From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pz0-f43.google.com (mail-pz0-f43.google.com [209.85.210.43]) (using TLSv1 with cipher RC4-SHA (128/128 bits)) (Client did not present a certificate) by huchra.bufferbloat.net (Postfix) with ESMTPS id 1B9A521F0AC for ; Fri, 31 Aug 2012 10:44:14 -0700 (PDT) Received: by daku36 with SMTP id u36so2831934dak.16 for ; Fri, 31 Aug 2012 10:44:13 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=sender:message-id:date:from:organization:user-agent:mime-version:to :cc:subject:references:in-reply-to:content-type :content-transfer-encoding; bh=tqmr8YXB1NxvBwBW3u/Ta0h+0Q/K/rfBmHJwWF8yuJs=; b=fHuuu2pVjRHGizCC/i50Er9ZUqw+OozpI7m3dBcQYi1xjYvgTjuOOwanKXEc4cdnDC uMG++SLFzZUI8Sy4ukbhyoxMxCVIVVoVQrKgkH21KucRADODpTggs+Ot6qocIpidddeQ A+nBZw7FVrmeENImDuj7r5/bSdx8GFw9z3O0J0f9AOyDZsLQahXzN9q+KAbjXHesMFUU GTwOWntZH7d7LYp7o+LjTTdxRcezGqpNVm7JMHERIRJ2OLY2mVytXtjqB9K217hpVgzw ujr26C0jc0yG+w7GbWE+DX1ylpYj9chRvboE5gUE0WsHtVp6QlY+/+P+BKefLt/gLhl+ tJMQ== Received: by 10.68.204.137 with SMTP id ky9mr18496815pbc.90.1346435053726; Fri, 31 Aug 2012 10:44:13 -0700 (PDT) Received: from [10.11.2.117] ([38.96.16.75]) by mx.google.com with ESMTPS id gf8sm3850368pbc.52.2012.08.31.10.44.12 (version=SSLv3 cipher=OTHER); Fri, 31 Aug 2012 10:44:12 -0700 (PDT) Sender: Jim Gettys Message-ID: <5040F7EB.5080909@freedesktop.org> Date: Fri, 31 Aug 2012 10:44:11 -0700 From: Jim Gettys Organization: Bell Labs User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:14.0) Gecko/20120714 Thunderbird/14.0 MIME-Version: 1.0 To: Rick Jones References: <1346396137.2586.301.camel@edumazet-glaptop> <5040DDE9.7030507@hp.com> <5040E8EE.2070900@freedesktop.org> <187CE1B3-6772-4E1C-A983-3AEC637C04FE@gmail.com> <5040F143.2010108@freedesktop.org> <5040F4E4.6000204@hp.com> In-Reply-To: <5040F4E4.6000204@hp.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: codel@lists.bufferbloat.net Subject: Re: [Codel] fq_codel : interval servo X-BeenThere: codel@lists.bufferbloat.net X-Mailman-Version: 2.1.13 Precedence: list List-Id: CoDel AQM discussions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 31 Aug 2012 17:44:14 -0000 On 08/31/2012 10:31 AM, Rick Jones wrote: > On 08/31/2012 10:15 AM, Jim Gettys wrote: >> What is more, consumer ethernet switches do do flow control, whether you >> want them to or not. > > My understanding is that Ethernet flow control (what ever its > 802.1mumble might be?) is negotiated when the link is brought-up, and > that both sides must agree before it will be active. So, if you (the > end station) do not want flow control, you can simply not accept it > during link-up. > > Under Linux, the ethtool utility can be used to affect the > configuration of "pause" (the name coming from the name of the frames > used by flow control - "pause frames" if I recall correctly) The cheap consumer switches typically have it on; and by default, most ethernet drivers have it on by default. That's how/why I found out about pause frames in the first place; I wasn't looking for it, and the existence of these frames in wireshark was a surprise to me. This can cause "interesting" performance problems most consumers won't understand when switches are layered. Most enterprise switches will often have it off by default, or plain never generate flow control frames at all. - Jim