From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755284Ab0IOTPA (ORCPT ); Wed, 15 Sep 2010 15:15:00 -0400 Received: from mail.perches.com ([173.55.12.10]:2071 "EHLO mail.perches.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755026Ab0IOTO7 (ORCPT ); Wed, 15 Sep 2010 15:14:59 -0400 Subject: Re: [RFC PATCH] drivers/net/tg3.c: Raise Jumbo Frame MTU to 9216? From: Joe Perches To: Michael Chan Cc: Matthew Carlson , Benjamin Li , "David S. Miller" , netdev , LKML In-Reply-To: <1284573454.8929.221.camel@HP1> References: <1284572516.10223.12.camel@Joe-Laptop> <1284573454.8929.221.camel@HP1> Content-Type: text/plain; charset="UTF-8" Date: Wed, 15 Sep 2010 12:14:55 -0700 Message-ID: <1284578095.10223.27.camel@Joe-Laptop> Mime-Version: 1.0 X-Mailer: Evolution 2.30.3 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 2010-09-15 at 10:57 -0700, Michael Chan wrote: > On Wed, 2010-09-15 at 10:41 -0700, Joe Perches wrote: > > The TG3 apparently supports 9K frame sizes. > > http://www.broadcom.com/collateral/pb/5704C-PB05-R.pdf > > Is exactly 9000 a hardware limit? > > Should the jumbo frame MTU be raised to 9216 or 9216 > > less the size of MAC, VLAN, IP and TCP headers? > 9000 has been the de facto standard, has it been changed recently? I know of a performance lab that's trying to use 9216 as a "standard" jumbo frame length. Unrelated to the performance lab: http://www.uoregon.edu/~joe/jumbo-clean-gear.html 9216 seems popular, especially with Cisco gear. Contrary to that link, the Cisco 3750 does work with 9216 length jumbo frames. > Anyway, we've never done any testing on 9216. As it uses up to 2 more > internal mbufs per packet, there may not be sufficient buffers inside > the chip for optimal operations. At best, some water marks will need to > be tweaked. The hardware statistics counters (ethtool -S) also may not > work for packets bigger than 9022 bytes. Thanks, do you have pointers to where the tweaking needs to be done? Is this define a hardware upper bound? #define TG3_RX_JMB_DMA_SZ 9046 cheers, Joe