Path: utzoo!utgpu!water!watmath!clyde!rutgers!cmcl2!nrl-cmf!ames!ucsd!sdcsvax!ucsdhub!hp-sdd!hplabs!hpda!hpcupt1!hpcuhb!hpindda!vandys
From: vandys@hpindda.HP.COM (Andy Valencia)
Newsgroups: comp.arch
Subject: Re: Today's dumb question...
Message-ID: <3450003@hpindda.HP.COM>
Date: 2 Apr 88 01:13:37 GMT
References: <503@xios.XIOS.UUCP>
Organization: HP Technical Networks, Cupertino, Calif.
Lines: 14


	From all I can tell from the various MPs which have been
built (or died trying... :->), the real point isn't which atomic
ops you offer; it's how you make multiple CPUs live together
in the same memory domain--cache consistency, bus bandwidth, and
memory cycle time.  I don't recall ever reading a post-mortem which
said "if we'd only used synchronization mechanism X instead of Y,
we would have been golden".  Most of them instead talked about the
unpleasant bus and memory traffic characteristics which show up
when you try to get a respectable number of processors going
simultaneously.  And never underestimate what cache consistency
is going to cost you.

				Andy Valencia