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Re: [PATCH RFC] locking/mutexes: don't spin on owner when wait list is not NULL.

From Peter Zijlstra <peterz@infradead.org>
Newsgroups linux.kernel
Subject Re: [PATCH RFC] locking/mutexes: don't spin on owner when wait list is not NULL.
Date 2016-01-22 12:10 +0100
Message-ID <qTHLj-3dT-1@gated-at.bofh.it> (permalink)
References (1 earlier) <qTwwA-3Hx-59@gated-at.bofh.it> <qTFJv-1Dd-5@gated-at.bofh.it> <qTH8B-2I1-3@gated-at.bofh.it> <qTHBE-2UG-11@gated-at.bofh.it> <qTHBE-2UG-15@gated-at.bofh.it>
Organization linux.* mail to news gateway

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On Fri, Jan 22, 2016 at 11:56:52AM +0100, Peter Zijlstra wrote:
> On Fri, Jan 22, 2016 at 11:53:12AM +0100, Peter Zijlstra wrote:
> 
> > There might be other details, but this is the one that stood out.
> 
> I think this also does the wrong thing for use_ww_ctx.

Something like so? 

---
 kernel/locking/mutex.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c
index 0551c219c40e..070a0ac34aa7 100644
--- a/kernel/locking/mutex.c
+++ b/kernel/locking/mutex.c
@@ -512,6 +512,7 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
 	struct task_struct *task = current;
 	struct mutex_waiter waiter;
 	unsigned long flags;
+	bool acquired;
 	int ret;
 
 	preempt_disable();
@@ -543,6 +544,7 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
 	lock_contended(&lock->dep_map, ip);
 
 	for (;;) {
+		acquired = false;
 		/*
 		 * Lets try to take the lock again - this is needed even if
 		 * we get here for the first time (shortly after failing to
@@ -577,7 +579,16 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
 		/* didn't get the lock, go to sleep: */
 		spin_unlock_mutex(&lock->wait_lock, flags);
 		schedule_preempt_disabled();
+
+		if (mutex_is_locked(lock))
+			acquired = mutex_optimistic_spin(lock, ww_ctx, use_ww_ctx);
+
 		spin_lock_mutex(&lock->wait_lock, flags);
+
+		if (acquired) {
+			atomic_set(&lock->count, -1);
+			break;
+		}
 	}
 	__set_task_state(task, TASK_RUNNING);
 
@@ -587,6 +598,9 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
 		atomic_set(&lock->count, 0);
 	debug_mutex_free_waiter(&waiter);
 
+	if (acquired)
+		goto unlock;
+
 skip_wait:
 	/* got the lock - cleanup and rejoice! */
 	lock_acquired(&lock->dep_map, ip);
@@ -597,6 +611,7 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
 		ww_mutex_set_context_slowpath(ww, ww_ctx);
 	}
 
+unlock:
 	spin_unlock_mutex(&lock->wait_lock, flags);
 	preempt_enable();
 	return 0;

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Thread

[PATCH RFC] locking/mutexes: don't spin on owner when wait list is  not NULL. Ding Tianhong <dingtianhong@huawei.com> - 2016-01-21 10:40 +0100
  Re: [PATCH RFC] locking/mutexes: don't spin on owner when wait list  is not NULL. Tim Chen <tim.c.chen@linux.intel.com> - 2016-01-21 22:30 +0100
    Re: [PATCH RFC] locking/mutexes: don't spin on owner when wait list  is not NULL. Davidlohr Bueso <dave@stgolabs.net> - 2016-01-22 03:50 +0100
      Re: [PATCH RFC] locking/mutexes: don't spin on owner when wait list  is not NULL. "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-01-22 04:20 +0100
    Re: [PATCH RFC] locking/mutexes: don't spin on owner when wait list  is not NULL. "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-01-22 03:50 +0100
  Re: [PATCH RFC] locking/mutexes: don't spin on owner when wait list  is not NULL. Waiman Long <waiman.long@hpe.com> - 2016-01-22 00:10 +0100
    Re: [PATCH RFC] locking/mutexes: don't spin on owner when wait list  is not NULL. Davidlohr Bueso <dave@stgolabs.net> - 2016-01-22 07:20 +0100
      Re: [PATCH RFC] locking/mutexes: don't spin on owner when wait list  is not NULL. Waiman Long <waiman.long@hpe.com> - 2016-01-22 14:40 +0100
        Re: [PATCH RFC] locking/mutexes: don't spin on owner when wait list  is not NULL. Davidlohr Bueso <dave@stgolabs.net> - 2016-01-22 17:50 +0100
          [PATCH] locking/mutex: Allow next waiter lockless wakeup Davidlohr Bueso <dave@stgolabs.net> - 2016-01-25 03:30 +0100
            Re: [PATCH] locking/mutex: Allow next waiter lockless wakeup Waiman Long <waiman.long@hpe.com> - 2016-01-26 00:10 +0100
    Re: [PATCH RFC] locking/mutexes: don't spin on owner when wait list  is not NULL. Peter Zijlstra <peterz@infradead.org> - 2016-01-22 10:00 +0100
      Re: [PATCH RFC] locking/mutexes: don't spin on owner when wait list  is not NULL. Jason Low <jason.low2@hp.com> - 2016-01-22 11:30 +0100
        Re: [PATCH RFC] locking/mutexes: don't spin on owner when wait list  is not NULL. Peter Zijlstra <peterz@infradead.org> - 2016-01-22 12:00 +0100
          Re: [PATCH RFC] locking/mutexes: don't spin on owner when wait list  is not NULL. Peter Zijlstra <peterz@infradead.org> - 2016-01-22 12:00 +0100
            Re: [PATCH RFC] locking/mutexes: don't spin on owner when wait list  is not NULL. Peter Zijlstra <peterz@infradead.org> - 2016-01-22 12:10 +0100
              Re: [PATCH RFC] locking/mutexes: don't spin on owner when wait list  is not NULL. Waiman Long <waiman.long@hpe.com> - 2016-01-22 15:10 +0100
                Re: [PATCH RFC] locking/mutexes: don't spin on owner when wait list  is not NULL. Ding Tianhong <dingtianhong@huawei.com> - 2016-01-24 09:10 +0100
      Re: [PATCH RFC] locking/mutexes: don't spin on owner when wait list  is not NULL. Waiman Long <waiman.long@hpe.com> - 2016-01-22 14:50 +0100

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