sched: Create a helper function to calculate imbalance

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>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Suresh Siddha <suresh.b.siddha@intel.com>
Cc: "Balbir Singh" <balbir@in.ibm.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Cc: "Dhaval Giani" <dhaval@linux.vnet.ibm.com>
Cc: Bharata B Rao <bharata@linux.vnet.ibm.com>
Cc: "Vaidyanathan Srinivasan" <svaidy@linux.vnet.ibm.com>
LKML-Reference: <20090325091411.13992.43293.stgit@sofia.in.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 45 insertions, 33 deletions

diff --git a/kernel/sched.c b/kernel/sched.c
index 540147e5e82b..934f615ccceb 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -3487,8 +3487,8 @@ 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.
@@ -3549,6 +3549,47 @@ 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 *********************/
 
 /*
@@ -3562,7 +3603,6 @@ 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));
 
@@ -3605,36 +3645,8 @@ 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: