From: paulmck@linux.vnet.ibm.com (Paul E. McKenney)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH 02/10] locking/qspinlock: Remove unbounded cmpxchg loop from locking slowpath
Date: Sat, 7 Apr 2018 16:37:42 -0700 [thread overview]
Message-ID: <20180407233741.GM3948@linux.vnet.ibm.com> (raw)
In-Reply-To: <20180407084732.GO4082@hirez.programming.kicks-ass.net>
On Sat, Apr 07, 2018 at 10:47:32AM +0200, Peter Zijlstra wrote:
> On Fri, Apr 06, 2018 at 02:09:53PM -0700, Paul E. McKenney wrote:
> > It would indeed be good to not be in the position of having to trade off
> > forward-progress guarantees against performance, but that does appear to
> > be where we are at the moment.
>
> Depends of course on how unfair cmpxchg is. On x86 we trade one cmpxchg
> loop for another so the patch doesn't cure anything at all there. And
> our cmpxchg has 'some' hardware fairness to it.
>
> So while the patch is 'good' for platforms that have native fetch-or,
> it doesn't help (or in our case even hurts) those that do not.
Might need different implementations for different architectures, then.
Or take advantage of the fact that x86 can do a native fetch-or to the
topmost bit, if that helps.
Thanx, Paul
next prev parent reply other threads:[~2018-04-07 23:37 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 [this message]
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
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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