sched: Fix clear NOHZ_BALANCE_KICK

I have faced a sequence where the Idle Load Balance was sometime
not
triggered for a while on my platform, in the following scenario:

CPU 0 and CPU 1 are running tasks and CPU 2 is idle

 CPU 1 kicks the
Idle Load Balance
 CPU 1 selects CPU 2 as the new Idle Load Balancer

CPU 2 sets NOHZ_BALANCE_KICK for CPU 2
 CPU 2 sends a reschedule IPI to
CPU 2

 While CPU 3 wakes up, CPU 0 or CPU 1 migrates a waking up task A
on CPU 2

 CPU 2 finally wakes up, runs task A and discards the Idle
Load Balance
       task A quickly goes back to sleep (before a tick
occurs on CPU 2)
 CPU 2 goes back to idle with NOHZ_BALANCE_KICK
set

Whenever CPU 2 will be selected as the ILB, no reschedule IPI will
be sent
because NOHZ_BALANCE_KICK is already set and no Idle Load
Balance will be
performed.

We must wait for the sched softirq to be
raised on CPU 2 thanks to another
part the kernel to come back to clear
NOHZ_BALANCE_KICK.

The proposed solution clears NOHZ_BALANCE_KICK in
schedule_ipi if
we can't raise the sched_softirq for the Idle Load
Balance.

Change since V1:

- move the clear of NOHZ_BALANCE_KICK in
got_nohz_idle_kick if the ILB
  can't run on this CPU (as suggested by
Peter)

Signed-off-by: Vincent Guittot
<vincent.guittot@linaro.org>
Signed-off-by: Peter Zijlstra
<peterz@infradead.org>
Link:
http://lkml.kernel.org/r/1370419991-13870-1-git-send-email-vincent.guittot@linaro.org
Signed-off-by:
Ingo Molnar <mingo@kernel.org>
Git-commit: 873b4c6
Git-repo:
git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
[smuckle@codeaurora.org:
minor merge resolution for 3.4 in scheduler_ipi()]
Signed-off-by: Steve
Muckle <smuckle@codeaurora.org>
Change-Id:
I3548612057cccc2ecc29429c129c44183083831f

idea is taken here -
https://github.com/jrior001/android_kernel_samsung_d2/commit/51c8bddb6812c3162a3115fb22f01b2a798d8754