SLIP working group?


Glenn Adams (glenn@XN.LL.MIT.EDU)
Wed, 13 Apr 88 10:18:36 EST


> It's straightforward to turn on UDP checksumming
> on a Sun, at worst you can fault them for not making it easier:

> % adb -w -k /vmunix /dev/mem
> udpcksum?W 1
> $q

Perhaps someone has pointed it out already, but Sun's NFS doesn't
use the standard udp_output() routine which allows enabling checksums
via the udpcksum variable. Instead, they chose to bypass udp_output(),
building UDP packets in ku_fastsend() (/sys/rpc/kudp_fastsend.c). This
routine has no provision for enabling checksums such as does udp_output().

I rewrote ku_fastsend() for Sun 3.2, but haven't done so for recent Sun
releases, primarily because I don't have the more recent sources. I think
we should make a lot of noise to Sun to at least code in checksumming
similar to udp_output(), giving the system manager the decision to enable
or disable checksums. By the way, performance tests which I performed
on my modified ku_fastsend(), indicated that the addition of checksumming
only resulted in a 2% decrease in performance. I don't believe they (SUN)
have actually tried it as they won't provide any data to back up their claim
that checksumming is a big performance loss.

Personally, I think Sun's decision to exclude checksums is quite
unconscionable.

Glenn Adams



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