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    SubjectRe: [RFC/RFT PATCH v3] sched: automated per tty task groups
    Peter Zijlstra, le Fri 19 Nov 2010 12:57:24 +0100, a écrit :
    > On Fri, 2010-11-19 at 01:07 +0100, Samuel Thibault wrote:
    > > Also note that having a hierarchical process structure should permit to
    > > make things globally more efficient: avoid putting e.g. your cpp, cc1,
    > > and asm processes at three corners of your 4-socket NUMA machine :)
    >
    > And no, using that to load-balance between CPUs doesn't necessarily help
    > with the NUMA case,

    It doesn't _necessarily_ help, but it should help in quite a few cases.

    > load-balancing is an impossible job (equivalent to
    > page-replacement -- you simply don't know the future), applications
    > simply do wildly weird stuff.

    Sure. Not a reason not to get the low-hanging fruits :)

    > From a process hierarchy there's absolutely no difference between a
    > cc1/cpp/asm and some MPI jobs, both can be parent-child relations with
    > pipes between, some just run short and have data affinity, others run
    > long and don't have any.

    MPI jobs typically communicate with each other. Keeping them on the same
    socket permits to keep shared-memory MPI drivers to mostly remain in
    e.g. the L3 cache. That typically gives benefits.

    Samuel
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