On 09/18/2015 03:34 AM, Dietmar Eggemann wrote:

quoted

Here should consider scenario for two groups have same capacity?
This will benefit for the case LITTLE.LITTLE. So the code will be
looks like below:

	int target_sg_cpu = INT_MAX;

	if (capacity_of(max_cap_cpu) <= target_max_cap &&
            task_fits_capacity(p, max_cap_cpu)) {

                if ((capacity_of(max_cap_cpu) == target_max_cap) &&
		    (target_sg_cpu < max_cap_cpu))
		        continue;

		target_sg_cpu = max_cap_cpu;
		sg_target = sg;
		target_max_cap = capacity_of(max_cap_cpu);
	}

It's true that on your SMP system the target sched_group 'sg_target'
depends only on 'task_cpu(p)' because this determines sched_domain 'sd'
(and so the order of sched_groups for the iteration).

So the current do-while loop to select 'sg_target' for an SMP system
makes little sense.

But why should we favour the first sched_group (cluster) (the one w/ the
lower max_cap_cpu number) in this situation?

Running the originally proposed code on a system with two identical
clusters, it looks like we'll always end up doing an energy-aware search
in the task's prev_cpu cluster (sched_group). If you had small tasks
scattered across both clusters, energy_aware_wake_cpu() would not
consider condensing them on a single cluster. Leo was this the issue you
were seeing?

However I think there may be negative side effects with the proposed
policy above as well - won't this cause us to pack the first cluster
until it's 100% full (running at fmax) before using the second cluster?
That would also be bad for power.

thanks,
Steve