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 cpu_time.cp_stallpc = 0; 715 goto haveidle; 716 717 havethread: 718 /* 719 * Clear gd_idle_repeat when doing a normal switch to a non-idle 720 * thread. 721 */ 722 ntd->td_wmesg = NULL; 723 ntd->td_contended = 0; 724 ++gd->gd_cnt.v_swtch; 725 gd->gd_idle_repeat = 0; 726 727 havethread_preempted: 728 /* 729 * If the new target does not need the MP lock and we are holding it, 730 * release the MP lock. If the new target requires the MP lock we have 731 * already acquired it for the target. 732 */ 733 ; 734 haveidle: 735 KASSERT(ntd->td_critcount, 736 ("priority problem in lwkt_switch %d %d", 737 td->td_critcount, ntd->td_critcount)); 738 739 if (td != ntd) { 740 /* 741 * Execute the actual thread switch operation. This function 742 * returns to the current thread and returns the previous thread 743 * (which may be different from the thread we switched to). 744 * 745 * We are responsible for marking ntd as TDF_RUNNING. 746 */ 747 KKASSERT((ntd->td_flags & TDF_RUNNING) == 0); 748 ++switch_count; 749 KTR_LOG(ctxsw_sw, gd->gd_cpuid, ntd); 750 ntd->td_flags |= TDF_RUNNING; 751 lwkt_switch_return(td->td_switch(ntd)); 752 /* ntd invalid, td_switch() can return a different thread_t */ 753 } 754 755 /* 756 * catch-all. XXX is this strictly needed? 757 */ 758 splz_check(); 759 760 /* NOTE: current cpu may have changed after switch */ 761 crit_exit_quick(td); 762 } 763 764 /* 765 * Called by assembly in the td_switch (thread restore path) for thread 766 * bootstrap cases which do not 'return' to lwkt_switch(). 767 */ 768 void 769 lwkt_switch_return(thread_t otd) 770 { 771 globaldata_t rgd; 772 773 /* 774 * Check if otd was migrating. Now that we are on ntd we can finish 775 * up the migration. This is a bit messy but it is the only place 776 * where td is known to be fully descheduled. 777 * 778 * We can only activate the migration if otd was migrating but not 779 * held on the cpu due to a preemption chain. We still have to 780 * clear TDF_RUNNING on the old thread either way. 781 * 782 * We are responsible for clearing the previously running thread's 783 * TDF_RUNNING. 784 */ 785 if ((rgd = otd->td_migrate_gd) != NULL && 786 (otd->td_flags & TDF_PREEMPT_LOCK) == 0) { 787 KKASSERT((otd->td_flags & (TDF_MIGRATING | TDF_RUNNING)) == 788 (TDF_MIGRATING | TDF_RUNNING)); 789 otd->td_migrate_gd = NULL; 790 otd->td_flags &= ~TDF_RUNNING; 791 lwkt_send_ipiq(rgd, lwkt_setcpu_remote, otd); 792 } else { 793 otd->td_flags &= ~TDF_RUNNING; 794 } 795 796 /* 797 * Final exit validations (see lwp_wait()). Note that otd becomes 798 * invalid the *instant* we set TDF_MP_EXITSIG. 799 */ 800 while (otd->td_flags & TDF_EXITING) { 801 u_int mpflags; 802 803 mpflags = otd->td_mpflags; 804 cpu_ccfence(); 805 806 if (mpflags & TDF_MP_EXITWAIT) { 807 if (atomic_cmpset_int(&otd->td_mpflags, mpflags, 808 mpflags | TDF_MP_EXITSIG)) { 809 wakeup(otd); 810 break; 811 } 812 } else { 813 if (atomic_cmpset_int(&otd->td_mpflags, mpflags, 814 mpflags | TDF_MP_EXITSIG)) { 815 wakeup(otd); 816 break; 817 } 818 } 819 } 820 } 821 822 /* 823 * Request that the target thread preempt the current thread. Preemption 824 * can only occur if our only critical section is the one that we were called 825 * with, the relative priority of the target thread is higher, and the target 826 * thread holds no tokens. This also only works if we are not holding any 827 * spinlocks (obviously). 