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Message-Id: <1250694317.2874.4.camel@achroite>
Date: Wed, 19 Aug 2009 16:05:17 +0100
From: Ben Hutchings <bhutchings@...arflare.com>
To: Johannes Stezenbach <js@...21.net>
Cc: linux-embedded@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: 100Mbit ethernet performance on embedded devices
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.
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