From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753383Ab2LER6u (ORCPT ); Wed, 5 Dec 2012 12:58:50 -0500 Received: from shards.monkeyblade.net ([149.20.54.216]:35460 "EHLO shards.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752721Ab2LER6t (ORCPT ); Wed, 5 Dec 2012 12:58:49 -0500 Date: Wed, 05 Dec 2012 12:58:47 -0500 (EST) Message-Id: <20121205.125847.649579012053540438.davem@davemloft.net> To: nicolas.ferre@atmel.com Cc: netdev@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, manabian@gmail.com, plagnioj@jcrosoft.com Subject: Re: [PATCH] net/macb: increase RX buffer size for GEM From: David Miller In-Reply-To: <50BF6366.8080600@atmel.com> References: <1354536943-6356-1-git-send-email-nicolas.ferre@atmel.com> <20121204.132227.1430662061932892582.davem@davemloft.net> <50BF6366.8080600@atmel.com> X-Mailer: Mew version 6.5 on Emacs 24.1 / Mule 6.0 (HANACHIRUSATO) Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Nicolas Ferre Date: Wed, 5 Dec 2012 16:08:22 +0100 > On 12/04/2012 07:22 PM, David Miller : >> From: Nicolas Ferre >> Date: Mon, 3 Dec 2012 13:15:43 +0100 >> >>> Macb Ethernet controller requires a RX buffer of 128 bytes. It is >>> highly sub-optimal for Gigabit-capable GEM that is able to use >>> a bigger DMA buffer. Change this constant and associated macros >>> with data stored in the private structure. >>> I also kept the result of buffers per page calculation to lower the >>> impact of this move to a variable rx buffer size on rx hot path. >>> RX DMA buffer size has to be multiple of 64 bytes as indicated in >>> DMA Configuration Register specification. >>> >>> Signed-off-by: Nicolas Ferre >> >> This looks like it will waste a couple hundred bytes for 1500 MTU >> frames, am I right? > > Yep! But buffers get recycled, and with the current memory management by > pages, it seems that I have to rework some part of it to optimize this > memory usage (8KB memory blocks split into 5 buffers each as David said...). > > Do you think it is worth digging this way or may I rework the rx buffer > management in case of the GEM interface. If I implement a different path > for GEM interface, I will have the possibility to tailor rx DMA buffers > from 1500 Bytes up to 10KB jumbo frames... I almost think you have to.