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