From: Waiman Long <waiman.long@hpe.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Davidlohr Bueso <dave@stgolabs.net>,
Ingo Molnar <mingo@redhat.com>, <linux-kernel@vger.kernel.org>,
<x86@kernel.org>, <linux-alpha@vger.kernel.org>,
<linux-ia64@vger.kernel.org>, <linux-s390@vger.kernel.org>,
<linux-arch@vger.kernel.org>, Jason Low <jason.low2@hp.com>,
Dave Chinner <david@fromorbit.com>,
Scott J Norton <scott.norton@hpe.com>,
Douglas Hatch <doug.hatch@hpe.com>
Subject: Re: [RFC PATCH-tip v2 1/6] locking/osq: Make lock/unlock proper acquire/release barrier
Date: Wed, 15 Jun 2016 15:08:48 -0400 [thread overview]
Message-ID: <5761A7C0.6000709@hpe.com> (raw)
In-Reply-To: <20160615171250.GO30921@twins.programming.kicks-ass.net>
On 06/15/2016 01:12 PM, Peter Zijlstra wrote:
> On Wed, Jun 15, 2016 at 09:56:59AM -0700, Davidlohr Bueso wrote:
>> On Tue, 14 Jun 2016, Waiman Long wrote:
>>> +++ b/kernel/locking/osq_lock.c
>>> @@ -115,7 +115,7 @@ bool osq_lock(struct optimistic_spin_queue *lock)
>>> * cmpxchg in an attempt to undo our queueing.
>>> */
>>>
>>> - while (!READ_ONCE(node->locked)) {
>>> + while (!smp_load_acquire(&node->locked)) {
>> Hmm this being a polling path, that barrier can get pretty expensive and
>> last I checked it was unnecessary:
> I think he'll go rely on it later on.
>
> In any case, its fairly simple to cure, just add
> smp_acquire__after_ctrl_dep() at the end. If we bail because
> need_resched() we don't need the acquire I think.
Yes, I only need the acquire barrier when the locking is successful.
Thanks for the suggestion. I will make the change accordingly.
Cheers,
Longman
next prev parent reply other threads:[~2016-06-15 19:09 UTC|newest]
Thread overview: 44+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-06-14 22:48 [RFC PATCH-tip v2 0/6] locking/rwsem: Enable reader optimistic spinning Waiman Long
2016-06-14 22:48 ` [RFC PATCH-tip v2 1/6] locking/osq: Make lock/unlock proper acquire/release barrier Waiman Long
2016-06-15 8:04 ` Boqun Feng
2016-06-15 17:18 ` Peter Zijlstra
2016-06-15 19:01 ` Waiman Long
2016-06-16 2:19 ` Boqun Feng
2016-06-16 10:16 ` Will Deacon
2016-06-16 21:35 ` Waiman Long
2016-06-17 0:48 ` Boqun Feng
2016-06-17 15:26 ` Waiman Long
2016-06-17 15:45 ` Will Deacon
2016-06-17 18:17 ` Waiman Long
2016-06-18 8:46 ` Boqun Feng
2016-06-20 7:59 ` Will Deacon
2016-06-15 16:56 ` Davidlohr Bueso
2016-06-15 17:12 ` Peter Zijlstra
2016-06-15 18:27 ` Davidlohr Bueso
2016-06-15 18:40 ` Peter Zijlstra
2016-06-15 18:56 ` Davidlohr Bueso
2016-06-17 1:11 ` Davidlohr Bueso
2016-06-17 14:28 ` Waiman Long
2016-06-17 16:29 ` Davidlohr Bueso
2016-06-17 16:46 ` Davidlohr Bueso
2016-06-15 19:08 ` Waiman Long [this message]
2016-06-15 20:04 ` Waiman Long
2016-06-15 21:59 ` Peter Zijlstra
2016-06-14 22:48 ` [RFC PATCH-tip v2 2/6] locking/rwsem: Stop active read lock ASAP Waiman Long
2016-06-15 17:22 ` Peter Zijlstra
2016-06-15 19:17 ` Waiman Long
2016-06-16 2:14 ` Davidlohr Bueso
2016-06-16 21:25 ` Waiman Long
2016-06-14 22:48 ` [RFC PATCH-tip v2 3/6] locking/rwsem: Enable count-based spinning on reader Waiman Long
2016-06-15 17:38 ` Peter Zijlstra
2016-06-15 19:28 ` Waiman Long
2016-06-14 22:48 ` [RFC PATCH-tip v2 4/6] locking/rwsem: move down rwsem_down_read_failed function Waiman Long
2016-06-15 17:40 ` Peter Zijlstra
2016-06-15 19:21 ` Waiman Long
2016-06-14 22:48 ` [RFC PATCH-tip v2 5/6] locking/rwsem: Change RWSEM_WAITING_BIAS for better disambiguation Waiman Long
2016-06-15 17:43 ` Peter Zijlstra
2016-06-15 19:31 ` Waiman Long
2016-06-15 21:57 ` Peter Zijlstra
2016-06-15 17:45 ` Peter Zijlstra
2016-06-15 19:35 ` Waiman Long
2016-06-14 22:48 ` [RFC PATCH-tip v2 6/6] locking/rwsem: Enable spinning readers Waiman Long
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