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 = 0; 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 td->td_mpflags = 0; 295 return (1); 296 } 297 298 static void 299 _lwkt_thread_dtor(void *obj, void *privdata) 300 { 301 struct thread *td = (struct thread *)obj; 302 303 KASSERT(td->td_flags & TDF_ALLOCATED_THREAD, 304 ("_lwkt_thread_dtor: not allocated from objcache")); 305 KASSERT((td->td_flags & TDF_ALLOCATED_STACK) && td->td_kstack && 306 td->td_kstack_size > 0, 307 ("_lwkt_thread_dtor: corrupted stack")); 308 kmem_free(&kernel_map, (vm_offset_t)td->td_kstack, td->td_kstack_size); 309 td->td_kstack = NULL; 310 td->td_flags = 0; 311 } 312 313 /* 314 * Initialize the lwkt s/system. 315 * 316 * Nominally cache up to 32 thread + kstack structures. Cache more on 317 * systems with a lot of cpu cores. 318 */ 319 void 320 lwkt_init(void) 321 { 322 TUNABLE_INT("lwkt.cache_threads", &lwkt_cache_threads); 323 if (lwkt_cache_threads == 0) { 324 lwkt_cache_threads = ncpus * 4; 325 if (lwkt_cache_threads < 32) 326 lwkt_cache_threads = 32; 327 } 328 thread_cache = objcache_create_mbacked( 329 M_THREAD, sizeof(struct thread), 330 NULL, lwkt_cache_threads, 331 _lwkt_thread_ctor, _lwkt_thread_dtor, NULL); 332 } 333 334 /* 335 * Schedule a thread to run. As the current thread we can always safely 336 * schedule ourselves, and a shortcut procedure is provided for that 337 * function. 338 * 339 * (non-blocking, self contained on a per cpu basis) 340 */ 341 void 342 lwkt_schedule_self(thread_t td) 343 { 344 KKASSERT((td->td_flags & TDF_MIGRATING) == 0); 345 crit_enter_quick(td); 346 KASSERT(td != &td->td_gd->gd_idlethread, 347 ("lwkt_schedule_self(): scheduling gd_idlethread is illegal!")); 348 KKASSERT(td->td_lwp == NULL || 349 (td->td_lwp->lwp_mpflags & LWP_MP_ONRUNQ) == 0); 350 _lwkt_enqueue(td); 351 crit_exit_quick(td); 352 } 353 354 /* 355 * Deschedule a thread. 356 * 357 * (non-blocking, self contained on a per cpu basis) 358 */ 359 void 360 lwkt_deschedule_self(thread_t td) 361 { 362 crit_enter_quick(td); 363 _lwkt_dequeue(td); 364 crit_exit_quick(td); 365 } 366 367 /* 368 * LWKTs operate on a per-cpu basis 369 * 370 * WARNING! Called from early boot, 'mycpu' may not work yet. 371 */ 372 void 373 lwkt_gdinit(struct globaldata *gd) 374 { 375 TAILQ_INIT(&gd->gd_tdrunq); 376 TAILQ_INIT(&gd->gd_tdallq); 377 } 378 379 /* 380 * Create a new thread. The thread must be associated with a process context 381 * or LWKT start address before it can be scheduled. If the target cpu is 382 * -1 the thread will be created on the current cpu. 383 * 384 * If you intend to create a thread without a process context this function 385 * does everything except load the startup and switcher function. 386 */ 387 thread_t 388 lwkt_alloc_thread(struct thread *td, int stksize, int cpu, int flags) 389 { 390 static int cpu_rotator; 391 globaldata_t gd = mycpu; 392 void *stack; 393 394 /* 395 * If static thread storage is not supplied allocate a thread. Reuse 396 * a cached free thread if possible. gd_freetd is used to keep an exiting 397 * thread intact through the exit. 398 */ 399 if (td == NULL) { 400 crit_enter_gd(gd); 401 if ((td = gd->gd_freetd) != NULL) { 402 KKASSERT((td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK| 403 TDF_RUNQ)) == 0); 404 gd->gd_freetd = NULL; 405 } else { 406 td = objcache_get(thread_cache, M_WAITOK); 407 KKASSERT((td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK| 408 TDF_RUNQ)) == 0); 409 } 410 crit_exit_gd(gd); 411 KASSERT((td->td_flags & 412 (TDF_ALLOCATED_THREAD|TDF_RUNNING|TDF_PREEMPT_LOCK)) == 413 TDF_ALLOCATED_THREAD, 414 ("lwkt_alloc_thread: corrupted td flags 0x%X", td->td_flags)); 415 flags |= td->td_flags & (TDF_ALLOCATED_THREAD|TDF_ALLOCATED_STACK); 416 } 417 418 /* 419 * Try to reuse cached stack. 420 */ 421 if ((stack = td->td_kstack) != NULL && td->td_kstack_size != stksize) { 422 if (flags & TDF_ALLOCATED_STACK) { 423 kmem_free(&kernel_map, (vm_offset_t)stack, td->td_kstack_size); 424 stack = NULL; 425 } 426 } 427 if (stack == NULL) { 428 stack = (void *)kmem_alloc_stack(&kernel_map, stksize); 429 flags |= TDF_ALLOCATED_STACK; 430 } 431 if (cpu < 0) { 432 cpu = ++cpu_rotator; 433 cpu_ccfence(); 434 cpu %= ncpus; 435 } 436 lwkt_init_thread(td, stack, stksize, flags, globaldata_find(cpu)); 437 return(td); 438 } 439 440 /* 441 * Initialize a preexisting thread structure. This function is used by 442 * lwkt_alloc_thread() and also used to initialize the per-cpu idlethread. 443 * 444 * All threads start out in a critical section at a priority of 445 * TDPRI_KERN_DAEMON. Higher level code will modify the priority as 446 * appropriate. This function may send an IPI message when the 447 * requested cpu is not the current cpu and consequently gd_tdallq may 448 * not be initialized synchronously from the point of view of the originating 449 * cpu. 450 * 451 * NOTE! we have to be careful in regards to creating threads for other cpus 452 * if SMP has not yet been activated. 453 */ 454 #ifdef SMP 455 456 static void 457 lwkt_init_thread_remote(void *arg) 458 { 459 thread_t td = arg; 460 461 /* 462 * Protected by critical section held by IPI dispatch 463 */ 464 TAILQ_INSERT_TAIL(&td->td_gd->gd_tdallq, td, td_allq); 465 } 466 467 #endif 468 469 /* 470 * lwkt core thread structural initialization. 471 * 472 * NOTE: All threads are initialized as mpsafe threads. 