sched: cfs: cpu frequency scaling arch functions

arch_eval_cpu_freq and arch_scale_cpu_freq are added to allow the
scheduler to evaluate if cpu frequency should change and to invoke that
change from a safe context.

They are weakly defined arch functions that do nothing by default. A
CPUfreq governor could use these functions to implement a frequency
scaling policy based on updates to per-task statistics or updates to
per-cpu utilization.

As discussed at Linux Plumbers Conference 2014, the goal will be to
focus on a single cpu frequency scaling policy that works for everyone.
That may mean that the weak arch functions definitions can be removed
entirely and a single policy implements that logic for all
architectures.

Not-signed-off-by: Mike Turquette <mturquette@linaro.org>

1 files changed, 12 insertions, 0 deletions

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index a6e7beec3b27..422e1f8ab049 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -2470,6 +2470,8 @@ static u32 __compute_runnable_contrib(u64 n)
 }
 
 unsigned long __weak arch_scale_freq_capacity(struct sched_domain *sd, int cpu);
+void arch_eval_cpu_freq(struct cpumask *cpus);
+void arch_scale_cpu_freq(void);
 
 /*
  * We can represent the historical contribution to runnable average as the
@@ -6022,6 +6024,16 @@ unsigned long __weak arch_scale_cpu_capacity(struct sched_domain *sd, int cpu)
 	return default_scale_cpu_capacity(sd, cpu);
 }
 
+void __weak arch_eval_cpu_freq(struct cpumask *cpus)
+{
+	return;
+}
+
+void __weak arch_scale_cpu_freq(void)
+{
+	return;
+}
+
 static unsigned long scale_rt_capacity(int cpu)
 {
 	struct rq *rq = cpu_rq(cpu);