[PATCH 23/32] sched: Update rq clock on nohz CPU before migrating tasks

[Steven Rostedt]

From: Frederic Weisbecker <fweisbec@xxxxxxxxx>

Because the sched_class::put_prev_task() callback of rt and fair
classes are referring to the rq clock to update their runtime
statistics. A CPU running in tickless mode may carry a stale value.
We need to update it there.

Signed-off-by: Frederic Weisbecker <fweisbec@xxxxxxxxx>
Cc: Alessio Igor Bogani <abogani@xxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Avi Kivity <avi@xxxxxxxxxx>
Cc: Chris Metcalf <cmetcalf@xxxxxxxxxx>
Cc: Christoph Lameter <cl@xxxxxxxxx>
Cc: Daniel Lezcano <daniel.lezcano@xxxxxxxxxx>
Cc: Geoff Levand <geoff@xxxxxxxxxxxxx>
Cc: Gilad Ben Yossef <gilad@xxxxxxxxxxxxx>
Cc: Hakan Akkan <hakanakkan@xxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Kevin Hilman <khilman@xxxxxx>
Cc: Max Krasnyansky <maxk@xxxxxxxxxxxx>
Cc: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Stephen Hemminger <shemminger@xxxxxxxxxx>
Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
Cc: Sven-Thorsten Dietrich <thebigcorporation@xxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
---
 kernel/sched/core.c  |    6 ++++++
 kernel/sched/sched.h |    6 ++++++
 2 files changed, 12 insertions(+)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 783d5e4..f0fa54d 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -4851,6 +4851,12 @@ static void migrate_tasks(unsigned int dead_cpu)
 	 */
 	rq->stop = NULL;
 
+	/*
+	 * ->put_prev_task() need to have an up-to-date value
+	 * of rq->clock[_task]
+	 */
+	update_nohz_rq_clock(rq);
+
 	for ( ; ; ) {
 		/*
 		 * There's this thread running, bail when that's the only
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index c6cd9ec..1956494 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -948,6 +948,12 @@ static inline void dec_nr_running(struct rq *rq)
 
 extern void update_rq_clock(struct rq *rq);
 
+static inline void update_nohz_rq_clock(struct rq *rq)
+{
+	if (cpuset_cpu_adaptive_nohz(cpu_of(rq)))
+		update_rq_clock(rq);
+}
+
 extern void activate_task(struct rq *rq, struct task_struct *p, int flags);
 extern void deactivate_task(struct rq *rq, struct task_struct *p, int flags);
 
-- 
1.7.10.4


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