linux-kernel - Re: [PATCH 4/4] locking: Introduce smp_cond

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Message-ID: <20151112150149.GY3972@linux.vnet.ibm.com>
Date:	Thu, 12 Nov 2015 07:01:49 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Oleg Nesterov <oleg@...hat.com>, Boqun Feng <boqun.feng@...il.com>,
	mingo@...nel.org, linux-kernel@...r.kernel.org, corbet@....net,
	mhocko@...nel.org, dhowells@...hat.com,
	torvalds@...ux-foundation.org, will.deacon@....com,
	Michael Ellerman <mpe@...erman.id.au>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Paul Mackerras <paulus@...ba.org>
Subject: Re: [PATCH 4/4] locking: Introduce smp_cond_acquire()

On Thu, Nov 12, 2015 at 03:50:13PM +0100, Peter Zijlstra wrote:
> On Thu, Nov 12, 2015 at 06:40:04AM -0800, Paul E. McKenney wrote:
> > I cannot resist suggesting that any lock that interacts with
> > spin_unlock_wait() must have all relevant acquisitions followed by
> > smp_mb__after_unlock_lock().
> 
> Ha! that would certainly help here. But it would mean that argh64v8 also
> needs to define that, even though that is already RCsc.

Maybe.  It could also be that arm64 avoids the need somehow, for example
via their RCsc behavior.  Their memory model is similar to PPC, but not
exactly the same.

Will?

							Thanx, Paul

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