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/spinlock.h> 54 #include <sys/ktr.h> 55 56 #include <sys/thread2.h> 57 #include <sys/spinlock2.h> 58 #include <sys/mplock2.h> 59 60 #include <sys/dsched.h> 61 62 #include <vm/vm.h> 63 #include <vm/vm_param.h> 64 #include <vm/vm_kern.h> 65 #include <vm/vm_object.h> 66 #include <vm/vm_page.h> 67 #include <vm/vm_map.h> 68 #include <vm/vm_pager.h> 69 #include <vm/vm_extern.h> 70 71 #include <machine/stdarg.h> 72 #include <machine/smp.h> 73 74 #ifdef _KERNEL_VIRTUAL 75 #include <pthread.h> 76 #endif 77 78 #if !defined(KTR_CTXSW) 79 #define KTR_CTXSW KTR_ALL 80 #endif 81 KTR_INFO_MASTER(ctxsw); 82 KTR_INFO(KTR_CTXSW, ctxsw, sw, 0, "#cpu[%d].td = %p", int cpu, struct thread *td); 83 KTR_INFO(KTR_CTXSW, ctxsw, pre, 1, "#cpu[%d].td = %p", int cpu, struct thread *td); 84 KTR_INFO(KTR_CTXSW, ctxsw, newtd, 2, "#threads[%p].name = %s", struct thread *td, char *comm); 85 KTR_INFO(KTR_CTXSW, ctxsw, deadtd, 3, "#threads[%p].name = <dead>", struct thread *td); 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 int lwkt_use_spin_port; 97 static struct objcache *thread_cache; 98 int cpu_mwait_spin = 0; 99 100 static void lwkt_schedule_remote(void *arg, int arg2, struct intrframe *frame); 101 static void lwkt_setcpu_remote(void *arg); 102 103 extern void cpu_heavy_restore(void); 104 extern void cpu_lwkt_restore(void); 105 extern void cpu_kthread_restore(void); 106 extern void cpu_idle_restore(void); 107 108 /* 109 * We can make all thread ports use the spin backend instead of the thread 110 * backend. This should only be set to debug the spin backend. 111 */ 112 TUNABLE_INT("lwkt.use_spin_port", &lwkt_use_spin_port); 113 114 #ifdef INVARIANTS 115 SYSCTL_INT(_lwkt, OID_AUTO, panic_on_cscount, CTLFLAG_RW, &panic_on_cscount, 0, 116 "Panic if attempting to switch lwkt's while mastering cpusync"); 117 #endif 118 SYSCTL_INT(_hw, OID_AUTO, cpu_mwait_spin, CTLFLAG_RW, &cpu_mwait_spin, 0, 119 "monitor/mwait target state"); 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 static int fairq_enable = 0; 129 SYSCTL_INT(_lwkt, OID_AUTO, fairq_enable, CTLFLAG_RW, 130 &fairq_enable, 0, "Turn on fairq priority accumulators"); 131 static int fairq_bypass = -1; 132 SYSCTL_INT(_lwkt, OID_AUTO, fairq_bypass, CTLFLAG_RW, 133 &fairq_bypass, 0, "Allow fairq to bypass td on token failure"); 134 extern int lwkt_sched_debug; 135 int lwkt_sched_debug = 0; 136 SYSCTL_INT(_lwkt, OID_AUTO, sched_debug, CTLFLAG_RW, 137 &lwkt_sched_debug, 0, "Scheduler debug"); 138 static int lwkt_spin_loops = 10; 139 SYSCTL_INT(_lwkt, OID_AUTO, spin_loops, CTLFLAG_RW, 140 &lwkt_spin_loops, 0, "Scheduler spin loops until sorted decon"); 141 static int lwkt_spin_reseq = 0; 142 SYSCTL_INT(_lwkt, OID_AUTO, spin_reseq, CTLFLAG_RW, 143 &lwkt_spin_reseq, 0, "Scheduler resequencer enable"); 144 static int lwkt_spin_monitor = 0; 145 SYSCTL_INT(_lwkt, OID_AUTO, spin_monitor, CTLFLAG_RW, 146 &lwkt_spin_monitor, 0, "Scheduler uses monitor/mwait"); 147 static int lwkt_spin_fatal = 0; /* disabled */ 148 SYSCTL_INT(_lwkt, OID_AUTO, spin_fatal, CTLFLAG_RW, 149 &lwkt_spin_fatal, 0, "LWKT scheduler spin loops till fatal panic"); 150 static int preempt_enable = 1; 151 SYSCTL_INT(_lwkt, OID_AUTO, preempt_enable, CTLFLAG_RW, 152 &preempt_enable, 0, "Enable preemption"); 153 static int lwkt_cache_threads = 0; 154 SYSCTL_INT(_lwkt, OID_AUTO, cache_threads, CTLFLAG_RD, 155 &lwkt_cache_threads, 0, "thread+kstack cache"); 156 157 #ifndef _KERNEL_VIRTUAL 158 static __cachealign int lwkt_cseq_rindex; 159 static __cachealign int lwkt_cseq_windex; 160 #endif 161 162 /* 163 * These helper procedures handle the runq, they can only be called from 164 * within a critical section. 165 * 166 * WARNING! Prior to SMP being brought up it is possible to enqueue and 167 * dequeue threads belonging to other cpus, so be sure to use td->td_gd 168 * instead of 'mycpu' when referencing the globaldata structure. Once 169 * SMP live enqueuing and dequeueing only occurs on the current cpu. 170 */ 171 static __inline 172 void 173 _lwkt_dequeue(thread_t td) 174 { 175 if (td->td_flags & TDF_RUNQ) { 176 struct globaldata *gd = td->td_gd; 177 178 td->td_flags &= ~TDF_RUNQ; 179 TAILQ_REMOVE(&gd->gd_tdrunq, td, td_threadq); 180 --gd->gd_tdrunqcount; 181 if (TAILQ_FIRST(&gd->gd_tdrunq) == NULL) 182 atomic_clear_int(&gd->gd_reqflags, RQF_RUNNING); 183 } 184 } 185 186 /* 187 * Priority enqueue. 188 * 189 * There are a limited number of lwkt threads runnable since user 190 * processes only schedule one at a time per cpu. However, there can 191 * be many user processes in kernel mode exiting from a tsleep() which 192 * become runnable. 193 * 194 * NOTE: lwkt_schedulerclock() will force a round-robin based on td_pri and 195 * will ignore user priority. This is to ensure that user threads in 196 * kernel mode get cpu at some point regardless of what the user 197 * scheduler thinks. 198 */ 199 static __inline 200 void 201 _lwkt_enqueue(thread_t td) 202 { 203 thread_t xtd; 204 205 if ((td->td_flags & (TDF_RUNQ|TDF_MIGRATING|TDF_BLOCKQ)) == 0) { 206 struct globaldata *gd = td->td_gd; 207 208 td->td_flags |= TDF_RUNQ; 209 xtd = TAILQ_FIRST(&gd->gd_tdrunq); 210 if (xtd == NULL) { 211 TAILQ_INSERT_TAIL(&gd->gd_tdrunq, td, td_threadq); 212 atomic_set_int(&gd->gd_reqflags, RQF_RUNNING); 213 } else { 214 /* 215 * NOTE: td_upri - higher numbers more desireable, same sense 216 * as td_pri (typically reversed from lwp_upri). 217 * 218 * In the equal priority case we want the best selection 219 * at the beginning so the less desireable selections know 220 * that they have to setrunqueue/go-to-another-cpu, even 221 * though it means switching back to the 'best' selection. 222 * This also avoids degenerate situations when many threads 223 * are runnable or waking up at the same time. 224 * 225 * If upri matches exactly place at end/round-robin. 226 */ 227 while (xtd && 228 (xtd->td_pri >= td->td_pri || 229 (xtd->td_pri == td->td_pri && 230 xtd->td_upri >= td->td_upri))) { 231 xtd = TAILQ_NEXT(xtd, td_threadq); 232 } 233 if (xtd) 234 TAILQ_INSERT_BEFORE(xtd, td, td_threadq); 235 else 236 TAILQ_INSERT_TAIL(&gd->gd_tdrunq, td, td_threadq); 237 } 238 ++gd->gd_tdrunqcount; 239 240 /* 241 * Request a LWKT reschedule if we are now at the head of the queue. 