From 9321f8152d9a764208c3f0dad49e0c55f293b7ab Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Tue, 28 Sep 2021 17:00:06 +0200 Subject: [PATCH] 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 Signed-off-by: Thomas Gleixner Signed-off-by: Sebastian Andrzej Siewior Signed-off-by: Peter Zijlstra (Intel) Link: https://lkml.kernel.org/r/20210928150006.597310-3-bigeasy@linutronix.de --- kernel/locking/rtmutex.c | 23 +++++++++++++++-------- kernel/locking/rwbase_rt.c | 6 +++++- 2 files changed, 20 insertions(+), 9 deletions(-) diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c index cafc259ec59d..0c6a48dfcecb 100644 --- a/kernel/locking/rtmutex.c +++ b/kernel/locking/rtmutex.c @@ -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) diff --git a/kernel/locking/rwbase_rt.c b/kernel/locking/rwbase_rt.c index 4ba15088e640..6b143fb294f6 100644 --- a/kernel/locking/rwbase_rt.c +++ b/kernel/locking/rwbase_rt.c @@ -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,