* [PATCH 1/5] sched: Rename init_rq_hrtick to hrtick_rq_init
2017-12-21 17:14 [PATCH 0/5] isolation: 1Hz residual tick offloading v2 Frederic Weisbecker
@ 2017-12-21 17:14 ` Frederic Weisbecker
2017-12-21 17:14 ` [PATCH 2/5] sched/isolation: Add scheduler tick offloading interface Frederic Weisbecker
` (3 subsequent siblings)
4 siblings, 0 replies; 6+ messages in thread
From: Frederic Weisbecker @ 2017-12-21 17:14 UTC (permalink / raw)
To: LKML
Cc: Frederic Weisbecker, Peter Zijlstra, Chris Metcalf,
Thomas Gleixner, Luiz Capitulino, Christoph Lameter,
Paul E . McKenney, Ingo Molnar, Wanpeng Li, Mike Galbraith,
Rik van Riel
Do that rename in order to normalize the hrtick namespace.
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Cc: Chris Metcalf <cmetcalf@mellanox.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Luiz Capitulino <lcapitulino@redhat.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Wanpeng Li <kernellwp@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
---
kernel/sched/core.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 644fa2e..d72d0e9 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -333,7 +333,7 @@ void hrtick_start(struct rq *rq, u64 delay)
}
#endif /* CONFIG_SMP */
-static void init_rq_hrtick(struct rq *rq)
+static void hrtick_rq_init(struct rq *rq)
{
#ifdef CONFIG_SMP
rq->hrtick_csd_pending = 0;
@@ -351,7 +351,7 @@ static inline void hrtick_clear(struct rq *rq)
{
}
-static inline void init_rq_hrtick(struct rq *rq)
+static inline void hrtick_rq_init(struct rq *rq)
{
}
#endif /* CONFIG_SCHED_HRTICK */
@@ -5955,7 +5955,7 @@ void __init sched_init(void)
rq->last_sched_tick = 0;
#endif
#endif /* CONFIG_SMP */
- init_rq_hrtick(rq);
+ hrtick_rq_init(rq);
atomic_set(&rq->nr_iowait, 0);
}
--
2.7.4
^ permalink raw reply related [flat|nested] 6+ messages in thread* [PATCH 2/5] sched/isolation: Add scheduler tick offloading interface
2017-12-21 17:14 [PATCH 0/5] isolation: 1Hz residual tick offloading v2 Frederic Weisbecker
2017-12-21 17:14 ` [PATCH 1/5] sched: Rename init_rq_hrtick to hrtick_rq_init Frederic Weisbecker
@ 2017-12-21 17:14 ` Frederic Weisbecker
2017-12-21 17:14 ` [PATCH 3/5] nohz: Allow to check if remote CPU tick is stopped Frederic Weisbecker
` (2 subsequent siblings)
4 siblings, 0 replies; 6+ messages in thread
From: Frederic Weisbecker @ 2017-12-21 17:14 UTC (permalink / raw)
To: LKML
Cc: Frederic Weisbecker, Peter Zijlstra, Chris Metcalf,
Thomas Gleixner, Luiz Capitulino, Christoph Lameter,
Paul E . McKenney, Ingo Molnar, Wanpeng Li, Mike Galbraith,
Rik van Riel
Add the boot option that will allow us to offload the 1Hz scheduler tick
to the housekeeping CPU.
