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 /* 104 * We can make all thread ports use the spin backend instead of the thread 105 * backend. This should only be set to debug the spin backend. 106 */ 107 TUNABLE_INT("lwkt.use_spin_port", &lwkt_use_spin_port); 108 109 #ifdef INVARIANTS 110 SYSCTL_INT(_lwkt, OID_AUTO, panic_on_cscount, CTLFLAG_RW, &panic_on_cscount, 0, 111 "Panic if attempting to switch lwkt's while mastering cpusync"); 112 #endif 113 SYSCTL_QUAD(_lwkt, OID_AUTO, switch_count, CTLFLAG_RW, &switch_count, 0, 114 "Number of switched threads"); 115 SYSCTL_QUAD(_lwkt, OID_AUTO, preempt_hit, CTLFLAG_RW, &preempt_hit, 0, 116 "Successful preemption events"); 117 SYSCTL_QUAD(_lwkt, OID_AUTO, preempt_miss, CTLFLAG_RW, &preempt_miss, 0, 118 "Failed preemption events"); 119 SYSCTL_QUAD(_lwkt, OID_AUTO, preempt_weird, CTLFLAG_RW, &preempt_weird, 0, 120 "Number of preempted threads."); 121 static int fairq_enable = 0; 122 SYSCTL_INT(_lwkt, OID_AUTO, fairq_enable, CTLFLAG_RW, 123 &fairq_enable, 0, "Turn on fairq priority accumulators"); 124 static int fairq_bypass = -1; 125 SYSCTL_INT(_lwkt, OID_AUTO, fairq_bypass, CTLFLAG_RW, 126 &fairq_bypass, 0, "Allow fairq to bypass td on token failure"); 127 extern int lwkt_sched_debug; 128 int lwkt_sched_debug = 0; 129 SYSCTL_INT(_lwkt, OID_AUTO, sched_debug, CTLFLAG_RW, 130 &lwkt_sched_debug, 0, "Scheduler debug"); 131 static int lwkt_spin_loops = 10; 132 SYSCTL_INT(_lwkt, OID_AUTO, spin_loops, CTLFLAG_RW, 133 &lwkt_spin_loops, 0, "Scheduler spin loops until sorted decon"); 134 static int preempt_enable = 1; 135 SYSCTL_INT(_lwkt, OID_AUTO, preempt_enable, CTLFLAG_RW, 136 &preempt_enable, 0, "Enable preemption"); 137 static int lwkt_cache_threads = 0; 138 SYSCTL_INT(_lwkt, OID_AUTO, cache_threads, CTLFLAG_RD, 139 &lwkt_cache_threads, 0, "thread+kstack cache"); 140 141 /* 142 * These helper procedures handle the runq, they can only be called from 143 * within a critical section. 144 * 145 * WARNING! Prior to SMP being brought up it is possible to enqueue and 146 * dequeue threads belonging to other cpus, so be sure to use td->td_gd 147 * instead of 'mycpu' when referencing the globaldata structure. Once 148 * SMP live enqueuing and dequeueing only occurs on the current cpu. 149 */ 150 static __inline 151 void 152 _lwkt_dequeue(thread_t td) 153 { 154 if (td->td_flags & TDF_RUNQ) { 155 struct globaldata *gd = td->td_gd; 156 157 td->td_flags &= ~TDF_RUNQ; 158 TAILQ_REMOVE(&gd->gd_tdrunq, td, td_threadq); 159 --gd->gd_tdrunqcount; 160 if (TAILQ_FIRST(&gd->gd_tdrunq) == NULL) 161 atomic_clear_int(&gd->gd_reqflags, RQF_RUNNING); 162 } 163 } 164 165 /* 166 * Priority enqueue. 167 * 168 * There are a limited number of lwkt threads runnable since user 169 * processes only schedule one at a time per cpu. However, there can 170 * be many user processes in kernel mode exiting from a tsleep() which 171 * become runnable. 172 * 173 * NOTE: lwkt_schedulerclock() will force a round-robin based on td_pri and 174 * will ignore user priority. This is to ensure that user threads in 175 * kernel mode get cpu at some point regardless of what the user 176 * scheduler thinks. 177 */ 178 static __inline 179 void 180 _lwkt_enqueue(thread_t td) 181 { 182 thread_t xtd; 183 184 if ((td->td_flags & (TDF_RUNQ|TDF_MIGRATING|TDF_BLOCKQ)) == 0) { 185 struct globaldata *gd = td->td_gd; 186 187 td->td_flags |= TDF_RUNQ; 188 xtd = TAILQ_FIRST(&gd->gd_tdrunq); 189 if (xtd == NULL) { 190 TAILQ_INSERT_TAIL(&gd->gd_tdrunq, td, td_threadq); 191 atomic_set_int(&gd->gd_reqflags, RQF_RUNNING); 192 } else { 193 /* 194 * NOTE: td_upri - higher numbers more desireable, same sense 195 * as td_pri (typically reversed from lwp_upri). 196 * 197 * In the equal priority case we want the best selection 198 * at the beginning so the less desireable selections know 199 * that they have to setrunqueue/go-to-another-cpu, even 200 * though it means switching back to the 'best' selection. 201 * This also avoids degenerate situations when many threads 202 * are runnable or waking up at the same time. 203 * 204 * If upri matches exactly place at end/round-robin. 205 */ 206 while (xtd && 207 (xtd->td_pri >= td->td_pri || 208 (xtd->td_pri == td->td_pri && 209 xtd->td_upri >= td->td_upri))) { 210 xtd = TAILQ_NEXT(xtd, td_threadq); 211 } 212 if (xtd) 213 TAILQ_INSERT_BEFORE(xtd, td, td_threadq); 214 else 215 TAILQ_INSERT_TAIL(&gd->gd_tdrunq, td, td_threadq); 216 } 217 ++gd->gd_tdrunqcount; 218 219 /* 220 * Request a LWKT reschedule if we are now at the head of the queue. 221 */ 222 if (TAILQ_FIRST(&gd->gd_tdrunq) == td) 223 need_lwkt_resched(); 224 } 225 } 226 227 static boolean_t 228 _lwkt_thread_ctor(void *obj, void *privdata, int ocflags) 229 { 230 struct thread *td = (struct thread *)obj; 231 232 td->td_kstack = NULL; 233 td->td_kstack_size = 0; 234 td->td_flags = TDF_ALLOCATED_THREAD; 235 td->td_mpflags = 0; 236 return (1); 237 } 238 239 static void 240 _lwkt_thread_dtor(void *obj, void *privdata) 241 { 242 struct thread *td = (struct thread *)obj; 243 244 KASSERT(td->td_flags & TDF_ALLOCATED_THREAD, 245 ("_lwkt_thread_dtor: not allocated from objcache")); 246 KASSERT((td->td_flags & TDF_ALLOCATED_STACK) && td->td_kstack && 247 td->td_kstack_size > 0, 248 ("_lwkt_thread_dtor: corrupted stack")); 249 kmem_free(&kernel_map, (vm_offset_t)td->td_kstack, td->td_kstack_size); 250 td->td_kstack = NULL; 251 td->td_flags = 0; 252 } 253 254 /* 255 * Initialize the lwkt s/system. 256 * 257 * Nominally cache up to 32 thread + kstack structures. Cache more on 258 * systems with a lot of cpu cores. 259 */ 260 static void 261 lwkt_init(void) 262 { 263 TUNABLE_INT("lwkt.cache_threads", &lwkt_cache_threads); 264 if (lwkt_cache_threads == 0) { 265 lwkt_cache_threads = ncpus * 4; 266 if (lwkt_cache_threads < 32) 267 lwkt_cache_threads = 32; 268 } 269 thread_cache = objcache_create_mbacked( 270 M_THREAD, sizeof(struct thread), 271 0, lwkt_cache_threads, 272 _lwkt_thread_ctor, _lwkt_thread_dtor, NULL); 273 } 274 SYSINIT(lwkt_init, SI_BOOT2_LWKT_INIT, SI_ORDER_FIRST, lwkt_init, NULL); 275 276 /* 277 * Schedule a thread to run. As the current thread we can always safely 278 * schedule ourselves, and a shortcut procedure is provided for that 279 * function. 