cpufreq: schedutil: Don't set next_freq to UINT_MAX

The schedutil driver sets sg_policy->next_freq to UINT_MAX on certain
occasions to discard the cached value of next freq:
- In sugov_start(), when the schedutil governor is started for a group
  of CPUs.
- And whenever we need to force a freq update before rate-limit
  duration, which happens when:
  - there is an update in cpufreq policy limits.
  - Or when the utilization of DL scheduling class increases.

In return, get_next_freq() doesn't return a cached next_freq value but
recalculates the next frequency instead.

But having special meaning for a particular value of frequency makes the
code less readable and error prone. We recently fixed a bug where the
UINT_MAX value was considered as valid frequency in
sugov_update_single().

All we need is a flag which can be used to discard the value of
sg_policy->next_freq and we already have need_freq_update for that. Lets
reuse it instead of setting next_freq to UINT_MAX.

Change-Id: Ia37ef416d5ecac11fe0c6a2be7e21fdbca708a1a
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Yaroslav Furman <yaro330@gmail.com> - backported to 4.4

1 files changed, 4 insertions, 8 deletions

diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
index d625301e83de..a50b0435db39 100644
--- a/kernel/sched/cpufreq_schedutil.c
+++ b/kernel/sched/cpufreq_schedutil.c
@@ -91,12 +91,6 @@ static bool sugov_should_update_freq(struct sugov_policy *sg_policy, u64 time)
 	s64 delta_ns;
 
 	if (unlikely(sg_policy->need_freq_update)) {
-		sg_policy->need_freq_update = false;
-		/*
-		 * This happens when limits change, so forget the previous
-		 * next_freq value and force an update.
-		 */
-		sg_policy->next_freq = UINT_MAX;
 		return true;
 	}
 
@@ -185,8 +179,10 @@ static unsigned int get_next_freq(struct sugov_policy *sg_policy,
 
 	freq = (freq + (freq >> 2)) * util / max;
 
-	if (freq == sg_policy->cached_raw_freq && sg_policy->next_freq != UINT_MAX)
+	if (freq == sg_policy->cached_raw_freq && !sg_policy->need_freq_update)
 		return sg_policy->next_freq;
+
+	sg_policy->need_freq_update = false;
 	sg_policy->cached_raw_freq = freq;
 	return cpufreq_driver_resolve_freq(policy, freq);
 }
@@ -838,7 +834,7 @@ static int sugov_start(struct cpufreq_policy *policy)
 		sg_policy->tunables->down_rate_limit_us * NSEC_PER_USEC;
 	update_min_rate_limit_us(sg_policy);
 	sg_policy->last_freq_update_time = 0;
-	sg_policy->next_freq = UINT_MAX;
+	sg_policy->next_freq = 0;
 	sg_policy->work_in_progress = false;
 	sg_policy->need_freq_update = false;
 	sg_policy->cached_raw_freq = 0;