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=-7.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS autolearn=ham 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 F2C7AC43381 for ; Wed, 27 Feb 2019 10:10:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id CBA082084D for ; Wed, 27 Feb 2019 10:10:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728831AbfB0KKd convert rfc822-to-8bit (ORCPT ); Wed, 27 Feb 2019 05:10:33 -0500 Received: from eu-smtp-delivery-151.mimecast.com ([146.101.78.151]:59612 "EHLO eu-smtp-delivery-151.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726012AbfB0KKd (ORCPT ); Wed, 27 Feb 2019 05:10:33 -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-61-qny5IP1sOFumKKQftRw4YQ-1; Wed, 27 Feb 2019 10:10:30 +0000 Received: from AcuMS.Aculab.com (fd9f:af1c:a25b::d117) by AcuMS.aculab.com (fd9f:af1c:a25b::d117) with Microsoft SMTP Server (TLS) id 15.0.1347.2; Wed, 27 Feb 2019 10:11:14 +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; Wed, 27 Feb 2019 10:11:14 +0000 From: David Laight To: 'Leslie Monis' , "davem@davemloft.net" CC: "netdev@vger.kernel.org" Subject: RE: [PATCH net-next] net: sched: pie: fix 64-bit division Thread-Topic: [PATCH net-next] net: sched: pie: fix 64-bit division Thread-Index: AQHUzjfw/QEeBPQQhkKavgHbwVOxNKXzazRQ Date: Wed, 27 Feb 2019 10:11:14 +0000 Message-ID: <44c1c447befd45e49a06b1e3d3f5f7a6@AcuMS.aculab.com> References: <20190227010006.22219-1-lesliemonis@gmail.com> In-Reply-To: <20190227010006.22219-1-lesliemonis@gmail.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 X-MC-Unique: qny5IP1sOFumKKQftRw4YQ-1 X-Mimecast-Spam-Score: 0 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: Leslie Monis > Sent: 27 February 2019 01:00 > Use div_u64() to resolve build failures on 32-bit platforms. > > Fixes: 3f7ae5f3dc52 ("net: sched: pie: add more cases to auto-tune alpha and beta") > Signed-off-by: Leslie Monis > --- > net/sched/sch_pie.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/net/sched/sch_pie.c b/net/sched/sch_pie.c > index 4c0670b6aec1..f93cfe034c72 100644 > --- a/net/sched/sch_pie.c > +++ b/net/sched/sch_pie.c > @@ -429,7 +429,7 @@ static void calculate_probability(struct Qdisc *sch) > */ > > if (qdelay == 0 && qdelay_old == 0 && update_prob) > - q->vars.prob = (q->vars.prob * 98) / 100; > + q->vars.prob = 98 * div_u64(q->vars.prob, 100); This has significantly different rounding after the change. The result for small values is very different. The alterative: q->vars.prob -= div_u64(q->vars.prob, 50); is much nearer to the original - but never goes to zero. If the 98% decay factor isn't critical then you could remove 1/64th or 1/32nd + 1/16th to avoid the slow division. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)