242 */ 243 if (TAILQ_FIRST(&gd->gd_tdrunq) == td) 244 need_lwkt_resched(); 245 } 246 } 247 248 static __boolean_t 249 _lwkt_thread_ctor(void *obj, void *privdata, int ocflags) 250 { 251 struct thread *td = (struct thread *)obj; 252 253 td->td_kstack = NULL; 254 td->td_kstack_size = 0; 255 td->td_flags = TDF_ALLOCATED_THREAD; 256 td->td_mpflags = 0; 257 return (1); 258 } 259 260 static void 261 _lwkt_thread_dtor(void *obj, void *privdata) 262 { 263 struct thread *td = (struct thread *)obj; 264 265 KASSERT(td->td_flags & TDF_ALLOCATED_THREAD, 266 ("_lwkt_thread_dtor: not allocated from objcache")); 267 KASSERT((td->td_flags & TDF_ALLOCATED_STACK) && td->td_kstack && 268 td->td_kstack_size > 0, 269 ("_lwkt_thread_dtor: corrupted stack")); 270 kmem_free(&kernel_map, (vm_offset_t)td->td_kstack, td->td_kstack_size); 271 td->td_kstack = NULL; 272 td->td_flags = 0; 273 } 274 275 /* 276 * Initialize the lwkt s/system. 277 * 278 * Nominally cache up to 32 thread + kstack structures. Cache more on 279 * systems with a lot of cpu cores. 280 */ 281 void 282 lwkt_init(void) 283 { 284 TUNABLE_INT("lwkt.cache_threads", &lwkt_cache_threads); 285 if (lwkt_cache_threads == 0) { 286 lwkt_cache_threads = ncpus * 4; 287 if (lwkt_cache_threads < 32) 288 lwkt_cache_threads = 32; 289 } 290 thread_cache = objcache_create_mbacked( 291 M_THREAD, sizeof(struct thread), 292 0, lwkt_cache_threads, 293 _lwkt_thread_ctor, _lwkt_thread_dtor, NULL); 294 } 295 296 /* 297 * Schedule a thread to run. As the current thread we can always safely 298 * schedule ourselves, and a shortcut procedure is provided for that 299 * function. 300 * 301 * (non-blocking, self contained on a per cpu basis) 302 */ 303 void 304 lwkt_schedule_self(thread_t td) 305 { 306 KKASSERT((td->td_flags & TDF_MIGRATING) == 0); 307 crit_enter_quick(td); 308 KASSERT(td != &td->td_gd->gd_idlethread, 309 ("lwkt_schedule_self(): scheduling gd_idlethread is illegal!")); 310 KKASSERT(td->td_lwp == NULL || 311 (td->td_lwp->lwp_mpflags & LWP_MP_ONRUNQ) == 0); 312 _lwkt_enqueue(td); 313 crit_exit_quick(td); 314 } 315 316 /* 317 * Deschedule a thread. 318 * 319 * (non-blocking, self contained on a per cpu basis) 320 */ 321 void 322 lwkt_deschedule_self(thread_t td) 323 { 324 crit_enter_quick(td); 325 _lwkt_dequeue(td); 326 crit_exit_quick(td); 327 } 328 329 /* 330 * LWKTs operate on a per-cpu basis 331 * 332 * WARNING! Called from early boot, 'mycpu' may not work yet. 333 */ 334 void 335 lwkt_gdinit(struct globaldata *gd) 336 { 337 TAILQ_INIT(&gd->gd_tdrunq); 338 TAILQ_INIT(&gd->gd_tdallq); 339 } 340 341 /* 342 * Create a new thread. The thread must be associated with a process context 343 * or LWKT start address before it can be scheduled. If the target cpu is 344 * -1 the thread will be created on the current cpu. 345 * 346 * If you intend to create a thread without a process context this function 347 * does everything except load the startup and switcher function. 348 */ 349 thread_t 350 lwkt_alloc_thread(struct thread *td, int stksize, int cpu, int flags) 351 { 352 static int cpu_rotator; 353 globaldata_t gd = mycpu; 354 void *stack; 355 356 /* 357 * If static thread storage is not supplied allocate a thread. Reuse 358 * a cached free thread if possible. gd_freetd is used to keep an exiting 359 * thread intact through the exit. 360 */ 361 if (td == NULL) { 362 crit_enter_gd(gd); 363 if ((td = gd->gd_freetd) != NULL) { 364 KKASSERT((td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK| 365 TDF_RUNQ)) == 0); 366 gd->gd_freetd = NULL; 367 } else { 368 td = objcache_get(thread_cache, M_WAITOK); 369 KKASSERT((td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK| 370 TDF_RUNQ)) == 0); 371 } 372 crit_exit_gd(gd); 373 KASSERT((td->td_flags & 374 (TDF_ALLOCATED_THREAD|TDF_RUNNING|TDF_PREEMPT_LOCK)) == 375 TDF_ALLOCATED_THREAD, 376 ("lwkt_alloc_thread: corrupted td flags 0x%X", td->td_flags)); 377 flags |= td->td_flags & (TDF_ALLOCATED_THREAD|TDF_ALLOCATED_STACK); 378 } 379 380 /* 381 * Try to reuse cached stack. 382 */ 383 if ((stack = td->td_kstack) != NULL && td->td_kstack_size != stksize) { 384 if (flags & TDF_ALLOCATED_STACK) { 385 kmem_free(&kernel_map, (vm_offset_t)stack, td->td_kstack_size); 386 stack = NULL; 387 } 388 } 389 if (stack == NULL) { 390 stack = (void *)kmem_alloc_stack(&kernel_map, stksize); 391 flags |= TDF_ALLOCATED_STACK; 392 } 393 if (cpu < 0) { 394 cpu = ++cpu_rotator; 395 cpu_ccfence(); 396 cpu %= ncpus; 397 } 398 lwkt_init_thread(td, stack, stksize, flags, globaldata_find(cpu)); 399 return(td); 400 } 401 402 /* 403 * Initialize a preexisting thread structure. This function is used by 404 * lwkt_alloc_thread() and also used to initialize the per-cpu idlethread. 405 * 406 * All threads start out in a critical section at a priority of 407 * TDPRI_KERN_DAEMON. Higher level code will modify the priority as 408 * appropriate. This function may send an IPI message when the 409 * requested cpu is not the current cpu and consequently gd_tdallq may 410 * not be initialized synchronously from the point of view of the originating 411 * cpu. 412 * 413 * NOTE! we have to be careful in regards to creating threads for other cpus 414 * if SMP has not yet been activated. 415 */ 416 static void 417 lwkt_init_thread_remote(void *arg) 418 { 419 thread_t td = arg; 420 421 /* 422 * Protected by critical section held by IPI dispatch 423 */ 424 TAILQ_INSERT_TAIL(&td->td_gd->gd_tdallq, td, td_allq); 425 } 426 427 /* 428 * lwkt core thread structural initialization. 429 * 430 * NOTE: All threads are initialized as mpsafe threads. 431 */ 432 void 433 lwkt_init_thread(thread_t td, void *stack, int stksize, int flags, 434 struct globaldata *gd) 435 { 436 globaldata_t mygd = mycpu; 437 438 bzero(td, sizeof(struct thread)); 439 td->td_kstack = stack; 440 td->td_kstack_size = stksize; 441 td->td_flags = flags; 442 td->td_mpflags = 0; 443 td->td_type = TD_TYPE_GENERIC; 444 td->td_gd = gd; 445 td->td_pri = TDPRI_KERN_DAEMON; 446 td->td_critcount = 1; 447 td->td_toks_have = NULL; 448 td->td_toks_stop = &td->td_toks_base; 449 if (lwkt_use_spin_port || (flags & TDF_FORCE_SPINPORT)) { 450 lwkt_initport_spin(&td->td_msgport, td, 451 (flags & TDF_FIXEDCPU) ? TRUE : FALSE); 452 } else { 453 lwkt_initport_thread(&td->td_msgport, td); 454 } 455 pmap_init_thread(td); 456 /* 457 * Normally initializing a thread for a remote cpu requires sending an 458 * IPI. However, the idlethread is setup before the other cpus are 459 * activated so we have to treat it as a special case. XXX manipulation 460 * of gd_tdallq requires the BGL. 461 */ 462 if (gd == mygd || td == &gd->gd_idlethread) { 463 crit_enter_gd(mygd); 464 TAILQ_INSERT_TAIL(&gd->gd_tdallq, td, td_allq); 465 crit_exit_gd(mygd); 466 } else { 467 lwkt_send_ipiq(gd, lwkt_init_thread_remote, td); 468 } 469 dsched_new_thread(td); 470 } 471 472 void 473 lwkt_set_comm(thread_t td, const char *ctl, ...) 