From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ben Hutchings Subject: Re: 100Mbit ethernet performance on embedded devices Date: Wed, 19 Aug 2009 16:05:17 +0100 Message-ID: <1250694317.2874.4.camel@achroite> References: <20090819145057.GA25400@sig21.net> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20090819145057.GA25400@sig21.net> Sender: netdev-owner@vger.kernel.org List-ID: Content-Type: text/plain; charset="us-ascii" To: Johannes Stezenbach Cc: linux-embedded@vger.kernel.org, netdev@vger.kernel.org On Wed, 2009-08-19 at 16:50 +0200, Johannes Stezenbach wrote: > Hi, > > a while ago I was working on a SoC with 200MHz ARM926EJ-S CPU > and integrated 100Mbit ethernet core, connected on internal > (fast) memory bus, with DMA. With iperf I measured: > > TCP RX ~70Mbit/sec (iperf -s on SoC, iperf -c on destop PC) > TCP TX ~56Mbit/sec (iperf -s on destop PC, iperf -c o SoC) > > The CPU load during the iperf test is around > 1% user, 44% system, 4% irq, 48% softirq, with 7500 irqs/sec. > > The kernel used in these measurements does not have iptables > support, I think packet filtering will slow it down noticably, > but I didn't actually try. The ethernet driver uses NAPI, > but it doesn't seem to be a win judging from the irq/sec number. > The kernel was an ancient 2.6.20. Which driver is this? Is it possible that it does not use NAPI correctly? > I tried hard, but I couldn't find any performance figures for > comparison. (All performance figures I found refer to 1Gbit > or 10Gbit server type systems.) > > What I'm interested in are some numbers for similar hardware, > to find out if my hardware and/or ethernet driver can be improved, > or if the CPU will always be the limiting factor. > I'd also be interested to know if hardware checksumming > support would improve throughput noticably in such a system, > or if it is only useful for 1Gbit and above. I have no recent experience with this sort of system, but checksum offload and scatter/gather DMA support should significantly reduce both CPU and memory bus load. Ben. -- Ben Hutchings, Senior Software Engineer, Solarflare Communications Not speaking for my employer; that's the marketing department's job. They asked us to note that Solarflare product names are trademarked.