From: Frederic Weisbecker 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 Cc: Alessio Igor Bogani Cc: Andrew Morton Cc: Avi Kivity Cc: Chris Metcalf Cc: Christoph Lameter Cc: Daniel Lezcano Cc: Geoff Levand Cc: Gilad Ben Yossef Cc: Hakan Akkan Cc: Ingo Molnar Cc: Kevin Hilman Cc: Max Krasnyansky Cc: Paul E. McKenney Cc: Peter Zijlstra Cc: Stephen Hemminger Cc: Steven Rostedt Cc: Sven-Thorsten Dietrich Cc: Thomas Gleixner --- arch/x86/kernel/smp.c | 2 ++ include/linux/sched.h | 6 ++++ include/linux/tick.h | 11 +++++- init/Kconfig | 2 +- kernel/sched/core.c | 24 +++++++++++++ kernel/sched/sched.h | 12 +++++++ kernel/softirq.c | 6 ++-- kernel/time/tick-sched.c | 86 +++++++++++++++++++++++++++++++++++++++++----- 8 files changed, 137 insertions(+), 12 deletions(-) diff --git a/arch/x86/kernel/smp.c b/arch/x86/kernel/smp.c index 4c0b7d2..0bad72d 100644 --- a/arch/x86/kernel/smp.c +++ b/arch/x86/kernel/smp.c @@ -23,6 +23,7 @@ #include #include #include +#include #include #include @@ -275,6 +276,7 @@ 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 0dd42a0..749752e 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -2753,6 +2753,12 @@ 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 ffdeeab..418e078 100644 --- a/init/Kconfig +++ b/init/Kconfig @@ -751,7 +751,7 @@ 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 2d8927f..2716b79 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -1196,6 +1196,29 @@ 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(); + + /* + * This is called right after cpuset_adaptive_nohz() that + * uses atomic_add_return() so that we are ordered against + * cpu_adaptive_nohz_ref. When inc_nr_running() sends an + * IPI to this CPU, we are guaranteed to see the update on + * nr_running. + */ + + /* 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) { @@ -1897,6 +1920,7 @@ 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 7a7db09..c6cd9ec 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -1,6 +1,7 @@ #include #include +#include #include #include @@ -927,6 +928,17 @@ static inline u64 steal_ticks(u64 steal) static inline void inc_nr_running(struct rq *rq) { rq->nr_running++; + + if (rq->nr_running == 2) { + /* + * cpuset_cpu_adaptive_nohz() uses atomic_add_return() + * to order against rq->nr_running updates. This way + * the CPU that receives the IPI is guaranteed to see + * the update on nr_running without the rq->lock. + */ + 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 cc96bdc..e06b8eb 100644 --- a/kernel/softirq.c +++ b/kernel/softirq.c @@ -25,6 +25,7 @@ #include #include #include +#include #define CREATE_TRACE_POINTS #include @@ -307,7 +308,8 @@ 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 c7a78c6..35047b2 100644 --- a/kernel/time/tick-sched.c +++ b/kernel/time/tick-sched.c @@ -512,6 +512,24 @@ 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 * @@ -524,10 +542,12 @@ 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); + } } /** @@ -568,7 +588,7 @@ 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); @@ -584,6 +604,31 @@ 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 @@ -630,7 +675,7 @@ void tick_nohz_idle_exit(void) if (ts->tick_stopped) { nohz_balance_enter_idle(cpu); calc_load_exit_idle(); - tick_nohz_restart_sched_tick(ts, now); + __tick_nohz_restart_sched_tick(ts, now); tick_nohz_account_idle_ticks(ts); } @@ -791,7 +836,6 @@ 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, @@ -810,6 +854,31 @@ 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 (cpuset_adaptive_nohz()) { + 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) @@ -856,6 +925,7 @@ 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 @@ -869,7 +939,7 @@ static enum hrtimer_restart tick_sched_timer(struct hrtimer *timer) if (is_idle_task(current)) ts->idle_jiffies++; } - update_process_times(user_mode(regs)); + update_process_times(user); profile_tick(CPU_PROFILING); } -- 1.7.10.4 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/