Messages in this thread | | | Date | Tue, 7 Feb 2006 13:58:45 +0100 | From | Ingo Molnar <> | Subject | Re: [PATCH 1/5] cpuset memory spread basic implementation |
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* Andi Kleen <ak@suse.de> 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?
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