1 /* 2 * Copyright (c) 2003-2011 The DragonFly Project. All rights reserved. 3 * 4 * This code is derived from software contributed to The DragonFly Project 5 * by Matthew Dillon <dillon@backplane.com> 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 * 11 * 1. Redistributions of source code must retain the above copyright 12 * notice, this list of conditions and the following disclaimer. 13 * 2. Redistributions in binary form must reproduce the above copyright 14 * notice, this list of conditions and the following disclaimer in 15 * the documentation and/or other materials provided with the 16 * distribution. 17 * 3. Neither the name of The DragonFly Project nor the names of its 18 * contributors may be used to endorse or promote products derived 19 * from this software without specific, prior written permission. 20 * 21 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 22 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT 23 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS 24 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE 25 * COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, 26 * INCIDENTAL, SPECIAL, EXEMPLARY OR CONSEQUENTIAL DAMAGES (INCLUDING, 27 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; 28 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED 29 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, 30 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT 31 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 32 * SUCH DAMAGE. 33 */ 34 35 /* 36 * Each cpu in a system has its own self-contained light weight kernel 37 * thread scheduler, which means that generally speaking we only need 38 * to use a critical section to avoid problems. Foreign thread 39 * scheduling is queued via (async) IPIs. 40 */ 41 42 #include <sys/param.h> 43 #include <sys/systm.h> 44 #include <sys/kernel.h> 45 #include <sys/proc.h> 46 #include <sys/rtprio.h> 47 #include <sys/kinfo.h> 48 #include <sys/queue.h> 49 #include <sys/sysctl.h> 50 #include <sys/kthread.h> 51 #include <machine/cpu.h> 52 #include <sys/lock.h> 53 #include <sys/caps.h> 54 #include <sys/spinlock.h> 55 #include <sys/ktr.h> 56 57 #include <sys/thread2.h> 58 #include <sys/spinlock2.h> 59 #include <sys/mplock2.h> 60 61 #include <sys/dsched.h> 62 63 #include <vm/vm.h> 64 #include <vm/vm_param.h> 65 #include <vm/vm_kern.h> 66 #include <vm/vm_object.h> 67 #include <vm/vm_page.h> 68 #include <vm/vm_map.h> 69 #include <vm/vm_pager.h> 70 #include <vm/vm_extern.h> 71 72 #include <machine/stdarg.h> 73 #include <machine/smp.h> 74 75 #if !defined(KTR_CTXSW) 76 #define KTR_CTXSW KTR_ALL 77 #endif 78 KTR_INFO_MASTER(ctxsw); 79 KTR_INFO(KTR_CTXSW, ctxsw, sw, 0, "#cpu[%d].td = %p", 80 sizeof(int) + sizeof(struct thread *)); 81 KTR_INFO(KTR_CTXSW, ctxsw, pre, 1, "#cpu[%d].td = %p", 82 sizeof(int) + sizeof(struct thread *)); 83 KTR_INFO(KTR_CTXSW, ctxsw, newtd, 2, "#threads[%p].name = %s", 84 sizeof (struct thread *) + sizeof(char *)); 85 KTR_INFO(KTR_CTXSW, ctxsw, deadtd, 3, "#threads[%p].name = <dead>", sizeof (struct thread *)); 86 87 static MALLOC_DEFINE(M_THREAD, "thread", "lwkt threads"); 88 89 #ifdef INVARIANTS 90 static int panic_on_cscount = 0; 91 #endif 92 static __int64_t switch_count = 0; 93 static __int64_t preempt_hit = 0; 94 static __int64_t preempt_miss = 0; 95 static __int64_t preempt_weird = 0; 96 static __int64_t token_contention_count[TDPRI_MAX+1] __debugvar; 97 static int lwkt_use_spin_port; 98 static struct objcache *thread_cache; 99 100 #ifdef SMP 101 static void lwkt_schedule_remote(void *arg, int arg2, struct intrframe *frame); 102 static void lwkt_setcpu_remote(void *arg); 103 #endif 104 105 extern void cpu_heavy_restore(void); 106 extern void cpu_lwkt_restore(void); 107 extern void cpu_kthread_restore(void); 108 extern void cpu_idle_restore(void); 109 110 /* 111 * We can make all thread ports use the spin backend instead of the thread 112 * backend. This should only be set to debug the spin backend. 113 */ 114 TUNABLE_INT("lwkt.use_spin_port", &lwkt_use_spin_port); 115 116 #ifdef INVARIANTS 117 SYSCTL_INT(_lwkt, OID_AUTO, panic_on_cscount, CTLFLAG_RW, &panic_on_cscount, 0, 118 "Panic if attempting to switch lwkt's while mastering cpusync"); 119 #endif 120 SYSCTL_QUAD(_lwkt, OID_AUTO, switch_count, CTLFLAG_RW, &switch_count, 0, 121 "Number of switched threads"); 122 SYSCTL_QUAD(_lwkt, OID_AUTO, preempt_hit, CTLFLAG_RW, &preempt_hit, 0, 123 "Successful preemption events"); 124 SYSCTL_QUAD(_lwkt, OID_AUTO, preempt_miss, CTLFLAG_RW, &preempt_miss, 0, 125 "Failed preemption events"); 126 SYSCTL_QUAD(_lwkt, OID_AUTO, preempt_weird, CTLFLAG_RW, &preempt_weird, 0, 127 "Number of preempted threads."); 128 #ifdef INVARIANTS 129 SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count_00, CTLFLAG_RW, 130 &token_contention_count[0], 0, "spinning due to token contention"); 131 SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count_01, CTLFLAG_RW, 132 &token_contention_count[1], 0, "spinning due to token contention"); 133 SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count_02, CTLFLAG_RW, 134 &token_contention_count[2], 0, "spinning due to token contention"); 135 SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count_03, CTLFLAG_RW, 136 &token_contention_count[3], 0, "spinning due to token contention"); 137 SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count_04, CTLFLAG_RW, 138 &token_contention_count[4], 0, "spinning due to token contention"); 139 SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count_05, CTLFLAG_RW, 140 &token_contention_count[5], 0, "spinning due to token contention"); 141 SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count_06, CTLFLAG_RW, 142 &token_contention_count[6], 0, "spinning due to token contention"); 143 SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count_07, CTLFLAG_RW, 144 &token_contention_count[7], 0, "spinning due to token contention"); 145 SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count_08, CTLFLAG_RW, 146 &token_contention_count[8], 0, "spinning due to token contention"); 147 SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count_09, CTLFLAG_RW, 148 &token_contention_count[9], 0, "spinning due to token contention"); 149 SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count_10, CTLFLAG_RW, 150 &token_contention_count[10], 0, "spinning due to token contention"); 151 SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count_11, CTLFLAG_RW, 152 &token_contention_count[11], 0, "spinning due to token contention"); 153 SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count_12, CTLFLAG_RW, 154 &token_contention_count[12], 0, "spinning due to token contention"); 155 SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count_13, CTLFLAG_RW, 156 &token_contention_count[13], 0, "spinning due to token contention"); 157 SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count_14, CTLFLAG_RW, 158 &token_contention_count[14], 0, "spinning due to token contention"); 159 SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count_15, CTLFLAG_RW, 160 &token_contention_count[15], 0, "spinning due to token contention"); 161 SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count_16, CTLFLAG_RW, 