280 * 281 * (non-blocking, self contained on a per cpu basis) 282 */ 283 void 284 lwkt_schedule_self(thread_t td) 285 { 286 KKASSERT((td->td_flags & TDF_MIGRATING) == 0); 287 crit_enter_quick(td); 288 KASSERT(td != &td->td_gd->gd_idlethread, 289 ("lwkt_schedule_self(): scheduling gd_idlethread is illegal!")); 290 KKASSERT(td->td_lwp == NULL || 291 (td->td_lwp->lwp_mpflags & LWP_MP_ONRUNQ) == 0); 292 _lwkt_enqueue(td); 293 crit_exit_quick(td); 294 } 295 296 /* 297 * Deschedule a thread. 298 * 299 * (non-blocking, self contained on a per cpu basis) 300 */ 301 void 302 lwkt_deschedule_self(thread_t td) 303 { 304 crit_enter_quick(td); 305 _lwkt_dequeue(td); 306 crit_exit_quick(td); 307 } 308 309 /* 310 * LWKTs operate on a per-cpu basis 311 * 312 * WARNING! Called from early boot, 'mycpu' may not work yet. 313 */ 314 void 315 lwkt_gdinit(struct globaldata *gd) 316 { 317 TAILQ_INIT(&gd->gd_tdrunq); 318 TAILQ_INIT(&gd->gd_tdallq); 319 } 320 321 /* 322 * Create a new thread. The thread must be associated with a process context 323 * or LWKT start address before it can be scheduled. If the target cpu is 324 * -1 the thread will be created on the current cpu. 325 * 326 * If you intend to create a thread without a process context this function 327 * does everything except load the startup and switcher function. 328 */ 329 thread_t 330 lwkt_alloc_thread(struct thread *td, int stksize, int cpu, int flags) 331 { 332 static int cpu_rotator; 333 globaldata_t gd = mycpu; 334 void *stack; 335 336 /* 337 * If static thread storage is not supplied allocate a thread. Reuse 338 * a cached free thread if possible. gd_freetd is used to keep an exiting 339 * thread intact through the exit. 340 */ 341 if (td == NULL) { 342 crit_enter_gd(gd); 343 if ((td = gd->gd_freetd) != NULL) { 344 KKASSERT((td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK| 345 TDF_RUNQ)) == 0); 346 gd->gd_freetd = NULL; 347 } else { 348 td = objcache_get(thread_cache, M_WAITOK); 349 KKASSERT((td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK| 350 TDF_RUNQ)) == 0); 351 } 352 crit_exit_gd(gd); 353 KASSERT((td->td_flags & 354 (TDF_ALLOCATED_THREAD|TDF_RUNNING|TDF_PREEMPT_LOCK)) == 355 TDF_ALLOCATED_THREAD, 356 ("lwkt_alloc_thread: corrupted td flags 0x%X", td->td_flags)); 357 flags |= td->td_flags & (TDF_ALLOCATED_THREAD|TDF_ALLOCATED_STACK); 358 } 359 360 /* 361 * Try to reuse cached stack. 362 */ 363 if ((stack = td->td_kstack) != NULL && td->td_kstack_size != stksize) { 364 if (flags & TDF_ALLOCATED_STACK) { 365 kmem_free(&kernel_map, (vm_offset_t)stack, td->td_kstack_size); 366 stack = NULL; 367 } 368 } 369 if (stack == NULL) { 370 stack = (void *)kmem_alloc_stack(&kernel_map, stksize); 371 flags |= TDF_ALLOCATED_STACK; 372 } 373 if (cpu < 0) { 374 cpu = ++cpu_rotator; 375 cpu_ccfence(); 376 cpu %= ncpus; 377 } 378 lwkt_init_thread(td, stack, stksize, flags, globaldata_find(cpu)); 379 return(td); 380 } 381 382 /* 383 * Initialize a preexisting thread structure. This function is used by 384 * lwkt_alloc_thread() and also used to initialize the per-cpu idlethread. 385 * 386 * All threads start out in a critical section at a priority of 387 * TDPRI_KERN_DAEMON. Higher level code will modify the priority as 388 * appropriate. This function may send an IPI message when the 389 * requested cpu is not the current cpu and consequently gd_tdallq may 390 * not be initialized synchronously from the point of view of the originating 391 * cpu. 392 * 393 * NOTE! we have to be careful in regards to creating threads for other cpus 394 * if SMP has not yet been activated. 395 */ 396 static void 397 lwkt_init_thread_remote(void *arg) 398 { 399 thread_t td = arg; 400 401 /* 402 * Protected by critical section held by IPI dispatch 403 */ 404 TAILQ_INSERT_TAIL(&td->td_gd->gd_tdallq, td, td_allq); 405 } 406 407 /* 408 * lwkt core thread structural initialization. 409 * 410 * NOTE: All threads are initialized as mpsafe threads. 411 */ 412 void 413 lwkt_init_thread(thread_t td, void *stack, int stksize, int flags, 414 struct globaldata *gd) 415 { 416 globaldata_t mygd = mycpu; 417 418 bzero(td, sizeof(struct thread)); 419 td->td_kstack = stack; 420 td->td_kstack_size = stksize; 421 td->td_flags = flags; 422 td->td_mpflags = 0; 423 td->td_type = TD_TYPE_GENERIC; 424 td->td_gd = gd; 425 td->td_pri = TDPRI_KERN_DAEMON; 426 td->td_critcount = 1; 427 td->td_toks_have = NULL; 428 td->td_toks_stop = &td->td_toks_base; 429 if (lwkt_use_spin_port || (flags & TDF_FORCE_SPINPORT)) { 430 lwkt_initport_spin(&td->td_msgport, td, 431 (flags & TDF_FIXEDCPU) ? TRUE : FALSE); 432 } else { 433 lwkt_initport_thread(&td->td_msgport, td); 434 } 435 pmap_init_thread(td); 436 /* 437 * Normally initializing a thread for a remote cpu requires sending an 438 * IPI. However, the idlethread is setup before the other cpus are 439 * activated so we have to treat it as a special case. XXX manipulation 440 * of gd_tdallq requires the BGL. 441 */ 442 if (gd == mygd || td == &gd->gd_idlethread) { 443 crit_enter_gd(mygd); 444 TAILQ_INSERT_TAIL(&gd->gd_tdallq, td, td_allq); 445 crit_exit_gd(mygd); 446 } else { 447 lwkt_send_ipiq(gd, lwkt_init_thread_remote, td); 448 } 449 dsched_enter_thread(td); 450 } 451 452 void 453 lwkt_set_comm(thread_t td, const char *ctl, ...) 