[GIT PULL v2] nohz: Posix cpu timers handling on full dynticks

[GIT PULL v2] nohz: Posix cpu timers handling on full dynticks

[Frederic Weisbecker]

Ingo,

Please pull this second version of the dynticks handling of posix cpu
timers from:

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

This fixes an issue with a race between run_posix_cpu_timers() and full
dynticks CPUs that we found while discussing a patch with Olivier Langlois.

As a bonus, it also provides the other side of posix cpu timers handling
in dynticks with the new helper to check before stopping the tick.

Thanks.

Frederic Weisbecker (3):
  nohz: New APIs to re-evaluate the tick on full dynticks CPUs
  posix_timers: Kick full dynticks CPUs when a posix cpu timer is armed
  posix_timers: New API to prevent from stopping the tick when timers
    are running

 include/linux/posix-timers.h |    2 +
 include/linux/tick.h         |    4 ++
 kernel/posix-cpu-timers.c    |   76 +++++++++++++++++++++++++++++++++---------
 kernel/time/Kconfig          |    1 +
 kernel/time/tick-sched.c     |   51 ++++++++++++++++++++++++++++
 5 files changed, 118 insertions(+), 16 deletions(-)

-- 
1.7.5.4

[PATCH 1/3] nohz: New APIs to re-evaluate the tick on full dynticks CPUs

[Frederic Weisbecker]

Provide two new helpers in order to notify the full dynticks CPUs about
some internal system changes against which they may reconsider the state
of their tick. Some practical examples include: posix cpu timers, perf tick
and sched clock tick.

For now the notifying handler, implemented through IPIs, is a stub
that will be implemented when we get the tick stop/restart infrastructure
in.

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Chris Metcalf <cmetcalf@tilera.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Geoff Levand <geoff@infradead.org>
Cc: Gilad Ben Yossef <gilad@benyossef.com>
Cc: Hakan Akkan <hakanakkan@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Kevin Hilman <khilman@linaro.org>
Cc: Li Zhong <zhong@linux.vnet.ibm.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Paul Gortmaker <paul.gortmaker@windriver.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
---
 include/linux/tick.h     |    4 +++
 kernel/time/Kconfig      |    1 +
 kernel/time/tick-sched.c |   51 ++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 56 insertions(+), 0 deletions(-)

diff --git a/include/linux/tick.h b/include/linux/tick.h
index b4e3b0c..c2dcfb1 100644
--- a/include/linux/tick.h
+++ b/include/linux/tick.h
@@ -159,8 +159,12 @@ static inline u64 get_cpu_iowait_time_us(int cpu, u64 *unused) { return -1; }
 
 #ifdef CONFIG_NO_HZ_FULL
 extern int tick_nohz_full_cpu(int cpu);
+extern void tick_nohz_full_kick(void);
+extern void tick_nohz_full_kick_all(void);
 #else
 static inline int tick_nohz_full_cpu(int cpu) { return 0; }
+static inline void tick_nohz_full_kick(void) { }
+static inline void tick_nohz_full_kick_all(void) { }
 #endif
 
 
diff --git a/kernel/time/Kconfig b/kernel/time/Kconfig
index 358d601..fbb4c7e 100644
--- a/kernel/time/Kconfig
+++ b/kernel/time/Kconfig
@@ -111,6 +111,7 @@ config NO_HZ_FULL
 	select RCU_USER_QS
 	select RCU_NOCB_CPU
 	select CONTEXT_TRACKING_FORCE
+	select IRQ_WORK
 	help
 	 Adaptively try to shutdown the tick whenever possible, even when
 	 the CPU is running tasks. Typically this requires running a single
diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index 369b576..2bcad5b 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -147,6 +147,57 @@ static void tick_sched_handle(struct tick_sched *ts, struct pt_regs *regs)
 static cpumask_var_t nohz_full_mask;
 bool have_nohz_full_mask;
 
+/*
+ * Re-evaluate the need for the tick on the current CPU
+ * and restart it if necessary.
+ */
+static void tick_nohz_full_check(void)
+{
+	/*
+	 * STUB for now, will be filled with the full tick stop/restart
+	 * infrastructure patches
+	 */
+}
+
+static void nohz_full_kick_work_func(struct irq_work *work)
+{
+	tick_nohz_full_check();
+}
+
+static DEFINE_PER_CPU(struct irq_work, nohz_full_kick_work) = {
+	.func = nohz_full_kick_work_func,
+};
+
+/*
+ * Kick the current CPU if it's full dynticks in order to force it to
+ * re-evaluate its dependency on the tick and restart it if necessary.
+ */
+void tick_nohz_full_kick(void)
+{
+	if (tick_nohz_full_cpu(smp_processor_id()))
+		irq_work_queue(&__get_cpu_var(nohz_full_kick_work));
+}
+
+static void nohz_full_kick_ipi(void *info)
+{
+	tick_nohz_full_check();
+}
+
+/*
+ * Kick all full dynticks CPUs in order to force these to re-evaluate
+ * their dependency on the tick and restart it if necessary.
+ */
+void tick_nohz_full_kick_all(void)
+{
+	if (!have_nohz_full_mask)
+		return;
+
+	preempt_disable();
+	smp_call_function_many(nohz_full_mask,
+			       nohz_full_kick_ipi, NULL, false);
+	preempt_enable();
+}
+
 int tick_nohz_full_cpu(int cpu)
 {
 	if (!have_nohz_full_mask)
-- 
1.7.5.4

