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 mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id DDC22C433EF for ; Thu, 18 Nov 2021 19:00:16 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id BC1E9611F2 for ; Thu, 18 Nov 2021 19:00:16 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230290AbhKRTDQ (ORCPT ); Thu, 18 Nov 2021 14:03:16 -0500 Received: from mail-db8eur05on2057.outbound.protection.outlook.com ([40.107.20.57]:10105 "EHLO EUR05-DB8-obe.outbound.protection.outlook.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S233955AbhKRTDQ (ORCPT ); Thu, 18 Nov 2021 14:03:16 -0500 ARC-Seal: i=1; a=rsa-sha256; s=arcselector9901; d=microsoft.com; cv=none; b=Rzn7IwzkBFEmWLTIbk1uUT2cDaYLFxhED9/vFjayLTZndsv5gLQcijb0t+y+XZ1yIBCmUutDTmwcKL/s53StvOG3zQaoHEvhXgIbQ9Ev2OOVjH44iHfteNF5JU4RgQSVpHCPv/FbFqP0PxQdhtJaUiSHvZot5fBu/jcRUz0jPa89gcIjocgXgJlnUCGMRu1otoN9M9bw5V57ZpIAUm8ePlmAeM4XLEZTfzHmiPmh3BeKgiY1Ph97hMNkqG/lS+kOOpPrqH1Hf8JwjbrW39of1v0YCFYRAzoymQXcmk7fbFecALtLHVsj3drmK509f4VCpF/b1Xo9N8x7LB7IZULtrg== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=microsoft.com; s=arcselector9901; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-AntiSpam-MessageData-ChunkCount:X-MS-Exchange-AntiSpam-MessageData-0:X-MS-Exchange-AntiSpam-MessageData-1; bh=rL5GuEcwhYOFaXOsFKoXPyD9mk5jjwozdyza2QUwK5A=; b=Mxv+BagOOOjGNtiTzIJzt9QQ9ABp83o+E3DNrnaMFsIo9CdRXUXzbhQVSaYDgRlfyw4i0mdvOTg9pnu1xbUOwsKkptHo0LcPmmRTuvZM+91OnyJxwOfjx2PC1TFR1OSojOCRr4CJ2brJifNib23ZTwBC0wH55gsrpNO3edhKez6cKJHbsFZJHnddu6EmNmLRYRb0HED22n5zo9BvXYM44ZGbkF3EN+CQ/lAgFQGffCi7Enm7hq4dPQ8Iw2YMth+ONk5Y/BkXanvN4FUC1S/CgxDgnPTj9g2wDyOk06srggT37EpQ6Bfy7yzXNEfa51h1tgRD3aEUdtoamW1XeN01Xw== ARC-Authentication-Results: i=1; mx.microsoft.com 1; spf=pass smtp.mailfrom=nxp.com; dmarc=pass action=none header.from=nxp.com; dkim=pass header.d=nxp.com; arc=none DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=nxp.com; s=selector2; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-SenderADCheck; bh=rL5GuEcwhYOFaXOsFKoXPyD9mk5jjwozdyza2QUwK5A=; b=oWsGpHzm5+bsmirW5bACmVHodsZxRQrTiE5yc1P/5WVzLRy0zzZKAeqyTry/i/pm0BEO0ELAi0kplBTmZWRgmIGaXsHk25OFlFfRi1/0VMpEKhGzvm10ZShVQRPIP0XqZh9gAaEvzZfUXyyXiwOw64Vswa5TyCz10WvYsLxp0aA= Received: from VI1PR04MB5136.eurprd04.prod.outlook.com (2603:10a6:803:55::19) by VI1PR0402MB3549.eurprd04.prod.outlook.com (2603:10a6:803:8::30) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.4713.21; Thu, 18 Nov 2021 19:00:13 +0000 Received: from VI1PR04MB5136.eurprd04.prod.outlook.com ([fe80::e4ed:b009:ae4:83c5]) by VI1PR04MB5136.eurprd04.prod.outlook.com ([fe80::e4ed:b009:ae4:83c5%7]) with mapi id 15.20.4713.022; Thu, 18 Nov 2021 19:00:13 +0000 From: Vladimir Oltean To: "netdev@vger.kernel.org" CC: "David S. Miller" , Jakub Kicinski , Claudiu Manoil , Alexandre Belloni , "UNGLinuxDriver@microchip.com" , Andrew Lunn , Vivien Didelot , Florian Fainelli , Xiaoliang Yang Subject: Re: [PATCH net-next] net: dsa: felix: enable cut-through forwarding between ports by default Thread-Topic: [PATCH net-next] net: dsa: felix: enable cut-through forwarding between ports by default Thread-Index: AQHX3K3cxGGrwwaPrkmUPx6r0o3O1awJo6sA