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 2599EC433E1 for ; Fri, 21 Aug 2020 21:18:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D9C4520791 for ; Fri, 21 Aug 2020 21:18:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726705AbgHUVSr convert rfc822-to-8bit (ORCPT ); Fri, 21 Aug 2020 17:18:47 -0400 Received: from eu-smtp-delivery-151.mimecast.com ([207.82.80.151]:44900 "EHLO eu-smtp-delivery-151.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726495AbgHUVSq (ORCPT ); Fri, 21 Aug 2020 17:18:46 -0400 Received: from AcuMS.aculab.com (156.67.243.126 [156.67.243.126]) (Using TLS) by relay.mimecast.com with ESMTP id uk-mta-180-nRitbC59MfCis-3-n_PeQw-1; Fri, 21 Aug 2020 22:18:43 +0100 X-MC-Unique: nRitbC59MfCis-3-n_PeQw-1 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; Fri, 21 Aug 2020 22:18:42 +0100 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; Fri, 21 Aug 2020 22:18:42 +0100 From: David Laight To: 'Marcelo Ricardo Leitner' CC: "'linux-sctp@vger.kernel.org'" , "'netdev@vger.kernel.org'" Subject: RE: Use of genradix in sctp Thread-Topic: Use of genradix in sctp Thread-Index: AdZ1ckZAY2qe63tNS/O9MsxVdvHiSAALTAcAAANIG8AAkcwnAAACvT6A Date: Fri, 21 Aug 2020 21:18:42 +0000 Message-ID: <9f5b892bcf4f41f9b32990fb6049fce2@AcuMS.aculab.com> References: <2ffb7752d3e8403ebb220e0a5e2cf3cd@AcuMS.aculab.com> <20200818213800.GJ906397@localhost.localdomain> <357ded60999a4957addb766a29431ad7@AcuMS.aculab.com> <20200821204636.GO3399@localhost.localdomain> In-Reply-To: <20200821204636.GO3399@localhost.localdomain> Accept-Language: en-GB, en-US Content-Language: 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: 0.001 X-Mimecast-Originator: aculab.com Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org From: 'Marcelo Ricardo Leitner' > Sent: 21 August 2020 21:47 ... > > > > 2) Optimise the genradix lookup for the case where there > > is a single page - it can be completely inlined. > > And/or our struct sizes. > > __idx_to_offset() will basically do: > if (!is_power_of_2(obj_size)) { > return (idx / objs_per_page) * PAGE_SIZE + > (idx % objs_per_page) * obj_size; > } else { > return idx * obj_size; > > if we can get it to his the else block, it saves some CPU cycles already (at > the expense of memory). I'm penning some changes to the genradix code: That expression can be written: idx * obj_size + (idx / objs_per_page) * (PAGE_SIZE % obj_size) which is simpler and doesn't need the is_power_of_2() test. You can then do the early test: if (idx * obj_size <= PAGE_SIZE - obj_size) && root && !llevel) return root + idx * obj_size; in the inline function. A slight increase in code size, but a reduction in code path. (Better still if you increment 'level'.) Which catches most SCTP uses and the only other place I've found it used. There is actually a nasty bug in the genradix code. If the cmpxchg 'fails' when adding extra root levels then the page can get reused later - but child[0] has been set. This could add a loop to the tree! David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)