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Re: mips octeon memory model questions

To: Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: mips octeon memory model questions
From: Peter Zijlstra <peterz@infradead.org>
Date: Tue, 4 Feb 2014 20:05:35 +0100
Cc: David Daney <ddaney@caviumnetworks.com>, Ralf Baechle <ralf@linux-mips.org>, "linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>, linux-mips <linux-mips@linux-mips.org>, Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, Paul McKenney <paulmck@linux.vnet.ibm.com>, Will Deacon <will.deacon@arm.com>
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On Tue, Feb 04, 2014 at 10:58:40AM -0800, Linus Torvalds wrote:
> On Tue, Feb 4, 2014 at 10:41 AM, Peter Zijlstra <peterz@infradead.org> wrote:
> >
> > Still doesn't make sense, because if we need the first sync to stop
> > writes from being re-ordered with the ll-sc, we also need the second
> > sync to avoid the same.
> 
> Presumably octeon doesn't do speculative writes, only *buffered* writes.

Speculative writes are bad.. :-)

> So writes move down, not up.

Right, but the ll-sc store might move down over a later store. Say
because the ll-sc needs to first get exclusive ownership of the
cacheline where the later store would be to an already owned line.



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