828 * 829 * THE CALLER OF LWKT_PREEMPT() MUST BE IN A CRITICAL SECTION. Typically 830 * this is called via lwkt_schedule() through the td_preemptable callback. 831 * critcount is the managed critical priority that we should ignore in order 832 * to determine whether preemption is possible (aka usually just the crit 833 * priority of lwkt_schedule() itself). 834 * 835 * Preemption is typically limited to interrupt threads. 836 * 837 * Operation works in a fairly straight-forward manner. The normal 838 * scheduling code is bypassed and we switch directly to the target 839 * thread. When the target thread attempts to block or switch away 840 * code at the base of lwkt_switch() will switch directly back to our 841 * thread. Our thread is able to retain whatever tokens it holds and 842 * if the target needs one of them the target will switch back to us 843 * and reschedule itself normally. 844 */ 845 void 846 lwkt_preempt(thread_t ntd, int critcount) 847 { 848 struct globaldata *gd = mycpu; 849 thread_t xtd; 850 thread_t td; 851 int save_gd_intr_nesting_level; 852 853 /* 854 * The caller has put us in a critical section. We can only preempt 855 * if the caller of the caller was not in a critical section (basically 856 * a local interrupt), as determined by the 'critcount' parameter. We 857 * also can't preempt if the caller is holding any spinlocks (even if 858 * he isn't in a critical section). This also handles the tokens test. 859 * 860 * YYY The target thread must be in a critical section (else it must 861 * inherit our critical section? I dunno yet). 862 */ 863 KASSERT(ntd->td_critcount, ("BADCRIT0 %d", ntd->td_pri)); 864 865 td = gd->gd_curthread; 866 if (preempt_enable == 0) { 867 ++preempt_miss; 868 return; 869 } 870 if (ntd->td_pri <= td->td_pri) { 871 ++preempt_miss; 872 return; 873 } 874 if (td->td_critcount > critcount) { 875 ++preempt_miss; 876 return; 877 } 878 if (td->td_cscount) { 879 ++preempt_miss; 880 return; 881 } 882 if (ntd->td_gd != gd) { 883 ++preempt_miss; 884 return; 885 } 886 /* 887 * We don't have to check spinlocks here as they will also bump 888 * td_critcount. 889 * 890 * Do not try to preempt if the target thread is holding any tokens. 891 * We could try to acquire the tokens but this case is so rare there 892 * is no need to support it. 893 */ 894 KKASSERT(gd->gd_spinlocks == 0); 895 896 if (TD_TOKS_HELD(ntd)) { 897 ++preempt_miss; 898 return; 899 } 900 if (td == ntd || ((td->td_flags | ntd->td_flags) & TDF_PREEMPT_LOCK)) { 901 ++preempt_weird; 902 return; 903 } 904 if (ntd->td_preempted) { 905 ++preempt_hit; 906 return; 907 } 908 KKASSERT(gd->gd_processing_ipiq == 0); 909 910 /* 911 * Since we are able to preempt the current thread, there is no need to 912 * call need_lwkt_resched(). 913 * 914 * We must temporarily clear gd_intr_nesting_level around the switch 915 * since switchouts from the target thread are allowed (they will just 916 * return to our thread), and since the target thread has its own stack. 917 * 918 * A preemption must switch back to the original thread, assert the 919 * case. 920 */ 921 ++preempt_hit; 922 ntd->td_preempted = td; 923 td->td_flags |= TDF_PREEMPT_LOCK; 924 KTR_LOG(ctxsw_pre, gd->gd_cpuid, ntd); 925 save_gd_intr_nesting_level = gd->gd_intr_nesting_level; 926 gd->gd_intr_nesting_level = 0; 927 928 KKASSERT((ntd->td_flags & TDF_RUNNING) == 0); 929 ntd->td_flags |= TDF_RUNNING; 930 xtd = td->td_switch(ntd); 931 KKASSERT(xtd == ntd); 932 lwkt_switch_return(xtd); 933 gd->gd_intr_nesting_level = save_gd_intr_nesting_level; 934 935 KKASSERT(ntd->td_preempted && (td->td_flags & TDF_PREEMPT_DONE)); 936 ntd->td_preempted = NULL; 937 td->td_flags &= ~(TDF_PREEMPT_LOCK|TDF_PREEMPT_DONE); 938 } 939 940 /* 941 * Conditionally call splz() if gd_reqflags indicates work is pending. 