From: Peter Zijlstra <peterz@infradead.org>
To: Oleg Nesterov <oleg@redhat.com>
Cc: mingo@kernel.org, linux-kernel@vger.kernel.org,
paulmck@linux.vnet.ibm.com, boqun.feng@gmail.com, corbet@lwn.net,
mhocko@kernel.org, dhowells@redhat.com,
torvalds@linux-foundation.org, will.deacon@arm.com
Subject: Re: [PATCH 4/4] locking: Introduce smp_cond_acquire()
Date: Tue, 3 Nov 2015 19:23:05 +0100 [thread overview]
Message-ID: <20151103182304.GF17308@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <20151103175958.GA4800@redhat.com>
On Tue, Nov 03, 2015 at 06:59:58PM +0100, Oleg Nesterov wrote:
> > - raw_spin_unlock_wait(&task->pi_lock);
> > - smp_mb();
> > + smp_cond_acquire(!raw_spin_is_locked(&task->pi_lock));
>
> Unfortunately this doesn't look exactly right...
>
> spin_unlock_wait() is not equal to "while (locked) relax", the latter
> is live-lockable or at least sub-optimal: we do not really need to spin
> until we observe !spin_is_locked(), we only need to synchronize with the
> current owner of this lock. Once it drops the lock we can proceed, we
> do not care if another thread takes the same lock right after that.
Ah indeed. And while every use of spin_unlock_wait() has 'interesting'
barriers associated, they all seem different.
next prev parent reply other threads:[~2015-11-03 18:23 UTC|newest]
Thread overview: 78+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-11-02 13:29 [PATCH 0/4] scheduler ordering bits Peter Zijlstra
2015-11-02 13:29 ` [PATCH 1/4] sched: Better document the try_to_wake_up() barriers Peter Zijlstra
2015-12-04 0:09 ` Byungchul Park
2015-12-04 0:58 ` Byungchul Park
2015-11-02 13:29 ` [PATCH 2/4] sched: Document Program-Order guarantees Peter Zijlstra
2015-11-02 20:27 ` Paul Turner
2015-11-02 20:34 ` Peter Zijlstra
2015-11-02 22:09 ` Paul Turner
2015-11-02 22:12 ` Peter Zijlstra
2015-11-20 10:02 ` Peter Zijlstra
2015-11-20 14:08 ` Boqun Feng
2015-11-20 14:18 ` Peter Zijlstra
2015-11-20 14:21 ` Boqun Feng
2015-11-20 19:41 ` Peter Zijlstra
2015-11-02 13:29 ` [PATCH 3/4] sched: Fix a race in try_to_wake_up() vs schedule() Peter Zijlstra
2015-11-02 13:29 ` [PATCH 4/4] locking: Introduce smp_cond_acquire() Peter Zijlstra
2015-11-02 13:57 ` Peter Zijlstra
2015-11-02 17:43 ` Will Deacon
2015-11-03 1:14 ` Paul E. McKenney
2015-11-03 1:25 ` Linus Torvalds
2015-11-02 17:42 ` Will Deacon
2015-11-02 18:08 ` Linus Torvalds
2015-11-02 18:37 ` Will Deacon
2015-11-02 19:17 ` Linus Torvalds
2015-11-02 19:57 ` Will Deacon
2015-11-02 20:23 ` Peter Zijlstra
2015-11-02 21:56 ` Peter Zijlstra
2015-11-03 1:57 ` Paul E. McKenney
2015-11-03 19:40 ` Linus Torvalds
2015-11-04 3:57 ` Paul E. McKenney
2015-11-04 4:43 ` Linus Torvalds
2015-11-04 12:54 ` Paul E. McKenney
2015-11-02 20:36 ` David Howells
2015-11-02 20:40 ` Peter Zijlstra
2015-11-02 21:11 ` Linus Torvalds
2015-11-03 17:59 ` Oleg Nesterov
2015-11-03 18:23 ` Peter Zijlstra [this message]
2015-11-11 9:39 ` Boqun Feng
2015-11-11 10:34 ` Boqun Feng
2015-11-11 19:53 ` Oleg Nesterov
2015-11-12 13:50 ` Paul E. McKenney
2015-11-11 12:12 ` Peter Zijlstra
2015-11-11 19:39 ` Oleg Nesterov
2015-11-11 21:23 ` Linus Torvalds
2015-11-12 7:14 ` Boqun Feng
2015-11-12 10:28 ` Peter Zijlstra
2015-11-12 15:00 ` Oleg Nesterov
2015-11-12 14:40 ` Paul E. McKenney
2015-11-12 14:49 ` Boqun Feng
2015-11-12 15:02 ` Paul E. McKenney
2015-11-12 21:53 ` Will Deacon
2015-11-12 14:50 ` Peter Zijlstra
2015-11-12 15:01 ` Paul E. McKenney
2015-11-12 15:08 ` Peter Zijlstra
2015-11-12 15:20 ` Paul E. McKenney
2015-11-12 21:25 ` Will Deacon
2015-11-12 15:18 ` Boqun Feng
2015-11-12 18:38 ` Oleg Nesterov
2015-11-12 18:02 ` Peter Zijlstra
2015-11-12 19:33 ` Oleg Nesterov
2015-11-12 18:59 ` Paul E. McKenney
2015-11-12 21:33 ` Will Deacon
2015-11-12 23:43 ` Paul E. McKenney
2015-11-16 13:58 ` Will Deacon
2015-11-12 18:21 ` Linus Torvalds
2015-11-12 22:09 ` Will Deacon
2015-11-16 15:56 ` Peter Zijlstra
2015-11-16 16:04 ` Peter Zijlstra
2015-11-16 16:24 ` Will Deacon
2015-11-16 16:44 ` Paul E. McKenney
2015-11-16 16:46 ` Will Deacon
2015-11-16 17:15 ` Paul E. McKenney
2015-11-16 21:58 ` Linus Torvalds
2015-11-17 11:51 ` Will Deacon
2015-11-17 21:01 ` Paul E. McKenney
2015-11-18 11:25 ` Will Deacon
2015-11-19 18:01 ` Will Deacon
2015-11-20 10:09 ` Peter Zijlstra
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