linux-kernel - [PATCH 34/41] sched: Update clock of nohz busiest rq before balancing

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Date:	Tue,  1 May 2012 01:55:08 +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 34/41] sched: Update clock of nohz busiest rq before balancing

move_tasks() and active_load_balance_cpu_stop() both need
to have the busiest rq clock uptodate because they may end
up calling can_migrate_task() that uses rq->clock_task
to determine if the task running in the busiest runqueue
is cache hot.

Hence if the busiest runqueue is tickless, update its clock
before reading it.

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/fair.c |   15 +++++++++++++++
 1 files changed, 15 insertions(+), 0 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 42a87d7..eff80e0 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -4455,6 +4455,7 @@ static int load_balance(int this_cpu, struct rq *this_rq,
 			int *balance)
 {
 	int ld_moved, lb_flags = 0, active_balance = 0;
+	int clock_updated;
 	struct sched_group *group;
 	unsigned long imbalance;
 	struct rq *busiest;
@@ -4488,6 +4489,7 @@ redo:
 	schedstat_add(sd, lb_imbalance[idle], imbalance);
 
 	ld_moved = 0;
+	clock_updated = 0;
 	if (busiest->nr_running > 1) {
 		/*
 		 * Attempt to move tasks. If find_busiest_group has found
@@ -4498,6 +4500,12 @@ redo:
 		lb_flags |= LBF_ALL_PINNED;
 		local_irq_save(flags);
 		double_rq_lock(this_rq, busiest);
+		/*
+		 * Move tasks may end up calling can_migrate_task() which
+		 * requires an uptodate value of the rq clock.
+		 */
+		update_nohz_rq_clock(busiest);
+		clock_updated = 1;
 		ld_moved = move_tasks(this_rq, this_cpu, busiest,
 				      imbalance, sd, idle, &lb_flags);
 		double_rq_unlock(this_rq, busiest);
@@ -4563,6 +4571,13 @@ redo:
 				busiest->active_balance = 1;
 				busiest->push_cpu = this_cpu;
 				active_balance = 1;
+				/*
+				 * active_load_balance_cpu_stop may end up calling
+				 * can_migrate_task() which requires an uptodate
+				 * value of the rq clock.
+				 */
+				if (!clock_updated)
+					update_nohz_rq_clock(busiest);
 			}
 			raw_spin_unlock_irqrestore(&busiest->lock, flags);
 
-- 
1.7.5.4

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