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 27 28#include <sys/cdefs.h> 29__FBSDID("$FreeBSD: releng/11.0/sys/kern/kern_switch.c 277528 2015-01-22 11:12:42Z hselasky $"); 30 31#include "opt_sched.h" 32 33#include <sys/param.h> 34#include <sys/systm.h> 35#include <sys/kdb.h> 36#include <sys/kernel.h> 37#include <sys/ktr.h> 38#include <sys/lock.h> 39#include <sys/mutex.h> 40#include <sys/proc.h> 41#include <sys/queue.h> 42#include <sys/sched.h> 43#include <sys/smp.h> 44#include <sys/sysctl.h> 45 46#include <machine/cpu.h> 47 48/* Uncomment this to enable logging of critical_enter/exit. */ 49#if 0 50#define KTR_CRITICAL KTR_SCHED 51#else 52#define KTR_CRITICAL 0 53#endif 54 55#ifdef FULL_PREEMPTION 56#ifndef PREEMPTION 57#error "The FULL_PREEMPTION option requires the PREEMPTION option" 58#endif 59#endif 60 61CTASSERT((RQB_BPW * RQB_LEN) == RQ_NQS); 62 63/* 64 * kern.sched.preemption allows user space to determine if preemption support 65 * is compiled in or not. It is not currently a boot or runtime flag that 66 * can be changed. 67 */ 68#ifdef PREEMPTION 69static int kern_sched_preemption = 1; 70#else 71static int kern_sched_preemption = 0; 72#endif 73SYSCTL_INT(_kern_sched, OID_AUTO, preemption, CTLFLAG_RD, 74 &kern_sched_preemption, 0, "Kernel preemption enabled"); 75 76/* 77 * Support for scheduler stats exported via kern.sched.stats. All stats may 78 * be reset with kern.sched.stats.reset = 1. Stats may be defined elsewhere 79 * with SCHED_STAT_DEFINE(). 80 */ 81#ifdef SCHED_STATS 82SYSCTL_NODE(_kern_sched, OID_AUTO, stats, CTLFLAG_RW, 0, "switch stats"); 83 84/* Switch reasons from mi_switch(). */ 85DPCPU_DEFINE(long, sched_switch_stats[SWT_COUNT]); 86SCHED_STAT_DEFINE_VAR(uncategorized, 87 &DPCPU_NAME(sched_switch_stats[SWT_NONE]), ""); 88SCHED_STAT_DEFINE_VAR(preempt, 89 &DPCPU_NAME(sched_switch_stats[SWT_PREEMPT]), ""); 90SCHED_STAT_DEFINE_VAR(owepreempt, 91 &DPCPU_NAME(sched_switch_stats[SWT_OWEPREEMPT]), ""); 92SCHED_STAT_DEFINE_VAR(turnstile, 93 &DPCPU_NAME(sched_switch_stats[SWT_TURNSTILE]), ""); 94SCHED_STAT_DEFINE_VAR(sleepq, 95 &DPCPU_NAME(sched_switch_stats[SWT_SLEEPQ]), ""); 96SCHED_STAT_DEFINE_VAR(sleepqtimo, 97 &DPCPU_NAME(sched_switch_stats[SWT_SLEEPQTIMO]), ""); 98SCHED_STAT_DEFINE_VAR(relinquish, 99 &DPCPU_NAME(sched_switch_stats[SWT_RELINQUISH]), ""); 100SCHED_STAT_DEFINE_VAR(needresched, 101 &DPCPU_NAME(sched_switch_stats[SWT_NEEDRESCHED]), ""); 102SCHED_STAT_DEFINE_VAR(idle, 103 &DPCPU_NAME(sched_switch_stats[SWT_IDLE]), ""); 104SCHED_STAT_DEFINE_VAR(iwait, 105 &DPCPU_NAME(sched_switch_stats[SWT_IWAIT]), ""); 106SCHED_STAT_DEFINE_VAR(suspend, 107 &DPCPU_NAME(sched_switch_stats[SWT_SUSPEND]), ""); 108SCHED_STAT_DEFINE_VAR(remotepreempt, 109 &DPCPU_NAME(sched_switch_stats[SWT_REMOTEPREEMPT]), ""); 110SCHED_STAT_DEFINE_VAR(remotewakeidle, 111 &DPCPU_NAME(sched_switch_stats[SWT_REMOTEWAKEIDLE]), ""); 112 113static int 114sysctl_stats_reset(SYSCTL_HANDLER_ARGS) 115{ 116 struct sysctl_oid *p; 117 uintptr_t counter; 118 int error; 119 int val; 120 int i; 121 122 val = 0; 123 error = sysctl_handle_int(oidp, &val, 0, req); 124 if (error != 0 || req->newptr == NULL) 125 return (error); 126 if (val == 0) 127 return (0); 128 /* 129 * Traverse the list of children of _kern_sched_stats and reset each 130 * to 0. Skip the reset entry. 