From mboxrd@z Thu Jan 1 00:00:00 1970 X-Spam-Checker-Version: SpamAssassin 3.4.5-pre1 (2020-06-20) on ip-172-31-74-118.ec2.internal X-Spam-Level: X-Spam-Status: No, score=-0.0 required=3.0 tests=BAYES_20 autolearn=ham autolearn_force=no version=3.4.5-pre1 Date: 28 Oct 92 20:34:15 GMT From: cis.ohio-state.edu!zaphod.mps.ohio-state.edu!moe.ksu.ksu.edu!hobbes.physi cs.uiowa.edu!news.uiowa.edu!news@ucbvax.Berkeley.EDU (Douglas W. Jones,201H ML H,3193350740,3193382879) Subject: Re: Real Time Scheduling Methods Message-ID: <1992Oct28.203415.9815@news.uiowa.edu> List-Id: >>From article <92302.34020.LJ10891@LMSC5.IS.LMSC.LOCKHEED.COM>, by LJ10891@LMSC5.IS.LMSC.LOCKHEED.COM: > > Sorry about that guys, but it looks like Rate Monotonic is the only game > in town. No, there's deadline based scheduling. Deadline based scheduling is incompatable with Ada, because it requires that the priority of each process be, at any instant, the deadline by which the process must complete its next critical action. Once the process completes the action, it changes its deadline to the time of the next action (note that in Ada, priorities are fixed). Liu and Leyland, the people who proved the sufficiency of rate monotonic scheduling as long as there is not too much over 60% cpu utilization, also proved that deadline based real-time scheduling was sufficient if there is up to 100% utilization. Thus, deadline based scheduling can be superior to rate monotonic scheduling, but it's illegal in Ada. Deadline based scheduling may also be a bit more difficult than rate monotonic scheduling because it requires that processes state their deadlines explicitly instead of merely bumbling along, but it can also be more flexible, because deadlines need not be strictly periodic, while rate monotonic scheduling theory is only good for processes with strictly periodic real-time deadlines. Doug Jones jones@cs.uiowa.edu