162 &token_contention_count[16], 0, "spinning due to token contention"); 163 SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count_17, CTLFLAG_RW, 164 &token_contention_count[17], 0, "spinning due to token contention"); 165 SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count_18, CTLFLAG_RW, 166 &token_contention_count[18], 0, "spinning due to token contention"); 167 SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count_19, CTLFLAG_RW, 168 &token_contention_count[19], 0, "spinning due to token contention"); 169 SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count_20, CTLFLAG_RW, 170 &token_contention_count[20], 0, "spinning due to token contention"); 171 SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count_21, CTLFLAG_RW, 172 &token_contention_count[21], 0, "spinning due to token contention"); 173 SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count_22, CTLFLAG_RW, 174 &token_contention_count[22], 0, "spinning due to token contention"); 175 SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count_23, CTLFLAG_RW, 176 &token_contention_count[23], 0, "spinning due to token contention"); 177 SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count_24, CTLFLAG_RW, 178 &token_contention_count[24], 0, "spinning due to token contention"); 179 SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count_25, CTLFLAG_RW, 180 &token_contention_count[25], 0, "spinning due to token contention"); 181 SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count_26, CTLFLAG_RW, 182 &token_contention_count[26], 0, "spinning due to token contention"); 183 SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count_27, CTLFLAG_RW, 184 &token_contention_count[27], 0, "spinning due to token contention"); 185 SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count_28, CTLFLAG_RW, 186 &token_contention_count[28], 0, "spinning due to token contention"); 187 SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count_29, CTLFLAG_RW, 188 &token_contention_count[29], 0, "spinning due to token contention"); 189 SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count_30, CTLFLAG_RW, 190 &token_contention_count[30], 0, "spinning due to token contention"); 191 SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count_31, CTLFLAG_RW, 192 &token_contention_count[31], 0, "spinning due to token contention"); 193 #endif 194 static int fairq_enable = 0; 195 SYSCTL_INT(_lwkt, OID_AUTO, fairq_enable, CTLFLAG_RW, 196 &fairq_enable, 0, "Turn on fairq priority accumulators"); 197 static int fairq_bypass = -1; 198 SYSCTL_INT(_lwkt, OID_AUTO, fairq_bypass, CTLFLAG_RW, 199 &fairq_bypass, 0, "Allow fairq to bypass td on token failure"); 200 extern int lwkt_sched_debug; 201 int lwkt_sched_debug = 0; 202 SYSCTL_INT(_lwkt, OID_AUTO, sched_debug, CTLFLAG_RW, 203 &lwkt_sched_debug, 0, "Scheduler debug"); 204 static int lwkt_spin_loops = 10; 205 SYSCTL_INT(_lwkt, OID_AUTO, spin_loops, CTLFLAG_RW, 206 &lwkt_spin_loops, 0, "Scheduler spin loops until sorted decon"); 207 static int lwkt_spin_reseq = 0; 208 SYSCTL_INT(_lwkt, OID_AUTO, spin_reseq, CTLFLAG_RW, 209 &lwkt_spin_reseq, 0, "Scheduler resequencer enable"); 210 static int lwkt_spin_monitor = 0; 211 SYSCTL_INT(_lwkt, OID_AUTO, spin_monitor, CTLFLAG_RW, 212 &lwkt_spin_monitor, 0, "Scheduler uses monitor/mwait"); 213 static int lwkt_spin_fatal = 0; /* disabled */ 214 SYSCTL_INT(_lwkt, OID_AUTO, spin_fatal, CTLFLAG_RW, 215 &lwkt_spin_fatal, 0, "LWKT scheduler spin loops till fatal panic"); 216 static int preempt_enable = 1; 217 SYSCTL_INT(_lwkt, OID_AUTO, preempt_enable, CTLFLAG_RW, 218 &preempt_enable, 0, "Enable preemption"); 219 static int lwkt_cache_threads = 32; 220 SYSCTL_INT(_lwkt, OID_AUTO, cache_threads, CTLFLAG_RD, 221 &lwkt_cache_threads, 0, "thread+kstack cache"); 222 223 static __cachealign int lwkt_cseq_rindex; 224 static __cachealign int lwkt_cseq_windex; 225 226 /* 227 * These helper procedures handle the runq, they can only be called from 228 * within a critical section. 229 * 230 * WARNING! Prior to SMP being brought up it is possible to enqueue and 231 * dequeue threads belonging to other cpus, so be sure to use td->td_gd 232 * instead of 'mycpu' when referencing the globaldata structure. Once 233 * SMP live enqueuing and dequeueing only occurs on the current cpu. 234 */ 235 static __inline 236 void 237 _lwkt_dequeue(thread_t td) 238 { 239 if (td->td_flags & TDF_RUNQ) { 240 struct globaldata *gd = td->td_gd; 241 242 td->td_flags &= ~TDF_RUNQ; 243 TAILQ_REMOVE(&gd->gd_tdrunq, td, td_threadq); 244 if (TAILQ_FIRST(&gd->gd_tdrunq) == NULL) 245 atomic_clear_int(&gd->gd_reqflags, RQF_RUNNING); 246 } 247 } 248 249 /* 250 * Priority enqueue. 251 * 252 * NOTE: There are a limited number of lwkt threads runnable since user 253 * processes only schedule one at a time per cpu. 254 */ 255 static __inline 256 void 257 _lwkt_enqueue(thread_t td) 258 { 259 thread_t xtd; 260 261 if ((td->td_flags & (TDF_RUNQ|TDF_MIGRATING|TDF_BLOCKQ)) == 0) { 262 struct globaldata *gd = td->td_gd; 263 264 td->td_flags |= TDF_RUNQ; 265 xtd = TAILQ_FIRST(&gd->gd_tdrunq); 266 if (xtd == NULL) { 267 TAILQ_INSERT_TAIL(&gd->gd_tdrunq, td, td_threadq); 268 atomic_set_int(&gd->gd_reqflags, RQF_RUNNING); 269 } else { 270 while (xtd && xtd->td_pri >= td->td_pri) 271 xtd = TAILQ_NEXT(xtd, td_threadq); 272 if (xtd) 273 TAILQ_INSERT_BEFORE(xtd, td, td_threadq); 274 else 275 TAILQ_INSERT_TAIL(&gd->gd_tdrunq, td, td_threadq); 276 } 277 278 /* 279 * Request a LWKT reschedule if we are now at the head of the queue. 280 */ 281 if (TAILQ_FIRST(&gd->gd_tdrunq) == td) 282 need_lwkt_resched(); 283 } 284 } 285 286 static __boolean_t 287 _lwkt_thread_ctor(void *obj, void *privdata, int ocflags) 288 { 289 struct thread *td = (struct thread *)obj; 290 291 td->td_kstack = NULL; 292 td->td_kstack_size = 0; 293 td->td_flags = TDF_ALLOCATED_THREAD; 294 return (1); 295 } 296 297 static void 298 _lwkt_thread_dtor(void *obj, void *privdata) 299 { 300 struct thread *td = (struct thread *)obj; 301 302 KASSERT(td->td_flags & TDF_ALLOCATED_THREAD, 303 ("_lwkt_thread_dtor: not allocated from objcache")); 304 KASSERT((td->td_flags & TDF_ALLOCATED_STACK) && td->td_kstack && 305 td->td_kstack_size > 0, 306 ("_lwkt_thread_dtor: corrupted stack")); 307 kmem_free(&kernel_map, (vm_offset_t)td->td_kstack, td->td_kstack_size); 308 } 309 310 /* 311 * Initialize the lwkt s/system. 312 * 313 * Nominally cache up to 32 thread + kstack structures. 314 */ 315 void 316 lwkt_init(void) 317 { 318 TUNABLE_INT("lwkt.cache_threads", &lwkt_cache_threads); 319 thread_cache = objcache_create_mbacked( 320 M_THREAD, sizeof(struct thread), 321 NULL, lwkt_cache_threads, 322 _lwkt_thread_ctor, _lwkt_thread_dtor, NULL); 323 } 324 325 /* 326 * Schedule a thread to run. As the current thread we can always safely 327 * schedule ourselves, and a shortcut procedure is provided for that 328 * function. 329 * 330 * (non-blocking, self contained on a per cpu basis) 331 */ 332 void 333 lwkt_schedule_self(thread_t td) 334 { 335 KKASSERT((td->td_flags & TDF_MIGRATING) == 0); 336 crit_enter_quick(td); 337 KASSERT(td != &td->td_gd->gd_idlethread, 338 ("lwkt_schedule_self(): scheduling gd_idlethread is illegal!")); 339 KKASSERT(td->td_lwp == NULL || (td->td_lwp->lwp_flag & LWP_ONRUNQ) == 0); 340 _lwkt_enqueue(td); 341 crit_exit_quick(td); 342 } 343 344 /* 345 * Deschedule a thread. 