Re: bit fields && data tearing
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- To: James Bottomley <James.Bottomley@xxxxxxxxxxxxxxxxxxxxx>
- Subject: Re: bit fields && data tearing
- From: "H. Peter Anvin" <hpa@xxxxxxxxx>
- Date: Mon, 08 Sep 2014 12:12:50 -0700
- Cc: paulmck@xxxxxxxxxxxxxxxxxx, Peter Hurley <peter@xxxxxxxxxxxxxxxxxx>, One Thousand Gnomes <gnomes@xxxxxxxxxxxxxxxxxxx>, Jakub Jelinek <jakub@xxxxxxxxxx>, Mikael Pettersson <mikpelinux@xxxxxxxxx>, Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>, Richard Henderson <rth@xxxxxxxxxxx>, Oleg Nesterov <oleg@xxxxxxxxxx>, Miroslav Franc <mfranc@xxxxxxxxxx>, Paul Mackerras <paulus@xxxxxxxxx>, linuxppc-dev@xxxxxxxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, linux-arch@xxxxxxxxxxxxxxx, Tony Luck <tony.luck@xxxxxxxxx>, linux-ia64@xxxxxxxxxxxxxxx
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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
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