[GIT PULL v2] dynticks updates for 3.14

[GIT PULL v2] dynticks updates for 3.14

[Frederic Weisbecker]

Ingo,

Please pull the timers/core-v2 branch that can be found at:

git://git.kernel.org/pub/scm/linux/kernel/git/frederic/linux-dynticks.git
	timers/core-v2

It's a rebase of the previous pull request against 3.13-rc2 which addresses
your reviews:

* Fix build error with tick_check_nohz() off case

* Refine changelog of "posix-timers: Fix full dynticks CPUs kick on timer rescheduling"
  to make it clearer that it's a bug fix and not just an optimization.
  Also add more overall details in the changelog about the description of the issue.

* Rename tick_check_nohz() and tick_check_oneshot_broadcast() to extend with *_this_cpu()
  suffix. Note that I left functions that use *_idle_* based naming as is because idle
  itself is a per cpu notion already. Now I can still extend these functions as well
  in a delta if you want, although IMHO I fear that would uglify the code more than helping.

---
Here is a summary of the overall changes against tip:timers/core :

* Optimizations and cleanups on the use of per CPU APIs to improve code readability,
performance and debuggability in the nohz subsystem;

* Rename some functions to extend with *_this_cpu() suffix for clarity

* Refine the naming of some context tracking subsystem state accessors

* Optimize posix cpu timer by sparing stub workqueue queue with full dynticks off case

* Trivial spelling fix by Paul Gortmaker

* Fix a bug where posix cpu timers requeued due to interval got ignored on full
  dynticks CPUs (not a regression though as it only impacts full dynticks and the
  bug is there since we merged full dynticks).


Let me know if you find any issue.

Thanks,
	Frederic
---

Frederic Weisbecker (5):
      nohz: Convert a few places to use local per cpu accesses
      context_tracking: Wrap static key check into more intuitive function name
      context_tracking: Rename context_tracking_active() to context_tracking_cpu_is_enabled()
      posix-timers: Spare workqueue if there is no full dynticks CPU to kick
      posix-timers: Fix full dynticks CPUs kick on timer rescheduling

Paul Gortmaker (1):
      trivial: fix spelling in CONTEXT_TRACKING_FORCE help text


 include/linux/context_tracking.h       | 10 ++++-----
 include/linux/context_tracking_state.h | 11 +++++++---
 include/linux/tick.h                   |  8 +++----
 include/linux/vtime.h                  |  4 ++--
 init/Kconfig                           |  2 +-
 kernel/context_tracking.c              |  8 +++----
 kernel/posix-cpu-timers.c              | 21 ++++++++----------
 kernel/softirq.c                       |  4 +---
 kernel/time/tick-broadcast.c           |  6 +++---
 kernel/time/tick-internal.h            |  4 ++--
 kernel/time/tick-sched.c               | 39 ++++++++++++++--------------------
 11 files changed, 55 insertions(+), 62 deletions(-)

[PATCH 1/6] nohz: Convert a few places to use local per cpu accesses

[Frederic Weisbecker]

A few functions use remote per CPU access APIs when they
deal with local values.

Just do the right conversion to improve performance, code
readability and debug checks.

While at it, lets extend some of these function names with *_this_cpu()
suffix in order to display their purpose more clearly.

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
---
 include/linux/tick.h         |  6 +++---
 kernel/softirq.c             |  4 +---
 kernel/time/tick-broadcast.c |  6 +++---
 kernel/time/tick-internal.h  |  4 ++--
 kernel/time/tick-sched.c     | 39 ++++++++++++++++-----------------------
 5 files changed, 25 insertions(+), 34 deletions(-)

diff --git a/include/linux/tick.h b/include/linux/tick.h
index 5128d33..a004f66 100644
--- a/include/linux/tick.h
+++ b/include/linux/tick.h
@@ -104,7 +104,7 @@ extern struct cpumask *tick_get_broadcast_oneshot_mask(void);
 extern void tick_clock_notify(void);
 extern int tick_check_oneshot_change(int allow_nohz);
 extern struct tick_sched *tick_get_tick_sched(int cpu);
-extern void tick_check_idle(int cpu);
+extern void tick_check_idle(void);
 extern int tick_oneshot_mode_active(void);
 #  ifndef arch_needs_cpu
 #   define arch_needs_cpu(cpu) (0)
@@ -112,7 +112,7 @@ extern int tick_oneshot_mode_active(void);
 # else
 static inline void tick_clock_notify(void) { }
 static inline int tick_check_oneshot_change(int allow_nohz) { return 0; }
-static inline void tick_check_idle(int cpu) { }
+static inline void tick_check_idle(void) { }
 static inline int tick_oneshot_mode_active(void) { return 0; }
 # endif
 
