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Bossa, a Framework for Scheduler Development
Eugenia writes "The recent activity in Linux kernel development caused by the introduction of a new scheduler by Ingo Molnar has emphasized for ordinary Linux users the importance of schedulers in modern operating systems. This article gives you a glimpse of what scheduling development is like by letting you implement your own Linux scheduler thanks to Bossa, a framework for scheduler development."
It's the part of the OS that determines what task to run.
The problem is this: You want to run tasks A, B, and C, and need to do it in the most optimal way possible.
The simplest way is FIFO, like say, DOS. If A starts first, then A runs until completion, then B starts. This is bad for many reasons, like that if A gets stuck for any reason nothing gets done, and that while A is waiting for input the free resources can't be used for anything else.
A simple way of multitasking would be simply alternating between A, B and C every fixed interval. But that's not very good either, perhaps B doesn't need to do any processing now, and only wastes time, while C could really use that.
A better way is to do it by priorities, but then you need to find a good way of calculating this priority.
One of the reasons there's so much talk about them is that most become slower when you have more tasks. Most of the simple ones need to examine every running task to determine what should run now, and if you want to launch 10000 processes at once, that's not good. O(1) schedulers are a solution for that, because they use algorithms that always take the same amount of time to execute, irregardless of whether there's 3 or 10000 tasks. That doesn't mean a simpler scheduler wouldn't work faster for 10 tasks, though.
The other problem is how to determine how to distribute CPU time. Say, for servers you mostly want fast and fair3o determine which processes are interactive, and which are on the background and won't mind some interruption.