> Turning off a meter was the only to transparently stop one or more
> domains. As far as I know, outside of measuring CPU usage, stopping
> processes was the only actual use of meters. There never was any code
> which used them for scheduling in the model of schedulers in e.g. Unix.
>
> Does this mean that the process control function (transparently
> halting a group of processes) could, in your view, be seperated from
> the issue of determining how many cycles a process should be given?
Many people who have looked at the meter architecture think that meter traps are too inefficent for millisecond level scheduling. If you want to limit some piece of processing to a maximum of 30 seconds of compute, they are ideal. (This kind of limit was a requirement for many of Tymshare's commercial customers.)
I think the the hiearchial model (as reflected in the meter design), is the correct model for both this gross form of processing limit and for the transparently halting a group of processes, I like using the meter mechanism for both. I also think they could be separated without hurting things too much.
For the millisecond level scheduling I think the field is wide open. We ended up with a "fair" scheduler that scheduled each domain independently. Those with a recent history of little CPU usage had a better priority than those with a recent history of large usage. (As a trivia note, I believe KeyKOS is the only system which keeps the millisecond CPU scheduling information when a process is saved on the disk.) Later we biased this scheduler with the idea that a domain should inherit a better priority from any domain which was stalled waiting to call it. This change made our transaction processing benchmark run noticably better, but it also made it much easier to fool the scheduler and get a better priority for your work. (Even without this change, breaking the work into several domains gave you effectivly, better priority. This change let you get better priority without breaking up the work.)
Bill Frantz Periwinkle -- Computer Consulting (408)356-8506 16345 Englewood Ave. frantz@netcom.com Los Gatos, CA 95032, USA