From: Peter Zijlstra <peterz@infradead.org>
To: Will Deacon <will.deacon@arm.com>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
Michael Ellerman <mpe@ellerman.id.au>,
linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org,
Boqun Feng <boqun.feng@gmail.com>,
Anton Blanchard <anton@samba.org>,
Benjamin Herrenschmidt <benh@kernel.crashing.org>,
Paul Mackerras <paulus@samba.org>,
linuxppc-dev@lists.ozlabs.org
Subject: Re: [PATCH v2] barriers: introduce smp_mb__release_acquire and update documentation
Date: Fri, 9 Oct 2015 13:02:46 +0200 [thread overview]
Message-ID: <20151009110246.GY3816@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <20151009094039.GD26278@arm.com>
On Fri, Oct 09, 2015 at 10:40:39AM +0100, Will Deacon wrote:
> Stepping back a second, I believe that there are three cases:
>
>
> RELEASE X -> ACQUIRE Y (same CPU)
> * Needs a barrier on TSO architectures for full ordering
+PPC
> UNLOCK X -> LOCK Y (same CPU)
> * Needs a barrier on PPC for full ordering
> RELEASE X -> ACQUIRE X (different CPUs)
* Fully ordered everywhere...
* ... but needs a barrier on TSO + PPC to become a full barrier
> UNLOCK X -> ACQUIRE X (different CPUs)
s/ACQUIRE/LOCK/ ?
> * Fully ordered everywhere...
> * ... but needs a barrier on PPC to become a full barrier
If you really meant ACQUIRE, then x86 also needs a barrier in order to
upgrade, seeing how our unlock is equivalent to smp_store_release(). Our
LOCK otoh is far heavier than smp_load_acquire() and would result in
different rules.
And I'm not sure the "(different CPUs)" bit makes sense, as the same is
true if they're on the same CPU.
next prev parent reply other threads:[~2015-10-09 11:02 UTC|newest]
Thread overview: 48+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-10-07 10:59 [PATCH v2] barriers: introduce smp_mb__release_acquire and update documentation Will Deacon
2015-10-07 11:19 ` Peter Zijlstra
2015-10-07 13:23 ` Will Deacon
2015-10-07 13:23 ` Will Deacon
2015-10-07 14:53 ` Peter Zijlstra
2015-10-07 15:25 ` Paul E. McKenney
2015-10-08 3:50 ` Michael Ellerman
2015-10-08 3:50 ` Michael Ellerman
2015-10-08 11:16 ` Peter Zijlstra
2015-10-08 12:59 ` Will Deacon
2015-10-08 22:17 ` Paul E. McKenney
2015-10-09 9:51 ` Will Deacon
2015-10-09 9:51 ` Will Deacon
2015-10-09 11:25 ` Peter Zijlstra
2015-10-09 11:25 ` Peter Zijlstra
2015-10-09 17:44 ` Paul E. McKenney
2015-10-09 17:44 ` Paul E. McKenney
2015-10-09 17:43 ` Paul E. McKenney
2015-10-09 18:33 ` Will Deacon
2015-10-12 23:30 ` Paul E. McKenney
2015-10-20 14:20 ` Boqun Feng
2015-10-08 21:44 ` Paul E. McKenney
2015-10-09 7:29 ` Peter Zijlstra
2015-10-09 8:31 ` Peter Zijlstra
2015-10-09 9:40 ` Will Deacon
2015-10-09 9:40 ` Will Deacon
2015-10-09 11:02 ` Peter Zijlstra [this message]
2015-10-09 12:41 ` Will Deacon
2015-10-09 11:12 ` Peter Zijlstra
2015-10-09 12:51 ` Will Deacon
2015-10-09 13:06 ` Peter Zijlstra
2015-10-09 11:13 ` Peter Zijlstra
2015-10-09 17:21 ` Paul E. McKenney
2015-10-19 1:17 ` Boqun Feng
2015-10-19 1:17 ` Boqun Feng
2015-10-19 10:23 ` Peter Zijlstra
2015-10-19 10:23 ` Peter Zijlstra
2015-10-20 7:35 ` Boqun Feng
2015-10-20 7:35 ` Boqun Feng
2015-10-20 23:34 ` Paul E. McKenney
2015-10-21 8:24 ` Peter Zijlstra
2015-10-21 19:29 ` Paul E. McKenney
2015-10-21 19:36 ` Peter Zijlstra
2015-10-21 19:36 ` Peter Zijlstra
2015-10-21 19:56 ` Paul E. McKenney
2015-10-21 16:04 ` David Laight
2015-10-21 16:04 ` David Laight
2015-10-21 19:34 ` Paul E. McKenney
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