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    SubjectRe: [PATCH 1/6] sched/fair: remove update of blocked load from newidle_balance
    Date
    On 05/02/21 12:48, Vincent Guittot wrote:
    > @@ -10517,16 +10499,11 @@ static void nohz_newidle_balance(struct rq *this_rq)
    > time_before(jiffies, READ_ONCE(nohz.next_blocked)))
    > return;
    >

    I was wondering whether all the conditions above were still relevant. I
    think they are, but this one:

    /* Will wake up very soon. No time for doing anything else*/
    if (this_rq->avg_idle < sysctl_sched_migration_cost)
    return;

    should have its comment updated to something like:

    /*
    * Will wake up very soon. Blocked load will be updated
    * periodically, no need to wake an idle CPU.
    */

    given kick_ilb() isn't the costliest of things.

    > - raw_spin_unlock(&this_rq->lock);
    > /*
    > - * This CPU is going to be idle and blocked load of idle CPUs
    > - * need to be updated. Run the ilb locally as it is a good
    > - * candidate for ilb instead of waking up another idle CPU.
    > - * Kick an normal ilb if we failed to do the update.
    > + * Blocked load of idle CPUs need to be updated.
    > + * Kick an ILB to update statistics.
    > */
    > - if (!_nohz_idle_balance(this_rq, NOHZ_STATS_KICK, CPU_NEWLY_IDLE))
    > - kick_ilb(NOHZ_STATS_KICK);
    > - raw_spin_lock(&this_rq->lock);

    With this change, the return value of _nohz_idle_balance() is no longer
    used. This means we could get rid of the tracking of whether it iterated
    over all nohz CPUs or not.

    > + kick_ilb(NOHZ_STATS_KICK);
    > }
    >
    > #else /* !CONFIG_NO_HZ_COMMON */

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