From: Davidlohr Bueso <dave@stgolabs.net>
To: will.deacon@arm.com, paulmck@linux.vnet.ibm.com,
peterz@infradead.org, mingo@kernel.org,
linux-kernel@vger.kernel.org, doug.hatch@hp.com,
torvalds@linux-foundation.org, hpa@zytor.com,
akpm@linux-foundation.org, corbet@lwn.net, scott.norton@hp.com,
waiman.long@hp.com, tglx@linutronix.de
Cc: linux-tip-commits@vger.kernel.org
Subject: Re: [tip:locking/core] locking/Documentation: Clarify failed cmpxchg( ) memory ordering semantics
Date: Mon, 03 Aug 2015 10:36:53 -0700 [thread overview]
Message-ID: <1438623413.17146.3.camel@stgolabs.net> (raw)
In-Reply-To: <tip-ed2de9f74ecbbf3063d29b2334e7b455d7f35189@git.kernel.org>
On Mon, 2015-08-03 at 09:59 -0700, tip-bot for Will Deacon wrote:
> Commit-ID: ed2de9f74ecbbf3063d29b2334e7b455d7f35189
> Gitweb: http://git.kernel.org/tip/ed2de9f74ecbbf3063d29b2334e7b455d7f35189
> Author: Will Deacon <will.deacon@arm.com>
> AuthorDate: Thu, 16 Jul 2015 16:10:06 +0100
> Committer: Ingo Molnar <mingo@kernel.org>
> CommitDate: Mon, 3 Aug 2015 10:57:09 +0200
>
> locking/Documentation: Clarify failed cmpxchg() memory ordering semantics
>
> A failed cmpxchg does not provide any memory ordering guarantees, a
> property that is used to optimise the cmpxchg implementations on Alpha,
> PowerPC and arm64.
>
> This patch updates atomic_ops.txt and memory-barriers.txt to reflect
> this.
>
> Signed-off-by: Will Deacon <will.deacon@arm.com>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Davidlohr Bueso <dave@stgolabs.net>
> Cc: Douglas Hatch <doug.hatch@hp.com>
> Cc: H. Peter Anvin <hpa@zytor.com>
> Cc: Jonathan Corbet <corbet@lwn.net>
> Cc: Linus Torvalds <torvalds@linux-foundation.org>
> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Scott J Norton <scott.norton@hp.com>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Waiman Long <waiman.long@hp.com>
> Link: http://lkml.kernel.org/r/20150716151006.GH26390@arm.com
> Signed-off-by: Ingo Molnar <mingo@kernel.org>
> ---
> Documentation/atomic_ops.txt | 4 +++-
> Documentation/memory-barriers.txt | 6 +++---
> 2 files changed, 6 insertions(+), 4 deletions(-)
>
> diff --git a/Documentation/atomic_ops.txt b/Documentation/atomic_ops.txt
> index dab6da3..b19fc34 100644
> --- a/Documentation/atomic_ops.txt
> +++ b/Documentation/atomic_ops.txt
> @@ -266,7 +266,9 @@ with the given old and new values. Like all atomic_xxx operations,
> atomic_cmpxchg will only satisfy its atomicity semantics as long as all
> other accesses of *v are performed through atomic_xxx operations.
>
> -atomic_cmpxchg must provide explicit memory barriers around the operation.
> +atomic_cmpxchg must provide explicit memory barriers around the operation,
> +although if the comparison fails then no memory ordering guarantees are
> +required.
Thanks, I also stumbled upon this with the wake-q stuff.
next prev parent reply other threads:[~2015-08-03 17:37 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-07-15 2:13 [PATCH 0/6 v2] locking/qspinlock: Enhance pvqspinlock performance Waiman Long
2015-07-15 2:13 ` [PATCH v2 1/6] locking/pvqspinlock: Unconditional PV kick with _Q_SLOW_VAL Waiman Long
2015-07-15 9:10 ` Peter Zijlstra
2015-07-16 0:18 ` Waiman Long
2015-07-16 5:42 ` Peter Zijlstra
2015-07-16 14:07 ` Waiman Long
2015-07-16 15:04 ` Waiman Long
2015-07-16 15:10 ` Will Deacon
2015-08-03 16:59 ` [tip:locking/core] locking/Documentation: Clarify failed cmpxchg( ) memory ordering semantics tip-bot for Will Deacon
2015-08-03 17:36 ` Davidlohr Bueso [this message]
2015-07-15 2:13 ` [PATCH v2 2/6] locking/pvqspinlock: Add pending bit support Waiman Long
2015-07-15 2:13 ` [PATCH v2 3/6] locking/pvqspinlock: Collect slowpath lock statistics Waiman Long
2015-07-15 2:13 ` [PATCH v2 4/6] locking/pvqspinlock: Allow vCPUs kick-ahead Waiman Long
2015-07-15 9:39 ` Peter Zijlstra
2015-07-16 2:01 ` Waiman Long
2015-07-16 5:46 ` Peter Zijlstra
2015-07-16 14:51 ` Waiman Long
2015-07-15 2:13 ` [PATCH v2 5/6] locking/pvqspinlock: Opportunistically defer kicking to unlock time Waiman Long
2015-07-15 6:14 ` Raghavendra K T
2015-07-15 10:03 ` Peter Zijlstra
2015-07-16 2:18 ` Waiman Long
2015-07-16 5:49 ` Peter Zijlstra
2015-07-15 2:13 ` [PATCH v2 6/6] locking/pvqspinlock: Queue node adaptive spinning Waiman Long
2015-07-15 10:01 ` Peter Zijlstra
2015-07-16 2:13 ` Waiman Long
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