Path: utzoo!utgpu!utstat!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!ucbvax!decwrl!labrea!polya!carcoar!wilson
From: wilson@carcoar.Stanford.EDU (Paul Wilson)
Newsgroups: comp.arch
Subject: Re: "General-purpose" architectures and symbolic languages
Message-ID: <7051@polya.Stanford.EDU>
Date: 21 Feb 89 23:41:25 GMT
References: <28113@ucbvax.BERKELEY.EDU>
Sender: news@polya.Stanford.EDU
Reply-To: wilson@carcoar.Stanford.EDU (Paul Wilson)
Organization: Stanford University
Lines: 37

I too am interested in such issues.

One thing I've been wondering about is the compatibility of RISC-style
caches and Lisp Machine-style forwarding pointers.

On Lisp Machines, the time required to check for invisible forwarding
pointers is generally hidden in time required for cache operation,
but I'm unsure of the details.  Do the new cache architectures still
allow this.  (I know they don't generally support such snazzy features.
The question is whether other design decisions directly conflict with
invisible forwarding.)


Also, is anybody doing any work on coordinating cache operation with
garbage collection?  With a large cache (100 KB or larger), you should
be able to have a small Newest generation (say, 50 KB) that is scavenged
completely within the cache -- no thrashing.

Even if the Newest generation won't fit in the cache, you should be
able to avoid swapping a lot of cache blocks out by telling the cache
hardware if they only contain garbage.  (i.e., force them to appear
clean, so they won't be written back, or tell the cache to "create"
a block without actually reading in the corresponding block from
main memory).  It seems that this would cut cache-memory traffic by
approximately half (?) for the Newest generation.

Anybody out there doing such work?


Paul R. Wilson                         
Human-Computer Interaction Laboratory    lab ph.: (312) 413-0042
U. of Ill. at Chi. EECS Dept. (M/C 154) 
Box 4348   Chicago,IL 60680              wilson@carcoar.stanford.edu
Paul R. Wilson                         
Human-Computer Interaction Laboratory    lab ph.: (312) 413-0042
U. of Ill. at Chi. EECS Dept. (M/C 154) 
Box 4348   Chicago,IL 60680              wilson@carcoar.stanford.edu