131 */ 132 SLIST_FOREACH(p, oidp->oid_parent, oid_link) { 133 if (p == oidp || p->oid_arg1 == NULL) 134 continue; 135 counter = (uintptr_t)p->oid_arg1; 136 CPU_FOREACH(i) { 137 *(long *)(dpcpu_off[i] + counter) = 0; 138 } 139 } 140 return (0); 141} 142 143SYSCTL_PROC(_kern_sched_stats, OID_AUTO, reset, CTLTYPE_INT | CTLFLAG_WR, NULL, 144 0, sysctl_stats_reset, "I", "Reset scheduler statistics"); 145#endif 146 147/************************************************************************ 148 * Functions that manipulate runnability from a thread perspective. * 149 ************************************************************************/ 150/* 151 * Select the thread that will be run next. 152 */ 153struct thread * 154choosethread(void) 155{ 156 struct thread *td; 157 158retry: 159 td = sched_choose(); 160 161 /* 162 * If we are in panic, only allow system threads, 163 * plus the one we are running in, to be run. 164 */ 165 if (panicstr && ((td->td_proc->p_flag & P_SYSTEM) == 0 && 166 (td->td_flags & TDF_INPANIC) == 0)) { 167 /* note that it is no longer on the run queue */ 168 TD_SET_CAN_RUN(td); 169 goto retry; 170 } 171 172 TD_SET_RUNNING(td); 173 return (td); 174} 175 176/* 177 * Kernel thread preemption implementation. Critical sections mark 178 * regions of code in which preemptions are not allowed. 179 * 180 * It might seem a good idea to inline critical_enter() but, in order 181 * to prevent instructions reordering by the compiler, a __compiler_membar() 182 * would have to be used here (the same as sched_pin()). The performance 183 * penalty imposed by the membar could, then, produce slower code than 184 * the function call itself, for most cases. 185 */ 186void 187critical_enter(void) 188{ 189 struct thread *td; 190 191 td = curthread; 192 td->td_critnest++; 193 CTR4(KTR_CRITICAL, "critical_enter by thread %p (%ld, %s) to %d", td, 194 (long)td->td_proc->p_pid, td->td_name, td->td_critnest); 195} 196 197void 198critical_exit(void) 199{ 200 struct thread *td; 201 int flags; 202 203 td = curthread; 204 KASSERT(td->td_critnest != 0, 205 ("critical_exit: td_critnest == 0")); 206 207 if (td->td_critnest == 1) { 208 td->td_critnest = 0; 209 if (td->td_owepreempt && !kdb_active) { 210 td->td_critnest = 1; 211 thread_lock(td); 212 td->td_critnest--; 213 flags = SW_INVOL | SW_PREEMPT; 214 if (TD_IS_IDLETHREAD(td)) 215 flags |= SWT_IDLE; 216 else 217 flags |= SWT_OWEPREEMPT; 218 mi_switch(flags, NULL); 219 thread_unlock(td); 220 } 221 } else 222 td->td_critnest--; 223 224 CTR4(KTR_CRITICAL, "critical_exit by thread %p (%ld, %s) to %d", td, 225 (long)td->td_proc->p_pid, td->td_name, td->td_critnest); 226} 227 228/************************************************************************ 229 * SYSTEM RUN QUEUE manipulations and tests * 230 ************************************************************************/ 231/* 232 * Initialize a run structure. 233 */ 234void 235runq_init(struct runq *rq) 236{ 237 int i; 238 239 bzero(rq, sizeof *rq); 240 for (i = 0; i < RQ_NQS; i++) 241 TAILQ_INIT(&rq->rq_queues[i]); 242} 243 244/* 245 * Clear the status bit of the queue corresponding to priority level pri, 246 * indicating that it is empty. 