@@ -121,7 +121,7 @@ static inline void tick_init(void) { }
 static inline void tick_cancel_sched_timer(int cpu) { }
 static inline void tick_clock_notify(void) { }
 static inline int tick_check_oneshot_change(int allow_nohz) { return 0; }
-static inline void tick_check_idle(int cpu) { }
+static inline void tick_check_idle(void) { }
 static inline int tick_oneshot_mode_active(void) { return 0; }
 #endif /* !CONFIG_GENERIC_CLOCKEVENTS */
 
diff --git a/kernel/softirq.c b/kernel/softirq.c
index 11025cc..11348de 100644
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -311,8 +311,6 @@ asmlinkage void do_softirq(void)
  */
 void irq_enter(void)
 {
-	int cpu = smp_processor_id();
-
 	rcu_irq_enter();
 	if (is_idle_task(current) && !in_interrupt()) {
 		/*
@@ -320,7 +318,7 @@ void irq_enter(void)
 		 * here, as softirq will be serviced on return from interrupt.
 		 */
 		local_bh_disable();
-		tick_check_idle(cpu);
+		tick_check_idle();
 		_local_bh_enable();
 	}
 
diff --git a/kernel/time/tick-broadcast.c b/kernel/time/tick-broadcast.c
index 9532690..43780ab 100644
--- a/kernel/time/tick-broadcast.c
+++ b/kernel/time/tick-broadcast.c
@@ -538,10 +538,10 @@ int tick_resume_broadcast_oneshot(struct clock_event_device *bc)
  * Called from irq_enter() when idle was interrupted to reenable the
  * per cpu device.
  */
-void tick_check_oneshot_broadcast(int cpu)
+void tick_check_oneshot_broadcast_this_cpu(void)
 {
-	if (cpumask_test_cpu(cpu, tick_broadcast_oneshot_mask)) {
-		struct tick_device *td = &per_cpu(tick_cpu_device, cpu);
+	if (cpumask_test_cpu(smp_processor_id(), tick_broadcast_oneshot_mask)) {
+		struct tick_device *td = &__get_cpu_var(tick_cpu_device);
 
 		/*
 		 * We might be in the middle of switching over from
diff --git a/kernel/time/tick-internal.h b/kernel/time/tick-internal.h
index 18e71f7..e2bced5 100644
--- a/kernel/time/tick-internal.h
+++ b/kernel/time/tick-internal.h
@@ -51,7 +51,7 @@ extern void tick_broadcast_switch_to_oneshot(void);
 extern void tick_shutdown_broadcast_oneshot(unsigned int *cpup);
 extern int tick_resume_broadcast_oneshot(struct clock_event_device *bc);
 extern int tick_broadcast_oneshot_active(void);
-extern void tick_check_oneshot_broadcast(int cpu);
+extern void tick_check_oneshot_broadcast_this_cpu(void);
 bool tick_broadcast_oneshot_available(void);
 # else /* BROADCAST */
 static inline void tick_broadcast_setup_oneshot(struct clock_event_device *bc)
@@ -62,7 +62,7 @@ static inline void tick_broadcast_oneshot_control(unsigned long reason) { }
 static inline void tick_broadcast_switch_to_oneshot(void) { }
 static inline void tick_shutdown_broadcast_oneshot(unsigned int *cpup) { }
 static inline int tick_broadcast_oneshot_active(void) { return 0; }
-static inline void tick_check_oneshot_broadcast(int cpu) { }
+static inline void tick_check_oneshot_broadcast_this_cpu(void) { }
 static inline bool tick_broadcast_oneshot_available(void) { return true; }
 # endif /* !BROADCAST */
 
diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index 3612fc7..2afd43f 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -391,11 +391,9 @@ __setup("nohz=", setup_tick_nohz);
  */
 static void tick_nohz_update_jiffies(ktime_t now)
 {
-	int cpu = smp_processor_id();
-	struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
 	unsigned long flags;
 
