From mboxrd@z Thu Jan 1 00:00:00 1970 From: "H. Peter Anvin" Subject: Re: bit fields && data tearing Date: Mon, 08 Sep 2014 19:27:14 -0700 Message-ID: <540E6582.9020403@zytor.com> 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> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: base64 Return-path: In-Reply-To: <1410216228.2027.88.camel@jarvis.lan> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: linuxppc-dev-bounces+glppe-linuxppc-embedded-2=m.gmane.org@lists.ozlabs.org Sender: "Linuxppc-dev" To: James Bottomley , Chris Metcalf Cc: Jakub Jelinek , One Thousand Gnomes , Tony Luck , linux-ia64@vger.kernel.org, Peter Hurley , Mikael Pettersson , Oleg Nesterov , linux-kernel@vger.kernel.org, Paul Mackerras , linux-arch@vger.kernel.org, paulmck@linux.vnet.ibm.com, linuxppc-dev@lists.ozlabs.org, Miroslav Franc , Richard Henderson List-Id: linux-arch.vger.kernel.org T24gMDkvMDgvMjAxNCAwMzo0MyBQTSwgSmFtZXMgQm90dG9tbGV5IHdyb3RlOgo+IAo+IFRoaXMg d2FzIHllYXJzIGFnbyAocG9zc2libHkgZGVjYWRlcykuICBXZSBoYWQgdG8gaW1wbGVtZW50IGlu LWtlcm5lbAo+IHVuYWxpZ25lZCB0cmFwcyBmb3IgdGhlIG5ldHdvcmtpbmcgbGF5ZXIgYmVjYXVz ZSBpdCBjb3VsZCBhY2Nlc3Mgc2hvcnQKPiBhbmQgaW50IGZpZWxkcyB0aGF0IHdlcmVuJ3Qgb2Yg dGhlIGNvcnJlY3QgYWxpZ25tZW50IHdoZW4gcHJvY2Vzc2luZwo+IHBhY2tldHMuICBJdCB0aGF0 J3MgYWxsIGNvcnJlY3RlZCBub3csIHdlIHdvdWxkbid0IHJlYWxseSBub3RpY2UgKGV4Y2VwdAo+ IGEgYml0IG9mIGEgc3BlZWQgdXAgc2luY2UgYW4gdW5hbGlnbmVkIHRyYXAgZWZmZWN0aXZlbHkg cGxhY2VzIHRoZQo+IGJyb2tlbiBvdXQgaW5zdHJ1Y3Rpb25zIGludG8gdGhlIGJpdCBzdHJlYW0p Lgo+IAo+IEphbWVzCj4gCgpXZWxsLCBBUk0gZG9lc24ndCB0cmFwLCBpdCBqdXN0IHNpbGVudGx5 IGdpdmVzIGdhcmJhZ2Ugb24gdW5hbGlnbmVkCm1lbW9yeSByZWZlcmVuY2VzLgoKCS1ocGEKCgpf X19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fXwpMaW51eHBwYy1k ZXYgbWFpbGluZyBsaXN0CkxpbnV4cHBjLWRldkBsaXN0cy5vemxhYnMub3JnCmh0dHBzOi8vbGlz dHMub3psYWJzLm9yZy9saXN0aW5mby9saW51eHBwYy1kZXY= From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from terminus.zytor.com ([198.137.202.10]:34464 "EHLO mail.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754730AbaIICc7 (ORCPT ); Mon, 8 Sep 2014 22:32:59 -0400 Message-ID: <540E6582.9020403@zytor.com> Date: Mon, 08 Sep 2014 19:27:14 -0700 From: "H. Peter Anvin" MIME-Version: 1.0 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> <540E1587.3060108@tilera.com> <1410216228.2027.88.camel@jarvis.lan> In-Reply-To: <1410216228.2027.88.camel@jarvis.lan> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Sender: linux-arch-owner@vger.kernel.org List-ID: 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 Message-ID: <20140909022714.7yhZoG5s2CQZASKOTQXWLJXM4vyh5ta7LAGBZ2iqRo0@z> 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 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 From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail.zytor.com (terminus.zytor.com [IPv6:2001:1868:205::10]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 2E68A1A021A for ; Tue, 9 Sep 2014 12:32:40 +1000 (EST) Message-ID: <540E6582.9020403@zytor.com> Date: Mon, 08 Sep 2014 19:27:14 -0700 From: "H. Peter Anvin" MIME-Version: 1.0 To: James Bottomley , Chris Metcalf 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> <540E1587.3060108@tilera.com> <1410216228.2027.88.camel@jarvis.lan> In-Reply-To: <1410216228.2027.88.camel@jarvis.lan> Content-Type: text/plain; charset=UTF-8 Cc: Jakub Jelinek , One Thousand Gnomes , Tony Luck , linux-ia64@vger.kernel.org, Peter Hurley , Mikael Pettersson , Oleg Nesterov , linux-kernel@vger.kernel.org, Paul Mackerras , linux-arch@vger.kernel.org, paulmck@linux.vnet.ibm.com, linuxppc-dev@lists.ozlabs.org, Miroslav Franc , Richard Henderson List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , 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