454 { 455 __va_list va; 456 457 __va_start(va, ctl); 458 kvsnprintf(td->td_comm, sizeof(td->td_comm), ctl, va); 459 __va_end(va); 460 KTR_LOG(ctxsw_newtd, td, td->td_comm); 461 } 462 463 /* 464 * Prevent the thread from getting destroyed. Note that unlike PHOLD/PRELE 465 * this does not prevent the thread from migrating to another cpu so the 466 * gd_tdallq state is not protected by this. 467 */ 468 void 469 lwkt_hold(thread_t td) 470 { 471 atomic_add_int(&td->td_refs, 1); 472 } 473 474 void 475 lwkt_rele(thread_t td) 476 { 477 KKASSERT(td->td_refs > 0); 478 atomic_add_int(&td->td_refs, -1); 479 } 480 481 void 482 lwkt_free_thread(thread_t td) 483 { 484 KKASSERT(td->td_refs == 0); 485 KKASSERT((td->td_flags & (TDF_RUNNING | TDF_PREEMPT_LOCK | 486 TDF_RUNQ | TDF_TSLEEPQ)) == 0); 487 if (td->td_flags & TDF_ALLOCATED_THREAD) { 488 objcache_put(thread_cache, td); 489 } else if (td->td_flags & TDF_ALLOCATED_STACK) { 490 /* client-allocated struct with internally allocated stack */ 491 KASSERT(td->td_kstack && td->td_kstack_size > 0, 492 ("lwkt_free_thread: corrupted stack")); 493 kmem_free(&kernel_map, (vm_offset_t)td->td_kstack, td->td_kstack_size); 494 td->td_kstack = NULL; 495 td->td_kstack_size = 0; 496 } 497 498 KTR_LOG(ctxsw_deadtd, td); 499 } 500 501 502 /* 503 * Switch to the next runnable lwkt. If no LWKTs are runnable then 504 * switch to the idlethread. Switching must occur within a critical 505 * section to avoid races with the scheduling queue. 506 * 507 * We always have full control over our cpu's run queue. Other cpus 508 * that wish to manipulate our queue must use the cpu_*msg() calls to 509 * talk to our cpu, so a critical section is all that is needed and 510 * the result is very, very fast thread switching. 511 * 512 * The LWKT scheduler uses a fixed priority model and round-robins at 513 * each priority level. User process scheduling is a totally 514 * different beast and LWKT priorities should not be confused with 515 * user process priorities. 516 * 517 * PREEMPTION NOTE: Preemption occurs via lwkt_preempt(). lwkt_switch() 518 * is not called by the current thread in the preemption case, only when 519 * the preempting thread blocks (in order to return to the original thread). 520 * 521 * SPECIAL NOTE ON SWITCH ATOMICY: Certain operations such as thread 522 * migration and tsleep deschedule the current lwkt thread and call 523 * lwkt_switch(). In particular, the target cpu of the migration fully 524 * expects the thread to become non-runnable and can deadlock against 525 * cpusync operations if we run any IPIs prior to switching the thread out. 526 * 527 * WE MUST BE VERY CAREFUL NOT TO RUN SPLZ DIRECTLY OR INDIRECTLY IF 528 * THE CURRENT THREAD HAS BEEN DESCHEDULED! 529 */ 530 void 531 lwkt_switch(void) 532 { 533 globaldata_t gd = mycpu; 534 thread_t td = gd->gd_curthread; 535 thread_t ntd; 536 int upri; 537 538 KKASSERT(gd->gd_processing_ipiq == 0); 539 KKASSERT(td->td_flags & TDF_RUNNING); 540 541 /* 542 * Switching from within a 'fast' (non thread switched) interrupt or IPI 543 * is illegal. However, we may have to do it anyway if we hit a fatal 544 * kernel trap or we have paniced. 545 * 546 * If this case occurs save and restore the interrupt nesting level. 547 */ 548 if (gd->gd_intr_nesting_level) { 549 int savegdnest; 550 int savegdtrap; 551 552 if (gd->gd_trap_nesting_level == 0 && panic_cpu_gd != mycpu) { 553 panic("lwkt_switch: Attempt to switch from a " 554 "fast interrupt, ipi, or hard code section, " 555 "td %p\n", 556 td); 557 } else { 558 savegdnest = gd->gd_intr_nesting_level; 559 savegdtrap = gd->gd_trap_nesting_level; 560 gd->gd_intr_nesting_level = 0; 561 gd->gd_trap_nesting_level = 0; 562 if ((td->td_flags & TDF_PANICWARN) == 0) { 563 td->td_flags |= TDF_PANICWARN; 564 kprintf("Warning: thread switch from interrupt, IPI, " 565 "or hard code section.\n" 566 "thread %p (%s)\n", td, td->td_comm); 567 print_backtrace(-1); 568 } 569 lwkt_switch(); 570 gd->gd_intr_nesting_level = savegdnest; 571 gd->gd_trap_nesting_level = savegdtrap; 572 return; 573 } 574 } 575 576 /* 577 * Release our current user process designation if we are blocking 578 * or if a user reschedule was requested. 579 * 580 * NOTE: This function is NOT called if we are switching into or 581 * returning from a preemption. 582 * 583 * NOTE: Releasing our current user process designation may cause 584 * it to be assigned to another thread, which in turn will 585 * cause us to block in the usched acquire code when we attempt 586 * to return to userland. 587 * 588 * NOTE: On SMP systems this can be very nasty when heavy token 589 * contention is present so we want to be careful not to 590 * release the designation gratuitously. 591 */ 592 if (td->td_release && 593 (user_resched_wanted() || (td->td_flags & TDF_RUNQ) == 0)) { 594 td->td_release(td); 595 } 596 597 /* 598 * Release all tokens. Once we do this we must remain in the critical 599 * section and cannot run IPIs or other interrupts until we switch away 600 * because they may implode if they try to get a token using our thread 601 * context. 602 */ 603 crit_enter_gd(gd); 604 if (TD_TOKS_HELD(td)) 605 lwkt_relalltokens(td); 606 607 /* 608 * We had better not be holding any spin locks, but don't get into an 609 * endless panic loop. 610 */ 611 KASSERT(gd->gd_spinlocks == 0 || panicstr != NULL, 612 ("lwkt_switch: still holding %d exclusive spinlocks!", 613 gd->gd_spinlocks)); 614 615 #ifdef INVARIANTS 616 if (td->td_cscount) { 617 kprintf("Diagnostic: attempt to switch while mastering cpusync: %p\n", 618 td); 619 if (panic_on_cscount) 620 panic("switching while mastering cpusync"); 621 } 622 #endif 623 624 /* 625 * If we had preempted another thread on this cpu, resume the preempted 626 * thread. This occurs transparently, whether the preempted thread 627 * was scheduled or not (it may have been preempted after descheduling 628 * itself). 629 * 630 * We have to setup the MP lock for the original thread after backing 631 * out the adjustment that was made to curthread when the original 632 * was preempted. 633 */ 634 if ((ntd = td->td_preempted) != NULL) { 635 KKASSERT(ntd->td_flags & TDF_PREEMPT_LOCK); 636 ntd->td_flags |= TDF_PREEMPT_DONE; 637 638 /* 639 * The interrupt may have woken a thread up, we need to properly 640 * set the reschedule flag if the originally interrupted thread is 641 * at a lower priority. 