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Subject[tip:sched/core] sched, rt: Update rq clock when unthrottling of an otherwise idle CPU
Commit-ID:  61eadef6a9bde9ea62fda724a9cb501ce9bc925a
Gitweb: http://git.kernel.org/tip/61eadef6a9bde9ea62fda724a9cb501ce9bc925a
Author: Mike Galbraith <efault@gmx.de>
AuthorDate: Fri, 29 Apr 2011 08:36:50 +0200
Committer: Ingo Molnar <mingo@elte.hu>
CommitDate: Mon, 16 May 2011 11:01:17 +0200

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>
---
kernel/sched.c | 6 +++---
kernel/sched_rt.c | 7 +++++++
2 files changed, 10 insertions(+), 3 deletions(-)

diff --git a/kernel/sched.c b/kernel/sched.c
index f9778c0..b8b9a7d 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -466,7 +466,7 @@ struct rq {
u64 nohz_stamp;
unsigned char nohz_balance_kick;
#endif
- unsigned int skip_clock_update;
+ int skip_clock_update;

/* capture load from *all* tasks on this cpu: */
struct load_weight load;
@@ -652,7 +652,7 @@ static void update_rq_clock(struct rq *rq)
{
s64 delta;

- if (rq->skip_clock_update)
+ if (rq->skip_clock_update > 0)
return;

delta = sched_clock_cpu(cpu_of(rq)) - rq->clock;
@@ -4127,7 +4127,7 @@ static inline void schedule_debug(struct task_struct *prev)

static void put_prev_task(struct rq *rq, struct task_struct *prev)
{
- if (prev->on_rq)
+ if (prev->on_rq || rq->skip_clock_update < 0)
update_rq_clock(rq);
prev->sched_class->put_prev_task(rq, prev);
}
diff --git a/kernel/sched_rt.c b/kernel/sched_rt.c
index 19ecb31..0943ed7 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;

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