linux-kernel - Re: [RFC] arch: Introduce new TSO memory barrier smp

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Message-ID: <20131105144900.GD3947@linux.vnet.ibm.com>
Date:	Tue, 5 Nov 2013 06:49:00 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Will Deacon <will.deacon@....com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Victor Kaplansky <VICTORK@...ibm.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Anton Blanchard <anton@...ba.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Linux PPC dev <linuxppc-dev@...abs.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	Michael Ellerman <michael@...erman.id.au>,
	Michael Neuling <mikey@...ling.org>,
	"linux@....linux.org.uk" <linux@....linux.org.uk>,
	"schwidefsky@...ibm.com" <schwidefsky@...ibm.com>,
	"heiko.carstens@...ibm.com" <heiko.carstens@...ibm.com>
Subject: Re: [RFC] arch: Introduce new TSO memory barrier smp_tmb()

On Tue, Nov 05, 2013 at 02:05:48PM +0000, Will Deacon wrote:
> On Mon, Nov 04, 2013 at 08:53:44PM +0000, Paul E. McKenney wrote:
> > On Mon, Nov 04, 2013 at 08:11:27PM +0100, Peter Zijlstra wrote:
> > Some comments below.  I believe that opcodes need to be fixed for IA64.
> > I am unsure of the ifdefs and opcodes for arm64, but the ARM folks should
> > be able to tell us.

[ . . . ]

> > > +} while (0)
> > > +
> > > +#define smp_load_acquire(p)                                          \
> > > +do {                                                                 \
> > > +     typeof(p) ___p1;                                                \
> > > +     asm volatile ("ldar %w0, [%1]"                                  \
> > > +                     : "=r" (___p1) : "r" (&p) : "memory");          \
> > > +     return ___p1;                                                   \
> 
> Similar comments here wrt Q constraint.
> 
> Random other question: have you considered how these accessors should behave
> when presented with __iomem pointers?

Should we have something to make sparse yell if not __kernel or some such?

								Thanx, Paul

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