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    SubjectRe: [PATCH v6 05/16] sched/core: uclamp: Update CPU's refcount on clamp changes
    On Tue, Jan 15, 2019 at 10:15:02AM +0000, Patrick Bellasi wrote:

    > +static inline void
    > +uclamp_task_update_active(struct task_struct *p, unsigned int clamp_id)
    > +{
    > + struct rq_flags rf;
    > + struct rq *rq;
    > +
    > + /*
    > + * Lock the task and the CPU where the task is (or was) queued.
    > + *
    > + * We might lock the (previous) rq of a !RUNNABLE task, but that's the
    > + * price to pay to safely serialize util_{min,max} updates with
    > + * enqueues, dequeues and migration operations.
    > + * This is the same locking schema used by __set_cpus_allowed_ptr().
    > + */
    > + rq = task_rq_lock(p, &rf);
    > +
    > + /*
    > + * Setting the clamp bucket is serialized by task_rq_lock().
    > + * If the task is not yet RUNNABLE and its task_struct is not
    > + * affecting a valid clamp bucket, the next time it's enqueued,
    > + * it will already see the updated clamp bucket value.
    > + */
    > + if (!p->uclamp[clamp_id].active)
    > + goto done;
    > +
    > + uclamp_cpu_dec_id(p, rq, clamp_id);
    > + uclamp_cpu_inc_id(p, rq, clamp_id);
    > +
    > +done:
    > + task_rq_unlock(rq, p, &rf);
    > +}

    > @@ -1008,11 +1043,11 @@ static int __setscheduler_uclamp(struct task_struct *p,
    >
    > mutex_lock(&uclamp_mutex);
    > if (attr->sched_flags & SCHED_FLAG_UTIL_CLAMP_MIN) {
    > - uclamp_bucket_inc(&p->uclamp[UCLAMP_MIN],
    > + uclamp_bucket_inc(p, &p->uclamp[UCLAMP_MIN],
    > UCLAMP_MIN, lower_bound);
    > }
    > if (attr->sched_flags & SCHED_FLAG_UTIL_CLAMP_MAX) {
    > - uclamp_bucket_inc(&p->uclamp[UCLAMP_MAX],
    > + uclamp_bucket_inc(p, &p->uclamp[UCLAMP_MAX],
    > UCLAMP_MAX, upper_bound);
    > }
    > mutex_unlock(&uclamp_mutex);


    But.... __sched_setscheduler() actually does the whole dequeue + enqueue
    thing already ?!? See where it does __setscheduler().


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