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SubjectRe: [RFC][PATCH 8/8] sched: remove reciprocal for cpu_power
On Tue, Sep 01, 2009 at 10:34:39AM +0200, Peter Zijlstra wrote:
> Its a source of fail, also, now that cpu_power is dynamical, its a
> waste of time.
>
> before:
> <idle>-0 [000] 132.877936: find_busiest_group: avg_load: 0 group_load: 8241 power: 1
>
> after:
> bash-1689 [001] 137.862151: find_busiest_group: avg_load: 10636288 group_load: 10387 power: 1
>
> Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
> ---
> include/linux/sched.h | 10 +----
> kernel/sched.c | 100 +++++++++++++++++---------------------------------
> 2 files changed, 36 insertions(+), 74 deletions(-)
>
> Index: linux-2.6/kernel/sched.c
> ===================================================================
> --- linux-2.6.orig/kernel/sched.c
> +++ linux-2.6/kernel/sched.c
> @@ -120,30 +120,8 @@
> */
> #define RUNTIME_INF ((u64)~0ULL)
>
> -#ifdef CONFIG_SMP
> -
> static void double_rq_lock(struct rq *rq1, struct rq *rq2);
>
> -/*
> - * Divide a load by a sched group cpu_power : (load / sg->__cpu_power)
> - * Since cpu_power is a 'constant', we can use a reciprocal divide.
> - */
> -static inline u32 sg_div_cpu_power(const struct sched_group *sg, u32 load)
> -{
> - return reciprocal_divide(load, sg->reciprocal_cpu_power);
> -}
> -
> -/*
> - * Each time a sched group cpu_power is changed,
> - * we must compute its reciprocal value
> - */
> -static inline void sg_inc_cpu_power(struct sched_group *sg, u32 val)
> -{
> - sg->__cpu_power += val;
> - sg->reciprocal_cpu_power = reciprocal_value(sg->__cpu_power);
> -}
> -#endif
> -
> static inline int rt_policy(int policy)
> {
> if (unlikely(policy == SCHED_FIFO || policy == SCHED_RR))
> @@ -2335,8 +2313,7 @@ find_idlest_group(struct sched_domain *s
> }
>
> /* Adjust by relative CPU power of the group */
> - avg_load = sg_div_cpu_power(group,
> - avg_load * SCHED_LOAD_SCALE);
> + avg_load = (avg_load * SCHED_LOAD_SCALE) / group->cpu_power;
>
> if (local_group) {
> this_load = avg_load;
> @@ -3768,7 +3745,6 @@ static void update_cpu_power(struct sche
> unsigned long weight = cpumask_weight(sched_domain_span(sd));
> unsigned long power = SCHED_LOAD_SCALE;
> struct sched_group *sdg = sd->groups;
> - unsigned long old = sdg->__cpu_power;
>
> /* here we could scale based on cpufreq */
>
> @@ -3783,33 +3759,26 @@ static void update_cpu_power(struct sche
> if (!power)
> power = 1;
>
> - if (power != old) {
> - sdg->__cpu_power = power;
> - sdg->reciprocal_cpu_power = reciprocal_value(power);
> - }
> + sdg->cpu_power = power;
> }
>
> static void update_group_power(struct sched_domain *sd, int cpu)
> {
> struct sched_domain *child = sd->child;
> struct sched_group *group, *sdg = sd->groups;
> - unsigned long power = sdg->__cpu_power;
>
> if (!child) {
> update_cpu_power(sd, cpu);
> return;
> }
>
> - sdg->__cpu_power = 0;
> + sdg->cpu_power = 0;
>
> group = child->groups;
> do {
> - sdg->__cpu_power += group->__cpu_power;
> + sdg->cpu_power += group->cpu_power;
> group = group->next;
> } while (group != child->groups);
> -
> - if (power != sdg->__cpu_power)
> - sdg->reciprocal_cpu_power = reciprocal_value(sdg->__cpu_power);
> }
>
> /**
> @@ -3889,8 +3858,7 @@ static inline void update_sg_lb_stats(st
> }
>
> /* Adjust by relative CPU power of the group */
> - sgs->avg_load = sg_div_cpu_power(group,
> - sgs->group_load * SCHED_LOAD_SCALE);
> + sgs->avg_load = (sgs->group_load * SCHED_LOAD_SCALE) / group->cpu_power;
>
>
> /*
> @@ -3902,14 +3870,14 @@ static inline void update_sg_lb_stats(st
> * normalized nr_running number somewhere that negates
> * the hierarchy?
