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One is related to the time distribution when a new child is created. If the parent has one tick left, then both child and parent received zero tick. When combined with current_irq_nest_count = 1 voluntary_preempt = 0 values, this caused the scheduler from being invoked. Second is related to the overall time distribution. When a thread runs out of time, its new time slice is calculated by the below formula: new_timeslice = (thread_prio * SCHED_TICKS) / total_prio If we consider total_prio is equal to the sum of the priorities of all the threads in the system, it imposes a problem of getting zero tick. In the new scenario, total_prio is equal to the priority types in the system so it is fixed. Every thread gets a timeslice in proportion of their priorities. Thus, there is no risk of taking zero tick.
75 lines
1.8 KiB
C
75 lines
1.8 KiB
C
/*
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* Scheduler and runqueue API definitions.
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*
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* Copyright (C) 2007 Bahadir Balban
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*/
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#ifndef __SCHEDULER_H__
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#define __SCHEDULER_H__
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#include <l4/generic/tcb.h>
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#include INC_SUBARCH(mm.h)
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#include INC_GLUE(memory.h)
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/* Task priorities */
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#define TASK_PRIO_MAX 10
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#define TASK_PRIO_REALTIME 10
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#define TASK_PRIO_PAGER 8
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#define TASK_PRIO_SERVER 6
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#define TASK_PRIO_NORMAL 4
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#define TASK_PRIO_LOW 2
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#define TASK_PRIO_TOTAL 30
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/* Ticks per second, try ticks = 1000 + timeslice = 1 for regressed preemption test. */
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#define SCHED_TICKS 100
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/*
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* A task can run continuously at this granularity,
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* even if it has a greater total time slice.
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*/
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#define SCHED_GRANULARITY SCHED_TICKS/50
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static inline struct ktcb *current_task(void)
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{
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register u32 stack asm("sp");
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return (struct ktcb *)(stack & (~PAGE_MASK));
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}
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#define current current_task()
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#define need_resched (current->ts_need_resched)
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#define SCHED_RQ_TOTAL 2
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/* A basic runqueue */
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struct runqueue {
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struct spinlock lock; /* Lock */
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struct link task_list; /* List of tasks in rq */
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unsigned int total; /* Total tasks */
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};
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/* Contains per-container scheduling structures */
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struct scheduler {
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struct runqueue sched_rq[SCHED_RQ_TOTAL];
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struct runqueue *rq_runnable;
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struct runqueue *rq_expired;
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/* Total priority of all tasks in container */
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int prio_total;
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};
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extern struct scheduler scheduler;
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void sched_init_runqueue(struct runqueue *rq);
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void sched_init_task(struct ktcb *task, int priority);
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void sched_prepare_sleep(void);
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void sched_pager_exit(void);
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void sched_exit_sync(void);
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void sched_suspend_sync(void);
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void sched_suspend_async(void);
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void sched_resume_sync(struct ktcb *task);
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void sched_resume_async(struct ktcb *task);
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void scheduler_start(void);
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void schedule(void);
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void sched_init(struct scheduler *scheduler);
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#endif /* __SCHEDULER_H__ */
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