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    Subject[PATCH v3 5/7] sched/topology: Add more flags to the SD degeneration mask
    Date
    I don't think it is going to change much in practice, but we were missing
    those:

    o SD_BALANCE_WAKE: Used just like the other SD_BALANCE_* flags, so also
    needs > 1 group.
    o SD_ASYM_PACKING: Hinges on load balancing (periodic / wakeup), thus needs
    > 1 group to happen
    o SD_OVERLAP: Describes domains with overlapping groups; can't have
    overlaps with a single group.

    SD_PREFER_SIBLING is as always the odd one out: we currently consider it
    in sd_parent_degenerate() but not in sd_degenerate(). It too hinges on load
    balancing, and thus won't have any effect when set on a domain with a
    single group. Add it to the sd_degenerate() groups mask.

    Signed-off-by: Valentin Schneider <valentin.schneider@arm.com>
    ---
    kernel/sched/topology.c | 9 ++++++++-
    1 file changed, 8 insertions(+), 1 deletion(-)

    diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
    index 6047d491abe9..fe393b295444 100644
    --- a/kernel/sched/topology.c
    +++ b/kernel/sched/topology.c
    @@ -161,11 +161,15 @@ static int sd_degenerate(struct sched_domain *sd)

    /* Following flags need at least 2 groups */
    if (sd->flags & (SD_BALANCE_NEWIDLE |
    + SD_BALANCE_WAKE |
    SD_BALANCE_FORK |
    SD_BALANCE_EXEC |
    + SD_ASYM_PACKING |
    SD_SHARE_CPUCAPACITY |
    SD_ASYM_CPUCAPACITY |
    - SD_SHARE_PKG_RESOURCES)) {
    + SD_SHARE_PKG_RESOURCES |
    + SD_OVERLAP |
    + SD_PREFER_SIBLING)) {
    if (sd->groups != sd->groups->next)
    return 0;
    }
    @@ -191,11 +195,14 @@ sd_parent_degenerate(struct sched_domain *sd, struct sched_domain *parent)
    /* Flags needing groups don't count if only 1 group in parent */
    if (parent->groups == parent->groups->next) {
    pflags &= ~(SD_BALANCE_NEWIDLE |
    + SD_BALANCE_WAKE |
    SD_BALANCE_FORK |
    SD_BALANCE_EXEC |
    + SD_ASYM_PACKING |
    SD_ASYM_CPUCAPACITY |
    SD_SHARE_CPUCAPACITY |
    SD_SHARE_PKG_RESOURCES |
    + SD_OVERLAP |
    SD_PREFER_SIBLING);
    if (nr_node_ids == 1)
    pflags &= ~SD_SERIALIZE;
    --
    2.27.0
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