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From: bader+@andrew.cmu.edu (Miles Bader)
Newsgroups: comp.arch
Subject: Re: Phys vs Virtual Addr Caches
Message-ID: 
Date: Thu, 16-Jul-87 10:57:11 EDT
Article-I.D.: andrew.YUzCb7y00UkaU7k0Rj
Posted: Thu Jul 16 10:57:11 1987
Date-Received: Sat, 18-Jul-87 07:05:27 EDT
Organization: Carnegie Mellon University
Lines: 12
In-Reply-To: <3904@spool.WISC.EDU>


> Here's a question.  Why do people build their caches to respond to physical
> addresses instead of virtual addresses?  Another way to state the question
> is: why not put the VM -> PM translation logic next to (in parallel with)
> the data cache, rather than before it?

If different processes have different parts of their virtual address space
mapped to the same physical memory, a physical cache allows them to share the
same cache entries.  Also, each cache entry in a virtual cache has to have a
field describing which address map it's from if you don't want to have to
flush the cache upon context switch, etc.

				-Miles