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Date: Tue, 12 Jan 2016 11:25:55 +0100
From: Peter Zijlstra <peterz@infradead.org>
To: Leonid Yegoshin <Leonid.Yegoshin@imgtec.com>
Cc: "Michael S. Tsirkin" <mst@redhat.com>, linux-kernel@vger.kernel.org,
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Subject: Re: [v3,11/41] mips: reuse asm-generic/barrier.h
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On Tue, Jan 12, 2016 at 10:27:11AM +0100, Peter Zijlstra wrote:
> 2) the changelog _completely_ fails to explain the sync 0x11 and sync
> 0x12 semantics nor does it provide a publicly accessible link to
> documentation that does.

Ralf pointed me at: https://imgtec.com/mips/architectures/mips64/

> 3) it really should have explained what you did with
> smp_llsc_mb/smp_mb__before_llsc() in _detail_.

And reading the MIPS64 v6.04 instruction set manual, I think 0x11/0x12
are _NOT_ transitive and therefore cannot be used to implement the
smp_mb__{before,after} stuff.

That is, in MIPS speak, those SYNC types are Ordering Barriers, not
Completion Barriers. They need not be globally performed.