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    SubjectRe: [RFC 00/15] x86_64: Optimize percpu accesses

    * Eric W. Biederman <ebiederm@xmission.com> wrote:

    > Mike Travis <travis@sgi.com> writes:
    >
    >
    > > The biggest growth came from moving all the xxx[NR_CPUS] arrays into
    > > the per cpu area. So you free up a huge amount of unused memory
    > > when the NR_CPUS count starts getting into the ozone layer. 4k now,
    > > 16k real soon now, ??? future?
    >
    > Hmm. Do you know how big a role kernel_stat plays.
    >
    > It is a per cpu structure that is sized via NR_IRQS. NR_IRQS is by
    > NR_CPUS. So ultimately the amount of memory take up is
    > NR_CPUS*NR_CPUS*32 or so.
    >
    > I have a patch I wrote long ago, that addresses that specific nasty
    > configuration by moving the per cpu irq counters into pointer
    > available from struct irq_desc.
    >
    > The next step which I did not get to (but is interesting from a
    > scaling perspective) was to start dynamically allocating the irq
    > structures.

    /me willing to test & babysit any test-patch in that area ...

    this is a big problem and it's getting worse quadratically ;-)

    Ingo


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