Re: 2.6.4-mm1

Andi Kleen
2004-03-11T20:21:39Z

> > For SMT there is a patch from Intel pending that teaches x86-64
> > to set up the SMT scheduler. They said they got slightly better
> > benchmark results. The SMT setup seems to be racy though.
>
> Am I correct in thinking that this patch provides the necessary hooks to
> integrate x86_4 into the new functionality which sched-domains provides, or
> is the Intel patch independent of sched-domains?

It sets up the sched-domains code to know about HyperThreading CPUs
on x86-64 too (basically same thing as the i386 code does with a
few minor tweaks)

So it's dependent on that.

I will send it to you in separate mail.

> > Some kind of SMT scheduler is definitely needed, we have a serious
> > regression compared to 2.4 here right now. I'm not sure this
> > is the right approach though, it seems to be far too complex.
>
> Well that's discouraging. I really do want to push this thing along a bit.
>
> Yours is the only report of regression of which I am aware. Is the reason
> understood?

I think the reason is that it doesn't do balance on clone/fork. The
normal scheduler also doesn't do that, but for some reason it still does
better on the benchmarks (but worse than the old 2.4 -aa/Intel O(1) HT
scheduler)

> And is anyone developing alternative SMT enhancements?

I thought there was a patch from Ingo Molnar? ("shared runqueue")
I must admit I never tried it, just remember seeing the patches.

Also I've been playing with the entitlement scheduler to fix
some of the interactivity problems I have on UP, but it also
seems to still have problems.

-Andi