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    SubjectRe: NUMA scheduler (was: 2.5 merge candidate list 1.5)
    >> Erich, what does all the pool stuff actually buy us over what
    >> Michael is doing? Seems to be rather more complex, but maybe
    >> it's useful for something we're just not measuring here?
    >
    > The more complicated stuff is for achieving equal load between the
    > nodes. It delays steals more when the stealing node is averagely loaded,
    > less when it is unloaded. This is the place where we can make it cope
    > with more complex machines with multiple levels of memory hierarchy
    > (like our 32 CPU TX7). Equal load among the nodes is important if you
    > have memory bandwidth eaters, as the bandwidth in a node is limited.
    >
    > When introducing node affinity (which shows good results for me!) you
    > also need a more careful ranking of the tasks which are candidates to
    > be stolen. The routine task_to_steal does this and is another source
    > of complexity. It is another point where the multilevel stuff comes in.
    > In the core part of the patch the rank of the steal candidates is computed
    > by only taking into account the time which a task has slept.

    OK, it all sounds sane, just rather complicated ;-) I'm going to trawl
    through your stuff with Michael, and see if we can simplify it a bit
    somehow whilst not changing the functionality. Your first patch seems
    to work just fine, it's just the complexity that bugs me a bit.

    The combination of your first patch with Michael's balance_exec stuff
    actually seems to work pretty well ... I'll poke at the new patch you
    sent me + Michael's exec balance + the little perf tweak I made to it,
    and see what happens ;-)

    > I attach the script for getting some statistics on the numa_test. I
    > consider this test more sensitive to NUMA effects, as it is a bandwidth
    > eater also needing good latency.
    > (BTW, Martin: in the numa_test script I've sent you the PROBLEMSIZE must
    > be set to 1000000!).

    It is ;-) I'm running 44-mm4, not virgin remember, so things like hot&cold
    page lists may make it faster?

    M.

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