-	ts->idle_waketime = now;
+	__this_cpu_write(tick_cpu_sched.idle_waketime, now);
 
 	local_irq_save(flags);
 	tick_do_update_jiffies64(now);
@@ -426,17 +424,15 @@ update_ts_time_stats(int cpu, struct tick_sched *ts, ktime_t now, u64 *last_upda
 
 }
 
-static void tick_nohz_stop_idle(int cpu, ktime_t now)
+static void tick_nohz_stop_idle(struct tick_sched *ts, ktime_t now)
 {
-	struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
-
-	update_ts_time_stats(cpu, ts, now, NULL);
+	update_ts_time_stats(smp_processor_id(), ts, now, NULL);
 	ts->idle_active = 0;
 
 	sched_clock_idle_wakeup_event(0);
 }
 
-static ktime_t tick_nohz_start_idle(int cpu, struct tick_sched *ts)
+static ktime_t tick_nohz_start_idle(struct tick_sched *ts)
 {
 	ktime_t now = ktime_get();
 
@@ -752,7 +748,7 @@ static void __tick_nohz_idle_enter(struct tick_sched *ts)
 	ktime_t now, expires;
 	int cpu = smp_processor_id();
 
-	now = tick_nohz_start_idle(cpu, ts);
+	now = tick_nohz_start_idle(ts);
 
 	if (can_stop_idle_tick(cpu, ts)) {
 		int was_stopped = ts->tick_stopped;
@@ -914,8 +910,7 @@ static void tick_nohz_account_idle_ticks(struct tick_sched *ts)
  */
 void tick_nohz_idle_exit(void)
 {
-	int cpu = smp_processor_id();
-	struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
+	struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
 	ktime_t now;
 
 	local_irq_disable();
@@ -928,7 +923,7 @@ void tick_nohz_idle_exit(void)
 		now = ktime_get();
 
 	if (ts->idle_active)
-		tick_nohz_stop_idle(cpu, now);
+		tick_nohz_stop_idle(ts, now);
 
 	if (ts->tick_stopped) {
 		tick_nohz_restart_sched_tick(ts, now);
@@ -1012,12 +1007,10 @@ static void tick_nohz_switch_to_nohz(void)
  * timer and do not touch the other magic bits which need to be done
  * when idle is left.
  */
-static void tick_nohz_kick_tick(int cpu, ktime_t now)
+static void tick_nohz_kick_tick(struct tick_sched *ts, ktime_t now)
 {
 #if 0
 	/* Switch back to 2.6.27 behaviour */
-
-	struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
 	ktime_t delta;
 
 	/*
@@ -1032,36 +1025,36 @@ static void tick_nohz_kick_tick(int cpu, ktime_t now)
 #endif
 }
 
-static inline void tick_check_nohz(int cpu)
+static inline void tick_check_nohz_this_cpu(void)
 {
-	struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
+	struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
 	ktime_t now;
 
 	if (!ts->idle_active && !ts->tick_stopped)
 		return;
 	now = ktime_get();
 	if (ts->idle_active)
-		tick_nohz_stop_idle(cpu, now);
+		tick_nohz_stop_idle(ts, now);
 	if (ts->tick_stopped) {
 		tick_nohz_update_jiffies(now);
-		tick_nohz_kick_tick(cpu, now);
+		tick_nohz_kick_tick(ts, now);
 	}
 }
 
 #else
 
 static inline void tick_nohz_switch_to_nohz(void) { }
-static inline void tick_check_nohz(int cpu) { }
+static inline void tick_check_nohz_this_cpu(void) { }
 
