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Subject[RFC PATCH 03/11] sched: Define structure to store the sched_group statistics for fbg()
Date
Currently a whole bunch of variables are used to store the various statistics
pertaining to the groups we iterate over in find_busiest_group().

Group them together in a single data structure and add appropriate comments.

This will be useful later on when we create helper functions to calculate the
sched_group statistics.

Credit: Vaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com>
Signed-off-by: Gautham R Shenoy <ego@in.ibm.com>
---
kernel/sched.c | 79 +++++++++++++++++++++++++++++++++-----------------------
1 files changed, 46 insertions(+), 33 deletions(-)
diff --git a/kernel/sched.c b/kernel/sched.c
index d95dcc0..6da9939 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -3088,6 +3088,18 @@ static int move_one_task(struct rq *this_rq, int this_cpu, struct rq *busiest,
/********** Helpers for find_busiest_group ************************/

/**
+ * sg_lb_stats - stats of a sched_group required for load_balancing
+ */
+struct sg_lb_stats {
+ unsigned long avg_load; /*Avg load across the CPUs of the group */
+ unsigned long group_load; /* Total load over the CPUs of the group */
+ unsigned long sum_nr_running; /* Nr tasks running in the group */
+ unsigned long sum_weighted_load; /* Weighted load of group's tasks */
+ unsigned long group_capacity;
+ int group_imb; /* Is there an imbalance in the group ? */
+};
+
+/**
* group_first_cpu - Returns the first cpu in the cpumask of a sched_group.
* @group: The group whose first cpu is to be returned.
*/
@@ -3153,23 +3165,22 @@ find_busiest_group(struct sched_domain *sd, int this_cpu,
load_idx = get_sd_load_idx(sd, idle);

do {
- unsigned long load, group_capacity, max_cpu_load, min_cpu_load;
+ struct sg_lb_stats sgs;
+ unsigned long load, max_cpu_load, min_cpu_load;
int local_group;
int i;
- int __group_imb = 0;
unsigned int balance_cpu = -1, first_idle_cpu = 0;
- unsigned long sum_nr_running, sum_weighted_load;
unsigned long sum_avg_load_per_task;
unsigned long avg_load_per_task;

local_group = cpumask_test_cpu(this_cpu,
sched_group_cpus(group));
+ memset(&sgs, 0, sizeof(sgs));

if (local_group)
balance_cpu = group_first_cpu(group);

/* Tally up the load of all CPUs in the group */
- sum_weighted_load = sum_nr_running = avg_load = 0;
sum_avg_load_per_task = avg_load_per_task = 0;

max_cpu_load = 0;
@@ -3197,9 +3208,9 @@ find_busiest_group(struct sched_domain *sd, int this_cpu,
min_cpu_load = load;
}

- avg_load += load;
- sum_nr_running += rq->nr_running;
- sum_weighted_load += weighted_cpuload(i);
+ sgs.group_load += load;
+ sgs.sum_nr_running += rq->nr_running;
+ sgs.sum_weighted_load += weighted_cpuload(i);

sum_avg_load_per_task += cpu_avg_load_per_task(i);
}
@@ -3216,12 +3227,12 @@ find_busiest_group(struct sched_domain *sd, int this_cpu,
goto ret;
}

- total_load += avg_load;
+ total_load += sgs.group_load;
total_pwr += group->__cpu_power;

/* Adjust by relative CPU power of the group */
- avg_load = sg_div_cpu_power(group,
- avg_load * SCHED_LOAD_SCALE);
+ sgs.avg_load = sg_div_cpu_power(group,
+ sgs.group_load * SCHED_LOAD_SCALE);


/*
@@ -3237,22 +3248,23 @@ find_busiest_group(struct sched_domain *sd, int this_cpu,
sum_avg_load_per_task * SCHED_LOAD_SCALE);

if ((max_cpu_load - min_cpu_load) > 2*avg_load_per_task)
- __group_imb = 1;
+ sgs.group_imb = 1;

- group_capacity = group->__cpu_power / SCHED_LOAD_SCALE;
+ sgs.group_capacity = group->__cpu_power / SCHED_LOAD_SCALE;

if (local_group) {
- this_load = avg_load;
+ this_load = sgs.avg_load;
this = group;
- this_nr_running = sum_nr_running;
- this_load_per_task = sum_weighted_load;
- } else if (avg_load > max_load &&
- (sum_nr_running > group_capacity || __group_imb)) {
- max_load = avg_load;
+ this_nr_running = sgs.sum_nr_running;
+ this_load_per_task = sgs.sum_weighted_load;
+ } else if (sgs.avg_load > max_load &&
+ (sgs.sum_nr_running > sgs.group_capacity ||
+ sgs.group_imb)) {
+ max_load = sgs.avg_load;
busiest = group;
- busiest_nr_running = sum_nr_running;
- busiest_load_per_task = sum_weighted_load;
- group_imb = __group_imb;
+ busiest_nr_running = sgs.sum_nr_running;
+ busiest_load_per_task = sgs.sum_weighted_load;
+ group_imb = sgs.group_imb;
}

#if defined(CONFIG_SCHED_MC) || defined(CONFIG_SCHED_SMT)
@@ -3268,7 +3280,7 @@ find_busiest_group(struct sched_domain *sd, int this_cpu,
* If the local group is idle or completely loaded
* no need to do power savings balance at this domain
*/
- if (local_group && (this_nr_running >= group_capacity ||
+ if (local_group && (this_nr_running >= sgs.group_capacity ||
!this_nr_running))
power_savings_balance = 0;

@@ -3276,8 +3288,9 @@ find_busiest_group(struct sched_domain *sd, int this_cpu,
* If a group is already running at full capacity or idle,
* don't include that group in power savings calculations
*/
- if (!power_savings_balance || sum_nr_running >= group_capacity
- || !sum_nr_running)
+ if (!power_savings_balance ||
+ sgs.sum_nr_running >= sgs.group_capacity ||
+ !sgs.sum_nr_running)
goto group_next;

/*
@@ -3285,13 +3298,13 @@ find_busiest_group(struct sched_domain *sd, int this_cpu,
* This is the group from where we need to pick up the load
* for saving power
*/
- if ((sum_nr_running < min_nr_running) ||
- (sum_nr_running == min_nr_running &&
+ if ((sgs.sum_nr_running < min_nr_running) ||
+ (sgs.sum_nr_running == min_nr_running &&
group_first_cpu(group) > group_first_cpu(group_min))) {
group_min = group;
- min_nr_running = sum_nr_running;
- min_load_per_task = sum_weighted_load /
- sum_nr_running;
+ min_nr_running = sgs.sum_nr_running;
+ min_load_per_task = sgs.sum_weighted_load /
+ sgs.sum_nr_running;
}

/*
@@ -3299,14 +3312,14 @@ find_busiest_group(struct sched_domain *sd, int this_cpu,
* capacity but still has some space to pick up some load
* from other group and save more power
*/
- if (sum_nr_running > group_capacity - 1)
+ if (sgs.sum_nr_running > sgs.group_capacity - 1)
goto group_next;

- if (sum_nr_running > leader_nr_running ||
- (sum_nr_running == leader_nr_running &&
+ if (sgs.sum_nr_running > leader_nr_running ||
+ (sgs.sum_nr_running == leader_nr_running &&
group_first_cpu(group) < group_first_cpu(group_leader))) {
group_leader = group;
- leader_nr_running = sum_nr_running;
+ leader_nr_running = sgs.sum_nr_running;
}
group_next:
#endif


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