642 * 643 * The interrupt may not have descheduled. 644 */ 645 if (TAILQ_FIRST(&gd->gd_tdrunq) != ntd) 646 need_lwkt_resched(); 647 goto havethread_preempted; 648 } 649 650 /* 651 * Figure out switch target. If we cannot switch to our desired target 652 * look for a thread that we can switch to. 653 * 654 * NOTE! The limited spin loop and related parameters are extremely 655 * important for system performance, particularly for pipes and 656 * concurrent conflicting VM faults. 657 */ 658 clear_lwkt_resched(); 659 ntd = TAILQ_FIRST(&gd->gd_tdrunq); 660 661 if (ntd) { 662 do { 663 if (TD_TOKS_NOT_HELD(ntd) || 664 lwkt_getalltokens(ntd, (ntd->td_contended > lwkt_spin_loops))) 665 { 666 goto havethread; 667 } 668 ++gd->gd_cnt.v_lock_colls; 669 ++ntd->td_contended; 670 } while (ntd->td_contended < (lwkt_spin_loops >> 1)); 671 upri = ntd->td_upri; 672 673 /* 674 * Bleh, the thread we wanted to switch to has a contended token. 675 * See if we can switch to another thread. 676 * 677 * We generally don't want to do this because it represents a 678 * priority inversion. Do not allow the case if the thread 679 * is returning to userland (not a kernel thread) AND the thread 680 * has a lower upri. 681 */ 682 while ((ntd = TAILQ_NEXT(ntd, td_threadq)) != NULL) { 683 if (ntd->td_pri < TDPRI_KERN_LPSCHED && upri > ntd->td_upri) 684 break; 685 upri = ntd->td_upri; 686 687 /* 688 * Try this one. 689 */ 690 if (TD_TOKS_NOT_HELD(ntd) || 691 lwkt_getalltokens(ntd, (ntd->td_contended > lwkt_spin_loops))) { 692 goto havethread; 693 } 694 ++ntd->td_contended; 695 ++gd->gd_cnt.v_lock_colls; 696 } 697 698 /* 699 * Fall through, switch to idle thread to get us out of the current 700 * context. Since we were contended, prevent HLT by flagging a 701 * LWKT reschedule. 702 */ 703 need_lwkt_resched(); 704 } 705 706 /* 707 * We either contended on ntd or the runq is empty. We must switch 708 * through the idle thread to get out of the current context. 709 */ 710 ntd = &gd->gd_idlethread; 711 if (gd->gd_trap_nesting_level == 0 && panicstr == NULL) 712 ASSERT_NO_TOKENS_HELD(ntd); 713 cpu_time.cp_msg[0] = 0; 714 goto haveidle; 715 716 havethread: 717 /* 718 * Clear gd_idle_repeat when doing a normal switch to a non-idle 719 * thread. 720 */ 721 ntd->td_wmesg = NULL; 722 ntd->td_contended = 0; 723 ++gd->gd_cnt.v_swtch; 724 gd->gd_idle_repeat = 0; 725 726 havethread_preempted: 727 /* 728 * If the new target does not need the MP lock and we are holding it, 729 * release the MP lock. If the new target requires the MP lock we have 730 * already acquired it for the target. 731 */ 732 ; 733 haveidle: 734 KASSERT(ntd->td_critcount, 735 ("priority problem in lwkt_switch %d %d", 736 td->td_critcount, ntd->td_critcount)); 737 738 if (td != ntd) { 739 /* 740 * Execute the actual thread switch operation. This function 741 * returns to the current thread and returns the previous thread 742 * (which may be different from the thread we switched to). 743 * 744 * We are responsible for marking ntd as TDF_RUNNING. 745 */ 746 KKASSERT((ntd->td_flags & TDF_RUNNING) == 0); 747 ++switch_count; 748 KTR_LOG(ctxsw_sw, gd->gd_cpuid, ntd); 749 ntd->td_flags |= TDF_RUNNING; 750 lwkt_switch_return(td->td_switch(ntd)); 751 /* ntd invalid, td_switch() can return a different thread_t */ 752 } 753 754 /* 755 * catch-all. XXX is this strictly needed? 756 */ 757 splz_check(); 758 759 /* NOTE: current cpu may have changed after switch */ 760 crit_exit_quick(td); 761 } 762 763 /* 764 * Called by assembly in the td_switch (thread restore path) for thread 765 * bootstrap cases which do not 'return' to lwkt_switch(). 766 */ 767 void 768 lwkt_switch_return(thread_t otd) 769 { 770 globaldata_t rgd; 771 772 /* 773 * Check if otd was migrating. Now that we are on ntd we can finish 774 * up the migration. This is a bit messy but it is the only place 775 * where td is known to be fully descheduled. 776 * 777 * We can only activate the migration if otd was migrating but not 778 * held on the cpu due to a preemption chain. We still have to 779 * clear TDF_RUNNING on the old thread either way. 780 * 781 * We are responsible for clearing the previously running thread's 782 * TDF_RUNNING. 783 */ 784 if ((rgd = otd->td_migrate_gd) != NULL && 785 (otd->td_flags & TDF_PREEMPT_LOCK) == 0) { 786 KKASSERT((otd->td_flags & (TDF_MIGRATING | TDF_RUNNING)) == 787 (TDF_MIGRATING | TDF_RUNNING)); 788 otd->td_migrate_gd = NULL; 789 otd->td_flags &= ~TDF_RUNNING; 790 lwkt_send_ipiq(rgd, lwkt_setcpu_remote, otd); 791 } else { 792 otd->td_flags &= ~TDF_RUNNING; 793 } 794 795 /* 796 * Final exit validations (see lwp_wait()). Note that otd becomes 797 * invalid the *instant* we set TDF_MP_EXITSIG. 798 */ 799 while (otd->td_flags & TDF_EXITING) { 800 u_int mpflags; 801 802 mpflags = otd->td_mpflags; 803 cpu_ccfence(); 804 805 if (mpflags & TDF_MP_EXITWAIT) { 806 if (atomic_cmpset_int(&otd->td_mpflags, mpflags, 807 mpflags | TDF_MP_EXITSIG)) { 808 wakeup(otd); 809 break; 810 } 811 } else { 812 if (atomic_cmpset_int(&otd->td_mpflags, mpflags, 813 mpflags | TDF_MP_EXITSIG)) { 814 wakeup(otd); 815 break; 816 } 817 } 818 } 819 } 820 821 /* 822 * Request that the target thread preempt the current thread. Preemption 823 * can only occur if our only critical section is the one that we were called 824 * with, the relative priority of the target thread is higher, and the target 825 * thread holds no tokens. This also only works if we are not holding any 826 * spinlocks (obviously). 827 * 828 * THE CALLER OF LWKT_PREEMPT() MUST BE IN A CRITICAL SECTION. Typically 829 * this is called via lwkt_schedule() through the td_preemptable callback. 830 * critcount is the managed critical priority that we should ignore in order 831 * to determine whether preemption is possible (aka usually just the crit 832 * priority of lwkt_schedule() itself). 