[GIT PULL] nohz: Bunch of fixes

[GIT PULL] nohz: Bunch of fixes

[Frederic Weisbecker]

Ingo,

Please pull the timers/nohz-hz1 branch that can be found at:

git://git.kernel.org/pub/scm/linux/kernel/git/frederic/linux-dynticks.git
	timers/nohz-hz1

HEAD: a7f4d69bb1d5e1f573b680355a2ad51566338887

It fixes a Kconfig dependency issue and forces a minimum of 1 tick every seconds
to keep handling the scheduler_tick() duties, even at a very low granularity. This
is a workaround until we can handle all these duties through on-demand driven
solutions rather than using periodic events, as per your suggestion.

I just noted two things:

* update_cpu_load_active() seem to rely on the fixed periodic tick at the
  HZ rate. There is certainly something to tweak there to make it really correct
  with dynamick ticks. I have the feeling that modifying pending_updates won't work
  as it seems to decay assuming the time to catch up was idle.

* I'll probably have to disable CONFIG_CFS_BANDWIDTH when full dynticks
  is enabled. First of all it modifies rq->nr_running without using inc/dec_nr_running
  standard API, which is required for full dynticks. And second, I need to triple
  check it's safe to use with 1 tick per second.

Ah and please note the merge commit (c032862fba51a3ca504752d3a25186b324c5ce83)
that was needed to get latest RCU and sched updates for the Kconfig fix.

Thanks,
	Frederic
---

Frederic Weisbecker (2):
      rcu: Fix full dynticks' dependency on wide RCU nocb mode
      sched: Keep at least 1 tick per second for active dynticks tasks


 include/linux/sched.h    |    1 +
 init/Kconfig             |    4 ++--
 kernel/sched/core.c      |   30 ++++++++++++++++++++++++++++++
 kernel/sched/idle_task.c |    1 +
 kernel/sched/sched.h     |   10 ++++++++++
 kernel/time/Kconfig      |    1 -
 kernel/time/tick-sched.c |    7 +++++++
 7 files changed, 51 insertions(+), 3 deletions(-)

[PATCH 1/2] rcu: Fix full dynticks' dependency on wide RCU nocb mode

[Frederic Weisbecker]

Commit 0637e029392386e6996f5d6574aadccee8315efa
("nohz: Select wide RCU nocb for full dynticks") intended
to force CONFIG_RCU_NOCB_CPU_ALL=y when full dynticks is
enabled.

However this option is part of a choice menu and Kconfig's
"select" instruction has no effect on such targets.

Fix this by using reverse dependencies on the targets we
don't want instead.

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Christoph Lameter <cl@linux.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: 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>
---
 init/Kconfig        |    4 ++--
 kernel/time/Kconfig |    1 -
 2 files changed, 2 insertions(+), 3 deletions(-)

diff --git a/init/Kconfig b/init/Kconfig
index 66f67af..b3fdf9a 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -687,7 +687,7 @@ choice
 
 config RCU_NOCB_CPU_NONE
 	bool "No build_forced no-CBs CPUs"
-	depends on RCU_NOCB_CPU
+	depends on RCU_NOCB_CPU && !NO_HZ_FULL
 	help
 	  This option does not force any of the CPUs to be no-CBs CPUs.
 	  Only CPUs designated by the rcu_nocbs= boot parameter will be
@@ -695,7 +695,7 @@ config RCU_NOCB_CPU_NONE
 
 config RCU_NOCB_CPU_ZERO
 	bool "CPU 0 is a build_forced no-CBs CPU"
-	depends on RCU_NOCB_CPU
+	depends on RCU_NOCB_CPU && !NO_HZ_FULL
 	help
 	  This option forces CPU 0 to be a no-CBs CPU.  Additional CPUs
 	  may be designated as no-CBs CPUs using the rcu_nocbs= boot
diff --git a/kernel/time/Kconfig b/kernel/time/Kconfig
index a2ddd65..e4c07b0 100644
--- a/kernel/time/Kconfig
+++ b/kernel/time/Kconfig
@@ -109,7 +109,6 @@ config NO_HZ_FULL
 	select NO_HZ_COMMON
 	select RCU_USER_QS
 	select RCU_NOCB_CPU
-	select RCU_NOCB_CPU_ALL
 	select VIRT_CPU_ACCOUNTING_GEN
 	select CONTEXT_TRACKING_FORCE
 	select IRQ_WORK
-- 
1.7.5.4

