Maximum frequency of re-scheduling (minimum time quantum ) que stio n

F>>>>> "Nick" == Nick Piggin <[email protected]> writes:

Nick> However well tested your scheduler might be, it needs several Nick> orders of magnitude more testing ;) Maybe the best we can hope Nick> for is compile time selectable alternatives.

Well, Solaris and other SVr4-based systems have run-time selectable schedulers -- on a per-process basis. (Of course, it only makes sense to run schedulers that coexist nicely at the same time). These operating systems have the notion of a per-process scheduling class, that is essentially some private data, and a vector of functions to be called at particular times: when a thread is created, when something goes to sleep or wakes up, at timeslice expiration, etc. The dispatcher then does queue management only, so there's a nice separation of function.

By separating priority bands for each scheduler, you could have many different schedulers cooperating simultaneously. And if you don't like the SCHED_OTHER scheduler you could replace it. With care, this could be done retrospectively to running processes.

We could perhaps think of doing this for the 2.7 timeframe. I'm cerrtainly interested, to allow easier experimentation with Gang and other NUMA schedulers.

--
Dr Peter Chubb http://www.gelato.unsw.edu.au peterc AT gelato.unsw.edu.au The technical we do immediately, the political takes *forever*