sched, cgroup: Optimize load_balance_fair()
Use for_each_leaf_cfs_rq() instead of list_for_each_entry_rcu(), this
achieves that load_balance_fair() only iterates those task_groups that
actually have tasks on busiest, and that we iterate bottom-up, trying to
move light groups before the heavier ones.
No idea if it will actually work out to be beneficial in practice, does
anybody have a cgroup workload that might show a difference one way or
the other?
[ Also move update_h_load to sched_fair.c, loosing #ifdef-ery ]
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Reviewed-by: Paul Turner <pjt@google.com>
Link: http://lkml.kernel.org/r/1310557009.2586.28.camel@twins
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index 6cdff84..180bcf1 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -2232,11 +2232,43 @@
struct rq *rq = cpu_rq(cpu);
rcu_read_lock();
+ /*
+ * Iterates the task_group tree in a bottom up fashion, see
+ * list_add_leaf_cfs_rq() for details.
+ */
for_each_leaf_cfs_rq(rq, cfs_rq)
update_shares_cpu(cfs_rq->tg, cpu);
rcu_read_unlock();
}
+/*
+ * Compute the cpu's hierarchical load factor for each task group.
+ * This needs to be done in a top-down fashion because the load of a child
+ * group is a fraction of its parents load.
+ */
+static int tg_load_down(struct task_group *tg, void *data)
+{
+ unsigned long load;
+ long cpu = (long)data;
+
+ if (!tg->parent) {
+ load = cpu_rq(cpu)->load.weight;
+ } else {
+ load = tg->parent->cfs_rq[cpu]->h_load;
+ load *= tg->se[cpu]->load.weight;
+ load /= tg->parent->cfs_rq[cpu]->load.weight + 1;
+ }
+
+ tg->cfs_rq[cpu]->h_load = load;
+
+ return 0;
+}
+
+static void update_h_load(long cpu)
+{
+ walk_tg_tree(tg_load_down, tg_nop, (void *)cpu);
+}
+
static unsigned long
load_balance_fair(struct rq *this_rq, int this_cpu, struct rq *busiest,
unsigned long max_load_move,
@@ -2244,14 +2276,12 @@
int *all_pinned)
{
long rem_load_move = max_load_move;
- int busiest_cpu = cpu_of(busiest);
- struct task_group *tg;
+ struct cfs_rq *busiest_cfs_rq;
rcu_read_lock();
- update_h_load(busiest_cpu);
+ update_h_load(cpu_of(busiest));
- list_for_each_entry_rcu(tg, &task_groups, list) {
- struct cfs_rq *busiest_cfs_rq = tg->cfs_rq[busiest_cpu];
+ for_each_leaf_cfs_rq(busiest, busiest_cfs_rq) {
unsigned long busiest_h_load = busiest_cfs_rq->h_load;
unsigned long busiest_weight = busiest_cfs_rq->load.weight;
u64 rem_load, moved_load;
