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Subject[PATCH 10/32] nohz: Adaptive tick stop and restart on nohz cpuset
Date
When a CPU is included in a nohz cpuset, try to switch
it to nohz mode from the interrupt exit path if it is running
a single non-idle task.

Then restart the tick if necessary if we are enqueuing a
second task while the timer is stopped, so that the scheduler
tick is rearmed.

[TODO: Handle the many things done from scheduler_tick()]

[ Included build fix from Geoff Levand ]

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Alessio Igor Bogani <abogani@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Avi Kivity <avi@redhat.com>
Cc: Chris Metcalf <cmetcalf@tilera.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
Cc: Geoff Levand <geoff@infradead.org>
Cc: Gilad Ben Yossef <gilad@benyossef.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Max Krasnyansky <maxk@qualcomm.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephen Hemminger <shemminger@vyatta.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Sven-Thorsten Dietrich <thebigcorporation@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Zen Lin <zen@openhuawei.org>
---
arch/x86/kernel/smp.c | 2 +
include/linux/sched.h | 6 +++
include/linux/tick.h | 11 +++++-
init/Kconfig | 2 +-
kernel/sched/core.c | 22 ++++++++++++
kernel/sched/sched.h | 23 ++++++++++++
kernel/softirq.c | 6 ++-
kernel/time/tick-sched.c | 84 +++++++++++++++++++++++++++++++++++++++++----
8 files changed, 144 insertions(+), 12 deletions(-)

diff --git a/arch/x86/kernel/smp.c b/arch/x86/kernel/smp.c
index 94615a3..df83671 100644
--- a/arch/x86/kernel/smp.c
+++ b/arch/x86/kernel/smp.c
@@ -23,6 +23,7 @@
#include <linux/interrupt.h>
#include <linux/cpu.h>
#include <linux/gfp.h>
+#include <linux/tick.h>

#include <asm/mtrr.h>
#include <asm/tlbflush.h>
@@ -283,6 +284,7 @@ void smp_cpuset_update_nohz_interrupt(struct pt_regs *regs)
{
ack_APIC_irq();
irq_enter();
+ tick_nohz_check_adaptive();
inc_irq_stat(irq_call_count);
irq_exit();
}
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 0657368..dd5df2a 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -2746,6 +2746,12 @@ static inline void inc_syscw(struct task_struct *tsk)
#define TASK_SIZE_OF(tsk) TASK_SIZE
#endif

+#ifdef CONFIG_CPUSETS_NO_HZ
+extern bool sched_can_stop_tick(void);
+#else
+static inline bool sched_can_stop_tick(void) { return false; }
+#endif
+
#ifdef CONFIG_MM_OWNER
extern void mm_update_next_owner(struct mm_struct *mm);
extern void mm_init_owner(struct mm_struct *mm, struct task_struct *p);
diff --git a/include/linux/tick.h b/include/linux/tick.h
index f37fceb..9b66fd3 100644
--- a/include/linux/tick.h
+++ b/include/linux/tick.h
@@ -124,11 +124,12 @@ static inline int tick_oneshot_mode_active(void) { return 0; }
# ifdef CONFIG_NO_HZ
extern void tick_nohz_idle_enter(void);
extern void tick_nohz_idle_exit(void);
+extern void tick_nohz_restart_sched_tick(void);
extern void tick_nohz_irq_exit(void);
extern ktime_t tick_nohz_get_sleep_length(void);
extern u64 get_cpu_idle_time_us(int cpu, u64 *last_update_time);
extern u64 get_cpu_iowait_time_us(int cpu, u64 *last_update_time);
-# else
+# else /* !NO_HZ */
static inline void tick_nohz_idle_enter(void) { }
static inline void tick_nohz_idle_exit(void) { }

@@ -142,4 +143,12 @@ static inline u64 get_cpu_idle_time_us(int cpu, u64 *unused) { return -1; }
static inline u64 get_cpu_iowait_time_us(int cpu, u64 *unused) { return -1; }
# endif /* !NO_HZ */

