On 02/09/2018 11:05 PM, Rohit Jain wrote:


On 02/09/2018 07:46 AM, Dietmar Eggemann wrote:
On 02/09/2018 01:53 PM, Peter Zijlstra wrote:
On Mon, Jan 29, 2018 at 03:27:09PM -0800, Rohit Jain wrote:

[...]

@@ -6173,8 +6183,15 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, int t
              return -1;
          if (!cpumask_test_cpu(cpu, &p->cpus_allowed))
              continue;
+        if (idle_cpu(cpu)) {
+            if (full_capacity(cpu)) {
+                best_cpu = cpu;
+                break;
+            } else if (capacity_of(cpu) > best_cap) {
+                best_cap = capacity_of(cpu);
+                best_cpu = cpu;
+            }
+        }

No need for the else. And you'll note you're once again inconsistent
with your previous self.

But here I worry about big.little a wee bit. I think we're allowed big
and little cores on the same L3 these days, and you can't directly
compare capacity between them.

Morten / Dietmar, any comments?

Yes, for DynamIQ (big.little successor) systems, those cpus can have different capacity_orig_of() values already.


OK, given that there are asymmetric capacities in L3 cores, we would
probably have something like the below(?) in select_idle_cpu:

           if (!cpumask_test_cpu(cpu, &p->cpus_allowed))
               continue;
+        if (idle_cpu(cpu) && !reduced_capacity(cpu))
+            break;


Only returning the first idle cpu w/o reduced capacity will definitely work better here on future DynamIQ systems than trying to find the best_cap cpu by taking capacity_of() into consideration.

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