linux-kernel - [PATCH 12/24] sched: Update rq clock on nohz CPU before migrating tasks

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Message-Id: <1356028391-14427-13-git-send-email-fweisbec@gmail.com>
Date:	Thu, 20 Dec 2012 19:32:59 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	LKML <linux-kernel@...r.kernel.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>,
	Geoff Levand <geoff@...radead.org>,
	Gilad Ben Yossef <gilad@...yossef.com>,
	Hakan Akkan <hakanakkan@...il.com>,
	Ingo Molnar <mingo@...nel.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Paul Gortmaker <paul.gortmaker@...driver.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: [PATCH 12/24] sched: Update rq clock on nohz CPU before migrating tasks

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@...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: 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: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
Cc: Paul Gortmaker <paul.gortmaker@...driver.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Steven Rostedt <rostedt@...dmis.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
---
 kernel/sched/core.c  |    6 ++++++
 kernel/sched/sched.h |    7 +++++++
 2 files changed, 13 insertions(+), 0 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 02bd005..5d9060a 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -4832,6 +4832,12 @@ 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 5eca173..db3d4df 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -3,6 +3,7 @@
 #include <linux/mutex.h>
 #include <linux/spinlock.h>
 #include <linux/stop_machine.h>
+#include <linux/tick.h>
 
 #include "cpupri.h"
 
@@ -951,6 +952,12 @@ 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 (tick_nohz_full_cpu(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);
 
-- 
1.7.5.4

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