From: Peter Zijlstra <peterz@infradead.org>
To: Manfred Spraul <manfred@colorfullife.com>
Cc: benh@kernel.crashing.org, paulmck@linux.vnet.ibm.com,
Ingo Molnar <mingo@elte.hu>, Boqun Feng <boqun.feng@gmail.com>,
Andrew Morton <akpm@linux-foundation.org>,
LKML <linux-kernel@vger.kernel.org>,
1vier1@web.de, Davidlohr Bueso <dave@stgolabs.net>
Subject: Re: [PATCH 1/4] spinlock: Document memory barrier rules
Date: Mon, 29 Aug 2016 12:48:15 +0200 [thread overview]
Message-ID: <20160829104815.GI10153@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <1472385376-8801-2-git-send-email-manfred@colorfullife.com>
On Sun, Aug 28, 2016 at 01:56:13PM +0200, Manfred Spraul wrote:
> Right now, the spinlock machinery tries to guarantee barriers even for
> unorthodox locking cases, which ends up as a constant stream of updates
> as the architectures try to support new unorthodox ideas.
>
> The patch proposes to reverse that:
> spin_lock is ACQUIRE, spin_unlock is RELEASE.
> spin_unlock_wait is also ACQUIRE.
> Code that needs further guarantees must use appropriate explicit barriers.
>
> Architectures that can implement some barriers for free can define the
> barriers as NOPs.
>
> As the initial step, the patch converts ipc/sem.c to the new defines:
> - no more smp_rmb() after spin_unlock_wait(), that is part of
> spin_unlock_wait()
> - smp_mb__after_spin_lock() instead of a direct smp_mb().
>
Why? This does not explain why..
next prev parent reply other threads:[~2016-08-29 10:48 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-08-28 11:56 [PATCH 0/4] Clarify/standardize memory barriers for lock/unlock Manfred Spraul
2016-08-28 11:56 ` [PATCH 1/4] spinlock: Document memory barrier rules Manfred Spraul
2016-08-28 11:56 ` [PATCH 2/4] barrier.h: Move smp_mb__after_unlock_lock to barrier.h Manfred Spraul
2016-08-28 11:56 ` [PATCH 3/4] net/netfilter/nf_conntrack_core: update memory barriers Manfred Spraul
2016-08-28 11:56 ` [PATCH 4/4] qspinlock for x86: smp_mb__after_spin_lock() is free Manfred Spraul
2016-08-29 10:52 ` Peter Zijlstra
2016-08-29 10:51 ` [PATCH 3/4] net/netfilter/nf_conntrack_core: update memory barriers Peter Zijlstra
2016-08-28 13:43 ` [PATCH 2/4] barrier.h: Move smp_mb__after_unlock_lock to barrier.h Paul E. McKenney
2016-08-28 16:31 ` Manfred Spraul
2016-08-28 18:00 ` Manfred Spraul
2016-08-28 14:41 ` kbuild test robot
2016-08-28 17:43 ` [PATCH 2/4 v3] spinlock.h: Move smp_mb__after_unlock_lock to spinlock.h Manfred Spraul
2016-08-29 10:48 ` Peter Zijlstra [this message]
2016-08-29 12:54 ` [PATCH 1/4] spinlock: Document memory barrier rules Manfred Spraul
2016-08-29 13:44 ` Peter Zijlstra
2016-08-31 4:59 ` Manfred Spraul
2016-08-31 15:40 ` Peter Zijlstra
2016-08-31 16:40 ` Will Deacon
2016-08-31 18:32 ` Manfred Spraul
2016-09-01 8:44 ` Peter Zijlstra
2016-09-01 11:04 ` Manfred Spraul
2016-09-01 11:19 ` Will Deacon
2016-09-01 11:51 ` Peter Zijlstra
2016-09-01 14:05 ` Boqun Feng
2016-08-29 10:53 ` [PATCH 0/4] Clarify/standardize memory barriers for lock/unlock Peter Zijlstra
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