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=-2.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,PDS_BAD_THREAD_QP_64, 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 28B3BC433B4 for ; Wed, 14 Apr 2021 15:32:36 +0000 (UTC) Received: from lists.ozlabs.org (lists.ozlabs.org [112.213.38.117]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 902966100B for ; Wed, 14 Apr 2021 15:32:35 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 902966100B Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=ACULAB.COM Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Received: from boromir.ozlabs.org (localhost [IPv6:::1]) by lists.ozlabs.org (Postfix) with ESMTP id 4FL60x6gF3z3c0x for ; Thu, 15 Apr 2021 01:32:33 +1000 (AEST) Authentication-Results: lists.ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=aculab.com (client-ip=185.58.85.151; helo=eu-smtp-delivery-151.mimecast.com; envelope-from=david.laight@aculab.com; receiver=) Received: from eu-smtp-delivery-151.mimecast.com (eu-smtp-delivery-151.mimecast.com [185.58.85.151]) (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 4FL60b1hZ3z2yRD for ; Thu, 15 Apr 2021 01:32:13 +1000 (AEST) 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 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: quoted-printable X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: "linuxppc-dev@lists.ozlabs.org" , Paul Mackerras , "linux-kernel@vger.kernel.org" , Nicholas Piggin Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" 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 >=20 > 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. >=20 > 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. =09David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1= PT, UK Registration No: 1397386 (Wales)