Subject: Re: Silly GC question
From: (Rob Warnock)
Date: 2000/07/14
Newsgroups: comp.lang.lisp
Message-ID: <8km1gk$531tg$>
Lieven Marchand  <> wrote:
| You have barrier methods, but these have to have hardware support
| like the Symbolics or Explorer had to be effective.

Well, perhaps this might have been "obvious" at one time, but I suggest
that this old canard is worth re-examining in light of recent CPU speeds
and the continually worsening ratio of memory latency to CPU speed. Even
purely *software* read or write barriers may well be worth the overhead
these days, especially if it allows you to make effective *use* of a larger
number of CPUs.

Likewise, ISTR reading some papers [sorry, can't find the refs] that suggest
that explicit software card-marking write barriers (for generational copying
collectors) may now be *more* efficient than hardware-based write barriers,
if the latter are (1) only at page-sized granularity, and (2) require an
operating system trap on a write attempt of an unmarked page. A recommended
card size of 256 or 512 bytes sticks in my memory...


Rob Warnock, 41L-955
Applied Networking
Silicon Graphics, Inc.		Phone: 650-933-1673
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