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SubjectRe: [PATCH 12/16] sched: refactor update_shares_cpu() -> update_blocked_avgs()
On Fri, Jun 29, 2012 at 12:28 AM, Namhyung Kim <namhyung@kernel.org> wrote:
> 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?

Yes -- applied. Thanks!

>
> 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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