 #endif /* CONFIG_NO_HZ_COMMON */
 
 /*
  * Called from irq_enter to notify about the possible interruption of idle()
  */
-void tick_check_idle(int cpu)
+void tick_check_idle(void)
 {
-	tick_check_oneshot_broadcast(cpu);
-	tick_check_nohz(cpu);
+	tick_check_oneshot_broadcast_this_cpu();
+	tick_check_nohz_this_cpu();
 }
 
 /*
-- 
1.8.3.1

[PATCH 2/6] trivial: fix spelling in CONTEXT_TRACKING_FORCE help text

[Frederic Weisbecker]

From: Paul Gortmaker <paul.gortmaker@windriver.com>

Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
---
 init/Kconfig | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/init/Kconfig b/init/Kconfig
index 79383d3..12d61f8 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -532,7 +532,7 @@ config CONTEXT_TRACKING_FORCE
 	  dynticks subsystem by forcing the context tracking on all
 	  CPUs in the system.
 
-	  Say Y only if you're working on the developpement of an
+	  Say Y only if you're working on the development of an
 	  architecture backend for the context tracking.
 
 	  Say N otherwise, this option brings an overhead that you
-- 
1.8.3.1

[PATCH 3/6] context_tracking: Wrap static key check into more intuitive function name

[Frederic Weisbecker]

Use a function with a meaningful name to check the global context
tracking state. static_key_false() is a bit confusing for reviewers.

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
---
 include/linux/context_tracking.h       | 10 +++++-----
 include/linux/context_tracking_state.h |  4 ++++
 include/linux/tick.h                   |  2 +-
 include/linux/vtime.h                  |  2 +-
 kernel/context_tracking.c              |  8 ++++----
 5 files changed, 15 insertions(+), 11 deletions(-)

diff --git a/include/linux/context_tracking.h b/include/linux/context_tracking.h
index 1581587..37b81bd 100644
--- a/include/linux/context_tracking.h
+++ b/include/linux/context_tracking.h
@@ -17,13 +17,13 @@ extern void __context_tracking_task_switch(struct task_struct *prev,
 
 static inline void user_enter(void)
 {
-	if (static_key_false(&context_tracking_enabled))
+	if (context_tracking_is_enabled())
 		context_tracking_user_enter();
 
 }
 static inline void user_exit(void)
 {
-	if (static_key_false(&context_tracking_enabled))
+	if (context_tracking_is_enabled())
 		context_tracking_user_exit();
 }
 
@@ -31,7 +31,7 @@ static inline enum ctx_state exception_enter(void)
 {
 	enum ctx_state prev_ctx;
 
-	if (!static_key_false(&context_tracking_enabled))
+	if (!context_tracking_is_enabled())
 		return 0;
 
 	prev_ctx = this_cpu_read(context_tracking.state);
@@ -42,7 +42,7 @@ static inline enum ctx_state exception_enter(void)
 
 static inline void exception_exit(enum ctx_state prev_ctx)
 {
-	if (static_key_false(&context_tracking_enabled)) {
+	if (context_tracking_is_enabled()) {
 		if (prev_ctx == IN_USER)
 			context_tracking_user_enter();
 	}
@@ -51,7 +51,7 @@ static inline void exception_exit(enum ctx_state prev_ctx)
 static inline void context_tracking_task_switch(struct task_struct *prev,
 						struct task_struct *next)
 {
-	if (static_key_false(&context_tracking_enabled))
+	if (context_tracking_is_enabled())
 		__context_tracking_task_switch(prev, next);
 }
 #else
diff --git a/include/linux/context_tracking_state.h b/include/linux/context_tracking_state.h
index 0f1979d..0db535b 100644
--- a/include/linux/context_tracking_state.h
+++ b/include/linux/context_tracking_state.h
@@ -22,6 +22,10 @@ struct context_tracking {
 extern struct static_key context_tracking_enabled;
 DECLARE_PER_CPU(struct context_tracking, context_tracking);
 
