From mboxrd@z Thu Jan 1 00:00:00 1970 From: Nicolas Ferre Subject: Re: [PATCH] net/macb: increase RX buffer size for GEM Date: Wed, 5 Dec 2012 16:08:22 +0100 Message-ID: <50BF6366.8080600@atmel.com> References: <1354536943-6356-1-git-send-email-nicolas.ferre@atmel.com> <20121204.132227.1430662061932892582.davem@davemloft.net> Mime-Version: 1.0 Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: 7bit Cc: , , , , To: David Miller Return-path: In-Reply-To: <20121204.132227.1430662061932892582.davem@davemloft.net> Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org 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... Best regards, -- Nicolas Ferre