[PATCH 2/2] sched: Keep at least 1 tick per second for active dynticks tasks

[Frederic Weisbecker]

The scheduler doesn't yet fully support environments
with a single task running without a periodic tick.

In order to ensure we still maintain the duties of scheduler_tick(),
keep at least 1 tick per second.

This makes sure that we keep the progression of various scheduler
accounting and background maintainance even with a very low granularity.
Examples include cpu load, sched average, CFS entity vruntime,
avenrun and events such as load balancing, amongst other details
handled in sched_class::task_tick().

This limitation will be removed in the future once we get
these individual items to work in full dynticks CPUs.

Suggested-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Christoph Lameter <cl@linux.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: 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/sched.h    |    1 +
 kernel/sched/core.c      |   30 ++++++++++++++++++++++++++++++
 kernel/sched/idle_task.c |    1 +
 kernel/sched/sched.h     |   10 ++++++++++
 kernel/time/tick-sched.c |    7 +++++++
 5 files changed, 49 insertions(+), 0 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index ebf7095..af008d7 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1862,6 +1862,7 @@ static inline void wake_up_nohz_cpu(int cpu) { }
 
 #ifdef CONFIG_NO_HZ_FULL
 extern bool sched_can_stop_tick(void);
+extern u64 scheduler_tick_max_deferment(void);
 #else
 static inline bool sched_can_stop_tick(void) { return false; }
 #endif
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index e94842d..3bdf986 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2736,8 +2736,35 @@ void scheduler_tick(void)
 	rq->idle_balance = idle_cpu(cpu);
 	trigger_load_balance(rq, cpu);
 #endif
+	rq_last_tick_reset(rq);
 }
 
+#ifdef CONFIG_NO_HZ_FULL
+/**
+ * scheduler_tick_max_deferment
+ *
+ * Keep at least one tick per second when a single
+ * active task is running because the scheduler doesn't
+ * yet completely support full dynticks environment.
+ *
+ * This makes sure that uptime, CFS vruntime, load
+ * balancing, etc... continue to move forward, even
+ * with a very low granularity.
+ */
+u64 scheduler_tick_max_deferment(void)
+{
+	struct rq *rq = this_rq();
+	unsigned long next, now = ACCESS_ONCE(jiffies);
+
+	next = rq->last_sched_tick + HZ;
+
+	if (time_before_eq(next, now))
+		return 0;
+
+	return jiffies_to_usecs(next - now) * NSEC_PER_USEC;
+}
+#endif
+
 notrace unsigned long get_parent_ip(unsigned long addr)
 {
 	if (in_lock_functions(addr)) {
@@ -6993,6 +7020,9 @@ void __init sched_init(void)
 #ifdef CONFIG_NO_HZ_COMMON
 		rq->nohz_flags = 0;
 #endif
+#ifdef CONFIG_NO_HZ_FULL
+		rq->last_sched_tick = 0;
+#endif
 #endif
 		init_rq_hrtick(rq);
 		atomic_set(&rq->nr_iowait, 0);
diff --git a/kernel/sched/idle_task.c b/kernel/sched/idle_task.c
index b8ce773..d8da010 100644
--- a/kernel/sched/idle_task.c
+++ b/kernel/sched/idle_task.c
@@ -17,6 +17,7 @@ select_task_rq_idle(struct task_struct *p, int sd_flag, int flags)
 static void pre_schedule_idle(struct rq *rq, struct task_struct *prev)
 {
 	idle_exit_fair(rq);
+	rq_last_tick_reset(rq);
 }
 
