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 <[email protected]> --- V2: - Rebased over the fix sent by Rafael lkml.kernel.org/r/[email protected] - Remove the additional check from sugov_update_single() as well. - This is for 4.18 now instead of stable kernels. kernel/sched/cpufreq_schedutil.c | 18 ++++++------------ 1 file changed, 6 insertions(+), 12 deletions(-) diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c index e23e84724f39..daaca23697dc 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 */ @@ -671,7 +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; -- 2.15.0.194.g9af6a3dea062
