sched: fix MC/HT scheduler optimization, without breaking the FUZZ logic.

First fix the check
	if (*imbalance + SCHED_LOAD_SCALE_FUZZ < busiest_load_per_task)
with this
	if (*imbalance < busiest_load_per_task)

As the current check is always false for nice 0 tasks (as
SCHED_LOAD_SCALE_FUZZ is same as busiest_load_per_task for nice 0
tasks).

With the above change, imbalance was getting reset to 0 in the corner
case condition, making the FUZZ logic fail. Fix it by not corrupting the
imbalance and change the imbalance, only when it finds that the HT/MC
optimization is needed.

Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

diff --git a/kernel/sched.c b/kernel/sched.c
index b533d6d..c8759ec 100644 (file)
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -2512,7 +2512,7 @@ group_next:
         * a think about bumping its value to force at least one task to be
         * moved
         */
-       if (*imbalance + SCHED_LOAD_SCALE_FUZZ < busiest_load_per_task) {
+       if (*imbalance < busiest_load_per_task) {
                unsigned long tmp, pwr_now, pwr_move;
                unsigned int imbn;
 
@@ -2564,10 +2564,8 @@ small_imbalance:
                pwr_move /= SCHED_LOAD_SCALE;
 
                /* Move if we gain throughput */
-               if (pwr_move <= pwr_now)
-                       goto out_balanced;
-
-               *imbalance = busiest_load_per_task;
+               if (pwr_move > pwr_now)
+                       *imbalance = busiest_load_per_task;
        }
 
        return busiest;