[PATCH 4/5] cpufreq: schedutil: map raw required frequency to CPU-supported frequency

[Steve Muckle]

The mechanisms for remote CPU updates and slow-path frequency
transitions are relatively expensive - the former is an IPI while the
latter requires waking up a thread to do work. These activities should
be avoided if they are not necessary. To that end, calculate the
actual target-supported frequency required by the new utilization
value in schedutil. If it is the same as the previously requested
frequency then there is no need to continue with the update.

Signed-off-by: Steve Muckle <smuckle@xxxxxxxxxx>
---
 kernel/sched/cpufreq_schedutil.c | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
index 6cb2ecc204ec..e185075fcb5c 100644
--- a/kernel/sched/cpufreq_schedutil.c
+++ b/kernel/sched/cpufreq_schedutil.c
@@ -153,14 +153,26 @@ static void sugov_update_commit(struct sugov_cpu *sg_cpu, int cpu, u64 time,
  * next_freq = C * curr_freq * util_raw / max
  *
  * Take C = 1.25 for the frequency tipping point at (util / max) = 0.8.
+ *
+ * The lowest target-supported frequency which is equal or greater than the raw
+ * next_freq (as calculated above) is returned, or the CPU's max_freq if such
+ * a target-supported frequency does not exist.
  */
 static unsigned int get_next_freq(struct cpufreq_policy *policy,
 				  unsigned long util, unsigned long max)
 {
+	struct cpufreq_frequency_table *entry;
 	unsigned int freq = arch_scale_freq_invariant() ?
 				policy->cpuinfo.max_freq : policy->cur;
+	unsigned int target_freq = UINT_MAX;
+
+	freq = (freq + (freq >> 2)) * util / max;
+
+	cpufreq_for_each_valid_entry(entry, policy->freq_table)
+		if (entry->frequency >= freq && entry->frequency < target_freq)
+			target_freq = entry->frequency;
 
-	return (freq + (freq >> 2)) * util / max;
+	return target_freq != UINT_MAX ? target_freq : policy->cpuinfo.max_freq;
 }
 
 static void sugov_update_single(struct update_util_data *hook, u64 time,
-- 
2.4.10