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Cc: Chris Metcalf <cmetcalf@mellanox.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Luiz Capitulino <lcapitulino@redhat.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Wanpeng Li <kernellwp@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
---
include/linux/sched/isolation.h | 3 ++-
kernel/sched/isolation.c | 6 ++++++
2 files changed, 8 insertions(+), 1 deletion(-)
diff --git a/include/linux/sched/isolation.h b/include/linux/sched/isolation.h
index d849431..c831855 100644
--- a/include/linux/sched/isolation.h
+++ b/include/linux/sched/isolation.h
@@ -11,7 +11,8 @@ enum hk_flags {
HK_FLAG_MISC = (1 << 2),
HK_FLAG_SCHED = (1 << 3),
HK_FLAG_TICK = (1 << 4),
- HK_FLAG_DOMAIN = (1 << 5),
+ HK_FLAG_TICK_SCHED = (1 << 5),
+ HK_FLAG_DOMAIN = (1 << 6),
};
#ifdef CONFIG_CPU_ISOLATION
diff --git a/kernel/sched/isolation.c b/kernel/sched/isolation.c
index b71b436..264ddcd 100644
--- a/kernel/sched/isolation.c
+++ b/kernel/sched/isolation.c
@@ -136,6 +136,12 @@ static int __init housekeeping_isolcpus_setup(char *str)
continue;
}
+ if (!strncmp(str, "nohz_offload,", 13)) {
+ str += 13;
+ flags |= HK_FLAG_TICK | HK_FLAG_TICK_SCHED;
+ continue;
+ }
+
if (!strncmp(str, "domain,", 7)) {
str += 7;
flags |= HK_FLAG_DOMAIN;
--
2.7.4
^ permalink raw reply related [flat|nested] 6+ messages in thread* [PATCH 3/5] nohz: Allow to check if remote CPU tick is stopped
2017-12-21 17:14 [PATCH 0/5] isolation: 1Hz residual tick offloading v2 Frederic Weisbecker
2017-12-21 17:14 ` [PATCH 1/5] sched: Rename init_rq_hrtick to hrtick_rq_init Frederic Weisbecker
2017-12-21 17:14 ` [PATCH 2/5] sched/isolation: Add scheduler tick offloading interface Frederic Weisbecker
@ 2017-12-21 17:14 ` Frederic Weisbecker
2017-12-21 17:14 ` [PATCH 4/5] sched/isolation: Residual 1Hz scheduler tick offload Frederic Weisbecker
2017-12-21 17:14 ` [PATCH 5/5] sched/isolation: Document "nohz_offload" flag Frederic Weisbecker
4 siblings, 0 replies; 6+ messages in thread
From: Frederic Weisbecker @ 2017-12-21 17:14 UTC (permalink / raw)
To: LKML
Cc: Frederic Weisbecker, Peter Zijlstra, Chris Metcalf,
Thomas Gleixner, Luiz Capitulino, Christoph Lameter,
Paul E . McKenney, Ingo Molnar, Wanpeng Li, Mike Galbraith,
Rik van Riel
This check is racy but provides a good heuristic to determine whether
a CPU may need a remote tick or not.
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Cc: Chris Metcalf <cmetcalf@mellanox.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Luiz Capitulino <lcapitulino@redhat.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Wanpeng Li <kernellwp@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
---
include/linux/tick.h | 2 ++
kernel/time/tick-sched.c | 7 +++++++
2 files changed, 9 insertions(+)
diff --git a/include/linux/tick.h b/include/linux/tick.h
index f442d1a..417f8d2 100644
--- a/include/linux/tick.h
+++ b/include/linux/tick.h
@@ -114,6 +114,7 @@ enum tick_dep_bits {
#ifdef CONFIG_NO_HZ_COMMON
extern bool tick_nohz_enabled;
extern int tick_nohz_tick_stopped(void);
+extern int tick_nohz_tick_stopped_cpu(int cpu);
extern void tick_nohz_idle_enter(void);
extern void tick_nohz_idle_exit(void);
extern void tick_nohz_irq_exit(void);
@@ -124,6 +125,7 @@ extern u64 get_cpu_iowait_time_us(int cpu, u64 *last_update_time);
#else /* !CONFIG_NO_HZ_COMMON */
#define tick_nohz_enabled (0)
static inline int tick_nohz_tick_stopped(void) { return 0; }
+static inline int tick_nohz_tick_stopped_cpu(int cpu) { return 0; }
static inline void tick_nohz_idle_enter(void) { }
static inline void tick_nohz_idle_exit(void) { }
diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index 99578f0..ad07d6e 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -486,6 +486,13 @@ int tick_nohz_tick_stopped(void)
return __this_cpu_read(tick_cpu_sched.tick_stopped);
}
+int tick_nohz_tick_stopped_cpu(int cpu)
+{
+ struct tick_sched *ts = per_cpu_ptr(&tick_cpu_sched, cpu);
+
+ return ts->tick_stopped;
+}
+
/**
* tick_nohz_update_jiffies - update jiffies when idle was interrupted
*
--
2.7.4
^ permalink raw reply related [flat|nested] 6+ messages in thread* [PATCH 4/5] sched/isolation: Residual 1Hz scheduler tick offload
2017-12-21 17:14 [PATCH 0/5] isolation: 1Hz residual tick offloading v2 Frederic Weisbecker
` (2 preceding siblings ...)
