BACKPORT: schedutil: Reset cached freq if it is not in sync with next_freq

'cached_raw_freq' is used to get the next frequency quickly but should
always be in sync with sg_policy->next_freq. There are cases where it is
not and in such cases it should be reset to avoid switching to incorrect
frequencies.

Consider this case for example:
- policy->cur is 1.2 GHz (Max)
- New request comes for 780 MHz and we store that in cached_raw_freq.
- Based on 780 MHz, we calculate the effective frequency as 800 MHz.
- We then decide not to update the frequency as
  sugov_up_down_rate_limit() return true.
- Here cached_raw_freq is 780 MHz and sg_policy->next_freq is 1.2 GHz.
- Now if the utilization doesn't change in next request, then the next
  target frequency will still be 780 MHz and it will match with
  cached_raw_freq and so we will directly return 1.2 GHz instead of 800
  MHz.

BACKPORT of upstream commit 07458f6a5171 ("cpufreq: schedutil: Reset
cached_raw_freq when not in sync with next_freq").

This also updates sugov_update_commit() for handling up/down tunables, which
aren't present in mainline.

Change-Id: I70bca2c5dfdb545a0471d1c9e4c5addb30ab5494
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>

1 files changed, 9 insertions, 2 deletions

diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
index d3765f0cb699..6c84b4d28914 100644
--- a/kernel/sched/cpufreq_schedutil.c
+++ b/kernel/sched/cpufreq_schedutil.c
@@ -130,8 +130,11 @@ static void sugov_update_commit(struct sugov_policy *sg_policy, u64 time,
 {
 	struct cpufreq_policy *policy = sg_policy->policy;
 
-	if (sugov_up_down_rate_limit(sg_policy, time, next_freq))
+	if (sugov_up_down_rate_limit(sg_policy, time, next_freq)) {
+		/* Reset cached freq as next_freq isn't changed */
+		sg_policy->cached_raw_freq = 0;
 		return;
+	}
 
 	if (sg_policy->next_freq == next_freq)
 		return;
@@ -317,8 +320,12 @@ static void sugov_update_single(struct update_util_data *hook, u64 time,
 		 * Do not reduce the frequency if the CPU has not been idle
 		 * recently, as the reduction is likely to be premature then.
 		 */
-		if (busy && next_f < sg_policy->next_freq)
+		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;
+		}
 	}
 	sugov_update_commit(sg_policy, time, next_f);
 }