 static void post_schedule_idle(struct rq *rq)
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 24dc298..ce39224 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -410,6 +410,9 @@ struct rq {
 	u64 nohz_stamp;
 	unsigned long nohz_flags;
 #endif
+#ifdef CONFIG_NO_HZ_FULL
+	unsigned long last_sched_tick;
+#endif
 	int skip_clock_update;
 
 	/* capture load from *all* tasks on this cpu: */
@@ -1090,6 +1093,13 @@ static inline void dec_nr_running(struct rq *rq)
 	rq->nr_running--;
 }
 
+static inline void rq_last_tick_reset(struct rq *rq)
+{
+#ifdef CONFIG_NO_HZ_FULL
+	rq->last_sched_tick = jiffies;
+#endif
+}
+
 extern void update_rq_clock(struct rq *rq);
 
 extern void activate_task(struct rq *rq, struct task_struct *p, int flags);
diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index 1c9f53b..07929c6 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -600,6 +600,13 @@ static ktime_t tick_nohz_stop_sched_tick(struct tick_sched *ts,
 			time_delta = KTIME_MAX;
 		}
 
+#ifdef CONFIG_NO_HZ_FULL
+		if (!ts->inidle) {
+			time_delta = min(time_delta,
+					 scheduler_tick_max_deferment());
+		}
+#endif
+
 		/*
 		 * calculate the expiry time for the next timer wheel
 		 * timer. delta_jiffies >= NEXT_TIMER_MAX_DELTA signals
-- 
1.7.5.4

Re: [PATCH 1/2] rcu: Fix full dynticks' dependency on wide RCU nocb mode

[Paul E. McKenney]

On Fri, May 03, 2013 at 06:47:55PM +0200, Frederic Weisbecker wrote:
> Commit 0637e029392386e6996f5d6574aadccee8315efa
> ("nohz: Select wide RCU nocb for full dynticks") intended
> to force CONFIG_RCU_NOCB_CPU_ALL=y when full dynticks is
> enabled.
> 
> However this option is part of a choice menu and Kconfig's
> "select" instruction has no effect on such targets.
> 
> Fix this by using reverse dependencies on the targets we
> don't want instead.
> 
> Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
> Cc: Christoph Lameter <cl@linux.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: 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>

Reviewed-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

> ---
>  init/Kconfig        |    4 ++--
>  kernel/time/Kconfig |    1 -
>  2 files changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/init/Kconfig b/init/Kconfig
> index 66f67af..b3fdf9a 100644
> --- a/init/Kconfig
> +++ b/init/Kconfig
> @@ -687,7 +687,7 @@ choice
> 
>  config RCU_NOCB_CPU_NONE
>  	bool "No build_forced no-CBs CPUs"
> -	depends on RCU_NOCB_CPU
> +	depends on RCU_NOCB_CPU && !NO_HZ_FULL
>  	help
>  	  This option does not force any of the CPUs to be no-CBs CPUs.
>  	  Only CPUs designated by the rcu_nocbs= boot parameter will be
> @@ -695,7 +695,7 @@ config RCU_NOCB_CPU_NONE
> 
>  config RCU_NOCB_CPU_ZERO
>  	bool "CPU 0 is a build_forced no-CBs CPU"
> -	depends on RCU_NOCB_CPU
> +	depends on RCU_NOCB_CPU && !NO_HZ_FULL
>  	help
>  	  This option forces CPU 0 to be a no-CBs CPU.  Additional CPUs
>  	  may be designated as no-CBs CPUs using the rcu_nocbs= boot
> diff --git a/kernel/time/Kconfig b/kernel/time/Kconfig
> index a2ddd65..e4c07b0 100644
> --- a/kernel/time/Kconfig
> +++ b/kernel/time/Kconfig
> @@ -109,7 +109,6 @@ config NO_HZ_FULL
>  	select NO_HZ_COMMON
>  	select RCU_USER_QS
>  	select RCU_NOCB_CPU
> -	select RCU_NOCB_CPU_ALL
>  	select VIRT_CPU_ACCOUNTING_GEN
>  	select CONTEXT_TRACKING_FORCE
>  	select IRQ_WORK
> -- 
> 1.7.5.4
> 