Date: Thu, 18 Nov 2021 19:00:13 +0000 Message-ID: <20211118190012.dvmdrw7upisna2na@skbuf> References: <20211118185352.2504417-1-vladimir.oltean@nxp.com> In-Reply-To: <20211118185352.2504417-1-vladimir.oltean@nxp.com> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: authentication-results: dkim=none (message not signed) header.d=none;dmarc=none action=none header.from=nxp.com; x-ms-publictraffictype: Email x-ms-office365-filtering-correlation-id: db3f0091-24e7-4fe5-bf1d-08d9aac5a71d x-ms-traffictypediagnostic: VI1PR0402MB3549: x-microsoft-antispam-prvs: x-ms-oob-tlc-oobclassifiers: OLM:10000; x-ms-exchange-senderadcheck: 1 x-ms-exchange-antispam-relay: 0 x-microsoft-antispam: BCL:0; x-microsoft-antispam-message-info: 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 x-forefront-antispam-report: CIP:255.255.255.255;CTRY:;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:VI1PR04MB5136.eurprd04.prod.outlook.com;PTR:;CAT:NONE;SFS:(4636009)(7916004)(366004)(44832011)(508600001)(4326008)(9686003)(86362001)(2906002)(83380400001)(33716001)(316002)(38070700005)(54906003)(66476007)(186003)(6506007)(8676002)(66946007)(66556008)(6512007)(6916009)(5660300002)(1076003)(38100700002)(122000001)(66446008)(8936002)(6486002)(76116006)(91956017)(71200400001)(26005)(64756008);DIR:OUT;SFP:1101; x-ms-exchange-antispam-messagedata-chunkcount: 1 x-ms-exchange-antispam-messagedata-0: =?us-ascii?Q?gQ3TuCj5j6hjI5OuMVwEtnEMO43kYGyJ0xqDrSrEAT5ytij7Yw3c5sMTXP+h?= =?us-ascii?Q?T6Khh3y69yt5PMI4uroUjpYqhpVlpJIs1eWEMK6Njr4ZKuAEn7s7yaXSWhKW?= =?us-ascii?Q?H5co6hhTCviqlQnRTebMIYJ1wLlWAna4Lm6Vm2neVVBpXr610x/sOfd4/9cy?= =?us-ascii?Q?tyJBxAAXAATWzc+NT91+o+V4Er6rwTuokASqQJa9gB6j/5RV+HwHqCgMoC9a?= =?us-ascii?Q?mpHXavjRGwq4/Q5Ml1p84ENu66CdxwzuGs+iokxuwDewFuFb4ojJFfaVK2Fn?= =?us-ascii?Q?CiadfDkr3DVZnDLccddMn1xm4xUXCOZ20ofcZY2P7+kqbXy5DNoTqOFt9ScP?= =?us-ascii?Q?ncqNQq3i+LV9e4TeuOLXuvZa4DpPYR8DBPOBEEfNmeRJe3ERUbS7vNDGBqSH?= =?us-ascii?Q?KGE+DxB6nUwLsnLKtCQvcmZPDox4RlFc+Tk8L1Y0CbA7sVtWXalCk3wHJ0gP?= =?us-ascii?Q?vGJaGVZDbcWXZm1dvKfAfBd1I62QA34AcISnEQsEa0jPUtMa7fJiX2ECNfcP?= =?us-ascii?Q?+KhIqC74vHl2if5eLFEEYs8FHyjlUUPiiMdugpO0DnHvq61f/+YxUKbci13J?= =?us-ascii?Q?hA+dCD+sQD2T8atkHOjusAgHbehXIoWEsjZQD0xgsL4ShjbrOW1Cyf1U1WQG?= =?us-ascii?Q?dW3mwOFMDS0ugGRSEkHFKosGMks+4T5i3QrXITNBnRmw7dLR9Svz4eB6Oh22?= =?us-ascii?Q?iKSlYqFLxgWy1XcWeqL5c/heHdYOFKnfvA6nTuX0sockFKWGXc/4melEKZM7?= =?us-ascii?Q?ggvHcRfg3UkEjayHEBrn9tblydEqee0k8kI0fFF7K0AJZiIAl32hbzyanrwl?= =?us-ascii?Q?lvAqvMJ2fOvM+iZzET9EX5clatR22u6dFyqq3Ulm+URBvrCJLsmrhLA8khzP?= =?us-ascii?Q?1KUfQ+CO3GxrVioSlcAOhXI8dPVKO1cWwa6HFdmjSvUDlk8WD3zgEiu6yjOX?= =?us-ascii?Q?XL9wun54TbHTGpWNJjBUS0eT3f7yeWYZUHiGUq7C+gsMs16q//Mqv9+zPN1N?= =?us-ascii?Q?fLQ1k6KEfNeErhxPrCoXV/Dbh+R1hyUTPi6q6lHpQc7tnNLs7A2P44f0i4LC?= =?us-ascii?Q?KyBX1XdLy6zJHdkP3rQ+5wB4A4Uej8cVJ3soTTO/FemTCogv/7LHaekRc+wv?= =?us-ascii?Q?nDqOcUoamDK4ERDaQONcppc8VSGvTg/DiNwdoBoSI+/uj47ytkrjq7+Yy/9b?= =?us-ascii?Q?G2X+hz8jkc7ilJMjY6zZevrejlblocagmAzwdRNxbqkZh4rI1Aex/SJZ73I1?= =?us-ascii?Q?2wrsbOGzV0nVx/o/rykiaFNAnhRIMA/phbCm9k10uLYIDZReXf02QvG5Bmz4?= =?us-ascii?Q?0BivPATuZx7aT1ynBkukHPigNJayrMuJJY1dUmRnW0h69ewdZBqUymDZRyht?