Path: utzoo!mnetor!uunet!husc6!cmcl2!nrl-cmf!ames!pasteur!ucbvax!XN.LL.MIT.EDU!glenn
From: glenn@XN.LL.MIT.EDU (Glenn Adams)
Newsgroups: comp.protocols.tcp-ip
Subject: SLIP working group?
Message-ID: <8804131518.AA11956@XN.LL.MIT.EDU>
Date: 13 Apr 88 15:18:36 GMT
References: <8803301649.AA24991@bu-cs.bu.edu>
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The Internet
Lines: 28


>   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