474 { 475 __va_list va; 476 477 __va_start(va, ctl); 478 kvsnprintf(td->td_comm, sizeof(td->td_comm), ctl, va); 479 __va_end(va); 480 KTR_LOG(ctxsw_newtd, td, td->td_comm); 481 } 482 483 /* 484 * Prevent the thread from getting destroyed. Note that unlike PHOLD/PRELE 485 * this does not prevent the thread from migrating to another cpu so the 486 * gd_tdallq state is not protected by this. 487 */ 488 void 489 lwkt_hold(thread_t td) 490 { 491 atomic_add_int(&td->td_refs, 1); 492 } 493 494 void 495 lwkt_rele(thread_t td) 496 { 497 KKASSERT(td->td_refs > 0); 498 atomic_add_int(&td->td_refs, -1); 499 } 500 501 void 502 lwkt_free_thread(thread_t td) 503 { 504 KKASSERT(td->td_refs == 0); 505 KKASSERT((td->td_flags & (TDF_RUNNING | TDF_PREEMPT_LOCK | 506 TDF_RUNQ | TDF_TSLEEPQ)) == 0); 507 if (td->td_flags & TDF_ALLOCATED_THREAD) { 508 objcache_put(thread_cache, td); 509 } else if (td->td_flags & TDF_ALLOCATED_STACK) { 510 /* client-allocated struct with internally allocated stack */ 511 KASSERT(td->td_kstack && td->td_kstack_size > 0, 512 ("lwkt_free_thread: corrupted stack")); 513 kmem_free(&kernel_map, (vm_offset_t)td->td_kstack, td->td_kstack_size); 514 td->td_kstack = NULL; 515 td->td_kstack_size = 0; 516 } 517 518 KTR_LOG(ctxsw_deadtd, td); 519 } 520 521 522 /* 523 * Switch to the next runnable lwkt. If no LWKTs are runnable then 524 * switch to the idlethread. Switching must occur within a critical 525 * section to avoid races with the scheduling queue. 526 * 527 * We always have full control over our cpu's run queue. Other cpus 528 * that wish to manipulate our queue must use the cpu_*msg() calls to 529 * talk to our cpu, so a critical section is all that is needed and 530 * the result is very, very fast thread switching. 531 * 532 * The LWKT scheduler uses a fixed priority model and round-robins at 533 * each priority level. User process scheduling is a totally 534 * different beast and LWKT priorities should not be confused with 535 * user process priorities. 536 * 537 * PREEMPTION NOTE: Preemption occurs via lwkt_preempt(). lwkt_switch() 538 * is not called by the current thread in the preemption case, only when 539 * the preempting thread blocks (in order to return to the original thread). 540 * 541 * SPECIAL NOTE ON SWITCH ATOMICY: Certain operations such as thread 542 * migration and tsleep deschedule the current lwkt thread and call 543 * lwkt_switch(). In particular, the target cpu of the migration fully 544 * expects the thread to become non-runnable and can deadlock against 545 * cpusync operations if we run any IPIs prior to switching the thread out. 546 * 547 * WE MUST BE VERY CAREFUL NOT TO RUN SPLZ DIRECTLY OR INDIRECTLY IF 548 * THE CURRENT THREAD HAS BEEN DESCHEDULED! 549 */ 550 void 551 lwkt_switch(void) 552 { 553 globaldata_t gd = mycpu; 554 thread_t td = gd->gd_curthread; 555 thread_t ntd; 556 int spinning = 0; 557 558 KKASSERT(gd->gd_processing_ipiq == 0); 559 KKASSERT(td->td_flags & TDF_RUNNING); 560 561 /* 562 * Switching from within a 'fast' (non thread switched) interrupt or IPI 563 * is illegal. However, we may have to do it anyway if we hit a fatal 564 * kernel trap or we have paniced. 565 * 566 * If this case occurs save and restore the interrupt nesting level. 567 */ 568 if (gd->gd_intr_nesting_level) { 569 int savegdnest; 570 int savegdtrap; 571 572 if (gd->gd_trap_nesting_level == 0 && panic_cpu_gd != mycpu) { 573 panic("lwkt_switch: Attempt to switch from a " 574 "fast interrupt, ipi, or hard code section, " 575 "td %p\n", 576 td); 577 } else { 578 savegdnest = gd->gd_intr_nesting_level; 579 savegdtrap = gd->gd_trap_nesting_level; 580 gd->gd_intr_nesting_level = 0; 581 gd->gd_trap_nesting_level = 0; 582 if ((td->td_flags & TDF_PANICWARN) == 0) { 583 td->td_flags |= TDF_PANICWARN; 584 kprintf("Warning: thread switch from interrupt, IPI, " 585 "or hard code section.\n" 586 "thread %p (%s)\n", td, td->td_comm); 587 print_backtrace(-1); 588 } 589 lwkt_switch(); 590 gd->gd_intr_nesting_level = savegdnest; 591 gd->gd_trap_nesting_level = savegdtrap; 592 return; 593 } 594 } 595 596 /* 597 * Release our current user process designation if we are blocking 598 * or if a user reschedule was requested. 599 * 600 * NOTE: This function is NOT called if we are switching into or 601 * returning from a preemption. 602 * 603 * NOTE: Releasing our current user process designation may cause 604 * it to be assigned to another thread, which in turn will 605 * cause us to block in the usched acquire code when we attempt 606 * to return to userland. 607 * 608 * NOTE: On SMP systems this can be very nasty when heavy token 609 * contention is present so we want to be careful not to 610 * release the designation gratuitously. 611 */ 612 if (td->td_release && 613 (user_resched_wanted() || (td->td_flags & TDF_RUNQ) == 0)) { 614 td->td_release(td); 615 } 616 617 /* 618 * Release all tokens 619 */ 620 crit_enter_gd(gd); 621 if (TD_TOKS_HELD(td)) 622 lwkt_relalltokens(td); 623 624 /* 625 * We had better not be holding any spin locks, but don't get into an 626 * endless panic loop. 627 */ 628 KASSERT(gd->gd_spinlocks == 0 || panicstr != NULL, 629 ("lwkt_switch: still holding %d exclusive spinlocks!", 630 gd->gd_spinlocks)); 631 632 633 #ifdef INVARIANTS 634 if (td->td_cscount) { 635 kprintf("Diagnostic: attempt to switch while mastering cpusync: %p\n", 636 td); 637 if (panic_on_cscount) 638 panic("switching while mastering cpusync"); 639 } 640 #endif 641 642 /* 643 * If we had preempted another thread on this cpu, resume the preempted 644 * thread. This occurs transparently, whether the preempted thread 645 * was scheduled or not (it may have been preempted after descheduling 646 * itself). 647 * 648 * We have to setup the MP lock for the original thread after backing 649 * out the adjustment that was made to curthread when the original 650 * was preempted. 651 */ 652 if ((ntd = td->td_preempted) != NULL) { 653 KKASSERT(ntd->td_flags & TDF_PREEMPT_LOCK); 654 ntd->td_flags |= TDF_PREEMPT_DONE; 655 656 /* 657 * The interrupt may have woken a thread up, we need to properly 658 * set the reschedule flag if the originally interrupted thread is 659 * at a lower priority. 660 * 661 * The interrupt may not have descheduled. 662 */ 663 if (TAILQ_FIRST(&gd->gd_tdrunq) != ntd) 664 need_lwkt_resched(); 665 goto havethread_preempted; 666 } 667 668 /* 669 * If we cannot obtain ownership of the tokens we cannot immediately 670 * schedule the target thread. 