kern_switch.c revision 97261
1/* 2 * Copyright (c) 2001 Jake Burkholder <jake@FreeBSD.org> 3 * All rights reserved. 4 * 5 * Redistribution and use in source and binary forms, with or without 6 * modification, are permitted provided that the following conditions 7 * are met: 8 * 1. Redistributions of source code must retain the above copyright 9 * notice, this list of conditions and the following disclaimer. 10 * 2. Redistributions in binary form must reproduce the above copyright 11 * notice, this list of conditions and the following disclaimer in the 12 * documentation and/or other materials provided with the distribution. 13 * 14 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 15 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 16 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 17 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 18 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 19 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 20 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 21 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 22 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 23 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 24 * SUCH DAMAGE. 25 * 26 * $FreeBSD: head/sys/kern/kern_switch.c 97261 2002-05-25 01:12:23Z jake $ 27 */ 28 29#include <sys/param.h> 30#include <sys/systm.h> 31#include <sys/kernel.h> 32#include <sys/ktr.h> 33#include <sys/lock.h> 34#include <sys/mutex.h> 35#include <sys/proc.h> 36#include <sys/queue.h> 37#include <machine/critical.h> 38 39CTASSERT((RQB_BPW * RQB_LEN) == RQ_NQS); 40 41/* 42 * Global run queue. 43 */ 44static struct runq runq; 45SYSINIT(runq, SI_SUB_RUN_QUEUE, SI_ORDER_FIRST, runq_init, &runq) 46 47/* 48 * Wrappers which implement old interface; act on global run queue. 49 */ 50 51struct thread * 52choosethread(void) 53{ 54 return (runq_choose(&runq)->ke_thread); 55} 56 57int 58procrunnable(void) 59{ 60 return runq_check(&runq); 61} 62 63void 64remrunqueue(struct thread *td) 65{ 66 runq_remove(&runq, td->td_kse); 67} 68 69void 70setrunqueue(struct thread *td) 71{ 72 runq_add(&runq, td->td_kse); 73} 74 75/* Critical sections that prevent preemption. */ 76void 77critical_enter(void) 78{ 79 struct thread *td; 80 81 td = curthread; 82 if (td->td_critnest == 0) 83 cpu_critical_enter(); 84 td->td_critnest++; 85} 86 87void 88critical_exit(void) 89{ 90 struct thread *td; 91 92 td = curthread; 93 if (td->td_critnest == 1) { 94 td->td_critnest = 0; 95 cpu_critical_exit(); 96 } else { 97 td->td_critnest--; 98 } 99} 100 101/* 102 * Clear the status bit of the queue corresponding to priority level pri, 103 * indicating that it is empty. 104 */ 105static __inline void 106runq_clrbit(struct runq *rq, int pri) 107{ 108 struct rqbits *rqb; 109 110 rqb = &rq->rq_status; 111 CTR4(KTR_RUNQ, "runq_clrbit: bits=%#x %#x bit=%#x word=%d", 112 rqb->rqb_bits[RQB_WORD(pri)], 113 rqb->rqb_bits[RQB_WORD(pri)] & ~RQB_BIT(pri), 114 RQB_BIT(pri), RQB_WORD(pri)); 115 rqb->rqb_bits[RQB_WORD(pri)] &= ~RQB_BIT(pri); 116} 117 118/* 119 * Find the index of the first non-empty run queue. This is done by 120 * scanning the status bits, a set bit indicates a non-empty queue. 121 */ 122static __inline int 123runq_findbit(struct runq *rq) 124{ 125 struct rqbits *rqb; 126 int pri; 127 int i; 128 129 rqb = &rq->rq_status; 130 for (i = 0; i < RQB_LEN; i++) 131 if (rqb->rqb_bits[i]) { 132 pri = (RQB_FFS(rqb->rqb_bits[i]) - 1) + 133 (i << RQB_L2BPW); 134 CTR3(KTR_RUNQ, "runq_findbit: bits=%#x i=%d pri=%d", 135 rqb->rqb_bits[i], i, pri); 136 return (pri); 137 } 138 139 return (-1); 140} 141 142/* 143 * Set the status bit of the queue corresponding to priority level pri, 144 * indicating that it is non-empty. 