根据Linux2.6.26源码分析其进程模型

pid_t pid; 

/* PID/PID hash table linkage. */ 
struct pid_link pids[PIDTYPE_MAX];
struct list_head thread_group;

/* 
     * pointers to (original) parent process, youngest child, younger sibling,
     * older sibling, respectively.  (p->father can be replaced with 
     * p->parent->pid)
     */
    struct task_struct *real_parent; /* real parent process (when being debugged) */
    struct task_struct *parent;    /* parent process */
    /*
     * children/sibling forms the list of my children plus the
     * tasks I‘m ptracing.
     */
    struct list_head children;    /* list of my children */
    struct list_head sibling;    /* linkage in my parent‘s children list */
    struct task_struct *group_leader;    /* threadgroup leader */

    volatile long state;    /* -1 unrunnable, 0 runnable, >0 stopped */

#define TASK_RUNNING        0
#define TASK_INTERRUPTIBLE    1
#define TASK_UNINTERRUPTIBLE    2
#define __TASK_STOPPED        4
#define __TASK_TRACED        8
/* in tsk->exit_state */
#define EXIT_ZOMBIE        16
#define EXIT_DEAD        32
/* in tsk->state again */
#define TASK_DEAD        64
#define TASK_WAKEKILL        128

/*
 * CFS stats for a schedulable entity (task, task-group etc)
 *
 * Current field usage histogram:
 *
 *     4 se->block_start
 *     4 se->run_node
 *     4 se->sleep_start
 *     6 se->load.weight
 */
struct sched_entity {
    struct load_weight    load;        /* for load-balancing */
    struct rb_node        run_node;
    struct list_head    group_node;
    unsigned int        on_rq;

    u64            exec_start;
    u64            sum_exec_runtime;
    u64            vruntime;
    u64            prev_sum_exec_runtime;

    u64            last_wakeup;
    u64            avg_overlap;

#ifdef CONFIG_SCHEDSTATS
    u64            wait_start;
    u64            wait_max;
    u64            wait_count;
    u64            wait_sum;

    u64            sleep_start;
    u64            sleep_max;
    s64            sum_sleep_runtime;

    u64            block_start;
    u64            block_max;
    u64            exec_max;
    u64            slice_max;

    u64            nr_migrations;
    u64            nr_migrations_cold;
    u64            nr_failed_migrations_affine;
    u64            nr_failed_migrations_running;
    u64            nr_failed_migrations_hot;
    u64            nr_forced_migrations;
    u64            nr_forced2_migrations;

    u64            nr_wakeups;
    u64            nr_wakeups_sync;
    u64            nr_wakeups_migrate;
    u64            nr_wakeups_local;
    u64            nr_wakeups_remote;
    u64            nr_wakeups_affine;
    u64            nr_wakeups_affine_attempts;
    u64            nr_wakeups_passive;
    u64            nr_wakeups_idle;
#endif

#ifdef CONFIG_FAIR_GROUP_SCHED
    struct sched_entity    *parent;
    /* rq on which this entity is (to be) queued: */
    struct cfs_rq        *cfs_rq;
    /* rq "owned" by this entity/group: */
    struct cfs_rq        *my_q;
#endif
};

/*
 * schedule() is the main scheduler function.
 */
asmlinkage void __sched schedule(void)
{
    struct task_struct *prev, *next;
    unsigned long *switch_count;
    struct rq *rq;
    int cpu;

need_resched:
    preempt_disable();
    cpu = smp_processor_id();
    rq = cpu_rq(cpu);
    rcu_qsctr_inc(cpu);
    prev = rq->curr;
    switch_count = &prev->nivcsw;

    release_kernel_lock(prev);
need_resched_nonpreemptible:

    schedule_debug(prev);

    hrtick_clear(rq);

    /*
     * Do the rq-clock update outside the rq lock:
     */
    local_irq_disable();
    update_rq_clock(rq);
    spin_lock(&rq->lock);
    clear_tsk_need_resched(prev);

    if (prev->state && !(preempt_count() & PREEMPT_ACTIVE)) {
        if (unlikely(signal_pending_state(prev->state, prev)))
            prev->state = TASK_RUNNING;
        else
            deactivate_task(rq, prev, 1);
        switch_count = &prev->nvcsw;
    }

#ifdef CONFIG_SMP
    if (prev->sched_class->pre_schedule)
        prev->sched_class->pre_schedule(rq, prev);
#endif

    if (unlikely(!rq->nr_running))
        idle_balance(cpu, rq);

    prev->sched_class->put_prev_task(rq, prev);
    next = pick_next_task(rq, prev);

    if (likely(prev != next)) {
        sched_info_switch(prev, next);

        rq->nr_switches++;
        rq->curr = next;
        ++*switch_count;

        context_switch(rq, prev, next); /* unlocks the rq */
        /*
         * the context switch might have flipped the stack from under
         * us, hence refresh the local variables.
         */
        cpu = smp_processor_id();
        rq = cpu_rq(cpu);
    } else
        spin_unlock_irq(&rq->lock);

    hrtick_set(rq);

    if (unlikely(reacquire_kernel_lock(current) < 0))
        goto need_resched_nonpreemptible;

    preempt_enable_no_resched();
    if (unlikely(test_thread_flag(TIF_NEED_RESCHED)))
        goto need_resched;
}

/*
 * Pick up the highest-prio task:
 */
static inline struct task_struct *
pick_next_task(struct rq *rq, struct task_struct *prev)
{
    const struct sched_class *class;
    struct task_struct *p;

    /*
     * Optimization: we know that if all tasks are in
     * the fair class we can call that function directly:
     */
    if (likely(rq->nr_running == rq->cfs.nr_running)) {
        p = fair_sched_class.pick_next_task(rq);
        if (likely(p))
            return p;
    }

    class = sched_class_highest;
    for ( ; ; ) {
        p = class->pick_next_task(rq);
        if (p)
            return p;
        /*
         * Will never be NULL as the idle class always
         * returns a non-NULL p:
         */
        class = class->next;
    }
}