346 * 347 * (non-blocking, self contained on a per cpu basis) 348 */ 349 void 350 lwkt_deschedule_self(thread_t td) 351 { 352 crit_enter_quick(td); 353 _lwkt_dequeue(td); 354 crit_exit_quick(td); 355 } 356 357 /* 358 * LWKTs operate on a per-cpu basis 359 * 360 * WARNING! Called from early boot, 'mycpu' may not work yet. 361 */ 362 void 363 lwkt_gdinit(struct globaldata *gd) 364 { 365 TAILQ_INIT(&gd->gd_tdrunq); 366 TAILQ_INIT(&gd->gd_tdallq); 367 } 368 369 /* 370 * Create a new thread. The thread must be associated with a process context 371 * or LWKT start address before it can be scheduled. If the target cpu is 372 * -1 the thread will be created on the current cpu. 373 * 374 * If you intend to create a thread without a process context this function 375 * does everything except load the startup and switcher function. 376 */ 377 thread_t 378 lwkt_alloc_thread(struct thread *td, int stksize, int cpu, int flags) 379 { 380 static int cpu_rotator; 381 globaldata_t gd = mycpu; 382 void *stack; 383 384 /* 385 * If static thread storage is not supplied allocate a thread. Reuse 386 * a cached free thread if possible. gd_freetd is used to keep an exiting 387 * thread intact through the exit. 388 */ 389 if (td == NULL) { 390 crit_enter_gd(gd); 391 if ((td = gd->gd_freetd) != NULL) { 392 KKASSERT((td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK| 393 TDF_RUNQ)) == 0); 394 gd->gd_freetd = NULL; 395 } else { 396 td = objcache_get(thread_cache, M_WAITOK); 397 KKASSERT((td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK| 398 TDF_RUNQ)) == 0); 399 } 400 crit_exit_gd(gd); 401 KASSERT((td->td_flags & 402 (TDF_ALLOCATED_THREAD|TDF_RUNNING)) == TDF_ALLOCATED_THREAD, 403 ("lwkt_alloc_thread: corrupted td flags 0x%X", td->td_flags)); 404 flags |= td->td_flags & (TDF_ALLOCATED_THREAD|TDF_ALLOCATED_STACK); 405 } 406 407 /* 408 * Try to reuse cached stack. 409 */ 410 if ((stack = td->td_kstack) != NULL && td->td_kstack_size != stksize) { 411 if (flags & TDF_ALLOCATED_STACK) { 412 kmem_free(&kernel_map, (vm_offset_t)stack, td->td_kstack_size); 413 stack = NULL; 414 } 415 } 416 if (stack == NULL) { 417 stack = (void *)kmem_alloc_stack(&kernel_map, stksize); 418 flags |= TDF_ALLOCATED_STACK; 419 } 420 if (cpu < 0) { 421 cpu = ++cpu_rotator; 422 cpu_ccfence(); 423 cpu %= ncpus; 424 } 425 lwkt_init_thread(td, stack, stksize, flags, globaldata_find(cpu)); 426 return(td); 427 } 428 429 /* 430 * Initialize a preexisting thread structure. This function is used by 431 * lwkt_alloc_thread() and also used to initialize the per-cpu idlethread. 432 * 433 * All threads start out in a critical section at a priority of 434 * TDPRI_KERN_DAEMON. Higher level code will modify the priority as 435 * appropriate. This function may send an IPI message when the 436 * requested cpu is not the current cpu and consequently gd_tdallq may 437 * not be initialized synchronously from the point of view of the originating 438 * cpu. 439 * 440 * NOTE! we have to be careful in regards to creating threads for other cpus 441 * if SMP has not yet been activated. 442 */ 443 #ifdef SMP 444 445 static void 446 lwkt_init_thread_remote(void *arg) 447 { 448 thread_t td = arg; 449 450 /* 451 * Protected by critical section held by IPI dispatch 452 */ 453 TAILQ_INSERT_TAIL(&td->td_gd->gd_tdallq, td, td_allq); 454 } 455 456 #endif 457 458 /* 459 * lwkt core thread structural initialization. 460 * 461 * NOTE: All threads are initialized as mpsafe threads. 462 */ 463 void 464 lwkt_init_thread(thread_t td, void *stack, int stksize, int flags, 465 struct globaldata *gd) 466 { 467 globaldata_t mygd = mycpu; 468 469 bzero(td, sizeof(struct thread)); 470 td->td_kstack = stack; 471 td->td_kstack_size = stksize; 472 td->td_flags = flags; 473 td->td_gd = gd; 474 td->td_pri = TDPRI_KERN_DAEMON; 475 td->td_critcount = 1; 476 td->td_toks_stop = &td->td_toks_base; 477 if (lwkt_use_spin_port || (flags & TDF_FORCE_SPINPORT)) 478 lwkt_initport_spin(&td->td_msgport); 479 else 480 lwkt_initport_thread(&td->td_msgport, td); 481 pmap_init_thread(td); 482 #ifdef SMP 483 /* 484 * Normally initializing a thread for a remote cpu requires sending an 485 * IPI. However, the idlethread is setup before the other cpus are 486 * activated so we have to treat it as a special case. XXX manipulation 487 * of gd_tdallq requires the BGL. 488 */ 489 if (gd == mygd || td == &gd->gd_idlethread) { 490 crit_enter_gd(mygd); 491 TAILQ_INSERT_TAIL(&gd->gd_tdallq, td, td_allq); 492 crit_exit_gd(mygd); 493 } else { 494 lwkt_send_ipiq(gd, lwkt_init_thread_remote, td); 495 } 496 #else 497 crit_enter_gd(mygd); 498 TAILQ_INSERT_TAIL(&gd->gd_tdallq, td, td_allq); 499 crit_exit_gd(mygd); 500 #endif 501 502 dsched_new_thread(td); 503 } 504 505 void 506 lwkt_set_comm(thread_t td, const char *ctl, ...) 507 { 508 __va_list va; 509 510 __va_start(va, ctl); 511 kvsnprintf(td->td_comm, sizeof(td->td_comm), ctl, va); 512 __va_end(va); 513 KTR_LOG(ctxsw_newtd, td, &td->td_comm[0]); 514 } 515 516 void 517 lwkt_hold(thread_t td) 518 { 519 atomic_add_int(&td->td_refs, 1); 520 } 521 522 void 523 lwkt_rele(thread_t td) 524 { 525 KKASSERT(td->td_refs > 0); 526 atomic_add_int(&td->td_refs, -1); 527 } 528 529 void 530 lwkt_wait_free(thread_t td) 531 { 532 while (td->td_refs) 533 tsleep(td, 0, "tdreap", hz); 534 } 535 536 void 537 lwkt_free_thread(thread_t td) 538 { 539 KKASSERT(td->td_refs == 0); 540 KKASSERT((td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK|TDF_RUNQ)) == 0); 541 if (td->td_flags & TDF_ALLOCATED_THREAD) { 542 objcache_put(thread_cache, td); 543 } else if (td->td_flags & TDF_ALLOCATED_STACK) { 544 /* client-allocated struct with internally allocated stack */ 545 KASSERT(td->td_kstack && td->td_kstack_size > 0, 546 ("lwkt_free_thread: corrupted stack")); 547 kmem_free(&kernel_map, (vm_offset_t)td->td_kstack, td->td_kstack_size); 548 td->td_kstack = NULL; 549 td->td_kstack_size = 0; 550 } 551 KTR_LOG(ctxsw_deadtd, td); 552 } 553 554 555 /* 556 * Switch to the next runnable lwkt. If no LWKTs are runnable then 557 * switch to the idlethread. Switching must occur within a critical 558 * section to avoid races with the scheduling queue. 559 * 560 * We always have full control over our cpu's run queue. Other cpus 561 * that wish to manipulate our queue must use the cpu_*msg() calls to 562 * talk to our cpu, so a critical section is all that is needed and 563 * the result is very, very fast thread switching. 564 * 565 * The LWKT scheduler uses a fixed priority model and round-robins at 566 * each priority level. User process scheduling is a totally 567 * different beast and LWKT priorities should not be confused with 568 * user process priorities. 569 * 570 * PREEMPTION NOTE: Preemption occurs via lwkt_preempt(). lwkt_switch() 571 * is not called by the current thread in the preemption case, only when 572 * the preempting thread blocks (in order to return to the original thread). 