The Design and Implementation of the FreeBSD Operating System, Second Edition
Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)


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FreeBSD/Linux Kernel Cross Reference
sys/kern/kern_idle.c

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    1 /*      $NetBSD: kern_idle.c,v 1.34 2020/09/05 16:30:12 riastradh Exp $ */
    2 
    3 /*-
    4  * Copyright (c)2002, 2006, 2007 YAMAMOTO Takashi,
    5  * All rights reserved.
    6  *
    7  * Redistribution and use in source and binary forms, with or without
    8  * modification, are permitted provided that the following conditions
    9  * are met:
   10  * 1. Redistributions of source code must retain the above copyright
   11  *    notice, this list of conditions and the following disclaimer.
   12  * 2. Redistributions in binary form must reproduce the above copyright
   13  *    notice, this list of conditions and the following disclaimer in the
   14  *    documentation and/or other materials provided with the distribution.
   15  *
   16  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
   17  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   18  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   19  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
   20  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   21  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   22  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   23  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   24  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   25  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   26  * SUCH DAMAGE.
   27  */
   28 
   29 #include <sys/cdefs.h>
   30 
   31 __KERNEL_RCSID(0, "$NetBSD: kern_idle.c,v 1.34 2020/09/05 16:30:12 riastradh Exp $");
   32 
   33 #include <sys/param.h>
   34 #include <sys/cpu.h>
   35 #include <sys/idle.h>
   36 #include <sys/kthread.h>
   37 #include <sys/lockdebug.h>
   38 #include <sys/kmem.h>
   39 #include <sys/proc.h>
   40 #include <sys/atomic.h>
   41 
   42 #include <uvm/uvm.h>    /* uvm_idle */
   43 
   44 void
   45 idle_loop(void *dummy)
   46 {
   47         struct cpu_info *ci = curcpu();
   48         struct schedstate_percpu *spc;
   49         struct lwp *l = curlwp;
   50 
   51         lwp_lock(l);
   52         spc = &ci->ci_schedstate;
   53         KASSERT(lwp_locked(l, spc->spc_lwplock));
   54         kcpuset_atomic_set(kcpuset_running, cpu_index(ci));
   55         /* Update start time for this thread. */
   56         binuptime(&l->l_stime);
   57         spc->spc_flags |= SPCF_RUNNING;
   58         KASSERT((l->l_pflag & LP_RUNNING) != 0);
   59         l->l_stat = LSIDL;
   60         lwp_unlock(l);
   61 
   62         /*
   63          * Use spl0() here to ensure that we have the correct interrupt
   64          * priority.  This may be the first thread running on the CPU,
   65          * in which case we took an odd route to get here.
   66          */
   67         spl0();
   68         KERNEL_UNLOCK_ALL(l, NULL);
   69 
   70         for (;;) {
   71                 LOCKDEBUG_BARRIER(NULL, 0);
   72                 KASSERT((l->l_flag & LW_IDLE) != 0);
   73                 KASSERT(ci == curcpu());
   74                 KASSERT(l == curlwp);
   75                 KASSERT(CURCPU_IDLE_P());
   76                 KASSERT(l->l_priority == PRI_IDLE);
   77 
   78                 sched_idle();
   79                 if (!sched_curcpu_runnable_p()) {
   80                         if ((spc->spc_flags & SPCF_OFFLINE) == 0) {
   81                                 uvm_idle();
   82                         }
   83                         if (!sched_curcpu_runnable_p()) {
   84                                 cpu_idle();
   85                                 if (!sched_curcpu_runnable_p() &&
   86                                     !ci->ci_want_resched) {
   87                                         continue;
   88                                 }
   89                         }
   90                 }
   91                 KASSERT(l->l_mutex == l->l_cpu->ci_schedstate.spc_lwplock);
   92                 lwp_lock(l);
   93                 spc_lock(l->l_cpu);
   94                 mi_switch(l);
   95                 KASSERT(curlwp == l);
   96                 KASSERT(l->l_stat == LSIDL);
   97         }
   98 }
   99 
  100 int
  101 create_idle_lwp(struct cpu_info *ci)
  102 {
  103         lwp_t *l;
  104         int error;
  105 
  106         KASSERT(ci->ci_data.cpu_idlelwp == NULL);
  107         error = kthread_create(PRI_IDLE, KTHREAD_MPSAFE | KTHREAD_IDLE,
  108             ci, idle_loop, NULL, &l, "idle/%u", ci->ci_index);
  109         if (error != 0)
  110                 panic("create_idle_lwp: error %d", error);
  111         lwp_lock(l);
  112         l->l_flag |= LW_IDLE;
  113         if (ci != lwp0.l_cpu) {
  114                 /*
  115                  * For secondary CPUs, the idle LWP is the first to run, and
  116                  * it's directly entered from MD code without a trip through
  117                  * mi_switch().  Make the picture look good in case the CPU
  118                  * takes an interrupt before it calls idle_loop().
  119                  */
  120                 l->l_stat = LSIDL;
  121                 l->l_pflag |= LP_RUNNING;
  122                 ci->ci_onproc = l;
  123         }
  124         lwp_unlock(l);
  125         ci->ci_data.cpu_idlelwp = l;
  126 
  127         return error;
  128 }

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