473 */ 474 void 475 lwkt_init_thread(thread_t td, void *stack, int stksize, int flags, 476 struct globaldata *gd) 477 { 478 globaldata_t mygd = mycpu; 479 480 bzero(td, sizeof(struct thread)); 481 td->td_kstack = stack; 482 td->td_kstack_size = stksize; 483 td->td_flags = flags; 484 td->td_mpflags = 0; 485 td->td_gd = gd; 486 td->td_pri = TDPRI_KERN_DAEMON; 487 td->td_critcount = 1; 488 td->td_toks_have = NULL; 489 td->td_toks_stop = &td->td_toks_base; 490 if (lwkt_use_spin_port || (flags & TDF_FORCE_SPINPORT)) 491 lwkt_initport_spin(&td->td_msgport); 492 else 493 lwkt_initport_thread(&td->td_msgport, td); 494 pmap_init_thread(td); 495 #ifdef SMP 496 /* 497 * Normally initializing a thread for a remote cpu requires sending an 498 * IPI. However, the idlethread is setup before the other cpus are 499 * activated so we have to treat it as a special case. XXX manipulation 500 * of gd_tdallq requires the BGL. 501 */ 502 if (gd == mygd || td == &gd->gd_idlethread) { 503 crit_enter_gd(mygd); 504 TAILQ_INSERT_TAIL(&gd->gd_tdallq, td, td_allq); 505 crit_exit_gd(mygd); 506 } else { 507 lwkt_send_ipiq(gd, lwkt_init_thread_remote, td); 508 } 509 #else 510 crit_enter_gd(mygd); 511 TAILQ_INSERT_TAIL(&gd->gd_tdallq, td, td_allq); 512 crit_exit_gd(mygd); 513 #endif 514 515 dsched_new_thread(td); 516 } 517 518 void 519 lwkt_set_comm(thread_t td, const char *ctl, ...) 520 { 521 __va_list va; 522 523 __va_start(va, ctl); 524 kvsnprintf(td->td_comm, sizeof(td->td_comm), ctl, va); 525 __va_end(va); 526 KTR_LOG(ctxsw_newtd, td, &td->td_comm[0]); 527 } 528 529 /* 530 * Prevent the thread from getting destroyed. Note that unlike PHOLD/PRELE 531 * this does not prevent the thread from migrating to another cpu so the 532 * gd_tdallq state is not protected by this. 533 */ 534 void 535 lwkt_hold(thread_t td) 536 { 537 atomic_add_int(&td->td_refs, 1); 538 } 539 540 void 541 lwkt_rele(thread_t td) 542 { 543 KKASSERT(td->td_refs > 0); 544 atomic_add_int(&td->td_refs, -1); 545 } 546 547 void 548 lwkt_free_thread(thread_t td) 549 { 550 KKASSERT(td->td_refs == 0); 551 KKASSERT((td->td_flags & (TDF_RUNNING | TDF_PREEMPT_LOCK | 552 TDF_RUNQ | TDF_TSLEEPQ)) == 0); 553 if (td->td_flags & TDF_ALLOCATED_THREAD) { 554 objcache_put(thread_cache, td); 555 } else if (td->td_flags & TDF_ALLOCATED_STACK) { 556 /* client-allocated struct with internally allocated stack */ 557 KASSERT(td->td_kstack && td->td_kstack_size > 0, 558 ("lwkt_free_thread: corrupted stack")); 559 kmem_free(&kernel_map, (vm_offset_t)td->td_kstack, td->td_kstack_size); 560 td->td_kstack = NULL; 561 td->td_kstack_size = 0; 562 } 563 KTR_LOG(ctxsw_deadtd, td); 564 } 565 566 567 /* 568 * Switch to the next runnable lwkt. If no LWKTs are runnable then 569 * switch to the idlethread. Switching must occur within a critical 570 * section to avoid races with the scheduling queue. 571 * 572 * We always have full control over our cpu's run queue. Other cpus 573 * that wish to manipulate our queue must use the cpu_*msg() calls to 574 * talk to our cpu, so a critical section is all that is needed and 575 * the result is very, very fast thread switching. 576 * 577 * The LWKT scheduler uses a fixed priority model and round-robins at 578 * each priority level. User process scheduling is a totally 579 * different beast and LWKT priorities should not be confused with 580 * user process priorities. 581 * 582 * PREEMPTION NOTE: Preemption occurs via lwkt_preempt(). lwkt_switch() 583 * is not called by the current thread in the preemption case, only when 584 * the preempting thread blocks (in order to return to the original thread). 585 * 586 * SPECIAL NOTE ON SWITCH ATOMICY: Certain operations such as thread 587 * migration and tsleep deschedule the current lwkt thread and call 588 * lwkt_switch(). In particular, the target cpu of the migration fully 589 * expects the thread to become non-runnable and can deadlock against 590 * cpusync operations if we run any IPIs prior to switching the thread out. 591 * 592 * WE MUST BE VERY CAREFUL NOT TO RUN SPLZ DIRECTLY OR INDIRECTLY IF 593 * THE CURRENT THREAD HAS BEEN DESCHEDULED! 594 */ 595 void 596 lwkt_switch(void) 597 { 598 globaldata_t gd = mycpu; 599 thread_t td = gd->gd_curthread; 600 thread_t ntd; 601 thread_t xtd; 602 int spinning = 0; 603 604 KKASSERT(gd->gd_processing_ipiq == 0); 605 KKASSERT(td->td_flags & TDF_RUNNING); 606 607 /* 608 * Switching from within a 'fast' (non thread switched) interrupt or IPI 609 * is illegal. However, we may have to do it anyway if we hit a fatal 610 * kernel trap or we have paniced. 611 * 612 * If this case occurs save and restore the interrupt nesting level. 613 */ 614 if (gd->gd_intr_nesting_level) { 615 int savegdnest; 616 int savegdtrap; 617 618 if (gd->gd_trap_nesting_level == 0 && panic_cpu_gd != mycpu) { 619 panic("lwkt_switch: Attempt to switch from a " 620 "a fast interrupt, ipi, or hard code section, " 621 "td %p\n", 622 td); 623 } else { 624 savegdnest = gd->gd_intr_nesting_level; 625 savegdtrap = gd->gd_trap_nesting_level; 626 gd->gd_intr_nesting_level = 0; 627 gd->gd_trap_nesting_level = 0; 628 if ((td->td_flags & TDF_PANICWARN) == 0) { 629 td->td_flags |= TDF_PANICWARN; 630 kprintf("Warning: thread switch from interrupt, IPI, " 631 "or hard code section.\n" 632 "thread %p (%s)\n", td, td->td_comm); 633 print_backtrace(-1); 634 } 635 lwkt_switch(); 636 gd->gd_intr_nesting_level = savegdnest; 637 gd->gd_trap_nesting_level = savegdtrap; 638 return; 639 } 640 } 641 642 /* 643 * Release our current user process designation if we are blocking 644 * or if a user reschedule was requested. 645 * 646 * NOTE: This function is NOT called if we are switching into or 647 * returning from a preemption. 