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 11:32:20 +0100 [thread overview]
Message-ID: <20150714103220.GB16213@arm.com> (raw)
In-Reply-To: <20150714102511.GI19282@twins.programming.kicks-ass.net>
On Tue, Jul 14, 2015 at 11:25:11AM +0100, Peter Zijlstra wrote:
> On Mon, Jul 13, 2015 at 01:31:23PM +0100, Will Deacon wrote:
> > +
> > +/*
> > + * Relaxed variants of xchg, cmpxchg and some atomic operations.
> > + *
> > + * We support four variants:
> > + *
> > + * - Fully ordered: The default implementation, no suffix required.
> > + * - Acquire: Provides ACQUIRE semantics, _acquire suffix.
> > + * - Release: Provides RELEASE semantics, _release suffix.
> > + * - Relaxed: No ordering guarantees, _relaxed suffix.
> > + *
> > + * See Documentation/memory-barriers.txt for ACQUIRE/RELEASE definitions.
> > + */
> > +
> > +#ifndef atomic_read_acquire
> > +#define atomic_read_acquire(v) smp_load_acquire(&(v)->counter)
> > +#endif
> > +
> > +#ifndef atomic_set_release
> > +#define atomic_set_release(v, i) smp_store_release(&(v)->counter, (i))
> > +#endif
> > +
> > +#ifndef atomic_add_return_relaxed
> > +#define atomic_add_return_relaxed atomic_add_return
> > +#endif
> > +#ifndef atomic_add_return_acquire
> > +#define atomic_add_return_acquire atomic_add_return
> > +#endif
> > +#ifndef atomic_add_return_release
> > +#define atomic_add_return_release atomic_add_return
> > +#endif
>
> Could we not define _{acquire,release} in terms of _relaxed and
> smp_mb__{after,before}_atomic() ?
I actually started out with that, but it penalises architectures that
don't have _relaxed implementations of some routines.
For example, cmpxchg_acquire would likely expand to:
cmpxchg_relaxed(); smp_mb__after_atomic();
-> cmpxchg(); smp_mb__after_atomic();
-> smp_mb(); __cmpxchg(); __smp_mb(); smp_mb();
(where __cmpxchg() is some arch-internal cmpxchg implementation)
Will
next prev parent reply other threads:[~2015-07-14 10:32 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 [this message]
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
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
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20150714103220.GB16213@arm.com \
--to=will.deacon@arm.com \
--cc=Waiman.Long@hp.com \
--cc=linux-arch@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=paulmck@linux.vnet.ibm.com \
--cc=peterz@infradead.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.