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From: honig@ics.uci.edu (David A. Honig)
Newsgroups: comp.arch
Subject: Re: Context switching on RISC chips
Message-ID: <25A13AB0.24734@paris.ics.uci.edu>
Date: 2 Jan 90 23:35:12 GMT
References: <3167@iitmax.IIT.EDU> <28573@amdcad.AMD.COM> <52104@srcsip.UUCP>
Reply-To: David A. Honig <honig@ics.uci.edu>
Organization: University of California, Irvine - Dept of ICS
Lines: 23

In article <52104@srcsip.UUCP> shankar@src.honeywell.com (Subash Shankar) writes:
>In article <28573@amdcad.AMD.COM> tim@amd.com (Tim Olson) writes:
>
>#  3) Saving/Restoring Live Registers Only (like your #2).  In systems
>#     where security (covert channels) is not an issue (as in most
>#     real-time embedded control systems), the context-switch time can
>#     be reduced by saving only the live local registers found between
>#     the current stack pointer and the top of the stack cache.  
>
>Why does security affect things here?
>Subash Shankar             Honeywell Systems & Research Center

Isn't it obvious?  The contents of registers, if not overwritten, provides a 
'hidden' communication path between processes.  If you worry about
that then your context switches will have to do more work.

And I don't do either architecture or security professionally!

--
David A. Honig		
 "As these houses are built, the lions continue to wander around those areas,
 and they bump into a poodle or a German shepard. That causes some trouble."
	---Prof. R. Barrett, UCB