648 * 649 * NOTE: Releasing our current user process designation may cause 650 * it to be assigned to another thread, which in turn will 651 * cause us to block in the usched acquire code when we attempt 652 * to return to userland. 653 * 654 * NOTE: On SMP systems this can be very nasty when heavy token 655 * contention is present so we want to be careful not to 656 * release the designation gratuitously. 657 */ 658 if (td->td_release && 659 (user_resched_wanted() || (td->td_flags & TDF_RUNQ) == 0)) { 660 td->td_release(td); 661 } 662 663 /* 664 * Release all tokens 665 */ 666 crit_enter_gd(gd); 667 if (TD_TOKS_HELD(td)) 668 lwkt_relalltokens(td); 669 670 /* 671 * We had better not be holding any spin locks, but don't get into an 672 * endless panic loop. 673 */ 674 KASSERT(gd->gd_spinlocks_wr == 0 || panicstr != NULL, 675 ("lwkt_switch: still holding %d exclusive spinlocks!", 676 gd->gd_spinlocks_wr)); 677 678 679 #ifdef SMP 680 #ifdef INVARIANTS 681 if (td->td_cscount) { 682 kprintf("Diagnostic: attempt to switch while mastering cpusync: %p\n", 683 td); 684 if (panic_on_cscount) 685 panic("switching while mastering cpusync"); 686 } 687 #endif 688 #endif 689 690 /* 691 * If we had preempted another thread on this cpu, resume the preempted 692 * thread. This occurs transparently, whether the preempted thread 693 * was scheduled or not (it may have been preempted after descheduling 694 * itself). 695 * 696 * We have to setup the MP lock for the original thread after backing 697 * out the adjustment that was made to curthread when the original 698 * was preempted. 699 */ 700 if ((ntd = td->td_preempted) != NULL) { 701 KKASSERT(ntd->td_flags & TDF_PREEMPT_LOCK); 702 ntd->td_flags |= TDF_PREEMPT_DONE; 703 704 /* 705 * The interrupt may have woken a thread up, we need to properly 706 * set the reschedule flag if the originally interrupted thread is 707 * at a lower priority. 708 * 709 * The interrupt may not have descheduled. 710 */ 711 if (TAILQ_FIRST(&gd->gd_tdrunq) != ntd) 712 need_lwkt_resched(); 713 goto havethread_preempted; 714 } 715 716 /* 717 * If we cannot obtain ownership of the tokens we cannot immediately 718 * schedule the target thread. 719 * 720 * Reminder: Again, we cannot afford to run any IPIs in this path if 721 * the current thread has been descheduled. 722 */ 723 for (;;) { 724 clear_lwkt_resched(); 725 726 /* 727 * Hotpath - pull the head of the run queue and attempt to schedule 728 * it. 729 */ 730 for (;;) { 731 ntd = TAILQ_FIRST(&gd->gd_tdrunq); 732 733 if (ntd == NULL) { 734 /* 735 * Runq is empty, switch to idle to allow it to halt. 736 */ 737 ntd = &gd->gd_idlethread; 738 #ifdef SMP 739 if (gd->gd_trap_nesting_level == 0 && panicstr == NULL) 740 ASSERT_NO_TOKENS_HELD(ntd); 741 #endif 742 cpu_time.cp_msg[0] = 0; 743 cpu_time.cp_stallpc = 0; 744 goto haveidle; 745 } 746 break; 747 } 748 749 /* 750 * Hotpath - schedule ntd. 751 * 752 * NOTE: For UP there is no mplock and lwkt_getalltokens() 753 * always succeeds. 754 */ 755 if (TD_TOKS_NOT_HELD(ntd) || 756 lwkt_getalltokens(ntd, (spinning >= lwkt_spin_loops))) 757 { 758 goto havethread; 759 } 760 761 /* 762 * Coldpath (SMP only since tokens always succeed on UP) 763 * 764 * We had some contention on the thread we wanted to schedule. 765 * What we do now is try to find a thread that we can schedule 766 * in its stead. 767 * 768 * The coldpath scan does NOT rearrange threads in the run list. 769 * The lwkt_schedulerclock() will assert need_lwkt_resched() on 770 * the next tick whenever the current head is not the current thread. 771 */ 772 #ifdef INVARIANTS 773 ++token_contention_count[ntd->td_pri]; 774 ++ntd->td_contended; 775 #endif 776 777 if (fairq_bypass > 0) 778 goto skip; 779 780 xtd = NULL; 781 while ((ntd = TAILQ_NEXT(ntd, td_threadq)) != NULL) { 782 /* 783 * Never schedule threads returning to userland or the 784 * user thread scheduler helper thread when higher priority 785 * threads are present. 786 */ 787 if (ntd->td_pri < TDPRI_KERN_LPSCHED) { 788 ntd = NULL; 789 break; 790 } 791 792 /* 793 * Try this one. 794 */ 795 if (TD_TOKS_NOT_HELD(ntd) || 796 lwkt_getalltokens(ntd, (spinning >= lwkt_spin_loops))) { 797 goto havethread; 798 } 799 #ifdef INVARIANTS 800 ++token_contention_count[ntd->td_pri]; 801 ++ntd->td_contended; 802 #endif 803 } 804 805 skip: 806 /* 807 * We exhausted the run list, meaning that all runnable threads 808 * are contested. 809 */ 810 cpu_pause(); 811 ntd = &gd->gd_idlethread; 812 #ifdef SMP 813 if (gd->gd_trap_nesting_level == 0 && panicstr == NULL) 814 ASSERT_NO_TOKENS_HELD(ntd); 815 /* contention case, do not clear contention mask */ 816 #endif 817 818 /* 819 * We are going to have to retry but if the current thread is not 820 * on the runq we instead switch through the idle thread to get away 821 * from the current thread. We have to flag for lwkt reschedule 822 * to prevent the idle thread from halting. 823 * 824 * NOTE: A non-zero spinning is passed to lwkt_getalltokens() to 825 * instruct it to deal with the potential for deadlocks by 826 * ordering the tokens by address. 