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    SubjectRe: [Announce] [patch] Modular Scheduler Core and Completely Fair Scheduler [CFS]
    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.

    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).

    I wouldn't like to see a significant drop in any micro or macro
    benchmarks or even worse real workloads, but I could accept some if it
    means haaving a fair scheduler by default.

    Now it isn't actually too hard to achieve the above, I think. The hard bit
    is trying to compare interactivity. Ideally, we'd be able to get scripted
    dumps of login sessions, and measure scheduling latencies of key proceses
    (sh/X/wm/xmms/firefox/etc). People would send a dump if they were having
    problems with any scheduler, and we could compare all of them against it.
    Wishful thinking!
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