From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wg0-f47.google.com (mail-wg0-f47.google.com [74.125.82.47]) (using TLSv1 with cipher RC4-SHA (128/128 bits)) (Client CN "smtp.gmail.com", Issuer "Google Internet Authority" (verified OK)) by huchra.bufferbloat.net (Postfix) with ESMTPS id 8316A201044 for ; Sat, 7 Apr 2012 15:36:04 -0700 (PDT) Received: by wgbge7 with SMTP id ge7so2531832wgb.28 for ; Sat, 07 Apr 2012 15:36:02 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :content-type:content-transfer-encoding; bh=PteUheH5asGdVrxqozgfQSkgqxXDb7W7EOySY9ICB2Q=; b=PI22yQcYkq/5uUrlKtz7kgKcg30Q7LO4CsySe4NFfoNnq5pQUHh7u8bTzpnPu1Y0zj bMnDFzXJFPpzY8WVwni0+8YCIfoS//HLDsRuP5GhWYcr8wxQdAQ1WQIxGv8HIHk0dJDj ES2QMGFaCFQLJhg0qF97nIiXuTfF8XgGh4WZq0lYanWiiNcOls2nAZ3I/7YuN5jfnnHA sDFYsa+esg7jvnUrzu0RgYhLVUvwkx2quW4WTEfMBEWquwmOGHyyX6KVXcBeYRJfft4a mrcP0Jtg71Y7uO+fLPvSuoxnr920vz7qi/Cla5JQ/KAI79/7tnCf5kEikYIO0yqqMO9N ct8g== MIME-Version: 1.0 Received: by 10.180.82.132 with SMTP id i4mr5646377wiy.12.1333838162376; Sat, 07 Apr 2012 15:36:02 -0700 (PDT) Received: by 10.223.127.194 with HTTP; Sat, 7 Apr 2012 15:36:02 -0700 (PDT) In-Reply-To: <6D19B807-1B09-4AB5-A727-E9A7449C6A1D@cisco.com> References: <20120406213725.GA12641@uio.no> <20120406222138.GB12641@uio.no> <1333811327.30705.4.camel@edumazet-laptop> <20120407153548.GC21452@uio.no> <20120407181034.GD21452@uio.no> <6D19B807-1B09-4AB5-A727-E9A7449C6A1D@cisco.com> Date: Sat, 7 Apr 2012 23:36:02 +0100 Message-ID: From: Dave Taht To: bloat Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable Subject: Re: [Bloat] Best practices for paced TCP on Linux? 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: Sat, 07 Apr 2012 22:36:05 -0000 On Sat, Apr 7, 2012 at 2:49 PM, Fred Baker wrote: > > On Apr 7, 2012, at 11:50 AM, Dave Taht wrote: > >> http://www.kernel.org/doc/man-pages/online/pages/man7/tcp.7.html >> >> 64-256k seems about right but the math is eluding me this morning. > > For a 5 MBPS data stream, Path MTU =3D 1460, 100 ms RTT, you're looking a= t > > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 rate in bps =A0 =A0rtt in mic= roseconds > cwnd_limit =3D ceiling ( ----------- * ------------------- ) > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A08*pmtu =A0 =A0 =A0 =A0= 1e6 > > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A05e6 =A0 =A0 =A0 =A0 =A0100= e 3 > =A0 =A0 =A0 =A0 =A0 =3D ceiling ( ------ * ------------------- ) > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 8*1460 =A0 =A0 =A0 =A0 =A01e6 > > =A0 =A0 =A0 =A0 =A0 =3D ceiling ( 428 * 0.100 ) > > =A0 =A0 =A0 =A0 =A0 =3D 43 > > you probably want to bump that by one or two to account for 43*40 bytes o= f IP and TCP headers. > > 43*1460 is 62780 bytes per RTT, which is frightfully close to 65K bytes p= er RTT, 524,280 bits per RTT, or 5,242,800 bits per second with the stated = RTT. Hmmm. > > Speaking strictly for myself, I would throw in one caveat, which is that = a variable bit rate codec that averages 5 MBPS sometimes sends faster, and = there may be good reason to allow it to. I think I'd recalculate for 6 MBPS= on average, and carefully insert the RTT I cared about into the calculatio= n. Doing that also accounts for the Mathis formula, which is far more compl= ex and requires a lot more assumptions, but will come up with a number belo= w 6 MBPS for a .1% loss rate. In my case I'm 196ms away and running this for the past hour or so vlc -6 http://pannekake.samfundet.no:3015/ seems to show it never really getting out of slow start. Regrettably my favorite graph crashes xplot (grr)... so I can't see the canonical bloat pattern or not. Could be a problem in my lab (but the udp stream is ok), am checking now... Captures are up here: http://huchra.bufferbloat.net/~d/captures/gathering/pannekake_3015.cap --=20 Dave T=E4ht SKYPE: davetaht US Tel: 1-239-829-5608 http://www.bufferbloat.net