+static inline bool context_tracking_is_enabled(void)
+{
+	return static_key_false(&context_tracking_enabled);
+}
 static inline bool context_tracking_in_user(void)
 {
 	return __this_cpu_read(context_tracking.state) == IN_USER;
diff --git a/include/linux/tick.h b/include/linux/tick.h
index a004f66..0175d86 100644
--- a/include/linux/tick.h
+++ b/include/linux/tick.h
@@ -165,7 +165,7 @@ extern cpumask_var_t tick_nohz_full_mask;
 
 static inline bool tick_nohz_full_enabled(void)
 {
-	if (!static_key_false(&context_tracking_enabled))
+	if (!context_tracking_is_enabled())
 		return false;
 
 	return tick_nohz_full_running;
diff --git a/include/linux/vtime.h b/include/linux/vtime.h
index f5b72b3..807c732 100644
--- a/include/linux/vtime.h
+++ b/include/linux/vtime.h
@@ -19,7 +19,7 @@ static inline bool vtime_accounting_enabled(void) { return true; }
 #ifdef CONFIG_VIRT_CPU_ACCOUNTING_GEN
 static inline bool vtime_accounting_enabled(void)
 {
-	if (static_key_false(&context_tracking_enabled)) {
+	if (context_tracking_is_enabled()) {
 		if (context_tracking_active())
 			return true;
 	}
diff --git a/kernel/context_tracking.c b/kernel/context_tracking.c
index e5f3917..6cb20d2 100644
--- a/kernel/context_tracking.c
+++ b/kernel/context_tracking.c
@@ -53,10 +53,10 @@ void context_tracking_user_enter(void)
 	/*
 	 * Repeat the user_enter() check here because some archs may be calling
 	 * this from asm and if no CPU needs context tracking, they shouldn't
-	 * go further. Repeat the check here until they support the static key
-	 * check.
+	 * go further. Repeat the check here until they support the inline static
+	 * key check.
 	 */
-	if (!static_key_false(&context_tracking_enabled))
+	if (!context_tracking_is_enabled())
 		return;
 
 	/*
@@ -160,7 +160,7 @@ void context_tracking_user_exit(void)
 {
 	unsigned long flags;
 
-	if (!static_key_false(&context_tracking_enabled))
+	if (!context_tracking_is_enabled())
 		return;
 
 	if (in_interrupt())
-- 
1.8.3.1

[PATCH 4/6] context_tracking: Rename context_tracking_active() to context_tracking_cpu_is_enabled()

[Frederic Weisbecker]

We currently have a confusing couple of API naming with the existing
context_tracking_active() and context_tracking_is_enabled().

Lets keep the latter one, context_tracking_is_enabled(), for global
context tracking state check and use context_tracking_cpu_is_enabled()
for local state check.

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
---
 include/linux/context_tracking_state.h | 9 +++++----
 include/linux/vtime.h                  | 2 +-
 2 files changed, 6 insertions(+), 5 deletions(-)

diff --git a/include/linux/context_tracking_state.h b/include/linux/context_tracking_state.h
index 0db535b..97a8122 100644
--- a/include/linux/context_tracking_state.h
+++ b/include/linux/context_tracking_state.h
@@ -26,14 +26,15 @@ static inline bool context_tracking_is_enabled(void)
 {
 	return static_key_false(&context_tracking_enabled);
 }
-static inline bool context_tracking_in_user(void)
+
+static inline bool context_tracking_cpu_is_enabled(void)
 {
-	return __this_cpu_read(context_tracking.state) == IN_USER;
+	return __this_cpu_read(context_tracking.active);
 }
 
-static inline bool context_tracking_active(void)
+static inline bool context_tracking_in_user(void)
 {
-	return __this_cpu_read(context_tracking.active);
+	return __this_cpu_read(context_tracking.state) == IN_USER;
 }
 #else
 static inline bool context_tracking_in_user(void) { return false; }
diff --git a/include/linux/vtime.h b/include/linux/vtime.h
index 807c732..c5165fd 100644
--- a/include/linux/vtime.h
+++ b/include/linux/vtime.h
@@ -20,7 +20,7 @@ static inline bool vtime_accounting_enabled(void) { return true; }
 static inline bool vtime_accounting_enabled(void)
 {
 	if (context_tracking_is_enabled()) {
-		if (context_tracking_active())
+		if (context_tracking_cpu_is_enabled())
 			return true;
 	}
 
-- 
1.8.3.1

[PATCH 5/6] posix-timers: Spare workqueue if there is no full dynticks CPU to kick

[Frederic Weisbecker]

After a posix cpu timer is set, a workqueue is scheduled in order to
kick the full dynticks CPUs and let them restart their tick if
necessary in case the task they are running is concerned by the
new timer.

