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SubjectRe: [patch 09/15] sched: unthrottle cfs_rq(s) who ran out of quota at period refresh
Some comments...

(2011/05/03 18:28), Paul Turner wrote:
> At the start of a new period there are several actions we must refresh the
> global bandwidth pool as well as unthrottle any cfs_rq entities who previously
> ran out of bandwidth (as quota permits).
>
> Unthrottled entities have the cfs_rq->throttled flag cleared and are re-enqueued
> into the cfs entity hierarchy.
>
> Signed-off-by: Paul Turner <pjt@google.com>
> Signed-off-by: Nikhil Rao <ncrao@google.com>
> Signed-off-by: Bharata B Rao <bharata@linux.vnet.ibm.com>
> ---
> kernel/sched.c | 3 +
> kernel/sched_fair.c | 105 +++++++++++++++++++++++++++++++++++++++++++++++++++-
> 2 files changed, 107 insertions(+), 1 deletion(-)
>
> Index: tip/kernel/sched.c
> ===================================================================
> --- tip.orig/kernel/sched.c
> +++ tip/kernel/sched.c
> @@ -9294,6 +9294,9 @@ static int tg_set_cfs_bandwidth(struct t
> cfs_rq->runtime_enabled = quota != RUNTIME_INF;
> cfs_rq->runtime_remaining = 0;
> cfs_rq->runtime_expires = runtime_expires;
> +
> + if (cfs_rq_throttled(cfs_rq))
> + unthrottle_cfs_rq(cfs_rq);
> raw_spin_unlock_irq(&rq->lock);
> }
> out_unlock:
> Index: tip/kernel/sched_fair.c
> ===================================================================
> --- tip.orig/kernel/sched_fair.c
> +++ tip/kernel/sched_fair.c
> @@ -1456,10 +1456,88 @@ static void check_enqueue_throttle(struc
> throttle_cfs_rq(cfs_rq);
> }
>
> +static void unthrottle_cfs_rq(struct cfs_rq *cfs_rq)
> +{
> + struct rq *rq = rq_of(cfs_rq);
> + struct cfs_bandwidth *cfs_b = tg_cfs_bandwidth(cfs_rq->tg);
> + struct sched_entity *se;
> + int enqueue = 1;
> + long task_delta;
> +
> + se = cfs_rq->tg->se[cpu_of(rq_of(cfs_rq))];
> +
> + cfs_rq->throttled = 0;
> + raw_spin_lock(&cfs_b->lock);
> + list_del_rcu(&cfs_rq->throttled_list);
> + raw_spin_unlock(&cfs_b->lock);
> +
> + if (!cfs_rq->load.weight)
> + return;
> +
> + task_delta = cfs_rq->h_nr_running;
> + for_each_sched_entity(se) {
> + if (se->on_rq)
> + enqueue = 0;
> +
> + cfs_rq = cfs_rq_of(se);
> + if (enqueue)
> + enqueue_entity(cfs_rq, se, ENQUEUE_WAKEUP);
> + cfs_rq->h_nr_running += task_delta;
> +
> + if (cfs_rq_throttled(cfs_rq))
> + break;
> + }
> +
> + if (!se)
> + rq->nr_running += task_delta;
> +
> + /* determine whether we need to wake up potentially idle cpu */
> + if (rq->curr == rq->idle && rq->cfs.nr_running)
> + resched_task(rq->curr);
> +}
> +
> +static u64 distribute_cfs_runtime(struct cfs_bandwidth *cfs_b,
> + u64 remaining, u64 expires)
> +{
> + struct cfs_rq *cfs_rq;
> + u64 runtime = remaining;
> +
> + rcu_read_lock();
> + list_for_each_entry_rcu(cfs_rq, &cfs_b->throttled_cfs_rq,
> + throttled_list) {
> + struct rq *rq = rq_of(cfs_rq);
> +
> + raw_spin_lock(&rq->lock);
> + if (!cfs_rq_throttled(cfs_rq))
> + goto next;
> +
> + runtime = -cfs_rq->runtime_remaining + 1;

It will helpful if a comment can explain why negative and 1.

> + if (runtime > remaining)
> + runtime = remaining;
> + remaining -= runtime;
> +
> + cfs_rq->runtime_remaining += runtime;
> + cfs_rq->runtime_expires = expires;
> +
> + /* we check whether we're throttled above */
> + if (cfs_rq->runtime_remaining > 0)
> + unthrottle_cfs_rq(cfs_rq);
> +
> +next:
> + raw_spin_unlock(&rq->lock);
> +
> + if (!remaining)
> + break;
> + }
> + rcu_read_unlock();
> +
> + return remaining;
> +}
> +
> static int do_sched_cfs_period_timer(struct cfs_bandwidth *cfs_b, int overrun)
> {
> u64 quota, runtime = 0, runtime_expires;
> - int idle = 0;
> + int idle = 0, throttled = 0;
>
> runtime_expires = sched_clock_cpu(smp_processor_id());
>
> @@ -1469,6 +1547,7 @@ static int do_sched_cfs_period_timer(str
> if (quota != RUNTIME_INF) {
> runtime = quota;
> runtime_expires += ktime_to_ns(cfs_b->period);
> + throttled = !list_empty(&cfs_b->throttled_cfs_rq);
>
> cfs_b->runtime = runtime;
> cfs_b->runtime_expires = runtime_expires;
> @@ -1477,6 +1556,30 @@ static int do_sched_cfs_period_timer(str
> }
> raw_spin_unlock(&cfs_b->lock);
>
> + if (!throttled || quota == RUNTIME_INF)
> + goto out;
> + idle = 0;
> +
> +retry:
> + runtime = distribute_cfs_runtime(cfs_b, runtime, runtime_expires);
> +
> + raw_spin_lock(&cfs_b->lock);
> + /* new new bandwidth may have been set */

Typo? new, newer, newest...?

> + if (unlikely(runtime_expires != cfs_b->runtime_expires))
> + goto out_unlock;
> + /*
> + * make sure no-one was throttled while we were handing out the new
> + * runtime.
> + */
> + if (runtime > 0 && !list_empty(&cfs_b->throttled_cfs_rq)) {
> + raw_spin_unlock(&cfs_b->lock);
> + goto retry;
> + }
> + cfs_b->runtime = runtime;
> + cfs_b->idle = idle;
> +out_unlock:
> + raw_spin_unlock(&cfs_b->lock);
> +out:
> return idle;
> }
> #else

Reviewed-by: Hidetoshi Seto <seto.hidetoshi@jp.fujitsu.com>

It would be better if this unthrottle patch (09/15) comes before
throttle patch (08/15) in this series, not to make a small window
in the history that throttled entity never back to the run queue.
But I'm just paranoid...


Thanks,
H.Seto



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