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

Matt Mackall
2007-04-18T07:09:46Z

On Wed, Apr 18, 2007 at 08:37:11AM +0200, Nick Piggin wrote:
> I don't know how that supports your argument for unfairness,

I never had such an argument. I like fairness.

My argument is that -you- don't have an argument for making fairness a
-requirement-.

> processes are special only because that's how we've always done
> scheduling. I'm not precluding other groupings for fairness, though.

If you make one form of fairness a -requirement- for all acceptable
algorithms, your -are- precluding most other forms of fairness.

If you refuse to define what "fairness" means when specifying your
requirement, what's the point of requiring it?

> What do you mean optimal? If your criteria is fairness, then of course
> it is optimal. If your criteria is throughput, then it probably isn't.

I don't know what optimal behavior is. And neither do you. It may or
may not be fair. It very likely includes small deviations from fair.

> > [2] It's trivial to construct two or more perfectly reasonable and
> > desirable definitions of fairness that are mutually incompatible.
>
> Probably not if you use common sense, and in the context of a replacement
> for the 2.6 scheduler.

Ok, trivial example. You cannot allocate equal CPU time to
processes/tasks and simultaneously allocate equal time to thread
groups. Is it common sense that a heavily-threaded app should be able
to get hugely more CPU than a well-written app? No. I don't want Joe's
stupid Java app to make my compile crawl.

On the other hand, if my heavily threaded app is, say, a voicemail
server serving 30 customers, I probably want it to get 30x the CPU of
my gzip job.

--
Mathematics is the supreme nostalgia of our time.