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From: cook@pinocchio.Encore.COM (Dale C. Cook)
Newsgroups: comp.sys.pyramid,comp.sys.sequent
Subject: Re: Questions about Pyramid/Sequent
Summary: Effects of scheduling and concurrent hardware
Keywords: pyramid sequent
Message-ID: <5605@xenna.Encore.COM>
Date: 3 Apr 89 13:19:19 GMT
References: <764@sactoh0.UUCP> <404@sequoia.UUCP> <63984@pyramid.pyramid.com> <13305@sequent.UUCP> <9903@polyslo.CalPoly.EDU>
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Reply-To: cook@pinocchio.UUCP (Dale C. Cook)
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In article <9903@polyslo.CalPoly.EDU> cquenel@polyslo.CalPoly.EDU (48 more school days) writes:
>The point I always have to make whenever this comes up:
>
>Suppose for the sake of argument you have a single processor
>machine on one side and an 8 processor machine on the other side
>with each processor exactly equal to 1/8 of the larger CPU.
>Suppose the prices and total performances are equal.
>
Good analysis, 48 more school days!  However, I think you overlook the time
lost to context switching and scheduling with the single compute engine.
In the Alliant (and I think Convex) boxes, a lot of the work of executing
concurrent DO loops is done in the hardware.  Thus the scheduler only need
incur the overhead of setup once per loop.

Also, as another poster pointed out, the costs of a single hot box (Cray,
NEC, etc) far exceeds N x's the minisuper cost.  That defines the niche
that every parallel minisuper maker has targeted.

On the general purpose multi-processing side, I doubt that the "latency"
and general interactivity (is that a word?) of a single processor being
rapidly rescheduled amongst a large number of users will ever approach
that of a multiheaded machine such as an Encore or Sequent.  That's
mostly subjective, but I think it's real.
	- Dale (N1US)	
INTERNET:	cook@pinocchio.encore.com
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