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: <20160601121333.GC355@arm.com>
Date:	Wed, 1 Jun 2016 13:13:33 +0100
From:	Will Deacon <will.deacon@....com>
To:	Peter Zijlstra <peterz@...radead.org>
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 02:06:54PM +0200, Peter Zijlstra wrote:
> On Wed, Jun 01, 2016 at 01:00:10PM +0100, Will Deacon wrote:
> > On Wed, Jun 01, 2016 at 11:31:58AM +0200, Peter Zijlstra wrote:
> > > Will, since ARM64 seems to want to use this, does the below make sense
> > > to you?
> > 
> > Not especially -- I was going to override smp_cond_load_acquire anyway
> > because I want to build it using cmpwait_acquire and get rid of the
> > smp_acquire__after_ctrl_dep trick, which is likely slower on arm64.
> > 
> > So I'd be happier nuking cmpwait from the generic interfaces and using
> > smp_cond_load_acquire everywhere, if that's possible.
> 
> 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?

Will