573 * 574 * SPECIAL NOTE ON SWITCH ATOMICY: Certain operations such as thread 575 * migration and tsleep deschedule the current lwkt thread and call 576 * lwkt_switch(). In particular, the target cpu of the migration fully 577 * expects the thread to become non-runnable and can deadlock against 578 * cpusync operations if we run any IPIs prior to switching the thread out. 579 * 580 * WE MUST BE VERY CAREFUL NOT TO RUN SPLZ DIRECTLY OR INDIRECTLY IF 581 * THE CURRENT THREAD HAS BEEN DESCHEDULED! 582 */ 583 void 584 lwkt_switch(void) 585 { 586 globaldata_t gd = mycpu; 587 thread_t td = gd->gd_curthread; 588 thread_t ntd; 589 thread_t xtd; 590 int spinning = 0; 591 592 KKASSERT(gd->gd_processing_ipiq == 0); 593 594 /* 595 * Switching from within a 'fast' (non thread switched) interrupt or IPI 596 * is illegal. However, we may have to do it anyway if we hit a fatal 597 * kernel trap or we have paniced. 598 * 599 * If this case occurs save and restore the interrupt nesting level. 600 */ 601 if (gd->gd_intr_nesting_level) { 602 int savegdnest; 603 int savegdtrap; 604 605 if (gd->gd_trap_nesting_level == 0 && panic_cpu_gd != mycpu) { 606 panic("lwkt_switch: Attempt to switch from a " 607 "a fast interrupt, ipi, or hard code section, " 608 "td %p\n", 609 td); 610 } else { 611 savegdnest = gd->gd_intr_nesting_level; 612 savegdtrap = gd->gd_trap_nesting_level; 613 gd->gd_intr_nesting_level = 0; 614 gd->gd_trap_nesting_level = 0; 615 if ((td->td_flags & TDF_PANICWARN) == 0) { 616 td->td_flags |= TDF_PANICWARN; 617 kprintf("Warning: thread switch from interrupt, IPI, " 618 "or hard code section.\n" 619 "thread %p (%s)\n", td, td->td_comm); 620 print_backtrace(-1); 621 } 622 lwkt_switch(); 623 gd->gd_intr_nesting_level = savegdnest; 624 gd->gd_trap_nesting_level = savegdtrap; 625 return; 626 } 627 } 628 629 /* 630 * Release our current user process designation if we are blocking 631 * or if a user reschedule was requested. 632 * 633 * NOTE: This function is NOT called if we are switching into or 634 * returning from a preemption. 635 * 636 * NOTE: Releasing our current user process designation may cause 637 * it to be assigned to another thread, which in turn will 638 * cause us to block in the usched acquire code when we attempt 639 * to return to userland. 640 * 641 * NOTE: On SMP systems this can be very nasty when heavy token 642 * contention is present so we want to be careful not to 643 * release the designation gratuitously. 644 */ 645 if (td->td_release && 646 (user_resched_wanted() || (td->td_flags & TDF_RUNQ) == 0)) { 647 td->td_release(td); 648 } 649 650 /* 651 * Release all tokens 652 */ 653 crit_enter_gd(gd); 654 if (TD_TOKS_HELD(td)) 655 lwkt_relalltokens(td); 656 657 /* 658 * We had better not be holding any spin locks, but don't get into an 659 * endless panic loop. 660 */ 661 KASSERT(gd->gd_spinlocks_wr == 0 || panicstr != NULL, 662 ("lwkt_switch: still holding %d exclusive spinlocks!", 663 gd->gd_spinlocks_wr)); 664 665 666 #ifdef SMP 667 #ifdef INVARIANTS 668 if (td->td_cscount) { 669 kprintf("Diagnostic: attempt to switch while mastering cpusync: %p\n", 670 td); 671 if (panic_on_cscount) 672 panic("switching while mastering cpusync"); 673 } 674 #endif 675 #endif 676 677 /* 678 * If we had preempted another thread on this cpu, resume the preempted 679 * thread. This occurs transparently, whether the preempted thread 680 * was scheduled or not (it may have been preempted after descheduling 681 * itself). 682 * 683 * We have to setup the MP lock for the original thread after backing 684 * out the adjustment that was made to curthread when the original 685 * was preempted. 686 */ 687 if ((ntd = td->td_preempted) != NULL) { 688 KKASSERT(ntd->td_flags & TDF_PREEMPT_LOCK); 689 ntd->td_flags |= TDF_PREEMPT_DONE; 690 691 /* 692 * The interrupt may have woken a thread up, we need to properly 693 * set the reschedule flag if the originally interrupted thread is 694 * at a lower priority. 695 * 696 * The interrupt may not have descheduled. 697 */ 698 if (TAILQ_FIRST(&gd->gd_tdrunq) != ntd) 699 need_lwkt_resched(); 700 goto havethread_preempted; 701 } 702 703 /* 704 * If we cannot obtain ownership of the tokens we cannot immediately 705 * schedule the target thread. 706 * 707 * Reminder: Again, we cannot afford to run any IPIs in this path if 708 * the current thread has been descheduled. 709 */ 710 for (;;) { 711 clear_lwkt_resched(); 712 713 /* 714 * Hotpath - pull the head of the run queue and attempt to schedule 715 * it. 716 */ 717 for (;;) { 718 ntd = TAILQ_FIRST(&gd->gd_tdrunq); 719 720 if (ntd == NULL) { 721 /* 722 * Runq is empty, switch to idle to allow it to halt. 723 */ 724 ntd = &gd->gd_idlethread; 725 #ifdef SMP 726 if (gd->gd_trap_nesting_level == 0 && panicstr == NULL) 727 ASSERT_NO_TOKENS_HELD(ntd); 728 #endif 729 cpu_time.cp_msg[0] = 0; 730 cpu_time.cp_stallpc = 0; 731 goto haveidle; 732 } 733 break; 734 } 735 736 /* 737 * Hotpath - schedule ntd. 738 * 739 * NOTE: For UP there is no mplock and lwkt_getalltokens() 740 * always succeeds. 741 */ 742 if (TD_TOKS_NOT_HELD(ntd) || 743 lwkt_getalltokens(ntd, (spinning >= lwkt_spin_loops))) 744 { 745 goto havethread; 746 } 747 748 /* 749 * Coldpath (SMP only since tokens always succeed on UP) 750 * 751 * We had some contention on the thread we wanted to schedule. 752 * What we do now is try to find a thread that we can schedule 753 * in its stead. 754 * 755 * The coldpath scan does NOT rearrange threads in the run list. 756 * The lwkt_schedulerclock() will assert need_lwkt_resched() on 757 * the next tick whenever the current head is not the current thread. 758 */ 759 #ifdef INVARIANTS 760 ++token_contention_count[ntd->td_pri]; 761 ++ntd->td_contended; 762 #endif 763 764 if (fairq_bypass > 0) 765 goto skip; 766 767 xtd = NULL; 768 while ((ntd = TAILQ_NEXT(ntd, td_threadq)) != NULL) { 769 /* 770 * Never schedule threads returning to userland or the 771 * user thread scheduler helper thread when higher priority 772 * threads are present. 773 */ 774 if (ntd->td_pri < TDPRI_KERN_LPSCHED) { 775 ntd = NULL; 776 break; 777 } 778 779 /* 780 * Try this one. 781 */ 782 if (TD_TOKS_NOT_HELD(ntd) || 783 lwkt_getalltokens(ntd, (spinning >= lwkt_spin_loops))) { 784 goto havethread; 785 } 786 #ifdef INVARIANTS 787 ++token_contention_count[ntd->td_pri]; 788 ++ntd->td_contended; 789 #endif 790 } 791 792 skip: 793 /* 794 * We exhausted the run list, meaning that all runnable threads 795 * are contested. 796 */ 797 cpu_pause(); 798 ntd = &gd->gd_idlethread; 799 #ifdef SMP 800 if (gd->gd_trap_nesting_level == 0 && panicstr == NULL) 801 ASSERT_NO_TOKENS_HELD(ntd); 802 /* contention case, do not clear contention mask */ 803 #endif 804 805 /* 806 * We are going to have to retry but if the current thread is not 807 * on the runq we instead switch through the idle thread to get away 808 * from the current thread. We have to flag for lwkt reschedule 809 * to prevent the idle thread from halting. 810 * 811 * NOTE: A non-zero spinning is passed to lwkt_getalltokens() to 812 * instruct it to deal with the potential for deadlocks by 813 * ordering the tokens by address. 