When a runqueue is throttled we cannot disable the period timer
because that timer is the only way to undo the throttling.

We got stale throttling entries when a rq was throttled and then the
global sysctl was disabled, which stopped the timer.
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
[ Added changelog ]
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/n/tip-nuj34q52p6ro7szapuz84i0v@git.kernel.orgSigned-off-by: NIngo Molnar <mingo@elte.hu>