671 * 672 * Reminder: Again, we cannot afford to run any IPIs in this path if 673 * the current thread has been descheduled. 674 */ 675 for (;;) { 676 clear_lwkt_resched(); 677 678 /* 679 * Hotpath - pull the head of the run queue and attempt to schedule 680 * it. 681 */ 682 ntd = TAILQ_FIRST(&gd->gd_tdrunq); 683 684 if (ntd == NULL) { 685 /* 686 * Runq is empty, switch to idle to allow it to halt. 687 */ 688 ntd = &gd->gd_idlethread; 689 if (gd->gd_trap_nesting_level == 0 && panicstr == NULL) 690 ASSERT_NO_TOKENS_HELD(ntd); 691 cpu_time.cp_msg[0] = 0; 692 cpu_time.cp_stallpc = 0; 693 goto haveidle; 694 } 695 696 /* 697 * Hotpath - schedule ntd. 698 * 699 * NOTE: For UP there is no mplock and lwkt_getalltokens() 700 * always succeeds. 701 */ 702 if (TD_TOKS_NOT_HELD(ntd) || 703 lwkt_getalltokens(ntd, (spinning >= lwkt_spin_loops))) 704 { 705 goto havethread; 706 } 707 708 /* 709 * Coldpath (SMP only since tokens always succeed on UP) 710 * 711 * We had some contention on the thread we wanted to schedule. 712 * What we do now is try to find a thread that we can schedule 713 * in its stead. 714 * 715 * The coldpath scan does NOT rearrange threads in the run list. 716 * The lwkt_schedulerclock() will assert need_lwkt_resched() on 717 * the next tick whenever the current head is not the current thread. 718 */ 719 #ifdef INVARIANTS 720 ++ntd->td_contended; 721 #endif 722 ++gd->gd_cnt.v_lock_colls; 723 724 if (fairq_bypass > 0) 725 goto skip; 726 727 while ((ntd = TAILQ_NEXT(ntd, td_threadq)) != NULL) { 728 #ifndef NO_LWKT_SPLIT_USERPRI 729 /* 730 * Never schedule threads returning to userland or the 731 * user thread scheduler helper thread when higher priority 732 * threads are present. The runq is sorted by priority 733 * so we can give up traversing it when we find the first 734 * low priority thread. 735 */ 736 if (ntd->td_pri < TDPRI_KERN_LPSCHED) { 737 ntd = NULL; 738 break; 739 } 740 #endif 741 742 /* 743 * Try this one. 744 */ 745 if (TD_TOKS_NOT_HELD(ntd) || 746 lwkt_getalltokens(ntd, (spinning >= lwkt_spin_loops))) { 747 goto havethread; 748 } 749 #ifdef INVARIANTS 750 ++ntd->td_contended; 751 #endif 752 ++gd->gd_cnt.v_lock_colls; 753 } 754 755 skip: 756 /* 757 * We exhausted the run list, meaning that all runnable threads 758 * are contested. 759 */ 760 cpu_pause(); 761 #ifdef _KERNEL_VIRTUAL 762 pthread_yield(); 763 #endif 764 ntd = &gd->gd_idlethread; 765 if (gd->gd_trap_nesting_level == 0 && panicstr == NULL) 766 ASSERT_NO_TOKENS_HELD(ntd); 767 /* contention case, do not clear contention mask */ 768 769 /* 770 * We are going to have to retry but if the current thread is not 771 * on the runq we instead switch through the idle thread to get away 772 * from the current thread. We have to flag for lwkt reschedule 773 * to prevent the idle thread from halting. 774 * 775 * NOTE: A non-zero spinning is passed to lwkt_getalltokens() to 776 * instruct it to deal with the potential for deadlocks by 777 * ordering the tokens by address. 778 */ 779 if ((td->td_flags & TDF_RUNQ) == 0) { 780 need_lwkt_resched(); /* prevent hlt */ 781 goto haveidle; 782 } 783 #if defined(INVARIANTS) && defined(__x86_64__) 784 if ((read_rflags() & PSL_I) == 0) { 785 cpu_enable_intr(); 786 panic("lwkt_switch() called with interrupts disabled"); 787 } 788 #endif 789 790 /* 791 * Number iterations so far. After a certain point we switch to 792 * a sorted-address/monitor/mwait version of lwkt_getalltokens() 793 */ 794 if (spinning < 0x7FFFFFFF) 795 ++spinning; 796 797 #ifndef _KERNEL_VIRTUAL 798 /* 799 * lwkt_getalltokens() failed in sorted token mode, we can use 800 * monitor/mwait in this case. 801 */ 802 if (spinning >= lwkt_spin_loops && 803 (cpu_mi_feature & CPU_MI_MONITOR) && 804 lwkt_spin_monitor) 805 { 806 cpu_mmw_pause_int(&gd->gd_reqflags, 807 (gd->gd_reqflags | RQF_SPINNING) & 808 ~RQF_IDLECHECK_WK_MASK, 809 cpu_mwait_spin); 810 } 811 #endif 812 813 /* 814 * We already checked that td is still scheduled so this should be 815 * safe. 816 */ 817 splz_check(); 818 819 #ifndef _KERNEL_VIRTUAL 820 /* 821 * This experimental resequencer is used as a fall-back to reduce 822 * hw cache line contention by placing each core's scheduler into a 823 * time-domain-multplexed slot. 824 * 825 * The resequencer is disabled by default. It's functionality has 826 * largely been superceeded by the token algorithm which limits races 827 * to a subset of cores. 828 * 829 * The resequencer algorithm tends to break down when more than 830 * 20 cores are contending. What appears to happen is that new 831 * tokens can be obtained out of address-sorted order by new cores 832 * while existing cores languish in long delays between retries and 833 * wind up being starved-out of the token acquisition. 834 */ 835 if (lwkt_spin_reseq && spinning >= lwkt_spin_reseq) { 836 int cseq = atomic_fetchadd_int(&lwkt_cseq_windex, 1); 837 int oseq; 838 839 while ((oseq = lwkt_cseq_rindex) != cseq) { 840 cpu_ccfence(); 841 #if 1 842 if (cpu_mi_feature & CPU_MI_MONITOR) { 843 cpu_mmw_pause_int(&lwkt_cseq_rindex, oseq, cpu_mwait_spin); 844 } else { 845 #endif 846 cpu_pause(); 847 cpu_lfence(); 848 #if 1 849 } 850 #endif 851 } 852 DELAY(1); 853 atomic_add_int(&lwkt_cseq_rindex, 1); 854 } 855 #endif 856 /* highest level for(;;) loop */ 857 } 858 859 havethread: 860 /* 861 * Clear gd_idle_repeat when doing a normal switch to a non-idle 862 * thread. 863 */ 864 ntd->td_wmesg = NULL; 865 ++gd->gd_cnt.v_swtch; 866 gd->gd_idle_repeat = 0; 867 868 havethread_preempted: 869 /* 870 * If the new target does not need the MP lock and we are holding it, 871 * release the MP lock. If the new target requires the MP lock we have 872 * already acquired it for the target. 873 */ 874 ; 875 haveidle: 876 KASSERT(ntd->td_critcount, 877 ("priority problem in lwkt_switch %d %d", 878 td->td_critcount, ntd->td_critcount)); 879 880 if (td != ntd) { 881 /* 882 * Execute the actual thread switch operation. This function 883 * returns to the current thread and returns the previous thread 884 * (which may be different from the thread we switched to). 885 * 886 * We are responsible for marking ntd as TDF_RUNNING. 887 */ 888 KKASSERT((ntd->td_flags & TDF_RUNNING) == 0); 889 ++switch_count; 890 KTR_LOG(ctxsw_sw, gd->gd_cpuid, ntd); 891 ntd->td_flags |= TDF_RUNNING; 892 lwkt_switch_return(td->td_switch(ntd)); 893 /* ntd invalid, td_switch() can return a different thread_t */ 894 } 895 896 /* 897 * catch-all. XXX is this strictly needed? 