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>
Tested-by: Andreas Herrmann <andreas.herrmann3@amd.com>
Acked-by: Andreas Herrmann <andreas.herrmann3@amd.com>
Acked-by: Gautham R Shenoy <ego@in.ibm.com>
Cc: Balbir Singh <balbir@in.ibm.com>
LKML-Reference: <20090901083826.287778431@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 61 insertions, 3 deletions

diff --git a/kernel/sched.c b/kernel/sched.c
index 036600fd70bb..ab532b5de40e 100644
--- a/kernel/sched.c
+++ b/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_ratelimit = 250000;
 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_busiest_group(struct sd_lb_stats *sds,
 }
 #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(struct sched_domain *sd, int cpu)
         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 sched_domain *sd, int cpu)
         /* 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;