Linux Linux #! "! Linux

Transcription

1 #!!

2 ! 2.5.X % Understanding the Kernel &! 2.5.X kernel/sched.cinclude/linux/sched.h'! Ingo Molnar' ) time! sharing!! &! & Preemptive multitasking SCHED_OTHER * (

3 & *& real-time!!, & '!! ) TASK_RUNNING! ' % non-preemptive* 'SCHED_FIFO *!!-! %Round Robin 'SCHED_RR!! + SCHED_OTHER epochs time slice%!! runqueue time slice TASK_RUNNING!! time slice!! &!time slice! time slice time slice!!.

4 kernel/sched.c)! scheduler 012 schedule()!!012, &time_slice& ) scheduler_tick()! '!&& 3!! 012 (de)activate_task()! /!!! HZ=100Hz jiffies 4 (

5 process priority nice() API 3!!'!! IO-BOUND3 & CPU-BOUND 5 ' MAX_PRIO-15-- MAX_RT_PRIO &! niceniceness 65-20nice& 'TASK_NICE #define TASK_NICE(p) ((p)->static_prio MAX_RT_PRIO 20) +

6 runqueue runqueue process descriptors!!! ' runqueue runqueue %nr_running swapper )!%curr swapper!%idle runqueue!%active!!! &! TASK_RUNNING!) activate_task()!!%expired time slice! active %expired_timestamp expired.

7 runqueue struct prio_array '! %nr_active %bitmap[] ( i i O(1)%active &! %queue[] - ( -list_t (runqueue nr_active queue bitmap swapper prio_array_t prio_array_t runqueue nr_running curr idle active expired expired_ts (... /

8 ' %policy ' %need_resched set_tsk_need_resched clear_tsk_need_resched + %prio % %static_prio! %sleep_timestamp! %sleep_avg % %time_slice epoch!. 4

9 scheduler% schedule()!%! %context_switch() ' time slice % scheduler_tick() & sleep_on() ) runqueue )% wake_up()!!! sched_yield() / scheduler% 012!direct invocation schedule()! lazy invocation* kernel mode need_resched user mode schedule() time slice & ' need_resched scheduler_tick() & 4 5

10 schedule()! prev = current; rq = this_rq();.. spin_lock_irq(&rq->lock); switch(prev->state) { case TASK_INTERRUPTIBLE: if (signal_pending(prev)) { prev->state = TASK_RUNNING; break; } default: deactivate_task(prev, rq); case TASK_RUNNING: ; }!prev runqueue rq! runqueue!! 5 schedule()! if (!rq->nr_running) { next = rq->idle; rq->expired_timestamp = 0; goto switch_tasks; } array = rq->active; if (!array->nr_active) { rq->active = rq->expired; rq->expired = array; array = rq->active; rq->expired_timestamp = 0; } swapper &runqueue &active array expired active

11 schedule()! idx = sched_find_first_bit(array->bitmap); queue = array->queue + idx; next = list_entry(queue->next, task_t, run_list); switch_tasks: clear_tsk_need_resched(prev); if (prev!= next) {.. rq->curr = next; prev = context_switch(prev, next);.. spin_unlock_irq(&rq->lock); } else spin_unlock_irq(&rq->lock); next active array! context_switch()! # context_switch() next %scheduler_tick()! ) ' *!! ' &time_slice time_slice! expired' active need_resched%012

12 ! sleep_avg 7!!!& 'schedule() p->sleep_timestamp = jiffies;! * MAX_SLEEP_AVG activate_task() #define MAX_SLEEP_AVG (2*HZ) sleep_time = jiffies p->sleep_timestamp; p->sleep_avg += sleep_time; if (p->sleep_avg > MAX_SLEEP_AVG) p->sleep_avg = MAX_SLEEP_AVG;!) sheduler_tick()! if (p->sleep_avg) p->sleep_avg--;!!!!3 (

13 sleep_avg%! effective_prio()!! ' sleep _ avg 1 bonus 25% 40 5 bonus 5 MAX _ SLEEP _ AVG 2 prio = static_prio bonus if (prio < MAX_RT_PRIO) prio = MAX_RT_PRIO; if (prio > MAX_PRIO - 1) prio = MAX_PRIO 1; +!!+bonus * 5 nice 19 & nice 0 3!! HZ&MAX_SLEEP_AVG! * &.

14 ! time slice! ) / time slice! 'TASK_TIMESLICE!time slice #define MIN_TIMESLICE (10 * HZ / 1000) /* 10 msec */ #define MAX_TIMESLICE (300 * HZ / 1000) /* 300 msec */ #define TASK_TIMESLICE(p) \ MIN_TIMESLICE + (MAX_TIMESLICE MIN_TIMESLICE) * (MAX_PRIO 1 (p)->static_prio)/39!msec msec msec+ time slice!time slice scheduler_tick()! &!! &!time slice 4 (

15 time slice! time slice! &!!' '& )! &time slice *time slice -- &!& time slice fork()!do_fork()! kernel/fork.c ) p->time_slice = (current->time_slice + 1) >> 1; current->time_slice >>= 1; 5 time slices) ' %, &shell & %! time slice ) & +

16 * & 'expired #define EXPIRED_STARVING(rq) \ ((rq)->expired_timestamp && \ (jiffies (rq)->expired_timestamp >= \ STARVATION_LIMIT * ((rq)->nr_running + 1)) &*expired time slices &runqueue! * *&! &! 'TASK_INETRACTIVE #define TASK_INTERACTIVE(p) \ ((p)->prio <= (p)->static_prio DELTA(p)) ' DELTA(p) 1 TASK _ NICE( p) TASK _ NICE( p) DELTA( p) 25% !!.

17 ( &!!! '! nice -20 ' -3 nice 19 & '!batch!, & &' scheduler_tick()!!!! schedule()! time slice dequeue_task()enqueue_task()!! expiredactive! task_t *p = current; runqueue_t *rq = this_rq();.. if (p->sleep_avg) p->sleep_avg--; sleep_avg ( /

18 scheduler_tick()! if (!--p->time_slice) { dequeue_task(p, rq->active); set_tsk_need_resched(p); p->prio = effective_prio(p); p->time_slice = TASK_TIMESLICE(p); &!time slice &active! time slice! & schedule() if (!TASK_INTERACTIVE(p) EXPIRED_STARVING(rq)) { if (!rq->expired_timestamp) rq->expired_timestamp = jiffies; enqueue_task(p, rq->expired); } else enqueue_task(p, rq->active); &expired expired_timestamp time slice)active * + 4