@@ -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);
}
@@ -670,7 +665,7 @@ 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;
The schedutil driver sets sg_policy->next_freq to UINT_MAX on certain occasions: - 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 instead recalculates the next frequency. This has some side effects though and may significantly delay a required increase in frequency. In sugov_update_single() we try to avoid decreasing frequency if the CPU has not been idle recently. Consider this scenario, the available range of frequencies for a CPU are from 800 MHz to 2.5 GHz and current frequency is 800 MHz. From one of the call paths sg_policy->need_freq_update is set to true and hence sg_policy->next_freq is set to UINT_MAX. Now if the CPU had been busy, next_f will always be less than UINT_MAX, whatever the value of next_f is. And so even when we wanted to increase the frequency, we will overwrite next_f with UINT_MAX and will not change the frequency eventually. This will continue until the time CPU stays busy. This isn't cross checked with any specific test cases, but rather based on general code review. Fix that by not resetting the sg_policy->need_freq_update flag from sugov_should_update_freq() but get_next_freq() and we wouldn't need to overwrite sg_policy->next_freq anymore. Cc: 4.12+ <stable@vger.kernel.org> # 4.12+ Fixes: b7eaf1aab9f8 ("cpufreq: schedutil: Avoid reducing frequency of busy CPUs prematurely") Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org> --- kernel/sched/cpufreq_schedutil.c | 15 +++++---------- 1 file changed, 5 insertions(+), 10 deletions(-) -- 2.15.0.194.g9af6a3dea062