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From: dswartz@bbn.com (Dan Swartzendruber)
Newsgroups: comp.arch
Subject: Re: Instruction (dis)continuation
Message-ID: <45180@bbn.COM>
Date: 2 Sep 89 19:28:25 GMT
References: <AGLEW.89Aug21205533@chant.urbana.mcd.mot.com> <1989Aug24.215104.156@mentor.com> <231@ssp1.idca.tds.philips.nl> <2345@oakhill.UUCP> <204@bbxeng.UUCP> <5990@pt.cs.cmu.edu> <205@bbxeng.UUCP> <265@gp.govt.nz>
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Reply-To: dswartz@BBN.COM (Dan Swartzendruber)
Organization: Bolt Beranek and Newman Inc., Cambridge MA
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I think this is somewhat of a misleading point.  Ignoring the block move
case, a generic two-operand instruction on most any machine could take
up to six page faults (the instruction spans a page boundary, and each
of the operands does as well.)  Although it is possible to construct a
theoretical scenario where an instruction restart CPU could get into an
infinite page-fault loop, I will respectfully suggest that if your system
only has 6 free pages of memory, the effective result (as far as getting
any useful work done is concerned) will be pretty much the same!
Not to mention that this scenario assumes almost complete brain-damage on
the parts of: the compiler, the linker, the user and the sys admin...