linux-kernel - Re: [PATCH -v3 7/8] locking: Move smp_cond_load_acquire() and friends into asm-generic/barrier.h

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Message-ID: <20160601124541.GS3190@twins.programming.kicks-ass.net>
Date:	Wed, 1 Jun 2016 14:45:41 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Will Deacon <will.deacon@....com>
Cc:	Waiman Long <waiman.long@....com>, linux-kernel@...r.kernel.org,
	torvalds@...ux-foundation.org, manfred@...orfullife.com,
	dave@...olabs.net, paulmck@...ux.vnet.ibm.com,
	boqun.feng@...il.com, tj@...nel.org, pablo@...filter.org,
	kaber@...sh.net, davem@...emloft.net, oleg@...hat.com,
	netfilter-devel@...r.kernel.org, sasha.levin@...cle.com,
	hofrat@...dl.org
Subject: Re: [PATCH -v3 7/8] locking: Move smp_cond_load_acquire() and
 friends into asm-generic/barrier.h

On Wed, Jun 01, 2016 at 01:13:33PM +0100, Will Deacon wrote:
> On Wed, Jun 01, 2016 at 02:06:54PM +0200, Peter Zijlstra wrote:

> > Works for me; but that would loose using cmpwait() for
> > !smp_cond_load_acquire() spins, you fine with that?
> > 
> > The two conversions in the patch were both !acquire spins.
> 
> Maybe we could go the whole hog and add smp_cond_load_relaxed?

What about say the cmpxchg loops in queued_write_lock_slowpath()
? Would that be something you'd like to use wfe for?

Writing those in smp_cond_load_{acquire,relaxed)() is somewhat possible
but quite ugleh.