[PATCH 30/33] sched: Debug nohz rq clock

From: Frederic Weisbecker
Date: Mon Jan 07 2013 - 21:09:39 EST

The runqueue clock is supposed to be periodically updated by the
tick. On full dynticks CPU we call update_nohz_rq_clock() before
reading it. Now the scheduler code is complicated enough that we
may miss some update_nohz_rq_clock() calls before reading the
runqueue clock.

This therefore introduce a new debugging feature that detects
when the rq clock is stale due to missing updates on full
dynticks CPUs.

This can be later expanded to debug stale clocks on dynticks-idle

Signed-off-by: Frederic Weisbecker <fweisbec@xxxxxxxxx>
Cc: Alessio Igor Bogani <abogani@xxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
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: Li Zhong <zhong@xxxxxxxxxxxxxxxxxx>
Cc: Namhyung Kim <namhyung.kim@xxxxxxx>
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/sched.h | 23 +++++++++++++++++++++++
1 files changed, 23 insertions(+), 0 deletions(-)

diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index e1bac76..0fef0b3 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -502,16 +502,39 @@ DECLARE_PER_CPU(struct rq, runqueues);
#define cpu_curr(cpu) (cpu_rq(cpu)->curr)
#define raw_rq() (&__raw_get_cpu_var(runqueues))

+static inline void rq_clock_check(struct rq *rq)
+#if defined(CONFIG_SCHED_DEBUG) && defined(CONFIG_NO_HZ_FULL)
+ unsigned long long clock;
+ unsigned long flags;
+ int cpu;
+ cpu = cpu_of(rq);
+ if (!tick_nohz_full_cpu(cpu) || rq->curr == rq->idle)
+ return;
+ local_irq_save(flags);
+ clock = sched_clock_cpu(cpu_of(rq));
+ local_irq_restore(flags);
+ if (abs(clock - rq->clock) > (TICK_NSEC * 3))
static inline u64 rq_clock(struct rq *rq)
+ rq_clock_check(rq);
return rq->clock;

static inline u64 rq_clock_task(struct rq *rq)
+ rq_clock_check(rq);
return rq->clock_task;


#define rcu_dereference_check_sched_domain(p) \

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