sched: backport cpufreq hooks from 4.9-rc4

The scheduler cpufreq hooks are required by the schedutil cpufreq
governor.

Change-Id: Ied6c46262bb33b7e81bbb3d3d2761124e0c676b7
Signed-off-by: Steve Muckle <smuckle@linaro.org>
[trivial cherry-picking fixes]
Signed-off-by: Juri Lelli <juri.lelli@arm.com>
Signed-off-by: Chris Redpath <chris.redpath@arm.com>

1 files changed, 52 insertions, 0 deletions

diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 0386a2cdb008..237b0bcdd304 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -2038,3 +2038,55 @@ static inline void account_reset_rq(struct rq *rq)
 	rq->prev_steal_time_rq = 0;
 #endif
 }
+
+#ifdef CONFIG_CPU_FREQ
+DECLARE_PER_CPU(struct update_util_data *, cpufreq_update_util_data);
+
+/**
+ * cpufreq_update_util - Take a note about CPU utilization changes.
+ * @rq: Runqueue to carry out the update for.
+ * @flags: Update reason flags.
+ *
+ * This function is called by the scheduler on the CPU whose utilization is
+ * being updated.
+ *
+ * It can only be called from RCU-sched read-side critical sections.
+ *
+ * The way cpufreq is currently arranged requires it to evaluate the CPU
+ * performance state (frequency/voltage) on a regular basis to prevent it from
+ * being stuck in a completely inadequate performance level for too long.
+ * That is not guaranteed to happen if the updates are only triggered from CFS,
+ * though, because they may not be coming in if RT or deadline tasks are active
+ * all the time (or there are RT and DL tasks only).
+ *
+ * As a workaround for that issue, this function is called by the RT and DL
+ * sched classes to trigger extra cpufreq updates to prevent it from stalling,
+ * but that really is a band-aid.  Going forward it should be replaced with
+ * solutions targeted more specifically at RT and DL tasks.
+ */
+static inline void cpufreq_update_util(struct rq *rq, unsigned int flags)
+{
+        struct update_util_data *data;
+
+        data = rcu_dereference_sched(*this_cpu_ptr(&cpufreq_update_util_data));
+        if (data)
+                data->func(data, rq_clock(rq), flags);
+}
+
+static inline void cpufreq_update_this_cpu(struct rq *rq, unsigned int flags)
+{
+        if (cpu_of(rq) == smp_processor_id())
+                cpufreq_update_util(rq, flags);
+}
+#else
+static inline void cpufreq_update_util(struct rq *rq, unsigned int flags) {}
+static inline void cpufreq_update_this_cpu(struct rq *rq, unsigned int flags) {}
+#endif /* CONFIG_CPU_FREQ */
+
+#ifdef arch_scale_freq_capacity
+#ifndef arch_scale_freq_invariant
+#define arch_scale_freq_invariant()     (true)
+#endif
+#else /* arch_scale_freq_capacity */
+#define arch_scale_freq_invariant()     (false)
+#endif