From mboxrd@z Thu Jan 1 00:00:00 1970 From: "H. Peter Anvin" Date: Tue, 09 Sep 2014 02:27:14 +0000 Subject: Re: bit fields && data tearing Message-Id: <540E6582.9020403@zytor.com> List-Id: 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> <540E1587.3060108@tilera.com> <1410216228.2027.88.camel@jarvis.lan> In-Reply-To: <1410216228.2027.88.camel@jarvis.lan> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: James Bottomley , Chris Metcalf Cc: Peter Hurley , paulmck@linux.vnet.ibm.com, One Thousand Gnomes , Jakub Jelinek , Mikael Pettersson , Benjamin Herrenschmidt , Richard Henderson , Oleg Nesterov , Miroslav Franc , Paul Mackerras , linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, Tony Luck , linux-ia64@vger.kernel.org On 09/08/2014 03:43 PM, James Bottomley wrote: > > This was years ago (possibly decades). We had to implement in-kernel > unaligned traps for the networking layer because it could access short > and int fields that weren't of the correct alignment when processing > packets. It that's all corrected now, we wouldn't really notice (except > a bit of a speed up since an unaligned trap effectively places the > broken out instructions into the bit stream). > > James > Well, ARM doesn't trap, it just silently gives garbage on unaligned memory references. -hpa