From: Will Deacon <will.deacon@arm.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: "linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>,
"Waiman.Long@hp.com" <Waiman.Long@hp.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"paulmck@linux.vnet.ibm.com" <paulmck@linux.vnet.ibm.com>
Subject: Re: [PATCH 1/5] atomics: add acquire/release/relaxed variants of some atomic operations
Date: Tue, 14 Jul 2015 12:31:47 +0100 [thread overview]
Message-ID: <20150714113147.GF16213@arm.com> (raw)
In-Reply-To: <20150714112420.GK3644@twins.programming.kicks-ass.net>
On Tue, Jul 14, 2015 at 12:24:20PM +0100, Peter Zijlstra wrote:
> On Tue, Jul 14, 2015 at 12:08:11PM +0100, Will Deacon wrote:
> > On Tue, Jul 14, 2015 at 11:58:37AM +0100, Peter Zijlstra wrote:
>
>
> > > #ifndef atomic_add_return_relaxed
> > >
> > > #define atomic_add_return_relaxed atomic_add_return
> > > /*
> > > * If one cannot define a more relaxed version,
> > > * acquire/release are out the window too.
> > > */
> > > #define atomic_add_return_acquire atomic_add_return
> > > #define atomic_add_return_release atomic_add_return
> > >
> > > #else /* relaxed */
> > >
> > > #ifndef atomic_add_return_acquire
> > > #define atomic_add_return_acquire(args...) \
> > > do { \
> > > atomic_add_return_relaxed(args); \
> > > smp_mb__after_atomic(); \
> > > } while (0)
> > > #endif
> > >
> > > #ifndef atomic_add_return_release
> > > #define atomic_add_return_release(args...) \
> > > do { \
> > > smp_mb__before_atomic(); \
> > > atomic_add_return_relaxed(args); \
> > > } while (0)
> > > #endif
>
> One could even take it one step further and go:
>
> #ifndef atomic_add_return
> #define atomic_add_return(args...) \
> do { \
> smp_mb__before_atomic(); \
> atomid_add_return_relaxed(args); \
> smp_mb__after_atomic(); \
> } while (0)
...and
#ifndef atomic_add
#define atomic_add(args...) (void)atomic_add_return_relaxed(args);
It would mean a new architecture only has to define a barrier instruction
and a handful of relaxed atomics for a bare-minimum atomic.h avoiding
spinlocks.
Will
next prev parent reply other threads:[~2015-07-14 11:31 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-07-13 12:31 [PATCH 0/5] Add generic support for relaxed atomics Will Deacon
2015-07-13 12:31 ` [PATCH 1/5] atomics: add acquire/release/relaxed variants of some atomic operations Will Deacon
2015-07-14 10:25 ` Peter Zijlstra
2015-07-14 10:32 ` Will Deacon
2015-07-14 10:58 ` Peter Zijlstra
2015-07-14 11:08 ` Will Deacon
2015-07-14 11:24 ` Peter Zijlstra
2015-07-14 11:31 ` Will Deacon [this message]
2015-07-14 11:38 ` Peter Zijlstra
2015-07-14 15:55 ` Will Deacon
2015-07-13 12:31 ` [PATCH 2/5] asm-generic: rework atomic-long.h to avoid bulk code duplication Will Deacon
2015-07-13 12:31 ` [PATCH 3/5] asm-generic: add relaxed/acquire/release variants for atomic_long_t Will Deacon
2015-07-13 12:31 ` [PATCH 4/5] lockref: remove homebrew cmpxchg64_relaxed macro definition Will Deacon
2015-07-13 12:31 ` [PATCH 5/5] locking/qrwlock: make use of acquire/release/relaxed atomics Will Deacon
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