833 * 834 * Preemption is typically limited to interrupt threads. 835 * 836 * Operation works in a fairly straight-forward manner. The normal 837 * scheduling code is bypassed and we switch directly to the target 838 * thread. When the target thread attempts to block or switch away 839 * code at the base of lwkt_switch() will switch directly back to our 840 * thread. Our thread is able to retain whatever tokens it holds and 841 * if the target needs one of them the target will switch back to us 842 * and reschedule itself normally. 843 */ 844 void 845 lwkt_preempt(thread_t ntd, int critcount) 846 { 847 struct globaldata *gd = mycpu; 848 thread_t xtd; 849 thread_t td; 850 int save_gd_intr_nesting_level; 851 852 /* 853 * The caller has put us in a critical section. We can only preempt 854 * if the caller of the caller was not in a critical section (basically 855 * a local interrupt), as determined by the 'critcount' parameter. We 856 * also can't preempt if the caller is holding any spinlocks (even if 857 * he isn't in a critical section). This also handles the tokens test. 858 * 859 * YYY The target thread must be in a critical section (else it must 860 * inherit our critical section? I dunno yet). 861 */ 862 KASSERT(ntd->td_critcount, ("BADCRIT0 %d", ntd->td_pri)); 863 864 td = gd->gd_curthread; 865 if (preempt_enable == 0) { 866 ++preempt_miss; 867 return; 868 } 869 if (ntd->td_pri <= td->td_pri) { 870 ++preempt_miss; 871 return; 872 } 873 if (td->td_critcount > critcount) { 874 ++preempt_miss; 875 return; 876 } 877 if (td->td_cscount) { 878 ++preempt_miss; 879 return; 880 } 881 if (ntd->td_gd != gd) { 882 ++preempt_miss; 883 return; 884 } 885 /* 886 * We don't have to check spinlocks here as they will also bump 887 * td_critcount. 888 * 889 * Do not try to preempt if the target thread is holding any tokens. 890 * We could try to acquire the tokens but this case is so rare there 891 * is no need to support it. 892 */ 893 KKASSERT(gd->gd_spinlocks == 0); 894 895 if (TD_TOKS_HELD(ntd)) { 896 ++preempt_miss; 897 return; 898 } 899 if (td == ntd || ((td->td_flags | ntd->td_flags) & TDF_PREEMPT_LOCK)) { 900 ++preempt_weird; 901 return; 902 } 903 if (ntd->td_preempted) { 904 ++preempt_hit; 905 return; 906 } 907 KKASSERT(gd->gd_processing_ipiq == 0); 908 909 /* 910 * Since we are able to preempt the current thread, there is no need to 911 * call need_lwkt_resched(). 912 * 913 * We must temporarily clear gd_intr_nesting_level around the switch 914 * since switchouts from the target thread are allowed (they will just 915 * return to our thread), and since the target thread has its own stack. 916 * 917 * A preemption must switch back to the original thread, assert the 918 * case. 919 */ 920 ++preempt_hit; 921 ntd->td_preempted = td; 922 td->td_flags |= TDF_PREEMPT_LOCK; 923 KTR_LOG(ctxsw_pre, gd->gd_cpuid, ntd); 924 save_gd_intr_nesting_level = gd->gd_intr_nesting_level; 925 gd->gd_intr_nesting_level = 0; 926 927 KKASSERT((ntd->td_flags & TDF_RUNNING) == 0); 928 ntd->td_flags |= TDF_RUNNING; 929 xtd = td->td_switch(ntd); 930 KKASSERT(xtd == ntd); 931 lwkt_switch_return(xtd); 932 gd->gd_intr_nesting_level = save_gd_intr_nesting_level; 933 934 KKASSERT(ntd->td_preempted && (td->td_flags & TDF_PREEMPT_DONE)); 935 ntd->td_preempted = NULL; 936 td->td_flags &= ~(TDF_PREEMPT_LOCK|TDF_PREEMPT_DONE); 937 } 938 939 /* 940 * Conditionally call splz() if gd_reqflags indicates work is pending. 941 * This will work inside a critical section but not inside a hard code 942 * section. 943 * 944 * (self contained on a per cpu basis) 945 */ 946 void 947 splz_check(void) 948 { 949 globaldata_t gd = mycpu; 950 thread_t td = gd->gd_curthread; 951 952 if ((gd->gd_reqflags & RQF_IDLECHECK_MASK) && 953 gd->gd_intr_nesting_level == 0 && 954 td->td_nest_count < 2) 955 { 956 splz(); 957 } 958 } 959 960 /* 961 * This version is integrated into crit_exit, reqflags has already 962 * been tested but td_critcount has not. 963 * 964 * We only want to execute the splz() on the 1->0 transition of 965 * critcount and not in a hard code section or if too deeply nested. 966 * 967 * NOTE: gd->gd_spinlocks is implied to be 0 when td_critcount is 0. 968 */ 969 void 970 lwkt_maybe_splz(thread_t td) 971 { 972 globaldata_t gd = td->td_gd; 973 974 if (td->td_critcount == 0 && 975 gd->gd_intr_nesting_level == 0 && 976 td->td_nest_count < 2) 977 { 978 splz(); 979 } 980 } 981 982 /* 983 * Drivers which set up processing co-threads can call this function to 984 * run the co-thread at a higher priority and to allow it to preempt 985 * normal threads. 986 */ 987 void 988 lwkt_set_interrupt_support_thread(void) 989 { 990 thread_t td = curthread; 991 992 lwkt_setpri_self(TDPRI_INT_SUPPORT); 993 td->td_flags |= TDF_INTTHREAD; 994 td->td_preemptable = lwkt_preempt; 995 } 996 997 998 /* 999 * This function is used to negotiate a passive release of the current 1000 * process/lwp designation with the user scheduler, allowing the user 1001 * scheduler to schedule another user thread. The related kernel thread 1002 * (curthread) continues running in the released state. 1003 */ 1004 void 1005 lwkt_passive_release(struct thread *td) 1006 { 1007 struct lwp *lp = td->td_lwp; 1008 1009 td->td_release = NULL; 1010 lwkt_setpri_self(TDPRI_KERN_USER); 1011 1012 lp->lwp_proc->p_usched->release_curproc(lp); 1013 } 1014 1015 1016 /* 1017 * This implements a LWKT yield, allowing a kernel thread to yield to other 1018 * kernel threads at the same or higher priority. This function can be 1019 * called in a tight loop and will typically only yield once per tick. 1020 * 1021 * Most kernel threads run at the same priority in order to allow equal 1022 * sharing. 1023 * 1024 * (self contained on a per cpu basis) 1025 */ 1026 void 1027 lwkt_yield(void) 1028 { 1029 globaldata_t gd = mycpu; 1030 thread_t td = gd->gd_curthread; 1031 1032 if ((gd->gd_reqflags & RQF_IDLECHECK_MASK) && td->td_nest_count < 2) 1033 splz(); 1034 if (lwkt_resched_wanted()) { 1035 lwkt_schedule_self(curthread); 1036 lwkt_switch(); 1037 } 1038 } 1039 1040 /* 1041 * The quick version processes pending interrupts and higher-priority 1042 * LWKT threads but will not round-robin same-priority LWKT threads. 