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SubjectRe: [PATCH 12/16] sched: refactor update_shares_cpu() -> update_blocked_avgs()
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On Wed, 27 Jun 2012 19:24:15 -0700, Paul Turner wrote:
> Now that running entities maintain their own load-averages the work we must do
> in update_shares() is largely restricted to the periodic decay of blocked
> entities. This allows us to be a little less pessimistic regarding our
> occupancy on rq->lock and the associated rq->clock updates required.
>
> Signed-off-by: Paul Turner <pjt@google.com>
> ---
> kernel/sched/fair.c | 59 +++++++++++++++++++++++++++++----------------------
> 1 files changed, 33 insertions(+), 26 deletions(-)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 4a9a828..dd1ef8a 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -3678,23 +3678,20 @@ out:
> /*
> * update tg->load_weight by folding this cpu's load_avg
> */
> -static int update_shares_cpu(struct task_group *tg, int cpu)
> +static void __update_blocked_averages_cpu(struct task_group *tg, int cpu)
> {
> - struct sched_entity *se;
> - struct cfs_rq *cfs_rq;
> - unsigned long flags;
> - struct rq *rq;
> -
> -
> - rq = cpu_rq(cpu);
> - se = tg->se[cpu];
> - cfs_rq = tg->cfs_rq[cpu];
> + struct sched_entity *se = tg->se[cpu];
> + struct cfs_rq *cfs_rq = tg->cfs_rq[cpu];
>
> - raw_spin_lock_irqsave(&rq->lock, flags);
> + /* throttled entities do not contribute to load */
> + if (throttled_hierarchy(cfs_rq))
> + return;
>
> - update_rq_clock(rq);
> update_cfs_rq_blocked_load(cfs_rq, 1);
> - update_entity_load_avg(tg->se[cpu], 1);
> + if (se)
> + update_entity_load_avg(se, 1);
> + else
> + update_rq_runnable_avg(rq_of(cfs_rq), 1);
>
> if (se) {
> /*
> @@ -3707,29 +3704,39 @@ static int update_shares_cpu(struct task_group *tg, int cpu)
> else
> list_del_leaf_cfs_rq(cfs_rq);
> }
> -
> - raw_spin_unlock_irqrestore(&rq->lock, flags);
> -
> - return 0;
> }
>
> -static void update_shares(int cpu)
> +static void update_blocked_averages(int cpu)
> {
> - struct cfs_rq *cfs_rq;
> struct rq *rq = cpu_rq(cpu);
> + struct cfs_rq *cfs_rq;
> +
> + unsigned long flags;
> + int num_updates = 0;
>
> rcu_read_lock();
> + raw_spin_lock_irqsave(&rq->lock, flags);
> + update_rq_clock(rq);
> /*
> * Iterates the task_group tree in a bottom up fashion, see
> * list_add_leaf_cfs_rq() for details.
> */
> for_each_leaf_cfs_rq(rq, cfs_rq) {
> - /* throttled entities do not contribute to load */
> - if (throttled_hierarchy(cfs_rq))
> - continue;
> + __update_blocked_averages_cpu(cfs_rq->tg, rq->cpu);
>
> - update_shares_cpu(cfs_rq->tg, cpu);
> + /*
> + * Periodically release the lock so that a cfs_rq with many
> + * children cannot hold it for an arbitrary period of time.
> + */
> + if (num_updates++ % 20 == 0) {

Should it be '++num_updates'? Otherwise, it'll release the lock at the
first iteration?

Thanks,
Namhyung


> + raw_spin_unlock_irqrestore(&rq->lock, flags);
> + cpu_relax();
> + raw_spin_lock_irqsave(&rq->lock, flags);
> + update_rq_clock(rq);
> + }
> }
> +
> + raw_spin_unlock_irqrestore(&rq->lock, flags);
> rcu_read_unlock();
> }
>
> @@ -3774,7 +3781,7 @@ unsigned long task_h_load(struct task_struct *p)
> return load;
> }
> #else
> -static inline void update_shares(int cpu)
> +static inline void update_blocked_averages(int cpu)
> {
> }
>
> @@ -4936,7 +4943,7 @@ void idle_balance(int this_cpu, struct rq *this_rq)
> */
> raw_spin_unlock(&this_rq->lock);
>
> - update_shares(this_cpu);
> + update_blocked_averages(this_cpu);
> rcu_read_lock();
> for_each_domain(this_cpu, sd) {
> unsigned long interval;
> @@ -5196,7 +5203,7 @@ static void rebalance_domains(int cpu, enum cpu_idle_type idle)
> int update_next_balance = 0;
> int need_serialize;
>
> - update_shares(cpu);
> + update_blocked_averages(cpu);
>
> rcu_read_lock();
> for_each_domain(cpu, sd) {


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