From 265f22a975c1e4cc3a4d1f94a3ec53ffbb6f5b9f Mon Sep 17 00:00:00 2001 From: Frederic Weisbecker Date: Fri, 3 May 2013 03:39:05 +0200 Subject: sched: Keep at least 1 tick per second for active dynticks tasks 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 Signed-off-by: Frederic Weisbecker Cc: Christoph Lameter Cc: Hakan Akkan Cc: Ingo Molnar Cc: Kevin Hilman Cc: Li Zhong Cc: Paul E. McKenney Cc: Paul Gortmaker Cc: Peter Zijlstra Cc: Steven Rostedt Cc: Thomas Gleixner --- 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(+) diff --git a/include/linux/sched.h b/include/linux/sched.h index ebf7095158a9..af008d7bad57 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 e94842d4400c..3bdf986a091a 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 b8ce77328341..d8da01008d39 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 24dc29897749..ce39224d6155 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -409,6 +409,9 @@ struct rq { #ifdef CONFIG_NO_HZ_COMMON u64 nohz_stamp; unsigned long nohz_flags; +#endif +#ifdef CONFIG_NO_HZ_FULL + unsigned long last_sched_tick; #endif int skip_clock_update; @@ -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 1c9f53b2ddb7..07929c633570 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 -- cgit v1.2.2