From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 31945 invoked by alias); 28 Nov 2016 19:54:40 -0000 Mailing-List: contact cygwin-help@cygwin.com; run by ezmlm Precedence: bulk List-Id: List-Subscribe: List-Archive: List-Post: List-Help: , Sender: cygwin-owner@cygwin.com Mail-Followup-To: cygwin@cygwin.com Received: (qmail 31927 invoked by uid 89); 28 Nov 2016 19:54:40 -0000 Authentication-Results: sourceware.org; auth=none X-Virus-Found: No X-Spam-SWARE-Status: No, score=-1.2 required=5.0 tests=AWL,BAYES_00,FREEMAIL_FROM,RCVD_IN_DNSWL_NONE,SPF_PASS autolearn=ham version=3.3.2 spammy=formally, theoretical, Hx-languages-length:1021 X-HELO: mail-wj0-f179.google.com Received: from mail-wj0-f179.google.com (HELO mail-wj0-f179.google.com) (209.85.210.179) by sourceware.org (qpsmtpd/0.93/v0.84-503-g423c35a) with ESMTP; Mon, 28 Nov 2016 19:54:30 +0000 Received: by mail-wj0-f179.google.com with SMTP id xy5so126045119wjc.0 for ; Mon, 28 Nov 2016 11:54:29 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:mime-version:from:date:message-id:subject:to; bh=YuoeEuNzD20Exk+uv4Gr1ZCofZ74k5451xeMKLAj6yE=; b=Ip5vd7nZt79vn+53vtZHV13x6QkEMo50wl71iNeDpFBE14+9/ixxMv1cKAemAdQSkH CKbGP8jXMIMz7ODBsHHme8Tp7865vf8/Yy7o+UME8EbTMoZgsBIhRIH1dFJCIX4aqcaN Lmyq3TzpGsg+oFwAglVKgWAma4zgbfIggSBpHiyiulY3T+GVrJCZXriRG/QzfAlg6UPu IkhAKUYxdo3LRkSqR+SuT0OzI2NXgG6dE4SFJi5sblMyWDWZpqJpDEPfyaGnSm1zLPHw pW3yDhXO54KAZ6ETFBOnVBNJmq051cgGeyXljkytlcySAaAtTlozjGeJSqKDzsyZkTIn eRCw== X-Gm-Message-State: AKaTC02Oahva6gz+ZSjM5LcDpv8ei+RnyoVEcOfPBNE/6ExajSYU8FvnMuwcBbAB0ofX1qP57yVWF5E0sTcnCQ== X-Received: by 10.194.150.108 with SMTP id uh12mr22246884wjb.107.1480362867807; Mon, 28 Nov 2016 11:54:27 -0800 (PST) MIME-Version: 1.0 Received: by 10.80.136.77 with HTTP; Mon, 28 Nov 2016 11:54:27 -0800 (PST) From: Daniel Havey Date: Tue, 29 Nov 2016 01:25:00 -0000 Message-ID: Subject: Cygwin TCP slow To: cygwin@cygwin.com Content-Type: text/plain; charset=UTF-8 X-IsSubscribed: yes X-SW-Source: 2016-11/txt/msg00315.txt.bz2 Hello, We have had complaints from several large hardware vendors that Windows networking is slow for apps like iperf that are used to measure throughput. Iperf on Windows is compiled against the cygwin1.dll. We have root caused the problem to a couple of lines of code in net.cc that set SO_RCVBUF and SO_SNDBUF to about 200KB. The theoretical window/RTT plot for the buffer size set by Cygwin (0x34000 = 200KB) gives us: 1ms -> 1703Mbps 2ms -> 851Mbps 3ms -> 567Mbps 4ms -> 425Mbps 5ms -> 340Mbps 6ms -> 283Mbps 7ms -> 243Mbps 8ms -> 212Mbps 9ms -> 189Mbps 10ms -> 170Mbps 20ms -> 85Mbps 40ms -> 42Mbps 60ms -> 28Mbps 80ms -> 21Mbps We have confirmed this by experiment and also confirmed that the limitation goes away if the buffers are not manually set. Windows has autotuning and when the buffers are set manually the autotuning is disabled. This is causing the throughput limitation. So we would like to formally ask that you please not manually set SO_RCVBUF or SO_SNDBUF. thanxs ;^) ...Daniel -- Problem reports: http://cygwin.com/problems.html FAQ: http://cygwin.com/faq/ Documentation: http://cygwin.com/docs.html Unsubscribe info: http://cygwin.com/ml/#unsubscribe-simple