Re: [PATCH] 2.6.0 batch scheduling, HT aware

[Nick Piggin]

Con Kolivas wrote:

> On Tue, 23 Dec 2003 12:36, Nick Piggin wrote:
>
> > Con Kolivas wrote:
> >
> > > I discussed this with Ingo and that's the sort of thing we thought of.
> > > Perhaps a relative crossover of 10 dynamic priorities and an absolute
> > > crossover of 5 static priorities before things got queued together. This
> > > is really only required for the UP HT case.
> > Well I guess it would still be nice for "SMP HT" as well. Hopefully the
> > code can be generic enough that it would just carry over nicely. 
>
> I disagree. I can't think of a real world scenario where 2+ physical cpus 
> would benefit from this.

Well its the same problem. A nice -20 process can still lose 40-55% of its
performance to a nice 19 process, a figure of 10% is probably too high and
we'd really want it <= 5% like what happens with a single logical processor.

> > It does 
> > have complications though because the load balancer would have to be taught
> > about it, and those architectures that do hardware priorities probably
> > don't even want it.
>
> Probably the simple relative/absolute will have to suffice. However it still 
> doesn't help the fact that running something cpu bound concurrently at nice 0 
> with something interactive nice 0 is actually slower if you use a UP HT 
> processor in SMP mode instead of UP.

It will be based on dynamic priorities, possibly with some feedback from
nice as well, but it probably still won't be perfect and it will probably
be very complex *cough* hardware priorities *cough* ;)

I might try to fit it into a more general priority balancing system because
we currently have similar sorts of failings on regular SMP as well.


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