Path: utzoo!attcan!uunet!wuarchive!cs.utexas.edu!rice!uw-beaver!ubc-cs!alberta!calgary!cpsc!gintera
From: gintera@cpsc.ucalgary.ca (Andrew Ginter)
Newsgroups: comp.lang.lisp
Subject: Re: LISP compiler? (really future of MACL)
Summary: realtime GC costs
Message-ID: <2159@cs-spool.calgary.UUCP>
Date: 23 Nov 89 21:28:16 GMT
References: <5130@internal.Apple.COM> <5149@internal.Apple.COM> <616@pyuxf.UUCP>
Sender: news@calgary.UUCP
Lines: 19

In article <616@pyuxf.UUCP>, asg@pyuxf.UUCP (alan geller) writes:
> 1) Would it be possible to use an incremental garbage collector, rather than
> 	the current stop-and-copy?  Given that MACL 2.0 will usually be
> 	running under System 7.0, we'll have lots of virtual address space
> 	for from-space and to-space, maybe even multiple generations.

A real time (parallel or incremental) garbage collector is roughly
twice as costly as a comparable stop-and-collect collector.  The real
time version has to collect more frequently than stop-and-copy because
the real time version has to start it's collection well before memory
is exhausted.  A real time "two space copying" collector is even more
expensive because of the cost of checking for a forwarding pointer on
every reference to GC managed memory.  Real time collectors penalize
real performance while improving some aspects of perceived
performance.

So if you're going to add a real time collector, make it an option.

Andrew Ginter, 403-282-2984, gintera@CPSC.UCALGARY.CA, Ginter@UNCAMULT.BITNET