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 C7027C433E6 for ; Mon, 1 Feb 2021 16:04:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 856EF64E9B for ; Mon, 1 Feb 2021 16:04:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231217AbhBAQEa convert rfc822-to-8bit (ORCPT ); Mon, 1 Feb 2021 11:04:30 -0500 Received: from eu-smtp-delivery-151.mimecast.com ([207.82.80.151]:39554 "EHLO eu-smtp-delivery-151.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229908AbhBAQEQ (ORCPT ); Mon, 1 Feb 2021 11:04:16 -0500 Received: from AcuMS.aculab.com (156.67.243.126 [156.67.243.126]) (Using TLS) by relay.mimecast.com with ESMTP id uk-mta-126-PcACmDPgN8eBY-riyOM1Ww-2; Mon, 01 Feb 2021 16:02:34 +0000 X-MC-Unique: PcACmDPgN8eBY-riyOM1Ww-2 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; Mon, 1 Feb 2021 16:02:31 +0000 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; Mon, 1 Feb 2021 16:02:31 +0000 From: David Laight To: 'Andy Shevchenko' , Yury Norov CC: "linux-m68k@lists.linux-m68k.org" , "linux-kernel@vger.kernel.org" , "linux-sh@vger.kernel.org" , "linux-arch@vger.kernel.org" , Geert Uytterhoeven , Yoshinori Sato , "Rich Felker" , Arnd Bergmann , Dennis Zhou , Andrew Morton , Wolfram Sang , David Sterba , "Stefano Brivio" , "Ma, Jianpeng" , "Wei Yang" , Josh Poimboeuf , John Paul Adrian Glaubitz , Joe Perches Subject: RE: [PATCH 7/8] lib: add fast path for find_next_*_bit() Thread-Topic: [PATCH 7/8] lib: add fast path for find_next_*_bit() Thread-Index: AQHW+KGAlZZqB0fkUkaHyblyx7z9eqpDdQ9g Date: Mon, 1 Feb 2021 16:02:30 +0000 Message-ID: References: <20210130191719.7085-1-yury.norov@gmail.com> <20210130191719.7085-8-yury.norov@gmail.com> In-Reply-To: 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-sh@vger.kernel.org From: Andy Shevchenko > Sent: 01 February 2021 13:49 > > On Sat, Jan 30, 2021 at 11:17:18AM -0800, Yury Norov wrote: > > Similarly to bitmap functions, find_next_*_bit() users will benefit > > if we'll handle a case of bitmaps that fit into a single word. In the > > very best case, the compiler may replace a function call with a > > single ffs or ffz instruction. > > Would be nice to have the examples how it reduces the actual code size (based > on the existing code in kernel, especially in widely used frameworks / > subsystems, like PCI). I bet it makes the kernel bigger but very slightly faster. But the fact that the wrappers end up in the i-cache may mean that inlining actually makes it slower for some calling sequences. If a bitmap fits in a single word (as a compile-time constant) then you should (probably) be using different functions if you care about performance. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)