linux-kernel - Re: bit fields && data tearing

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Message-ID: <540E1587.3060108@tilera.com>
Date:	Mon, 8 Sep 2014 16:45:59 -0400
From:	Chris Metcalf <cmetcalf@...era.com>
To:	James Bottomley <James.Bottomley@...senPartnership.com>,
	Peter Hurley <peter@...leysoftware.com>
CC:	<paulmck@...ux.vnet.ibm.com>, "H. Peter Anvin" <hpa@...or.com>,
	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>,
	Jakub Jelinek <jakub@...hat.com>,
	Mikael Pettersson <mikpelinux@...il.com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Richard Henderson <rth@...ddle.net>,
	Oleg Nesterov <oleg@...hat.com>,
	Miroslav Franc <mfranc@...hat.com>,
	Paul Mackerras <paulus@...ba.org>,
	<linuxppc-dev@...ts.ozlabs.org>, <linux-kernel@...r.kernel.org>,
	<linux-arch@...r.kernel.org>, Tony Luck <tony.luck@...el.com>,
	<linux-ia64@...r.kernel.org>
Subject: Re: bit fields && data tearing

On 9/8/2014 1:50 AM, James Bottomley wrote:
> Actual alignment is pretty irrelevant.  That's why all architectures
> which require alignment also have to implement misaligned traps ... this
> is a fundamental requirement of the networking code, for instance.

Can you clarify what you think the requirement is?  The tile architecture
doesn't support misaligned load/store in general, but we do support it for
userspace (using a nifty JIT approach with a direct-map hash table kept
in userspace), and also for get_user/put_user.  But that's it, and,
the networking subsystem works fine for us.

Occasionally we report bugs for driver code that doesn't use the
get_unaligned_xxx() macros and friends, and our fixes are generally taken
upstream.

-- 
Chris Metcalf, Tilera Corp.
http://www.tilera.com
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