The energy cost of waking a cpu and sending it back to sleep can be quite significant for short running frequently waking tasks if placed on an idle cpu in a deep sleep state. By factoring task wakeups in such tasks can be placed on cpus where the wakeup energy cost is lower. For example, partly utilized cpus in a shallower idle state, or cpus in a cluster/die that is already awake.
Current cpu utilization of the target cpu is factored in to guess how many task wakeups translate into cpu wakeups (idle exits). It is a very naive approach, but it is virtually impossible to get an accurate estimate. wake_energy(task) = unused_util(cpu) * wakeups(task) * wakeup_energy(cpu) There is no per cpu wakeup tracking, so we can't estimate the energy savings when removing tasks from a cpu. It is also nearly impossible to figure out which task is the cause of cpu wakeups if multiple tasks are scheduled on the same cpu. wakeup_energy for each idle-state is obtained from the idle_states array. A prediction of the most likely idle-state is needed. cpuidle is best placed to provide that. It is not implemented yet. Signed-off-by: Morten Rasmussen <[email protected]> --- kernel/sched/fair.c | 21 +++++++++++++++++---- 1 file changed, 17 insertions(+), 4 deletions(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 6da8e2b..aebf3e2 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -4367,11 +4367,13 @@ static inline unsigned long get_curr_capacity(int cpu); * + (1-curr_util(sg)) * idle_power(sg) * energy_after = new_util(sg) * busy_power(sg) * + (1-new_util(sg)) * idle_power(sg) + * + (1-new_util(sg)) * task_wakeups + * * wakeup_energy(sg) * energy_diff += energy_before - energy_after * } * */ -static int energy_diff_util(int cpu, int util) +static int energy_diff_util(int cpu, int util, int wakeups) { struct sched_domain *sd; int i; @@ -4476,7 +4478,8 @@ static int energy_diff_util(int cpu, int util) * The utilization change has no impact at this level (or any * parent level). */ - if (aff_util_bef == aff_util_aft && curr_cap_idx == new_cap_idx) + if (aff_util_bef == aff_util_aft && curr_cap_idx == new_cap_idx + && unused_util_aft < 100) goto unlock; /* Energy before */ @@ -4486,6 +4489,14 @@ static int energy_diff_util(int cpu, int util) /* Energy after */ nrg_diff += (aff_util_aft*new_state->power)/new_state->cap; nrg_diff += (unused_util_aft * is->power)/new_state->cap; + + /* + * Estimate how many of the wakeups that happens while cpu is + * idle assuming they are uniformly distributed. Ignoring + * wakeups caused by other tasks. + */ + nrg_diff += (wakeups * is->wu_energy >> 10) + * unused_util_aft/new_state->cap; } /* @@ -4516,6 +4527,8 @@ static int energy_diff_util(int cpu, int util) /* Energy after */ nrg_diff += (aff_util_aft*new_state->power)/new_state->cap; nrg_diff += (unused_util_aft * is->power)/new_state->cap; + nrg_diff += (wakeups * is->wu_energy >> 10) + * unused_util_aft/new_state->cap; } unlock: @@ -4532,8 +4545,8 @@ static int energy_diff_task(int cpu, struct task_struct *p) if (!cpumask_test_cpu(cpu, tsk_cpus_allowed(p))) return INT_MAX; - return energy_diff_util(cpu, p->se.avg.uw_load_avg_contrib); - + return energy_diff_util(cpu, p->se.avg.uw_load_avg_contrib, + p->se.avg.wakeup_avg_sum); } static int wake_wide(struct task_struct *p) -- 1.7.9.5 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