[PATCH 2/3] posix_timers: Kick full dynticks CPUs when a posix cpu timer is armed

[Frederic Weisbecker]

Kick the full dynticks CPUs when a posix cpu timer is enqueued by
way of a standard call to posix_cpu_timer_set() or set_process_cpu_timer().
This also include rescheduled firing timers.

This way they can re-evaluate the state of (and possibly restart) their
tick against the new expiry modification.

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Chris Metcalf <cmetcalf@tilera.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Geoff Levand <geoff@infradead.org>
Cc: Gilad Ben Yossef <gilad@benyossef.com>
Cc: Hakan Akkan <hakanakkan@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Kevin Hilman <khilman@linaro.org>
Cc: Li Zhong <zhong@linux.vnet.ibm.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Paul Gortmaker <paul.gortmaker@windriver.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
---
 kernel/posix-cpu-timers.c |   35 ++++++++++++++++++++++++++++++++++-
 1 files changed, 34 insertions(+), 1 deletions(-)

diff --git a/kernel/posix-cpu-timers.c b/kernel/posix-cpu-timers.c
index 8fd709c..0bc3356 100644
--- a/kernel/posix-cpu-timers.c
+++ b/kernel/posix-cpu-timers.c
@@ -10,6 +10,8 @@
 #include <linux/kernel_stat.h>
 #include <trace/events/timer.h>
 #include <linux/random.h>
+#include <linux/tick.h>
+#include <linux/workqueue.h>
 
 /*
  * Called after updating RLIMIT_CPU to run cpu timer and update
@@ -636,6 +638,26 @@ static int cpu_timer_sample_group(const clockid_t which_clock,
 	return 0;
 }
 
+#ifdef CONFIG_NO_HZ_FULL
+static void nohz_kick_work_fn(struct work_struct *work)
+{
+	tick_nohz_full_kick_all();
+}
+
+static DECLARE_WORK(nohz_kick_work, nohz_kick_work_fn);
+
+/*
+ * We need the IPIs to be sent from sane process context.
+ * The posix cpu timers are always set with irqs disabled.
+ */
+static void posix_cpu_timer_kick_nohz(void)
+{
+	schedule_work(&nohz_kick_work);
+}
+#else
+static inline void posix_cpu_timer_kick_nohz(void) { }
+#endif
+
 /*
  * Guts of sys_timer_settime for CPU timers.
  * This is called with the timer locked and interrupts disabled.
@@ -794,6 +816,8 @@ static int posix_cpu_timer_set(struct k_itimer *timer, int flags,
 		sample_to_timespec(timer->it_clock,
 				   old_incr, &old->it_interval);
 	}
+	if (!ret)
+		posix_cpu_timer_kick_nohz();
 	return ret;
 }
 
@@ -1336,6 +1360,13 @@ 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();
 }
 
 /*
@@ -1366,7 +1397,7 @@ void set_process_cpu_timer(struct task_struct *tsk, unsigned int clock_idx,
 		}
 
 		if (!*newval)
-			return;
+			goto out;
 		*newval += now.cpu;
 	}
 
@@ -1384,6 +1415,8 @@ void set_process_cpu_timer(struct task_struct *tsk, unsigned int clock_idx,
 			tsk->signal->cputime_expires.virt_exp = *newval;
 		break;
 	}
+out:
+	posix_cpu_timer_kick_nohz();
 }
 
 static int do_cpu_nanosleep(const clockid_t which_clock, int flags,
-- 
1.7.5.4

[PATCH 3/3] posix_timers: New API to prevent from stopping the tick when timers are running

[Frederic Weisbecker]

Bring a new helper that the full dynticks infrastructure can
call in order to know if it can safely stop the tick from
the posix cpu timers subsystem point of view.

