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rtmutex: Wake up the waiters lockless while dropping the read lock. 

The rw_semaphore and rwlock_t implementation both wake the waiter while
holding the rt_mutex_base::wait_lock acquired.
This can be optimized by waking the waiter lockless outside of the
locked section to avoid a needless contention on the
rt_mutex_base::wait_lock lock.

Extend rt_mutex_wake_q_add() to also accept task and state and use it in
__rwbase_read_unlock().

Suggested-by: Davidlohr Bueso <dave@stgolabs.net>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20210928150006.597310-3-bigeasy@linutronix.de
This commit is contained in:
Thomas Gleixner 2021-09-28 17:00:06 +02:00 committed by Peter Zijlstra
parent 8fe46535e1
commit 9321f8152d
2 changed files with 20 additions and 9 deletions
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23
kernel/locking/rtmutex.c
View File

@ -446,17 +446,24 @@ static __always_inline void rt_mutex_adjust_prio(struct task_struct *p)
}
/* RT mutex specific wake_q wrappers */
static __always_inline void rt_mutex_wake_q_add_task(struct rt_wake_q_head *wqh,
struct task_struct *task,
unsigned int wake_state)
{
if (IS_ENABLED(CONFIG_PREEMPT_RT) && wake_state == TASK_RTLOCK_WAIT) {
if (IS_ENABLED(CONFIG_PROVE_LOCKING))
WARN_ON_ONCE(wqh->rtlock_task);
get_task_struct(task);
wqh->rtlock_task = task;
} else {
wake_q_add(&wqh->head, task);
}
}
static __always_inline void rt_mutex_wake_q_add(struct rt_wake_q_head *wqh,
struct rt_mutex_waiter *w)
{
if (IS_ENABLED(CONFIG_PREEMPT_RT) && w->wake_state == TASK_RTLOCK_WAIT) {
if (IS_ENABLED(CONFIG_PROVE_LOCKING))
WARN_ON_ONCE(wqh->rtlock_task);
get_task_struct(w->task);
wqh->rtlock_task = w->task;
} else {
wake_q_add(&wqh->head, w->task);
}
rt_mutex_wake_q_add_task(wqh, w->task, w->wake_state);
}
static __always_inline void rt_mutex_wake_up_q(struct rt_wake_q_head *wqh)

6
kernel/locking/rwbase_rt.c
View File

@ -141,6 +141,7 @@ static void __sched __rwbase_read_unlock(struct rwbase_rt *rwb,
{
struct rt_mutex_base *rtm = &rwb->rtmutex;
struct task_struct *owner;
DEFINE_RT_WAKE_Q(wqh);
raw_spin_lock_irq(&rtm->wait_lock);
/*
@ -151,9 +152,12 @@ static void __sched __rwbase_read_unlock(struct rwbase_rt *rwb,
*/
owner = rt_mutex_owner(rtm);
if (owner)
wake_up_state(owner, state);
rt_mutex_wake_q_add_task(&wqh, owner, state);
/* Pairs with the preempt_enable in rt_mutex_wake_up_q() */
preempt_disable();
raw_spin_unlock_irq(&rtm->wait_lock);
rt_mutex_wake_up_q(&wqh);
}
static __always_inline void rwbase_read_unlock(struct rwbase_rt *rwb,