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.

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>

1 files changed, 6 insertions, 12 deletions

diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
index d7e5194a820d..2442decbfec7 100644
--- a/kernel/sched/cpufreq_schedutil.c
+++ b/kernel/sched/cpufreq_schedutil.c
@@ -95,15 +95,8 @@ static bool sugov_should_update_freq(struct sugov_policy *sg_policy, u64 time)
         if (sg_policy->work_in_progress)
                 return false;
 
-        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;
+        if (unlikely(sg_policy->need_freq_update))
                 return true;
-        }
 
         delta_ns = time - sg_policy->last_freq_update_time;
 
@@ -165,8 +158,10 @@ 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);
 }
@@ -305,8 +300,7 @@ 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 &&
-            sg_policy->next_freq != UINT_MAX) {
+        if (busy && next_f < sg_policy->next_freq) {
                 next_f = sg_policy->next_freq;
 
                 /* Reset cached freq as next_freq has changed */
@@ -654,7 +648,7 @@ static int sugov_start(struct cpufreq_policy *policy)
 
         sg_policy->freq_update_delay_ns = sg_policy->tunables->rate_limit_us * NSEC_PER_USEC;
         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;