ANDROID: cpufreq: schedutil: maintain raw cache when next_f is not changed

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

Bug: 159936782
Bug: 158863204
Signed-off-by: Wei Wang <wvw@google.com>
[dereference23: Backport to 4.14]
Signed-off-by: Alexander Winkowski <dereference23@outlook.com>
Change-Id: I519ca02dd2e6038e3966e1f68fee641628827c82

kernel/sched/cpufreq_schedutil.c

@@ -164,8 +164,8 @@ static void sugov_update_commit(struct sugov_policy *sg_policy, u64 time,
 		return;
 
 	if (sugov_up_down_rate_limit(sg_policy, time, next_freq)) {
-		/* Don't cache a raw freq that didn't become next_freq */
-		sg_policy->cached_raw_freq = 0;
+		/* Restore cached freq as next_freq is not changed */
+		sg_policy->cached_raw_freq = sg_policy->prev_cached_raw_freq;
 		return;
 	}
 
@@ -335,8 +335,7 @@ static void sugov_update_single(struct update_util_data *hook, u64 time,
 	busy = use_pelt() && sugov_cpu_is_busy(sg_cpu);
 
 	if (flags & SCHED_CPUFREQ_RT_DL) {
-		/* clear cache when it's bypassed */
-		sg_policy->cached_raw_freq = 0;
+		sg_policy->cached_raw_freq = sg_policy->prev_cached_raw_freq;
 		next_f = policy->cpuinfo.max_freq;
 	} else {
 		sugov_get_util(&util, &max, sg_cpu->cpu);
@@ -384,8 +383,7 @@ static unsigned int sugov_next_freq_shared(struct sugov_cpu *sg_cpu, u64 time)
 			continue;
 		}
 		if (j_sg_cpu->flags & SCHED_CPUFREQ_RT_DL) {
-			/* clear cache when it's bypassed */
-			sg_policy->cached_raw_freq = 0;
+			sg_policy->cached_raw_freq = sg_policy->prev_cached_raw_freq;
 			return policy->cpuinfo.max_freq;
 		}
 
@@ -428,8 +426,7 @@ static void sugov_update_shared(struct update_util_data *hook, u64 time,
 		!(flags & SCHED_CPUFREQ_CONTINUE)) {
 		if (flags & SCHED_CPUFREQ_RT_DL) {
 			next_f = sg_policy->policy->cpuinfo.max_freq;
-			/* clear cache when it's bypassed */
-			sg_policy->cached_raw_freq = 0;
+			sg_policy->cached_raw_freq = sg_policy->prev_cached_raw_freq;
 		} else {
 			next_f = sugov_next_freq_shared(sg_cpu, time);
 		}