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synced 2025-11-04 10:40:15 +02:00
sched: Add p->pi_lock to task_rq_lock()
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
Ingo Molnar
parent
2acca55ed9
commit
0122ec5b02
1 changed files with 47 additions and 56 deletions
103
kernel/sched.c
103
kernel/sched.c
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@ -599,7 +599,7 @@ static inline int cpu_of(struct rq *rq)
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* Return the group to which this tasks belongs.
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*
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* We use task_subsys_state_check() and extend the RCU verification
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* with lockdep_is_held(&task_rq(p)->lock) because cpu_cgroup_attach()
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* with lockdep_is_held(&p->pi_lock) because cpu_cgroup_attach()
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* holds that lock for each task it moves into the cgroup. Therefore
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* by holding that lock, we pin the task to the current cgroup.
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*/
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@ -609,7 +609,7 @@ static inline struct task_group *task_group(struct task_struct *p)
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struct cgroup_subsys_state *css;
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css = task_subsys_state_check(p, cpu_cgroup_subsys_id,
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lockdep_is_held(&task_rq(p)->lock));
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lockdep_is_held(&p->pi_lock));
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tg = container_of(css, struct task_group, css);
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return autogroup_task_group(p, tg);
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@ -924,23 +924,15 @@ static inline void finish_lock_switch(struct rq *rq, struct task_struct *prev)
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#endif /* __ARCH_WANT_UNLOCKED_CTXSW */
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/*
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* Check whether the task is waking, we use this to synchronize ->cpus_allowed
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* against ttwu().
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*/
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static inline int task_is_waking(struct task_struct *p)
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{
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return unlikely(p->state == TASK_WAKING);
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}
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/*
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* __task_rq_lock - lock the runqueue a given task resides on.
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* Must be called interrupts disabled.
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* __task_rq_lock - lock the rq @p resides on.
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*/
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static inline struct rq *__task_rq_lock(struct task_struct *p)
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__acquires(rq->lock)
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{
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struct rq *rq;
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lockdep_assert_held(&p->pi_lock);
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for (;;) {
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rq = task_rq(p);
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raw_spin_lock(&rq->lock);
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@ -951,22 +943,22 @@ static inline struct rq *__task_rq_lock(struct task_struct *p)
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}
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/*
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* task_rq_lock - lock the runqueue a given task resides on and disable
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* interrupts. Note the ordering: we can safely lookup the task_rq without
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* explicitly disabling preemption.
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* task_rq_lock - lock p->pi_lock and lock the rq @p resides on.
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*/
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static struct rq *task_rq_lock(struct task_struct *p, unsigned long *flags)
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__acquires(p->pi_lock)
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__acquires(rq->lock)
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{
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struct rq *rq;
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for (;;) {
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local_irq_save(*flags);
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raw_spin_lock_irqsave(&p->pi_lock, *flags);
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rq = task_rq(p);
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raw_spin_lock(&rq->lock);
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if (likely(rq == task_rq(p)))
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return rq;
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raw_spin_unlock_irqrestore(&rq->lock, *flags);
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raw_spin_unlock(&rq->lock);
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raw_spin_unlock_irqrestore(&p->pi_lock, *flags);
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}
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}
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@ -976,10 +968,13 @@ static void __task_rq_unlock(struct rq *rq)
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raw_spin_unlock(&rq->lock);
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}
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static inline void task_rq_unlock(struct rq *rq, unsigned long *flags)
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static inline void
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task_rq_unlock(struct rq *rq, struct task_struct *p, unsigned long *flags)
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__releases(rq->lock)
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__releases(p->pi_lock)
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{
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raw_spin_unlock_irqrestore(&rq->lock, *flags);
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raw_spin_unlock(&rq->lock);
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raw_spin_unlock_irqrestore(&p->pi_lock, *flags);
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}
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/*
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@ -2175,6 +2170,11 @@ void set_task_cpu(struct task_struct *p, unsigned int new_cpu)
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*/
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WARN_ON_ONCE(p->state != TASK_RUNNING && p->state != TASK_WAKING &&
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!(task_thread_info(p)->preempt_count & PREEMPT_ACTIVE));
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#ifdef CONFIG_LOCKDEP
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WARN_ON_ONCE(debug_locks && !(lockdep_is_held(&p->pi_lock) ||
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lockdep_is_held(&task_rq(p)->lock)));
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#endif
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#endif
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trace_sched_migrate_task(p, new_cpu);
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@ -2270,7 +2270,7 @@ unsigned long wait_task_inactive(struct task_struct *p, long match_state)
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ncsw = 0;
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if (!match_state || p->state == match_state)
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ncsw = p->nvcsw | LONG_MIN; /* sets MSB */
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task_rq_unlock(rq, &flags);
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task_rq_unlock(rq, p, &flags);
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/*
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* If it changed from the expected state, bail out now.