Re: [PATCH 1/2] rcu: Fix full dynticks' dependency on wide RCU nocb mode

[Frederic Weisbecker]

2013/5/3 Paul E. McKenney <paulmck@linux.vnet.ibm.com>:
> On Fri, May 03, 2013 at 06:47:55PM +0200, Frederic Weisbecker wrote:
>> Commit 0637e029392386e6996f5d6574aadccee8315efa
>> ("nohz: Select wide RCU nocb for full dynticks") intended
>> to force CONFIG_RCU_NOCB_CPU_ALL=y when full dynticks is
>> enabled.
>>
>> However this option is part of a choice menu and Kconfig's
>> "select" instruction has no effect on such targets.
>>
>> Fix this by using reverse dependencies on the targets we
>> don't want instead.
>>
>> Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
>> Cc: Christoph Lameter <cl@linux.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: 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>
>
> Reviewed-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

Nice!

Ingo, if you haven't yet pulled, please rather pick the
"timers/nohz-hz1-v2" branch that has the Reviewed-by: tag from Paul.

Thanks.

Re: [GIT PULL] nohz: Bunch of fixes

[Ingo Molnar]

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

> Ingo,
> 
> Please pull the timers/nohz-hz1 branch that can be found at:
> 
> git://git.kernel.org/pub/scm/linux/kernel/git/frederic/linux-dynticks.git
> 	timers/nohz-hz1
> 
> HEAD: a7f4d69bb1d5e1f573b680355a2ad51566338887
> 
> It fixes a Kconfig dependency issue and forces a minimum of 1 tick every seconds
> to keep handling the scheduler_tick() duties, even at a very low granularity. This
> is a workaround until we can handle all these duties through on-demand driven
> solutions rather than using periodic events, as per your suggestion.
> 
> I just noted two things:
> 
> * update_cpu_load_active() seem to rely on the fixed periodic tick at the
>   HZ rate. There is certainly something to tweak there to make it really correct
>   with dynamick ticks. I have the feeling that modifying pending_updates won't work
>   as it seems to decay assuming the time to catch up was idle.
> 
> * I'll probably have to disable CONFIG_CFS_BANDWIDTH when full dynticks
>   is enabled. First of all it modifies rq->nr_running without using inc/dec_nr_running
>   standard API, which is required for full dynticks. And second, I need to triple
>   check it's safe to use with 1 tick per second.
> 
> Ah and please note the merge commit (c032862fba51a3ca504752d3a25186b324c5ce83)
> that was needed to get latest RCU and sched updates for the Kconfig fix.
> 
> Thanks,
> 	Frederic
> ---
> 
> Frederic Weisbecker (2):
>       rcu: Fix full dynticks' dependency on wide RCU nocb mode
>       sched: Keep at least 1 tick per second for active dynticks tasks
> 
> 
>  include/linux/sched.h    |    1 +
>  init/Kconfig             |    4 ++--
>  kernel/sched/core.c      |   30 ++++++++++++++++++++++++++++++
>  kernel/sched/idle_task.c |    1 +
>  kernel/sched/sched.h     |   10 ++++++++++
>  kernel/time/Kconfig      |    1 -
>  kernel/time/tick-sched.c |    7 +++++++
>  7 files changed, 51 insertions(+), 3 deletions(-)

Pulled, thanks Frederic!

	Ingo