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    SubjectRe: [RFC,1/2] powerpc/numa: fix cpu_to_node() usage during boot
    Date
    On Thu, 2015-02-07 at 23:02:02 UTC, Nishanth Aravamudan wrote:
    > Much like on x86, now that powerpc is using USE_PERCPU_NUMA_NODE_ID, we
    > have an ordering issue during boot with early calls to cpu_to_node().

    "now that .." implies we changed something and broke this. What commit was
    it that changed the behaviour?

    > The value returned by those calls now depend on the per-cpu area being
    > setup, but that is not guaranteed to be the case during boot. Instead,
    > we need to add an early_cpu_to_node() which doesn't use the per-CPU area
    > and call that from certain spots that are known to invoke cpu_to_node()
    > before the per-CPU areas are not configured.
    >
    > On an example 2-node NUMA system with the following topology:
    >
    > available: 2 nodes (0-1)
    > node 0 cpus: 0 1 2 3
    > node 0 size: 2029 MB
    > node 0 free: 1753 MB
    > node 1 cpus: 4 5 6 7
    > node 1 size: 2045 MB
    > node 1 free: 1945 MB
    > node distances:
    > node 0 1
    > 0: 10 40
    > 1: 40 10
    >
    > we currently emit at boot:
    >
    > [ 0.000000] pcpu-alloc: [0] 0 1 2 3 [0] 4 5 6 7
    >
    > After this commit, we correctly emit:
    >
    > [ 0.000000] pcpu-alloc: [0] 0 1 2 3 [1] 4 5 6 7


    So it looks fairly sane, and I guess it's a bug fix.

    But I'm a bit reluctant to put it in straight away without some time in next.

    It looks like the symptom is that the per-cpu areas are all allocated on node
    0, is that all that goes wrong?

    cheers


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