827 */ 828 if ((td->td_flags & TDF_RUNQ) == 0) { 829 need_lwkt_resched(); /* prevent hlt */ 830 goto haveidle; 831 } 832 #if defined(INVARIANTS) && defined(__amd64__) 833 if ((read_rflags() & PSL_I) == 0) { 834 cpu_enable_intr(); 835 panic("lwkt_switch() called with interrupts disabled"); 836 } 837 #endif 838 839 /* 840 * Number iterations so far. After a certain point we switch to 841 * a sorted-address/monitor/mwait version of lwkt_getalltokens() 842 */ 843 if (spinning < 0x7FFFFFFF) 844 ++spinning; 845 846 #ifdef SMP 847 /* 848 * lwkt_getalltokens() failed in sorted token mode, we can use 849 * monitor/mwait in this case. 850 */ 851 if (spinning >= lwkt_spin_loops && 852 (cpu_mi_feature & CPU_MI_MONITOR) && 853 lwkt_spin_monitor) 854 { 855 cpu_mmw_pause_int(&gd->gd_reqflags, 856 (gd->gd_reqflags | RQF_SPINNING) & 857 ~RQF_IDLECHECK_WK_MASK); 858 } 859 #endif 860 861 /* 862 * We already checked that td is still scheduled so this should be 863 * safe. 864 */ 865 splz_check(); 866 867 /* 868 * This experimental resequencer is used as a fall-back to reduce 869 * hw cache line contention by placing each core's scheduler into a 870 * time-domain-multplexed slot. 871 * 872 * The resequencer is disabled by default. It's functionality has 873 * largely been superceeded by the token algorithm which limits races 874 * to a subset of cores. 875 * 876 * The resequencer algorithm tends to break down when more than 877 * 20 cores are contending. What appears to happen is that new 878 * tokens can be obtained out of address-sorted order by new cores 879 * while existing cores languish in long delays between retries and 880 * wind up being starved-out of the token acquisition. 881 */ 882 if (lwkt_spin_reseq && spinning >= lwkt_spin_reseq) { 883 int cseq = atomic_fetchadd_int(&lwkt_cseq_windex, 1); 884 int oseq; 885 886 while ((oseq = lwkt_cseq_rindex) != cseq) { 887 cpu_ccfence(); 888 #if 1 889 if (cpu_mi_feature & CPU_MI_MONITOR) { 890 cpu_mmw_pause_int(&lwkt_cseq_rindex, oseq); 891 } else { 892 #endif 893 cpu_pause(); 894 cpu_lfence(); 895 #if 1 896 } 897 #endif 898 } 899 DELAY(1); 900 atomic_add_int(&lwkt_cseq_rindex, 1); 901 } 902 /* highest level for(;;) loop */ 903 } 904 905 havethread: 906 /* 907 * Clear gd_idle_repeat when doing a normal switch to a non-idle 908 * thread. 909 */ 910 ntd->td_wmesg = NULL; 911 ++gd->gd_cnt.v_swtch; 912 gd->gd_idle_repeat = 0; 913 914 havethread_preempted: 915 /* 916 * If the new target does not need the MP lock and we are holding it, 917 * release the MP lock. If the new target requires the MP lock we have 918 * already acquired it for the target. 919 */ 920 ; 921 haveidle: 922 KASSERT(ntd->td_critcount, 923 ("priority problem in lwkt_switch %d %d", 924 td->td_critcount, ntd->td_critcount)); 925 926 if (td != ntd) { 927 /* 928 * Execute the actual thread switch operation. This function 929 * returns to the current thread and returns the previous thread 930 * (which may be different from the thread we switched to). 931 * 932 * We are responsible for marking ntd as TDF_RUNNING. 933 */ 934 KKASSERT((ntd->td_flags & TDF_RUNNING) == 0); 935 ++switch_count; 936 KTR_LOG(ctxsw_sw, gd->gd_cpuid, ntd); 937 ntd->td_flags |= TDF_RUNNING; 938 lwkt_switch_return(td->td_switch(ntd)); 939 /* ntd invalid, td_switch() can return a different thread_t */ 940 } 941 942 /* 943 * catch-all. XXX is this strictly needed? 944 */ 945 splz_check(); 946 947 /* NOTE: current cpu may have changed after switch */ 948 crit_exit_quick(td); 949 } 950 951 /* 952 * Called by assembly in the td_switch (thread restore path) for thread 953 * bootstrap cases which do not 'return' to lwkt_switch(). 954 */ 955 void 956 lwkt_switch_return(thread_t otd) 957 { 958 #ifdef SMP 959 globaldata_t rgd; 960 961 /* 962 * Check if otd was migrating. Now that we are on ntd we can finish 963 * up the migration. This is a bit messy but it is the only place 964 * where td is known to be fully descheduled. 965 * 966 * We can only activate the migration if otd was migrating but not 967 * held on the cpu due to a preemption chain. We still have to 968 * clear TDF_RUNNING on the old thread either way. 969 * 970 * We are responsible for clearing the previously running thread's 971 * TDF_RUNNING. 972 */ 973 if ((rgd = otd->td_migrate_gd) != NULL && 974 (otd->td_flags & TDF_PREEMPT_LOCK) == 0) { 975 KKASSERT((otd->td_flags & (TDF_MIGRATING | TDF_RUNNING)) == 976 (TDF_MIGRATING | TDF_RUNNING)); 977 otd->td_migrate_gd = NULL; 978 otd->td_flags &= ~TDF_RUNNING; 979 lwkt_send_ipiq(rgd, lwkt_setcpu_remote, otd); 980 } else { 981 otd->td_flags &= ~TDF_RUNNING; 982 } 983 #else 984 otd->td_flags &= ~TDF_RUNNING; 985 #endif 986 } 987 988 /* 989 * Request that the target thread preempt the current thread. Preemption 990 * can only occur if our only critical section is the one that we were called 991 * with, the relative priority of the target thread is higher, and the target 992 * thread holds no tokens. This also only works if we are not holding any 993 * spinlocks (obviously). 994 * 995 * THE CALLER OF LWKT_PREEMPT() MUST BE IN A CRITICAL SECTION. Typically 996 * this is called via lwkt_schedule() through the td_preemptable callback. 997 * critcount is the managed critical priority that we should ignore in order 998 * to determine whether preemption is possible (aka usually just the crit 999 * priority of lwkt_schedule() itself). 1000 * 1001 * Preemption is typically limited to interrupt threads. 1002 * 1003 * Operation works in a fairly straight-forward manner. The normal 1004 * scheduling code is bypassed and we switch directly to the target 1005 * thread. When the target thread attempts to block or switch away 1006 * code at the base of lwkt_switch() will switch directly back to our 1007 * thread. Our thread is able to retain whatever tokens it holds and 1008 * if the target needs one of them the target will switch back to us 1009 * and reschedule itself normally. 