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sched: Remove reciprocal for cpu_power
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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

[ v2: build fix from From: Andreas Herrmann ]

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Tested-by: Andreas Herrmann <andreas.herrmann3@amd.com>
Acked-by: Andreas Herrmann <andreas.herrmann3@amd.com>
Acked-by: Gautham R Shenoy <ego@in.ibm.com>
Cc: Balbir Singh <balbir@in.ibm.com>
LKML-Reference: <20090901083826.425896304@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
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Peter Zijlstra authored and Ingo Molnar committed Sep 4, 2009
1 parent d899a78 commit 18a3885
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Showing 2 changed files with 36 additions and 75 deletions.
10 changes: 2 additions & 8 deletions include/linux/sched.h
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Original file line number Diff line number Diff line change
Expand Up @@ -860,15 +860,9 @@ 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.
Expand Down
101 changes: 34 additions & 67 deletions kernel/sched.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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>
Expand Down Expand Up @@ -120,30 +119,8 @@
*/
#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))
Expand Down Expand Up @@ -2335,8 +2312,7 @@ find_idlest_group(struct sched_domain *sd, struct task_struct *p, int this_cpu)
}

/* 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;
Expand Down Expand Up @@ -3768,7 +3744,6 @@ static void update_cpu_power(struct sched_domain *sd, int cpu)
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 */

Expand All @@ -3783,33 +3758,26 @@ static void update_cpu_power(struct sched_domain *sd, int cpu)
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);
}

/**
Expand Down Expand Up @@ -3889,8 +3857,7 @@ static inline void update_sg_lb_stats(struct sched_domain *sd,
}

/* 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;


/*
Expand All @@ -3902,14 +3869,14 @@ static inline void update_sg_lb_stats(struct sched_domain *sd,
* 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);
}

/**
Expand Down Expand Up @@ -3951,7 +3918,7 @@ static inline void update_sd_lb_stats(struct sched_domain *sd, int this_cpu,
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
Expand Down Expand Up @@ -4016,28 +3983,28 @@ static inline void fix_small_imbalance(struct sd_lb_stats *sds,
* 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;

Expand Down Expand Up @@ -4072,8 +4039,8 @@ static inline void calculate_imbalance(struct sd_lb_stats *sds, int this_cpu,
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;

/*
Expand Down Expand Up @@ -4208,7 +4175,7 @@ static unsigned long power_of(int cpu)
if (!group)
return SCHED_LOAD_SCALE;

return group->__cpu_power;
return group->cpu_power;
}

/*
Expand Down Expand Up @@ -7922,7 +7889,7 @@ static int sched_domain_debug_one(struct sched_domain *sd, int cpu, int level,
break;
}

if (!group->__cpu_power) {
if (!group->cpu_power) {
printk(KERN_CONT "\n");
printk(KERN_ERR "ERROR: domain->cpu_power not "
"set\n");
Expand All @@ -7946,9 +7913,9 @@ static int sched_domain_debug_one(struct sched_domain *sd, int cpu, int level,
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;
Expand Down Expand Up @@ -8233,7 +8200,7 @@ init_sched_build_groups(const struct cpumask *span,
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)
Expand Down Expand Up @@ -8491,7 +8458,7 @@ static void init_numa_sched_groups_power(struct sched_group *group_head)
continue;
}

sg_inc_cpu_power(sg, sd->groups->__cpu_power);
sg->cpu_power += sd->groups->cpu_power;
}
sg = sg->next;
} while (sg != group_head);
Expand Down Expand Up @@ -8528,7 +8495,7 @@ static int build_numa_sched_groups(struct s_data *d,
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);
Expand All @@ -8551,7 +8518,7 @@ static int build_numa_sched_groups(struct s_data *d,
"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);
Expand Down Expand Up @@ -8629,7 +8596,7 @@ static void init_sched_groups_power(int cpu, struct sched_domain *sd)

child = sd->child;

sd->groups->__cpu_power = 0;
sd->groups->cpu_power = 0;

if (!child) {
power = SCHED_LOAD_SCALE;
Expand All @@ -8645,7 +8612,7 @@ static void init_sched_groups_power(int cpu, struct sched_domain *sd)
power /= weight;
power >>= SCHED_LOAD_SHIFT;
}
sg_inc_cpu_power(sd->groups, power);
sd->groups->cpu_power += power;
return;
}

Expand All @@ -8654,7 +8621,7 @@ static void init_sched_groups_power(int cpu, struct sched_domain *sd)
*/
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);
}
Expand Down

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