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Subject[RFC PATCH 08/11] sched: Create a helper function to calculate imbalance.
Date
Move all the imbalance calculation out of find_busiest_group() through this
helper function.

With this change, the structure of find_busiest_group() will be as follows:

- update_sched_domain_statistics.

- Check if imbalance exits.

- Update imbalance and return busiest.


Signed-off-by: Gautham R Shenoy <ego@in.ibm.com>
---
kernel/sched.c | 78 ++++++++++++++++++++++++++++++++------------------------
1 files changed, 45 insertions(+), 33 deletions(-)
diff --git a/kernel/sched.c b/kernel/sched.c
index 364866f..b1b1b8a 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -3383,8 +3383,8 @@ group_next:

/**
* fix_small_imbalance - Calculate the minor imbalance that exists
- * amongst the groups of a sched_domain, during
- * load balancing.
+ * amongst the groups of a sched_domain, during
+ * load balancing.
* @sds: Statistics of the sched_domain whose imbalance is to be calculated.
* @this_cpu: The cpu at whose sched_domain we're performing load-balance.
* @imbalance: Variable to store the imbalance.
@@ -3445,6 +3445,47 @@ static inline void fix_small_imbalance(struct sd_lb_stats *sds,
if (pwr_move > pwr_now)
*imbalance = sds->busiest_load_per_task;
}
+
+/**
+ * calculate_imbalance - Calculate the amount of imbalance present within the
+ * groups of a given sched_domain during load balance.
+ * @sds: statistics of the sched_domain whose imbalance is to be calculated.
+ * @this_cpu: Cpu for which currently load balance is being performed.
+ * @imbalance: The variable to store the imbalance.
+ */
+static inline void calculate_imbalance(struct sd_lb_stats *sds, int this_cpu,
+ unsigned long *imbalance)
+{
+ unsigned long max_pull;
+ /*
+ * In the presence of smp nice balancing, certain scenarios can have
+ * max load less than avg load(as we skip the groups at or below
+ * its cpu_power, while calculating max_load..)
+ */
+ if (sds->max_load < sds->avg_load) {
+ *imbalance = 0;
+ return fix_small_imbalance(sds, this_cpu, imbalance);
+ }
+
+ /* Don't want to pull so many tasks that a group would go idle */
+ max_pull = min(sds->max_load - sds->avg_load,
+ 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)
+ / SCHED_LOAD_SCALE;
+
+ /*
+ * if *imbalance is less than the average load per runnable task
+ * there is no gaurantee that any tasks will be moved so we'll have
+ * a think about bumping its value to force at least one task to be
+ * moved
+ */
+ if (*imbalance < sds->busiest_load_per_task)
+ return fix_small_imbalance(sds, this_cpu, imbalance);
+
+}
/******* find_busiest_group() helpers end here *********************/

/*
@@ -3458,7 +3499,6 @@ find_busiest_group(struct sched_domain *sd, int this_cpu,
int *sd_idle, const struct cpumask *cpus, int *balance)
{
struct sd_lb_stats sds;
- unsigned long max_pull;

memset(&sds, 0, sizeof(sds));

@@ -3501,36 +3541,8 @@ find_busiest_group(struct sched_domain *sd, int this_cpu,
if (sds.max_load <= sds.busiest_load_per_task)
goto out_balanced;

- /*
- * In the presence of smp nice balancing, certain scenarios can have
- * max load less than avg load(as we skip the groups at or below
- * its cpu_power, while calculating max_load..)
- */
- if (sds.max_load < sds.avg_load) {
- *imbalance = 0;
- fix_small_imbalance(&sds, this_cpu, imbalance);
- goto ret_busiest;
- }
-
- /* Don't want to pull so many tasks that a group would go idle */
- max_pull = min(sds.max_load - sds.avg_load,
- 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)
- / SCHED_LOAD_SCALE;
-
- /*
- * if *imbalance is less than the average load per runnable task
- * there is no gaurantee that any tasks will be moved so we'll have
- * a think about bumping its value to force at least one task to be
- * moved
- */
- if (*imbalance < sds.busiest_load_per_task)
- fix_small_imbalance(&sds, this_cpu, imbalance);
-
-ret_busiest:
+ /* Looks like there is an imbalance. Compute it */
+ calculate_imbalance(&sds, this_cpu, imbalance);
return sds.busiest;

out_balanced:


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