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Date: Mon, 8 Sep 2014 16:45:59 -0400
From: Chris Metcalf <cmetcalf@tilera.com>
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To: James Bottomley <James.Bottomley@HansenPartnership.com>,
        Peter Hurley <peter@hurleysoftware.com>
CC: <paulmck@linux.vnet.ibm.com>, "H. Peter Anvin" <hpa@zytor.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
References: <21512.10628.412205.873477@gargle.gargle.HOWL>		 <20140904090952.GW17454@tucnak.redhat.com>		 <540859EC.5000407@hurleysoftware.com>		 <20140904175044.4697aee4@alan.etchedpixels.co.uk>		 <5408C0AB.6050801@hurleysoftware.com>		 <20140905001751.GL5001@linux.vnet.ibm.com>		 <1409883098.5078.14.camel@jarvis.lan>	 <5409243C.4080704@hurleysoftware.com>		 <20140905040645.GO5001@linux.vnet.ibm.com>		 <1410066442.12512.13.camel@jarvis.lan>		 <20140907162146.GK5001@linux.vnet.ibm.com>	 <1410116687.2027.19.camel@jarvis.lan> <540CC305.8010407@hurleysoftware.com> <1410155407.2027.29.camel@jarvis.lan>
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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