From: Peter Zijlstra <peterz@infradead.org>
To: longman@redhat.com, mingo@redhat.com, will@kernel.org
Cc: linux-kernel@vger.kernel.org, boqun.feng@gmail.com
Subject: Re: [PATCH 3/6] locking/rwsem: Rework writer wakeup
Date: Sun, 26 Feb 2023 16:04:35 +0100 [thread overview]
Message-ID: <Y/t1AwGC9OoN/lFc@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20230223123319.487908155@infradead.org>
On Thu, Feb 23, 2023 at 01:26:45PM +0100, Peter Zijlstra wrote:
> @@ -1072,7 +1067,7 @@ rwsem_down_read_slowpath(struct rw_semap
> for (;;) {
> set_current_state(state);
> if (!smp_load_acquire(&waiter.task)) {
> - /* Matches rwsem_mark_wake()'s smp_store_release(). */
> + /* Matches rwsem_waiter_wake()'s smp_store_release(). */
> break;
> }
> if (signal_pending_state(state, current)) {
> @@ -1143,54 +1138,36 @@ rwsem_down_write_slowpath(struct rw_sema
> } else {
> atomic_long_or(RWSEM_FLAG_WAITERS, &sem->count);
Found it; if we remove the try_write_lock below, then at least this
new-waiter path needs to still do a trylock.
Let me go test the other patches on top of all this and push out a fresh
set if that all still works.
> }
> + raw_spin_unlock_irq(&sem->wait_lock);
>
> /* wait until we successfully acquire the lock */
> - set_current_state(state);
> trace_contention_begin(sem, LCB_F_WRITE);
>
> for (;;) {
> - if (rwsem_try_write_lock(sem, &waiter)) {
> - /* rwsem_try_write_lock() implies ACQUIRE on success */
> + set_current_state(state);
> + if (!smp_load_acquire(&waiter.task)) {
> + /* Matches rwsem_waiter_wake()'s smp_store_release(). */
> break;
> }
> -
> - raw_spin_unlock_irq(&sem->wait_lock);
> -
> - if (signal_pending_state(state, current))
> - goto out_nolock;
> -
> - /*
> - * After setting the handoff bit and failing to acquire
> - * the lock, attempt to spin on owner to accelerate lock
> - * transfer. If the previous owner is a on-cpu writer and it
> - * has just released the lock, OWNER_NULL will be returned.
> - * In this case, we attempt to acquire the lock again
> - * without sleeping.
> - */
> - if (waiter.handoff_set) {
> - enum owner_state owner_state;
> -
> - owner_state = rwsem_spin_on_owner(sem);
> - if (owner_state == OWNER_NULL)
> - goto trylock_again;
> + if (signal_pending_state(state, current)) {
> + raw_spin_lock_irq(&sem->wait_lock);
> + if (waiter.task)
> + goto out_nolock;
> + raw_spin_unlock_irq(&sem->wait_lock);
> + /* Ordered by sem->wait_lock against rwsem_mark_wake(). */
> + break;
> }
> -
> schedule_preempt_disabled();
> lockevent_inc(rwsem_sleep_writer);
> - set_current_state(state);
> -trylock_again:
> - raw_spin_lock_irq(&sem->wait_lock);
> }
> __set_current_state(TASK_RUNNING);
> - raw_spin_unlock_irq(&sem->wait_lock);
> lockevent_inc(rwsem_wlock);
> trace_contention_end(sem, 0);
> return sem;
>
> out_nolock:
> - __set_current_state(TASK_RUNNING);
> - raw_spin_lock_irq(&sem->wait_lock);
> rwsem_del_wake_waiter(sem, &waiter, &wake_q);
> + __set_current_state(TASK_RUNNING);
> lockevent_inc(rwsem_wlock_fail);
> trace_contention_end(sem, -EINTR);
> return ERR_PTR(-EINTR);
>
>
next prev parent reply other threads:[~2023-02-26 16:02 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-02-23 12:26 [PATCH 0/6] locking/rwsem: Rework writer wakeup and handoff Peter Zijlstra
2023-02-23 12:26 ` [PATCH 1/6] locking/rwsem: Minor code refactoring in rwsem_mark_wake() Peter Zijlstra
2023-02-23 12:26 ` [PATCH 2/6] locking/rwsem: Enforce queueing when HANDOFF Peter Zijlstra
2023-02-23 12:26 ` [PATCH 3/6] locking/rwsem: Rework writer wakeup Peter Zijlstra
2023-02-23 21:38 ` Waiman Long
2023-02-26 11:58 ` Peter Zijlstra
2023-02-26 12:00 ` Peter Zijlstra
2023-02-26 21:31 ` Waiman Long
2023-02-26 11:59 ` Peter Zijlstra
2023-02-26 15:04 ` Peter Zijlstra [this message]
2023-02-26 16:51 ` Peter Zijlstra
2023-02-27 0:22 ` Waiman Long
2023-02-27 10:31 ` Peter Zijlstra
2023-02-27 20:16 ` Waiman Long
2023-03-20 8:12 ` Peter Zijlstra
2023-03-20 17:36 ` Waiman Long
2023-02-23 12:26 ` [PATCH 4/6] locking/rwsem: Split out rwsem_reader_wake() Peter Zijlstra
2023-02-23 12:26 ` [PATCH 5/6] locking/rwsem: Unify wait loop Peter Zijlstra
2023-02-23 19:31 ` Boqun Feng
2023-02-24 1:33 ` Boqun Feng
2023-02-26 12:01 ` Peter Zijlstra
2023-02-26 18:22 ` Boqun Feng
2023-02-23 22:45 ` Waiman Long
2023-02-26 16:15 ` Peter Zijlstra
2023-02-23 12:26 ` [PATCH 6/6] locking/rwsem: Use the force Peter Zijlstra
2023-02-24 1:19 ` [PATCH 0/6] locking/rwsem: Rework writer wakeup and handoff Waiman Long
2023-02-24 11:55 ` Jiri Wiesner
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