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 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id C2A15C433F5 for ; Fri, 7 Oct 2022 09:15:18 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:MIME-Version:In-Reply-To:References: Message-ID:Date:Subject:CC:To:From:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=vGm30rKWwX6aOQs0SddRm5UEOesMbUbYsv3jruvqb9w=; b=4Qr/UpP9QRASU4 FrtXMo8We+cDmlAkfTPTlN2F8bvcSbeK4HdOyqX1K5EYpBf5MxryIHAUR+zG12cGA/ezqagvYzQvM uSpWe7K8PqNzZO62ZZv2ApN9uNXCg/yI247Vc4HVlpLfzf70T75r7HwMeHdzsw30G2dIH1GkWArgn DiVg4NHRZQq7suwtmRQKvKJg6xr4F7ESrFsW6MwEwnbWUZ+eJX3r7d5Gc8LBH6t0oDwcfDSHCv6Wq nBNhZKAZlySHPKbBs1QOUShS7GiiQDsPnzvS5We8pX8/ZW7C2Ue0RaWVQUY26/DDsBV7s5xTvHcWx utclidLLBUugf5CoDuBg==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1ogjRn-008FR0-HY; Fri, 07 Oct 2022 09:15:11 +0000 Received: from eu-smtp-delivery-151.mimecast.com ([185.58.86.151]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1ogjRk-008FLT-1p for linux-mtd@lists.infradead.org; Fri, 07 Oct 2022 09:15:10 +0000 Received: from AcuMS.aculab.com (156.67.243.121 [156.67.243.121]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA384) id uk-mta-165-SM2il4aTNXS-NQtWmWJl3A-1; Fri, 07 Oct 2022 10:14:58 +0100 X-MC-Unique: SM2il4aTNXS-NQtWmWJl3A-1 Received: from AcuMS.Aculab.com (10.202.163.6) by AcuMS.aculab.com (10.202.163.6) with Microsoft SMTP Server (TLS) id 15.0.1497.38; Fri, 7 Oct 2022 10:14:54 +0100 Received: from AcuMS.Aculab.com ([::1]) by AcuMS.aculab.com ([::1]) with mapi id 15.00.1497.040; Fri, 7 Oct 2022 10:14:54 +0100 From: David Laight To: 'Christophe Leroy' , "Jason A. Donenfeld" CC: "linux-kernel@vger.kernel.org" , "patches@lists.linux.dev" , Andreas Noever , Andrew Morton , "Andy Shevchenko" , Borislav Petkov , Catalin Marinas , =?utf-8?B?Q2hyaXN0b3BoIELDtmhtd2FsZGVy?= , Christoph Hellwig , Daniel Borkmann , "Dave Airlie" , Dave Hansen , "David S . Miller" , Eric Dumazet , Florian Westphal , Greg Kroah-Hartman , "H . Peter Anvin" , "Heiko Carstens" , Helge Deller , Herbert Xu , Huacai Chen , "Hugh Dickins" , Jakub Kicinski , "James E . J . Bottomley" , Jan Kara , Jason Gunthorpe , Jens Axboe , Johannes Berg , Jonathan Corbet , "Jozsef Kadlecsik" , KP Singh , Kees Cook , Marco Elver , "Mauro Carvalho Chehab" , Michael Ellerman , "Pablo Neira Ayuso" , Paolo Abeni , "Peter Zijlstra" , Richard Weinberger , "Russell King" , Theodore Ts'o , "Thomas Bogendoerfer" , Thomas Gleixner , Thomas Graf , Ulf Hansson , Vignesh Raghavendra , WANG Xuerui , Will Deacon , Yury Norov , "dri-devel@lists.freedesktop.org" , "kasan-dev@googlegroups.com" , "kernel-janitors@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" , "linux-block@vger.kernel.org" , "linux-crypto@vger.kernel.org" , "linux-doc@vger.kernel.org" , "linux-fsdevel@vger.kernel.org" , "linux-media@vger.kernel.org" , "linux-mips@vger.kernel.org" , "linux-mm@kvack.org" , "linux-mmc@vger.kernel.org" , "linux-mtd@lists.infradead.org" , "linux-nvme@lists.infradead.org" , "linux-parisc@vger.kernel.org" , "linux-rdma@vger.kernel.org" , "linux-s390@vger.kernel.org" , "linux-um@lists.infradead.org" , "linux-usb@vger.kernel.org" , "linux-wireless@vger.kernel.org" , "linuxppc-dev@lists.ozlabs.org" , "loongarch@lists.linux.dev" , "netdev@vger.kernel.org" , "sparclinux@vger.kernel.org" , "x86@kernel.org" , =?utf-8?B?VG9rZSBIw7hpbGFuZC1Kw7hyZ2Vuc2Vu?= , Chuck Lever , Jan Kara Subject: RE: [PATCH v3 3/5] treewide: use get_random_u32() when possible Thread-Topic: [PATCH v3 3/5] treewide: use get_random_u32() when possible Thread-Index: AQHY2asa0LDp17FxT0u8eu+L+6kCF64CocNw Date: Fri, 7 Oct 2022 09:14:54 +0000 Message-ID: References: <20221006165346.73159-1-Jason@zx2c4.com> <20221006165346.73159-4-Jason@zx2c4.com> <848ed24c-13ef-6c38-fd13-639b33809194@csgroup.eu> <6396875c-146a-acf5-dd9e-7f93ba1b4bc3@csgroup.eu> In-Reply-To: <6396875c-146a-acf5-dd9e-7f93ba1b4bc3@csgroup.eu> 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 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: aculab.com Content-Language: en-US X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20221007_021508_385501_075AD468 X-CRM114-Status: GOOD ( 13.84 ) X-BeenThere: linux-mtd@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: Linux MTD discussion mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-mtd" Errors-To: linux-mtd-bounces+linux-mtd=archiver.kernel.org@lists.infradead.org From: Christophe Leroy > Sent: 06 October 2022 18:43 ... > But taking into account that sp must remain 16 bytes aligned, would it > be better to do something like ? > > sp -= prandom_u32_max(PAGE_SIZE >> 4) << 4; That makes me think... If prandom_u32_max() is passed a (constant) power of 2 it doesn't need to do the multiply, it can just do a shift right. Doesn't it also always get a 32bit random value? So actually get_random_u32() & PAGE_MASK & ~0xf is faster! When PAGE_SIZE is 4k, PAGE_SIZE >> 4 is 256 so it could use: get_ramdom_u8() << 4 You also seem to have removed prandom_u32() in favour of get_random_u32() but have added more prandom_xxxx() functions. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales) ______________________________________________________ Linux MTD discussion mailing list http://lists.infradead.org/mailman/listinfo/linux-mtd/