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    Subject[PATCH v2 0/2] sched/topology: Optimize topology_span_sane()
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    A soft lockup is being detected in build_sched_domains() on 32 socket
    Sapphire Rapids systems with 3840 processors.

    topology_span_sane(), called by build_sched_domains(), checks that each
    processor's non-NUMA scheduling domains are completely equal or
    completely disjoint. If a non-NUMA scheduling domain partially overlaps
    another, scheduling groups can break.

    This series adds for_each_cpu_from() as a generic cpumask macro to
    optimize topology_span_sane() by removing duplicate comparisons. The
    total number of comparisons is reduced from N * (N - 1) to
    N * (N - 1) / 2 on each non-NUMA scheduling domain level, decreasing
    the boot time by approximately 20 seconds and preventing the soft lockup
    on the mentioned systems.

    Changes in v2:
    * 1/2: Change for_each_cpu()'s description.
    * 2/2: Add more information to the commit message.
    * https://lore.kernel.org/linux-kernel/20240409155250.3660517-1-kyle.meyer@hpe.com/T/

    Kyle Meyer (2):
    cpumask: Add for_each_cpu_from()
    sched/topology: Optimize topology_span_sane()

    include/linux/cpumask.h | 10 ++++++++++
    kernel/sched/topology.c | 6 ++----
    2 files changed, 12 insertions(+), 4 deletions(-)

    --
    2.44.0


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