Path: utzoo!utgpu!cunews!bnrgate!bwdls61.bnr.ca!bwdls58!mlord
From: mlord@bwdls58.bnr.ca (Mark Lord)
Newsgroups: comp.arch
Subject: Re: Stack Cache with O/S driven copyback ?
Keywords: stack cache caching
Message-ID: <5241@bwdls58.UUCP>
Date: 15 Jan 91 20:18:31 GMT
References: <5229@bwdls58.UUCP> <4513@skye.cs.ed.ac.uk>
Sender: mlord@bwdls58.UUCP
Reply-To: mlord@bwdls58.bnr.ca (Mark Lord)
Organization: Bell-Northern Research, Ottawa, Canada
Lines: 30

In article <4513@skye.cs.ed.ac.uk> ddr@cs.edinburgh.ac.uk (Doug Rogers) writes:
<In article <5229@bwdls58.UUCP>, mlord@bwdls58.UUCP (Mark Lord) writes:
<> 
<> Specifically, how about an operating system controlled cache, devoted to
<> caching the call stack of the current task and/or interrupt handler?
<> 
<> 	5) copyback has lowest bus priority - gets done only when nothing
<> 		else wants the bus (reads, writes, dma, other caches).
<
<The problem is in multi processor systems maintaining cache consistency. Within
<the Futurebus spec. one user has the right to modify at any time. Clearly
<if there was only one copy of the information then it should not matter how slowly
<the information is passed back but what happens if while this is going on another
<cache wishes to gain access to this information. (this would include the data cache
<for the same processor).

I'm not particularly worried about the multi-processor case for this stack
cache.  Shared memory variables tend not to be procedure locals on a call stack,
as it becomes tricky to communicate their current addresses to other processors.

Also, note that this proposal is in addition to regular data caches, which
can handle multi-processor consistency using one's favorite means for the REST
of memory, just not the process STACKs.  We could agree to document this very
unlikely deficiency and let the O/S programmers read our notes before they
try to set up globals in stack variables which are shared between CPUs.  :)
-- 
 ___Mark S. Lord__________________________________________
| ..uunet!bnrgate!mlord%bmerh724 | Climb Free Or Die (NH) |
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