Re: [RFCv5 PATCH 22/46] sched: Calculate energy consumption of sched_group

Leo Yan
2015-09-02T17:19:33Z

On Tue, Jul 07, 2015 at 07:24:05PM +0100, Morten Rasmussen wrote:
> For energy-aware load-balancing decisions it is necessary to know the
> energy consumption estimates of groups of cpus. This patch introduces a
> basic function, sched_group_energy(), which estimates the energy
> consumption of the cpus in the group and any resources shared by the
> members of the group.
>
> NOTE: The function has five levels of identation and breaks the 80
> character limit. Refactoring is necessary.
>
> cc: Ingo Molnar <mingo@redhat.com>
> cc: Peter Zijlstra <peterz@infradead.org>
>
> Signed-off-by: Morten Rasmussen <morten.rasmussen@arm.com>
> ---
> kernel/sched/fair.c | 146 ++++++++++++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 146 insertions(+)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 78d3081..bd0be9d 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -4846,6 +4846,152 @@ static inline bool energy_aware(void)
> return sched_feat(ENERGY_AWARE);
> }
>
> +/*
> + * cpu_norm_usage() returns the cpu usage relative to a specific capacity,
> + * i.e. it's busy ratio, in the range [0..SCHED_LOAD_SCALE] which is useful for
> + * energy calculations. Using the scale-invariant usage returned by
> + * get_cpu_usage() and approximating scale-invariant usage by:
> + *
> + * usage ~ (curr_freq/max_freq)*1024 * capacity_orig/1024 * running_time/time
> + *
> + * the normalized usage can be found using the specific capacity.
> + *
> + * capacity = capacity_orig * curr_freq/max_freq
> + *
> + * norm_usage = running_time/time ~ usage/capacity
> + */
> +static unsigned long cpu_norm_usage(int cpu, unsigned long capacity)
> +{
> + int usage = __get_cpu_usage(cpu);
> +
> + if (usage >= capacity)
> + return SCHED_CAPACITY_SCALE;
> +
> + return (usage << SCHED_CAPACITY_SHIFT)/capacity;
> +}
> +
> +static unsigned long group_max_usage(struct sched_group *sg)
> +{
> + int i;
> + unsigned long max_usage = 0;
> +
> + for_each_cpu(i, sched_group_cpus(sg))
> + max_usage = max(max_usage, get_cpu_usage(i));
> +
> + return max_usage;
> +}
> +
> +/*
> + * group_norm_usage() returns the approximated group usage relative to it's
> + * current capacity (busy ratio) in the range [0..SCHED_LOAD_SCALE] for use in
> + * energy calculations. Since task executions may or may not overlap in time in
> + * the group the true normalized usage is between max(cpu_norm_usage(i)) and
> + * sum(cpu_norm_usage(i)) when iterating over all cpus in the group, i. The
> + * latter is used as the estimate as it leads to a more pessimistic energy
> + * estimate (more busy).
> + */
> +static unsigned long group_norm_usage(struct sched_group *sg, int cap_idx)
> +{
> + int i;
> + unsigned long usage_sum = 0;
> + unsigned long capacity = sg->sge->cap_states[cap_idx].cap;
> +
> + for_each_cpu(i, sched_group_cpus(sg))
> + usage_sum += cpu_norm_usage(i, capacity);
> +
> + if (usage_sum > SCHED_CAPACITY_SCALE)
> + return SCHED_CAPACITY_SCALE;
> + return usage_sum;
> +}
> +
> +static int find_new_capacity(struct sched_group *sg,
> + struct sched_group_energy *sge)
> +{
> + int idx;
> + unsigned long util = group_max_usage(sg);
> +
> + for (idx = 0; idx < sge->nr_cap_states; idx++) {
> + if (sge->cap_states[idx].cap >= util)
> + return idx;
> + }
> +
> + return idx;
> +}
> +
> +/*
> + * sched_group_energy(): Returns absolute energy consumption of cpus belonging
> + * to the sched_group including shared resources shared only by members of the
> + * group. Iterates over all cpus in the hierarchy below the sched_group starting
> + * from the bottom working it's way up before going to the next cpu until all
> + * cpus are covered at all levels. The current implementation is likely to
> + * gather the same usage statistics multiple times. This can probably be done in
> + * a faster but more complex way.
> + */
> +static unsigned int sched_group_energy(struct sched_group *sg_top)
> +{
> + struct sched_domain *sd;
> + int cpu, total_energy = 0;
> + struct cpumask visit_cpus;
> + struct sched_group *sg;
> +
> + WARN_ON(!sg_top->sge);
> +
> + cpumask_copy(&visit_cpus, sched_group_cpus(sg_top));
> +
> + while (!cpumask_empty(&visit_cpus)) {
> + struct sched_group *sg_shared_cap = NULL;
> +
> + cpu = cpumask_first(&visit_cpus);
> +
> + /*
> + * Is the group utilization affected by cpus outside this
> + * sched_group?
> + */
> + sd = highest_flag_domain(cpu, SD_SHARE_CAP_STATES);
> + if (sd && sd->parent)
> + sg_shared_cap = sd->parent->groups;

If the sched domain is already the highest level, should directly use
its group to calculate shared capacity? so the code like below:

if (sd && sd->parent)
sg_shared_cap = sd->parent->groups;
else if (sd && !sd->parent)
sg_shared_cap = sd->groups;

> +
> + for_each_domain(cpu, sd) {
> + sg = sd->groups;
> +
> + /* Has this sched_domain already been visited? */
> + if (sd->child && group_first_cpu(sg) != cpu)
> + break;
> +
> + do {
> + struct sched_group *sg_cap_util;
> + unsigned long group_util;
> + int sg_busy_energy, sg_idle_energy, cap_idx;
> +
> + if (sg_shared_cap && sg_shared_cap->group_weight >= sg->group_weight)
> + sg_cap_util = sg_shared_cap;
> + else
> + sg_cap_util = sg;
> +
> + cap_idx = find_new_capacity(sg_cap_util, sg->sge);
> + group_util = group_norm_usage(sg, cap_idx);
> + sg_busy_energy = (group_util * sg->sge->cap_states[cap_idx].power)
> + >> SCHED_CAPACITY_SHIFT;
> + sg_idle_energy = ((SCHED_LOAD_SCALE-group_util) * sg->sge->idle_states[0].power)
> + >> SCHED_CAPACITY_SHIFT;
> +
> + total_energy += sg_busy_energy + sg_idle_energy;
> +
> + if (!sd->child)
> + cpumask_xor(&visit_cpus, &visit_cpus, sched_group_cpus(sg));
> +
> + if (cpumask_equal(sched_group_cpus(sg), sched_group_cpus(sg_top)))
> + goto next_cpu;
> +
> + } while (sg = sg->next, sg != sd->groups);
> + }
> +next_cpu:
> + continue;
> + }
> +
> + return total_energy;
> +}
> +
> static int wake_wide(struct task_struct *p)
> {
> int factor = this_cpu_read(sd_llc_size);
> --
> 1.9.1
>
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