898 */ 899 splz_check(); 900 901 /* NOTE: current cpu may have changed after switch */ 902 crit_exit_quick(td); 903 } 904 905 /* 906 * Called by assembly in the td_switch (thread restore path) for thread 907 * bootstrap cases which do not 'return' to lwkt_switch(). 908 */ 909 void 910 lwkt_switch_return(thread_t otd) 911 { 912 globaldata_t rgd; 913 914 /* 915 * Check if otd was migrating. Now that we are on ntd we can finish 916 * up the migration. This is a bit messy but it is the only place 917 * where td is known to be fully descheduled. 918 * 919 * We can only activate the migration if otd was migrating but not 920 * held on the cpu due to a preemption chain. We still have to 921 * clear TDF_RUNNING on the old thread either way. 922 * 923 * We are responsible for clearing the previously running thread's 924 * TDF_RUNNING. 925 */ 926 if ((rgd = otd->td_migrate_gd) != NULL && 927 (otd->td_flags & TDF_PREEMPT_LOCK) == 0) { 928 KKASSERT((otd->td_flags & (TDF_MIGRATING | TDF_RUNNING)) == 929 (TDF_MIGRATING | TDF_RUNNING)); 930 otd->td_migrate_gd = NULL; 931 otd->td_flags &= ~TDF_RUNNING; 932 lwkt_send_ipiq(rgd, lwkt_setcpu_remote, otd); 933 } else { 934 otd->td_flags &= ~TDF_RUNNING; 935 } 936 937 /* 938 * Final exit validations (see lwp_wait()). Note that otd becomes 939 * invalid the *instant* we set TDF_MP_EXITSIG. 940 */ 941 while (otd->td_flags & TDF_EXITING) { 942 u_int mpflags; 943 944 mpflags = otd->td_mpflags; 945 cpu_ccfence(); 946 947 if (mpflags & TDF_MP_EXITWAIT) { 948 if (atomic_cmpset_int(&otd->td_mpflags, mpflags, 949 mpflags | TDF_MP_EXITSIG)) { 950 wakeup(otd); 951 break; 952 } 953 } else { 954 if (atomic_cmpset_int(&otd->td_mpflags, mpflags, 955 mpflags | TDF_MP_EXITSIG)) { 956 wakeup(otd); 957 break; 958 } 959 } 960 } 961 } 962 963 /* 964 * Request that the target thread preempt the current thread. Preemption 965 * can only occur if our only critical section is the one that we were called 966 * with, the relative priority of the target thread is higher, and the target 967 * thread holds no tokens. This also only works if we are not holding any 968 * spinlocks (obviously). 969 * 970 * THE CALLER OF LWKT_PREEMPT() MUST BE IN A CRITICAL SECTION. Typically 971 * this is called via lwkt_schedule() through the td_preemptable callback. 972 * critcount is the managed critical priority that we should ignore in order 973 * to determine whether preemption is possible (aka usually just the crit 974 * priority of lwkt_schedule() itself). 975 * 976 * Preemption is typically limited to interrupt threads. 977 * 978 * Operation works in a fairly straight-forward manner. The normal 979 * scheduling code is bypassed and we switch directly to the target 980 * thread. When the target thread attempts to block or switch away 981 * code at the base of lwkt_switch() will switch directly back to our 982 * thread. Our thread is able to retain whatever tokens it holds and 983 * if the target needs one of them the target will switch back to us 984 * and reschedule itself normally. 985 */ 986 void 987 lwkt_preempt(thread_t ntd, int critcount) 988 { 989 struct globaldata *gd = mycpu; 990 thread_t xtd; 991 thread_t td; 992 int save_gd_intr_nesting_level; 993 994 /* 995 * The caller has put us in a critical section. We can only preempt 996 * if the caller of the caller was not in a critical section (basically 997 * a local interrupt), as determined by the 'critcount' parameter. We 998 * also can't preempt if the caller is holding any spinlocks (even if 999 * he isn't in a critical section). This also handles the tokens test. 1000 * 1001 * YYY The target thread must be in a critical section (else it must 1002 * inherit our critical section? I dunno yet). 1003 */ 1004 KASSERT(ntd->td_critcount, ("BADCRIT0 %d", ntd->td_pri)); 1005 1006 td = gd->gd_curthread; 1007 if (preempt_enable == 0) { 1008 ++preempt_miss; 1009 return; 1010 } 1011 if (ntd->td_pri <= td->td_pri) { 1012 ++preempt_miss; 1013 return; 1014 } 1015 if (td->td_critcount > critcount) { 1016 ++preempt_miss; 1017 return; 1018 } 1019 if (td->td_cscount) { 1020 ++preempt_miss; 1021 return; 1022 } 1023 if (ntd->td_gd != gd) { 1024 ++preempt_miss; 1025 return; 1026 } 1027 /* 1028 * We don't have to check spinlocks here as they will also bump 1029 * td_critcount. 1030 * 1031 * Do not try to preempt if the target thread is holding any tokens. 1032 * We could try to acquire the tokens but this case is so rare there 1033 * is no need to support it. 1034 */ 1035 KKASSERT(gd->gd_spinlocks == 0); 1036 1037 if (TD_TOKS_HELD(ntd)) { 1038 ++preempt_miss; 1039 return; 1040 } 1041 if (td == ntd || ((td->td_flags | ntd->td_flags) & TDF_PREEMPT_LOCK)) { 1042 ++preempt_weird; 1043 return; 1044 } 1045 if (ntd->td_preempted) { 1046 ++preempt_hit; 1047 return; 1048 } 1049 KKASSERT(gd->gd_processing_ipiq == 0); 1050 1051 /* 1052 * Since we are able to preempt the current thread, there is no need to 1053 * call need_lwkt_resched(). 1054 * 1055 * We must temporarily clear gd_intr_nesting_level around the switch 1056 * since switchouts from the target thread are allowed (they will just 1057 * return to our thread), and since the target thread has its own stack. 1058 * 1059 * A preemption must switch back to the original thread, assert the 1060 * case. 1061 */ 1062 ++preempt_hit; 1063 ntd->td_preempted = td; 1064 td->td_flags |= TDF_PREEMPT_LOCK; 1065 KTR_LOG(ctxsw_pre, gd->gd_cpuid, ntd); 1066 save_gd_intr_nesting_level = gd->gd_intr_nesting_level; 1067 gd->gd_intr_nesting_level = 0; 1068 1069 KKASSERT((ntd->td_flags & TDF_RUNNING) == 0); 1070 ntd->td_flags |= TDF_RUNNING; 1071 xtd = td->td_switch(ntd); 1072 KKASSERT(xtd == ntd); 1073 lwkt_switch_return(xtd); 1074 gd->gd_intr_nesting_level = save_gd_intr_nesting_level; 1075 1076 KKASSERT(ntd->td_preempted && (td->td_flags & TDF_PREEMPT_DONE)); 1077 ntd->td_preempted = NULL; 1078 td->td_flags &= ~(TDF_PREEMPT_LOCK|TDF_PREEMPT_DONE); 1079 } 1080 1081 /* 1082 * Conditionally call splz() if gd_reqflags indicates work is pending. 1083 * This will work inside a critical section but not inside a hard code 1084 * section. 1085 * 1086 * (self contained on a per cpu basis) 1087 */ 1088 void 1089 splz_check(void) 1090 { 1091 globaldata_t gd = mycpu; 1092 thread_t td = gd->gd_curthread; 1093 1094 if ((gd->gd_reqflags & RQF_IDLECHECK_MASK) && 1095 gd->gd_intr_nesting_level == 0 && 1096 td->td_nest_count < 2) 1097 { 1098 splz(); 1099 } 1100 } 1101 1102 /* 1103 * This version is integrated into crit_exit, reqflags has already 1104 * been tested but td_critcount has not. 1105 * 1106 * We only want to execute the splz() on the 1->0 transition of 1107 * critcount and not in a hard code section or if too deeply nested. 