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Chris Metcalf <cmetcalf@tilera.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Geoff Levand <geoff@infradead.org>
Cc: Gilad Ben Yossef <gilad@benyossef.com>
Cc: Hakan Akkan <hakanakkan@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Kevin Hilman <khilman@linaro.org>
Cc: Li Zhong <zhong@linux.vnet.ibm.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Paul Gortmaker <paul.gortmaker@windriver.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
---
 include/linux/posix-timers.h |    2 ++
 kernel/posix-cpu-timers.c    |   41 ++++++++++++++++++++++++++---------------
 2 files changed, 28 insertions(+), 15 deletions(-)

diff --git a/include/linux/posix-timers.h b/include/linux/posix-timers.h
index 042058f..3698d9d 100644
--- a/include/linux/posix-timers.h
+++ b/include/linux/posix-timers.h
@@ -122,6 +122,8 @@ void run_posix_cpu_timers(struct task_struct *task);
 void posix_cpu_timers_exit(struct task_struct *task);
 void posix_cpu_timers_exit_group(struct task_struct *task);
 
+bool posix_cpu_timers_can_stop_tick(struct task_struct *tsk);
+
 void set_process_cpu_timer(struct task_struct *task, unsigned int clock_idx,
 			   cputime_t *newval, cputime_t *oldval);
 
diff --git a/kernel/posix-cpu-timers.c b/kernel/posix-cpu-timers.c
index 0bc3356..84d5cb3 100644
--- a/kernel/posix-cpu-timers.c
+++ b/kernel/posix-cpu-timers.c
@@ -155,6 +155,21 @@ static void bump_cpu_timer(struct k_itimer *timer,
 	}
 }
 
+/**
+ * task_cputime_zero - Check a task_cputime struct for all zero fields.
+ *
+ * @cputime:	The struct to compare.
+ *
+ * Checks @cputime to see if all fields are zero.  Returns true if all fields
+ * are zero, false if any field is nonzero.
+ */
+static inline int task_cputime_zero(const struct task_cputime *cputime)
+{
+	if (!cputime->utime && !cputime->stime && !cputime->sum_exec_runtime)
+		return 1;
+	return 0;
+}
+
 static inline cputime_t prof_ticks(struct task_struct *p)
 {
 	cputime_t utime, stime;
@@ -654,6 +669,17 @@ static void posix_cpu_timer_kick_nohz(void)
 {
 	schedule_work(&nohz_kick_work);
 }
+
+bool posix_cpu_timers_can_stop_tick(struct task_struct *tsk)
+{
+	if (!task_cputime_zero(&tsk->cputime_expires))
+		return true;
+
+	if (tsk->signal->cputimer.running)
+		return true;
+
+	return false;
+}
 #else
 static inline void posix_cpu_timer_kick_nohz(void) { }
 #endif
@@ -1032,21 +1058,6 @@ static void check_cpu_itimer(struct task_struct *tsk, struct cpu_itimer *it,
 	}
 }
 
-/**
- * task_cputime_zero - Check a task_cputime struct for all zero fields.
- *
- * @cputime:	The struct to compare.
- *
- * Checks @cputime to see if all fields are zero.  Returns true if all fields
- * are zero, false if any field is nonzero.
- */
-static inline int task_cputime_zero(const struct task_cputime *cputime)
-{
-	if (!cputime->utime && !cputime->stime && !cputime->sum_exec_runtime)
-		return 1;
-	return 0;
-}
-
 /*
  * Check for any per-thread CPU timers that have fired and move them
  * off the tsk->*_timers list onto the firing list.  Per-thread timers
-- 
1.7.5.4

Re: [GIT PULL v2] nohz: Posix cpu timers handling on full dynticks

[Ingo Molnar]

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

> Ingo,
> 
> Please pull this second version of the dynticks handling of posix cpu
> timers from:
> 
> git://git.kernel.org/pub/scm/linux/kernel/git/frederic/linux-dynticks.git
> 	timers/nohz-posix-timers-v2
> 
> This fixes an issue with a race between run_posix_cpu_timers() and full
> dynticks CPUs that we found while discussing a patch with Olivier Langlois.
> 
> As a bonus, it also provides the other side of posix cpu timers handling
> in dynticks with the new helper to check before stopping the tick.
> 
> Thanks.
> 
> Frederic Weisbecker (3):
>   nohz: New APIs to re-evaluate the tick on full dynticks CPUs
>   posix_timers: Kick full dynticks CPUs when a posix cpu timer is armed
>   posix_timers: New API to prevent from stopping the tick when timers
>     are running
> 
>  include/linux/posix-timers.h |    2 +
>  include/linux/tick.h         |    4 ++
>  kernel/posix-cpu-timers.c    |   76 +++++++++++++++++++++++++++++++++---------
>  kernel/time/Kconfig          |    1 +
>  kernel/time/tick-sched.c     |   51 ++++++++++++++++++++++++++++
>  5 files changed, 118 insertions(+), 16 deletions(-)

Pulled, thanks Frederic!

	Ingo