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

From: Frederic Weisbecker
Date: Thu Dec 20 2012 - 13:40:14 EST

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@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 ++++++
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);


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