sched, rt: Update rq clock when unthrottling of an otherwise idle CPU

If an RT task is awakened while it's rt_rq is throttled, the time between
wakeup/enqueue and unthrottle/selection may be accounted as rt_time
if the CPU is idle.  Set rq->skip_clock_update negative upon throttle
release to tell put_prev_task() that we need a clock update.

Reported-by: Thomas Giesel <skoe@directbox.com>
Signed-off-by: Mike Galbraith <efault@gmx.de>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1304059010.7472.1.camel@marge.simson.net
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 7 insertions, 0 deletions

diff --git a/kernel/sched_rt.c b/kernel/sched_rt.c
index 19ecb3127379..0943ed7a4038 100644
--- a/kernel/sched_rt.c
+++ b/kernel/sched_rt.c
@@ -562,6 +562,13 @@ static int do_sched_rt_period_timer(struct rt_bandwidth *rt_b, int overrun)
                         if (rt_rq->rt_throttled && rt_rq->rt_time < runtime) {
                                 rt_rq->rt_throttled = 0;
                                 enqueue = 1;
+
+                                /*
+                                 * Force a clock update if the CPU was idle,
+                                 * lest wakeup -> unthrottle time accumulate.
+                                 */
+                                if (rt_rq->rt_nr_running && rq->curr == rq->idle)
+                                        rq->skip_clock_update = -1;
                         }
                         if (rt_rq->rt_time || rt_rq->rt_nr_running)
                                 idle = 0;