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@ -2652,6 +2652,7 @@ static void __sched_fork(struct task_struct *p)
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*/
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void sched_fork(struct task_struct *p, int clone_flags)
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{
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unsigned long flags;
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int cpu = get_cpu();
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__sched_fork(p);
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@ -2702,9 +2703,9 @@ void sched_fork(struct task_struct *p, int clone_flags)
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*
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* Silence PROVE_RCU.
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*/
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rcu_read_lock();
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raw_spin_lock_irqsave(&p->pi_lock, flags);
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set_task_cpu(p, cpu);
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rcu_read_unlock();
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raw_spin_unlock_irqrestore(&p->pi_lock, flags);
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#if defined(CONFIG_SCHEDSTATS) || defined(CONFIG_TASK_DELAY_ACCT)
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if (likely(sched_info_on()))
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@ -2753,7 +2754,7 @@ void wake_up_new_task(struct task_struct *p, unsigned long clone_flags)
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set_task_cpu(p, cpu);
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p->state = TASK_RUNNING;
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task_rq_unlock(rq, &flags);
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task_rq_unlock(rq, p, &flags);
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#endif
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rq = task_rq_lock(p, &flags);
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@ -2765,7 +2766,7 @@ void wake_up_new_task(struct task_struct *p, unsigned long clone_flags)
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if (p->sched_class->task_woken)
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p->sched_class->task_woken(rq, p);
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#endif
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task_rq_unlock(rq, &flags);
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task_rq_unlock(rq, p, &flags);
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put_cpu();
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}
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@ -3490,12 +3491,12 @@ void sched_exec(void)
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likely(cpu_active(dest_cpu)) && need_migrate_task(p)) {
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struct migration_arg arg = { p, dest_cpu };
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task_rq_unlock(rq, &flags);
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task_rq_unlock(rq, p, &flags);
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stop_one_cpu(cpu_of(rq), migration_cpu_stop, &arg);
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return;
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}
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unlock:
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task_rq_unlock(rq, &flags);
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task_rq_unlock(rq, p, &flags);
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}
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#endif
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@ -3532,7 +3533,7 @@ unsigned long long task_delta_exec(struct task_struct *p)
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rq = task_rq_lock(p, &flags);
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ns = do_task_delta_exec(p, rq);
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task_rq_unlock(rq, &flags);
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task_rq_unlock(rq, p, &flags);
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return ns;
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}
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@ -3550,7 +3551,7 @@ unsigned long long task_sched_runtime(struct task_struct *p)
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rq = task_rq_lock(p, &flags);
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ns = p->se.sum_exec_runtime + do_task_delta_exec(p, rq);
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task_rq_unlock(rq, &flags);
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task_rq_unlock(rq, p, &flags);
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return ns;
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}
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@ -3574,7 +3575,7 @@ unsigned long long thread_group_sched_runtime(struct task_struct *p)
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rq = task_rq_lock(p, &flags);
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thread_group_cputime(p, &totals);
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ns = totals.sum_exec_runtime + do_task_delta_exec(p, rq);
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task_rq_unlock(rq, &flags);
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task_rq_unlock(rq, p, &flags);
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return ns;
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}
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@ -4693,16 +4694,13 @@ EXPORT_SYMBOL(sleep_on_timeout);
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*/
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void rt_mutex_setprio(struct task_struct *p, int prio)
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{
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unsigned long flags;
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int oldprio, on_rq, running;
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struct rq *rq;
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const struct sched_class *prev_class;
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BUG_ON(prio < 0 || prio > MAX_PRIO);
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lockdep_assert_held(&p->pi_lock);
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rq = task_rq_lock(p, &flags);
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rq = __task_rq_lock(p);
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trace_sched_pi_setprio(p, prio);
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oldprio = p->prio;
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@ -4727,7 +4725,7 @@ void rt_mutex_setprio(struct task_struct *p, int prio)
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enqueue_task(rq, p, oldprio < prio ? ENQUEUE_HEAD : 0);
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check_class_changed(rq, p, prev_class, oldprio);
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task_rq_unlock(rq, &flags);
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__task_rq_unlock(rq);
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}
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#endif
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@ -4775,7 +4773,7 @@ void set_user_nice(struct task_struct *p, long nice)
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resched_task(rq->curr);
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}
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out_unlock:
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task_rq_unlock(rq, &flags);
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task_rq_unlock(rq, p, &flags);
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}
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EXPORT_SYMBOL(set_user_nice);
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@ -5003,20 +5001,17 @@ static int __sched_setscheduler(struct task_struct *p, int policy,
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/*
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* make sure no PI-waiters arrive (or leave) while we are
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* changing the priority of the task:
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*/
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raw_spin_lock_irqsave(&p->pi_lock, flags);
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/*
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*
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* To be able to change p->policy safely, the appropriate
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* runqueue lock must be held.
