Messages in this thread | | | Date | Mon, 14 Jan 2008 11:11:33 +0100 | From | Ingo Molnar <> | Subject | Re: [PATCH 00/10] x86: Reduce memory and intra-node effects with large count NR_CPUs |
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* Andi Kleen <ak@suse.de> wrote:
> > i.e. we've got ~22K bloat per CPU - which is not bad, but because > > it's a static component, it hurts smaller boxes. For distributors to > > enable CONFIG_NR_CPU=1024 by default i guess that bloat has to drop > > below 1-2K per CPU :-/ [that would still mean 1-2MB total bloat but > > that's much more acceptable than 23MB] > > Even 1-2MB overhead would be too much for distributors I think. > Ideally there must be near zero overhead for possible CPUs (and I see > no principle reason why this is not possible) Worst case a low few > hundred KBs, but even that would be much.
i think this patchset already gives a net win, by moving stuff from NR_CPUS arrays into per_cpu area. (Travis please confirm that this is indeed what the numbers show)
The (total-)size of the per-cpu area(s) grows linearly with the number of CPUs, so we'll have the expected near-zero overhead on 4-8-16-32 CPUs and the expected larger total overhead on 1024 CPUs.
Ingo
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