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

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Date:	Tue,  8 Jan 2013 03:08:30 +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>,
	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>,
	Li Zhong <zhong@...ux.vnet.ibm.com>,
	Namhyung Kim <namhyung.kim@....com>,
	"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 30/33] sched: Debug nohz rq clock

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
CPUs.

Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>
Cc: Alessio Igor Bogani <abogani@...nel.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>
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: Li Zhong <zhong@...ux.vnet.ibm.com>
Cc: Namhyung Kim <namhyung.kim@....com>
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/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))
+		WARN_ON_ONCE(1);
+#endif
+}
+
 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;
 }
 
+
 #ifdef CONFIG_SMP
 
 #define rcu_dereference_check_sched_domain(p) \
-- 
1.7.5.4

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