linux-kernel - Re: [v3,11/41] mips: reuse asm-generic/barrier.h

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Date:	Fri, 15 Jan 2016 14:01:47 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Leonid Yegoshin <Leonid.Yegoshin@...tec.com>,
	Will Deacon <will.deacon@....com>,
	"Michael S. Tsirkin" <mst@...hat.com>,
	linux-kernel@...r.kernel.org, Arnd Bergmann <arnd@...db.de>,
	linux-arch@...r.kernel.org,
	Andrew Cooper <andrew.cooper3@...rix.com>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	virtualization@...ts.linux-foundation.org,
	Stefano Stabellini <stefano.stabellini@...citrix.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>, "H. Peter Anvin" <hpa@...or.com>,
	Joe Perches <joe@...ches.com>,
	David Miller <davem@...emloft.net>, linux-ia64@...r.kernel.org,
	linuxppc-dev@...ts.ozlabs.org, linux-s390@...r.kernel.org,
	sparclinux@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-metag@...r.kernel.org, linux-mips@...ux-mips.org,
	x86@...nel.org, user-mode-linux-devel@...ts.sourceforge.net,
	adi-buildroot-devel@...ts.sourceforge.net,
	linux-sh@...r.kernel.org, linux-xtensa@...ux-xtensa.org,
	xen-devel@...ts.xenproject.org, Ralf Baechle <ralf@...ux-mips.org>,
	Ingo Molnar <mingo@...nel.org>, ddaney.cavm@...il.com,
	james.hogan@...tec.com, Michael Ellerman <mpe@...erman.id.au>
Subject: Re: [v3,11/41] mips: reuse asm-generic/barrier.h

On Fri, Jan 15, 2016 at 10:29:12PM +0100, Peter Zijlstra wrote:
> On Fri, Jan 15, 2016 at 09:39:12AM -0800, Paul E. McKenney wrote:
> > Should we start putting litmus tests for the various examples
> > somewhere, perhaps in a litmus-tests directory within each participating
> > architecture?  I have a pile of powerpc-related litmus tests on my laptop,
> > but they probably aren't doing all that much good there.
> 
> Yeah, or a version of them in C that we can 'compile'?

That would be good as well.  I am guessing that architecture-specific
litmus tests will also be needed, but you are right that
architecture-independent versions are higher priority.

> > commit 2cb4e83a1b5c89c8e39b8a64bd89269d05913e41
> > Author: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> > Date:   Fri Jan 15 09:30:42 2016 -0800
> > 
> >     documentation: Distinguish between local and global transitivity
> >     
> >     The introduction of smp_load_acquire() and smp_store_release() had
> >     the side effect of introducing a weaker notion of transitivity:
> >     The transitivity of full smp_mb() barriers is global, but that
> >     of smp_store_release()/smp_load_acquire() chains is local.  This
> >     commit therefore introduces the notion of local transitivity and
> >     gives an example.
> >     
> >     Reported-by: Peter Zijlstra <peterz@...radead.org>
> >     Reported-by: Will Deacon <will.deacon@....com>
> >     Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> 
> I think it fails to mention smp_mb__after_release_acquire(), although I
> suspect we didn't actually introduce the primitive yet, which raises the
> point, do we want to?

Well, it is not in v4.4.  I believe that we need good use cases before
we add it.

							Thanx, Paul