FROMLIST: sched/fair: Set rq->rd->overload when misfit

Idle balance is a great opportunity to pull a misfit task. However,
there are scenarios where misfit tasks are present but idle balance is
prevented by the overload flag.

A good example of this is a workload of n identical tasks. Let's suppose
we have a 2+2 Arm big.LITTLE system. We then spawn 4 fairly
CPU-intensive tasks - for the sake of simplicity let's say they are just
CPU hogs, even when running on big CPUs.

They are identical tasks, so on an SMP system they should all end at
(roughly) the same time. However, in our case the LITTLE CPUs are less
performing than the big CPUs, so tasks running on the LITTLEs will have
a longer completion time.

This means that the big CPUs will complete their work earlier, at which
point they should pull the tasks from the LITTLEs. What we want to
happen is summarized as follows:

a,b,c,d are our CPU-hogging tasks
_ signifies idling

LITTLE_0 | a a a a _ _
LITTLE_1 | b b b b _ _
---------|-------------
  big_0  | c c c c a a
  big_1  | d d d d b b
		  ^
		  ^
    Tasks end on the big CPUs, idle balance happens
    and the misfit tasks are pulled straight away

This however won't happen, because currently the overload flag is only
set when there is any CPU that has more than one runnable task - which
may very well not be the case here if our CPU-hogging workload is all
there is to run.

As such, this commit sets the overload flag in update_sg_lb_stats when
a group is flagged as having a misfit task.

cc: Ingo Molnar <mingo@redhat.com>
cc: Peter Zijlstra <peterz@infradead.org>

Change-Id: I131f9ad90f7fb53f4946f61f2fb65ab0798f23c5
Signed-off-by: Valentin Schneider <valentin.schneider@arm.com>
[from https://lore.kernel.org/lkml/1530699470-29808-10-git-send-email-morten.rasmussen@arm.com/

]
Signed-off-by: Valentin Schneider <valentin.schneider@arm.com>
Signed-off-by: Chris Redpath <chris.redpath@arm.com>
Git-commit: 96a2daab
Git-repo: https://android.googlesource.com/kernel/common/


Signed-off-by: Puja Gupta <pujag@codeaurora.org>