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Wed, 4 Apr 2018 16:55:37 +0000 From: "Scheffenegger, Richard" To: "freebsd-transport@freebsd.org" Subject: rwnd autotuning & cwnd growth Thread-Topic: rwnd autotuning & cwnd growth Thread-Index: AdPMNFOwXUDmcoxfSEKztN/AjldvrA== Date: Wed, 4 Apr 2018 16:55:37 +0000 Message-ID: Accept-Language: de-AT, en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-dg-ref: PG1ldGE+PGF0IG5tPSJib2R5Lmh0bWwiIHA9ImM6XHVzZXJzXHNyaWNoYXJkXGFwcGRhdGFccm9hbWluZ1wwOWQ4NDliNi0zMmQzLTRhNDAtODVlZS02Yjg0YmEyOWUzNWJcbXNnc1xtc2ctZmRlZTk4YzEtMzgyOC0xMWU4LWI1ZDUtMDAxOWQyZTRlY2Q3XGFtZS10ZXN0XGZkZWU5OGMzLTM4MjgtMTFlOC1iNWQ1LTAwMTlkMmU0ZWNkN2JvZHkuaHRtbCIgc3o9IjQ2ODEiIHQ9IjEzMTY3MzM0NTM1NTM0OTQ0MCIgaD0iWkVXWGV6anZ4alk0a29sdXR5SlZRN3drRnRZPSIgaWQ9IiIgYmw9IjAiIGJvPSIxIi8+PC9tZXRhPg== x-originating-ip: [80.109.181.140] x-ms-publictraffictype: Email x-microsoft-exchange-diagnostics: 1; CY4PR0601MB3633; 7:7e3RBW6MDkSMR0mYWwgxIG+Hz+8Ege21spKZr9bo20Z0opQLj3PxqPM3iD2oEMbhdIcyjVNieGX+NqtQDq4rqrRcuOnWluSpMME/8DKCKAAvvuigD5AR83R11YxW127+vGD7Oj8nX0mXw/I914Jpx7YzL2LijzxRxOOTw7G5FxAVrFJLM8cgqch9s0DNNoy28cZ83D5EBx6IGy3M22fPwUAcwEAMXHHdbw0HIk5punu3StEXVIs9h0lRo6aeU9Fd x-ms-exchange-antispam-srfa-diagnostics: SOS; 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charset="us-ascii" Content-Transfer-Encoding: quoted-printable X-Content-Filtered-By: Mailman/MimeDel 2.1.25 X-BeenThere: freebsd-transport@freebsd.org X-Mailman-Version: 2.1.25 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 Apr 2018 16:55:41 -0000 Hi, Wasn't there a burst limit included in freebsd tcp at some point in time? Today I observed the following scenario: client window host, with receive w= indow autotuning enabled; server freebsd 10.4; latency around 20ms (bufferb= loated; unloaded latency around 1-2ms), the link stretches about 5 links wi= th 10G,25G,40G each (server at 10G), client is 100Mbit. The client signals for the longest time a receive window of around 350kB, w= hich the server hogs for transmitting data (effective throughput < 100Mbit)= , after growth of cwnd hits rwnd. Then, after a couple seconds, the client = signals an increase of the receive window by a factor of ~2 (700kB), about = where the cwnd has grown in the background if the transmission rate weren't= clamped by rwnd. Thus the server sends a line rate (10G) burst of about 300kB (cwnd has not = increased to completely include the new rwnd), which is queued up (and the = tail dropped...), increasing the effective latency to about 40ms... Just looked at rfc5681, 2861 - but apparently receive window autoscaling is= too new a technology for those; Linux does have a burst clamping heuristic implemented, to prevent humongou= s burst of data to be sent, when for whatever reason cwnd would allow it (r= wnd clamping and increasing, application limitated operation, ...) But that= apparently never made it into any spec? IMHO, limiting the maximum burst size per RTT, or doing slow start when cwn= d suddenly allows for an "excessive" amount of data to be sent, would be th= e sensible thing to do - but whats your view on this? Best regards, Richard Scheffenegger From owner-freebsd-transport@freebsd.org Wed Apr 4 19:34:15 2018 Return-Path: Delivered-To: