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    Subject[RFC][PATCH 06/13] sched/fair: Export newidle_balance()
    For pick_next_task_fair() it is the newidle balance that requires
    dropping the rq->lock; provided we do put_prev_task() early, we can
    also detect the condition for doing newidle early.

    Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
    ---
    kernel/sched/fair.c | 18 ++++++++----------
    kernel/sched/sched.h | 4 ++++
    2 files changed, 12 insertions(+), 10 deletions(-)

    --- a/kernel/sched/fair.c
    +++ b/kernel/sched/fair.c
    @@ -3635,8 +3635,6 @@ static inline unsigned long cfs_rq_load_
    return cfs_rq->avg.load_avg;
    }

    -static int idle_balance(struct rq *this_rq, struct rq_flags *rf);
    -
    static inline unsigned long task_util(struct task_struct *p)
    {
    return READ_ONCE(p->se.avg.util_avg);
    @@ -6848,11 +6846,10 @@ done: __maybe_unused;
    return p;

    idle:
    - update_misfit_status(NULL, rq);
    - new_tasks = idle_balance(rq, rf);
    + new_tasks = newidle_balance(rq, rf);

    /*
    - * Because idle_balance() releases (and re-acquires) rq->lock, it is
    + * Because newidle_balance() releases (and re-acquires) rq->lock, it is
    * possible for any higher priority task to appear. In that case we
    * must re-start the pick_next_entity() loop.
    */
    @@ -9016,10 +9013,10 @@ static int load_balance(int this_cpu, st
    ld_moved = 0;

    /*
    - * idle_balance() disregards balance intervals, so we could repeatedly
    - * reach this code, which would lead to balance_interval skyrocketting
    - * in a short amount of time. Skip the balance_interval increase logic
    - * to avoid that.
    + * newidle_balance() disregards balance intervals, so we could
    + * repeatedly reach this code, which would lead to balance_interval
    + * skyrocketting in a short amount of time. Skip the balance_interval
    + * increase logic to avoid that.
    */
    if (env.idle == CPU_NEWLY_IDLE)
    goto out;
    @@ -9729,7 +9726,7 @@ static inline void nohz_newidle_balance(
    * idle_balance is called by schedule() if this_cpu is about to become
    * idle. Attempts to pull tasks from other CPUs.
    */
    -static int idle_balance(struct rq *this_rq, struct rq_flags *rf)
    +int newidle_balance(struct rq *this_rq, struct rq_flags *rf)
    {
    unsigned long next_balance = jiffies + HZ;
    int this_cpu = this_rq->cpu;
    @@ -9737,6 +9734,7 @@ static int idle_balance(struct rq *this_
    int pulled_task = 0;
    u64 curr_cost = 0;

    + update_misfit_status(NULL, this_rq);
    /*
    * We must set idle_stamp _before_ calling idle_balance(), such that we
    * measure the duration of idle_balance() as idle time.
    --- a/kernel/sched/sched.h
    +++ b/kernel/sched/sched.h
    @@ -1449,10 +1449,14 @@ static inline void unregister_sched_doma
    }
    #endif

    +extern int newidle_balance(struct rq *this_rq, struct rq_flags *rf);
    +
    #else

    static inline void sched_ttwu_pending(void) { }

    +static inline int newidle_balance(struct rq *this_rq, struct rq_flags *rf) { return 0; }
    +
    #endif /* CONFIG_SMP */

    #include "stats.h"

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