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    SubjectRe: [PATCH][RFC] make cpu_sibling_map a cpumask_t
    On Sunday 07 December 2003 8:25 pm, Nick Piggin wrote:
    > Hi guys,
    > This is rather a trivial change but is not for 2.6.0.
    > The patch is actually on top of some of my HT stuff so one part is
    > slightly different, but its purpose is to gather feedback.
    > It turns the cpu_sibling_map array from an array of cpus to an array
    > of cpumasks. This allows handling of more than 2 siblings, not that
    > I know of any immediate need.

    There will probably be a need, although I don't know how soon. Some of the
    Intel folks have not been hinting that there will be more than two siblings
    in a future CPU. No, they have not been hinting at all. ;^)

    > I think it generalises cpu_sibling_map sufficiently that it can become
    > generic code. This would allow architecture specific code to build the
    > sibling map, and then Ingo's or my HT implementations to build their
    > scheduling descriptions in generic code.
    > I'm not aware of any reason why the kernel should not become generally
    > SMT aware. It is sufficiently different to SMP that it is worth
    > specialising it, although I am only aware of P4 and POWER5 implementations.
    > Best regards
    > Nick
    > P.S.
    > I have an alternative to Ingo's HT scheduler which basically does
    > the same thing. It is showing a 20% elapsed time improvement with a
    > make -j3 on a 2xP4 Xeon (4 logical CPUs).
    > Before Ingo's is merged, I would like to discuss the pros and cons of
    > both approaches with those interested. If Ingo's is accepted I should
    > still be able to port my other SMP/NUMA improvements on top of it.

    James Cleverdon
    IBM xSeries Linux Solutions
    {jamesclv(Unix, preferred), cleverdj(Notes)} at us dot ibm dot comm
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