On 4 November 2014 11:42, Wanpeng Li [off-list ref] wrote:

Hi Vincent,

quoted

quoted

quoted

+
+/*
    * Group imbalance indicates (and tries to solve) the problem where
balancing
    * groups is inadequate due to tsk_cpus_allowed() constraints.
    *

@@ -6562,6 +6574,28 @@ static int need_active_balance(struct lb_env

*env)
                         return 1;
         }
   +     /*
+        * The dst_cpu is idle and the src_cpu CPU has only 1 CFS task.

Why specify one task instead of not less than one?

if cfs.h_nr_running == 0 (which should not occurs at that point), we
don't need to do more test to check if it's worth moving the task
because there is no task to move.

Sorry for my confusing statement. I mean cfs.h_nr_running >= 1.

ok.

If we have more than 1 task, we fall back into the default balancing
policy than should move a not running task or that will use the
imbalance field in case of the presence of pinned tasks

Regards,
Vincent

Regards,
Wanpeng Li

quoted

Regards,
Vincent

quoted

Regards,
Wanpeng Li

quoted

+        * It's worth migrating the task if the src_cpu's capacity is
reduced
+        * because of other sched_class or IRQs whereas capacity stays
+        * available on dst_cpu.
+        */
+       if ((env->idle != CPU_NOT_IDLE) &&
+                       (env->src_rq->cfs.h_nr_running == 1)) {
+               unsigned long src_eff_capacity, dst_eff_capacity;
+
+               dst_eff_capacity = 100;
+               dst_eff_capacity *= capacity_of(env->dst_cpu);
+               dst_eff_capacity *= capacity_orig_of(env->src_cpu);
+
+               src_eff_capacity = sd->imbalance_pct;
+               src_eff_capacity *= capacity_of(env->src_cpu);
+               src_eff_capacity *= capacity_orig_of(env->dst_cpu);
+
+               if (src_eff_capacity < dst_eff_capacity)
+                       return 1;
+       }
+