Een nieuwe “Proportional Share Scheduler” is bescikbaar als patch voor FreeBSD. Luigi Rizzo noemt het een “weight-based process scheduler”‚ dat gebruik maakt van het “”WF2Q+ algorithm” (ook gebruikt in dummynet).
De reden voor het gebruik van deze scheduler wordt hieronder uitgelegt a.d.h.v. een document van de universiteit van Utah:
[quote]There are compelling reasons to use proportional share scheduling techniques to support multimedia and other soft real-time applications on general-purpose operating systems. First‚ proportional share (PS) schedulers are a good match for existing infrastructure such as a periodic timer interrupt and mechanisms for assigning priorities to applications — priorities can be mapped to shares in a proportional-share environment. Second‚ PS schedulers provide stronger guarantees to applications than do traditional time-sharing schedulers: they allocate a specific fraction of the CPU to each thread‚ and some schedulers provide error bounds on the allocation rate. Third‚ PS schedulers have clear semantics during underload: excess CPU time is allocated fairly‚ in contrast with some reservation-based schedulers that must idle or back off to a secondary scheduling policy once all application budgets are exhausted.[/quote]
Om daadwerkelijk gebruik te maken van de process scheduler is men in dit project ook bezig om het mogelijk om te switchen tussen de verschilende schedulers.
[quote]to make the process/thread/kse scheduler a replaceable piece of the kernel‚ requiring no modificationsto the “struct proc”‚ and with the ability of switching from one scheduler to another one at runtime (this both for testing purposes and for whatever need may arise).[/quote]
Voor meer info:
[url=http://www.kerneltrap.com/node.php?id=349]Het artikel[/url]
[url=http://www.cs.utah.edu/flux/papers/ps-rtss01/]Info over de scheduler[/url]
Dit is pas cool, switchen tijdens runtime tussen verschillende schedulers :>)