X-Recipient: archive-cygwin AT delorie DOT com DomainKey-Signature: a=rsa-sha1; c=nofws; d=sourceware.org; h=list-id :list-unsubscribe:list-subscribe:list-archive:list-post :list-help:sender:mime-version:from:date:message-id:subject:to :content-type; q=dns; s=default; b=DEIVBjEuVfxC2i9k7wwYHLJ9yYJnm IUCvXKzK1+pNujHngRJYYdltjYHWCZxcRsu8xhbe1AGk+IeRFyITp1LHCBossOzp WlfkRo0KrifCsnQHNZc1JdLG2nDqqSBE1SR31N9mhampM29It8Xvf90DiiaHY1lf KphrYI1hfe0uL0= DKIM-Signature: v=1; a=rsa-sha1; c=relaxed; d=sourceware.org; h=list-id :list-unsubscribe:list-subscribe:list-archive:list-post :list-help:sender:mime-version:from:date:message-id:subject:to :content-type; s=default; bh=N8DXffbeHJkshOZKewN2BUz/2Ek=; b=R6j 3AqlpGqtLcM1s6zZMVwu/Yw6TSZmeE/U4eKFkEGUp9/S4fxtXwe4ofyhjgCMeO// YPr+qwr7Pi23sLsz8iBRauaGHa5oh4oE1XxDJh45XPzuvz5HX5uRGwsp088EQAVj MJXsTJ9ICDSlua92YAr9fp45C1Z66jltxqv2LgD8= Mailing-List: contact cygwin-help AT cygwin DOT com; run by ezmlm List-Id: List-Subscribe: List-Archive: List-Post: List-Help: , Sender: cygwin-owner AT cygwin DOT com Mail-Followup-To: cygwin AT cygwin DOT com Delivered-To: mailing list cygwin AT cygwin DOT com 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 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 From: Daniel Havey Date: Mon, 28 Nov 2016 11:54:27 -0800 Message-ID: Subject: Cygwin TCP slow To: cygwin AT cygwin DOT com Content-Type: text/plain; charset=UTF-8 X-IsSubscribed: yes 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