Hello,
the FreeBSD TCP/IP stack uses the "system tick timer" for some delay
(maybe only for TCP).
you may want to use a HZ=1000 option (see the LINT config file) in a
recompiled kernel and see if things go better. (moreover, the dc(4)
driver which is used for your NIC has some interesting performance
improvements in the forthcoming 4.3-Release)
TfH
Mårten Wikström wrote:
>
> I've performed a routing test between a FreeBSD box and a Linux box. I
> measured the latency and the result was not what I had expected. Both
> systems had the peak at 100 us (microseconds), but whereas the Linux box had
> _no_ packet over 200 us, the FreeBSD box delayed some packets up to 2 ms!
> Looking at the time series, it seems that the packets are delayed at regular
> intervals, about every second. My guess is that some timer interrupt
> triggers every second and steals too much cpu. So my question is, how can I
> decrease this routing delay?
>
> Test info:
> I used two identical boxes, each equipped with a Pentium Pro 200Mhz and 64Mb
> mem. RedHat 7.0 with 2.4 kernel in one and FreeBSD 4.2-RELEASE in the other.
> I used two DEC 100Mbit ethernet cards (21140 I think).
> I measured the latency with a SmartBits instrument. Fastforwarding was
> disabled. Three UDP streams was sent from the SmartBits to one of the
> ethernet cards in the box, which routed the streams to the other interface,
> which in turn was connected back to the SmartBits.
> I had not made any changes to the standard kernel configuration. No other
> processes was running in the background, apart from those necessary to
> perform the test. The ARP table was set statically, so no ARP traffic would
> disturb.
>
> I would at least want to know what is causing the extra delays.
>
> /Mårten
>
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--
Thierry Herbelot
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