From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-3.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id E8A94C4727D for ; Tue, 6 Oct 2020 15:07:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 92A01206DD for ; Tue, 6 Oct 2020 15:07:46 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726013AbgJFPHq convert rfc822-to-8bit (ORCPT ); Tue, 6 Oct 2020 11:07:46 -0400 Received: from eu-smtp-delivery-151.mimecast.com ([185.58.86.151]:43427 "EHLO eu-smtp-delivery-151.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725947AbgJFPHq (ORCPT ); Tue, 6 Oct 2020 11:07:46 -0400 Received: from AcuMS.aculab.com (156.67.243.126 [156.67.243.126]) (Using TLS) by relay.mimecast.com with ESMTP id uk-mta-209-WYOHOSPgPXCtjBzSb6bOjQ-1; Tue, 06 Oct 2020 16:07:42 +0100 X-MC-Unique: WYOHOSPgPXCtjBzSb6bOjQ-1 Received: from AcuMS.Aculab.com (fd9f:af1c:a25b:0:43c:695e:880f:8750) by AcuMS.aculab.com (fd9f:af1c:a25b:0:43c:695e:880f:8750) with Microsoft SMTP Server (TLS) id 15.0.1347.2; Tue, 6 Oct 2020 16:07:41 +0100 Received: from AcuMS.Aculab.com ([fe80::43c:695e:880f:8750]) by AcuMS.aculab.com ([fe80::43c:695e:880f:8750%12]) with mapi id 15.00.1347.000; Tue, 6 Oct 2020 16:07:41 +0100 From: David Laight To: 'Peter Zijlstra' CC: "linux-toolchains@vger.kernel.org" , Will Deacon , Paul McKenney , "linux-kernel@vger.kernel.org" , "stern@rowland.harvard.edu" , "parri.andrea@gmail.com" , "boqun.feng@gmail.com" , "npiggin@gmail.com" , "dhowells@redhat.com" , "j.alglave@ucl.ac.uk" , "luc.maranget@inria.fr" , "akiyks@gmail.com" , "dlustig@nvidia.com" , "joel@joelfernandes.org" , "torvalds@linux-foundation.org" Subject: RE: Control Dependencies vs C Compilers Thread-Topic: Control Dependencies vs C Compilers Thread-Index: AQHWm9Z2gJDHxIOMJkCFRnXrafG7EamKgJsQgAAA4oCAACf9EA== Date: Tue, 6 Oct 2020 15:07:41 +0000 Message-ID: <0a0403a430b14484a026b52a5ecbbeeb@AcuMS.aculab.com> References: <20201006114710.GQ2628@hirez.programming.kicks-ass.net> <3dfe7daed3c44f46a6989b6513ad7bb0@AcuMS.aculab.com> <20201006133115.GT2628@hirez.programming.kicks-ass.net> In-Reply-To: <20201006133115.GT2628@hirez.programming.kicks-ass.net> Accept-Language: en-GB, en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-ms-exchange-transport-fromentityheader: Hosted x-originating-ip: [10.202.205.107] MIME-Version: 1.0 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=C51A453 smtp.mailfrom=david.laight@aculab.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: aculab.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Precedence: bulk List-ID: X-Mailing-List: linux-toolchains@vger.kernel.org > Please go read memory-barriers.txt for a bunch of other examples. My brain hurts. It's not as though I've not known about most of this since the first SMP capable SPARC cpus that had a 'store buffer'. (Probably 30 years ago.) I sometimes wonder whether compiling things like the kernel requires a compiler mode that defaults everything (except function locals) to 'volatile'. Although that still does fix control dependencies. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)