From: Will Deacon <will.deacon@arm.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Waiman Long <longman@redhat.com>, Ingo Molnar <mingo@redhat.com>,
linux-kernel@vger.kernel.org,
Pan Xinhui <xinhui@linux.vnet.ibm.com>,
Boqun Feng <boqun.feng@gmail.com>,
Andrea Parri <parri.andrea@gmail.com>
Subject: Re: [RESEND PATCH v5] locking/pvqspinlock: Relax cmpxchg's to improve performance on some archs
Date: Mon, 14 Aug 2017 13:01:22 +0100 [thread overview]
Message-ID: <20170814120121.GA24249@arm.com> (raw)
In-Reply-To: <20170811090601.2owslxi4lgv3kond@hirez.programming.kicks-ass.net>
On Fri, Aug 11, 2017 at 11:06:01AM +0200, Peter Zijlstra wrote:
> On Thu, Aug 10, 2017 at 02:18:30PM -0400, Waiman Long wrote:
> > On 08/10/2017 12:22 PM, Waiman Long wrote:
> > > On 08/10/2017 12:15 PM, Peter Zijlstra wrote:
>
> > >> Might as well do an explicit:
> > >>
> > >> smp_mb__before_atomic()
> > >> cmpxchg_relaxed()
> > >> smp_mb__after_atomic()
> > >>
> > >> I suppose and not introduce new primitives.
> >
> > I think we don't need smp_mb__after_atomic(). The read has to be fully
> > ordered, but the write part may not need it as the control dependency of
> > the old value should guard against incorrect action. Right?
>
> You'd think that, but IIRC there was something funny about using the SC
> return flag for control dependencies. Will?
Yeah, that's right, you can't use the STXR status flag to create control
dependencies.
Will
next prev parent reply other threads:[~2017-08-14 12:01 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-05-24 13:38 [RESEND PATCH v5] locking/pvqspinlock: Relax cmpxchg's to improve performance on some archs Waiman Long
2017-08-09 13:39 ` Waiman Long
2017-08-09 15:06 ` Peter Zijlstra
2017-08-09 15:15 ` Peter Zijlstra
2017-08-10 8:12 ` Boqun Feng
2017-08-10 9:13 ` Peter Zijlstra
2017-08-10 20:49 ` Paul E. McKenney
2017-08-10 11:50 ` Peter Zijlstra
2017-08-10 13:27 ` Waiman Long
2017-08-10 13:58 ` Waiman Long
2017-08-10 16:15 ` Peter Zijlstra
2017-08-10 16:22 ` Waiman Long
2017-08-10 18:18 ` Waiman Long
2017-08-11 9:06 ` Peter Zijlstra
2017-08-14 12:01 ` Will Deacon [this message]
2017-08-14 15:01 ` Waiman Long
2017-08-14 16:02 ` Will Deacon
2017-08-14 18:47 ` Peter Zijlstra
2017-08-15 18:40 ` Will Deacon
2017-08-21 10:55 ` Peter Zijlstra
2017-08-21 18:00 ` Will Deacon
2017-08-21 19:25 ` Peter Zijlstra
2017-08-21 19:42 ` Peter Zijlstra
2017-08-22 15:35 ` Waiman Long
2017-08-22 10:40 ` Will Deacon
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