This kick is implemented by way of IPIs, which require interrupts
to be enabled, hence the need for a workqueue to raise them because
the posix cpu timer set path has interrupts disabled.

Now if there is no full dynticks CPU on the system, the workqueue is
still scheduled but it simply won't send any IPI and return immediately.

So lets spare that worqueue when it is not needed.

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
---
 kernel/posix-cpu-timers.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/posix-cpu-timers.c b/kernel/posix-cpu-timers.c
index c7f31aa..35509c5 100644
--- a/kernel/posix-cpu-timers.c
+++ b/kernel/posix-cpu-timers.c
@@ -608,7 +608,8 @@ static DECLARE_WORK(nohz_kick_work, nohz_kick_work_fn);
  */
 static void posix_cpu_timer_kick_nohz(void)
 {
-	schedule_work(&nohz_kick_work);
+	if (context_tracking_is_enabled())
+		schedule_work(&nohz_kick_work);
 }
 
 bool posix_cpu_timers_can_stop_tick(struct task_struct *tsk)
-- 
1.8.3.1

[PATCH 6/6] posix-timers: Fix full dynticks CPUs kick on timer rescheduling

[Frederic Weisbecker]

A posix CPU timer can be rearmed while it is firing or after it is
notified with a signal. This can happen for example with timers that
were set with a non zero interval in timer_settime().

This rearming can happen in two places:

1) On timer firing time, which happens on the target's tick. If the timer
can't trigger a signal because it is ignored, it reschedules itself
to honour the timer interval.

2) On signal handling from the timer's notification target. This one
can be a different task than the timer's target itself. Once the
signal is notified, the notification target rearms the timer, again
to honour the timer interval.

When a timer is rearmed, we need to notify the full dynticks CPUs
such that they restart their tick in case they are running tasks that
may have a share in elapsing this timer.

Now the 1st case above handles full dynticks CPUs with a call to
posix_cpu_timer_kick_nohz() from the posix cpu timer firing code. But
the second case ignores the fact that some CPUs may run non-idle tasks
with their tick off. As a result, when a timer is resheduled after its signal
notification, the full dynticks CPUs may completely ignore it and not
tick on the timer as expected

This patch fixes this bug by handling both cases in one. All we need
is to move the kick to the rearming common code in posix_cpu_timer_schedule().

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Olivier Langlois <olivier@olivierlanglois.net>
---
 kernel/posix-cpu-timers.c | 18 +++++++-----------
 1 file changed, 7 insertions(+), 11 deletions(-)

diff --git a/kernel/posix-cpu-timers.c b/kernel/posix-cpu-timers.c
index 35509c5..79747b7 100644
--- a/kernel/posix-cpu-timers.c
+++ b/kernel/posix-cpu-timers.c
@@ -1091,7 +1091,8 @@ void posix_cpu_timer_schedule(struct k_itimer *timer)
 			put_task_struct(p);
 			timer->it.cpu.task = p = NULL;
 			timer->it.cpu.expires = 0;
-			goto out_unlock;
+			read_unlock(&tasklist_lock);
+			goto out;
 		} else if (unlikely(p->exit_state) && thread_group_empty(p)) {
 			/*
 			 * We've noticed that the thread is dead, but
@@ -1100,7 +1101,8 @@ void posix_cpu_timer_schedule(struct k_itimer *timer)
 			 */
 			cpu_timer_sample_group(timer->it_clock, p, &now);
 			clear_dead_task(timer, now);
-			goto out_unlock;
+			read_unlock(&tasklist_lock);
+			goto out;
 		}
 		spin_lock(&p->sighand->siglock);
 		cpu_timer_sample_group(timer->it_clock, p, &now);
@@ -1114,10 +1116,11 @@ void posix_cpu_timer_schedule(struct k_itimer *timer)
 	BUG_ON(!irqs_disabled());
 	arm_timer(timer);
 	spin_unlock(&p->sighand->siglock);
-
-out_unlock:
 	read_unlock(&tasklist_lock);
 
