From: Will Deacon <will.deacon@arm.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Waiman Long <waiman.long@hp.com>,
"linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>,
"linux-arm-kernel@lists.infradead.org"
<linux-arm-kernel@lists.infradead.org>,
"mingo@redhat.com" <mingo@redhat.com>
Subject: Re: [PATCH 2/9] locking/qrwlock: avoid redundant atomic_add_return on read_lock_slowpath
Date: Wed, 8 Jul 2015 14:37:04 +0100 [thread overview]
Message-ID: <20150708133704.GE9283@arm.com> (raw)
In-Reply-To: <20150708095944.GA3644@twins.programming.kicks-ass.net>
On Wed, Jul 08, 2015 at 10:59:44AM +0100, Peter Zijlstra wrote:
> On Tue, Jul 07, 2015 at 03:28:13PM -0400, Waiman Long wrote:
> > #ifndef queued_inc_reader_return
> > static inline u32 queued_inc_reader_return(struct qrwlock *lock)
>
> That's actually a misleading name, we don't do an inc_return, we do a
> fetch_inc.
>
> > {
> > return atomic_add_return(_QR_BIAS, &lock->cnts) - _QR_BIAS;
> > }
> > #endif
>
> With that you (Will) could even reuse the ll/sc load and avoid issuing a
> second load. You basically need atomic_fetch_add_relaxed().
ARMv8.1 has an instruction for that :) [ldadd].
Will
WARNING: multiple messages have this Message-ID (diff)
From: will.deacon@arm.com (Will Deacon)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH 2/9] locking/qrwlock: avoid redundant atomic_add_return on read_lock_slowpath
Date: Wed, 8 Jul 2015 14:37:04 +0100 [thread overview]
Message-ID: <20150708133704.GE9283@arm.com> (raw)
In-Reply-To: <20150708095944.GA3644@twins.programming.kicks-ass.net>
On Wed, Jul 08, 2015 at 10:59:44AM +0100, Peter Zijlstra wrote:
> On Tue, Jul 07, 2015 at 03:28:13PM -0400, Waiman Long wrote:
> > #ifndef queued_inc_reader_return
> > static inline u32 queued_inc_reader_return(struct qrwlock *lock)
>
> That's actually a misleading name, we don't do an inc_return, we do a
> fetch_inc.
>
> > {
> > return atomic_add_return(_QR_BIAS, &lock->cnts) - _QR_BIAS;
> > }
> > #endif
>
> With that you (Will) could even reuse the ll/sc load and avoid issuing a
> second load. You basically need atomic_fetch_add_relaxed().
ARMv8.1 has an instruction for that :) [ldadd].
Will
next prev parent reply other threads:[~2015-07-08 13:37 UTC|newest]
Thread overview: 42+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-07-07 17:24 [PATCH 0/9] locking/qrwlock: get qrwlocks up and running on arm64 Will Deacon
2015-07-07 17:24 ` Will Deacon
2015-07-07 17:24 ` [PATCH 1/9] locking/qrwlock: include <linux/spinlock.h> for arch_spin_{lock,unlock} Will Deacon
2015-07-07 17:24 ` [PATCH 1/9] locking/qrwlock: include <linux/spinlock.h> for arch_spin_{lock, unlock} Will Deacon
2015-07-07 17:24 ` [PATCH 2/9] locking/qrwlock: avoid redundant atomic_add_return on read_lock_slowpath Will Deacon
2015-07-07 17:24 ` Will Deacon
2015-07-07 17:51 ` Waiman Long
2015-07-07 17:51 ` Waiman Long
2015-07-07 18:19 ` Will Deacon
2015-07-07 18:19 ` Will Deacon
2015-07-07 19:28 ` Waiman Long
2015-07-07 19:28 ` Waiman Long
2015-07-08 9:59 ` Peter Zijlstra
2015-07-08 9:59 ` Peter Zijlstra
2015-07-08 13:37 ` Will Deacon [this message]
2015-07-08 13:37 ` Will Deacon
2015-07-07 21:30 ` Peter Zijlstra
2015-07-07 21:30 ` Peter Zijlstra
2015-07-07 17:24 ` [PATCH 3/9] locking/qrwlock: tidy up rspin_until_writer_unlock Will Deacon
2015-07-07 17:24 ` Will Deacon
2015-07-07 17:24 ` [PATCH 4/9] locking/qrwlock: implement queue_write_unlock using smp_store_release Will Deacon
2015-07-07 17:24 ` Will Deacon
2015-07-08 10:00 ` Peter Zijlstra
2015-07-08 10:00 ` Peter Zijlstra
2015-07-07 17:24 ` [PATCH 5/9] locking/qrwlock: remove redundant cmpxchg barriers on writer slow-path Will Deacon
2015-07-07 17:24 ` Will Deacon
2015-07-08 10:05 ` Peter Zijlstra
2015-07-08 10:05 ` Peter Zijlstra
2015-07-08 13:34 ` Will Deacon
2015-07-08 13:34 ` Will Deacon
2015-07-07 17:24 ` [PATCH 6/9] locking/qrwlock: allow architectures to hook in to contended paths Will Deacon
2015-07-07 17:24 ` Will Deacon
2015-07-08 10:06 ` Peter Zijlstra
2015-07-08 10:06 ` Peter Zijlstra
2015-07-08 13:35 ` Will Deacon
2015-07-08 13:35 ` Will Deacon
2015-07-07 17:24 ` [PATCH 7/9] locking/qrwlock: expose internal lock structure in qrwlock definition Will Deacon
2015-07-07 17:24 ` Will Deacon
2015-07-07 17:24 ` [PATCH 8/9] arm64: cmpxchg: implement cmpxchg_relaxed Will Deacon
2015-07-07 17:24 ` Will Deacon
2015-07-07 17:24 ` [PATCH 9/9] arm64: locking: replace read/write locks with generic qrwlock code Will Deacon
2015-07-07 17:24 ` Will Deacon
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