1043 * 1044 * When called while attempting to return to userland the only same-pri 1045 * threads are the ones which have already tried to become the current 1046 * user process. 1047 */ 1048 void 1049 lwkt_yield_quick(void) 1050 { 1051 globaldata_t gd = mycpu; 1052 thread_t td = gd->gd_curthread; 1053 1054 if ((gd->gd_reqflags & RQF_IDLECHECK_MASK) && td->td_nest_count < 2) 1055 splz(); 1056 if (lwkt_resched_wanted()) { 1057 crit_enter(); 1058 if (TAILQ_FIRST(&gd->gd_tdrunq) == td) { 1059 clear_lwkt_resched(); 1060 } else { 1061 lwkt_schedule_self(curthread); 1062 lwkt_switch(); 1063 } 1064 crit_exit(); 1065 } 1066 } 1067 1068 /* 1069 * This yield is designed for kernel threads with a user context. 1070 * 1071 * The kernel acting on behalf of the user is potentially cpu-bound, 1072 * this function will efficiently allow other threads to run and also 1073 * switch to other processes by releasing. 1074 * 1075 * The lwkt_user_yield() function is designed to have very low overhead 1076 * if no yield is determined to be needed. 1077 */ 1078 void 1079 lwkt_user_yield(void) 1080 { 1081 globaldata_t gd = mycpu; 1082 thread_t td = gd->gd_curthread; 1083 1084 /* 1085 * Always run any pending interrupts in case we are in a critical 1086 * section. 1087 */ 1088 if ((gd->gd_reqflags & RQF_IDLECHECK_MASK) && td->td_nest_count < 2) 1089 splz(); 1090 1091 /* 1092 * Switch (which forces a release) if another kernel thread needs 1093 * the cpu, if userland wants us to resched, or if our kernel 1094 * quantum has run out. 1095 */ 1096 if (lwkt_resched_wanted() || 1097 user_resched_wanted()) 1098 { 1099 lwkt_switch(); 1100 } 1101 1102 #if 0 1103 /* 1104 * Reacquire the current process if we are released. 1105 * 1106 * XXX not implemented atm. The kernel may be holding locks and such, 1107 * so we want the thread to continue to receive cpu. 1108 */ 1109 if (td->td_release == NULL && lp) { 1110 lp->lwp_proc->p_usched->acquire_curproc(lp); 1111 td->td_release = lwkt_passive_release; 1112 lwkt_setpri_self(TDPRI_USER_NORM); 1113 } 1114 #endif 1115 } 1116 1117 /* 1118 * Generic schedule. Possibly schedule threads belonging to other cpus and 1119 * deal with threads that might be blocked on a wait queue. 1120 * 1121 * We have a little helper inline function which does additional work after 1122 * the thread has been enqueued, including dealing with preemption and 1123 * setting need_lwkt_resched() (which prevents the kernel from returning 1124 * to userland until it has processed higher priority threads). 1125 * 1126 * It is possible for this routine to be called after a failed _enqueue 1127 * (due to the target thread migrating, sleeping, or otherwise blocked). 1128 * We have to check that the thread is actually on the run queue! 1129 */ 1130 static __inline 1131 void 1132 _lwkt_schedule_post(globaldata_t gd, thread_t ntd, int ccount) 1133 { 1134 if (ntd->td_flags & TDF_RUNQ) { 1135 if (ntd->td_preemptable) { 1136 ntd->td_preemptable(ntd, ccount); /* YYY +token */ 1137 } 1138 } 1139 } 1140 1141 static __inline 1142 void 1143 _lwkt_schedule(thread_t td) 1144 { 1145 globaldata_t mygd = mycpu; 1146 1147 KASSERT(td != &td->td_gd->gd_idlethread, 1148 ("lwkt_schedule(): scheduling gd_idlethread is illegal!")); 1149 KKASSERT((td->td_flags & TDF_MIGRATING) == 0); 1150 crit_enter_gd(mygd); 1151 KKASSERT(td->td_lwp == NULL || 1152 (td->td_lwp->lwp_mpflags & LWP_MP_ONRUNQ) == 0); 1153 1154 if (td == mygd->gd_curthread) { 1155 _lwkt_enqueue(td); 1156 } else { 1157 /* 1158 * If we own the thread, there is no race (since we are in a 1159 * critical section). If we do not own the thread there might 1160 * be a race but the target cpu will deal with it. 1161 */ 1162 if (td->td_gd == mygd) { 1163 _lwkt_enqueue(td); 1164 _lwkt_schedule_post(mygd, td, 1); 1165 } else { 1166 lwkt_send_ipiq3(td->td_gd, lwkt_schedule_remote, td, 0); 1167 } 1168 } 1169 crit_exit_gd(mygd); 1170 } 1171 1172 void 1173 lwkt_schedule(thread_t td) 1174 { 1175 _lwkt_schedule(td); 1176 } 1177 1178 void 1179 lwkt_schedule_noresched(thread_t td) /* XXX not impl */ 1180 { 1181 _lwkt_schedule(td); 1182 } 1183 1184 /* 1185 * When scheduled remotely if frame != NULL the IPIQ is being 1186 * run via doreti or an interrupt then preemption can be allowed. 1187 * 1188 * To allow preemption we have to drop the critical section so only 1189 * one is present in _lwkt_schedule_post. 1190 */ 1191 static void 1192 lwkt_schedule_remote(void *arg, int arg2, struct intrframe *frame) 1193 { 1194 thread_t td = curthread; 1195 thread_t ntd = arg; 1196 1197 if (frame && ntd->td_preemptable) { 1198 crit_exit_noyield(td); 1199 _lwkt_schedule(ntd); 1200 crit_enter_quick(td); 1201 } else { 1202 _lwkt_schedule(ntd); 1203 } 1204 } 1205 1206 /* 1207 * Thread migration using a 'Pull' method. The thread may or may not be 1208 * the current thread. It MUST be descheduled and in a stable state. 1209 * lwkt_giveaway() must be called on the cpu owning the thread. 1210 * 1211 * At any point after lwkt_giveaway() is called, the target cpu may 1212 * 'pull' the thread by calling lwkt_acquire(). 1213 * 1214 * We have to make sure the thread is not sitting on a per-cpu tsleep 1215 * queue or it will blow up when it moves to another cpu. 1216 * 1217 * MPSAFE - must be called under very specific conditions. 