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Subject[RFC][PATCH 6/8] sched: scale down cpu_power due to RT tasks
Keep an average on the amount of time spend on RT tasks and use that
fraction to scale down the cpu_power for regular tasks.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
---
include/linux/sched.h | 1
kernel/sched.c | 64 +++++++++++++++++++++++++++++++++++++++++++++++---
kernel/sched_rt.c | 6 +---
kernel/sysctl.c | 8 ++++++
4 files changed, 72 insertions(+), 7 deletions(-)
Index: linux-2.6/include/linux/sched.h
===================================================================
--- linux-2.6.orig/include/linux/sched.h
+++ linux-2.6/include/linux/sched.h
@@ -1863,6 +1863,7 @@ extern unsigned int sysctl_sched_child_r
extern unsigned int sysctl_sched_features;
extern unsigned int sysctl_sched_migration_cost;
extern unsigned int sysctl_sched_nr_migrate;
+extern unsigned int sysctl_sched_time_avg;
extern unsigned int sysctl_timer_migration;

int sched_nr_latency_handler(struct ctl_table *table, int write,
Index: linux-2.6/kernel/sched.c
===================================================================
--- linux-2.6.orig/kernel/sched.c
+++ linux-2.6/kernel/sched.c
@@ -627,6 +627,9 @@ struct rq {

struct task_struct *migration_thread;
struct list_head migration_queue;
+
+ u64 rt_avg;
+ u64 age_stamp;
#endif

/* calc_load related fields */
@@ -863,6 +866,14 @@ unsigned int sysctl_sched_shares_ratelim
unsigned int sysctl_sched_shares_thresh = 4;

/*
+ * period over which we average the RT time consumption, measured
+ * in ms.
+ *
+ * default: 1s
+ */
+const_debug unsigned int sysctl_sched_time_avg = MSEC_PER_SEC;
+
+/*
* period over which we measure -rt task cpu usage in us.
* default: 1s
*/
@@ -1280,12 +1291,37 @@ void wake_up_idle_cpu(int cpu)
}
#endif /* CONFIG_NO_HZ */

+static u64 sched_avg_period(void)
+{
+ return (u64)sysctl_sched_time_avg * NSEC_PER_MSEC / 2;
+}
+
+static void sched_avg_update(struct rq *rq)
+{
+ s64 period = sched_avg_period();
+
+ while ((s64)(rq->clock - rq->age_stamp) > period) {
+ rq->age_stamp += period;
+ rq->rt_avg /= 2;
+ }
+}
+
+static void sched_rt_avg_update(struct rq *rq, u64 rt_delta)
+{
+ rq->rt_avg += rt_delta;
+ sched_avg_update(rq);
+}
+
#else /* !CONFIG_SMP */
static void resched_task(struct task_struct *p)
{
assert_spin_locked(&task_rq(p)->lock);
set_tsk_need_resched(p);
}
+
+static void sched_rt_avg_update(struct rq *rq, u64 rt_delta)
+{
+}
#endif /* CONFIG_SMP */

#if BITS_PER_LONG == 32
@@ -3699,7 +3735,7 @@ static inline int check_power_save_busie
}
#endif /* CONFIG_SCHED_MC || CONFIG_SCHED_SMT */

-unsigned long __weak arch_smt_gain(struct sched_domain *sd, int cpu)
+unsigned long __weak arch_scale_smt_power(struct sched_domain *sd, int cpu)
{
unsigned long weight = cpumask_weight(sched_domain_span(sd));
unsigned long smt_gain = sd->smt_gain;
@@ -3709,6 +3745,24 @@ unsigned long __weak arch_smt_gain(struc
return smt_gain;
}

+unsigned long scale_rt_power(int cpu)
+{
+ struct rq *rq = cpu_rq(cpu);
+ u64 total, available;
+
+ sched_avg_update(rq);
+
+ total = sched_avg_period() + (rq->clock - rq->age_stamp);
+ available = total - rq->rt_avg;
+
+ if (unlikely((s64)total < SCHED_LOAD_SCALE))
+ total = SCHED_LOAD_SCALE;
+
+ total >>= SCHED_LOAD_SHIFT;
+
+ return div_u64(available, total);
+}
+
static void update_cpu_power(struct sched_domain *sd, int cpu)
{
unsigned long weight = cpumask_weight(sched_domain_span(sd));
@@ -3719,11 +3773,15 @@ static void update_cpu_power(struct sche
/* here we could scale based on cpufreq */

if ((sd->flags & SD_SHARE_CPUPOWER) && weight > 1) {
- power *= arch_smt_gain(sd, cpu);
+ power *= arch_scale_smt_power(sd, cpu);
power >>= SCHED_LOAD_SHIFT;
}

- /* here we could scale based on RT time */
+ power *= scale_rt_power(cpu);
+ power >>= SCHED_LOAD_SHIFT;
+
+ if (!power)
+ power = 1;

if (power != old) {
sdg->__cpu_power = power;
Index: linux-2.6/kernel/sched_rt.c
===================================================================
--- linux-2.6.orig/kernel/sched_rt.c
+++ linux-2.6/kernel/sched_rt.c
@@ -615,6 +615,8 @@ static void update_curr_rt(struct rq *rq
curr->se.exec_start = rq->clock;
cpuacct_charge(curr, delta_exec);

+ sched_rt_avg_update(rq, delta_exec);
+
if (!rt_bandwidth_enabled())
return;

@@ -887,8 +889,6 @@ static void enqueue_task_rt(struct rq *r

if (!task_current(rq, p) && p->rt.nr_cpus_allowed > 1)
enqueue_pushable_task(rq, p);
-
- inc_cpu_load(rq, p->se.load.weight);
}

static void dequeue_task_rt(struct rq *rq, struct task_struct *p, int sleep)
@@ -899,8 +899,6 @@ static void dequeue_task_rt(struct rq *r
dequeue_rt_entity(rt_se);

dequeue_pushable_task(rq, p);
-
- dec_cpu_load(rq, p->se.load.weight);
}

/*
Index: linux-2.6/kernel/sysctl.c
===================================================================
--- linux-2.6.orig/kernel/sysctl.c
+++ linux-2.6/kernel/sysctl.c
@@ -332,6 +332,14 @@ static struct ctl_table kern_table[] = {
},
{
.ctl_name = CTL_UNNUMBERED,
+ .procname = "sched_time_avg",
+ .data = &sysctl_sched_time_avg,
+ .maxlen = sizeof(unsigned int),
+ .mode = 0644,
+ .proc_handler = &proc_dointvec,
+ },
+ {
+ .ctl_name = CTL_UNNUMBERED,
.procname = "timer_migration",
.data = &sysctl_timer_migration,
.maxlen = sizeof(unsigned int),
--



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