Path: utzoo!attcan!uunet!tut.cis.ohio-state.edu!zaphod.mps.ohio-state.edu!van-bc!sl
From: sl@van-bc.UUCP (Stuart Lynne)
Newsgroups: comp.arch
Subject: Re: Single user vs. shared (was Re: Killer Micros and vectorized code)
Message-ID: <268@van-bc.UUCP>
Date: 21 Mar 90 20:17:05 GMT
References: <51771@lll-winken.LLNL.GOV> <100598@convex.convex.com> <52661@lll-winken.LLNL.GOV> <1990Mar18.023523.4034@ultra.com> <52817@lll-winken.LLNL.GOV> <1990Mar19.220617.26370@world.std.com> <500@sibyl.eleceng.ua.OZ>
Reply-To: sl@van-bc.UUCP (Stuart Lynne)
Organization: Wimsey Associates
Lines: 39

In article <500@sibyl.eleceng.ua.OZ> ian@sibyl.OZ (Ian Dall) writes:
>In article <1990Mar19.220617.26370@world.std.com> bzs@world.std.com (Barry Shein) writes:
>>

>The other problem seems to be that, sure people would like to be able
>to use spare capacity, but they like to be guaranteed a certain
>minimum number of cycles. Well, let me propose the guaranteed share
>scheduler! I doubt if this is new but I'll propose it anyway!  Suppose
>the total number of cycles per unit time is T, the maximum number of
>users is M and the number of active users is A. Every user should get
>max(T/A, T/M) cycles per unit time. The T/M is guaranteed, the T/A -
>T/M is the bonus for being shared. Of course, for the convenience to
>approach that of your own workstation you need T/M to be reasonably
>large. One killer micro worth maybe?

You have to have a scheduler that is aware of the number of users currently
requesting CPU cycles. When the number of cycles available is less than
requested divide it up via a formula where all possible users are allocated
a fixed percentage of CPU cycles (such that the total of all users
allocations add's up to 100 per cent).

When cycles are scarce you get at least your allocation. When cycles are 
available because there is no one else around (at 3:00 AM for example) you 
can get access to a MUCH larger amount of cycles.

For example if there are 50 people using a 50MIPS Killer Micro Mini
Mainframe (TM), each would be allocated 2%. During the day when *all* 50
people are in and pounding on the keyboard they would each get about 1MIPS
worth of CPU if they need it. At night two late night programmers doing big 
make's could each get 50% or 25MIPS.

The scheduler will have to factor in system overheads as well of course.

Personally I'd much rather get a guaranteed 2% of a KMMM(TM) with the
potential of using it *all* when no one else is around than to get 100% of a
much smaller machine.

-- 
Stuart.Lynne@wimsey.bc.ca ubc-cs!van-bc!sl 604-937-7532(voice) 604-939-4768(fax)