942 * This will work inside a critical section but not inside a hard code 943 * section. 944 * 945 * (self contained on a per cpu basis) 946 */ 947 void 948 splz_check(void) 949 { 950 globaldata_t gd = mycpu; 951 thread_t td = gd->gd_curthread; 952 953 if ((gd->gd_reqflags & RQF_IDLECHECK_MASK) && 954 gd->gd_intr_nesting_level == 0 && 955 td->td_nest_count < 2) 956 { 957 splz(); 958 } 959 } 960 961 /* 962 * This version is integrated into crit_exit, reqflags has already 963 * been tested but td_critcount has not. 964 * 965 * We only want to execute the splz() on the 1->0 transition of 966 * critcount and not in a hard code section or if too deeply nested. 967 * 968 * NOTE: gd->gd_spinlocks is implied to be 0 when td_critcount is 0. 969 */ 970 void 971 lwkt_maybe_splz(thread_t td) 972 { 973 globaldata_t gd = td->td_gd; 974 975 if (td->td_critcount == 0 && 976 gd->gd_intr_nesting_level == 0 && 977 td->td_nest_count < 2) 978 { 979 splz(); 980 } 981 } 982 983 /* 984 * Drivers which set up processing co-threads can call this function to 985 * run the co-thread at a higher priority and to allow it to preempt 986 * normal threads. 987 */ 988 void 989 lwkt_set_interrupt_support_thread(void) 990 { 991 thread_t td = curthread; 992 993 lwkt_setpri_self(TDPRI_INT_SUPPORT); 994 td->td_flags |= TDF_INTTHREAD; 995 td->td_preemptable = lwkt_preempt; 996 } 997 998 999 /* 1000 * This function is used to negotiate a passive release of the current 1001 * process/lwp designation with the user scheduler, allowing the user 1002 * scheduler to schedule another user thread. The related kernel thread 1003 * (curthread) continues running in the released state. 1004 */ 1005 void 1006 lwkt_passive_release(struct thread *td) 1007 { 1008 struct lwp *lp = td->td_lwp; 1009 1010 td->td_release = NULL; 1011 lwkt_setpri_self(TDPRI_KERN_USER); 1012 1013 lp->lwp_proc->p_usched->release_curproc(lp); 1014 } 1015 1016 1017 /* 1018 * This implements a LWKT yield, allowing a kernel thread to yield to other 1019 * kernel threads at the same or higher priority. This function can be 1020 * called in a tight loop and will typically only yield once per tick. 1021 * 1022 * Most kernel threads run at the same priority in order to allow equal 1023 * sharing. 1024 * 1025 * (self contained on a per cpu basis) 1026 */ 1027 void 1028 lwkt_yield(void) 1029 { 1030 globaldata_t gd = mycpu; 1031 thread_t td = gd->gd_curthread; 1032 1033 if ((gd->gd_reqflags & RQF_IDLECHECK_MASK) && td->td_nest_count < 2) 1034 splz(); 1035 if (lwkt_resched_wanted()) { 1036 lwkt_schedule_self(curthread); 1037 lwkt_switch(); 1038 } 1039 } 1040 1041 /* 1042 * The quick version processes pending interrupts and higher-priority 1043 * LWKT threads but will not round-robin same-priority LWKT threads. 1044 * 1045 * When called while attempting to return to userland the only same-pri 1046 * threads are the ones which have already tried to become the current 1047 * user process. 