From: Peter Zijlstra <peterz@infradead.org>
To: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Waiman Long <longman@redhat.com>,
Will Deacon <will.deacon@arm.com>,
linux-kernel@vger.kernel.org,
linux-arm-kernel@lists.infradead.org, mingo@kernel.org,
boqun.feng@gmail.com, catalin.marinas@arm.com
Subject: Re: [PATCH 02/10] locking/qspinlock: Remove unbounded cmpxchg loop from locking slowpath
Date: Sat, 7 Apr 2018 10:47:32 +0200 [thread overview]
Message-ID: <20180407084732.GO4082@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20180406210953.GA24165@linux.vnet.ibm.com>
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.
WARNING: multiple messages have this Message-ID (diff)
From: peterz@infradead.org (Peter Zijlstra)
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 10:47:32 +0200 [thread overview]
Message-ID: <20180407084732.GO4082@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20180406210953.GA24165@linux.vnet.ibm.com>
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.
next prev parent reply other threads:[~2018-04-07 8:47 UTC|newest]
Thread overview: 94+ 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 ` 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 ` Will Deacon
2018-04-05 16:58 ` [PATCH 02/10] locking/qspinlock: Remove unbounded cmpxchg loop from locking slowpath Will Deacon
2018-04-05 16:58 ` Will Deacon
2018-04-05 17:07 ` Peter Zijlstra
2018-04-05 17:07 ` Peter Zijlstra
2018-04-06 15:08 ` Will Deacon
2018-04-06 15:08 ` Will Deacon
2018-04-05 17:13 ` Peter Zijlstra
2018-04-05 17:13 ` Peter Zijlstra
2018-04-05 21:16 ` Waiman Long
2018-04-05 21:16 ` Waiman Long
2018-04-06 15:08 ` Will Deacon
2018-04-06 15:08 ` Will Deacon
2018-04-06 20:50 ` Waiman Long
2018-04-06 20:50 ` Waiman Long
2018-04-06 21:09 ` Paul E. McKenney
2018-04-06 21:09 ` Paul E. McKenney
2018-04-07 8:47 ` Peter Zijlstra [this message]
2018-04-07 8:47 ` Peter Zijlstra
2018-04-07 23:37 ` Paul E. McKenney
2018-04-07 23:37 ` Paul E. McKenney
2018-04-09 10:58 ` Will Deacon
2018-04-09 10:58 ` Will Deacon
2018-04-07 9:07 ` Peter Zijlstra
2018-04-07 9:07 ` Peter Zijlstra
2018-04-09 10:58 ` Will Deacon
2018-04-09 10:58 ` Will Deacon
2018-04-09 14:54 ` Will Deacon
2018-04-09 14:54 ` Will Deacon
2018-04-09 15:54 ` Peter Zijlstra
2018-04-09 15:54 ` Peter Zijlstra
2018-04-09 17:19 ` Will Deacon
2018-04-09 17:19 ` Will Deacon
2018-04-10 9:35 ` Peter Zijlstra
2018-04-10 9:35 ` Peter Zijlstra
2018-09-20 16:08 ` Peter Zijlstra
2018-09-20 16:08 ` Peter Zijlstra
2018-09-20 16:22 ` Peter Zijlstra
2018-09-20 16:22 ` Peter Zijlstra
2018-04-09 19:33 ` Waiman Long
2018-04-09 19:33 ` Waiman Long
2018-04-09 17:55 ` Waiman Long
2018-04-09 17:55 ` Waiman Long
2018-04-10 13:49 ` Sasha Levin
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 16:59 ` Will Deacon
2018-04-05 17:19 ` Peter Zijlstra
2018-04-05 17:19 ` Peter Zijlstra
2018-04-06 10:54 ` Will Deacon
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 ` 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 ` 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 16:59 ` Will Deacon
2018-04-05 17:22 ` Peter Zijlstra
2018-04-05 17:22 ` Peter Zijlstra
2018-04-06 10:55 ` Will Deacon
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 ` Will Deacon
2018-04-05 16:59 ` [PATCH 08/10] locking/qspinlock: Merge struct __qspinlock into struct qspinlock Will Deacon
2018-04-05 16:59 ` Will Deacon
2018-04-07 5:23 ` Boqun Feng
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 ` 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 16:59 ` Will Deacon
2018-04-05 17:28 ` Peter Zijlstra
2018-04-05 17:28 ` Peter Zijlstra
2018-04-06 11:34 ` Will Deacon
2018-04-06 11:34 ` Will Deacon
2018-04-06 13:05 ` Andrea Parri
2018-04-06 13:05 ` Andrea Parri
2018-04-06 15:27 ` Will Deacon
2018-04-06 15:27 ` Will Deacon
2018-04-06 15:49 ` Andrea Parri
2018-04-06 15:49 ` Andrea Parri
2018-04-07 5:47 ` Boqun Feng
2018-04-07 5:47 ` Boqun Feng
2018-04-09 10:47 ` Will Deacon
2018-04-09 10:47 ` Will Deacon
2018-04-06 13:22 ` [PATCH 00/10] kernel/locking: qspinlock improvements Andrea Parri
2018-04-06 13:22 ` Andrea Parri
2018-04-11 10:20 ` Catalin Marinas
2018-04-11 10:20 ` Catalin Marinas
2018-04-11 15:39 ` Andrea Parri
2018-04-11 15:39 ` Andrea Parri
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