kern_switch.c revision 91328
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 91328 2002-02-26 20:33:41Z dillon $ 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 38/* 39 * Global run queue. 40 */ 41static struct runq runq; 42SYSINIT(runq, SI_SUB_RUN_QUEUE, SI_ORDER_FIRST, runq_init, &runq) 43 44/* 45 * Wrappers which implement old interface; act on global run queue. 46 */ 47 48struct thread * 49choosethread(void) 50{ 51 return (runq_choose(&runq)->ke_thread); 52} 53 54int 55procrunnable(void) 56{ 57 return runq_check(&runq); 58} 59 60void 61remrunqueue(struct thread *td) 62{ 63 runq_remove(&runq, td->td_kse); 64} 65 66void 67setrunqueue(struct thread *td) 68{ 69 runq_add(&runq, td->td_kse); 70} 71 72/* Critical sections that prevent preemption. */ 73void 74critical_enter(void) 75{ 76 struct thread *td; 77 78 td = curthread; 79 if (td->td_critnest == 0) 80 td->td_savecrit = cpu_critical_enter(); 81 td->td_critnest++; 82} 83 84void 85critical_exit(void) 86{ 87 struct thread *td; 88 89 td = curthread; 90 if (td->td_critnest == 1) { 91 td->td_critnest = 0; 92 cpu_critical_exit(td->td_savecrit); 93 } else 94 td->td_critnest--; 95} 96 97/* 98 * Clear the status bit of the queue corresponding to priority level pri, 99 * indicating that it is empty. 100 */ 101static __inline void 102runq_clrbit(struct runq *rq, int pri) 103{ 104 struct rqbits *rqb; 105 106 rqb = &rq->rq_status; 107 CTR4(KTR_RUNQ, "runq_clrbit: bits=%#x %#x bit=%#x word=%d", 108 rqb->rqb_bits[RQB_WORD(pri)], 109 rqb->rqb_bits[RQB_WORD(pri)] & ~RQB_BIT(pri), 110 RQB_BIT(pri), RQB_WORD(pri)); 111 rqb->rqb_bits[RQB_WORD(pri)] &= ~RQB_BIT(pri); 112} 113 114/* 115 * Find the index of the first non-empty run queue. This is done by 116 * scanning the status bits, a set bit indicates a non-empty queue. 117 */ 118static __inline int 119runq_findbit(struct runq *rq) 120{ 121 struct rqbits *rqb; 122 int pri; 123 int i; 124 125 rqb = &rq->rq_status; 126 for (i = 0; i < RQB_LEN; i++) 127 if (rqb->rqb_bits[i]) { 128 pri = (RQB_FFS(rqb->rqb_bits[i]) - 1) + 129 (i << RQB_L2BPW); 130 CTR3(KTR_RUNQ, "runq_findbit: bits=%#x i=%d pri=%d", 131 rqb->rqb_bits[i], i, pri); 132 return (pri); 133 } 134 135 return (-1); 136} 137 138/* 139 * Set the status bit of the queue corresponding to priority level pri, 140 * indicating that it is non-empty. 141 */ 142static __inline void 143runq_setbit(struct runq *rq, int pri) 144{ 145 struct rqbits *rqb; 146 147 rqb = &rq->rq_status; 148 CTR4(KTR_RUNQ, "runq_setbit: bits=%#x %#x bit=%#x word=%d", 149 rqb->rqb_bits[RQB_WORD(pri)], 150 rqb->rqb_bits[RQB_WORD(pri)] | RQB_BIT(pri), 151 RQB_BIT(pri), RQB_WORD(pri)); 152 rqb->rqb_bits[RQB_WORD(pri)] |= RQB_BIT(pri); 153} 154 155#ifdef INVARIANT_SUPPORT 156/* 157 * Return true if the specified process is already in the run queue. 