linux-kernel - Re: [RFC] locking/rwsem: Avoid issuing wakeup before setting the reader waiter to nil

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Message-ID: <20181129220544.GE11632@hirez.programming.kicks-ass.net>
Date:   Thu, 29 Nov 2018 23:05:44 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Waiman Long <longman@...hat.com>
Cc:     Will Deacon <will.deacon@....com>, Yongji Xie <elohimes@...il.com>,
        mingo@...hat.com, linux-kernel@...r.kernel.org,
        xieyongji@...du.com, zhangyu31@...du.com, liuqi16@...du.com,
        yuanlinsi01@...du.com, nixun@...du.com, lilin24@...du.com,
        Davidlohr Bueso <dave@...olabs.net>
Subject: Re: [RFC] locking/rwsem: Avoid issuing wakeup before setting the
 reader waiter to nil

On Thu, Nov 29, 2018 at 01:34:05PM -0500, Waiman Long wrote:

> That will certainly work for x86. However, I am not sure if that will be
> optimal for arm and powerpc.

	smp_mb__before_atomic()
	cmpxchg_relaxed()

works. Also see pv_kick_node()'s commit:

  34d54f3d6917 ("locking/pvqspinlock: Relax cmpxchg's to improve performance on some architectures")

you might know the author of that :-)