1218 */ 1219 void 1220 lwkt_giveaway(thread_t td) 1221 { 1222 globaldata_t gd = mycpu; 1223 1224 crit_enter_gd(gd); 1225 if (td->td_flags & TDF_TSLEEPQ) 1226 tsleep_remove(td); 1227 KKASSERT(td->td_gd == gd); 1228 TAILQ_REMOVE(&gd->gd_tdallq, td, td_allq); 1229 td->td_flags |= TDF_MIGRATING; 1230 crit_exit_gd(gd); 1231 } 1232 1233 void 1234 lwkt_acquire(thread_t td) 1235 { 1236 globaldata_t gd; 1237 globaldata_t mygd; 1238 int retry = 10000000; 1239 1240 KKASSERT(td->td_flags & TDF_MIGRATING); 1241 gd = td->td_gd; 1242 mygd = mycpu; 1243 if (gd != mycpu) { 1244 cpu_lfence(); 1245 KKASSERT((td->td_flags & TDF_RUNQ) == 0); 1246 crit_enter_gd(mygd); 1247 DEBUG_PUSH_INFO("lwkt_acquire"); 1248 while (td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK)) { 1249 lwkt_process_ipiq(); 1250 cpu_lfence(); 1251 if (--retry == 0) { 1252 kprintf("lwkt_acquire: stuck: td %p td->td_flags %08x\n", 1253 td, td->td_flags); 1254 retry = 10000000; 1255 } 1256 #ifdef _KERNEL_VIRTUAL 1257 pthread_yield(); 1258 #endif 1259 } 1260 DEBUG_POP_INFO(); 1261 cpu_mfence(); 1262 td->td_gd = mygd; 1263 TAILQ_INSERT_TAIL(&mygd->gd_tdallq, td, td_allq); 1264 td->td_flags &= ~TDF_MIGRATING; 1265 crit_exit_gd(mygd); 1266 } else { 1267 crit_enter_gd(mygd); 1268 TAILQ_INSERT_TAIL(&mygd->gd_tdallq, td, td_allq); 1269 td->td_flags &= ~TDF_MIGRATING; 1270 crit_exit_gd(mygd); 1271 } 1272 } 1273 1274 /* 1275 * Generic deschedule. Descheduling threads other then your own should be 1276 * done only in carefully controlled circumstances. Descheduling is 1277 * asynchronous. 1278 * 1279 * This function may block if the cpu has run out of messages. 1280 */ 1281 void 1282 lwkt_deschedule(thread_t td) 1283 { 1284 crit_enter(); 1285 if (td == curthread) { 1286 _lwkt_dequeue(td); 1287 } else { 1288 if (td->td_gd == mycpu) { 1289 _lwkt_dequeue(td); 1290 } else { 1291 lwkt_send_ipiq(td->td_gd, (ipifunc1_t)lwkt_deschedule, td); 1292 } 1293 } 1294 crit_exit(); 1295 } 1296 1297 /* 1298 * Set the target thread's priority. This routine does not automatically 1299 * switch to a higher priority thread, LWKT threads are not designed for 1300 * continuous priority changes. Yield if you want to switch. 1301 */ 1302 void 1303 lwkt_setpri(thread_t td, int pri) 1304 { 1305 if (td->td_pri != pri) { 1306 KKASSERT(pri >= 0); 1307 crit_enter(); 1308 if (td->td_flags & TDF_RUNQ) { 1309 KKASSERT(td->td_gd == mycpu); 1310 _lwkt_dequeue(td); 1311 td->td_pri = pri; 1312 _lwkt_enqueue(td); 1313 } else { 1314 td->td_pri = pri; 1315 } 1316 crit_exit(); 1317 } 1318 } 1319 1320 /* 1321 * Set the initial priority for a thread prior to it being scheduled for 1322 * the first time. The thread MUST NOT be scheduled before or during 1323 * this call. The thread may be assigned to a cpu other then the current 1324 * cpu. 1325 * 1326 * Typically used after a thread has been created with TDF_STOPPREQ, 1327 * and before the thread is initially scheduled. 1328 */ 1329 void 1330 lwkt_setpri_initial(thread_t td, int pri) 1331 { 1332 KKASSERT(pri >= 0); 1333 KKASSERT((td->td_flags & TDF_RUNQ) == 0); 1334 td->td_pri = pri; 1335 } 1336 1337 void 1338 lwkt_setpri_self(int pri) 1339 { 1340 thread_t td = curthread; 1341 1342 KKASSERT(pri >= 0 && pri <= TDPRI_MAX); 1343 crit_enter(); 1344 if (td->td_flags & TDF_RUNQ) { 1345 _lwkt_dequeue(td); 1346 td->td_pri = pri; 1347 _lwkt_enqueue(td); 1348 } else { 1349 td->td_pri = pri; 1350 } 1351 crit_exit(); 1352 } 1353 1354 /* 1355 * hz tick scheduler clock for LWKT threads 1356 */ 1357 void 1358 lwkt_schedulerclock(thread_t td) 1359 { 1360 globaldata_t gd = td->td_gd; 1361 thread_t xtd; 1362 1363 if (TAILQ_FIRST(&gd->gd_tdrunq) == td) { 1364 /* 1365 * If the current thread is at the head of the runq shift it to the 1366 * end of any equal-priority threads and request a LWKT reschedule 1367 * if it moved. 1368 * 1369 * Ignore upri in this situation. There will only be one user thread 1370 * in user mode, all others will be user threads running in kernel 1371 * mode and we have to make sure they get some cpu. 1372 */ 1373 xtd = TAILQ_NEXT(td, td_threadq); 1374 if (xtd && xtd->td_pri == td->td_pri) { 1375 TAILQ_REMOVE(&gd->gd_tdrunq, td, td_threadq); 1376 while (xtd && xtd->td_pri == td->td_pri) 1377 xtd = TAILQ_NEXT(xtd, td_threadq); 1378 if (xtd) 1379 TAILQ_INSERT_BEFORE(xtd, td, td_threadq); 1380 else 1381 TAILQ_INSERT_TAIL(&gd->gd_tdrunq, td, td_threadq); 1382 need_lwkt_resched(); 1383 } 1384 } else { 1385 /* 1386 * If we scheduled a thread other than the one at the head of the 1387 * queue always request a reschedule every tick. 1388 */ 1389 need_lwkt_resched(); 1390 } 1391 } 1392 1393 /* 1394 * Migrate the current thread to the specified cpu. 1395 * 1396 * This is accomplished by descheduling ourselves from the current cpu 1397 * and setting td_migrate_gd. The lwkt_switch() code will detect that the 1398 * 'old' thread wants to migrate after it has been completely switched out 1399 * and will complete the migration. 1400 * 1401 * TDF_MIGRATING prevents scheduling races while the thread is being migrated. 1402 * 1403 * We must be sure to release our current process designation (if a user 1404 * process) before clearing out any tsleepq we are on because the release 1405 * code may re-add us. 1406 * 1407 * We must be sure to remove ourselves from the current cpu's tsleepq 1408 * before potentially moving to another queue. The thread can be on 1409 * a tsleepq due to a left-over tsleep_interlock(). 1410 */ 1411 1412 void 1413 lwkt_setcpu_self(globaldata_t rgd) 1414 { 1415 thread_t td = curthread; 1416 1417 if (td->td_gd != rgd) { 1418 crit_enter_quick(td); 1419 1420 if (td->td_release) 1421 td->td_release(td); 1422 if (td->td_flags & TDF_TSLEEPQ) 1423 tsleep_remove(td); 1424 1425 /* 1426 * Set TDF_MIGRATING to prevent a spurious reschedule while we are 1427 * trying to deschedule ourselves and switch away, then deschedule 1428 * ourself, remove us from tdallq, and set td_migrate_gd. Finally, 1429 * call lwkt_switch() to complete the operation. 1430 */ 1431 td->td_flags |= TDF_MIGRATING; 1432 lwkt_deschedule_self(td); 1433 TAILQ_REMOVE(&td->td_gd->gd_tdallq, td, td_allq); 1434 td->td_migrate_gd = rgd; 1435 lwkt_switch(); 1436 1437 /* 1438 * We are now on the target cpu 1439 */ 1440 KKASSERT(rgd == mycpu); 1441 TAILQ_INSERT_TAIL(&rgd->gd_tdallq, td, td_allq); 1442 crit_exit_quick(td); 1443 } 1444 } 1445 1446 void 1447 lwkt_migratecpu(int cpuid) 1448 { 1449 globaldata_t rgd; 1450 1451 rgd = globaldata_find(cpuid); 1452 lwkt_setcpu_self(rgd); 1453 } 1454 1455 /* 1456 * Remote IPI for cpu migration (called while in a critical section so we 1457 * do not have to enter another one). 