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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id E1E1FC61D97 for ; Wed, 22 Nov 2023 11:16:11 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1343610AbjKVLQG convert rfc822-to-8bit (ORCPT ); Wed, 22 Nov 2023 06:16:06 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52768 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233910AbjKVLQC (ORCPT ); Wed, 22 Nov 2023 06:16:02 -0500 Received: from eu-smtp-delivery-151.mimecast.com (eu-smtp-delivery-151.mimecast.com [185.58.85.151]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C0357B9 for ; Wed, 22 Nov 2023 03:15:58 -0800 (PST) Received: from AcuMS.aculab.com (156.67.243.121 [156.67.243.121]) by relay.mimecast.com with ESMTP with both STARTTLS and AUTH (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA384) id uk-mta-72-nmAAUN1cNVK2s83WvssOog-1; Wed, 22 Nov 2023 11:15:53 +0000 X-MC-Unique: nmAAUN1cNVK2s83WvssOog-1 Received: from AcuMS.Aculab.com (10.202.163.6) by AcuMS.aculab.com (10.202.163.6) with Microsoft SMTP Server (TLS) id 15.0.1497.48; Wed, 22 Nov 2023 11:16:23 +0000 Received: from AcuMS.Aculab.com ([::1]) by AcuMS.aculab.com ([::1]) with mapi id 15.00.1497.048; Wed, 22 Nov 2023 11:16:23 +0000 From: David Laight To: 'Jisheng Zhang' , Paul Walmsley , Palmer Dabbelt , Albert Ou CC: "linux-riscv@lists.infradead.org" , "linux-kernel@vger.kernel.org" Subject: RE: [PATCH] riscv: select ARCH_HAS_FAST_MULTIPLIER Thread-Topic: [PATCH] riscv: select ARCH_HAS_FAST_MULTIPLIER Thread-Index: AQHaHIr3F/LmUcOCEUqs//JJARgdtrCGLu+Q Date: Wed, 22 Nov 2023 11:16:23 +0000 Message-ID: <47995b4daafb43348fc839ffb486f56b@AcuMS.aculab.com> References: <20231121144340.3492-1-jszhang@kernel.org> In-Reply-To: <20231121144340.3492-1-jszhang@kernel.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 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 ... > However, the > situation exists on x86 too, for example, P4 doesn't have fast > integer multiplies ... P4 doesn't have fast anything :-) More interestingly does anything modern not have fast multiplies? (that you'd consider running Linux on). The silicon required isn't that big. IIRC an 'n' bit multiplier requires n^2 full adders and has the latency of 2n adders. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)