1108 * 1109 * NOTE: gd->gd_spinlocks is implied to be 0 when td_critcount is 0. 1110 */ 1111 void 1112 lwkt_maybe_splz(thread_t td) 1113 { 1114 globaldata_t gd = td->td_gd; 1115 1116 if (td->td_critcount == 0 && 1117 gd->gd_intr_nesting_level == 0 && 1118 td->td_nest_count < 2) 1119 { 1120 splz(); 1121 } 1122 } 1123 1124 /* 1125 * Drivers which set up processing co-threads can call this function to 1126 * run the co-thread at a higher priority and to allow it to preempt 1127 * normal threads. 1128 */ 1129 void 1130 lwkt_set_interrupt_support_thread(void) 1131 { 1132 thread_t td = curthread; 1133 1134 lwkt_setpri_self(TDPRI_INT_SUPPORT); 1135 td->td_flags |= TDF_INTTHREAD; 1136 td->td_preemptable = lwkt_preempt; 1137 } 1138 1139 1140 /* 1141 * This function is used to negotiate a passive release of the current 1142 * process/lwp designation with the user scheduler, allowing the user 1143 * scheduler to schedule another user thread. The related kernel thread 1144 * (curthread) continues running in the released state. 1145 */ 1146 void 1147 lwkt_passive_release(struct thread *td) 1148 { 1149 struct lwp *lp = td->td_lwp; 1150 1151 #ifndef NO_LWKT_SPLIT_USERPRI 1152 td->td_release = NULL; 1153 lwkt_setpri_self(TDPRI_KERN_USER); 1154 #endif 1155 1156 lp->lwp_proc->p_usched->release_curproc(lp); 1157 } 1158 1159 1160 /* 1161 * This implements a LWKT yield, allowing a kernel thread to yield to other 1162 * kernel threads at the same or higher priority. This function can be 1163 * called in a tight loop and will typically only yield once per tick. 1164 * 1165 * Most kernel threads run at the same priority in order to allow equal 1166 * sharing. 1167 * 1168 * (self contained on a per cpu basis) 1169 */ 1170 void 1171 lwkt_yield(void) 1172 { 1173 globaldata_t gd = mycpu; 1174 thread_t td = gd->gd_curthread; 1175 1176 if ((gd->gd_reqflags & RQF_IDLECHECK_MASK) && td->td_nest_count < 2) 1177 splz(); 1178 if (lwkt_resched_wanted()) { 1179 lwkt_schedule_self(curthread); 1180 lwkt_switch(); 1181 } 1182 } 1183 1184 /* 1185 * The quick version processes pending interrupts and higher-priority 1186 * LWKT threads but will not round-robin same-priority LWKT threads. 1187 * 1188 * When called while attempting to return to userland the only same-pri 1189 * threads are the ones which have already tried to become the current 1190 * user process. 1191 */ 1192 void 1193 lwkt_yield_quick(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 crit_enter(); 1202 if (TAILQ_FIRST(&gd->gd_tdrunq) == td) { 1203 clear_lwkt_resched(); 1204 } else { 1205 lwkt_schedule_self(curthread); 1206 lwkt_switch(); 1207 } 1208 crit_exit(); 1209 } 1210 } 1211 1212 /* 1213 * This yield is designed for kernel threads with a user context. 1214 * 1215 * The kernel acting on behalf of the user is potentially cpu-bound, 1216 * this function will efficiently allow other threads to run and also 1217 * switch to other processes by releasing. 1218 * 1219 * The lwkt_user_yield() function is designed to have very low overhead 1220 * if no yield is determined to be needed. 1221 */ 1222 void 1223 lwkt_user_yield(void) 1224 { 1225 globaldata_t gd = mycpu; 1226 thread_t td = gd->gd_curthread; 1227 1228 /* 1229 * Always run any pending interrupts in case we are in a critical 1230 * section. 1231 */ 1232 if ((gd->gd_reqflags & RQF_IDLECHECK_MASK) && td->td_nest_count < 2) 1233 splz(); 1234 1235 /* 1236 * Switch (which forces a release) if another kernel thread needs 1237 * the cpu, if userland wants us to resched, or if our kernel 1238 * quantum has run out. 1239 */ 1240 if (lwkt_resched_wanted() || 1241 user_resched_wanted()) 1242 { 1243 lwkt_switch(); 1244 } 1245 1246 #if 0 1247 /* 1248 * Reacquire the current process if we are released. 1249 * 1250 * XXX not implemented atm. The kernel may be holding locks and such, 1251 * so we want the thread to continue to receive cpu. 1252 */ 1253 if (td->td_release == NULL && lp) { 1254 lp->lwp_proc->p_usched->acquire_curproc(lp); 1255 td->td_release = lwkt_passive_release; 1256 lwkt_setpri_self(TDPRI_USER_NORM); 1257 } 1258 #endif 1259 } 1260 1261 /* 1262 * Generic schedule. Possibly schedule threads belonging to other cpus and 1263 * deal with threads that might be blocked on a wait queue. 1264 * 1265 * We have a little helper inline function which does additional work after 1266 * the thread has been enqueued, including dealing with preemption and 1267 * setting need_lwkt_resched() (which prevents the kernel from returning 1268 * to userland until it has processed higher priority threads). 1269 * 1270 * It is possible for this routine to be called after a failed _enqueue 1271 * (due to the target thread migrating, sleeping, or otherwise blocked). 1272 * We have to check that the thread is actually on the run queue! 1273 */ 1274 static __inline 1275 void 1276 _lwkt_schedule_post(globaldata_t gd, thread_t ntd, int ccount) 1277 { 1278 if (ntd->td_flags & TDF_RUNQ) { 1279 if (ntd->td_preemptable) { 1280 ntd->td_preemptable(ntd, ccount); /* YYY +token */ 1281 } 1282 } 1283 } 1284 1285 static __inline 1286 void 1287 _lwkt_schedule(thread_t td) 1288 { 1289 globaldata_t mygd = mycpu; 1290 1291 KASSERT(td != &td->td_gd->gd_idlethread, 1292 ("lwkt_schedule(): scheduling gd_idlethread is illegal!")); 1293 KKASSERT((td->td_flags & TDF_MIGRATING) == 0); 1294 crit_enter_gd(mygd); 1295 KKASSERT(td->td_lwp == NULL || 1296 (td->td_lwp->lwp_mpflags & LWP_MP_ONRUNQ) == 0); 1297 1298 if (td == mygd->gd_curthread) { 1299 _lwkt_enqueue(td); 1300 } else { 1301 /* 1302 * If we own the thread, there is no race (since we are in a 1303 * critical section). If we do not own the thread there might 1304 * be a race but the target cpu will deal with it. 1305 */ 1306 if (td->td_gd == mygd) { 1307 _lwkt_enqueue(td); 1308 _lwkt_schedule_post(mygd, td, 1); 1309 } else { 1310 lwkt_send_ipiq3(td->td_gd, lwkt_schedule_remote, td, 0); 1311 } 1312 } 1313 crit_exit_gd(mygd); 1314 } 1315 1316 void 1317 lwkt_schedule(thread_t td) 1318 { 1319 _lwkt_schedule(td); 1320 } 1321 1322 void 1323 lwkt_schedule_noresched(thread_t td) /* XXX not impl */ 1324 { 1325 _lwkt_schedule(td); 1326 } 1327 1328 /* 1329 * When scheduled remotely if frame != NULL the IPIQ is being 1330 * run via doreti or an interrupt then preemption can be allowed. 