814 */ 815 if ((td->td_flags & TDF_RUNQ) == 0) { 816 need_lwkt_resched(); /* prevent hlt */ 817 goto haveidle; 818 } 819 #if defined(INVARIANTS) && defined(__amd64__) 820 if ((read_rflags() & PSL_I) == 0) { 821 cpu_enable_intr(); 822 panic("lwkt_switch() called with interrupts disabled"); 823 } 824 #endif 825 826 /* 827 * Number iterations so far. After a certain point we switch to 828 * a sorted-address/monitor/mwait version of lwkt_getalltokens() 829 */ 830 if (spinning < 0x7FFFFFFF) 831 ++spinning; 832 833 #ifdef SMP 834 /* 835 * lwkt_getalltokens() failed in sorted token mode, we can use 836 * monitor/mwait in this case. 837 */ 838 if (spinning >= lwkt_spin_loops && 839 (cpu_mi_feature & CPU_MI_MONITOR) && 840 lwkt_spin_monitor) 841 { 842 cpu_mmw_pause_int(&gd->gd_reqflags, 843 (gd->gd_reqflags | RQF_SPINNING) & 844 ~RQF_IDLECHECK_WK_MASK); 845 } 846 #endif 847 848 /* 849 * We already checked that td is still scheduled so this should be 850 * safe. 851 */ 852 splz_check(); 853 854 /* 855 * This experimental resequencer is used as a fall-back to reduce 856 * hw cache line contention by placing each core's scheduler into a 857 * time-domain-multplexed slot. 858 * 859 * The resequencer is disabled by default. It's functionality has 860 * largely been superceeded by the token algorithm which limits races 861 * to a subset of cores. 862 * 863 * The resequencer algorithm tends to break down when more than 864 * 20 cores are contending. What appears to happen is that new 865 * tokens can be obtained out of address-sorted order by new cores 866 * while existing cores languish in long delays between retries and 867 * wind up being starved-out of the token acquisition. 868 */ 869 if (lwkt_spin_reseq && spinning >= lwkt_spin_reseq) { 870 int cseq = atomic_fetchadd_int(&lwkt_cseq_windex, 1); 871 int oseq; 872 873 while ((oseq = lwkt_cseq_rindex) != cseq) { 874 cpu_ccfence(); 875 #if 1 876 if (cpu_mi_feature & CPU_MI_MONITOR) { 877 cpu_mmw_pause_int(&lwkt_cseq_rindex, oseq); 878 } else { 879 #endif 880 cpu_pause(); 881 cpu_lfence(); 882 #if 1 883 } 884 #endif 885 } 886 DELAY(1); 887 atomic_add_int(&lwkt_cseq_rindex, 1); 888 } 889 /* highest level for(;;) loop */ 890 } 891 892 havethread: 893 /* 894 * If the thread we came up with is a higher or equal priority verses 895 * the thread at the head of the queue we move our thread to the 896 * front. This way we can always check the front of the queue. 897 * 898 * Clear gd_idle_repeat when doing a normal switch to a non-idle 899 * thread. 900 */ 901 ntd->td_wmesg = NULL; 902 ++gd->gd_cnt.v_swtch; 903 #if 0 904 xtd = TAILQ_FIRST(&gd->gd_tdrunq); 905 if (ntd != xtd && ntd->td_pri >= xtd->td_pri) { 906 TAILQ_REMOVE(&gd->gd_tdrunq, ntd, td_threadq); 907 TAILQ_INSERT_HEAD(&gd->gd_tdrunq, ntd, td_threadq); 908 } 909 #endif 910 gd->gd_idle_repeat = 0; 911 912 havethread_preempted: 913 /* 914 * If the new target does not need the MP lock and we are holding it, 915 * release the MP lock. If the new target requires the MP lock we have 916 * already acquired it for the target. 917 */ 918 ; 919 haveidle: 920 KASSERT(ntd->td_critcount, 921 ("priority problem in lwkt_switch %d %d", 922 td->td_critcount, ntd->td_critcount)); 923 924 if (td != ntd) { 925 /* 926 * Execute the actual thread switch operation. This function 927 * returns to the current thread and returns the previous thread 928 * (which may be different from the thread we switched to). 929 * 930 * We are responsible for marking ntd as TDF_RUNNING. 931 */ 932 ++switch_count; 933 KTR_LOG(ctxsw_sw, gd->gd_cpuid, ntd); 934 ntd->td_flags |= TDF_RUNNING; 935 lwkt_switch_return(td->td_switch(ntd)); 936 /* ntd invalid, td_switch() can return a different thread_t */ 937 } 938 939 #if 1 940 /* 941 * catch-all 942 */ 943 splz_check(); 944 #endif 945 /* NOTE: current cpu may have changed after switch */ 946 crit_exit_quick(td); 947 } 948 949 /* 950 * Called by assembly in the td_switch (thread restore path) for thread 951 * bootstrap cases which do not 'return' to lwkt_switch(). 952 */ 953 void 954 lwkt_switch_return(thread_t otd) 955 { 956 #ifdef SMP 957 globaldata_t rgd; 958 959 /* 960 * Check if otd was migrating. Now that we are on ntd we can finish 961 * up the migration. This is a bit messy but it is the only place 962 * where td is known to be fully descheduled. 963 * 964 * We can only activate the migration if otd was migrating but not 965 * held on the cpu due to a preemption chain. We still have to 966 * clear TDF_RUNNING on the old thread either way. 967 * 968 * We are responsible for clearing the previously running thread's 969 * TDF_RUNNING. 970 */ 971 if ((rgd = otd->td_migrate_gd) != NULL && 972 (otd->td_flags & TDF_PREEMPT_LOCK) == 0) { 973 KKASSERT((otd->td_flags & (TDF_MIGRATING | TDF_RUNNING)) == 974 (TDF_MIGRATING | TDF_RUNNING)); 975 otd->td_migrate_gd = NULL; 976 otd->td_flags &= ~TDF_RUNNING; 977 lwkt_send_ipiq(rgd, lwkt_setcpu_remote, otd); 978 } else { 979 otd->td_flags &= ~TDF_RUNNING; 980 } 981 #else 982 otd->td_flags &= ~TDF_RUNNING; 983 #endif 984 } 985 986 /* 987 * Request that the target thread preempt the current thread. Preemption 988 * only works under a specific set of conditions: 989 * 990 * - We are not preempting ourselves 991 * - The target thread is owned by the current cpu 992 * - We are not currently being preempted 993 * - The target is not currently being preempted 994 * - We are not holding any spin locks 995 * - The target thread is not holding any tokens 996 * - We are able to satisfy the target's MP lock requirements (if any). 997 * 998 * THE CALLER OF LWKT_PREEMPT() MUST BE IN A CRITICAL SECTION. Typically 999 * this is called via lwkt_schedule() through the td_preemptable callback. 1000 * critcount is the managed critical priority that we should ignore in order 1001 * to determine whether preemption is possible (aka usually just the crit 1002 * priority of lwkt_schedule() itself). 1003 * 1004 * XXX at the moment we run the target thread in a critical section during 1005 * the preemption in order to prevent the target from taking interrupts 1006 * that *WE* can't. Preemption is strictly limited to interrupt threads 1007 * and interrupt-like threads, outside of a critical section, and the 1008 * preempted source thread will be resumed the instant the target blocks 1009 * whether or not the source is scheduled (i.e. preemption is supposed to 1010 * be as transparent as possible). 1011 */ 1012 void 1013 lwkt_preempt(thread_t ntd, int critcount) 1014 { 1015 struct globaldata *gd = mycpu; 1016 thread_t xtd; 1017 thread_t td; 1018 int save_gd_intr_nesting_level; 1019 1020 /* 1021 * The caller has put us in a critical section. We can only preempt 1022 * if the caller of the caller was not in a critical section (basically 1023 * a local interrupt), as determined by the 'critcount' parameter. We 1024 * also can't preempt if the caller is holding any spinlocks (even if 1025 * he isn't in a critical section). This also handles the tokens test. 1026 * 1027 * YYY The target thread must be in a critical section (else it must 1028 * inherit our critical section? I dunno yet). 