From mboxrd@z Thu Jan 1 00:00:00 1970 From: =?ISO-8859-1?Q?R=E9mi?= Denis-Courmont Subject: Re: about tx_queue_len for phonet driver Date: Thu, 12 Jan 2012 13:56:28 +0200 Message-ID: <2151675.UOkxvXJjp1@hector> References: <81C3A93C17462B4BBD7E272753C105791FB10F9968@EXDCVYMBSTM005.EQ1STM.local> Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: "netdev@vger.kernel.org" To: ext Hemant-vilas RAMDASI Return-path: Received: from smtp.nokia.com ([147.243.1.47]:35162 "EHLO mgw-sa01.nokia.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751860Ab2ALLzn convert rfc822-to-8bit (ORCPT ); Thu, 12 Jan 2012 06:55:43 -0500 In-Reply-To: <81C3A93C17462B4BBD7E272753C105791FB10F9968@EXDCVYMBSTM005.EQ1STM.local> Sender: netdev-owner@vger.kernel.org List-ID: Hello, Le Jeudi 12 Janvier 2012 11:45:48 ext Hemant-vilas RAMDASI a =E9crit : > Can anyone guide me about when should a network driver set tx_queue_l= en to > 0? We are facing a network congestion issue with phonet packets where= one > of the control message packet is dropped because of congestion. In ou= r > phonet network driver the tx_queue_len is set to 3 (taken from usb-ph= onet > mostly). If phonet cannot handle packet-drop (for pipe messages), the= n > should network driver always set tx_queue_len as 0? In theory, I guess the network device queuing discipline should be avoi= ded=20 altogether, unless there is another way to prevent packet loss, that I = am not=20 aware of. Unfortunately dropping qdisc, and thus net_device also, would= have=20 major redesign implications on the Linux Phonet infrastructure to say t= he=20 least. In any case, Phonet devices typically fail to provide sane, reliable an= d race- free congestion control. I have seen some Phonet modem firmwares that j= ust=20 crash if they receive too many and/or too large packets. Alas, this can= not be=20 fixed on the Linux / application processor side. So you have to find a value large enough to avoid packet loss, but also= small=20 enough to avoid overflow and who-knows-what bugs on the modem side. For= the=20 record, the SSI driver queue length found on Nokia N9/N950 defaults to = 100. --=20 R=E9mi Denis-Courmont http://www.remlab.net/