> */
> - avg_load_per_task = sg_div_cpu_power(group,
> - sum_avg_load_per_task * SCHED_LOAD_SCALE);
> + avg_load_per_task = (sum_avg_load_per_task * SCHED_LOAD_SCALE) /
> + group->cpu_power;
>
> if ((max_cpu_load - min_cpu_load) > 2*avg_load_per_task)
> sgs->group_imb = 1;
>
> sgs->group_capacity =
> - DIV_ROUND_CLOSEST(group->__cpu_power, SCHED_LOAD_SCALE);
> + DIV_ROUND_CLOSEST(group->cpu_power, SCHED_LOAD_SCALE);
> }
>
> /**
> @@ -3951,7 +3919,7 @@ static inline void update_sd_lb_stats(st
> return;
>
> sds->total_load += sgs.group_load;
> - sds->total_pwr += group->__cpu_power;
> + sds->total_pwr += group->cpu_power;
>
> /*
> * In case the child domain prefers tasks go to siblings
> @@ -4016,28 +3984,28 @@ static inline void fix_small_imbalance(s
> * moving them.
> */
>
> - pwr_now += sds->busiest->__cpu_power *
> + pwr_now += sds->busiest->cpu_power *
> min(sds->busiest_load_per_task, sds->max_load);
> - pwr_now += sds->this->__cpu_power *
> + pwr_now += sds->this->cpu_power *
> min(sds->this_load_per_task, sds->this_load);
> pwr_now /= SCHED_LOAD_SCALE;
>
> /* Amount of load we'd subtract */
> - tmp = sg_div_cpu_power(sds->busiest,
> - sds->busiest_load_per_task * SCHED_LOAD_SCALE);
> + tmp = (sds->busiest_load_per_task * SCHED_LOAD_SCALE) /
> + sds->busiest->cpu_power;
> if (sds->max_load > tmp)
> - pwr_move += sds->busiest->__cpu_power *
> + pwr_move += sds->busiest->cpu_power *
> min(sds->busiest_load_per_task, sds->max_load - tmp);
>
> /* Amount of load we'd add */
> - if (sds->max_load * sds->busiest->__cpu_power <
> + if (sds->max_load * sds->busiest->cpu_power <
> sds->busiest_load_per_task * SCHED_LOAD_SCALE)
> - tmp = sg_div_cpu_power(sds->this,
> - sds->max_load * sds->busiest->__cpu_power);
> + tmp = (sds->max_load * sds->busiest->cpu_power) /
> + sds->this->cpu_power;
> else
> - tmp = sg_div_cpu_power(sds->this,
> - sds->busiest_load_per_task * SCHED_LOAD_SCALE);
> - pwr_move += sds->this->__cpu_power *
> + tmp = (sds->busiest_load_per_task * SCHED_LOAD_SCALE) /
> + sds->this->cpu_power;
> + pwr_move += sds->this->cpu_power *
> min(sds->this_load_per_task, sds->this_load + tmp);
> pwr_move /= SCHED_LOAD_SCALE;
>
> @@ -4072,8 +4040,8 @@ static inline void calculate_imbalance(s
> sds->max_load - sds->busiest_load_per_task);
>
> /* How much load to actually move to equalise the imbalance */
> - *imbalance = min(max_pull * sds->busiest->__cpu_power,
> - (sds->avg_load - sds->this_load) * sds->this->__cpu_power)
> + *imbalance = min(max_pull * sds->busiest->cpu_power,
> + (sds->avg_load - sds->this_load) * sds->this->cpu_power)
> / SCHED_LOAD_SCALE;
>
> /*
> @@ -4208,7 +4176,7 @@ static unsigned long power_of(int cpu)
> if (!group)
> return SCHED_LOAD_SCALE;
>
> - return group->__cpu_power;
> + return group->cpu_power;
> }
>
> /*
> @@ -7934,7 +7902,7 @@ static int sched_domain_debug_one(struct
> break;
> }
>
> - if (!group->__cpu_power) {
> + if (!group->cpu_power) {
> printk(KERN_CONT "\n");
> printk(KERN_ERR "ERROR: domain->cpu_power not "
> "set\n");
> @@ -7958,9 +7926,9 @@ static int sched_domain_debug_one(struct
> cpulist_scnprintf(str, sizeof(str), sched_group_cpus(group));
