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 12:12:50 -0700 Message-ID: <540DFFB2.4000509@zytor.com> References: <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> <20140907230019.GO5001@linux.vnet.ibm.com> <6092b453-e0c9-4f6d-922b-48bce988f774@email.android.com> <20140907233655.GR5001@linux.vnet.ibm.com> <154b540a-df47-4f3e-bdda-ab5d2e72723a@email.android.com> <1410155802.2027.36.camel@jarvis.lan> <540DF17C.9080509@zytor.com> <1410203369.2027.56.camel@jarvis.lan> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: base64 Return-path: In-Reply-To: <1410203369.2027.56.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 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 T24gMDkvMDgvMjAxNCAxMjowOSBQTSwgSmFtZXMgQm90dG9tbGV5IHdyb3RlOgo+IAo+IFVtLCBJ IHRoaW5rIHlvdSBuZWVkIHRvIHJlLXJlYWQgdGhlIHRocmVhZDsgdGhhdCdzIG5vdCB3aGF0IEkg c2FpZCBhdAo+IGFsbC4gSXQncyBldmVuIHdyaXR0ZW4gbG93ZXIgZG93bjogIlBBIGNhbid0IGRv IGF0b21pYyBiaXQgc2V0cyAobm8KPiBhdG9taWMgUk1XIGV4Y2VwdCB0aGUgbGRjdyBvcGVyYXRp b24pIGl0IGNhbiBkbyBhdG9taWMgd3JpdGVzIHRvCj4gZnVuZGFtZW50YWwgc2l6ZXMgKGJ5dGUs IHNob3J0LCBpbnQsIGxvbmcpIHByb3ZpZGVkIGdjYyBlbWl0cyB0aGUKPiBjb3JyZWN0IHByaW1p dGl2ZSIuICBUaGUgb3JpZ2luYWwgcXVlc3Rpb24gd2FzIHdoZXRoZXIgYXRvbWljaXR5Cj4gcmVx dWlyZWQgbmF0aXZlIGJ1cyB3aWR0aCBhY2Nlc3MsIHdoaWNoIHdlIGN1cnJlbnRseSBhc3N1bWUs IHNvIHRoZXJlJ3MKPiBubyBleHRhbnQgcHJvYmxlbS4KPiAKClRoZSBpc3N1ZSBhdCBoYW5kIHdh cyB3aGV0aGVyIG9yIG5vdCBwYXJ0aWFsbHkgb3ZlcmxhcHBlZCAoYnV0IG5hdHVhbGx5CmFsaWdu ZWQpIHdyaXRlcyBjYW4gcGFzcyBlYWNoIG90aGVyLiAgKlRoaXMqIGlzIHRoZSBhZ2dyZXNzaXZl CnJlbGF4YXRpb24gdG8gd2hpY2ggSSBhbSByZWZlcnJpbmcuCgpJIHdvdWxkIGd1ZXNzIHRoYXQg dGhhdCBpcyBhIHZlcnkgdW51c3VhbCBjb25zdHJhaW50LgoKCS1ocGEKCl9fX19fX19fX19fX19f X19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fCkxpbnV4cHBjLWRldiBtYWlsaW5nIGxp c3QKTGludXhwcGMtZGV2QGxpc3RzLm96bGFicy5vcmcKaHR0cHM6Ly9saXN0cy5vemxhYnMub3Jn L2xpc3RpbmZvL2xpbnV4cHBjLWRldg== From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from terminus.zytor.com ([198.137.202.10]:59168 "EHLO mail.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753963AbaIHTQD (ORCPT ); Mon, 8 Sep 2014 15:16:03 -0400 Message-ID: <540DFFB2.4000509@zytor.com> Date: Mon, 08 Sep 2014 12:12:50 -0700 From: "H. Peter Anvin" MIME-Version: 1.0 Subject: Re: bit fields && data tearing References: <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> <20140907230019.GO5001@linux.vnet.ibm.com> <6092b453-e0c9-4f6d-922b-48bce988f774@email.android.com> <20140907233655.GR5001@linux.vnet.ibm.com> <154b540a-df47-4f3e-bdda-ab5d2e72723a@email.android.com> <1410155802.2027.36.camel@jarvis.lan> <540DF17C.9080509@zytor.com> <1410203369.2027.56.camel@jarvis.lan> In-Reply-To: <1410203369.2027.56.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 Cc: paulmck@linux.vnet.ibm.com, Peter Hurley , 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: <20140908191250.AwYsxcFqdzgIxTBwLyaXSRLRcujxIaZ7G97BSx0ZDLA@z> 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