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*/
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rq = __task_rq_lock(p);
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rq = task_rq_lock(p, &flags);
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/*
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* Changing the policy of the stop threads its a very bad idea
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*/
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if (p == rq->stop) {
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__task_rq_unlock(rq);
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raw_spin_unlock_irqrestore(&p->pi_lock, flags);
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task_rq_unlock(rq, p, &flags);
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return -EINVAL;
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}
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@ -5040,8 +5035,7 @@ static int __sched_setscheduler(struct task_struct *p, int policy,
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if (rt_bandwidth_enabled() && rt_policy(policy) &&
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task_group(p)->rt_bandwidth.rt_runtime == 0 &&
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!task_group_is_autogroup(task_group(p))) {
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__task_rq_unlock(rq);
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raw_spin_unlock_irqrestore(&p->pi_lock, flags);
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task_rq_unlock(rq, p, &flags);
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return -EPERM;
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}
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}
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@ -5050,8 +5044,7 @@ static int __sched_setscheduler(struct task_struct *p, int policy,
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/* recheck policy now with rq lock held */
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if (unlikely(oldpolicy != -1 && oldpolicy != p->policy)) {
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policy = oldpolicy = -1;
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__task_rq_unlock(rq);
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raw_spin_unlock_irqrestore(&p->pi_lock, flags);
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task_rq_unlock(rq, p, &flags);
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goto recheck;
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}
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on_rq = p->on_rq;
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@ -5073,8 +5066,7 @@ static int __sched_setscheduler(struct task_struct *p, int policy,
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activate_task(rq, p, 0);
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check_class_changed(rq, p, prev_class, oldprio);
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__task_rq_unlock(rq);
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raw_spin_unlock_irqrestore(&p->pi_lock, flags);
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task_rq_unlock(rq, p, &flags);
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rt_mutex_adjust_pi(p);
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@ -5666,7 +5658,7 @@ SYSCALL_DEFINE2(sched_rr_get_interval, pid_t, pid,
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rq = task_rq_lock(p, &flags);
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time_slice = p->sched_class->get_rr_interval(rq, p);
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task_rq_unlock(rq, &flags);
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task_rq_unlock(rq, p, &flags);
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rcu_read_unlock();
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jiffies_to_timespec(time_slice, &t);
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@ -5889,8 +5881,7 @@ int set_cpus_allowed_ptr(struct task_struct *p, const struct cpumask *new_mask)
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unsigned int dest_cpu;
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int ret = 0;
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raw_spin_lock_irqsave(&p->pi_lock, flags);
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rq = __task_rq_lock(p);
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rq = task_rq_lock(p, &flags);
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if (!cpumask_intersects(new_mask, cpu_active_mask)) {
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ret = -EINVAL;
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@ -5918,15 +5909,13 @@ int set_cpus_allowed_ptr(struct task_struct *p, const struct cpumask *new_mask)
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if (need_migrate_task(p)) {
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struct migration_arg arg = { p, dest_cpu };
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/* Need help from migration thread: drop lock and wait. */
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__task_rq_unlock(rq);
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raw_spin_unlock_irqrestore(&p->pi_lock, flags);
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task_rq_unlock(rq, p, &flags);
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stop_one_cpu(cpu_of(rq), migration_cpu_stop, &arg);
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tlb_migrate_finish(p->mm);
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return 0;
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}
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out:
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__task_rq_unlock(rq);
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raw_spin_unlock_irqrestore(&p->pi_lock, flags);
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task_rq_unlock(rq, p, &flags);
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return ret;
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}
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@ -5954,6 +5943,7 @@ static int __migrate_task(struct task_struct *p, int src_cpu, int dest_cpu)
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rq_src = cpu_rq(src_cpu);
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rq_dest = cpu_rq(dest_cpu);
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raw_spin_lock(&p->pi_lock);
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double_rq_lock(rq_src, rq_dest);
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/* Already moved. */
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if (task_cpu(p) != src_cpu)
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@ -5976,6 +5966,7 @@ static int __migrate_task(struct task_struct *p, int src_cpu, int dest_cpu)
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ret = 1;
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fail:
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double_rq_unlock(rq_src, rq_dest);
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raw_spin_unlock(&p->pi_lock);
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return ret;
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}
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@ -8702,7 +8693,7 @@ void sched_move_task(struct task_struct *tsk)
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if (on_rq)
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enqueue_task(rq, tsk, 0);
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task_rq_unlock(rq, &flags);
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task_rq_unlock(rq, tsk, &flags);
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}
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#endif /* CONFIG_CGROUP_SCHED */
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