>
> printk(KERN_CONT " %s", str);
> - if (group->__cpu_power != SCHED_LOAD_SCALE) {
> - printk(KERN_CONT " (__cpu_power = %d)",
> - group->__cpu_power);
> + if (group->cpu_power != SCHED_LOAD_SCALE) {
> + printk(KERN_CONT " (cpu_power = %d)",
> + group->cpu_power);
> }
>
> group = group->next;
> @@ -8245,7 +8213,7 @@ init_sched_build_groups(const struct cpu
> continue;
>
> cpumask_clear(sched_group_cpus(sg));
> - sg->__cpu_power = 0;
> + sg->cpu_power = 0;
>
> for_each_cpu(j, span) {
> if (group_fn(j, cpu_map, NULL, tmpmask) != group)
> @@ -8503,7 +8471,7 @@ static void init_numa_sched_groups_power
> continue;
> }
>
> - sg_inc_cpu_power(sg, sd->groups->__cpu_power);
> + sg->cpu_power += sd->groups->cpu_power;
> }
> sg = sg->next;
> } while (sg != group_head);
> @@ -8540,7 +8508,7 @@ static int build_numa_sched_groups(struc
> sd->groups = sg;
> }
>
> - sg->__cpu_power = 0;
> + sg->cpu_power = 0;
> cpumask_copy(sched_group_cpus(sg), d->nodemask);
> sg->next = sg;
> cpumask_or(d->covered, d->covered, d->nodemask);
> @@ -8563,7 +8531,7 @@ static int build_numa_sched_groups(struc
> "Can not alloc domain group for node %d\n", j);
> return -ENOMEM;
> }
> - sg->__cpu_power = 0;
> + sg->cpu_power = 0;
> cpumask_copy(sched_group_cpus(sg), d->tmpmask);
> sg->next = prev->next;
> cpumask_or(d->covered, d->covered, d->tmpmask);
> @@ -8641,7 +8609,7 @@ static void init_sched_groups_power(int
>
> child = sd->child;
>
> - sd->groups->__cpu_power = 0;
> + sd->groups->cpu_power = 0;
>
> if (!child) {
> power = SCHED_LOAD_SCALE;
> @@ -8657,7 +8625,7 @@ static void init_sched_groups_power(int
> power /= weight;
> power >>= SCHED_LOAD_SHIFT;
> }
> - sg_inc_cpu_power(sd->groups, power);
> + sd->groups->cpu_power += power;
> return;
> }
>
> @@ -8666,7 +8634,7 @@ static void init_sched_groups_power(int
> */
> group = child->groups;
> do {
> - sg_inc_cpu_power(sd->groups, group->__cpu_power);
> + sd->groups->cpu_power += group->cpu_power;
> group = group->next;
> } while (group != child->groups);
> }
> Index: linux-2.6/include/linux/sched.h
> ===================================================================
> --- linux-2.6.orig/include/linux/sched.h
> +++ linux-2.6/include/linux/sched.h
> @@ -870,15 +870,9 @@ struct sched_group {
>
> /*
> * CPU power of this group, SCHED_LOAD_SCALE being max power for a
> - * single CPU. This is read only (except for setup, hotplug CPU).
> - * Note : Never change cpu_power without recompute its reciprocal
> + * single CPU.
> */
> - unsigned int __cpu_power;
> - /*
> - * reciprocal value of cpu_power to avoid expensive divides
> - * (see include/linux/reciprocal_div.h)
> - */
> - u32 reciprocal_cpu_power;
> + unsigned int cpu_power;
>
> /*
> * The CPUs this group covers.
>
> --
>

Nice.
You might also want to remove the respective header file:

--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -64,7 +64,6 @@
#include <linux/tsacct_kern.h>
#include <linux/kprobes.h>
#include <linux/delayacct.h>
-#include <linux/reciprocal_div.h>
#include <linux/unistd.h>
#include <linux/pagemap.h>
#include <linux/hrtimer.h>

Regards,
Andreas

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