2017-12-21 17:14 ` [PATCH 3/5] nohz: Allow to check if remote CPU tick is stopped Frederic Weisbecker
@ 2017-12-21 17:14 ` Frederic Weisbecker
2017-12-21 17:14 ` [PATCH 5/5] sched/isolation: Document "nohz_offload" flag Frederic Weisbecker
4 siblings, 0 replies; 6+ messages in thread
From: Frederic Weisbecker @ 2017-12-21 17:14 UTC (permalink / raw)
To: LKML
Cc: Frederic Weisbecker, Peter Zijlstra, Chris Metcalf,
Thomas Gleixner, Luiz Capitulino, Christoph Lameter,
Paul E . McKenney, Ingo Molnar, Wanpeng Li, Mike Galbraith,
Rik van Riel
When a CPU runs in full dynticks mode, a 1Hz tick remains in order to
keep the scheduler stats alive. However this residual tick is a burden
for bare metal tasks that can't stand no interruption at all, or want
to minimize them.
Adding the boot parameter "isolcpus=nohz_offload" will now outsource
these scheduler ticks to the global workqueue so that a housekeeping CPU
handles that tick remotely.
Note it's still up to the user to affine the global workqueues to the
housekeeping CPUs through /sys/devices/virtual/workqueue/cpumask or
domains isolation.
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Cc: Chris Metcalf <cmetcalf@mellanox.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Luiz Capitulino <lcapitulino@redhat.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Wanpeng Li <kernellwp@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
---
kernel/sched/core.c | 89 ++++++++++++++++++++++++++++++++++++++++++++++--
kernel/sched/isolation.c | 4 +++
kernel/sched/sched.h | 2 ++
3 files changed, 92 insertions(+), 3 deletions(-)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index d72d0e9..a12008c 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -3052,9 +3052,14 @@ void scheduler_tick(void)
*/
u64 scheduler_tick_max_deferment(void)
{
- struct rq *rq = this_rq();
- unsigned long next, now = READ_ONCE(jiffies);
+ struct rq *rq;
+ unsigned long next, now;
+ if (!housekeeping_cpu(smp_processor_id(), HK_FLAG_TICK_SCHED))
+ return ktime_to_ns(KTIME_MAX);
+
+ rq = this_rq();
+ now = READ_ONCE(jiffies);
next = rq->last_sched_tick + HZ;
if (time_before_eq(next, now))
@@ -3062,7 +3067,83 @@ u64 scheduler_tick_max_deferment(void)
return jiffies_to_nsecs(next - now);
}
-#endif
+
+struct tick_work {
+ int cpu;
+ struct delayed_work work;
+};
+
+static struct tick_work __percpu *tick_work_cpu;
+
+static void sched_tick_remote(struct work_struct *work)
+{
+ struct delayed_work *dwork = to_delayed_work(work);
+ struct tick_work *twork = container_of(dwork, struct tick_work, work);
+ int cpu = twork->cpu;
+ struct rq *rq = cpu_rq(cpu);
+ struct rq_flags rf;
+
+ /*
+ * Handle the tick only if it appears the remote CPU is running
+ * in full dynticks mode. The check is racy by nature, but
+ * missing a tick or having one too much is no big deal.
+ */
+ if (!idle_cpu(cpu) && tick_nohz_tick_stopped_cpu(cpu)) {
+ rq_lock_irq(rq, &rf);
+ update_rq_clock(rq);
+ rq->curr->sched_class->task_tick(rq, rq->curr, 0);
+ rq_unlock_irq(rq, &rf);
+ }
+
+ queue_delayed_work(system_unbound_wq, dwork, HZ);
+}
+
+static void sched_tick_start(int cpu)
+{
+ struct tick_work *twork;
+
+ if (housekeeping_cpu(cpu, HK_FLAG_TICK_SCHED))
+ return;
+
+ WARN_ON_ONCE(!tick_work_cpu);
+
+ twork = per_cpu_ptr(tick_work_cpu, cpu);
+ twork->cpu = cpu;
+ INIT_DELAYED_WORK(&twork->work, sched_tick_remote);
+ queue_delayed_work(system_unbound_wq, &twork->work, HZ);
+
+ return;
+}
+
+#ifdef CONFIG_HOTPLUG_CPU
+static void sched_tick_stop(int cpu)
+{
+ struct tick_work *twork;
+
+ if (housekeeping_cpu(cpu, HK_FLAG_TICK_SCHED))
+ return;
+
+ WARN_ON_ONCE(!tick_work_cpu);
+
+ twork = per_cpu_ptr(tick_work_cpu, cpu);
+ cancel_delayed_work_sync(&twork->work);
+
+ return;
+}
+#endif /* CONFIG_HOTPLUG_CPU */
+
+int __init sched_tick_offload_init(void)
+{
+ tick_work_cpu = alloc_percpu(struct tick_work);
+ if (!tick_work_cpu) {
