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kern_idle.c revision 1.17 
      1 /*	$NetBSD: kern_idle.c,v 1.17 2008/05/24 12:59:06 ad 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 1.17 2008/05/24 12:59:06 ad 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>
     43 #include <uvm/uvm_extern.h>
     44 
     45 #if MAXCPUS > 32
     46 #error fix this code
     47 #endif
     48 
     49 static volatile uint32_t *idle_cpus;
     50 
     51 void
     52 idle_loop(void *dummy)
     53 {
     54 	struct cpu_info *ci = curcpu();
     55 	struct lwp *l = curlwp;
     56 	uint32_t mask = 1 << cpu_index(ci);
     57 	bool set = false;
     58 	int s;
     59 
     60 	ci->ci_data.cpu_onproc = l;
     61 
     62 	/* Update start time for this thread. */
     63 	lwp_lock(l);
     64 	binuptime(&l->l_stime);
     65 	lwp_unlock(l);
     66 
     67 	s = splsched();
     68 	ci->ci_schedstate.spc_flags |= SPCF_RUNNING;
     69 	splx(s);
     70 
     71 	KERNEL_UNLOCK_ALL(l, NULL);
     72 	l->l_stat = LSONPROC;
     73 	while (1 /* CONSTCOND */) {
     74 		LOCKDEBUG_BARRIER(NULL, 0);
     75 		KASSERT((l->l_flag & LW_IDLE) != 0);
     76 		KASSERT(ci == curcpu());
     77 		KASSERT(l == curlwp);
     78 		KASSERT(CURCPU_IDLE_P());
     79 		KASSERT(l->l_priority == PRI_IDLE);
     80 
     81 		if (uvm.page_idle_zero) {
     82 			if (sched_curcpu_runnable_p()) {
     83 				goto schedule;
     84 			}
     85 			if (!set) {
     86 				set = true;
     87 				atomic_or_32(idle_cpus, mask);
     88 			}
     89 			uvm_pageidlezero();
     90 		}
     91 		if (!sched_curcpu_runnable_p()) {
     92 			if (!set) {
     93 				set = true;
     94 				atomic_or_32(idle_cpus, mask);
     95 			}
     96 			cpu_idle();
     97 			if (!sched_curcpu_runnable_p() &&
     98 			    !ci->ci_want_resched) {
     99 				continue;
    100 			}
    101 		}
    102 schedule:
    103 		if (set) {
    104 			set = false;
    105 			atomic_and_32(idle_cpus, ~mask);
    106 		}
    107 		KASSERT(l->l_mutex == l->l_cpu->ci_schedstate.spc_lwplock);
    108 		lwp_lock(l);
    109 		mi_switch(l);
    110 		KASSERT(curlwp == l);
    111 		KASSERT(l->l_stat == LSONPROC);
    112 	}
    113 }
    114 
    115 /*
    116  * Find an idle CPU and remove from the idle bitmask.  The bitmask
    117  * is not always accurate but is "good enough" for the purpose of finding
    118  * a CPU to run a job on.
    119  */
    120 struct cpu_info *
    121 idle_pick(void)
    122 {
    123 	uint32_t mask;
    124 	u_int index;
    125 
    126 	do {
    127 		if ((mask = *idle_cpus) == 0)
    128 			return NULL;
    129 		index = ffs(mask) - 1;
    130 	} while (atomic_cas_32(idle_cpus, mask, mask ^ (1 << index)) != mask);
    131 
    132 	return cpu_lookup_byindex(index);
    133 }
    134 
    135 int
    136 create_idle_lwp(struct cpu_info *ci)
    137 {
    138 	static bool again;
    139 	uintptr_t addr;
    140 	lwp_t *l;
    141 	int error;
    142 
    143 	if (!again) {
    144 		again = true;
    145 		addr = (uintptr_t)kmem_alloc(coherency_unit * 2, KM_SLEEP);
    146 		addr = roundup(addr, coherency_unit);
    147 		idle_cpus = (uint32_t *)addr;
    148 	}
    149 
    150 	KASSERT(ci->ci_data.cpu_idlelwp == NULL);
    151 	error = kthread_create(PRI_IDLE, KTHREAD_MPSAFE | KTHREAD_IDLE,
    152 	    ci, idle_loop, NULL, &l, "idle/%u", ci->ci_index);
    153 	if (error != 0)
    154 		panic("create_idle_lwp: error %d", error);
    155 	lwp_lock(l);
    156 	l->l_flag |= LW_IDLE;
    157 	lwp_unlock(l);
    158 	l->l_cpu = ci;
    159 	ci->ci_data.cpu_idlelwp = l;
    160 
    161 	return error;
    162 }
    163