1010 */ 1011 void 1012 lwkt_preempt(thread_t ntd, int critcount) 1013 { 1014 struct globaldata *gd = mycpu; 1015 thread_t xtd; 1016 thread_t td; 1017 int save_gd_intr_nesting_level; 1018 1019 /* 1020 * The caller has put us in a critical section. We can only preempt 1021 * if the caller of the caller was not in a critical section (basically 1022 * a local interrupt), as determined by the 'critcount' parameter. We 1023 * also can't preempt if the caller is holding any spinlocks (even if 1024 * he isn't in a critical section). This also handles the tokens test. 1025 * 1026 * YYY The target thread must be in a critical section (else it must 1027 * inherit our critical section? I dunno yet). 1028 */ 1029 KASSERT(ntd->td_critcount, ("BADCRIT0 %d", ntd->td_pri)); 1030 1031 td = gd->gd_curthread; 1032 if (preempt_enable == 0) { 1033 ++preempt_miss; 1034 return; 1035 } 1036 if (ntd->td_pri <= td->td_pri) { 1037 ++preempt_miss; 1038 return; 1039 } 1040 if (td->td_critcount > critcount) { 1041 ++preempt_miss; 1042 return; 1043 } 1044 #ifdef SMP 1045 if (td->td_cscount) { 1046 ++preempt_miss; 1047 return; 1048 } 1049 if (ntd->td_gd != gd) { 1050 ++preempt_miss; 1051 return; 1052 } 1053 #endif 1054 /* 1055 * We don't have to check spinlocks here as they will also bump 1056 * td_critcount. 1057 * 1058 * Do not try to preempt if the target thread is holding any tokens. 1059 * We could try to acquire the tokens but this case is so rare there 1060 * is no need to support it. 1061 */ 1062 KKASSERT(gd->gd_spinlocks_wr == 0); 1063 1064 if (TD_TOKS_HELD(ntd)) { 1065 ++preempt_miss; 1066 return; 1067 } 1068 if (td == ntd || ((td->td_flags | ntd->td_flags) & TDF_PREEMPT_LOCK)) { 1069 ++preempt_weird; 1070 return; 1071 } 1072 if (ntd->td_preempted) { 1073 ++preempt_hit; 1074 return; 1075 } 1076 KKASSERT(gd->gd_processing_ipiq == 0); 1077 1078 /* 1079 * Since we are able to preempt the current thread, there is no need to 1080 * call need_lwkt_resched(). 1081 * 1082 * We must temporarily clear gd_intr_nesting_level around the switch 1083 * since switchouts from the target thread are allowed (they will just 1084 * return to our thread), and since the target thread has its own stack. 1085 * 1086 * A preemption must switch back to the original thread, assert the 1087 * case. 1088 */ 1089 ++preempt_hit; 1090 ntd->td_preempted = td; 1091 td->td_flags |= TDF_PREEMPT_LOCK; 1092 KTR_LOG(ctxsw_pre, gd->gd_cpuid, ntd); 1093 save_gd_intr_nesting_level = gd->gd_intr_nesting_level; 1094 gd->gd_intr_nesting_level = 0; 1095 1096 KKASSERT((ntd->td_flags & TDF_RUNNING) == 0); 1097 ntd->td_flags |= TDF_RUNNING; 1098 xtd = td->td_switch(ntd); 1099 KKASSERT(xtd == ntd); 1100 lwkt_switch_return(xtd); 1101 gd->gd_intr_nesting_level = save_gd_intr_nesting_level; 1102 1103 KKASSERT(ntd->td_preempted && (td->td_flags & TDF_PREEMPT_DONE)); 1104 ntd->td_preempted = NULL; 1105 td->td_flags &= ~(TDF_PREEMPT_LOCK|TDF_PREEMPT_DONE); 1106 } 1107 1108 /* 1109 * Conditionally call splz() if gd_reqflags indicates work is pending. 1110 * This will work inside a critical section but not inside a hard code 1111 * section. 1112 * 1113 * (self contained on a per cpu basis) 1114 */ 1115 void 1116 splz_check(void) 1117 { 1118 globaldata_t gd = mycpu; 1119 thread_t td = gd->gd_curthread; 1120 1121 if ((gd->gd_reqflags & RQF_IDLECHECK_MASK) && 1122 gd->gd_intr_nesting_level == 0 && 1123 td->td_nest_count < 2) 1124 { 1125 splz(); 1126 } 1127 } 1128 1129 /* 1130 * This version is integrated into crit_exit, reqflags has already 1131 * been tested but td_critcount has not. 1132 * 1133 * We only want to execute the splz() on the 1->0 transition of 1134 * critcount and not in a hard code section or if too deeply nested. 1135 */ 1136 void 1137 lwkt_maybe_splz(thread_t td) 1138 { 1139 globaldata_t gd = td->td_gd; 1140 1141 if (td->td_critcount == 0 && 1142 gd->gd_intr_nesting_level == 0 && 1143 td->td_nest_count < 2) 1144 { 1145 splz(); 1146 } 1147 } 1148 1149 /* 1150 * Drivers which set up processing co-threads can call this function to 1151 * run the co-thread at a higher priority and to allow it to preempt 1152 * normal threads. 1153 */ 1154 void 1155 lwkt_set_interrupt_support_thread(void) 1156 { 1157 thread_t td = curthread; 1158 1159 lwkt_setpri_self(TDPRI_INT_SUPPORT); 1160 td->td_flags |= TDF_INTTHREAD; 1161 td->td_preemptable = lwkt_preempt; 1162 } 1163 1164 1165 /* 1166 * This function is used to negotiate a passive release of the current 1167 * process/lwp designation with the user scheduler, allowing the user 1168 * scheduler to schedule another user thread. The related kernel thread 1169 * (curthread) continues running in the released state. 1170 */ 1171 void 1172 lwkt_passive_release(struct thread *td) 1173 { 1174 struct lwp *lp = td->td_lwp; 1175 1176 td->td_release = NULL; 1177 lwkt_setpri_self(TDPRI_KERN_USER); 1178 lp->lwp_proc->p_usched->release_curproc(lp); 1179 } 1180 1181 1182 /* 1183 * This implements a LWKT yield, allowing a kernel thread to yield to other 1184 * kernel threads at the same or higher priority. This function can be 1185 * called in a tight loop and will typically only yield once per tick. 1186 * 1187 * Most kernel threads run at the same priority in order to allow equal 1188 * sharing. 1189 * 1190 * (self contained on a per cpu basis) 1191 */ 1192 void 1193 lwkt_yield(void) 1194 { 1195 globaldata_t gd = mycpu; 1196 thread_t td = gd->gd_curthread; 1197 1198 if ((gd->gd_reqflags & RQF_IDLECHECK_MASK) && td->td_nest_count < 2) 1199 splz(); 1200 if (lwkt_resched_wanted()) { 1201 lwkt_schedule_self(curthread); 1202 lwkt_switch(); 1203 } 1204 } 1205 1206 /* 1207 * This yield is designed for kernel threads with a user context. 1208 * 1209 * The kernel acting on behalf of the user is potentially cpu-bound, 1210 * this function will efficiently allow other threads to run and also 1211 * switch to other processes by releasing. 