[PATCH] sched: cpufreq_schedutil: maintain raw cache when next_f is not changed

[Wei Wang]

Currently, raw cache will be reset when next_f is changed after
get_next_freq for correctness. However, it may introduce more
cycles. This patch changes it to maintain the cached value instead of
dropping it.

This is adapted from https://android-review.googlesource.com/1352810/

Signed-off-by: Wei Wang <wvw@xxxxxxxxxx>
---
 kernel/sched/cpufreq_schedutil.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
index 5ae7b4e6e8d6..ae3ae7fcd027 100644
--- a/kernel/sched/cpufreq_schedutil.c
+++ b/kernel/sched/cpufreq_schedutil.c
@@ -31,6 +31,7 @@ struct sugov_policy {
 	s64			freq_update_delay_ns;
 	unsigned int		next_freq;
 	unsigned int		cached_raw_freq;
+	unsigned int		prev_cached_raw_freq;
 
 	/* The next fields are only needed if fast switch cannot be used: */
 	struct			irq_work irq_work;
@@ -165,6 +166,7 @@ static unsigned int get_next_freq(struct sugov_policy *sg_policy,
 		return sg_policy->next_freq;
 
 	sg_policy->need_freq_update = false;
+	sg_policy->prev_cached_raw_freq = sg_policy->cached_raw_freq;
 	sg_policy->cached_raw_freq = freq;
 	return cpufreq_driver_resolve_freq(policy, freq);
 }
@@ -464,8 +466,8 @@ static void sugov_update_single(struct update_util_data *hook, u64 time,
 	if (busy && next_f < sg_policy->next_freq) {
 		next_f = sg_policy->next_freq;
 
-		/* Reset cached freq as next_freq has changed */
-		sg_policy->cached_raw_freq = 0;
+		/* Restore cached freq as next_freq has changed */
+		sg_policy->cached_raw_freq = sg_policy->prev_cached_raw_freq;
 	}
 
 	/*
@@ -828,6 +830,7 @@ static int sugov_start(struct cpufreq_policy *policy)
 	sg_policy->limits_changed		= false;
 	sg_policy->need_freq_update		= false;
 	sg_policy->cached_raw_freq		= 0;
+	sg_policy->prev_cached_raw_freq		= 0;
 
 	for_each_cpu(cpu, policy->cpus) {
 		struct sugov_cpu *sg_cpu = &per_cpu(sugov_cpu, cpu);
-- 
2.29.0.rc1.297.gfa9743e501-goog