1048 */ 1049 void 1050 lwkt_yield_quick(void) 1051 { 1052 globaldata_t gd = mycpu; 1053 thread_t td = gd->gd_curthread; 1054 1055 if ((gd->gd_reqflags & RQF_IDLECHECK_MASK) && td->td_nest_count < 2) 1056 splz(); 1057 if (lwkt_resched_wanted()) { 1058 crit_enter(); 1059 if (TAILQ_FIRST(&gd->gd_tdrunq) == td) { 1060 clear_lwkt_resched(); 1061 } else { 1062 lwkt_schedule_self(curthread); 1063 lwkt_switch(); 1064 } 1065 crit_exit(); 1066 } 1067 } 1068 1069 /* 1070 * This yield is designed for kernel threads with a user context. 1071 * 1072 * The kernel acting on behalf of the user is potentially cpu-bound, 1073 * this function will efficiently allow other threads to run and also 1074 * switch to other processes by releasing. 1075 * 1076 * The lwkt_user_yield() function is designed to have very low overhead 1077 * if no yield is determined to be needed. 1078 */ 1079 void 1080 lwkt_user_yield(void) 1081 { 1082 globaldata_t gd = mycpu; 1083 thread_t td = gd->gd_curthread; 1084 1085 /* 1086 * Always run any pending interrupts in case we are in a critical 1087 * section. 1088 */ 1089 if ((gd->gd_reqflags & RQF_IDLECHECK_MASK) && td->td_nest_count < 2) 1090 splz(); 1091 1092 /* 1093 * Switch (which forces a release) if another kernel thread needs 1094 * the cpu, if userland wants us to resched, or if our kernel 1095 * quantum has run out. 1096 */ 1097 if (lwkt_resched_wanted() || 1098 user_resched_wanted()) 1099 { 1100 lwkt_switch(); 1101 } 1102 1103 #if 0 1104 /* 1105 * Reacquire the current process if we are released. 1106 * 1107 * XXX not implemented atm. The kernel may be holding locks and such, 1108 * so we want the thread to continue to receive cpu. 1109 */ 1110 if (td->td_release == NULL && lp) { 1111 lp->lwp_proc->p_usched->acquire_curproc(lp); 1112 td->td_release = lwkt_passive_release; 1113 lwkt_setpri_self(TDPRI_USER_NORM); 1114 } 1115 #endif 1116 } 1117 1118 /* 1119 * Generic schedule. Possibly schedule threads belonging to other cpus and 1120 * deal with threads that might be blocked on a wait queue. 1121 * 1122 * We have a little helper inline function which does additional work after 1123 * the thread has been enqueued, including dealing with preemption and 1124 * setting need_lwkt_resched() (which prevents the kernel from returning 1125 * to userland until it has processed higher priority threads). 1126 * 1127 * It is possible for this routine to be called after a failed _enqueue 1128 * (due to the target thread migrating, sleeping, or otherwise blocked). 1129 * We have to check that the thread is actually on the run queue! 1130 */ 1131 static __inline 1132 void 1133 _lwkt_schedule_post(globaldata_t gd, thread_t ntd, int ccount) 1134 { 1135 if (ntd->td_flags & TDF_RUNQ) { 1136 if (ntd->td_preemptable) { 1137 ntd->td_preemptable(ntd, ccount); /* YYY +token */ 1138 } 1139 } 1140 } 1141 1142 static __inline 1143 void 1144 _lwkt_schedule(thread_t td) 1145 { 1146 globaldata_t mygd = mycpu; 1147 1148 KASSERT(td != &td->td_gd->gd_idlethread, 1149 ("lwkt_schedule(): scheduling gd_idlethread is illegal!")); 1150 KKASSERT((td->td_flags & TDF_MIGRATING) == 0); 1151 crit_enter_gd(mygd); 1152 KKASSERT(td->td_lwp == NULL || 1153 (td->td_lwp->lwp_mpflags & LWP_MP_ONRUNQ) == 0); 1154 1155 if (td == mygd->gd_curthread) { 1156 _lwkt_enqueue(td); 1157 } else { 1158 /* 1159 * If we own the thread, there is no race (since we are in a 1160 * critical section). If we do not own the thread there might 1161 * be a race but the target cpu will deal with it. 1162 */ 1163 if (td->td_gd == mygd) { 1164 _lwkt_enqueue(td); 