CC can be seen as either decayed average run queue length, or run-queue-lengh- weighted CPU utilization. CC is calculated by two steps:
1) Divide continuous time into periods of time, and average task concurrency in period, for tolerating the transient bursts: a = sum(concurrency * time) / period 2) Exponentially decay past periods, and synthesize them all, for hysteresis to load drops or resilience to load rises (let f be decaying factor, and a_x the xth period average since period 0): s = a_n + f^1 * a_n-1 + f^2 * a_n-2 +, ..., + f^(n-1) * a_1 + f^n * a_0 We reuse __update_entity_runnable_avg to calc CC. CC can only be modified when enqueue and dequeue the CPU rq. We also update it in scheduler tick, load balancing, and idle enter/exit in case we may not have enqueue and dequeue for a long time. Therefore, we update/track CC in and only in these points: we update cpu concurrency at: 1) enqueue task, which increases concurrency 2) dequeue task, which decreases concurrency 3) periodic scheduler tick, in case no en/dequeue for long 4) enter and exit idle 5) update_blocked_averages Signed-off-by: Yuyang Du <[email protected]> --- kernel/sched/fair.c | 45 +++++++++++++++++++++++++++++++++++++++++++-- kernel/sched/sched.h | 2 ++ 2 files changed, 45 insertions(+), 2 deletions(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index e914e32..c4270cf 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -2605,6 +2605,8 @@ static inline void dequeue_entity_load_avg(struct cfs_rq *cfs_rq, } /* migrations, e.g. sleep=0 leave decay_count == 0 */ } +static inline void update_cpu_concurrency(struct rq *rq); + /* * Update the rq's load with the elapsed running time before entering * idle. if the last scheduled task is not a CFS task, idle_enter will @@ -2612,6 +2614,7 @@ static inline void dequeue_entity_load_avg(struct cfs_rq *cfs_rq, */ void idle_enter_fair(struct rq *this_rq) { + update_cpu_concurrency(this_rq); } /* @@ -2621,6 +2624,7 @@ void idle_enter_fair(struct rq *this_rq) */ void idle_exit_fair(struct rq *this_rq) { + update_cpu_concurrency(this_rq); } static int idle_balance(struct rq *this_rq); @@ -2638,6 +2642,8 @@ static inline void dequeue_entity_load_avg(struct cfs_rq *cfs_rq, static inline void update_cfs_rq_blocked_load(struct cfs_rq *cfs_rq, int force_update) {} +static inline void update_cpu_concurrency(struct rq *rq) {} + static inline int idle_balance(struct rq *rq) { return 0; @@ -3931,8 +3937,10 @@ enqueue_task_fair(struct rq *rq, struct task_struct *p, int flags) update_entity_load_avg(se, 1); } - if (!se) + if (!se) { + update_cpu_concurrency(rq); add_nr_running(rq, 1); + } hrtick_update(rq); } @@ -3991,8 +3999,10 @@ static void dequeue_task_fair(struct rq *rq, struct task_struct *p, int flags) update_entity_load_avg(se, 1); } - if (!se) + if (!se) { + update_cpu_concurrency(rq); sub_nr_running(rq, 1); + } hrtick_update(rq); } @@ -5454,6 +5464,8 @@ static void update_blocked_averages(int cpu) __update_blocked_averages_cpu(cfs_rq->tg, rq->cpu); } + update_cpu_concurrency(rq); + raw_spin_unlock_irqrestore(&rq->lock, flags); } @@ -7342,6 +7354,8 @@ static void task_tick_fair(struct rq *rq, struct task_struct *curr, int queued) if (numabalancing_enabled) task_tick_numa(rq, curr); + + update_cpu_concurrency(rq); } /* @@ -7801,3 +7815,30 @@ __init void init_sched_fair_class(void) #endif /* SMP */ } + +#ifdef CONFIG_SMP + +/* + * CPU ConCurrency (CC) measures the CPU load by averaging + * the number of running tasks. Using CC, the scheduler can + * evaluate the load of CPUs to improve load balance for power + * efficiency without sacrificing performance. + */ + +/* + * we update cpu concurrency at: + * 1) enqueue task, which increases concurrency + * 2) dequeue task, which decreases concurrency + * 3) periodic scheduler tick, in case no en/dequeue for long + * 4) enter and exit idle + * 5) update_blocked_averages + */ +static void update_cpu_concurrency(struct rq *rq) +{ + struct sched_avg *sa = &rq->avg; + if (__update_entity_runnable_avg(rq->clock, sa, rq->nr_running)) { + sa->load_avg_contrib = sa->runnable_avg_sum << NICE_0_SHIFT; + sa->load_avg_contrib /= (sa->runnable_avg_period + 1); + } +} +#endif /* CONFIG_SMP */ diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index a147571..eb47ce2 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -579,6 +579,8 @@ struct rq { struct list_head cfs_tasks; + struct sched_avg avg; + u64 rt_avg; u64 age_stamp; u64 idle_stamp; -- 1.7.9.5 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