+#ifdef CONFIG_CPUSETS_NO_HZ
+extern void tick_nohz_check_adaptive(void);
+extern void tick_nohz_post_schedule(void);
+#else /* !CPUSETS_NO_HZ */
+static inline void tick_nohz_check_adaptive(void) { }
+static inline void tick_nohz_post_schedule(void) { }
+#endif /* CPUSETS_NO_HZ */
+
#endif
diff --git a/init/Kconfig b/init/Kconfig
index 43f7687..7cdb8be 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -640,7 +640,7 @@ config PROC_PID_CPUSET

config CPUSETS_NO_HZ
bool "Tickless cpusets"
- depends on CPUSETS && HAVE_CPUSETS_NO_HZ
+ depends on CPUSETS && HAVE_CPUSETS_NO_HZ && NO_HZ && HIGH_RES_TIMERS
help
This options let you apply a nohz property to a cpuset such
that the periodic timer tick tries to be avoided when possible on
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index b342f57..4f80a81 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1323,6 +1323,27 @@ static void update_avg(u64 *avg, u64 sample)
}
#endif

+#ifdef CONFIG_CPUSETS_NO_HZ
+bool sched_can_stop_tick(void)
+{
+ struct rq *rq;
+
+ rq = this_rq();
+
+ /*
+ * Ensure nr_running updates are visible
+ * FIXME: the barrier is probably not enough to ensure
+ * the updates are visible right away.
+ */
+ smp_rmb();
+ /* More than one running task need preemption */
+ if (rq->nr_running > 1)
+ return false;
+
+ return true;
+}
+#endif
+
static void
ttwu_stat(struct task_struct *p, int cpu, int wake_flags)
{
@@ -2059,6 +2080,7 @@ context_switch(struct rq *rq, struct task_struct *prev,
* frame will be invalid.
*/
finish_task_switch(this_rq(), prev);
+ tick_nohz_post_schedule();
}

/*
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 98c0c26..b89f254 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1,6 +1,7 @@

#include <linux/sched.h>
#include <linux/mutex.h>
+#include <linux/cpuset.h>
#include <linux/spinlock.h>
#include <linux/stop_machine.h>

@@ -925,6 +926,28 @@ static inline void cpuacct_charge(struct task_struct *tsk, u64 cputime) {}
static inline void inc_nr_running(struct rq *rq)
{
rq->nr_running++;
+
+ if (rq->nr_running == 2) {
+ /*
+ * Make rq->nr_running update visible right away so that
+ * remote CPU knows that it must restart the tick.
+ * FIXME: This is probably not enough to ensure the update is visible
+ */
+ smp_wmb();
+ /*
+ * Make updates to cpu_adaptive_nohz_ref visible right now.
+ * If the CPU is not yet in a nohz cpuset then it will see
+ * the value on rq->nr_running later on the first time it
+ * tries to shutdown the tick. Otherwise we must send it
+ * it an IPI. But the ordering must be strict to ensure
+ * the first case.
+ * FIXME: That too is probably not enough to ensure the
+ * update is visible.
+ */
+ smp_rmb();
+ if (cpuset_cpu_adaptive_nohz(rq->cpu))
+ smp_cpuset_update_nohz(rq->cpu);
+ }
}

static inline void dec_nr_running(struct rq *rq)
diff --git a/kernel/softirq.c b/kernel/softirq.c
index 5ace266..1bacb20 100644
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -24,6 +24,7 @@
#include <linux/ftrace.h>
#include <linux/smp.h>
#include <linux/tick.h>
+#include <linux/cpuset.h>

#define CREATE_TRACE_POINTS
#include <trace/events/irq.h>
@@ -297,7 +298,8 @@ void irq_enter(void)
int cpu = smp_processor_id();

rcu_irq_enter();
- if (is_idle_task(current) && !in_interrupt()) {
+
+ if ((is_idle_task(current) || cpuset_adaptive_nohz()) && !in_interrupt()) {
/*
* Prevent raise_softirq from needlessly waking up ksoftirqd
* here, as softirq will be serviced on return from interrupt.
@@ -349,7 +351,7 @@ void irq_exit(void)

#ifdef CONFIG_NO_HZ
/* Make sure that timer wheel updates are propagated */
- if (idle_cpu(smp_processor_id()) && !in_interrupt() && !need_resched())
+ if (!in_interrupt())
tick_nohz_irq_exit();
#endif
rcu_irq_exit();
diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index f1142d5..43fa7ac 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -506,6 +506,24 @@ void tick_nohz_idle_enter(void)
local_irq_enable();
}

