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Date: Thu, 14 Jan 2016 21:15:13 +0100
From: Peter Zijlstra <peterz@infradead.org>
Subject: Re: [v3,11/41] mips: reuse asm-generic/barrier.h
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To: Leonid Yegoshin <Leonid.Yegoshin@imgtec.com>
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>, paulmck@linux.vnet.ibm.com, 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, ddaney.cavm@gmail.com, Thomas Gleixner <tglx@linutronix.de>, linux-metag@vger.kernel.org, linux-arm-kernel@lists.infradead.org, Andrew Cooper <andrew.cooper3@citrix.com>, linux-kernel@vger.kernel.org, Ralf Baechle <ralf@linux-mips.org>, Joe Perches <joe@perches.com>, linuxppc-dev@lists.ozlabs.org, David Miller <davem@davemloft.net>
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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.

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.

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