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    SubjectRe: [PATCH 2/3] sched/fair: don't set LBF_ALL_PINNED unnecessarily
    On Wed, Jan 06, 2021 at 02:34:18PM +0100, Vincent Guittot wrote:
    > Setting LBF_ALL_PINNED during active load balance is only valid when there
    > is only 1 running task on the rq otherwise this ends up increasing the
    > balance interval whereas other tasks could migrate after the next interval
    > once they become cache-cold as an example.
    >
    > Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
    > ---
    > kernel/sched/fair.c | 3 ++-
    > 1 file changed, 2 insertions(+), 1 deletion(-)
    >
    > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
    > index 5428b8723e61..69a455113b10 100644
    > --- a/kernel/sched/fair.c
    > +++ b/kernel/sched/fair.c
    > @@ -9759,7 +9759,8 @@ static int load_balance(int this_cpu, struct rq *this_rq,
    > if (!cpumask_test_cpu(this_cpu, busiest->curr->cpus_ptr)) {
    > raw_spin_unlock_irqrestore(&busiest->lock,
    > flags);
    > - env.flags |= LBF_ALL_PINNED;
    > + if (busiest->nr_running == 1)
    > + env.flags |= LBF_ALL_PINNED;
    > goto out_one_pinned;
    > }

    Hmm.. that wasn't the intention. It's entirely possible to have multiple
    tasks pinned.

    ISTR we set all-pinned and then clear it in can_migrate_task() when we
    actually find a task that can be moved to the destination CPU. That's a
    construct that works perfectly fine with multiple tasks.


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