+ pr_err("Can't allocate remote tick struct\n");
+ return -ENOMEM;
+ }
+
+ return 0;
+}
+
+#endif /* CONFIG_NO_HZ_FULL */
#if defined(CONFIG_PREEMPT) && (defined(CONFIG_DEBUG_PREEMPT) || \
defined(CONFIG_PREEMPT_TRACER))
@@ -5713,6 +5794,7 @@ int sched_cpu_starting(unsigned int cpu)
{
set_cpu_rq_start_time(cpu);
sched_rq_cpu_starting(cpu);
+ sched_tick_start(cpu);
return 0;
}
@@ -5724,6 +5806,7 @@ int sched_cpu_dying(unsigned int cpu)
/* Handle pending wakeups and then migrate everything off */
sched_ttwu_pending();
+ sched_tick_stop(cpu);
rq_lock_irqsave(rq, &rf);
if (rq->rd) {
diff --git a/kernel/sched/isolation.c b/kernel/sched/isolation.c
index 264ddcd..c5e7e90a 100644
--- a/kernel/sched/isolation.c
+++ b/kernel/sched/isolation.c
@@ -12,6 +12,7 @@
#include <linux/kernel.h>
#include <linux/static_key.h>
#include <linux/ctype.h>
+#include "sched.h"
DEFINE_STATIC_KEY_FALSE(housekeeping_overriden);
EXPORT_SYMBOL_GPL(housekeeping_overriden);
@@ -60,6 +61,9 @@ void __init housekeeping_init(void)
static_branch_enable(&housekeeping_overriden);
+ if (housekeeping_flags & HK_FLAG_TICK_SCHED)
+ sched_tick_offload_init();
+
/* We need at least one CPU to handle housekeeping work */
WARN_ON_ONCE(cpumask_empty(housekeeping_mask));
}
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index b19552a2..5a3b82c 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1587,6 +1587,7 @@ extern void post_init_entity_util_avg(struct sched_entity *se);
#ifdef CONFIG_NO_HZ_FULL
extern bool sched_can_stop_tick(struct rq *rq);
+extern int __init sched_tick_offload_init(void);
/*
* Tick may be needed by tasks in the runqueue depending on their policy and
@@ -1611,6 +1612,7 @@ static inline void sched_update_tick_dependency(struct rq *rq)
tick_nohz_dep_set_cpu(cpu, TICK_DEP_BIT_SCHED);
}
#else
+static inline int sched_tick_offload_init(void) { return 0; }
static inline void sched_update_tick_dependency(struct rq *rq) { }
#endif
--
2.7.4
^ permalink raw reply related [flat|nested] 6+ messages in thread* [PATCH 5/5] sched/isolation: Document "nohz_offload" flag
2017-12-21 17:14 [PATCH 0/5] isolation: 1Hz residual tick offloading v2 Frederic Weisbecker
` (3 preceding siblings ...)
2017-12-21 17:14 ` [PATCH 4/5] sched/isolation: Residual 1Hz scheduler tick offload Frederic Weisbecker
@ 2017-12-21 17:14 ` Frederic Weisbecker
4 siblings, 0 replies; 6+ messages in thread
From: Frederic Weisbecker @ 2017-12-21 17:14 UTC (permalink / raw)
To: LKML
Cc: Frederic Weisbecker, Peter Zijlstra, Chris Metcalf,
Thomas Gleixner, Luiz Capitulino, Christoph Lameter,
Paul E . McKenney, Ingo Molnar, Wanpeng Li, Mike Galbraith,
Rik van Riel
Document the interface to offload the 1Hz scheduler tick in full
dynticks mode. Also improve the comment about the existing "nohz" flag
in order to differentiate its behaviour.
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Cc: Chris Metcalf <cmetcalf@mellanox.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Luiz Capitulino <lcapitulino@redhat.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Wanpeng Li <kernellwp@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
---
Documentation/admin-guide/kernel-parameters.txt | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 1683107..fcc5fd9 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -1745,7 +1745,12 @@
specified in the flag list (default: domain):
nohz
- Disable the tick when a single task runs.
+ Disable the tick when a single task runs. A residual 1Hz
+ tick remains to maintain scheduler stats alive.
+ nohz_offload
+ Like nohz but the residual 1Hz tick is offloaded to
+ housekeeping CPUs, leaving the CPU free of any tick if
+ nothing else requests it.
domain
Isolate from the general SMP balancing and scheduling
algorithms. Note that performing domain isolation this way
--
2.7.4
^ permalink raw reply related [flat|nested] 6+ messages in thread