1029 */ 1030 KASSERT(ntd->td_critcount, ("BADCRIT0 %d", ntd->td_pri)); 1031 1032 td = gd->gd_curthread; 1033 if (preempt_enable == 0) { 1034 #if 0 1035 if (ntd->td_pri > td->td_pri) 1036 need_lwkt_resched(); 1037 #endif 1038 ++preempt_miss; 1039 return; 1040 } 1041 if (ntd->td_pri <= td->td_pri) { 1042 ++preempt_miss; 1043 return; 1044 } 1045 if (td->td_critcount > critcount) { 1046 ++preempt_miss; 1047 #if 0 1048 need_lwkt_resched(); 1049 #endif 1050 return; 1051 } 1052 #ifdef SMP 1053 if (ntd->td_gd != gd) { 1054 ++preempt_miss; 1055 #if 0 1056 need_lwkt_resched(); 1057 #endif 1058 return; 1059 } 1060 #endif 1061 /* 1062 * We don't have to check spinlocks here as they will also bump 1063 * td_critcount. 1064 * 1065 * Do not try to preempt if the target thread is holding any tokens. 1066 * We could try to acquire the tokens but this case is so rare there 1067 * is no need to support it. 1068 */ 1069 KKASSERT(gd->gd_spinlocks_wr == 0); 1070 1071 if (TD_TOKS_HELD(ntd)) { 1072 ++preempt_miss; 1073 #if 0 1074 need_lwkt_resched(); 1075 #endif 1076 return; 1077 } 1078 if (td == ntd || ((td->td_flags | ntd->td_flags) & TDF_PREEMPT_LOCK)) { 1079 ++preempt_weird; 1080 #if 0 1081 need_lwkt_resched(); 1082 #endif 1083 return; 1084 } 1085 if (ntd->td_preempted) { 1086 ++preempt_hit; 1087 #if 0 1088 need_lwkt_resched(); 1089 #endif 1090 return; 1091 } 1092 KKASSERT(gd->gd_processing_ipiq == 0); 1093 1094 /* 1095 * Since we are able to preempt the current thread, there is no need to 1096 * call need_lwkt_resched(). 1097 * 1098 * We must temporarily clear gd_intr_nesting_level around the switch 1099 * since switchouts from the target thread are allowed (they will just 1100 * return to our thread), and since the target thread has its own stack. 1101 * 1102 * A preemption must switch back to the original thread, assert the 1103 * case. 1104 */ 1105 ++preempt_hit; 1106 ntd->td_preempted = td; 1107 td->td_flags |= TDF_PREEMPT_LOCK; 1108 KTR_LOG(ctxsw_pre, gd->gd_cpuid, ntd); 1109 save_gd_intr_nesting_level = gd->gd_intr_nesting_level; 1110 gd->gd_intr_nesting_level = 0; 1111 ntd->td_flags |= TDF_RUNNING; 1112 xtd = td->td_switch(ntd); 1113 KKASSERT(xtd == ntd); 1114 lwkt_switch_return(xtd); 1115 gd->gd_intr_nesting_level = save_gd_intr_nesting_level; 1116 1117 KKASSERT(ntd->td_preempted && (td->td_flags & TDF_PREEMPT_DONE)); 1118 ntd->td_preempted = NULL; 1119 td->td_flags &= ~(TDF_PREEMPT_LOCK|TDF_PREEMPT_DONE); 1120 } 1121 1122 /* 1123 * Conditionally call splz() if gd_reqflags indicates work is pending. 1124 * This will work inside a critical section but not inside a hard code 1125 * section. 1126 * 1127 * (self contained on a per cpu basis) 1128 */ 1129 void 1130 splz_check(void) 1131 { 1132 globaldata_t gd = mycpu; 1133 thread_t td = gd->gd_curthread; 1134 1135 if ((gd->gd_reqflags & RQF_IDLECHECK_MASK) && 1136 gd->gd_intr_nesting_level == 0 && 1137 td->td_nest_count < 2) 1138 { 1139 splz(); 1140 } 1141 } 1142 1143 /* 1144 * This version is integrated into crit_exit, reqflags has already 1145 * been tested but td_critcount has not. 1146 * 1147 * We only want to execute the splz() on the 1->0 transition of 1148 * critcount and not in a hard code section or if too deeply nested. 1149 */ 1150 void 1151 lwkt_maybe_splz(thread_t td) 1152 { 1153 globaldata_t gd = td->td_gd; 1154 1155 if (td->td_critcount == 0 && 1156 gd->gd_intr_nesting_level == 0 && 1157 td->td_nest_count < 2) 1158 { 1159 splz(); 1160 } 1161 } 1162 1163 /* 1164 * Drivers which set up processing co-threads can call this function to 1165 * run the co-thread at a higher priority and to allow it to preempt 1166 * normal threads. 1167 */ 1168 void 1169 lwkt_set_interrupt_support_thread(void) 1170 { 1171 thread_t td = curthread; 1172 1173 lwkt_setpri_self(TDPRI_INT_SUPPORT); 1174 td->td_flags |= TDF_INTTHREAD; 1175 td->td_preemptable = lwkt_preempt; 1176 } 1177 1178 1179 /* 1180 * This function is used to negotiate a passive release of the current 1181 * process/lwp designation with the user scheduler, allowing the user 1182 * scheduler to schedule another user thread. The related kernel thread 1183 * (curthread) continues running in the released state. 1184 */ 1185 void 1186 lwkt_passive_release(struct thread *td) 1187 { 1188 struct lwp *lp = td->td_lwp; 1189 1190 td->td_release = NULL; 1191 lwkt_setpri_self(TDPRI_KERN_USER); 1192 lp->lwp_proc->p_usched->release_curproc(lp); 1193 } 1194 1195 1196 /* 1197 * This implements a LWKT yield, allowing a kernel thread to yield to other 1198 * kernel threads at the same or higher priority. This function can be 1199 * called in a tight loop and will typically only yield once per tick. 1200 * 1201 * Most kernel threads run at the same priority in order to allow equal 1202 * sharing. 1203 * 1204 * (self contained on a per cpu basis) 1205 */ 1206 void 1207 lwkt_yield(void) 1208 { 1209 globaldata_t gd = mycpu; 1210 thread_t td = gd->gd_curthread; 1211 1212 if ((gd->gd_reqflags & RQF_IDLECHECK_MASK) && td->td_nest_count < 2) 1213 splz(); 1214 if (lwkt_resched_wanted()) { 1215 lwkt_schedule_self(curthread); 1216 lwkt_switch(); 1217 } 1218 } 1219 1220 /* 1221 * This yield is designed for kernel threads with a user context. 1222 * 1223 * The kernel acting on behalf of the user is potentially cpu-bound, 1224 * this function will efficiently allow other threads to run and also 1225 * switch to other processes by releasing. 1226 * 1227 * The lwkt_user_yield() function is designed to have very low overhead 1228 * if no yield is determined to be needed. 1229 */ 1230 void 1231 lwkt_user_yield(void) 1232 { 1233 globaldata_t gd = mycpu; 1234 thread_t td = gd->gd_curthread; 1235 1236 /* 1237 * Always run any pending interrupts in case we are in a critical 1238 * section. 1239 */ 1240 if ((gd->gd_reqflags & RQF_IDLECHECK_MASK) && td->td_nest_count < 2) 1241 splz(); 1242 1243 /* 1244 * Switch (which forces a release) if another kernel thread needs 1245 * the cpu, if userland wants us to resched, or if our kernel 1246 * quantum has run out. 1247 */ 1248 if (lwkt_resched_wanted() || 1249 user_resched_wanted()) 1250 { 1251 lwkt_switch(); 1252 } 1253 1254 #if 0 1255 /* 1256 * Reacquire the current process if we are released. 1257 * 1258 * XXX not implemented atm. The kernel may be holding locks and such, 1259 * so we want the thread to continue to receive cpu. 1260 */ 1261 if (td->td_release == NULL && lp) { 1262 lp->lwp_proc->p_usched->acquire_curproc(lp); 1263 td->td_release = lwkt_passive_release; 1264 lwkt_setpri_self(TDPRI_USER_NORM); 1265 } 1266 #endif 1267 } 1268 1269 /* 1270 * Generic schedule. Possibly schedule threads belonging to other cpus and 1271 * deal with threads that might be blocked on a wait queue. 1272 * 1273 * We have a little helper inline function which does additional work after 1274 * the thread has been enqueued, including dealing with preemption and 1275 * setting need_lwkt_resched() (which prevents the kernel from returning 1276 * to userland until it has processed higher priority threads). 1277 * 1278 * It is possible for this routine to be called after a failed _enqueue 1279 * (due to the target thread migrating, sleeping, or otherwise blocked). 1280 * We have to check that the thread is actually on the run queue! 