145 */ 146static __inline void 147runq_setbit(struct runq *rq, int pri) 148{ 149 struct rqbits *rqb; 150 151 rqb = &rq->rq_status; 152 CTR4(KTR_RUNQ, "runq_setbit: bits=%#x %#x bit=%#x word=%d", 153 rqb->rqb_bits[RQB_WORD(pri)], 154 rqb->rqb_bits[RQB_WORD(pri)] | RQB_BIT(pri), 155 RQB_BIT(pri), RQB_WORD(pri)); 156 rqb->rqb_bits[RQB_WORD(pri)] |= RQB_BIT(pri); 157} 158 159/* 160 * Add the process to the queue specified by its priority, and set the 161 * corresponding status bit. 162 */ 163void 164runq_add(struct runq *rq, struct kse *ke) 165{ 166 struct rqhead *rqh; 167 int pri; 168 169#ifdef INVARIANTS 170 struct proc *p = ke->ke_proc; 171#endif 172 if (ke->ke_flags & KEF_ONRUNQ) 173 return; 174 mtx_assert(&sched_lock, MA_OWNED); 175 KASSERT(p->p_stat == SRUN, ("runq_add: proc %p (%s) not SRUN", 176 p, p->p_comm)); 177 pri = ke->ke_thread->td_priority / RQ_PPQ; 178 ke->ke_rqindex = pri; 179 runq_setbit(rq, pri); 180 rqh = &rq->rq_queues[pri]; 181 CTR4(KTR_RUNQ, "runq_add: p=%p pri=%d %d rqh=%p", 182 ke->ke_proc, ke->ke_thread->td_priority, pri, rqh); 183 TAILQ_INSERT_TAIL(rqh, ke, ke_procq); 184 ke->ke_flags |= KEF_ONRUNQ; 185} 186 187/* 188 * Return true if there are runnable processes of any priority on the run 189 * queue, false otherwise. Has no side effects, does not modify the run 190 * queue structure. 191 */ 192int 193runq_check(struct runq *rq) 194{ 195 struct rqbits *rqb; 196 int i; 197 198 rqb = &rq->rq_status; 199 for (i = 0; i < RQB_LEN; i++) 200 if (rqb->rqb_bits[i]) { 201 CTR2(KTR_RUNQ, "runq_check: bits=%#x i=%d", 202 rqb->rqb_bits[i], i); 203 return (1); 204 } 205 CTR0(KTR_RUNQ, "runq_check: empty"); 206 207 return (0); 208} 209 210/* 211 * Find and remove the highest priority process from the run queue. 212 * If there are no runnable processes, the per-cpu idle process is 213 * returned. Will not return NULL under any circumstances. 214 */ 215struct kse * 216runq_choose(struct runq *rq) 217{ 218 struct rqhead *rqh; 219 struct kse *ke; 220 int pri; 221 222 mtx_assert(&sched_lock, MA_OWNED); 223 if ((pri = runq_findbit(rq)) != -1) { 224 rqh = &rq->rq_queues[pri]; 225 ke = TAILQ_FIRST(rqh); 226 KASSERT(ke != NULL, ("runq_choose: no proc on busy queue")); 227 KASSERT(ke->ke_proc->p_stat == SRUN, 228 ("runq_choose: process %d(%s) in state %d", ke->ke_proc->p_pid, 229 ke->ke_proc->p_comm, ke->ke_proc->p_stat)); 230 CTR3(KTR_RUNQ, "runq_choose: pri=%d kse=%p rqh=%p", pri, ke, rqh); 231 TAILQ_REMOVE(rqh, ke, ke_procq); 232 if (TAILQ_EMPTY(rqh)) { 233 CTR0(KTR_RUNQ, "runq_choose: empty"); 234 runq_clrbit(rq, pri); 235 } 236 ke->ke_flags &= ~KEF_ONRUNQ; 237 return (ke); 238 } 239 CTR1(KTR_RUNQ, "runq_choose: idleproc pri=%d", pri); 240 241 return (PCPU_GET(idlethread)->td_kse); 242} 243 244/* 245 * Initialize a run structure. 246 */ 247void 248runq_init(struct runq *rq) 249{ 250 int i; 251 252 bzero(rq, sizeof *rq); 253 for (i = 0; i < RQ_NQS; i++) 254 TAILQ_INIT(&rq->rq_queues[i]); 255} 256 257/* 258 * Remove the process from the queue specified by its priority, and clear the 259 * corresponding status bit if the queue becomes empty. 260 */ 261void 262runq_remove(struct runq *rq, struct kse *ke) 263{ 264 struct rqhead *rqh; 265 int pri; 266 267 if (!(ke->ke_flags & KEF_ONRUNQ)) 268 return; 269 mtx_assert(&sched_lock, MA_OWNED); 270 pri = ke->ke_rqindex; 271 rqh = &rq->rq_queues[pri]; 272 CTR4(KTR_RUNQ, "runq_remove: p=%p pri=%d %d rqh=%p", 273 ke, ke->ke_thread->td_priority, pri, rqh); 274 KASSERT(ke != NULL, ("runq_remove: no proc on busy queue")); 275 TAILQ_REMOVE(rqh, ke, ke_procq); 276 if (TAILQ_EMPTY(rqh)) { 277 CTR0(KTR_RUNQ, "runq_remove: empty"); 278 runq_clrbit(rq, pri); 279 } 280 ke->ke_flags &= ~KEF_ONRUNQ; 281} 282