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Multics Scheduler
davecb wrote to us with a short description of three of the
Multics schedulers. The piece has some background information and history as well, which adds another element to the reading.
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It should be obvious that one of the primary reasons that Linux is as successful as it is is because when it appeared there were hundreds of thousands of coders and millions of lines of code all immediately available.
Infrastructure, infrastructure, infrastructure. You can't just tear it all down and make it perfect. You've got to work with the existing structure and move in little steps, so people aren't left holding the bag with nothing to show. Nobody wants to start from scratch. And really, nobody should have to start from scratch.
If you were to attempt to build up an OS to the level of Linux, from scratch, it would likely take you a decade. For what purpose? To end up with something that is a moderate improvement? Why not just improve what we've got?
Anyway, I am constantly amazed at the way people get all hyped out about a particular language or a particular OS. If you are a good coder, you can write good code in any language and on any OS. These are tools, people, and arguing about them is like two construction workers having a heated discussion over which hammer is better. Silly. Just pick the best tool available to you and go with it. If you don't like any of the tools, build your own. But don't whine because everyone else is too stupid to agree with you on what tool is the ultimate hammer. When I hear crap like that, I recall the old saying "it is a poor workman who blames his tools".
Yes, modern Unices are all "hacked together". But then, so is Windows. You see, there are two types of OS, those that people spend a lot of time hacking on, and those that no one uses. The latter have the sort of purity of an unlived in house. Everything is perfect, as the designer intended. But you have to realize that this would not last long were someone to move in.
The cake is a pie
What we need are some schedulers for the new century.
eBay: The Scheduler process posts information about available slots and processes bid for the time. After the auction period expires the slot is allocated to the winning process (once the 'cheque' has cleared). The duraction of an auction would be short. Reserve prices might be set but this could lead to idle cycles.
MiddleManagment: The Scheduler makes provisional assignments based upon its favourite strategy, but all of these have to be run past an administrative Daemon which has to authorise all slot allocations. The criteria would be very complex but factors include how sexy the process was and when the admin daemon last ran a golf game.
Such daemons only operate during core working hours and are easily distracted so the scheduler can sneak important but boring work through.
The government uses a variant of this called the RedTape scheme.
Boeing: The Scheduler runs a standard strategy but every so often it accidently allocates all the slots to the local refuse tip where processes dig through the mounds of trash looking for them.
OpenSource: The Scheduler insists on receiving a copy of the source code of any binary that applies for slots. It then allocates based upon the the degree of innovation (determined by metrics). Library calls or other attempts to restrict access to parts of the program reduce the priority.
SlashDot: The scheduler sets up pools of resource and processes submit requests for slots into this. Other processes enter their own bids or attach sub requests to other processes requests. Processes not engaged in bidding for resources on that pool rate the requests rewarding particularly appropriate requests and penalising irrelevant requests.
Particularly successful processes receive a bonus to future requests.
Gamma Testing - Where testing is extended to the full user community (AKA Shipping the Program)