[PATCH 11/24] sched: Comment on rq->clock correctness in ttwu_do_wakeup() in nohz

From: Frederic Weisbecker
Date: Thu Dec 20 2012 - 13:34:02 EST

Just to avoid confusion.

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: Geoff Levand <geoff@xxxxxxxxxxxxx>
Cc: Gilad Ben Yossef <gilad@xxxxxxxxxxxxx>
Cc: Hakan Akkan <hakanakkan@xxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
Cc: Paul Gortmaker <paul.gortmaker@xxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
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 1ca0a66..02bd005 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1279,6 +1279,12 @@ 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;

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