1331 * 1332 * To allow preemption we have to drop the critical section so only 1333 * one is present in _lwkt_schedule_post. 1334 */ 1335 static void 1336 lwkt_schedule_remote(void *arg, int arg2, struct intrframe *frame) 1337 { 1338 thread_t td = curthread; 1339 thread_t ntd = arg; 1340 1341 if (frame && ntd->td_preemptable) { 1342 crit_exit_noyield(td); 1343 _lwkt_schedule(ntd); 1344 crit_enter_quick(td); 1345 } else { 1346 _lwkt_schedule(ntd); 1347 } 1348 } 1349 1350 /* 1351 * Thread migration using a 'Pull' method. The thread may or may not be 1352 * the current thread. It MUST be descheduled and in a stable state. 1353 * lwkt_giveaway() must be called on the cpu owning the thread. 1354 * 1355 * At any point after lwkt_giveaway() is called, the target cpu may 1356 * 'pull' the thread by calling lwkt_acquire(). 1357 * 1358 * We have to make sure the thread is not sitting on a per-cpu tsleep 1359 * queue or it will blow up when it moves to another cpu. 1360 * 1361 * MPSAFE - must be called under very specific conditions. 1362 */ 1363 void 1364 lwkt_giveaway(thread_t td) 1365 { 1366 globaldata_t gd = mycpu; 1367 1368 crit_enter_gd(gd); 1369 if (td->td_flags & TDF_TSLEEPQ) 1370 tsleep_remove(td); 1371 KKASSERT(td->td_gd == gd); 1372 TAILQ_REMOVE(&gd->gd_tdallq, td, td_allq); 1373 td->td_flags |= TDF_MIGRATING; 1374 crit_exit_gd(gd); 1375 } 1376 1377 void 1378 lwkt_acquire(thread_t td) 1379 { 1380 globaldata_t gd; 1381 globaldata_t mygd; 1382 int retry = 10000000; 1383 1384 KKASSERT(td->td_flags & TDF_MIGRATING); 1385 gd = td->td_gd; 1386 mygd = mycpu; 1387 if (gd != mycpu) { 1388 cpu_lfence(); 1389 KKASSERT((td->td_flags & TDF_RUNQ) == 0); 1390 crit_enter_gd(mygd); 1391 DEBUG_PUSH_INFO("lwkt_acquire"); 1392 while (td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK)) { 1393 lwkt_process_ipiq(); 1394 cpu_lfence(); 1395 if (--retry == 0) { 1396 kprintf("lwkt_acquire: stuck: td %p td->td_flags %08x\n", 1397 td, td->td_flags); 1398 retry = 10000000; 1399 } 1400 #ifdef _KERNEL_VIRTUAL 1401 pthread_yield(); 1402 #endif 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 /* 1419 * Generic deschedule. Descheduling threads other then your own should be 1420 * done only in carefully controlled circumstances. Descheduling is 1421 * asynchronous. 1422 * 1423 * This function may block if the cpu has run out of messages. 1424 */ 1425 void 1426 lwkt_deschedule(thread_t td) 1427 { 1428 crit_enter(); 1429 if (td == curthread) { 1430 _lwkt_dequeue(td); 1431 } else { 1432 if (td->td_gd == mycpu) { 1433 _lwkt_dequeue(td); 1434 } else { 1435 lwkt_send_ipiq(td->td_gd, (ipifunc1_t)lwkt_deschedule, td); 1436 } 1437 } 1438 crit_exit(); 1439 } 1440 1441 /* 1442 * Set the target thread's priority. This routine does not automatically 1443 * switch to a higher priority thread, LWKT threads are not designed for 1444 * continuous priority changes. Yield if you want to switch. 1445 */ 1446 void 1447 lwkt_setpri(thread_t td, int pri) 1448 { 1449 if (td->td_pri != pri) { 1450 KKASSERT(pri >= 0); 1451 crit_enter(); 1452 if (td->td_flags & TDF_RUNQ) { 1453 KKASSERT(td->td_gd == mycpu); 1454 _lwkt_dequeue(td); 1455 td->td_pri = pri; 1456 _lwkt_enqueue(td); 1457 } else { 1458 td->td_pri = pri; 1459 } 1460 crit_exit(); 1461 } 1462 } 1463 1464 /* 1465 * Set the initial priority for a thread prior to it being scheduled for 1466 * the first time. The thread MUST NOT be scheduled before or during 1467 * this call. The thread may be assigned to a cpu other then the current 1468 * cpu. 1469 * 1470 * Typically used after a thread has been created with TDF_STOPPREQ, 1471 * and before the thread is initially scheduled. 1472 */ 1473 void 1474 lwkt_setpri_initial(thread_t td, int pri) 1475 { 1476 KKASSERT(pri >= 0); 1477 KKASSERT((td->td_flags & TDF_RUNQ) == 0); 1478 td->td_pri = pri; 1479 } 1480 1481 void 1482 lwkt_setpri_self(int pri) 1483 { 1484 thread_t td = curthread; 1485 1486 KKASSERT(pri >= 0 && pri <= TDPRI_MAX); 1487 crit_enter(); 1488 if (td->td_flags & TDF_RUNQ) { 1489 _lwkt_dequeue(td); 1490 td->td_pri = pri; 1491 _lwkt_enqueue(td); 1492 } else { 1493 td->td_pri = pri; 1494 } 1495 crit_exit(); 1496 } 1497 1498 /* 1499 * hz tick scheduler clock for LWKT threads 1500 */ 1501 void 1502 lwkt_schedulerclock(thread_t td) 1503 { 1504 globaldata_t gd = td->td_gd; 1505 thread_t xtd; 1506 1507 if (TAILQ_FIRST(&gd->gd_tdrunq) == td) { 1508 /* 1509 * If the current thread is at the head of the runq shift it to the 1510 * end of any equal-priority threads and request a LWKT reschedule 1511 * if it moved. 1512 * 1513 * Ignore upri in this situation. There will only be one user thread 1514 * in user mode, all others will be user threads running in kernel 1515 * mode and we have to make sure they get some cpu. 1516 */ 1517 xtd = TAILQ_NEXT(td, td_threadq); 1518 if (xtd && xtd->td_pri == td->td_pri) { 1519 TAILQ_REMOVE(&gd->gd_tdrunq, td, td_threadq); 1520 while (xtd && xtd->td_pri == td->td_pri) 1521 xtd = TAILQ_NEXT(xtd, td_threadq); 1522 if (xtd) 1523 TAILQ_INSERT_BEFORE(xtd, td, td_threadq); 1524 else 1525 TAILQ_INSERT_TAIL(&gd->gd_tdrunq, td, td_threadq); 1526 need_lwkt_resched(); 1527 } 1528 } else { 1529 /* 1530 * If we scheduled a thread other than the one at the head of the 1531 * queue always request a reschedule every tick. 1532 */ 1533 need_lwkt_resched(); 1534 } 1535 } 1536 1537 /* 1538 * Migrate the current thread to the specified cpu. 1539 * 1540 * This is accomplished by descheduling ourselves from the current cpu 1541 * and setting td_migrate_gd. The lwkt_switch() code will detect that the 1542 * 'old' thread wants to migrate after it has been completely switched out 1543 * and will complete the migration. 1544 * 1545 * TDF_MIGRATING prevents scheduling races while the thread is being migrated. 1546 * 1547 * We must be sure to release our current process designation (if a user 1548 * process) before clearing out any tsleepq we are on because the release 1549 * code may re-add us. 1550 * 1551 * We must be sure to remove ourselves from the current cpu's tsleepq 1552 * before potentially moving to another queue. The thread can be on 1553 * a tsleepq due to a left-over tsleep_interlock(). 1554 */ 1555 1556 void 1557 lwkt_setcpu_self(globaldata_t rgd) 1558 { 1559 thread_t td = curthread; 1560 1561 if (td->td_gd != rgd) { 1562 crit_enter_quick(td); 1563 1564 if (td->td_release) 1565 td->td_release(td); 1566 if (td->td_flags & TDF_TSLEEPQ) 1567 tsleep_remove(td); 1568 1569 /* 1570 * Set TDF_MIGRATING to prevent a spurious reschedule while we are 1571 * trying to deschedule ourselves and switch away, then deschedule 1572 * ourself, remove us from tdallq, and set td_migrate_gd. Finally, 1573 * call lwkt_switch() to complete the operation. 