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    Subject[PATCH] sched/eas: Don't update misfit status if the task is pinned
    Date
    If the task is pinned to a cpu, setting the misfit status means that
    we'll unnecessarily continuously attempt to migrate the task but fail.

    This continuous failure will cause the balance_interval to increase to
    a high value, and eventually cause unnecessary significant delays in
    balancing the system when real imbalance happens.

    Caught while testing uclamp where rt-app calibration loop was pinned to
    cpu 0, shortly after which we spawn another task with high util_clamp
    value. The task was failing to migrate after over 40ms of runtime due to
    balance_interval unnecessary expanded to a very high value from the
    calibration loop.

    Not done here, but it could be useful to extend the check for pinning to
    verify that the affinity of the task has a cpu that fits. We could end
    up in a similar situation otherwise.

    Fixes: 3b1baa6496e6 ("sched/fair: Add 'group_misfit_task' load-balance type")
    Signed-off-by: Qais Yousef <qais.yousef@arm.com>
    ---
    kernel/sched/fair.c | 2 +-
    1 file changed, 1 insertion(+), 1 deletion(-)

    diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
    index 197a51473e0c..9379a481dd8c 100644
    --- a/kernel/sched/fair.c
    +++ b/kernel/sched/fair.c
    @@ -4060,7 +4060,7 @@ static inline void update_misfit_status(struct task_struct *p, struct rq *rq)
    if (!static_branch_unlikely(&sched_asym_cpucapacity))
    return;

    - if (!p) {
    + if (!p || p->nr_cpus_allowed == 1) {
    rq->misfit_task_load = 0;
    return;
    }
    --
    2.25.1
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