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    SubjectRe: [RFC PATCH] scheduler: Dynamic sched_domains
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    On Wed, 2004-10-06 at 19:13, Nick Piggin wrote:
    > This is what I did in my first (that nobody ever saw) implementation of
    > sched domains. Ie. no sched_groups, just use sched_domains as the balancing
    > object... I'm not sure this works too well.
    >
    > For example, your bottom level domain is going to basically be a redundant,
    > single CPU on most topologies, isn't it?

    I forgot to respond to this part in my last mail... :(

    My benchmarks haven't shown any real deviation in performance from stock
    -mm. Granted, my benchmarking has been very limited, pretty much just
    running kernbench on a few different machines with different configs
    (ie: SMT, SMP & NUMA on/off). A performance NOOP is exactly what I was
    hoping for, though. I don't really expect these changes to be either a
    performance win or loss, but a functionality improvement.

    The patch is pretty dense because of all the renaming, but there are no
    single CPU domains. The lowest level domain would be:

    1) Node domains, for NUMA w/ SMP
    2) Sibling domains, for SMT or NUMA w/ SMT
    3) System domain, for flat SMP

    The pseudo code version of my arch_init_sched_domains() looks like:

    cpu_usable_map = cpu_online_map & ~cpu_isolated_map
    create system domain;
    if NUMA
    for_each_node()
    create node domain, parented to system domain;
    for_each_cpu(cpu_usable_map)
    if SCHED_SMT
    create sibling domain, parented to node domain;
    attach sibling cpu to it's domain;
    else
    attach cpu to either its node domain or system domain;

    So there shouldn't be any redundant CPU domains.

    -Matt

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