1212 * 1213 * The lwkt_user_yield() function is designed to have very low overhead 1214 * if no yield is determined to be needed. 1215 */ 1216 void 1217 lwkt_user_yield(void) 1218 { 1219 globaldata_t gd = mycpu; 1220 thread_t td = gd->gd_curthread; 1221 1222 /* 1223 * Always run any pending interrupts in case we are in a critical 1224 * section. 1225 */ 1226 if ((gd->gd_reqflags & RQF_IDLECHECK_MASK) && td->td_nest_count < 2) 1227 splz(); 1228 1229 /* 1230 * Switch (which forces a release) if another kernel thread needs 1231 * the cpu, if userland wants us to resched, or if our kernel 1232 * quantum has run out. 1233 */ 1234 if (lwkt_resched_wanted() || 1235 user_resched_wanted()) 1236 { 1237 lwkt_switch(); 1238 } 1239 1240 #if 0 1241 /* 1242 * Reacquire the current process if we are released. 1243 * 1244 * XXX not implemented atm. The kernel may be holding locks and such, 1245 * so we want the thread to continue to receive cpu. 1246 */ 1247 if (td->td_release == NULL && lp) { 1248 lp->lwp_proc->p_usched->acquire_curproc(lp); 1249 td->td_release = lwkt_passive_release; 1250 lwkt_setpri_self(TDPRI_USER_NORM); 1251 } 1252 #endif 1253 } 1254 1255 /* 1256 * Generic schedule. Possibly schedule threads belonging to other cpus and 1257 * deal with threads that might be blocked on a wait queue. 1258 * 1259 * We have a little helper inline function which does additional work after 1260 * the thread has been enqueued, including dealing with preemption and 1261 * setting need_lwkt_resched() (which prevents the kernel from returning 1262 * to userland until it has processed higher priority threads). 1263 * 1264 * It is possible for this routine to be called after a failed _enqueue 1265 * (due to the target thread migrating, sleeping, or otherwise blocked). 1266 * We have to check that the thread is actually on the run queue! 1267 */ 1268 static __inline 1269 void 1270 _lwkt_schedule_post(globaldata_t gd, thread_t ntd, int ccount) 1271 { 1272 if (ntd->td_flags & TDF_RUNQ) { 1273 if (ntd->td_preemptable) { 1274 ntd->td_preemptable(ntd, ccount); /* YYY +token */ 1275 } 1276 } 1277 } 1278 1279 static __inline 1280 void 1281 _lwkt_schedule(thread_t td) 1282 { 1283 globaldata_t mygd = mycpu; 1284 1285 KASSERT(td != &td->td_gd->gd_idlethread, 1286 ("lwkt_schedule(): scheduling gd_idlethread is illegal!")); 1287 KKASSERT((td->td_flags & TDF_MIGRATING) == 0); 1288 crit_enter_gd(mygd); 1289 KKASSERT(td->td_lwp == NULL || 1290 (td->td_lwp->lwp_mpflags & LWP_MP_ONRUNQ) == 0); 1291 1292 if (td == mygd->gd_curthread) { 1293 _lwkt_enqueue(td); 1294 } else { 1295 /* 1296 * If we own the thread, there is no race (since we are in a 1297 * critical section). If we do not own the thread there might 1298 * be a race but the target cpu will deal with it. 1299 */ 1300 #ifdef SMP 1301 if (td->td_gd == mygd) { 1302 _lwkt_enqueue(td); 1303 _lwkt_schedule_post(mygd, td, 1); 1304 } else { 1305 lwkt_send_ipiq3(td->td_gd, lwkt_schedule_remote, td, 0); 1306 } 1307 #else 1308 _lwkt_enqueue(td); 1309 _lwkt_schedule_post(mygd, td, 1); 1310 #endif 1311 } 1312 crit_exit_gd(mygd); 1313 } 1314 1315 void 1316 lwkt_schedule(thread_t td) 1317 { 1318 _lwkt_schedule(td); 1319 } 1320 1321 void 1322 lwkt_schedule_noresched(thread_t td) /* XXX not impl */ 1323 { 1324 _lwkt_schedule(td); 1325 } 1326 1327 #ifdef SMP 1328 1329 /* 1330 * When scheduled remotely if frame != NULL the IPIQ is being 1331 * run via doreti or an interrupt then preemption can be allowed. 1332 * 1333 * To allow preemption we have to drop the critical section so only 1334 * one is present in _lwkt_schedule_post. 1335 */ 1336 static void 1337 lwkt_schedule_remote(void *arg, int arg2, struct intrframe *frame) 1338 { 1339 thread_t td = curthread; 1340 thread_t ntd = arg; 1341 1342 if (frame && ntd->td_preemptable) { 1343 crit_exit_noyield(td); 1344 _lwkt_schedule(ntd); 1345 crit_enter_quick(td); 1346 } else { 1347 _lwkt_schedule(ntd); 1348 } 1349 } 1350 1351 /* 1352 * Thread migration using a 'Pull' method. The thread may or may not be 1353 * the current thread. It MUST be descheduled and in a stable state. 1354 * lwkt_giveaway() must be called on the cpu owning the thread. 1355 * 1356 * At any point after lwkt_giveaway() is called, the target cpu may 1357 * 'pull' the thread by calling lwkt_acquire(). 1358 * 1359 * We have to make sure the thread is not sitting on a per-cpu tsleep 1360 * queue or it will blow up when it moves to another cpu. 1361 * 1362 * MPSAFE - must be called under very specific conditions. 1363 */ 1364 void 1365 lwkt_giveaway(thread_t td) 1366 { 1367 globaldata_t gd = mycpu; 1368 1369 crit_enter_gd(gd); 1370 if (td->td_flags & TDF_TSLEEPQ) 1371 tsleep_remove(td); 1372 KKASSERT(td->td_gd == gd); 1373 TAILQ_REMOVE(&gd->gd_tdallq, td, td_allq); 1374 td->td_flags |= TDF_MIGRATING; 1375 crit_exit_gd(gd); 1376 } 1377 1378 void 1379 lwkt_acquire(thread_t td) 1380 { 1381 globaldata_t gd; 1382 globaldata_t mygd; 1383 int retry = 10000000; 1384 1385 KKASSERT(td->td_flags & TDF_MIGRATING); 1386 gd = td->td_gd; 1387 mygd = mycpu; 1388 if (gd != mycpu) { 1389 cpu_lfence(); 1390 KKASSERT((td->td_flags & TDF_RUNQ) == 0); 1391 crit_enter_gd(mygd); 1392 DEBUG_PUSH_INFO("lwkt_acquire"); 1393 while (td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK)) { 1394 #ifdef SMP 1395 lwkt_process_ipiq(); 1396 #endif 1397 cpu_lfence(); 1398 if (--retry == 0) { 1399 kprintf("lwkt_acquire: stuck: td %p td->td_flags %08x\n", 1400 td, td->td_flags); 1401 retry = 10000000; 1402 } 1403 } 1404 DEBUG_POP_INFO(); 1405 cpu_mfence(); 1406 td->td_gd = mygd; 1407 TAILQ_INSERT_TAIL(&mygd->gd_tdallq, td, td_allq); 1408 td->td_flags &= ~TDF_MIGRATING; 1409 crit_exit_gd(mygd); 1410 } else { 1411 crit_enter_gd(mygd); 1412 TAILQ_INSERT_TAIL(&mygd->gd_tdallq, td, td_allq); 1413 td->td_flags &= ~TDF_MIGRATING; 1414 crit_exit_gd(mygd); 1415 } 1416 } 1417 1418 #endif 1419 1420 /* 1421 * Generic deschedule. Descheduling threads other then your own should be 1422 * done only in carefully controlled circumstances. Descheduling is 1423 * asynchronous. 