= =?us-ascii?Q?BoPLfMO8+o4Njy6wGVUA0zPNBwOLOBzVF1tyiZbCQ3l5m14pNCor5Y8e/3ZV?= =?us-ascii?Q?zafblyVaET1q+cbju7+bvsK3xUJKEr/lNgmP4LTsuuEBvj0YVS7Ku85Fx8pg?= =?us-ascii?Q?l4cEHSL62WhvrQDzSVEySRs/sHMJSb/KcB7/hk45Qgm5gSdYYvsnMOgTkgZ1?= =?us-ascii?Q?lPBLs447JXIHS59xOg8FQStTUzQDWXKOvbfyjicEW/eE6EkWjH4S9b9PpWVM?= =?us-ascii?Q?WdsMJoQ3fVxP3NcoI9A4Yx4=3D?= Content-Type: text/plain; charset="us-ascii" Content-ID: Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-OriginatorOrg: nxp.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-AuthSource: VI1PR04MB5136.eurprd04.prod.outlook.com X-MS-Exchange-CrossTenant-Network-Message-Id: db3f0091-24e7-4fe5-bf1d-08d9aac5a71d X-MS-Exchange-CrossTenant-originalarrivaltime: 18 Nov 2021 19:00:13.7010 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: 686ea1d3-bc2b-4c6f-a92c-d99c5c301635 X-MS-Exchange-CrossTenant-mailboxtype: HOSTED X-MS-Exchange-CrossTenant-userprincipalname: pdz/WWVvdXQVE3eM2aox5m3et9A4B9wyjcd8oTMIKMWAo9LVe2hpoQsiHWT0yCh74bBO7/TV7B5494fQHAl4lQ== X-MS-Exchange-Transport-CrossTenantHeadersStamped: VI1PR0402MB3549 Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Thu, Nov 18, 2021 at 08:53:52PM +0200, Vladimir Oltean wrote: > The VSC9959 switch embedded within NXP LS1028A (and that version of > Ocelot switches only) supports cut-through forwarding - meaning it can > start the process of looking up the destination ports for a packet, and > forward towards those ports, before the entire packet has been received > (as opposed to the store-and-forward mode). >=20 > The up side is having lower forwarding latency for large packets. The > down side is that frames with FCS errors are forwarded instead of being > dropped. However, erroneous frames do not result in incorrect updates of > the FDB or incorrect policer updates, since these are processes are > deferred inside the switch to the end of frame. Since the switch starts > the cut-through forwarding process after all packet headers (including > IP, if any) have been processed, packets with large headers and small > payload do not see the benefit of lower forwarding latency. >=20 > There are two cases that need special attention. >=20 > The first is when a packet is multicast (or flooded) to multiple > destinations, one of which doesn't have cut-through forwarding enabled. > The switch deals with this automatically by disabling cut-through > forwarding for the frame towards all destination ports. >=20 > The second is when a packet is forwarded from a port of lower link speed > towards a port of higher link speed. This is not handled by the hardware > and needs software intervention. >=20 > Enabling cut-through forwarding is done per {egress port, traffic class}. > I don't see any reason why this would be a configurable option as long > as it works without issues, and there doesn't appear to be any user > space configuration tool to toggle this on/off, so this patch enables > cut-through forwarding on all eligible ports and traffic classes. >=20 > Signed-off-by: Vladimir Oltean > --- I forgot to mark this as such, but please treat it as RFC (aka do not apply just yet).=