1458 * 1459 * The thread (td) has already been completely descheduled from the 1460 * originating cpu and we can simply assert the case. The thread is 1461 * assigned to the new cpu and enqueued. 1462 * 1463 * The thread will re-add itself to tdallq when it resumes execution. 1464 */ 1465 static void 1466 lwkt_setcpu_remote(void *arg) 1467 { 1468 thread_t td = arg; 1469 globaldata_t gd = mycpu; 1470 1471 KKASSERT((td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK)) == 0); 1472 td->td_gd = gd; 1473 cpu_mfence(); 1474 td->td_flags &= ~TDF_MIGRATING; 1475 KKASSERT(td->td_migrate_gd == NULL); 1476 KKASSERT(td->td_lwp == NULL || 1477 (td->td_lwp->lwp_mpflags & LWP_MP_ONRUNQ) == 0); 1478 _lwkt_enqueue(td); 1479 } 1480 1481 struct lwp * 1482 lwkt_preempted_proc(void) 1483 { 1484 thread_t td = curthread; 1485 while (td->td_preempted) 1486 td = td->td_preempted; 1487 return(td->td_lwp); 1488 } 1489 1490 /* 1491 * Create a kernel process/thread/whatever. It shares it's address space 1492 * with proc0 - ie: kernel only. 1493 * 1494 * If the cpu is not specified one will be selected. In the future 1495 * specifying a cpu of -1 will enable kernel thread migration between 1496 * cpus. 1497 */ 1498 int 1499 lwkt_create(void (*func)(void *), void *arg, struct thread **tdp, 1500 thread_t template, int tdflags, int cpu, const char *fmt, ...) 1501 { 1502 thread_t td; 1503 __va_list ap; 1504 1505 td = lwkt_alloc_thread(template, LWKT_THREAD_STACK, cpu, 1506 tdflags); 1507 if (tdp) 1508 *tdp = td; 1509 cpu_set_thread_handler(td, lwkt_exit, func, arg); 1510 1511 /* 1512 * Set up arg0 for 'ps' etc 1513 */ 1514 __va_start(ap, fmt); 1515 kvsnprintf(td->td_comm, sizeof(td->td_comm), fmt, ap); 1516 __va_end(ap); 1517 1518 /* 1519 * Schedule the thread to run 1520 */ 1521 if (td->td_flags & TDF_NOSTART) 1522 td->td_flags &= ~TDF_NOSTART; 1523 else 1524 lwkt_schedule(td); 1525 return 0; 1526 } 1527 1528 /* 1529 * Destroy an LWKT thread. Warning! This function is not called when 1530 * a process exits, cpu_proc_exit() directly calls cpu_thread_exit() and 1531 * uses a different reaping mechanism. 1532 */ 1533 void 1534 lwkt_exit(void) 1535 { 1536 thread_t td = curthread; 1537 thread_t std; 1538 globaldata_t gd; 1539 1540 /* 1541 * Do any cleanup that might block here 1542 */ 1543 if (td->td_flags & TDF_VERBOSE) 1544 kprintf("kthread %p %s has exited\n", td, td->td_comm); 1545 biosched_done(td); 1546 dsched_exit_thread(td); 1547 1548 /* 1549 * Get us into a critical section to interlock gd_freetd and loop 1550 * until we can get it freed. 1551 * 1552 * We have to cache the current td in gd_freetd because objcache_put()ing 1553 * it would rip it out from under us while our thread is still active. 1554 * 1555 * We are the current thread so of course our own TDF_RUNNING bit will 1556 * be set, so unlike the lwp reap code we don't wait for it to clear. 1557 */ 1558 gd = mycpu; 1559 crit_enter_quick(td); 1560 for (;;) { 1561 if (td->td_refs) { 1562 tsleep(td, 0, "tdreap", 1); 1563 continue; 1564 } 1565 if ((std = gd->gd_freetd) != NULL) { 1566 KKASSERT((std->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK)) == 0); 1567 gd->gd_freetd = NULL; 1568 objcache_put(thread_cache, std); 1569 continue; 1570 } 1571 break; 1572 } 1573 1574 /* 1575 * Remove thread resources from kernel lists and deschedule us for 1576 * the last time. We cannot block after this point or we may end 1577 * up with a stale td on the tsleepq. 1578 * 1579 * None of this may block, the critical section is the only thing 1580 * protecting tdallq and the only thing preventing new lwkt_hold() 1581 * thread refs now. 1582 */ 1583 if (td->td_flags & TDF_TSLEEPQ) 1584 tsleep_remove(td); 1585 lwkt_deschedule_self(td); 1586 lwkt_remove_tdallq(td); 1587 KKASSERT(td->td_refs == 0); 1588 1589 /* 1590 * Final cleanup 1591 */ 1592 KKASSERT(gd->gd_freetd == NULL); 1593 if (td->td_flags & TDF_ALLOCATED_THREAD) 1594 gd->gd_freetd = td; 1595 cpu_thread_exit(); 1596 } 1597 1598 void 1599 lwkt_remove_tdallq(thread_t td) 1600 { 1601 KKASSERT(td->td_gd == mycpu); 1602 TAILQ_REMOVE(&td->td_gd->gd_tdallq, td, td_allq); 1603 } 1604 1605 /* 1606 * Code reduction and branch prediction improvements. Call/return 1607 * overhead on modern cpus often degenerates into 0 cycles due to 1608 * the cpu's branch prediction hardware and return pc cache. We 1609 * can take advantage of this by not inlining medium-complexity 1610 * functions and we can also reduce the branch prediction impact 1611 * by collapsing perfectly predictable branches into a single 1612 * procedure instead of duplicating it. 1613 * 1614 * Is any of this noticeable? Probably not, so I'll take the 1615 * smaller code size. 1616 */ 1617 void 1618 crit_exit_wrapper(__DEBUG_CRIT_ARG__) 1619 { 1620 _crit_exit(mycpu __DEBUG_CRIT_PASS_ARG__); 1621 } 1622 1623 void 1624 crit_panic(void) 1625 { 1626 thread_t td = curthread; 1627 int lcrit = td->td_critcount; 1628 1629 td->td_critcount = 0; 1630 panic("td_critcount is/would-go negative! %p %d", td, lcrit); 1631 /* NOT REACHED */ 1632 } 1633 1634 /* 1635 * Called from debugger/panic on cpus which have been stopped. We must still 1636 * process the IPIQ while stopped. 1637 * 1638 * If we are dumping also try to process any pending interrupts. This may 1639 * or may not work depending on the state of the cpu at the point it was 1640 * stopped. 1641 */ 1642 void 1643 lwkt_smp_stopped(void) 1644 { 1645 globaldata_t gd = mycpu; 1646 1647 if (dumping) { 1648 lwkt_process_ipiq(); 1649 --gd->gd_intr_nesting_level; 1650 splz(); 1651 ++gd->gd_intr_nesting_level; 1652 } else { 1653 lwkt_process_ipiq(); 1654 } 1655 } 1656