1424 * 1425 * This function may block if the cpu has run out of messages. 1426 */ 1427 void 1428 lwkt_deschedule(thread_t td) 1429 { 1430 crit_enter(); 1431 #ifdef SMP 1432 if (td == curthread) { 1433 _lwkt_dequeue(td); 1434 } else { 1435 if (td->td_gd == mycpu) { 1436 _lwkt_dequeue(td); 1437 } else { 1438 lwkt_send_ipiq(td->td_gd, (ipifunc1_t)lwkt_deschedule, td); 1439 } 1440 } 1441 #else 1442 _lwkt_dequeue(td); 1443 #endif 1444 crit_exit(); 1445 } 1446 1447 /* 1448 * Set the target thread's priority. This routine does not automatically 1449 * switch to a higher priority thread, LWKT threads are not designed for 1450 * continuous priority changes. Yield if you want to switch. 1451 */ 1452 void 1453 lwkt_setpri(thread_t td, int pri) 1454 { 1455 if (td->td_pri != pri) { 1456 KKASSERT(pri >= 0); 1457 crit_enter(); 1458 if (td->td_flags & TDF_RUNQ) { 1459 KKASSERT(td->td_gd == mycpu); 1460 _lwkt_dequeue(td); 1461 td->td_pri = pri; 1462 _lwkt_enqueue(td); 1463 } else { 1464 td->td_pri = pri; 1465 } 1466 crit_exit(); 1467 } 1468 } 1469 1470 /* 1471 * Set the initial priority for a thread prior to it being scheduled for 1472 * the first time. The thread MUST NOT be scheduled before or during 1473 * this call. The thread may be assigned to a cpu other then the current 1474 * cpu. 1475 * 1476 * Typically used after a thread has been created with TDF_STOPPREQ, 1477 * and before the thread is initially scheduled. 1478 */ 1479 void 1480 lwkt_setpri_initial(thread_t td, int pri) 1481 { 1482 KKASSERT(pri >= 0); 1483 KKASSERT((td->td_flags & TDF_RUNQ) == 0); 1484 td->td_pri = pri; 1485 } 1486 1487 void 1488 lwkt_setpri_self(int pri) 1489 { 1490 thread_t td = curthread; 1491 1492 KKASSERT(pri >= 0 && pri <= TDPRI_MAX); 1493 crit_enter(); 1494 if (td->td_flags & TDF_RUNQ) { 1495 _lwkt_dequeue(td); 1496 td->td_pri = pri; 1497 _lwkt_enqueue(td); 1498 } else { 1499 td->td_pri = pri; 1500 } 1501 crit_exit(); 1502 } 1503 1504 /* 1505 * hz tick scheduler clock for LWKT threads 1506 */ 1507 void 1508 lwkt_schedulerclock(thread_t td) 1509 { 1510 globaldata_t gd = td->td_gd; 1511 thread_t xtd; 1512 1513 if (TAILQ_FIRST(&gd->gd_tdrunq) == td) { 1514 /* 1515 * If the current thread is at the head of the runq shift it to the 1516 * end of any equal-priority threads and request a LWKT reschedule 1517 * if it moved. 1518 */ 1519 xtd = TAILQ_NEXT(td, td_threadq); 1520 if (xtd && xtd->td_pri == td->td_pri) { 1521 TAILQ_REMOVE(&gd->gd_tdrunq, td, td_threadq); 1522 while (xtd && xtd->td_pri == td->td_pri) 1523 xtd = TAILQ_NEXT(xtd, td_threadq); 1524 if (xtd) 1525 TAILQ_INSERT_BEFORE(xtd, td, td_threadq); 1526 else 1527 TAILQ_INSERT_TAIL(&gd->gd_tdrunq, td, td_threadq); 1528 need_lwkt_resched(); 1529 } 1530 } else { 1531 /* 1532 * If we scheduled a thread other than the one at the head of the 1533 * queue always request a reschedule every tick. 1534 */ 1535 need_lwkt_resched(); 1536 } 1537 } 1538 1539 /* 1540 * Migrate the current thread to the specified cpu. 1541 * 1542 * This is accomplished by descheduling ourselves from the current cpu 1543 * and setting td_migrate_gd. The lwkt_switch() code will detect that the 1544 * 'old' thread wants to migrate after it has been completely switched out 1545 * and will complete the migration. 1546 * 1547 * TDF_MIGRATING prevents scheduling races while the thread is being migrated. 1548 * 1549 * We must be sure to release our current process designation (if a user 1550 * process) before clearing out any tsleepq we are on because the release 1551 * code may re-add us. 1552 * 1553 * We must be sure to remove ourselves from the current cpu's tsleepq 1554 * before potentially moving to another queue. The thread can be on 1555 * a tsleepq due to a left-over tsleep_interlock(). 1556 */ 1557 1558 void 1559 lwkt_setcpu_self(globaldata_t rgd) 1560 { 1561 #ifdef SMP 1562 thread_t td = curthread; 1563 1564 if (td->td_gd != rgd) { 1565 crit_enter_quick(td); 1566 1567 if (td->td_release) 1568 td->td_release(td); 1569 if (td->td_flags & TDF_TSLEEPQ) 1570 tsleep_remove(td); 1571 1572 /* 1573 * Set TDF_MIGRATING to prevent a spurious reschedule while we are 1574 * trying to deschedule ourselves and switch away, then deschedule 1575 * ourself, remove us from tdallq, and set td_migrate_gd. Finally, 1576 * call lwkt_switch() to complete the operation. 1577 */ 1578 td->td_flags |= TDF_MIGRATING; 1579 lwkt_deschedule_self(td); 1580 TAILQ_REMOVE(&td->td_gd->gd_tdallq, td, td_allq); 1581 td->td_migrate_gd = rgd; 1582 lwkt_switch(); 1583 1584 /* 1585 * We are now on the target cpu 1586 */ 1587 KKASSERT(rgd == mycpu); 1588 TAILQ_INSERT_TAIL(&rgd->gd_tdallq, td, td_allq); 1589 crit_exit_quick(td); 1590 } 1591 #endif 1592 } 1593 1594 void 1595 lwkt_migratecpu(int cpuid) 1596 { 1597 #ifdef SMP 1598 globaldata_t rgd; 1599 1600 rgd = globaldata_find(cpuid); 1601 lwkt_setcpu_self(rgd); 1602 #endif 1603 } 1604 1605 #ifdef SMP 1606 /* 1607 * Remote IPI for cpu migration (called while in a critical section so we 1608 * do not have to enter another one). 