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 198E4C433DF for ; Tue, 18 Aug 2020 15:38:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0001C20786 for ; Tue, 18 Aug 2020 15:38:14 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728037AbgHRPiO convert rfc822-to-8bit (ORCPT ); Tue, 18 Aug 2020 11:38:14 -0400 Received: from eu-smtp-delivery-151.mimecast.com ([207.82.80.151]:59467 "EHLO eu-smtp-delivery-151.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726624AbgHRPiN (ORCPT ); Tue, 18 Aug 2020 11:38:13 -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-46-sOLneJyYMye81YaMlQPUsg-1; Tue, 18 Aug 2020 16:38:09 +0100 X-MC-Unique: sOLneJyYMye81YaMlQPUsg-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; Tue, 18 Aug 2020 16:38:09 +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; Tue, 18 Aug 2020 16:38:09 +0100 From: David Laight To: "'linux-sctp@vger.kernel.org'" , "'Marcelo Ricardo Leitner'" CC: "'netdev@vger.kernel.org'" Subject: Use of genradix in sctp Thread-Topic: Use of genradix in sctp Thread-Index: AdZ1ckZAY2qe63tNS/O9MsxVdvHiSA== Date: Tue, 18 Aug 2020 15:38:09 +0000 Message-ID: <2ffb7752d3e8403ebb220e0a5e2cf3cd@AcuMS.aculab.com> 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 A few years ago (for 5.1) the 'arrays' that sctp uses for info about data streams was changed to use the 'genradix' functions. I'm not sure of the reason for the change, but I don't thing anyone looked at the performance implications. The code contains lots of SCTP_SI(stream, i) with the probable expectation that the expansion is basically stream->foo[i] (a pointer to a big memory array). However the genradix functions are far more complicated. Basically it is a list of pointers to pages, each of which is split into the maximum number of items. (With the page pointers being in a tree of pages for large numbers of large items.) So every SCTP_S[IO]() has inline code to calculate the byte offset: idx / objs_per_page * PAGE_SIZE + idx % objs_per_page * obj_size (objs_per_page and obj_size are compile time constants) and then calls a function to do the actual lookup. This is all rather horrid when the array isn't even sparse. I also doubt it really helps if anyone is trying to allow a lot of streams. For 64k streams you might be trying to allocate ~700 pages in atomic context. For example look at the object code for sctp_stream_clear() (__genradix_ptr() is in lib/generic-radix-tree.c). There is only one other piece of code that uses genradix. All it needs is a fifo list. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)