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    SubjectRe: [sched] fix sched_domains hotplug bootstrap ordering vs. cpu_online_map issue

    * William Lee Irwin III <wli@holomorphy.com> wrote:

    > William Lee Irwin III <wli@holomorphy.com> wrote:
    > >> This is the whole thing; the "other half" referred to a new hunk added to
    > >> the patch (identical to this one) posted in its entirety.
    >
    > On Fri, Sep 03, 2004 at 03:34:34PM -0700, Andrew Morton wrote:
    > > ho-hum. changelog, please?
    >
    > cpu_online_map is not set up at the time of sched domain
    > initialization when hotplug cpu paths are used for SMP booting. At
    > this phase of bootstrapping, cpu_possible_map can be used by the
    > various architectures using cpu hotplugging for SMP bootstrap, but the
    > manipulations of cpu_online_map done on behalf of NUMA architectures,
    > done indirectly via node_to_cpumask(), can't, because cpu_online_map
    > starts depopulated and hasn't yet been populated. On true NUMA
    > architectures this is a distinct cpumask_t from cpu_online_map and so
    > the unpatched code works on NUMA; on non-NUMA architectures the
    > definition of node_to_cpumask() this way breaks and would require an
    > invasive sweeping of users of node_to_cpumask() to change it to e.g.
    > cpu_possible_map, as cpu_possible_map is not suitable for use at
    > runtime as a substitute for cpu_online_map.
    >
    > Signed-off-by: William Irwin <wli@holomorphy.com>

    Signed-off-by: Ingo Molnar <mingo@elte.hu>

    Ingo
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