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Date: Mon, 08 Sep 2014 12:12:50 -0700
From: "H. Peter Anvin" <hpa@zytor.com>
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To: James Bottomley <James.Bottomley@HansenPartnership.com>
CC: paulmck@linux.vnet.ibm.com, Peter Hurley <peter@hurleysoftware.com>,
        One Thousand Gnomes <gnomes@lxorguk.ukuu.org.uk>,
        Jakub Jelinek <jakub@redhat.com>,
        Mikael Pettersson <mikpelinux@gmail.com>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Richard Henderson <rth@twiddle.net>, Oleg Nesterov <oleg@redhat.com>,
        Miroslav Franc <mfranc@redhat.com>, Paul Mackerras <paulus@samba.org>,
        linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org,
        linux-arch@vger.kernel.org, Tony Luck <tony.luck@intel.com>,
        linux-ia64@vger.kernel.org
Subject: Re: bit fields && data tearing
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On 09/08/2014 12:09 PM, James Bottomley wrote:
> 
> Um, I think you need to re-read the thread; that's not what I said at
> all. It's even written lower down: "PA can't do atomic bit sets (no
> atomic RMW except the ldcw operation) it can do atomic writes to
> fundamental sizes (byte, short, int, long) provided gcc emits the
> correct primitive".  The original question was whether atomicity
> required native bus width access, which we currently assume, so there's
> no extant problem.
> 

The issue at hand was whether or not partially overlapped (but natually
aligned) writes can pass each other.  *This* is the aggressive
relaxation to which I am referring.

I would guess that that is a very unusual constraint.

	-hpa