247 */ 248static __inline void 249runq_clrbit(struct runq *rq, int pri) 250{ 251 struct rqbits *rqb; 252 253 rqb = &rq->rq_status; 254 CTR4(KTR_RUNQ, "runq_clrbit: bits=%#x %#x bit=%#x word=%d", 255 rqb->rqb_bits[RQB_WORD(pri)], 256 rqb->rqb_bits[RQB_WORD(pri)] & ~RQB_BIT(pri), 257 RQB_BIT(pri), RQB_WORD(pri)); 258 rqb->rqb_bits[RQB_WORD(pri)] &= ~RQB_BIT(pri); 259} 260 261/* 262 * Find the index of the first non-empty run queue. This is done by 263 * scanning the status bits, a set bit indicates a non-empty queue. 264 */ 265static __inline int 266runq_findbit(struct runq *rq) 267{ 268 struct rqbits *rqb; 269 int pri; 270 int i; 271 272 rqb = &rq->rq_status; 273 for (i = 0; i < RQB_LEN; i++) 274 if (rqb->rqb_bits[i]) { 275 pri = RQB_FFS(rqb->rqb_bits[i]) + (i << RQB_L2BPW); 276 CTR3(KTR_RUNQ, "runq_findbit: bits=%#x i=%d pri=%d", 277 rqb->rqb_bits[i], i, pri); 278 return (pri); 279 } 280 281 return (-1); 282} 283 284static __inline int 285runq_findbit_from(struct runq *rq, u_char pri) 286{ 287 struct rqbits *rqb; 288 rqb_word_t mask; 289 int i; 290 291 /* 292 * Set the mask for the first word so we ignore priorities before 'pri'. 293 */ 294 mask = (rqb_word_t)-1 << (pri & (RQB_BPW - 1)); 295 rqb = &rq->rq_status; 296again: 297 for (i = RQB_WORD(pri); i < RQB_LEN; mask = -1, i++) { 298 mask = rqb->rqb_bits[i] & mask; 299 if (mask == 0) 300 continue; 301 pri = RQB_FFS(mask) + (i << RQB_L2BPW); 302 CTR3(KTR_RUNQ, "runq_findbit_from: bits=%#x i=%d pri=%d", 303 mask, i, pri); 304 return (pri); 305 } 306 if (pri == 0) 307 return (-1); 308 /* 309 * Wrap back around to the beginning of the list just once so we 310 * scan the whole thing. 311 */ 312 pri = 0; 313 goto again; 314} 315 316/* 317 * Set the status bit of the queue corresponding to priority level pri, 318 * indicating that it is non-empty. 319 */ 320static __inline void 321runq_setbit(struct runq *rq, int pri) 322{ 323 struct rqbits *rqb; 324 325 rqb = &rq->rq_status; 326 CTR4(KTR_RUNQ, "runq_setbit: bits=%#x %#x bit=%#x word=%d", 327 rqb->rqb_bits[RQB_WORD(pri)], 328 rqb->rqb_bits[RQB_WORD(pri)] | RQB_BIT(pri), 329 RQB_BIT(pri), RQB_WORD(pri)); 330 rqb->rqb_bits[RQB_WORD(pri)] |= RQB_BIT(pri); 331} 332 333/* 334 * Add the thread to the queue specified by its priority, and set the 335 * corresponding status bit. 336 */ 337void 338runq_add(struct runq *rq, struct thread *td, int flags) 339{ 340 struct rqhead *rqh; 341 int pri; 342 343 pri = td->td_priority / RQ_PPQ; 344 td->td_rqindex = pri; 345 runq_setbit(rq, pri); 346 rqh = &rq->rq_queues[pri]; 347 CTR4(KTR_RUNQ, "runq_add: td=%p pri=%d %d rqh=%p", 348 td, td->td_priority, pri, rqh); 349 if (flags & SRQ_PREEMPTED) { 350 TAILQ_INSERT_HEAD(rqh, td, td_runq); 351 } else { 352 TAILQ_INSERT_TAIL(rqh, td, td_runq); 353 } 354} 355 356void 357runq_add_pri(struct runq *rq, struct thread *td, u_char pri, int flags) 358{ 359 struct rqhead *rqh; 360 361 KASSERT(pri < RQ_NQS, ("runq_add_pri: %d out of range", pri)); 362 td->td_rqindex = pri; 363 runq_setbit(rq, pri); 364 rqh = &rq->rq_queues[pri]; 365 CTR4(KTR_RUNQ, "runq_add_pri: td=%p pri=%d idx=%d rqh=%p", 366 td, td->td_priority, pri, rqh); 367 if (flags & SRQ_PREEMPTED) { 368 TAILQ_INSERT_HEAD(rqh, td, td_runq); 369 } else { 370 TAILQ_INSERT_TAIL(rqh, td, td_runq); 371 } 372} 373/* 374 * Return true if there are runnable processes of any priority on the run 375 * queue, false otherwise. Has no side effects, does not modify the run 376 * queue structure. 