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

William Lee Irwin III
2007-04-17T22:33:21Z

On Tue, Apr 17, 2007 at 11:24:22AM +0200, Ingo Molnar wrote:
>> yeah. If you could come up with a sane definition that also translates
>> into low overhead on the algorithm side that would be great!

On Tue, Apr 17, 2007 at 05:08:09PM -0500, Matt Mackall wrote:
> How's this:
> If you're running two identical CPU hog tasks A and B differing only by nice
> level (Anice, Bnice), the ratio cputime(A)/cputime(B) should be a
> constant f(Anice - Bnice).
> Other definitions make things hard to analyze and probably not
> well-bounded when confronted with > 2 tasks.
> I -think- this implies keeping a separate scaled CPU usage counter,
> where the scaling factor is a trivial exponential function of nice
> level where f(0) == 1. Then you schedule based on this scaled usage
> counter rather than unscaled.
> I also suspect we want to keep the exponential base small so that the
> maximal difference is 10x-100x.

I'm already working with this as my assumed nice semantics (actually
something with a specific exponential base, suggested in other emails)
until others start saying they want something different and agree.

-- wli