1281 */ 1282 static __inline 1283 void 1284 _lwkt_schedule_post(globaldata_t gd, thread_t ntd, int ccount) 1285 { 1286 if (ntd->td_flags & TDF_RUNQ) { 1287 if (ntd->td_preemptable) { 1288 ntd->td_preemptable(ntd, ccount); /* YYY +token */ 1289 } 1290 } 1291 } 1292 1293 static __inline 1294 void 1295 _lwkt_schedule(thread_t td) 1296 { 1297 globaldata_t mygd = mycpu; 1298 1299 KASSERT(td != &td->td_gd->gd_idlethread, 1300 ("lwkt_schedule(): scheduling gd_idlethread is illegal!")); 1301 KKASSERT((td->td_flags & TDF_MIGRATING) == 0); 1302 crit_enter_gd(mygd); 1303 KKASSERT(td->td_lwp == NULL || (td->td_lwp->lwp_flag & LWP_ONRUNQ) == 0); 1304 if (td == mygd->gd_curthread) { 1305 _lwkt_enqueue(td); 1306 } else { 1307 /* 1308 * If we own the thread, there is no race (since we are in a 1309 * critical section). If we do not own the thread there might 1310 * be a race but the target cpu will deal with it. 1311 */ 1312 #ifdef SMP 1313 if (td->td_gd == mygd) { 1314 _lwkt_enqueue(td); 1315 _lwkt_schedule_post(mygd, td, 1); 1316 } else { 1317 lwkt_send_ipiq3(td->td_gd, lwkt_schedule_remote, td, 0); 1318 } 1319 #else 1320 _lwkt_enqueue(td); 1321 _lwkt_schedule_post(mygd, td, 1); 1322 #endif 1323 } 1324 crit_exit_gd(mygd); 1325 } 1326 1327 void 1328 lwkt_schedule(thread_t td) 1329 { 1330 _lwkt_schedule(td); 1331 } 1332 1333 void 1334 lwkt_schedule_noresched(thread_t td) /* XXX not impl */ 1335 { 1336 _lwkt_schedule(td); 1337 } 1338 1339 #ifdef SMP 1340 1341 /* 1342 * When scheduled remotely if frame != NULL the IPIQ is being 1343 * run via doreti or an interrupt then preemption can be allowed. 1344 * 1345 * To allow preemption we have to drop the critical section so only 1346 * one is present in _lwkt_schedule_post. 1347 */ 1348 static void 1349 lwkt_schedule_remote(void *arg, int arg2, struct intrframe *frame) 1350 { 1351 thread_t td = curthread; 1352 thread_t ntd = arg; 1353 1354 if (frame && ntd->td_preemptable) { 1355 crit_exit_noyield(td); 1356 _lwkt_schedule(ntd); 1357 crit_enter_quick(td); 1358 } else { 1359 _lwkt_schedule(ntd); 1360 } 1361 } 1362 1363 /* 1364 * Thread migration using a 'Pull' method. The thread may or may not be 1365 * the current thread. It MUST be descheduled and in a stable state. 1366 * lwkt_giveaway() must be called on the cpu owning the thread. 1367 * 1368 * At any point after lwkt_giveaway() is called, the target cpu may 1369 * 'pull' the thread by calling lwkt_acquire(). 1370 * 1371 * We have to make sure the thread is not sitting on a per-cpu tsleep 1372 * queue or it will blow up when it moves to another cpu. 1373 * 1374 * MPSAFE - must be called under very specific conditions. 1375 */ 1376 void 1377 lwkt_giveaway(thread_t td) 1378 { 1379 globaldata_t gd = mycpu; 1380 1381 crit_enter_gd(gd); 1382 if (td->td_flags & TDF_TSLEEPQ) 1383 tsleep_remove(td); 1384 KKASSERT(td->td_gd == gd); 1385 TAILQ_REMOVE(&gd->gd_tdallq, td, td_allq); 1386 td->td_flags |= TDF_MIGRATING; 1387 crit_exit_gd(gd); 1388 } 1389 1390 void 1391 lwkt_acquire(thread_t td) 1392 { 1393 globaldata_t gd; 1394 globaldata_t mygd; 1395 int retry = 10000000; 1396 1397 KKASSERT(td->td_flags & TDF_MIGRATING); 1398 gd = td->td_gd; 1399 mygd = mycpu; 1400 if (gd != mycpu) { 1401 cpu_lfence(); 1402 KKASSERT((td->td_flags & TDF_RUNQ) == 0); 1403 crit_enter_gd(mygd); 1404 DEBUG_PUSH_INFO("lwkt_acquire"); 1405 while (td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK)) { 1406 #ifdef SMP 1407 lwkt_process_ipiq(); 1408 #endif 1409 cpu_lfence(); 1410 if (--retry == 0) { 1411 kprintf("lwkt_acquire: stuck: td %p td->td_flags %08x\n", 1412 td, td->td_flags); 1413 retry = 10000000; 1414 } 1415 } 1416 DEBUG_POP_INFO(); 1417 cpu_mfence(); 1418 td->td_gd = mygd; 1419 TAILQ_INSERT_TAIL(&mygd->gd_tdallq, td, td_allq); 1420 td->td_flags &= ~TDF_MIGRATING; 1421 crit_exit_gd(mygd); 1422 } else { 1423 crit_enter_gd(mygd); 1424 TAILQ_INSERT_TAIL(&mygd->gd_tdallq, td, td_allq); 1425 td->td_flags &= ~TDF_MIGRATING; 1426 crit_exit_gd(mygd); 1427 } 1428 } 1429 1430 #endif 1431 1432 /* 1433 * Generic deschedule. Descheduling threads other then your own should be 1434 * done only in carefully controlled circumstances. Descheduling is 1435 * asynchronous. 1436 * 1437 * This function may block if the cpu has run out of messages. 1438 */ 1439 void 1440 lwkt_deschedule(thread_t td) 1441 { 1442 crit_enter(); 1443 #ifdef SMP 1444 if (td == curthread) { 1445 _lwkt_dequeue(td); 1446 } else { 1447 if (td->td_gd == mycpu) { 1448 _lwkt_dequeue(td); 1449 } else { 1450 lwkt_send_ipiq(td->td_gd, (ipifunc1_t)lwkt_deschedule, td); 1451 } 1452 } 1453 #else 1454 _lwkt_dequeue(td); 1455 #endif 1456 crit_exit(); 1457 } 1458 1459 /* 1460 * Set the target thread's priority. This routine does not automatically 1461 * switch to a higher priority thread, LWKT threads are not designed for 1462 * continuous priority changes. Yield if you want to switch. 1463 */ 1464 void 1465 lwkt_setpri(thread_t td, int pri) 1466 { 1467 if (td->td_pri != pri) { 1468 KKASSERT(pri >= 0); 1469 crit_enter(); 1470 if (td->td_flags & TDF_RUNQ) { 1471 KKASSERT(td->td_gd == mycpu); 1472 _lwkt_dequeue(td); 1473 td->td_pri = pri; 1474 _lwkt_enqueue(td); 1475 } else { 1476 td->td_pri = pri; 1477 } 1478 crit_exit(); 1479 } 1480 } 1481 1482 /* 1483 * Set the initial priority for a thread prior to it being scheduled for 1484 * the first time. The thread MUST NOT be scheduled before or during 1485 * this call. The thread may be assigned to a cpu other then the current 1486 * cpu. 1487 * 1488 * Typically used after a thread has been created with TDF_STOPPREQ, 1489 * and before the thread is initially scheduled. 1490 */ 1491 void 1492 lwkt_setpri_initial(thread_t td, int pri) 1493 { 1494 KKASSERT(pri >= 0); 1495 KKASSERT((td->td_flags & TDF_RUNQ) == 0); 1496 td->td_pri = pri; 1497 } 1498 1499 void 1500 lwkt_setpri_self(int pri) 1501 { 1502 thread_t td = curthread; 1503 1504 KKASSERT(pri >= 0 && pri <= TDPRI_MAX); 1505 crit_enter(); 1506 if (td->td_flags & TDF_RUNQ) { 1507 _lwkt_dequeue(td); 1508 td->td_pri = pri; 1509 _lwkt_enqueue(td); 1510 } else { 1511 td->td_pri = pri; 1512 } 1513 crit_exit(); 1514 } 1515 1516 /* 1517 * hz tick scheduler clock for LWKT threads 1518 */ 1519 void 1520 lwkt_schedulerclock(thread_t td) 1521 { 1522 globaldata_t gd = td->td_gd; 1523 thread_t xtd; 1524 1525 if (TAILQ_FIRST(&gd->gd_tdrunq) == td) { 1526 /* 1527 * If the current thread is at the head of the runq shift it to the 1528 * end of any equal-priority threads and request a LWKT reschedule 1529 * if it moved. 1530 */ 1531 xtd = TAILQ_NEXT(td, td_threadq); 1532 if (xtd && xtd->td_pri == td->td_pri) { 1533 TAILQ_REMOVE(&gd->gd_tdrunq, td, td_threadq); 1534 while (xtd && xtd->td_pri == td->td_pri) 1535 xtd = TAILQ_NEXT(xtd, td_threadq); 1536 if (xtd) 1537 TAILQ_INSERT_BEFORE(xtd, td, td_threadq); 1538 else 1539 TAILQ_INSERT_TAIL(&gd->gd_tdrunq, td, td_threadq); 1540 need_lwkt_resched(); 1541 } 1542 } else { 1543 /* 1544 * If we scheduled a thread other than the one at the head of the 1545 * queue always request a reschedule every tick. 1546 */ 1547 need_lwkt_resched(); 1548 } 1549 } 1550 1551 /* 1552 * Migrate the current thread to the specified cpu. 1553 * 1554 * This is accomplished by descheduling ourselves from the current cpu 1555 * and setting td_migrate_gd. The lwkt_switch() code will detect that the 1556 * 'old' thread wants to migrate after it has been completely switched out 1557 * and will complete the migration. 