Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!csd4.csd.uwm.edu!cs.utexas.edu!oakhill!shebanow From: shebanow@oakhill.UUCP (Mike Shebanow) Newsgroups: comp.arch Subject: Re: Instruction (dis)continuation Summary: time of restart vs. continuation is not very important Message-ID: <2357@oakhill.UUCP> Date: 30 Aug 89 02:08:20 GMT References: <1989Aug24.215104.156@mentor.com> <231@ssp1.idca.tds.philips.nl> <2345@oakhill.UUCP> <204@bbxeng.UUCP> <5990@pt.cs.cmu.edu> <26418@winchester.mips.COM> <123909@sun.Eng.Sun.COM> Reply-To: shebanow@oakhill.UUCP (Mike Shebanow) Organization: Motorola Inc., Austin, Texas Lines: 23 In article <123909@sun.Eng.Sun.COM> rajivp@sun.UUCP (Rajiv Patel) writes: > state information. For VLIW machines it seems that instruction continuation ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ > might be better for restart might first need to roll back partially completed ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ > operations. ^^^^^^^^^^^ > This depends on how often you expect roll back to be necessary. From the perspective of a single instruction, all the data I have ever seen indicates that exceptions occur very infrequently. (on most machines, the most frequent exception is a page fault). So, is this really an issue? In addition, what fraction of time does the lost work account for in comparison to the amount of time spent by the OS just trying to figure out what the exception was and how to deal with it? Mike Shebanow PS: I do not consider OS calls (traps) or interrupts to be an exception -- the hardware can plan for those and hence not require any roll back. ------------- Disclaimer: the opinions expressed here are my own, not Motorola's.