377 */ 378int 379runq_check(struct runq *rq) 380{ 381 struct rqbits *rqb; 382 int i; 383 384 rqb = &rq->rq_status; 385 for (i = 0; i < RQB_LEN; i++) 386 if (rqb->rqb_bits[i]) { 387 CTR2(KTR_RUNQ, "runq_check: bits=%#x i=%d", 388 rqb->rqb_bits[i], i); 389 return (1); 390 } 391 CTR0(KTR_RUNQ, "runq_check: empty"); 392 393 return (0); 394} 395 396/* 397 * Find the highest priority process on the run queue. 398 */ 399struct thread * 400runq_choose_fuzz(struct runq *rq, int fuzz) 401{ 402 struct rqhead *rqh; 403 struct thread *td; 404 int pri; 405 406 while ((pri = runq_findbit(rq)) != -1) { 407 rqh = &rq->rq_queues[pri]; 408 /* fuzz == 1 is normal.. 0 or less are ignored */ 409 if (fuzz > 1) { 410 /* 411 * In the first couple of entries, check if 412 * there is one for our CPU as a preference. 413 */ 414 int count = fuzz; 415 int cpu = PCPU_GET(cpuid); 416 struct thread *td2; 417 td2 = td = TAILQ_FIRST(rqh); 418 419 while (count-- && td2) { 420 if (td2->td_lastcpu == cpu) { 421 td = td2; 422 break; 423 } 424 td2 = TAILQ_NEXT(td2, td_runq); 425 } 426 } else 427 td = TAILQ_FIRST(rqh); 428 KASSERT(td != NULL, ("runq_choose_fuzz: no proc on busy queue")); 429 CTR3(KTR_RUNQ, 430 "runq_choose_fuzz: pri=%d thread=%p rqh=%p", pri, td, rqh); 431 return (td); 432 } 433 CTR1(KTR_RUNQ, "runq_choose_fuzz: idleproc pri=%d", pri); 434 435 return (NULL); 436} 437 438/* 439 * Find the highest priority process on the run queue. 440 */ 441struct thread * 442runq_choose(struct runq *rq) 443{ 444 struct rqhead *rqh; 445 struct thread *td; 446 int pri; 447 448 while ((pri = runq_findbit(rq)) != -1) { 449 rqh = &rq->rq_queues[pri]; 450 td = TAILQ_FIRST(rqh); 451 KASSERT(td != NULL, ("runq_choose: no thread on busy queue")); 452 CTR3(KTR_RUNQ, 453 "runq_choose: pri=%d thread=%p rqh=%p", pri, td, rqh); 454 return (td); 455 } 456 CTR1(KTR_RUNQ, "runq_choose: idlethread pri=%d", pri); 457 458 return (NULL); 459} 460 461struct thread * 462runq_choose_from(struct runq *rq, u_char idx) 463{ 464 struct rqhead *rqh; 465 struct thread *td; 466 int pri; 467 468 if ((pri = runq_findbit_from(rq, idx)) != -1) { 469 rqh = &rq->rq_queues[pri]; 470 td = TAILQ_FIRST(rqh); 471 KASSERT(td != NULL, ("runq_choose: no thread on busy queue")); 472 CTR4(KTR_RUNQ, 473 "runq_choose_from: pri=%d thread=%p idx=%d rqh=%p", 474 pri, td, td->td_rqindex, rqh); 475 return (td); 476 } 477 CTR1(KTR_RUNQ, "runq_choose_from: idlethread pri=%d", pri); 478 479 return (NULL); 480} 481/* 482 * Remove the thread from the queue specified by its priority, and clear the 483 * corresponding status bit if the queue becomes empty. 484 * Caller must set state afterwards. 485 */ 486void 487runq_remove(struct runq *rq, struct thread *td) 488{ 489 490 runq_remove_idx(rq, td, NULL); 491} 492 493void 494runq_remove_idx(struct runq *rq, struct thread *td, u_char *idx) 495{ 496 struct rqhead *rqh; 497 u_char pri; 498 499 KASSERT(td->td_flags & TDF_INMEM, 500 ("runq_remove_idx: thread swapped out")); 501 pri = td->td_rqindex; 502 KASSERT(pri < RQ_NQS, ("runq_remove_idx: Invalid index %d\n", pri)); 503 rqh = &rq->rq_queues[pri]; 504 CTR4(KTR_RUNQ, "runq_remove_idx: td=%p, pri=%d %d rqh=%p", 505 td, td->td_priority, pri, rqh); 506 TAILQ_REMOVE(rqh, td, td_runq); 507 if (TAILQ_EMPTY(rqh)) { 508 CTR0(KTR_RUNQ, "runq_remove_idx: empty"); 509 runq_clrbit(rq, pri); 510 if (idx != NULL && *idx == pri) 511 *idx = (pri + 1) % RQ_NQS; 512 } 513} 514