linux-kernel - [PATCH 29/41] sched: Comment on rq->clock correctness in ttwu_do

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Date:	Tue,  1 May 2012 01:55:03 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	LKML <linux-kernel@...r.kernel.org>,
	linaro-sched-sig@...ts.linaro.org
Cc:	Frederic Weisbecker <fweisbec@...il.com>,
	Alessio Igor Bogani <abogani@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Avi Kivity <avi@...hat.com>,
	Chris Metcalf <cmetcalf@...era.com>,
	Christoph Lameter <cl@...ux.com>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Geoff Levand <geoff@...radead.org>,
	Gilad Ben Yossef <gilad@...yossef.com>,
	Hakan Akkan <hakanakkan@...il.com>,
	Ingo Molnar <mingo@...nel.org>, Kevin Hilman <khilman@...com>,
	Max Krasnyansky <maxk@...lcomm.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Stephen Hemminger <shemminger@...tta.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Sven-Thorsten Dietrich <thebigcorporation@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: [PATCH 29/41] sched: Comment on rq->clock correctness in ttwu_do_wakeup() in nohz

Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>
Cc: Alessio Igor Bogani <abogani@...nel.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Avi Kivity <avi@...hat.com>
Cc: Chris Metcalf <cmetcalf@...era.com>
Cc: Christoph Lameter <cl@...ux.com>
Cc: Daniel Lezcano <daniel.lezcano@...aro.org>
Cc: Geoff Levand <geoff@...radead.org>
Cc: Gilad Ben Yossef <gilad@...yossef.com>
Cc: Hakan Akkan <hakanakkan@...il.com>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: Kevin Hilman <khilman@...com>
Cc: Max Krasnyansky <maxk@...lcomm.com>
Cc: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Stephen Hemminger <shemminger@...tta.com>
Cc: Steven Rostedt <rostedt@...dmis.org>
Cc: Sven-Thorsten Dietrich <thebigcorporation@...il.com>
Cc: Thomas Gleixner <tglx@...utronix.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

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