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 72C61C433B4 for ; Wed, 14 Apr 2021 15:32:13 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 43BA86100B for ; Wed, 14 Apr 2021 15:32:13 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1345592AbhDNPcd convert rfc822-to-8bit (ORCPT ); Wed, 14 Apr 2021 11:32:33 -0400 Received: from eu-smtp-delivery-151.mimecast.com ([185.58.85.151]:21862 "EHLO eu-smtp-delivery-151.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233644AbhDNPc3 (ORCPT ); Wed, 14 Apr 2021 11:32:29 -0400 Received: from AcuMS.aculab.com (156.67.243.121 [156.67.243.121]) (Using TLS) by relay.mimecast.com with ESMTP id uk-mta-260-2ItaeQAlMXO4xATmhgmnXw-1; Wed, 14 Apr 2021 16:32:05 +0100 X-MC-Unique: 2ItaeQAlMXO4xATmhgmnXw-1 Received: from AcuMS.Aculab.com (fd9f:af1c:a25b:0:994c:f5c2:35d6:9b65) by AcuMS.aculab.com (fd9f:af1c:a25b:0:994c:f5c2:35d6:9b65) with Microsoft SMTP Server (TLS) id 15.0.1497.2; Wed, 14 Apr 2021 16:32:05 +0100 Received: from AcuMS.Aculab.com ([fe80::994c:f5c2:35d6:9b65]) by AcuMS.aculab.com ([fe80::994c:f5c2:35d6:9b65%12]) with mapi id 15.00.1497.012; Wed, 14 Apr 2021 16:32:04 +0100 From: David Laight To: 'Segher Boessenkool' , Christophe Leroy CC: Paul Mackerras , "linuxppc-dev@lists.ozlabs.org" , "linux-kernel@vger.kernel.org" , Nicholas Piggin Subject: RE: [PATCH v1 1/2] powerpc/bitops: Use immediate operand when possible Thread-Topic: [PATCH v1 1/2] powerpc/bitops: Use immediate operand when possible Thread-Index: AQHXMUHmVAfluj7FfEq84rYmesOs4qq0IuPA Date: Wed, 14 Apr 2021 15:32:04 +0000 Message-ID: References: <09da6fec57792d6559d1ea64e00be9870b02dab4.1617896018.git.christophe.leroy@csgroup.eu> <20210412215428.GM26583@gate.crashing.org> <20210413215803.GT26583@gate.crashing.org> <1618365589.67fxh7cot9.astroid@bobo.none> <20210414122409.GV26583@gate.crashing.org> <20210414151921.GW26583@gate.crashing.org> In-Reply-To: <20210414151921.GW26583@gate.crashing.org> 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-kernel@vger.kernel.org From: Segher Boessenkool > Sent: 14 April 2021 16:19 ... > > Could the kernel use GCC builtin atomic functions instead ? > > > > https://gcc.gnu.org/onlinedocs/gcc/_005f_005fatomic-Builtins.html > > Certainly that should work fine for the simpler cases that the atomic > operations are meant to provide. But esp. for not-so-simple cases the > kernel may require some behaviour provided by the existing assembler > implementation, and not by the atomic builtins. > > I'm not saying this cannot work, just that some serious testing will be > needed. If it works it should be the best of all worlds, so then it is > a really good idea yes :-) I suspect they just add an extra layer of abstraction that makes it even more difficult to verify and could easily get broken by a compiler update (etc). The other issue is that the code needs to be correct with compiled with (for example) -O0. That could very easily break anything except the asm implementation if additional memory accesses and/or increased code size cause grief. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)