1558 * 1559 * TDF_MIGRATING prevents scheduling races while the thread is being migrated. 1560 * 1561 * We must be sure to release our current process designation (if a user 1562 * process) before clearing out any tsleepq we are on because the release 1563 * code may re-add us. 1564 * 1565 * We must be sure to remove ourselves from the current cpu's tsleepq 1566 * before potentially moving to another queue. The thread can be on 1567 * a tsleepq due to a left-over tsleep_interlock(). 1568 */ 1569 1570 void 1571 lwkt_setcpu_self(globaldata_t rgd) 1572 { 1573 #ifdef SMP 1574 thread_t td = curthread; 1575 1576 if (td->td_gd != rgd) { 1577 crit_enter_quick(td); 1578 1579 if (td->td_release) 1580 td->td_release(td); 1581 if (td->td_flags & TDF_TSLEEPQ) 1582 tsleep_remove(td); 1583 1584 /* 1585 * Set TDF_MIGRATING to prevent a spurious reschedule while we are 1586 * trying to deschedule ourselves and switch away, then deschedule 1587 * ourself, remove us from tdallq, and set td_migrate_gd. Finally, 1588 * call lwkt_switch() to complete the operation. 1589 */ 1590 td->td_flags |= TDF_MIGRATING; 1591 lwkt_deschedule_self(td); 1592 TAILQ_REMOVE(&td->td_gd->gd_tdallq, td, td_allq); 1593 td->td_migrate_gd = rgd; 1594 lwkt_switch(); 1595 1596 /* 1597 * We are now on the target cpu 1598 */ 1599 KKASSERT(rgd == mycpu); 1600 TAILQ_INSERT_TAIL(&rgd->gd_tdallq, td, td_allq); 1601 crit_exit_quick(td); 1602 } 1603 #endif 1604 } 1605 1606 void 1607 lwkt_migratecpu(int cpuid) 1608 { 1609 #ifdef SMP 1610 globaldata_t rgd; 1611 1612 rgd = globaldata_find(cpuid); 1613 lwkt_setcpu_self(rgd); 1614 #endif 1615 } 1616 1617 #ifdef SMP 1618 /* 1619 * Remote IPI for cpu migration (called while in a critical section so we 1620 * do not have to enter another one). 1621 * 1622 * The thread (td) has already been completely descheduled from the 1623 * originating cpu and we can simply assert the case. The thread is 1624 * assigned to the new cpu and enqueued. 1625 * 1626 * The thread will re-add itself to tdallq when it resumes execution. 1627 */ 1628 static void 1629 lwkt_setcpu_remote(void *arg) 1630 { 1631 thread_t td = arg; 1632 globaldata_t gd = mycpu; 1633 1634 KKASSERT((td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK)) == 0); 1635 td->td_gd = gd; 1636 cpu_mfence(); 1637 td->td_flags &= ~TDF_MIGRATING; 1638 KKASSERT(td->td_migrate_gd == NULL); 1639 KKASSERT(td->td_lwp == NULL || (td->td_lwp->lwp_flag & LWP_ONRUNQ) == 0); 1640 _lwkt_enqueue(td); 1641 } 1642 #endif 1643 1644 struct lwp * 1645 lwkt_preempted_proc(void) 1646 { 1647 thread_t td = curthread; 1648 while (td->td_preempted) 1649 td = td->td_preempted; 1650 return(td->td_lwp); 1651 } 1652 1653 /* 1654 * Create a kernel process/thread/whatever. It shares it's address space 1655 * with proc0 - ie: kernel only. 1656 * 1657 * If the cpu is not specified one will be selected. In the future 1658 * specifying a cpu of -1 will enable kernel thread migration between 1659 * cpus. 1660 */ 1661 int 1662 lwkt_create(void (*func)(void *), void *arg, struct thread **tdp, 1663 thread_t template, int tdflags, int cpu, const char *fmt, ...) 1664 { 1665 thread_t td; 1666 __va_list ap; 1667 1668 td = lwkt_alloc_thread(template, LWKT_THREAD_STACK, cpu, 1669 tdflags); 1670 if (tdp) 1671 *tdp = td; 1672 cpu_set_thread_handler(td, lwkt_exit, func, arg); 1673 1674 /* 1675 * Set up arg0 for 'ps' etc 1676 */ 1677 __va_start(ap, fmt); 1678 kvsnprintf(td->td_comm, sizeof(td->td_comm), fmt, ap); 1679 __va_end(ap); 1680 1681 /* 1682 * Schedule the thread to run 1683 */ 1684 if ((td->td_flags & TDF_STOPREQ) == 0) 1685 lwkt_schedule(td); 1686 else 1687 td->td_flags &= ~TDF_STOPREQ; 1688 return 0; 1689 } 1690 1691 /* 1692 * Destroy an LWKT thread. Warning! This function is not called when 1693 * a process exits, cpu_proc_exit() directly calls cpu_thread_exit() and 1694 * uses a different reaping mechanism. 1695 */ 1696 void 1697 lwkt_exit(void) 1698 { 1699 thread_t td = curthread; 1700 thread_t std; 1701 globaldata_t gd; 1702 1703 /* 1704 * Do any cleanup that might block here 1705 */ 1706 if (td->td_flags & TDF_VERBOSE) 1707 kprintf("kthread %p %s has exited\n", td, td->td_comm); 1708 caps_exit(td); 1709 biosched_done(td); 1710 dsched_exit_thread(td); 1711 1712 /* 1713 * Get us into a critical section to interlock gd_freetd and loop 1714 * until we can get it freed. 1715 * 1716 * We have to cache the current td in gd_freetd because objcache_put()ing 1717 * it would rip it out from under us while our thread is still active. 1718 */ 1719 gd = mycpu; 1720 crit_enter_quick(td); 1721 while ((std = gd->gd_freetd) != NULL) { 1722 KKASSERT((std->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK)) == 0); 1723 gd->gd_freetd = NULL; 1724 objcache_put(thread_cache, std); 1725 } 1726 1727 /* 1728 * Remove thread resources from kernel lists and deschedule us for 1729 * the last time. We cannot block after this point or we may end 1730 * up with a stale td on the tsleepq. 1731 */ 1732 if (td->td_flags & TDF_TSLEEPQ) 1733 tsleep_remove(td); 1734 lwkt_deschedule_self(td); 1735 lwkt_remove_tdallq(td); 1736 KKASSERT(td->td_refs == 0); 1737 1738 /* 1739 * Final cleanup 1740 */ 1741 KKASSERT(gd->gd_freetd == NULL); 1742 if (td->td_flags & TDF_ALLOCATED_THREAD) 1743 gd->gd_freetd = td; 1744 cpu_thread_exit(); 1745 } 1746 1747 void 1748 lwkt_remove_tdallq(thread_t td) 1749 { 1750 KKASSERT(td->td_gd == mycpu); 1751 TAILQ_REMOVE(&td->td_gd->gd_tdallq, td, td_allq); 1752 } 1753 1754 /* 1755 * Code reduction and branch prediction improvements. Call/return 1756 * overhead on modern cpus often degenerates into 0 cycles due to 1757 * the cpu's branch prediction hardware and return pc cache. We 1758 * can take advantage of this by not inlining medium-complexity 1759 * functions and we can also reduce the branch prediction impact 1760 * by collapsing perfectly predictable branches into a single 1761 * procedure instead of duplicating it. 1762 * 1763 * Is any of this noticeable? Probably not, so I'll take the 1764 * smaller code size. 1765 */ 1766 void 1767 crit_exit_wrapper(__DEBUG_CRIT_ARG__) 1768 { 1769 _crit_exit(mycpu __DEBUG_CRIT_PASS_ARG__); 1770 } 1771 1772 void 1773 crit_panic(void) 1774 { 1775 thread_t td = curthread; 1776 int lcrit = td->td_critcount; 1777 1778 td->td_critcount = 0; 1779 panic("td_critcount is/would-go negative! %p %d", td, lcrit); 1780 /* NOT REACHED */ 1781 } 1782 1783 #ifdef SMP 1784 1785 /* 1786 * Called from debugger/panic on cpus which have been stopped. We must still 1787 * process the IPIQ while stopped, even if we were stopped while in a critical 1788 * section (XXX). 1789 * 1790 * If we are dumping also try to process any pending interrupts. This may 1791 * or may not work depending on the state of the cpu at the point it was 1792 * stopped. 1793 */ 1794 void 1795 lwkt_smp_stopped(void) 1796 { 1797 globaldata_t gd = mycpu; 1798 1799 crit_enter_gd(gd); 1800 if (dumping) { 1801 lwkt_process_ipiq(); 1802 splz(); 1803 } else { 1804 lwkt_process_ipiq(); 1805 } 1806 crit_exit_gd(gd); 1807 } 1808 1809 #endif 1810