deschall harmful to Irix?

Nelson Minar (nelson@media.mit.edu)
Fri, 30 May 1997 16:09:50 -0400


I take back all I said about nice -19 processes having little impact
on Unix system performances. One of our SGI users (a reasonably fast
box running Irix 6.2) was saying that deschall was getting in his way.
I did a quick test of compiling some files with javac on local disk
and over NFS, with deschall and without. The result is that having
deschall running slows down performance 50% on local disk, and 250%
with NFS! Our NFS server is busy but reasonable.

Irix is really doing something bad here. I suspect it's not context
switching fast enough, in particular to catch the NFS reply promptly.
Unfortunately, this means that we won't be running deschall on our
Irix boxes anymore.

Here's the numbers. These are for compiling 825 lines of Java in 9
files through SGI's javac 1.0.2:

deschall disk real user sys
----------------------------------------------------
no local 9.17 8.23 0.59
yes local 12.31 8.54 0.58
no NFS 12.77 8.41 0.68
yes NFS 32.83 8.62 0.73