Freebsd IP Forwarding performance (question, and some info) [7-stable, current, em, smp]

Bruce Evans brde at
Mon Jul 7 10:00:22 UTC 2008

On Mon, 7 Jul 2008, Andre Oppermann wrote:

> Ingo Flaschberger wrote:
>> I don't think you will be able to route 64byte packets at 1gbit wirespeed 
>> (2Mpps) with a current x86 platform.
> You have to take inter-frame gap and other overheads too.  That gives
> about 1.244Mpps max on a 1GigE interface.

What are the other overheads?  I calculate 1.644Mpps counting the inter-frame
gap, with 64-byte packets and 64-header_size payloads.  If the 64 bytes
is for the payload, then the max is much lower.

>> I hoped to reach 1Mpps with the hardware I mentioned some mails before, but 
>> 2Mpps is far far away.
>> Currently I get 160kpps via pci-32mbit-33mhz-1,2ghz mobile pentium.
> This is more or less expected.  PCI32 is not able to sustain high
> packet rates.  The bus setup times kill the speed.  For larger packets
> the ratio gets much better and some reasonable throughput can be achieved.

I get about 640 kpps without forwarding (sendto: slightly faster;
recvfrom: slightly slower) on a 2.2GHz A64.  Underclocking the memory
from 200MHz to 100MHz only reduces the speed by about 10%, while not
overclocking the CPU by 10% reduces the speed by the same 10%, so the
system is apparently still mainly CPU-bound.

> NetFPGA doesn't have enough TCAM space to be useful for real routing
> (as in Internet sized routing table).  The trick many embedded networking
> CPUs use is cache prefetching that is integrated with the network
> controller.  The first 64-128bytes of every packet are transferred
> automatically into the L2 cache by the hardware.  This allows relatively
> slow CPUs (700 MHz Broadcom BCM1250 in Cisco NPE-G1 or 1.67-GHz Freescale
> 7448 in NPE-G2) to get more than 1Mpps.  Until something like this is
> possible on Intel or AMD x86 CPUs we have a ceiling limited by RAM speed.

Does using fa$ter memory (speed and/or latency) help here?  64 bytes
is so small that latency may be more of a problem, especially without
a prefetch.


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