From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from n23.mail01.mtsvc.net (mailout32.mail01.mtsvc.net [216.70.64.70]) (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 AFABE1A01C0 for ; Tue, 9 Sep 2014 08:47:44 +1000 (EST) Message-ID: <540E3207.7090007@hurleysoftware.com> Date: Mon, 08 Sep 2014 18:47:35 -0400 From: Peter Hurley MIME-Version: 1.0 To: "H. Peter Anvin" , One Thousand Gnomes Subject: Re: bit fields && data tearing References: <20140712181328.GA8738@redhat.com> <54079B70.4050200@hurleysoftware.com> <1409785893.30640.118.camel@pasglop> <063D6719AE5E284EB5DD2968C1650D6D17487172@AcuExch.aculab.com> <1409824374.4246.62.camel@pasglop> <5408E458.3@zytor.com> <54090AF4.7060406@hurleysoftware.com> <54091B30.7080100@zytor.com> <5409D76D.2070203@hurleysoftware.com> <5409D9C0.7030403@zytor.com> <20140908185240.21f52ca0@alan.etchedpixels.co.uk> <540DEE6C.2060904@zytor.com> In-Reply-To: <540DEE6C.2060904@zytor.com> Content-Type: text/plain; charset=utf-8 Cc: Jakub Jelinek , "linux-arch@vger.kernel.org" , Tony Luck , "linux-ia64@vger.kernel.org" , Oleg Nesterov , "linux-kernel@vger.kernel.org" , David Laight , Paul Mackerras , linux-alpha@vger.kernel.org, "Paul E. McKenney" , "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 01:59 PM, H. Peter Anvin wrote: > On 09/08/2014 10:52 AM, One Thousand Gnomes wrote: >> On Fri, 05 Sep 2014 08:41:52 -0700 >> "H. Peter Anvin" wrote: >> >>> On 09/05/2014 08:31 AM, Peter Hurley wrote: >>>> >>>> Which is a bit ironic because I remember when Digital had a team >>>> working on emulating native x86 apps on Alpha/NT. >>>> >>> >>> Right, because the x86 architecture was obsolete and would never scale... >> >> Talking about "not scaling" can anyone explain how a "you need to use >> set_bit() and friends" bug report scaled into a hundred message plus >> discussion about ambiguous properties of processors (and nobody has >> audited all the embedded platforms we support yet, or the weirder ARMs) >> and a propsal to remove Alpha support. >> >> Wouldn't it be *much* simpler to do what I suggested in the first place >> and use the existing intended for purpose, deliberately put there, >> functions for atomic bitops, because they are fast on sane processors and >> they work on everything else. >> >> I think the whole "removing Alpha EV5" support is basically bonkers. Just >> use set_bit in the tty layer. Alpha will continue to work as well as it >> always has done and you won't design out support for any future processor >> that turns out not to do byte aligned stores. >> >> Alan >> > > Is *that* what we are talking about? I was added to this conversation > in the middle where it had already generalized, so I had no idea. No, this is just what brought this craziness to my attention. For example, byte- and short-sized circular buffers could not possibly be safe either, when the head nears the tail. Who has audited global storage and ensured that _every_ byte-sized write doesn't happen to be adjacent to some other storage that may not happen to be protected by the same (or any) lock? Regards, Peter Hurley