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From: mat@amdahl.UUCP (Mike Taylor)
Newsgroups: net.arch
Subject: Re:  Memory Rules of Thumb (really IBM 370 wait state)
Message-ID: <2365@amdahl.UUCP>
Date: Tue, 10-Dec-85 17:33:42 EST
Article-I.D.: amdahl.2365
Posted: Tue Dec 10 17:33:42 1985
Date-Received: Sat, 14-Dec-85 00:39:41 EST
References: <794@ecsvax.UUCP> <306@polaris.UUCP> <193@myrias.UUCP>
Organization: Amdahl Corp, Sunnyvale CA
Lines: 15

> Yes, it is true that you can busy wait on a 370, but it's a dumb idea.  Not
> only does it slow down your i/o channels, but it makes it impossible to
> give interrupts to the less busy cpu in a dyadic configuration.

You don't want to give interrupts to the less busy CPU, you want to
give interrupts to the one that is more likely to have the interrupt
supervisor code in its cache.  Interrupt windowing in MVS therefore
concentrates interrupts on one (arbitrarily chosen) CPU, for example.
BTW, a busy loop doesn't interfere with the I/O channels on any high
end systems, because there is no mainstore activity once the loop is in
the cache.
-- 
Mike Taylor                        ...!{ihnp4,hplabs,amd,sun}!amdahl!mat

[ This may not reflect my opinion, let alone anyone else's.  ]