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Wed, 4 Dec 2019 14:11:02 +0000 Received: from SN4PR0601MB3728.namprd06.prod.outlook.com ([fe80::3dad:d7cf:dac4:3277]) by SN4PR0601MB3728.namprd06.prod.outlook.com ([fe80::3dad:d7cf:dac4:3277%5]) with mapi id 15.20.2495.014; Wed, 4 Dec 2019 14:11:02 +0000 From: "Scheffenegger, Richard" To: "freebsd-transport@freebsd.org" Subject: acknow on cwr Thread-Topic: acknow on cwr Thread-Index: AdWqqzZTATkiyxP+S5KMY9Urhq3Pgg== Date: Wed, 4 Dec 2019 14:11:02 +0000 Message-ID: Accept-Language: de-AT, en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-dg-ref: =?us-ascii?Q?PG1ldGE+PGF0IG5tPSJib2R5Lmh0bWwiIHA9ImM6XHVzZXJzXHNyaWNoYXJk?= =?us-ascii?Q?XGFwcGRhdGFccm9hbWluZ1wwOWQ4NDliNi0zMmQzLTRhNDAtODVlZS02Yjg0?= =?us-ascii?Q?YmEyOWUzNWJcbXNnc1xtc2ctZTRmMzgzZDAtMTY5Zi0xMWVhLWI2MTQtMDAx?= =?us-ascii?Q?OWQyZTRlY2Q0XGFtZS10ZXN0XGU0ZjM4M2QxLTE2OWYtMTFlYS1iNjE0LTAw?= =?us-ascii?Q?MTlkMmU0ZWNkNGJvZHkuaHRtbCIgc3o9IjQ0MjIiIHQ9IjEzMjE5OTQyMjU5?= =?us-ascii?Q?NzczOTQ3NiIgaD0iRDNzcFhUWHZTaWpwYTFLMUlISlluYXBIS09VPSIgaWQ9?= =?us-ascii?Q?IiIgYmw9IjAiIGJvPSIxIiBjaT0iY0FBQUFFUkhVMVJTUlVGTkNnVUFBQ1FF?= =?us-ascii?Q?QUFEVU0zT25yS3JWQVhKZ1JKT2J5RmZuY21CRWs1dklWK2NHQUFBQUFBQUFB?= =?us-ascii?Q?QUFBQUFBQUFBQUFBQUFBQUhBQUFBQzBBd0FBQUFBQUFBQUFBQUFBQUFBQUFB?= =?us-ascii?Q?QUFBQUVBQVFBQkFBQUEycGt5WlFBQUFBQUFBQUFBQUFBQUFKNEFBQUJoQUdR?= =?us-ascii?Q?QVpBQnlBR1VBY3dCekFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFB?= =?us-ascii?Q?QUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFB?= =?us-ascii?Q?QUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFB?= =?us-ascii?Q?QUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFB?= =?us-ascii?Q?QUFBRUFBQUFBQUFBQUFnQUFBQUFBbmdBQUFHTUFZd0JmQUdNQWRRQnpBSFFB?= =?us-ascii?Q?YndCdEFGOEFZUUJ1QUhrQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFB?= =?us-ascii?Q?QUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFB?= =?us-ascii?Q?QUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFB?= =?us-ascii?Q?QUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQVFBQUFBQUFBQUFD?= =?us-ascii?Q?QUFBQUFBQ2VBQUFBWXdCMUFITUFkQUJ2QUcwQVh3QndBR1VBY2dCekFHOEFi?= =?us-ascii?Q?Z0FBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFB?= =?us-ascii?Q?QUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFB?= =?us-ascii?Q?QUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFB?= =?us-ascii?Q?QUFBQUFBQUFBQUFBQUFBQUFBQUJBQUFBQUFBQUFBSUFBQUFBQUo0QUFBQmpB?= =?us-ascii?Q?SFVBY3dCMEFHOEFiUUJmQUhBQWFBQnZBRzRBWlFCdUFIVUFiUUJpQUdVQWNn?= =?us-ascii?Q?QUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFB?= =?us-ascii?Q?QUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFB?= =?us-ascii?Q?QUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFB?= =?us-ascii?Q?QUFBQUFFQUFBQUFBQUFBQWdBQUFBQUFuZ0FBQUdNQWRRQnpBSFFBYndCdEFG?= =?us-ascii?Q?OEFjd0J6QUc0QUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFB?= =?us-ascii?Q?QUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFB?= =?us-ascii?Q?QUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFB?= =?us-ascii?Q?QUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBUUFBQUFBQUFB?= =?us-ascii?Q?QUNBQUFBQUFDZUFBQUFaUUJ0QUdFQWFRQnNBRjhBWVFCa0FHUUFjZ0JsQUhN?= =?us-ascii?Q?QWN3QUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFB?= =?us-ascii?Q?QUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFB?= =?us-ascii?Q?QUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFB?= =?us-ascii?Q?QUFBQUFBQUFBQUFBQUFBQUFBQUFBQkFBQUFBQUFBQUFJQUFBQUFBQT09Ii8+?= =?us-ascii?Q?PC9tZXRhPg=3D=3D?= x-originating-ip: [217.70.210.46] x-ms-publictraffictype: Email x-ms-office365-filtering-correlation-id: dd7cba1a-2c3a-45c0-6912-08d778c3cb63 x-ms-traffictypediagnostic: SN4PR0601MB3661: x-microsoft-antispam-prvs: x-ms-oob-tlc-oobclassifiers: OLM:3826; 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ASN(0.00)[asn:8075, ipnet:40.64.0.0/10, country:US]; ARC_ALLOW(-1.00)[i=1] Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable X-Content-Filtered-By: Mailman/MimeDel 2.1.29 X-BeenThere: freebsd-transport@freebsd.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Discussions of transport level network protocols in FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 04 Dec 2019 14:11:09 -0000 Hi guys (gals?), While further looking into DCTCP bugs and oddities, I was pointed to these = two linux patches: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?= id=3D9aee40006190 https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?= id=3Dfd2123a3d7527d4c7092633d55e877c0cc1d84a3 The gist of this is as follows - and likely holds true for RFC3168 also: When a tcp sender reduces cwnd due to CE marks, it is possible to end up wi= th very small cwnd (<2 mss). When the next packet is sent, with the CWR fla= g, the receiver will often wait for another packet before sending an ACK af= ter the delack timer expires. This can effectively drive up the high-perce= ntile latency on request-response type interactions. The above was found specifically for flows using dctcp, most likely as the = cwnd in dctcp environments is more likely to collapse to very small values = - but the patch seems to be generic also for rfc3168 sessions... Any strong opinions if this fix should be specific to dctcp in fbsd, or a g= eneric ecn improvement? Note that RFC3168 is silent on this particular topic (if CWR should trigger= an immediate ACK or not). Best regards, Richard Scheffenegger