Johannes Stezenbach wrote:

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.

You should see far fewer interrupts if NAPI was working properly.
Rather than NAPI not being a win, it looks like it's not active at
all.

7500/sec is close to the packet rate, for sending TCP with
full-size ethernet packages over a 100Mbit ethernet link.

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 have a SoC with a 166MHz ARMv4 (ARM7TDMI I think, but I'm not sure),
and an external RTL8139 100Mbit ethernet chip over the SoC's PCI bus.

It gets a little over 80Mbit/s actual data throughput in both
directions, running a simple FTP client.

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.

Did anyone actually manage to get close to 100Mbit/sec
with similar CPU resources?

Remember, the TCP throughput cannot reach 100Mbit/sec due to the
overhead of packet framing.  But it should be much closer to 100 than 70.

-- Jamie