+	/* Kick full dynticks CPUs in case they need to tick on the new timer */
+	posix_cpu_timer_kick_nohz();
+
 out:
 	timer->it_overrun_last = timer->it_overrun;
 	timer->it_overrun = -1;
@@ -1257,13 +1260,6 @@ void run_posix_cpu_timers(struct task_struct *tsk)
 			cpu_timer_fire(timer);
 		spin_unlock(&timer->it_lock);
 	}
-
-	/*
-	 * In case some timers were rescheduled after the queue got emptied,
-	 * wake up full dynticks CPUs.
-	 */
-	if (tsk->signal->cputimer.running)
-		posix_cpu_timer_kick_nohz();
 }
 
 /*
-- 
1.8.3.1

Re: [GIT PULL v2] dynticks updates for 3.14

[Ingo Molnar]

* Frederic Weisbecker <fweisbec@gmail.com> wrote:

> Ingo,
> 
> Please pull the timers/core-v2 branch that can be found at:
> 
> git://git.kernel.org/pub/scm/linux/kernel/git/frederic/linux-dynticks.git
> 	timers/core-v2
> 
> It's a rebase of the previous pull request against 3.13-rc2 which addresses
> your reviews:
> 
> * Fix build error with tick_check_nohz() off case
> 
> * Refine changelog of "posix-timers: Fix full dynticks CPUs kick on timer rescheduling"
>   to make it clearer that it's a bug fix and not just an optimization.
>   Also add more overall details in the changelog about the description of the issue.
> 
> * Rename tick_check_nohz() and tick_check_oneshot_broadcast() to extend with *_this_cpu()
>   suffix. Note that I left functions that use *_idle_* based naming as is because idle
>   itself is a per cpu notion already. Now I can still extend these functions as well
>   in a delta if you want, although IMHO I fear that would uglify the code more than helping.
> 
> ---
> Here is a summary of the overall changes against tip:timers/core :
> 
> * Optimizations and cleanups on the use of per CPU APIs to improve code readability,
> performance and debuggability in the nohz subsystem;
> 
> * Rename some functions to extend with *_this_cpu() suffix for clarity
> 
> * Refine the naming of some context tracking subsystem state accessors
> 
> * Optimize posix cpu timer by sparing stub workqueue queue with full dynticks off case
> 
> * Trivial spelling fix by Paul Gortmaker
> 
> * Fix a bug where posix cpu timers requeued due to interval got ignored on full
>   dynticks CPUs (not a regression though as it only impacts full dynticks and the
>   bug is there since we merged full dynticks).
> 
> 
> Let me know if you find any issue.
> 
> Thanks,
> 	Frederic
> ---
> 
> Frederic Weisbecker (5):
>       nohz: Convert a few places to use local per cpu accesses
>       context_tracking: Wrap static key check into more intuitive function name
>       context_tracking: Rename context_tracking_active() to context_tracking_cpu_is_enabled()
>       posix-timers: Spare workqueue if there is no full dynticks CPU to kick
>       posix-timers: Fix full dynticks CPUs kick on timer rescheduling
> 
> Paul Gortmaker (1):
>       trivial: fix spelling in CONTEXT_TRACKING_FORCE help text
> 
> 
>  include/linux/context_tracking.h       | 10 ++++-----
>  include/linux/context_tracking_state.h | 11 +++++++---
>  include/linux/tick.h                   |  8 +++----
>  include/linux/vtime.h                  |  4 ++--
>  init/Kconfig                           |  2 +-
>  kernel/context_tracking.c              |  8 +++----
>  kernel/posix-cpu-timers.c              | 21 ++++++++----------
>  kernel/softirq.c                       |  4 +---
>  kernel/time/tick-broadcast.c           |  6 +++---
>  kernel/time/tick-internal.h            |  4 ++--
>  kernel/time/tick-sched.c               | 39 ++++++++++++++--------------------
>  11 files changed, 55 insertions(+), 62 deletions(-)

Pulled into tip:timers/core, thanks a lot Frederic!

	Ingo