From: utzoo!decvax!harpo!ihnp4!ixn5c!inuxc!pur-ee!CSvax:Pucc-H:Physics:crl
Newsgroups: net.unix-wizar
Title: Re: automatic niceing by kernel - (nf)
Article-I.D.: pur-phy.585
Posted: Mon Nov 22 10:27:06 1982
Received: Tue Nov 23 01:48:24 1982

#R:micomvax:-10400:pur-phy:12700007:000:1201
pur-phy!crl    Nov 22 10:22:00 1982

We run Berkeley's 2.8bsd and some of the first things we did were:
1) to add a renice system call (so we didn't have to write over
/dev/kmem) and 2) to add an autonicing feature.  The way it was 
implemented here was to nice +5 all background jobs when a user
logged himself out.  Since all we have is a PDP-11/44, we decided
that we must give priority to interactive processes, and the best
way to do this was to renice background jobs.  We looked at basing
the renice on CPU time used, length of run, etc., but couldn't think
of a very good way to implement this, since all that information
is in the user structure which is only available when a process
is actually running.  Thus, to make the time checks, we'd have
to put the code in clock.c at every clock tick.  Therefore, we
opted to do the background renicing only.  It is probably the
best thing we ever did.  Even though our load occasionally rises
to over 5 due to 3 or more background jobs, interactive users
rarely get very impacted, which is our desire.  Furthermore,
the background jobs usually manage to get a fair share or runtime
anyways, since those interactive jobs rarely run continuously.

Charles LaBrec
... pur-ee!physics:crl