sched: Weaken SD_POWERSAVINGS_BALANCE

One of the problems of power-saving balancing is that under certain
scenarios it is too slow and allows tons of real work to pile up.

Avoid this by ignoring the powersave stuff when there's real work
to be done.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 18 insertions, 3 deletions

diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index 09d19f77eb3a..eaa00014b499 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -1333,10 +1333,25 @@ static int select_task_rq_fair(struct task_struct *p, int flag, int sync)
 
         for_each_domain(cpu, tmp) {
                 /*
-                 * If power savings logic is enabled for a domain, stop there.
+                 * If power savings logic is enabled for a domain, see if we
+                 * are not overloaded, if so, don't balance wider.
                  */
-                if (tmp->flags & SD_POWERSAVINGS_BALANCE)
-                        break;
+                if (tmp->flags & SD_POWERSAVINGS_BALANCE) {
+                        unsigned long power = 0;
+                        unsigned long nr_running = 0;
+                        unsigned long capacity;
+                        int i;
+
+                        for_each_cpu(i, sched_domain_span(tmp)) {
+                                power += power_of(i);
+                                nr_running += cpu_rq(i)->cfs.nr_running;
+                        }
+
+                        capacity = DIV_ROUND_CLOSEST(power, SCHED_LOAD_SCALE);
+
+                        if (nr_running/2 < capacity)
+                                break;
+                }
 
                 switch (flag) {
                 case SD_BALANCE_WAKE: