[PATCH 29/41] sched: Comment on rq->clock correctness in ttwu_do_wakeup() in nohz

[Frederic Weisbecker]

Signed-off-by: Frederic Weisbecker <fweisbec at gmail.com>
Cc: Alessio Igor Bogani <abogani at kernel.org>
Cc: Andrew Morton <akpm at linux-foundation.org>
Cc: Avi Kivity <avi at redhat.com>
Cc: Chris Metcalf <cmetcalf at tilera.com>
Cc: Christoph Lameter <cl at linux.com>
Cc: Daniel Lezcano <daniel.lezcano at linaro.org>
Cc: Geoff Levand <geoff at infradead.org>
Cc: Gilad Ben Yossef <gilad at benyossef.com>
Cc: Hakan Akkan <hakanakkan at gmail.com>
Cc: Ingo Molnar <mingo at kernel.org>
Cc: Kevin Hilman <khilman at ti.com>
Cc: Max Krasnyansky <maxk at qualcomm.com>
Cc: Paul E. McKenney <paulmck at linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz at infradead.org>
Cc: Stephen Hemminger <shemminger at vyatta.com>
Cc: Steven Rostedt <rostedt at goodmis.org>
Cc: Sven-Thorsten Dietrich <thebigcorporation at gmail.com>
Cc: Thomas Gleixner <tglx at linutronix.de>
---
 kernel/sched/core.c |    6 ++++++
 1 files changed, 6 insertions(+), 0 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 5debfd7..d24da6b 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1430,6 +1430,12 @@ ttwu_do_wakeup(struct rq *rq, struct task_struct *p, int wake_flags)
 	if (p->sched_class->task_woken)
 		p->sched_class->task_woken(rq, p);
 
+	/*
+	 * For adaptive nohz case: We called ttwu_activate()
+	 * which just updated the rq clock. There is an
+	 * exception with p->on_rq != 0 but in this case
+	 * we are not idle and rq->idle_stamp == 0
+	 */
 	if (rq->idle_stamp) {
 		u64 delta = rq->clock - rq->idle_stamp;
 		u64 max = 2*sysctl_sched_migration_cost;
-- 
1.7.5.4