cpufreq/sched: Consider max cpu capacity when choosing frequencies

When using schedfreq on cpus with max capacity significantly smaller than
1024, the tick update uses non-normalised capacities - this leads to
selecting an incorrect OPP as we were scaling the frequency as if the
max capacity achievable was 1024 rather than the max for that particular
cpu or group. This could result in a cpu being stuck at the lowest OPP
and unable to generate enough utilisation to climb out if the max
capacity is significantly smaller than 1024.

Instead, normalize the capacity to be in the range 0-1024 in the tick
so that when we later select a frequency, we get the correct one.

Also comments updated to be clearer about what is needed.

Change-Id: Id84391c7ac015311002ada21813a353ee13bee60
Signed-off-by: Chris Redpath <chris.redpath@arm.com>

1 files changed, 4 insertions, 0 deletions

diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 9f3d89faacdc..5256f05a26e8 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1621,6 +1621,10 @@ static inline bool sched_freq(void)
 	return static_key_false(&__sched_freq);
 }
 
+/*
+ * sched_capacity_reqs expects capacity requests to be normalised.
+ * All capacities should sum to the range of 0-1024.
+ */
 DECLARE_PER_CPU(struct sched_capacity_reqs, cpu_sched_capacity_reqs);
 void update_cpu_capacity_request(int cpu, bool request);