Linux 多核启动过程
以这篇博文来纪念自己与“Linux kernel多核启动”相处的两个多月。
本文章以2.6.33.1的linux内核在x86_64平台上为例进行说明。
本文参考了http://tldp.org/HOWTO/Linux-i386-Boot-Code-HOWTO/smpboot.html

Linux kernel启动的过程概览
init/main.c:start_kernel()
    |
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init/main.c:rest_init
{
……
kernel_thread(kernel_init, NULL, CLONES_FS | CLONE_SIGHAND)
……
cpu_idle()
}
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init/main.c:kernel_init//从上面代码可以看出，kernel_init是一个内核线程 
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init/main.c:init_post  //会在最后调用启动脚本
{
……
823         /*
824          * We try each of these until one succeeds.
825          *
826          * The Bourne shell can be used instead of init if we are
827          * trying to recover a really broken machine.
828          */
829         if (execute_command) {
830                 run_init_process(execute_command);
831                 printk(KERN_WARNING "Failed to execute %s.  Attempting "
832                                         "defaults...\n", execute_command);
833         }
834         run_init_process("/sbin/init");
835         run_init_process("/etc/init");
836         run_init_process("/bin/init");
837         run_init_process("/bin/sh");
838
839         panic("No init found.  Try passing init= option to kernel.");
……
}


我们再来看看内核启动多核的详细过程。

init/main.c:start_kernel()
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init/main.c:rest_init
{
……
kernel_thread(kernel_init, NULL, CLONES_FS | CLONE_SIGHAND)
……
}
    |
   \|/
kernel_init    
    |
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/* called by boot processor to activate the rest */
init/main.c: smp_init()
{
……
for_each_present_cpu(cpu) {
          if (num_onlien_cpus() >= setup_max_cpus)
               break;
          if ( !cpu_online(cpu))     
               cpu_up(cpu);
}
/* Any cleanup work */
printk(KERN_INFO "Brought up %ld CPUs\n", (long)num_online_cpus());
smp_cpu_done(setup_max_cpus);
……
}
--------------------------
cpu_up = native_cpu_up是一个回调函数。
注册地方是在：arch/x86/kernel/smp.c

struct smp_ops smp_ops = {
   ……
  .cpu_up = native_cpu_up,
   ……
}
--------------------------
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arch/x86/kernel/smpboot.c:native_cpu_up(unsigned int cpu)
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arch/x86/kernel/smpboot.c: do_boot_cpu(int apicid, int cpu)