时钟一

一切皆非难事，只要有恒心，蚂蚁也可啃掉大象，今天开始分析一下linux里的时钟机制。

首先贴一下该是的启动Linux 部分

asmlinkage void __init start_kernel(void)
{
        char * command_line;
        extern struct kernel_param __start___param[], __stop___param[];

        smp_setup_processor_id();

        /*
         * Need to run as early as possible, to initialize the
         * lockdep hash:
         */
        lockdep_init();
        debug_objects_early_init();

        /*
         * Set up the the initial canary ASAP:
         */
        boot_init_stack_canary();

        cgroup_init_early();

        local_irq_disable();
        early_boot_irqs_off();
        early_init_irq_lock_class();

/*
 * Interrupts are still disabled. Do necessary setups, then
 * enable them
 */
        lock_kernel();
        tick_init();
        boot_cpu_init();
        page_address_init();
        printk(KERN_NOTICE "%s", linux_banner);
        setup_arch(&command_line);
        mm_init_owner(&init_mm, &init_task);
        setup_command_line(command_line);
        setup_nr_cpu_ids();
        setup_per_cpu_areas();
        smp_prepare_boot_cpu(); /* arch-specific boot-cpu hooks */

        build_all_zonelists();

        page_alloc_init();

        printk(KERN_NOTICE "Kernel command line: %s\n", boot_command_line);
        parse_early_param();
        parse_args("Booting kernel", static_command_line, __start___param,
                   __stop___param - __start___param,
                   &unknown_bootoption);
        /*
         * These use large bootmem allocations and must precede
         * kmem_cache_init()
         */
        pidhash_init();
        vfs_caches_init_early();
        sort_main_extable();
        trap_init();
        mm_init();
        /*
         * Set up the scheduler prior starting any interrupts (such as the
         * timer interrupt). Full topology setup happens at smp_init()
         * time - but meanwhile we still have a functioning scheduler.
         */

 

        sched_init();
        /*
         * Disable preemption - early bootup scheduling is extremely
         * fragile until we cpu_idle() for the first time.
         */
        preempt_disable();
        if (!irqs_disabled()) {
                printk(KERN_WARNING "start_kernel(): bug: interrupts were "
                                "enabled *very* early, fixing it\n");
                local_irq_disable();
        }
        rcu_init();
        /* init some links before init_ISA_irqs() */
        early_irq_init();
        init_IRQ();
        prio_tree_init();
        init_timers();
        hrtimers_init();
        softirq_init();
        timekeeping_init();
        time_init();

        sched_clock_init();
        profile_init();
        if (!irqs_disabled())
                printk(KERN_CRIT "start_kernel(): bug: interrupts were "
                                 "enabled early\n");
        early_boot_irqs_on();
        local_irq_enable();

        /* Interrupts are enabled now so all GFP allocations are safe. */
        set_gfp_allowed_mask(__GFP_BITS_MASK);

        kmem_cache_init_late();

        /*
         * HACK ALERT! This is early. We're enabling the console before
         * we've done PCI setups etc, and console_init() must be aware of
         * this. But we do want output early, in case something goes wrong.
         */
        console_init();
        if (panic_later)
                panic(panic_later, panic_param);

        lockdep_info();

        /*
         * Need to run this when irqs are enabled, because it wants
         * to self-test [hard/soft]-irqs on/off lock inversion bugs
         * too:
         */
        locking_selftest();

#ifdef CONFIG_BLK_DEV_INITRD
        if (initrd_start && !initrd_below_start_ok &&
            page_to_pfn(virt_to_page((void *)initrd_start)) < min_low_pfn) {
                printk(KERN_CRIT "initrd overwritten (0x%08lx < 0x%08lx) - "
                    "disabling it.\n",
                    page_to_pfn(virt_to_page((void *)initrd_start)),
                    min_low_pfn);
                initrd_start = 0;
        }
#endif
        page_cgroup_init();

        enable_debug_pagealloc();
        kmemtrace_init();
        kmemleak_init();
        debug_objects_mem_init();
        idr_init_cache();
        setup_per_cpu_pageset();
        numa_policy_init();
        if (late_time_init)
                late_time_init();
        calibrate_delay();
        pidmap_init();
        anon_vma_init();
#ifdef CONFIG_X86
        if (efi_enabled)
                efi_enter_virtual_mode();
#endif
        thread_info_cache_init();
        cred_init();
        fork_init(num_physpages);
        proc_caches_init();
        buffer_init();

        key_init();
        security_init();
        vfs_caches_init(num_physpages);
        radix_tree_init();
        signals_init();
        /* rootfs populating might need page-writeback */
        page_writeback_init();
#ifdef CONFIG_PROC_FS
        proc_root_init();
#endif
        cgroup_init();
        cpuset_init();
        taskstats_init_early();
        delayacct_init();

        check_bugs();

        acpi_early_init(); /* before LAPIC and SMP init */

        ftrace_init();

        /* Do the rest non-__init'ed, we're now alive */
        rest_init();
}