From: Douglas RAILLARD <[email protected]> Avoid assuming a CPU is busy when it has begun being idle before get_next_freq() is called. This is achieved by making sure the CPU will not be detected as busy by other CPUs whenever its utilization is decreasing.
Signed-off-by: Douglas RAILLARD <[email protected]> --- kernel/sched/cpufreq_schedutil.c | 42 ++++++++++++++++++++++++++++---- 1 file changed, 37 insertions(+), 5 deletions(-) diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c index a12b7e5bc028..ce4b90cafbb5 100644 --- a/kernel/sched/cpufreq_schedutil.c +++ b/kernel/sched/cpufreq_schedutil.c @@ -62,6 +62,7 @@ struct sugov_cpu { /* The field below is for single-CPU policies only: */ #ifdef CONFIG_NO_HZ_COMMON unsigned long saved_idle_calls; + unsigned long previous_util; #endif }; @@ -181,14 +182,35 @@ static bool sugov_cpu_is_busy(struct sugov_cpu *sg_cpu) return ret; } -static void sugov_cpu_is_busy_update(struct sugov_cpu *sg_cpu) +static void sugov_cpu_is_busy_update(struct sugov_cpu *sg_cpu, + unsigned long util) { unsigned long idle_calls = tick_nohz_get_idle_calls_cpu(sg_cpu->cpu); sg_cpu->saved_idle_calls = idle_calls; + + /* + * Make sure that this CPU will not be immediately considered as busy in + * cases where the CPU has already entered an idle state. In that case, + * the number of idle_calls will not vary anymore until it exits idle, + * which would lead sugov_cpu_is_busy() to say that this CPU is busy, + * because it has not (re)entered idle since the last time we looked at + * it. + * Assuming cpu0 and cpu1 are in the same policy, that will make sure + * this sequence of events leads to right cpu1 business status from + * get_next_freq(cpu=1) + * cpu0: [enter idle] -> [get_next_freq] -> [doing nothing] -> [wakeup] + * cpu1: ... -> [get_next_freq] -> ... + */ + if (util <= sg_cpu->previous_util) + sg_cpu->saved_idle_calls--; + + sg_cpu->previous_util = util; } #else static inline bool sugov_cpu_is_busy(struct sugov_cpu *sg_cpu) { return false; } -static void sugov_cpu_is_busy_update(struct sugov_cpu *sg_cpu) {} +static void sugov_cpu_is_busy_update(struct sugov_cpu *sg_cpu + unsigned long util) +{} #endif /* CONFIG_NO_HZ_COMMON */ /** @@ -507,10 +529,9 @@ static void sugov_update_single(struct update_util_data *hook, u64 time, if (!sugov_should_update_freq(sg_policy, time)) return; - busy = sugov_cpu_is_busy(sg_cpu); - sugov_cpu_is_busy_update(sg_cpu); - util = sugov_get_util(sg_cpu); + busy = sugov_cpu_is_busy(sg_cpu); + sugov_cpu_is_busy_update(sg_cpu, util); max = sg_cpu->max; util = sugov_iowait_apply(sg_cpu, time, util, max); next_f = get_next_freq(sg_policy, util, max); @@ -545,12 +566,15 @@ static unsigned int sugov_next_freq_shared(struct sugov_cpu *sg_cpu, u64 time) struct cpufreq_policy *policy = sg_policy->policy; unsigned long util = 0, max = 1; unsigned int j; + unsigned long sg_cpu_util = 0; for_each_cpu(j, policy->cpus) { struct sugov_cpu *j_sg_cpu = &per_cpu(sugov_cpu, j); unsigned long j_util, j_max; j_util = sugov_get_util(j_sg_cpu); + if (j_sg_cpu == sg_cpu) + sg_cpu_util = j_util; j_max = j_sg_cpu->max; j_util = sugov_iowait_apply(j_sg_cpu, time, j_util, j_max); @@ -560,6 +584,14 @@ static unsigned int sugov_next_freq_shared(struct sugov_cpu *sg_cpu, u64 time) } } + /* + * Only update the business status if we are looking at the CPU for + * which a utilization change triggered a call to get_next_freq(). This + * way, we don't affect the "busy" status of CPUs that don't have any + * change in utilization. + */ + sugov_cpu_is_busy_update(sg_cpu, sg_cpu_util); + return get_next_freq(sg_policy, util, max); } -- 2.21.0
