* Andi Kleen <[email protected]> wrote:
> On Tuesday 07 February 2006 13:30, Ingo Molnar wrote:
>
> > you are a bit biased towards low-latency NUMA setups i guess (read:
> > Opterons) :-)
>
> Well they are the vast majority of NUMA systems Linux runs on.
>
> And there are more than just Opterons, e.g. IBM Summit. And even the
> majority of Altixes are not _that_ big.
>
> Of course we need to deal somehow with the big systems, but for the
> good defaults the smaller systems are more important.
i'm not sure i understand your point. You said that for small systems
with a low NUMA factor it doesnt really matter where the pagecache is
placed. I mostly agree with that. And since placement makes no
difference there, we can freely shape things for the systems where it
does make a difference. It will probably make a small win on smaller
systems too, as a bonus. Ok?
> Big systems tend to have capable administrators who are willing to
> tweak them. But that's rarely the case with the small systems. So I
> think as long as the big system can be somehow made to work with
> special configuration and ignoring corner cases that's fine. But for
> the low NUMA systems it should perform as well as possibly out of the
> box.
i also mentioned software-based clusters in the previous mail, so it's
not only about big systems. Caching attributes are very much relevant
there. Tightly integrated clusters can be considered NUMA systems with a
NUMA factor of 1000 or so (or worse).
> > Obviously with a low NUMA factor, we dont have to deal
> > with memory access assymetries all that much.
>
> That is why I proposed "nearby policy". It can turn a system with a
> large NUMA factor into a system with a small NUMA factor.
well, would the "nearby policy" make a difference on the small systems?
Small systems (to me) are just a flat and symmetric hierarchy of nodes -
the next step from SMP. So there's really just two distances: local to
the node, and one level of 'alien'. Or do you include systems in this
category that have bigger assymetries?
Ingo
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