freebsd-transport@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2610:1c1:1:606c::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id E7997F7007B for ; Wed, 4 Apr 2018 19:34:14 +0000 (UTC) (envelope-from Cheng.Cui@netapp.com) Received: from mx144.netapp.com (mx144.netapp.com [IPv6:2620:10a:4005:8000:2306::d]) (using TLSv1.2 with cipher RC4-SHA (128/128 bits)) (Client CN "mx141.netapp.com", Issuer "Entrust Certification Authority - L1K" (verified OK)) by mx1.freebsd.org (Postfix) with ESMTPS id F30EE6F93D for ; Wed, 4 Apr 2018 19:34:13 +0000 (UTC) (envelope-from Cheng.Cui@netapp.com) X-IronPort-AV: E=Sophos;i="5.48,408,1517904000"; d="scan'208";a="249920024" Received: from vmwexchts04-prd.hq.netapp.com ([10.122.105.32]) by mx144-out.netapp.com with ESMTP; 04 Apr 2018 12:33:26 -0700 Received: from VMWEXCCAS04-PRD.hq.netapp.com (10.122.105.20) by VMWEXCHTS04-PRD.hq.netapp.com (10.122.105.32) with Microsoft SMTP Server (TLS) id 15.0.1320.4; 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Wed, 4 Apr 2018 19:33:23 +0000 From: "Cui, Cheng" To: "Scheffenegger, Richard" , "freebsd-transport@freebsd.org" Subject: Re: rwnd autotuning & cwnd growth Thread-Topic: rwnd autotuning & cwnd growth Thread-Index: AdPMNFOwXUDmcoxfSEKztN/AjldvrP//698A Date: Wed, 4 Apr 2018 19:33:23 +0000 Message-ID: <133A8488-56A5-4B87-AA55-0917588C65DB@netapp.com> References: In-Reply-To: Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: authentication-results: spf=none (sender IP is ) smtp.mailfrom=Cheng.Cui@netapp.com; x-originating-ip: [216.240.30.11] x-ms-publictraffictype: Email x-microsoft-exchange-diagnostics: 1; CY4PR06MB3288; 7:UoEQ8mo8z/hbiXjPoiYeZ1wBwv5gxw2gx2rqvvXAcIqppCdiGn1rxLMuK6oH2Fh8W89ixG7s0gjjQi89+AzbyvyZUL3TPX9b2HFIRFfTesy3jZ87x9Seqa2+MHZF3lYLec9VPmtvkwRTvpMa0D6n6ngO5yt5e2eM83cAHjvdQX8WtnD+DmqlJfwvKneTC4DfuqNfkt+vrny/2YBZ/i0chOXdRD4QlvkbP8XFdyr65+Ryb4uBUqKT45KkgbAdKFKL x-ms-exchange-antispam-srfa-diagnostics: SOS;SOR; x-forefront-antispam-report: SFV:SKI; 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[209.85.128.180]) by smtp.gmail.com with ESMTPSA id i48sm6321446ede.39.2018.04.06.07.23.12 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 06 Apr 2018 07:23:12 -0700 (PDT) Received: by mail-wr0-f180.google.com with SMTP id s18so1945834wrg.9 for ; Fri, 06 Apr 2018 07:23:12 -0700 (PDT) X-Received: by 10.223.226.66 with SMTP id n2mr21118212wri.228.1523024591998; Fri, 06 Apr 2018 07:23:11 -0700 (PDT) MIME-Version: 1.0 Received: by 10.223.199.203 with HTTP; Fri, 6 Apr 2018 07:23:11 -0700 (PDT) From: "Jonathan T. Looney" Date: Fri, 6 Apr 2018 10:23:11 -0400 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: rwnd autotuning & cwnd growth To: "Scheffenegger, Richard" Cc: "freebsd-transport@freebsd.org" Content-Type: text/plain; charset="UTF-8" X-Content-Filtered-By: Mailman/MimeDel 2.1.25 X-BeenThere: freebsd-transport@freebsd.org X-Mailman-Version: 2.1.25 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: Fri, 06 Apr 2018 14:23:19 -0000 On Wed, Apr 4, 2018 at 12:55 PM, Scheffenegger, Richard < Richard.Scheffenegger@netapp.com> wrote: > Wasn't there a burst limit included in freebsd tcp at some point in time? > FWIW, one of my colleagues has implemented this and is planning to upstream it soon-ish (in the "months" timeframe). Jonathan