1609 * 1610 * The thread (td) has already been completely descheduled from the 1611 * originating cpu and we can simply assert the case. The thread is 1612 * assigned to the new cpu and enqueued. 1613 * 1614 * The thread will re-add itself to tdallq when it resumes execution. 1615 */ 1616 static void 1617 lwkt_setcpu_remote(void *arg) 1618 { 1619 thread_t td = arg; 1620 globaldata_t gd = mycpu; 1621 1622 KKASSERT((td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK)) == 0); 1623 td->td_gd = gd; 1624 cpu_mfence(); 1625 td->td_flags &= ~TDF_MIGRATING; 1626 KKASSERT(td->td_migrate_gd == NULL); 1627 KKASSERT(td->td_lwp == NULL || 1628 (td->td_lwp->lwp_mpflags & LWP_MP_ONRUNQ) == 0); 1629 _lwkt_enqueue(td); 1630 } 1631 #endif 1632 1633 struct lwp * 1634 lwkt_preempted_proc(void) 1635 { 1636 thread_t td = curthread; 1637 while (td->td_preempted) 1638 td = td->td_preempted; 1639 return(td->td_lwp); 1640 } 1641 1642 /* 1643 * Create a kernel process/thread/whatever. It shares it's address space 1644 * with proc0 - ie: kernel only. 1645 * 1646 * If the cpu is not specified one will be selected. In the future 1647 * specifying a cpu of -1 will enable kernel thread migration between 1648 * cpus. 1649 */ 1650 int 1651 lwkt_create(void (*func)(void *), void *arg, struct thread **tdp, 1652 thread_t template, int tdflags, int cpu, const char *fmt, ...) 1653 { 1654 thread_t td; 1655 __va_list ap; 1656 1657 td = lwkt_alloc_thread(template, LWKT_THREAD_STACK, cpu, 1658 tdflags); 1659 if (tdp) 1660 *tdp = td; 1661 cpu_set_thread_handler(td, lwkt_exit, func, arg); 1662 1663 /* 1664 * Set up arg0 for 'ps' etc 1665 */ 1666 __va_start(ap, fmt); 1667 kvsnprintf(td->td_comm, sizeof(td->td_comm), fmt, ap); 1668 __va_end(ap); 1669 1670 /* 1671 * Schedule the thread to run 1672 */ 1673 if (td->td_flags & TDF_NOSTART) 1674 td->td_flags &= ~TDF_NOSTART; 1675 else 1676 lwkt_schedule(td); 1677 return 0; 1678 } 1679 1680 /* 1681 * Destroy an LWKT thread. Warning! This function is not called when 1682 * a process exits, cpu_proc_exit() directly calls cpu_thread_exit() and 1683 * uses a different reaping mechanism. 1684 */ 1685 void 1686 lwkt_exit(void) 1687 { 1688 thread_t td = curthread; 1689 thread_t std; 1690 globaldata_t gd; 1691 1692 /* 1693 * Do any cleanup that might block here 1694 */ 1695 if (td->td_flags & TDF_VERBOSE) 1696 kprintf("kthread %p %s has exited\n", td, td->td_comm); 1697 caps_exit(td); 1698 biosched_done(td); 1699 dsched_exit_thread(td); 1700 1701 /* 1702 * Get us into a critical section to interlock gd_freetd and loop 1703 * until we can get it freed. 1704 * 1705 * We have to cache the current td in gd_freetd because objcache_put()ing 1706 * it would rip it out from under us while our thread is still active. 1707 * 1708 * We are the current thread so of course our own TDF_RUNNING bit will 1709 * be set, so unlike the lwp reap code we don't wait for it to clear. 1710 */ 1711 gd = mycpu; 1712 crit_enter_quick(td); 1713 for (;;) { 1714 if (td->td_refs) { 1715 tsleep(td, 0, "tdreap", 1); 1716 continue; 1717 } 1718 if ((std = gd->gd_freetd) != NULL) { 1719 KKASSERT((std->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK)) == 0); 1720 gd->gd_freetd = NULL; 1721 objcache_put(thread_cache, std); 1722 continue; 1723 } 1724 break; 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 * None of this may block, the critical section is the only thing 1733 * protecting tdallq and the only thing preventing new lwkt_hold() 1734 * thread refs now. 1735 */ 1736 if (td->td_flags & TDF_TSLEEPQ) 1737 tsleep_remove(td); 1738 lwkt_deschedule_self(td); 1739 lwkt_remove_tdallq(td); 1740 KKASSERT(td->td_refs == 0); 1741 1742 /* 1743 * Final cleanup 1744 */ 1745 KKASSERT(gd->gd_freetd == NULL); 1746 if (td->td_flags & TDF_ALLOCATED_THREAD) 1747 gd->gd_freetd = td; 1748 cpu_thread_exit(); 1749 } 1750 1751 void 1752 lwkt_remove_tdallq(thread_t td) 1753 { 1754 KKASSERT(td->td_gd == mycpu); 1755 TAILQ_REMOVE(&td->td_gd->gd_tdallq, td, td_allq); 1756 } 1757 1758 /* 1759 * Code reduction and branch prediction improvements. Call/return 1760 * overhead on modern cpus often degenerates into 0 cycles due to 1761 * the cpu's branch prediction hardware and return pc cache. We 1762 * can take advantage of this by not inlining medium-complexity 1763 * functions and we can also reduce the branch prediction impact 1764 * by collapsing perfectly predictable branches into a single 1765 * procedure instead of duplicating it. 1766 * 1767 * Is any of this noticeable? Probably not, so I'll take the 1768 * smaller code size. 1769 */ 1770 void 1771 crit_exit_wrapper(__DEBUG_CRIT_ARG__) 1772 { 1773 _crit_exit(mycpu __DEBUG_CRIT_PASS_ARG__); 1774 } 1775 1776 void 1777 crit_panic(void) 1778 { 1779 thread_t td = curthread; 1780 int lcrit = td->td_critcount; 1781 1782 td->td_critcount = 0; 1783 panic("td_critcount is/would-go negative! %p %d", td, lcrit); 1784 /* NOT REACHED */ 1785 } 1786 1787 #ifdef SMP 1788 1789 /* 1790 * Called from debugger/panic on cpus which have been stopped. We must still 1791 * process the IPIQ while stopped, even if we were stopped while in a critical 1792 * section (XXX). 1793 * 1794 * If we are dumping also try to process any pending interrupts. This may 1795 * or may not work depending on the state of the cpu at the point it was 1796 * stopped. 1797 */ 1798 void 1799 lwkt_smp_stopped(void) 1800 { 1801 globaldata_t gd = mycpu; 1802 1803 crit_enter_gd(gd); 1804 if (dumping) { 1805 lwkt_process_ipiq(); 1806 splz(); 1807 } else { 1808 lwkt_process_ipiq(); 1809 } 1810 crit_exit_gd(gd); 1811 } 1812 1813 #endif 1814