Path: utzoo!mnetor!uunet!lll-winken!lll-tis!ames!hao!gatech!mcnc!thorin!unc!ohbuchi
From: ohbuchi@unc.cs.unc.edu (Ryutarou Ohbuchi)
Newsgroups: comp.arch
Subject: Re: Cray 2 has 2GW address (Save Vec.Reg. or not.)
Message-ID: <1539@thorin.cs.unc.edu>
Date: 3 Mar 88 15:30:33 GMT
References: <235@amelia.nas.nasa.gov> <28200117@ccvaxa>
Sender: news@thorin.cs.unc.edu
Reply-To: ohbuchi@unc.UUCP (Ryutarou Ohbuchi)
Organization: University Of North Carolina, Chapel Hill
Lines: 24
Keywords: State saving, vector register
Summary: IBM 3090/VF have flag, too.

<aglew@ccvaxa.UUCP> writes;
>> ...although I wonder if processes that do not use the vector registers 
>> do, in fact, flush them...
>
>Gould NP has a VRIU (Vector Register IN Use) bit that is set whenever a
>vector register is written to. So processes that do not use the vector
>registers do not have to have them flushed (although for security they 
>are cleared). ......

As I recall, IBM people faced the same problem with their extension
of 370 architecture into VF (Vector Feature (or, was it 'Facility' ?)),
and did the same kind of thing (in 3090/VF).  I do not remember exactly,
but there is some kind of flag that tells whether the vector registers
are used or not, and not every context switch have to save/restore the
vector register.  The literature describing this was in IBM Journal of 
Res. & Dev. (or something like that), in 1987.

==============================================================================
Any opinion expressed here is my own.
------------------------------------------------------------------------------
Ryutarou Ohbuchi	"Life's rock."   "Climb now, work later." and, now,
			"Life's snow."   "Ski now, work later."
ohbuchi@cs.unc.edu	<on csnet>
Department of Computer Science, University of North Carolina at Chapel Hill
==============================================================================