linux-kernel - [RFC 0/5] atomics: powerpc: implement relaxed/acquire/release variants of some atomics

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Date:	Fri, 28 Aug 2015 10:48:14 +0800
From:	Boqun Feng <boqun.feng@...il.com>
To:	linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Paul Mackerras <paulus@...ba.org>,
	Michael Ellerman <mpe@...erman.id.au>,
	Thomas Gleixner <tglx@...utronix.de>,
	Will Deacon <will.deacon@....com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Waiman Long <waiman.long@...com>,
	Boqun Feng <boqun.feng@...il.com>
Subject: [RFC 0/5] atomics: powerpc: implement relaxed/acquire/release variants of some atomics

Relaxed/acquire/release variants of atomic operations {add,sub}_return and
{cmp,}xchg are introduced by commit:

"atomics: add acquire/release/relaxed variants of some atomic operations"

which is now on locking/core branch of tip tree.

By default, the generic code will implement relaxed variants as a full
ordered atomic operation and release/acquire variants as a relaxed variants
with a necessary general barrier before or after.

On powerpc, which has a weak memory order model, a relaxed variant can be
implemented more lightweightly than a full ordered one. Further more,
release and acquire variants can be implemented with arch-specific
lightweight barriers.

Therefore this patchset implements the relaxed/acquire/release variants
based on powerpc memory model and specific barriers. A trivial test for
these new variants is also included in this series, because some of these
variants are not used in kernel for now, I would like to make the code of
these variants at least generated somewhere.

The patchset consists of 5 parts:

1.	add trivial tests for the new variants in lib/atomic64_test.c

2.	introduce arch_atomic_op_*() helpers as the arch-specific helpers
	to build other variants based on relaxed.

3.	implement atomic{,64}_{add,sub}_return_* variants

4.	implement xchg_* and atomic{,64}_xchg_* variants

5.	implement cmpxchg_* atomic{,64}_cmpxchg_* variants

This patchset is based on locking/core branch of tip tree and all patches
are built and boot tested for LE pseries.

Regards,
Boqun

-- 
2.5.0

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