On 29 May 2014 16:02, Peter Zijlstra [off-list ref] wrote:

On Fri, May 23, 2014 at 05:53:05PM +0200, Vincent Guittot wrote:

quoted

@@ -6052,8 +6006,8 @@ static inline void update_sd_lb_stats(struct lb_env *env, struct sd_lb_stats *sd
               * with a large weight task outweighs the tasks on the system).
               */
              if (prefer_sibling && sds->local &&
-                 sds->local_stat.group_has_capacity)
-                     sgs->group_capacity = min(sgs->group_capacity, 1U);
+                 sds->local_stat.group_capacity > 0)
+                     sgs->group_capacity = min(sgs->group_capacity, 1L);

              if (update_sd_pick_busiest(env, sds, sg, sgs)) {
                      sds->busiest = sg;

@@ -6228,7 +6182,7 @@ static inline void calculate_imbalance(struct lb_env *env, struct sd_lb_stats *s
               * have to drop below capacity to reach cpu-load equilibrium.
               */
              load_above_capacity =
-                     (busiest->sum_nr_running - busiest->group_capacity);
+                     (busiest->sum_nr_running - busiest->group_weight);

              load_above_capacity *= (SCHED_LOAD_SCALE * SCHED_POWER_SCALE);
              load_above_capacity /= busiest->group_power;

I think you just broke PREFER_SIBLING here..

you mean by replacing the capacity which was reflecting the number of
core for SMT by the group_weight ?

So we want PREFER_SIBLING to work on nr_running, not utilization because
we want to spread single tasks around, regardless of their utilization.