Avancement analyse load_balancing

migrations/migrations.org

@@ -231,8 +231,8 @@ This function will never be called at runtime and probably be optimized away by
       => Seems to be only set for domain whose SD_NUMA flag is also set.
       => TODO Checks if when this lock is not used, this is because :
         - Another held lock might prevent concurrency problems
-        - It is (assumed) not (to be) a problem to do multiple load balancings concurrently
-    + TODO Use some kind of decay heuristics related to fields :
+        - It is not a problem to do multiple load balancings concurrently
+    + TODO Use some kind of decay heuristics related to the fields :
       - sched_domain.next_decay_max_lb_cost
       - sched_domain.max_newidle_lb_cost
     + Call load_balance to actually do the balancing for the current CPU and each relevant domain
@@ -278,6 +278,14 @@ This function will never be called at runtime and probably be optimized away by
     + Starts by computing stats inside a two level struct sd_lb_stats with field
       struct sg_lb_stats by calling update_sd_lb_stats.
     + Calls check_asym_packing.
+    + Differentiate between a group which is (enum group_type fair.c#6715):
+      - Overloaded, i.e. its load is greater than its capacity
+	=> Slight difference between being overloaded and having no capacity
+           (when the load is eaqual to the capacity)
+      - TODO Imbalanced, from field sched_group_capacity->imbalance
+        which may have been set by a previous call to load_balance
+        (set in function load_balance lines 7824 & unset line 7914)
+      - Other, for others cases
 
 *** TODO update_sd_lb_stats
     + Uses field sched_domain->{busy,idle,newidle}_idx which are not really documented
@@ -304,11 +312,17 @@ This function will never be called at runtime and probably be optimized away by
          the tasks on the system).
       """
 
-    + TLDR; Will iterates on all groups and update their stats. It will also sums them
-      for the domain.
+    + TLDR; Will iterates on all groups of the domain and update their stats.
+      It will also sums them for the domain.
 
 *** TODO update_sg_lb_stats
-    + TODO Contains a comment "Bias balancing toward cpus of our domain"
+    + The load of one group is computed as the sum of its CPUs (sched_capacity->cpumask)
+    + For each CPU the load stats is choosen between :
+      - Its runqueue load decaying average, field rq->cpu_load
+        (using the idx describe in update_sd_lb_stats)
+      - TODO Its runqueue field rq->runnable_load_avg
+      => Use minimum if the destination CPU is part of the considered group, maximum otherwise
+         Described as "Bias balancing toward cpus of our domain"
 
 *** TODO check_asym_packing
     + Related to the POWER7 family of processor