From mboxrd@z Thu Jan 1 00:00:00 1970 From: Pasi =?iso-8859-1?Q?K=E4rkk=E4inen?= Subject: Re: Bypass flow control problems Date: Mon, 27 Dec 2010 15:43:46 +0200 Message-ID: <20101227134346.GD2754@reaktio.net> References: <1293040291.1777.36.camel@alkis> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: netdev@vger.kernel.org To: Alkis Georgopoulos Return-path: Received: from smtp.tele.fi ([192.89.123.25]:47142 "EHLO vulpes-int.media.sonera.net" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1753880Ab0L0OTh (ORCPT ); Mon, 27 Dec 2010 09:19:37 -0500 Received: from smtp.tele.fi (smtp.tele.fi [192.89.123.25]) by vulpes-int.media.sonera.net (Postfix) with ESMTP id 04BB836BC for ; Mon, 27 Dec 2010 15:44:18 +0200 (EET) Content-Disposition: inline In-Reply-To: <1293040291.1777.36.camel@alkis> Sender: netdev-owner@vger.kernel.org List-ID: On Wed, Dec 22, 2010 at 07:51:31PM +0200, Alkis Georgopoulos wrote: > Hi, > > I'm an IT teacher/LTSP developer. In LTSP, thin clients are netbooted > from a server and receive a lot of X and remote disk traffic from it. > > Many installations have a gigabit NIC on the server, an unmanaged > gigabit switch, and 100 Mbps NICs on the clients. > > With flow control on, the server is limited to sending 100 Mbps to all > the clients. So with 10 thin clients the server can concurrently send > only 10 Mbps to each one of them. > > On NICs that support it, we turn flow control off and the server can > properly send 100 Mbps to each client, i.e. 1 Gbps to 10 clients. > > * Is there any way to bypass that problem on NICs that do not support > turning off flow control, like e.g. realteks? > I.e. when a client sends a pause signal to the server, instead of the > server pausing, to continue sending data to another client? > Or even to limit the amound of data the server sends to each client, > so that the clients never have to send pause signals? > You could set up QoS rules on the server to limit the network speed per client.. > * I really don't understand why flow control is enabled by default on > NICs and switches. In which case does it help? As far as I > understand, all it does is ruin gigabit => 100 Mbps connections... > > * As a side note, since rtl8169 is a very common chipset, is there a > way to disable flow control for that specific NIC? > > This problem affects thousands of LTSP installations, we'd much > appreciate your knowledge and feedback on it. > Did you try disabling flow control from the switch? -- Pasi