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Message-Id: <1403656568-32445-4-git-send-email-yuyang.du@intel.com>
Date: Wed, 25 Jun 2014 08:36:02 +0800
From: Yuyang Du <yuyang.du@...el.com>
To: mingo@...hat.com, peterz@...radead.org, rafael.j.wysocki@...el.com,
linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org
Cc: arjan.van.de.ven@...el.com, len.brown@...el.com,
alan.cox@...el.com, mark.gross@...el.com, morten.rasmussen@....com,
vincent.guittot@...aro.org, dietmar.eggemann@....com,
rajeev.d.muralidhar@...el.com, vishwesh.m.rudramuni@...el.com,
nicole.chalhoub@...el.com, ajaya.durg@...el.com,
harinarayanan.seshadri@...el.com, jacob.jun.pan@...ux.intel.com,
Yuyang Du <yuyang.du@...el.com>
Subject: [RFC PATCH 3/9 v4] How CPU ConCurrency (CC) accrues with runqueue change and time
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 <yuyang.du@...el.com>
---
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
--
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