158 */ 159static __inline int 160runq_find(struct runq *rq, struct kse *ke) 161{ 162 struct kse *ke2; 163 int i; 164 165 mtx_assert(&sched_lock, MA_OWNED); 166 for (i = 0; i < RQB_LEN; i++) 167 TAILQ_FOREACH(ke2, &rq->rq_queues[i], ke_procq) 168 if (ke2 == ke) 169 return 1; 170 return 0; 171} 172#endif 173 174/* 175 * Add the process to the queue specified by its priority, and set the 176 * corresponding status bit. 177 */ 178void 179runq_add(struct runq *rq, struct kse *ke) 180{ 181 struct rqhead *rqh; 182 int pri; 183 184#ifdef INVARIANTS 185 struct proc *p = ke->ke_proc; 186#endif 187 if (ke->ke_flags & KEF_ONRUNQ) 188 return; 189 mtx_assert(&sched_lock, MA_OWNED); 190 KASSERT(p->p_stat == SRUN, ("runq_add: proc %p (%s) not SRUN", 191 p, p->p_comm)); 192 KASSERT(runq_find(rq, ke) == 0, 193 ("runq_add: proc %p (%s) already in run queue", ke, p->p_comm)); 194 pri = ke->ke_thread->td_priority / RQ_PPQ; 195 ke->ke_rqindex = pri; 196 runq_setbit(rq, pri); 197 rqh = &rq->rq_queues[pri]; 198 CTR4(KTR_RUNQ, "runq_add: p=%p pri=%d %d rqh=%p", 199 ke->ke_proc, ke->ke_thread->td_priority, pri, rqh); 200 TAILQ_INSERT_TAIL(rqh, ke, ke_procq); 201 ke->ke_flags |= KEF_ONRUNQ; 202} 203 204/* 205 * Return true if there are runnable processes of any priority on the run 206 * queue, false otherwise. Has no side effects, does not modify the run 207 * queue structure. 208 */ 209int 210runq_check(struct runq *rq) 211{ 212 struct rqbits *rqb; 213 int i; 214 215 rqb = &rq->rq_status; 216 for (i = 0; i < RQB_LEN; i++) 217 if (rqb->rqb_bits[i]) { 218 CTR2(KTR_RUNQ, "runq_check: bits=%#x i=%d", 219 rqb->rqb_bits[i], i); 220 return (1); 221 } 222 CTR0(KTR_RUNQ, "runq_check: empty"); 223 224 return (0); 225} 226 227/* 228 * Find and remove the highest priority process from the run queue. 229 * If there are no runnable processes, the per-cpu idle process is 230 * returned. Will not return NULL under any circumstances. 231 */ 232struct kse * 233runq_choose(struct runq *rq) 234{ 235 struct rqhead *rqh; 236 struct kse *ke; 237 int pri; 238 239 mtx_assert(&sched_lock, MA_OWNED); 240 if ((pri = runq_findbit(rq)) != -1) { 241 rqh = &rq->rq_queues[pri]; 242 ke = TAILQ_FIRST(rqh); 243 KASSERT(ke != NULL, ("runq_choose: no proc on busy queue")); 244 KASSERT(ke->ke_proc->p_stat == SRUN, 245 ("runq_choose: process %d(%s) in state %d", ke->ke_proc->p_pid, 246 ke->ke_proc->p_comm, ke->ke_proc->p_stat)); 247 CTR3(KTR_RUNQ, "runq_choose: pri=%d kse=%p rqh=%p", pri, ke, rqh); 248 TAILQ_REMOVE(rqh, ke, ke_procq); 249 if (TAILQ_EMPTY(rqh)) { 250 CTR0(KTR_RUNQ, "runq_choose: empty"); 251 runq_clrbit(rq, pri); 252 } 253 ke->ke_flags &= ~KEF_ONRUNQ; 254 return (ke); 255 } 256 CTR1(KTR_RUNQ, "runq_choose: idleproc pri=%d", pri); 257 258 return (PCPU_GET(idlethread)->td_kse); 259} 260 261/* 262 * Initialize a run structure. 263 */ 264void 265runq_init(struct runq *rq) 266{ 267 int i; 268 269 bzero(rq, sizeof *rq); 270 for (i = 0; i < RQ_NQS; i++) 271 TAILQ_INIT(&rq->rq_queues[i]); 272} 273 274/* 275 * Remove the process from the queue specified by its priority, and clear the 276 * corresponding status bit if the queue becomes empty. 277 */ 278void 279runq_remove(struct runq *rq, struct kse *ke) 280{ 281 struct rqhead *rqh; 282 int pri; 283 284 if (!(ke->ke_flags & KEF_ONRUNQ)) 285 return; 286 mtx_assert(&sched_lock, MA_OWNED); 287 pri = ke->ke_rqindex; 288 rqh = &rq->rq_queues[pri]; 289 CTR4(KTR_RUNQ, "runq_remove: p=%p pri=%d %d rqh=%p", 290 ke, ke->ke_thread->td_priority, pri, rqh); 291 KASSERT(ke != NULL, ("runq_remove: no proc on busy queue")); 292 TAILQ_REMOVE(rqh, ke, ke_procq); 293 if (TAILQ_EMPTY(rqh)) { 294 CTR0(KTR_RUNQ, "runq_remove: empty"); 295 runq_clrbit(rq, pri); 296 } 297 ke->ke_flags &= ~KEF_ONRUNQ; 298} 299