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SubjectRe: [PATCH 00/10] x86: Reduce memory and intra-node effects with large count NR_CPUs

* Andi Kleen <> 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.


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