diff options
author | Vincent Guittot <vincent.guittot@linaro.org> | 2013-07-23 11:15:06 +0200 |
---|---|---|
committer | Vincent Guittot <vincent.guittot@linaro.org> | 2013-10-17 22:11:03 +0200 |
commit | 6cd288fa2f4ca4887705fbf48718f12d09a4ac5d (patch) | |
tree | 8d284b5306f61f20571d018f18bee85cea08a2e3 | |
parent | aff0c477fde9e6a3db6a3fdeb861b165e9595929 (diff) |
sched: differantiate idle cpu
The cost for waking up of a core varies according to its current idle state.
This includes C-state and intermediate state when some sync between cores is
required to reach a deep C-state.
Waking up a CPU in a deep C-state for running a short task is not efficient
from both a power and a performance point of view. We should take into account
the wake up latency of an idle CPU when the scheduler looks for the best CPU
to use for a waking task.
The wake up latency of a CPU is computed into a load that can be directly
compared with task load and other CPUs load.
Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
-rw-r--r-- | kernel/sched/fair.c | 22 |
1 files changed, 22 insertions, 0 deletions
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index ad8b99ae24b7..4863dad4f856 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -394,6 +394,20 @@ static int check_nohz_packing(int cpu) return false; } + +int sched_get_idle_load(int cpu) +{ + struct sched_pm *stat = &per_cpu(sched_stat, cpu); + int latency = atomic_read(&(stat->wake_latency)); + /* + * Transform the current wakeup latency (us) into an idle load that + * will be compared to task load to decide if it's worth to wake up + * the cpu. The current formula is quite simple but give good + * approximation in the range [0:10ms] + */ + return (latency * 21) >> 10; +} + #else /* CONFIG_SCHED_PACKING_TASKS */ static inline bool is_packing_cpu(int cpu) @@ -416,6 +430,10 @@ static inline int check_nohz_packing(int cpu) return false; } +static inline int sched_get_idle_load(int cpu) +{ + return 0; +} #endif /* CONFIG_SCHED_PACKING_TASKS */ #endif /* CONFIG_SMP */ @@ -3207,6 +3225,8 @@ static void dequeue_task_fair(struct rq *rq, struct task_struct *p, int flags) /* Used instead of source_load when we know the type == 0 */ static unsigned long weighted_cpuload(const int cpu) { + if (idle_cpu(cpu)) + return sched_get_idle_load(cpu); return cpu_rq(cpu)->cfs.runnable_load_avg; } @@ -3655,6 +3675,8 @@ static int select_idle_sibling(struct task_struct *p, int target) if (i == target || !idle_cpu(i) || !is_packing_cpu(i)) goto next; + if (weighted_cpuload(i) > p->se.avg.load_avg_contrib) + goto next; } target = cpumask_first_and(sched_group_cpus(sg), |