1574 */ 1575 td->td_flags |= TDF_MIGRATING; 1576 lwkt_deschedule_self(td); 1577 TAILQ_REMOVE(&td->td_gd->gd_tdallq, td, td_allq); 1578 td->td_migrate_gd = rgd; 1579 lwkt_switch(); 1580 1581 /* 1582 * We are now on the target cpu 1583 */ 1584 KKASSERT(rgd == mycpu); 1585 TAILQ_INSERT_TAIL(&rgd->gd_tdallq, td, td_allq); 1586 crit_exit_quick(td); 1587 } 1588 } 1589 1590 void 1591 lwkt_migratecpu(int cpuid) 1592 { 1593 globaldata_t rgd; 1594 1595 rgd = globaldata_find(cpuid); 1596 lwkt_setcpu_self(rgd); 1597 } 1598 1599 /* 1600 * Remote IPI for cpu migration (called while in a critical section so we 1601 * do not have to enter another one). 1602 * 1603 * The thread (td) has already been completely descheduled from the 1604 * originating cpu and we can simply assert the case. The thread is 1605 * assigned to the new cpu and enqueued. 1606 * 1607 * The thread will re-add itself to tdallq when it resumes execution. 1608 */ 1609 static void 1610 lwkt_setcpu_remote(void *arg) 1611 { 1612 thread_t td = arg; 1613 globaldata_t gd = mycpu; 1614 1615 KKASSERT((td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK)) == 0); 1616 td->td_gd = gd; 1617 cpu_mfence(); 1618 td->td_flags &= ~TDF_MIGRATING; 1619 KKASSERT(td->td_migrate_gd == NULL); 1620 KKASSERT(td->td_lwp == NULL || 1621 (td->td_lwp->lwp_mpflags & LWP_MP_ONRUNQ) == 0); 1622 _lwkt_enqueue(td); 1623 } 1624 1625 struct lwp * 1626 lwkt_preempted_proc(void) 1627 { 1628 thread_t td = curthread; 1629 while (td->td_preempted) 1630 td = td->td_preempted; 1631 return(td->td_lwp); 1632 } 1633 1634 /* 1635 * Create a kernel process/thread/whatever. It shares it's address space 1636 * with proc0 - ie: kernel only. 1637 * 1638 * If the cpu is not specified one will be selected. In the future 1639 * specifying a cpu of -1 will enable kernel thread migration between 1640 * cpus. 1641 */ 1642 int 1643 lwkt_create(void (*func)(void *), void *arg, struct thread **tdp, 1644 thread_t template, int tdflags, int cpu, const char *fmt, ...) 1645 { 1646 thread_t td; 1647 __va_list ap; 1648 1649 td = lwkt_alloc_thread(template, LWKT_THREAD_STACK, cpu, 1650 tdflags); 1651 if (tdp) 1652 *tdp = td; 1653 cpu_set_thread_handler(td, lwkt_exit, func, arg); 1654 1655 /* 1656 * Set up arg0 for 'ps' etc 1657 */ 1658 __va_start(ap, fmt); 1659 kvsnprintf(td->td_comm, sizeof(td->td_comm), fmt, ap); 1660 __va_end(ap); 1661 1662 /* 1663 * Schedule the thread to run 1664 */ 1665 if (td->td_flags & TDF_NOSTART) 1666 td->td_flags &= ~TDF_NOSTART; 1667 else 1668 lwkt_schedule(td); 1669 return 0; 1670 } 1671 1672 /* 1673 * Destroy an LWKT thread. Warning! This function is not called when 1674 * a process exits, cpu_proc_exit() directly calls cpu_thread_exit() and 1675 * uses a different reaping mechanism. 1676 */ 1677 void 1678 lwkt_exit(void) 1679 { 1680 thread_t td = curthread; 1681 thread_t std; 1682 globaldata_t gd; 1683 1684 /* 1685 * Do any cleanup that might block here 1686 */ 1687 if (td->td_flags & TDF_VERBOSE) 1688 kprintf("kthread %p %s has exited\n", td, td->td_comm); 1689 biosched_done(td); 1690 dsched_exit_thread(td); 1691 1692 /* 1693 * Get us into a critical section to interlock gd_freetd and loop 1694 * until we can get it freed. 1695 * 1696 * We have to cache the current td in gd_freetd because objcache_put()ing 1697 * it would rip it out from under us while our thread is still active. 1698 * 1699 * We are the current thread so of course our own TDF_RUNNING bit will 1700 * be set, so unlike the lwp reap code we don't wait for it to clear. 1701 */ 1702 gd = mycpu; 1703 crit_enter_quick(td); 1704 for (;;) { 1705 if (td->td_refs) { 1706 tsleep(td, 0, "tdreap", 1); 1707 continue; 1708 } 1709 if ((std = gd->gd_freetd) != NULL) { 1710 KKASSERT((std->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK)) == 0); 1711 gd->gd_freetd = NULL; 1712 objcache_put(thread_cache, std); 1713 continue; 1714 } 1715 break; 1716 } 1717 1718 /* 1719 * Remove thread resources from kernel lists and deschedule us for 1720 * the last time. We cannot block after this point or we may end 1721 * up with a stale td on the tsleepq. 1722 * 1723 * None of this may block, the critical section is the only thing 1724 * protecting tdallq and the only thing preventing new lwkt_hold() 1725 * thread refs now. 1726 */ 1727 if (td->td_flags & TDF_TSLEEPQ) 1728 tsleep_remove(td); 1729 lwkt_deschedule_self(td); 1730 lwkt_remove_tdallq(td); 1731 KKASSERT(td->td_refs == 0); 1732 1733 /* 1734 * Final cleanup 1735 */ 1736 KKASSERT(gd->gd_freetd == NULL); 1737 if (td->td_flags & TDF_ALLOCATED_THREAD) 1738 gd->gd_freetd = td; 1739 cpu_thread_exit(); 1740 } 1741 1742 void 1743 lwkt_remove_tdallq(thread_t td) 1744 { 1745 KKASSERT(td->td_gd == mycpu); 1746 TAILQ_REMOVE(&td->td_gd->gd_tdallq, td, td_allq); 1747 } 1748 1749 /* 1750 * Code reduction and branch prediction improvements. Call/return 1751 * overhead on modern cpus often degenerates into 0 cycles due to 1752 * the cpu's branch prediction hardware and return pc cache. We 1753 * can take advantage of this by not inlining medium-complexity 1754 * functions and we can also reduce the branch prediction impact 1755 * by collapsing perfectly predictable branches into a single 1756 * procedure instead of duplicating it. 1757 * 1758 * Is any of this noticeable? Probably not, so I'll take the 1759 * smaller code size. 1760 */ 1761 void 1762 crit_exit_wrapper(__DEBUG_CRIT_ARG__) 1763 { 1764 _crit_exit(mycpu __DEBUG_CRIT_PASS_ARG__); 1765 } 1766 1767 void 1768 crit_panic(void) 1769 { 1770 thread_t td = curthread; 1771 int lcrit = td->td_critcount; 1772 1773 td->td_critcount = 0; 1774 panic("td_critcount is/would-go negative! %p %d", td, lcrit); 1775 /* NOT REACHED */ 1776 } 1777 1778 /* 1779 * Called from debugger/panic on cpus which have been stopped. We must still 1780 * process the IPIQ while stopped, even if we were stopped while in a critical 1781 * section (XXX). 1782 * 1783 * If we are dumping also try to process any pending interrupts. This may 1784 * or may not work depending on the state of the cpu at the point it was 1785 * stopped. 1786 */ 1787 void 1788 lwkt_smp_stopped(void) 1789 { 1790 globaldata_t gd = mycpu; 1791 1792 crit_enter_gd(gd); 1793 if (dumping) { 1794 lwkt_process_ipiq(); 1795 splz(); 1796 } else { 1797 lwkt_process_ipiq(); 1798 } 1799 crit_exit_gd(gd); 1800 } 1801