From mboxrd@z Thu Jan  1 00:00:00 1970
From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Date: Thu, 14 Jan 2016 20:36:37 +0000
Subject: Re: [v3,11/41] mips: reuse asm-generic/barrier.h
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To: Peter Zijlstra <peterz@infradead.org>
Cc: linux-mips@linux-mips.org, linux-ia64@vger.kernel.org, "Michael S. Tsirkin" <mst@redhat.com>, Will Deacon <will.deacon@arm.com>, virtualization@lists.linux-foundation.org, "H. Peter Anvin" <hpa@zytor.com>, sparclinux@vger.kernel.org, Ingo Molnar <mingo@kernel.org>, linux-arch@vger.kernel.org, linux-s390@vger.kernel.org, Russell King - ARM Linux <linux@arm.linux.org.uk>, user-mode-linux-devel@lists.sourceforge.net, linux-sh@vger.kernel.org, Michael Ellerman <mpe@ellerman.id.au>, x86@kernel.org, xen-devel@lists.xenproject.org, Ingo Molnar <mingo@elte.hu>, linux-xtensa@linux-xtensa.org, james.hogan@imgtec.com, Arnd Bergmann <arnd@arndb.de>, Stefano Stabellini <stefano.stabellini@eu.citrix.com>, adi-buildroot-devel@lists.sourceforge.net, Leonid Yegoshin <Leonid.Yegoshin@imgtec.com>, ddaney.cavm@gmail.com, Thomas Gleixner <tglx@linutronix.de>, linux-metag@vger.kernel.org

On Thu, Jan 14, 2016 at 09:15:13PM +0100, Peter Zijlstra wrote:
> On Thu, Jan 14, 2016 at 11:42:02AM -0800, Leonid Yegoshin wrote:
> > An the only point - please use an appropriate SYNC_* barriers instead of
> > heavy bold hammer. That stuff was design explicitly to support the
> > requirements of Documentation/memory-barriers.txt
> 
> That's madness. That document changes from version to version as to what
> we _think_ the actual hardware does. It is _NOT_ a specification.

There is work in progress on a specification, but please don't hold
your breath.  And I am not as optimistic as I might be about any formal
specification keeping up with the Linux kernel or with the hardware that
it supports.  But it seems worth a good try.

> You cannot design hardware from that. Its incomplete and fails to
> specify a bunch of things. It not a mathematically sound definition of a
> memory model.
> 
> Please stop referring to that document for what a particular barrier
> _should_ do.  Explain what MIPS does, so we can attempt to integrate
> this knowledge with our knowledge of PPC/ARM/Alpha/x86/etc. and improve
> upon our understanding of hardware and improve the Linux memory model.

Please!

							Thanx, Paul