On Wed, Apr 18, 2007 at 09:23:42AM +1000, Peter Williams wrote: > Matt Mackall wrote: > >On Tue, Apr 17, 2007 at 09:01:55AM +0200, Nick Piggin wrote: > >>On Mon, Apr 16, 2007 at 11:26:21PM -0700, William Lee Irwin III wrote: > >>>On Mon, Apr 16, 2007 at 11:09:55PM -0700, William Lee Irwin III wrote: > >>>>>All things are not equal; they all have different properties. I like > >>>On Tue, Apr 17, 2007 at 08:15:03AM +0200, Nick Piggin wrote: > >>>>Exactly. So we have to explore those properties and evaluate performance > >>>>(in all meanings of the word). That's only logical. > >>>Any chance you'd be willing to put down a few thoughts on what sorts > >>>of standards you'd like to set for both correctness (i.e. the bare > >>>minimum a scheduler implementation must do to be considered valid > >>>beyond not oopsing) and performance metrics (i.e. things that produce > >>>numbers for each scheduler you can compare to say "this scheduler is > >>>better than this other scheduler at this."). > >>Yeah I guess that's the hard part :) > >> > >>For correctness, I guess fairness is an easy one. I think that unfairness > >>is basically a bug and that it would be very unfortunate to merge > >>something > >>unfair. But this is just within the context of a single runqueue... for > >>better or worse, we allow some unfairness in multiprocessors for > >>performance > >>reasons of course. > > > >I'm a big fan of fairness, but I think it's a bit early to declare it > >a mandatory feature. Bounded unfairness is probably something we can > >agree on, ie "if we decide to be unfair, no process suffers more than > >a factor of x". > > > >>Latency. Given N tasks in the system, an arbitrary task should get > >>onto the CPU in a bounded amount of time (excluding events like freak > >>IRQ holdoffs and such, obviously -- ie. just considering the context > >>of the scheduler's state machine). > > > >This is a slightly stronger statement than starvation-free (which is > >obviously mandatory). I think you're looking for something like > >"worst-case scheduling latency is proportional to the number of > >runnable tasks". > > add "taking into consideration nice and/or real time priorities of > runnable tasks". I.e. if a task is nice 19 it can expect to wait longer > to get onto the CPU than if it was nice 0.
Yes. Assuming we meet the "bounded unfairness" criterion above, this follows. -- Mathematics is the supreme nostalgia of our time. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/