From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ig0-x22a.google.com (mail-ig0-x22a.google.com [IPv6:2607:f8b0:4001:c05::22a]) (using TLSv1 with cipher RC4-SHA (128/128 bits)) (Client CN "smtp.gmail.com", Issuer "Google Internet Authority G2" (verified OK)) by huchra.bufferbloat.net (Postfix) with ESMTPS id 1357221F1D9 for ; Wed, 22 Apr 2015 14:43:01 -0700 (PDT) Received: by igblo3 with SMTP id lo3so8464876igb.0 for ; Wed, 22 Apr 2015 14:43:00 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=message-id:subject:from:to:cc:date:in-reply-to:references :content-type:mime-version:content-transfer-encoding; bh=8atuUfiQ3crsalCucAr+AVlnHktiOPW4a/9JZZN6XDc=; b=uNkkBMfGVgHkYLNfrGJO5nxbnrUaqhqroaD1s0hVAxOkYA7BJ272+MbwXdHIcusRFF jFQr60UViKattUuzcQGvlJLBT/9KStV+VsFopSQHSt/qg6CcEUri/naEpeOpo2lL80c3 cS6vTjR3WcJalD9IyOxO21PbkXyXfedHHC8LUwiYjSGUL8E8yhzo9Kz2bHc6L5Sp1q7I w08K9NLVI7I+dX13yaWdCyNsFg51VTAIeuxXkL9azrUu4zEclRl2e48bgG1lyVXcIyjG NUD8C161MYjsbJQRLpibzZKT+GjFT/Yo0HnkAEGVWmmRgfr4/EdaSCTM8GEcVqRP5Cin XGTA== X-Received: by 10.107.170.77 with SMTP id t74mr39702271ioe.85.1429738980823; Wed, 22 Apr 2015 14:43:00 -0700 (PDT) Received: from [172.26.55.207] ([172.26.55.207]) by mx.google.com with ESMTPSA id fs5sm10925139igb.0.2015.04.22.14.42.59 (version=TLSv1.2 cipher=AES128-GCM-SHA256 bits=128/128); Wed, 22 Apr 2015 14:43:00 -0700 (PDT) Message-ID: <1429738979.18561.150.camel@edumazet-glaptop2.roam.corp.google.com> From: Eric Dumazet To: "Steinar H. Gunderson" Date: Wed, 22 Apr 2015 14:42:59 -0700 In-Reply-To: <20150422210740.GA31348@sesse.net> References: <20150422191056.9C7AC406057@ip-64-139-1-69.sjc.megapath.net> <1429736552.18561.144.camel@edumazet-glaptop2.roam.corp.google.com> <20150422210740.GA31348@sesse.net> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.10.4-0ubuntu2 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Cc: Hal Murray , bloat Subject: Re: [Bloat] SO_SNDBUF and SO_RCVBUF X-BeenThere: bloat@lists.bufferbloat.net X-Mailman-Version: 2.1.13 Precedence: list List-Id: General list for discussing Bufferbloat List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 22 Apr 2015 21:43:30 -0000 On Wed, 2015-04-22 at 23:07 +0200, Steinar H. Gunderson wrote: > On Wed, Apr 22, 2015 at 02:02:32PM -0700, Eric Dumazet wrote: > > Yeah, the real nice thing is TCP_NOTSENT_LOWAT added in linux-3.12 > > But this is only for when your data could change underway, right? > Like, not relevant for sending one big file, but might be relevant for e.g. > VNC (or someone mentioned the usecase of HTTP/2, where a high-priority > request might come in, which you don't want buried behind a megabyte of > stuff in the send queue). Sorry, I do not understand you. The nice thing about TCP_NOTSENT_LOWAT is that you no longer have to care about choosing the 'right SO_SNDBUF' It is still CC responsibility to choose/set cwnd, but you hadn't set an artificial cap on cwnd. You control the amount of 'unsent data' per socket. If you set a low limit, application might have to issue more send() calls and get more EPOLLOUT events. This also means that if you get an abort / eof, you no longer have a huge unsent queue that TCP API does not allow to cancel. https://insouciant.org/tech/prioritization-only-works-when-theres-pending-data-to-prioritize/