task_rq_unlock(rq, p, &flags);
return -EINVAL;
}
@ -5040,8 +5035,7 @@ recheck:
if (rt_bandwidth_enabled() && rt_policy(policy) &&
task_group(p)->rt_bandwidth.rt_runtime == 0 &&
!task_group_is_autogroup(task_group(p))) {
__task_rq_unlock(rq);
raw_spin_unlock_irqrestore(&p->pi_lock, flags);
task_rq_unlock(rq, p, &flags);
return -EPERM;
}
}
@ -5050,8 +5044,7 @@ recheck:
/* recheck policy now with rq lock held */
if (unlikely(oldpolicy != -1 && oldpolicy != p->policy)) {
policy = oldpolicy = -1;
__task_rq_unlock(rq);
raw_spin_unlock_irqrestore(&p->pi_lock, flags);
task_rq_unlock(rq, p, &flags);
goto recheck;
}
on_rq = p->on_rq;
@ -5073,8 +5066,7 @@ recheck:
activate_task(rq, p, 0);
check_class_changed(rq, p, prev_class, oldprio);
__task_rq_unlock(rq);
raw_spin_unlock_irqrestore(&p->pi_lock, flags);
task_rq_unlock(rq, p, &flags);
rt_mutex_adjust_pi(p);
@ -5666,7 +5658,7 @@ SYSCALL_DEFINE2(sched_rr_get_interval, pid_t, pid,
rq = task_rq_lock(p, &flags);
time_slice = p->sched_class->get_rr_interval(rq, p);
task_rq_unlock(rq, &flags);
task_rq_unlock(rq, p, &flags);
rcu_read_unlock();
jiffies_to_timespec(time_slice, &t);
@ -5889,8 +5881,7 @@ int set_cpus_allowed_ptr(struct task_struct *p, const struct cpumask *new_mask)
unsigned int dest_cpu;
int ret = 0;
raw_spin_lock_irqsave(&p->pi_lock, flags);
rq = __task_rq_lock(p);
rq = task_rq_lock(p, &flags);
if (!cpumask_intersects(new_mask, cpu_active_mask)) {
ret = -EINVAL;
@ -5918,15 +5909,13 @@ int set_cpus_allowed_ptr(struct task_struct *p, const struct cpumask *new_mask)
if (need_migrate_task(p)) {
struct migration_arg arg = { p, dest_cpu };
/* Need help from migration thread: drop lock and wait. */
__task_rq_unlock(rq);
raw_spin_unlock_irqrestore(&p->pi_lock, flags);
task_rq_unlock(rq, p, &flags);
stop_one_cpu(cpu_of(rq), migration_cpu_stop, &arg);
tlb_migrate_finish(p->mm);
return 0;
}
out:
__task_rq_unlock(rq);
raw_spin_unlock_irqrestore(&p->pi_lock, flags);
task_rq_unlock(rq, p, &flags);
return ret;
}
@ -5954,6 +5943,7 @@ static int __migrate_task(struct task_struct *p, int src_cpu, int dest_cpu)
rq_src = cpu_rq(src_cpu);
rq_dest = cpu_rq(dest_cpu);
raw_spin_lock(&p->pi_lock);
double_rq_lock(rq_src, rq_dest);
/* Already moved. */
if (task_cpu(p) != src_cpu)
@ -5976,6 +5966,7 @@ done:
ret = 1;
fail:
double_rq_unlock(rq_src, rq_dest);
raw_spin_unlock(&p->pi_lock);
return ret;
}
@ -8702,7 +8693,7 @@ void sched_move_task(struct task_struct *tsk)
if (on_rq)
enqueue_task(rq, tsk, 0);
task_rq_unlock(rq, &flags);
task_rq_unlock(rq, tsk, &flags);
}
#endif /* CONFIG_CGROUP_SCHED */