+static void tick_nohz_cpuset_stop_tick(struct tick_sched *ts)
+{
+#ifdef CONFIG_CPUSETS_NO_HZ
+ int cpu = smp_processor_id();
+
+ if (!cpuset_adaptive_nohz() || is_idle_task(current))
+ return;
+
+ if (!ts->tick_stopped && ts->nohz_mode == NOHZ_MODE_INACTIVE)
+ return;
+
+ if (!sched_can_stop_tick())
+ return;
+
+ tick_nohz_stop_sched_tick(ts, ktime_get(), cpu);
+#endif
+}
+
/**
* tick_nohz_irq_exit - update next tick event from interrupt exit
*
@@ -518,10 +536,12 @@ void tick_nohz_irq_exit(void)
{
struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);

- if (!ts->inidle)
- return;
-
- __tick_nohz_idle_enter(ts);
+ if (ts->inidle) {
+ if (!need_resched())
+ __tick_nohz_idle_enter(ts);
+ } else {
+ tick_nohz_cpuset_stop_tick(ts);
+ }
}

/**
@@ -562,7 +582,7 @@ static void tick_nohz_restart(struct tick_sched *ts, ktime_t now)
}
}

-static void tick_nohz_restart_sched_tick(struct tick_sched *ts, ktime_t now)
+static void __tick_nohz_restart_sched_tick(struct tick_sched *ts, ktime_t now)
{
/* Update jiffies first */
tick_do_update_jiffies64(now);
@@ -577,6 +597,31 @@ static void tick_nohz_restart_sched_tick(struct tick_sched *ts, ktime_t now)
tick_nohz_restart(ts, now);
}

+/**
+ * tick_nohz_restart_sched_tick - restart the tick for a tickless CPU
+ *
+ * Restart the tick when the CPU is in adaptive tickless mode.
+ */
+void tick_nohz_restart_sched_tick(void)
+{
+ struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
+ unsigned long flags;
+ ktime_t now;
+
+ local_irq_save(flags);
+
+ if (!ts->tick_stopped) {
+ local_irq_restore(flags);
+ return;
+ }
+
+ now = ktime_get();
+ __tick_nohz_restart_sched_tick(ts, now);
+
+ local_irq_restore(flags);
+}
+
+
static void tick_nohz_account_idle_ticks(struct tick_sched *ts)
{
#ifndef CONFIG_VIRT_CPU_ACCOUNTING
@@ -623,7 +668,7 @@ void tick_nohz_idle_exit(void)

if (ts->tick_stopped) {
select_nohz_load_balancer(0);
- tick_nohz_restart_sched_tick(ts, now);
+ __tick_nohz_restart_sched_tick(ts, now);
tick_nohz_account_idle_ticks(ts);
}

@@ -784,7 +829,6 @@ void tick_check_idle(int cpu)
}

#ifdef CONFIG_CPUSETS_NO_HZ
-
/*
* Take the timer duty if nobody is taking care of it.
* If a CPU already does and and it's in a nohz cpuset,
@@ -803,6 +847,29 @@ static void tick_do_timer_check_handler(int cpu)
}
}

+void tick_nohz_check_adaptive(void)
+{
+ struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
+
+ if (ts->tick_stopped && !is_idle_task(current)) {
+ if (!sched_can_stop_tick())
+ tick_nohz_restart_sched_tick();
+ }
+}
+
+void tick_nohz_post_schedule(void)
+{
+ struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
+
+ /*
+ * No need to disable irqs here. The worst that can happen
+ * is an irq that comes and restart the tick before us.
+ * tick_nohz_restart_sched_tick() is irq safe.
+ */
+ if (ts->tick_stopped)
+ tick_nohz_restart_sched_tick();
+}
+
#else

static void tick_do_timer_check_handler(int cpu)
@@ -849,6 +916,7 @@ static enum hrtimer_restart tick_sched_timer(struct hrtimer *timer)
* no valid regs pointer
*/
if (regs) {
+ int user = user_mode(regs);
/*
* When we are idle and the tick is stopped, we have to touch
* the watchdog as we might not schedule for a really long
@@ -862,7 +930,7 @@ static enum hrtimer_restart tick_sched_timer(struct hrtimer *timer)
if (idle_cpu(cpu))
ts->idle_jiffies++;
}
- update_process_times(user_mode(regs));
+ update_process_times(user);
profile_tick(CPU_PROFILING);
}

--
1.7.5.4


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