From: Peter Zijlstra <peterz@infradead.org>
To: Will Deacon <will.deacon@arm.com>
Cc: linux-kernel@vger.kernel.org,
linux-arm-kernel@lists.infradead.org, mingo@kernel.org,
boqun.feng@gmail.com, paulmck@linux.vnet.ibm.com,
catalin.marinas@arm.com, Waiman Long <longman@redhat.com>
Subject: Re: [PATCH 03/10] locking/qspinlock: Kill cmpxchg loop when claiming lock from head of queue
Date: Thu, 5 Apr 2018 19:19:12 +0200 [thread overview]
Message-ID: <20180405171912.GE4082@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <1522947547-24081-4-git-send-email-will.deacon@arm.com>
On Thu, Apr 05, 2018 at 05:59:00PM +0100, Will Deacon wrote:
> +
> + /* In the PV case we might already have _Q_LOCKED_VAL set */
> + if ((val & _Q_TAIL_MASK) == tail) {
> /*
> * The smp_cond_load_acquire() call above has provided the
> + * necessary acquire semantics required for locking.
> */
> old = atomic_cmpxchg_relaxed(&lock->val, val, _Q_LOCKED_VAL);
> if (old == val)
> + goto release; /* No contention */
> }
--- a/kernel/locking/qspinlock.c
+++ b/kernel/locking/qspinlock.c
@@ -464,8 +464,7 @@ void queued_spin_lock_slowpath(struct qs
* The smp_cond_load_acquire() call above has provided the
* necessary acquire semantics required for locking.
*/
- old = atomic_cmpxchg_relaxed(&lock->val, val, _Q_LOCKED_VAL);
- if (old == val)
+ if (atomic_try_cmpxchg_release(&lock->val, &val, _Q_LOCKED_VAL))
goto release; /* No contention */
}
Does that also work for you? It would generate slightly better code for
x86 (not that it would matter much on this path).
next prev parent reply other threads:[~2018-04-05 17:19 UTC|newest]
Thread overview: 47+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-04-05 16:58 [PATCH 00/10] kernel/locking: qspinlock improvements Will Deacon
2018-04-05 16:58 ` [PATCH 01/10] locking/qspinlock: Don't spin on pending->locked transition in slowpath Will Deacon
2018-04-05 16:58 ` [PATCH 02/10] locking/qspinlock: Remove unbounded cmpxchg loop from locking slowpath Will Deacon
2018-04-05 17:07 ` Peter Zijlstra
2018-04-06 15:08 ` Will Deacon
2018-04-05 17:13 ` Peter Zijlstra
2018-04-05 21:16 ` Waiman Long
2018-04-06 15:08 ` Will Deacon
2018-04-06 20:50 ` Waiman Long
2018-04-06 21:09 ` Paul E. McKenney
2018-04-07 8:47 ` Peter Zijlstra
2018-04-07 23:37 ` Paul E. McKenney
2018-04-09 10:58 ` Will Deacon
2018-04-07 9:07 ` Peter Zijlstra
2018-04-09 10:58 ` Will Deacon
2018-04-09 14:54 ` Will Deacon
2018-04-09 15:54 ` Peter Zijlstra
2018-04-09 17:19 ` Will Deacon
2018-04-10 9:35 ` Peter Zijlstra
2018-09-20 16:08 ` Peter Zijlstra
2018-09-20 16:22 ` Peter Zijlstra
2018-04-09 19:33 ` Waiman Long
2018-04-09 17:55 ` Waiman Long
2018-04-10 13:49 ` Sasha Levin
2018-04-05 16:59 ` [PATCH 03/10] locking/qspinlock: Kill cmpxchg loop when claiming lock from head of queue Will Deacon
2018-04-05 17:19 ` Peter Zijlstra [this message]
2018-04-06 10:54 ` Will Deacon
2018-04-05 16:59 ` [PATCH 04/10] locking/qspinlock: Use atomic_cond_read_acquire Will Deacon
2018-04-05 16:59 ` [PATCH 05/10] locking/mcs: Use smp_cond_load_acquire() in mcs spin loop Will Deacon
2018-04-05 16:59 ` [PATCH 06/10] barriers: Introduce smp_cond_load_relaxed and atomic_cond_read_relaxed Will Deacon
2018-04-05 17:22 ` Peter Zijlstra
2018-04-06 10:55 ` Will Deacon
2018-04-05 16:59 ` [PATCH 07/10] locking/qspinlock: Use smp_cond_load_relaxed to wait for next node Will Deacon
2018-04-05 16:59 ` [PATCH 08/10] locking/qspinlock: Merge struct __qspinlock into struct qspinlock Will Deacon
2018-04-07 5:23 ` Boqun Feng
2018-04-05 16:59 ` [PATCH 09/10] locking/qspinlock: Make queued_spin_unlock use smp_store_release Will Deacon
2018-04-05 16:59 ` [PATCH 10/10] locking/qspinlock: Elide back-to-back RELEASE operations with smp_wmb() Will Deacon
2018-04-05 17:28 ` Peter Zijlstra
2018-04-06 11:34 ` Will Deacon
2018-04-06 13:05 ` Andrea Parri
2018-04-06 15:27 ` Will Deacon
2018-04-06 15:49 ` Andrea Parri
2018-04-07 5:47 ` Boqun Feng
2018-04-09 10:47 ` Will Deacon
2018-04-06 13:22 ` [PATCH 00/10] kernel/locking: qspinlock improvements Andrea Parri
2018-04-11 10:20 ` Catalin Marinas
2018-04-11 15:39 ` Andrea Parri
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