1165 _lwkt_schedule_post(mygd, td, 1); 1166 } else { 1167 lwkt_send_ipiq3(td->td_gd, lwkt_schedule_remote, td, 0); 1168 } 1169 } 1170 crit_exit_gd(mygd); 1171 } 1172 1173 void 1174 lwkt_schedule(thread_t td) 1175 { 1176 _lwkt_schedule(td); 1177 } 1178 1179 void 1180 lwkt_schedule_noresched(thread_t td) /* XXX not impl */ 1181 { 1182 _lwkt_schedule(td); 1183 } 1184 1185 /* 1186 * When scheduled remotely if frame != NULL the IPIQ is being 1187 * run via doreti or an interrupt then preemption can be allowed. 1188 * 1189 * To allow preemption we have to drop the critical section so only 1190 * one is present in _lwkt_schedule_post. 1191 */ 1192 static void 1193 lwkt_schedule_remote(void *arg, int arg2, struct intrframe *frame) 1194 { 1195 thread_t td = curthread; 1196 thread_t ntd = arg; 1197 1198 if (frame && ntd->td_preemptable) { 1199 crit_exit_noyield(td); 1200 _lwkt_schedule(ntd); 1201 crit_enter_quick(td); 1202 } else { 1203 _lwkt_schedule(ntd); 1204 } 1205 } 1206 1207 /* 1208 * Thread migration using a 'Pull' method. The thread may or may not be 1209 * the current thread. It MUST be descheduled and in a stable state. 1210 * lwkt_giveaway() must be called on the cpu owning the thread. 1211 * 1212 * At any point after lwkt_giveaway() is called, the target cpu may 1213 * 'pull' the thread by calling lwkt_acquire(). 1214 * 1215 * We have to make sure the thread is not sitting on a per-cpu tsleep 1216 * queue or it will blow up when it moves to another cpu. 1217 * 1218 * MPSAFE - must be called under very specific conditions. 1219 */ 1220 void 1221 lwkt_giveaway(thread_t td) 1222 { 1223 globaldata_t gd = mycpu; 1224 1225 crit_enter_gd(gd); 1226 if (td->td_flags & TDF_TSLEEPQ) 1227 tsleep_remove(td); 1228 KKASSERT(td->td_gd == gd); 1229 TAILQ_REMOVE(&gd->gd_tdallq, td, td_allq); 1230 td->td_flags |= TDF_MIGRATING; 1231 crit_exit_gd(gd); 1232 } 1233 1234 void 1235 lwkt_acquire(thread_t td) 1236 { 1237 globaldata_t gd; 1238 globaldata_t mygd; 1239 int retry = 10000000; 1240 1241 KKASSERT(td->td_flags & TDF_MIGRATING); 1242 gd = td->td_gd; 1243 mygd = mycpu; 1244 if (gd != mycpu) { 1245 cpu_lfence(); 1246 KKASSERT((td->td_flags & TDF_RUNQ) == 0); 1247 crit_enter_gd(mygd); 1248 DEBUG_PUSH_INFO("lwkt_acquire"); 1249 while (td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK)) { 1250 lwkt_process_ipiq(); 1251 cpu_lfence(); 1252 if (--retry == 0) { 1253 kprintf("lwkt_acquire: stuck: td %p td->td_flags %08x\n", 1254 td, td->td_flags); 1255 retry = 10000000; 1256 } 1257 #ifdef _KERNEL_VIRTUAL 1258 pthread_yield(); 1259 #endif 1260 } 1261 DEBUG_POP_INFO(); 1262 cpu_mfence(); 1263 td->td_gd = mygd; 1264 TAILQ_INSERT_TAIL(&mygd->gd_tdallq, td, td_allq); 1265 td->td_flags &= ~TDF_MIGRATING; 1266 crit_exit_gd(mygd); 1267 } else { 1268 crit_enter_gd(mygd); 1269 TAILQ_INSERT_TAIL(&mygd->gd_tdallq, td, td_allq); 1270 td->td_flags &= ~TDF_MIGRATING; 1271 crit_exit_gd(mygd); 1272 } 1273 } 1274 1275 /* 1276 * Generic deschedule. Descheduling threads other then your own should be 1277 * done only in carefully controlled circumstances. Descheduling is 1278 * asynchronous. 1279 * 1280 * This function may block if the cpu has run out of messages. 1281 */ 1282 void 1283 lwkt_deschedule(thread_t td) 1284 { 1285 crit_enter(); 1286 if (td == curthread) { 1287 _lwkt_dequeue(td); 1288 } else { 1289 if (td->td_gd == mycpu) { 1290 _lwkt_dequeue(td); 1291 } else { 1292 lwkt_send_ipiq(td->td_gd, (ipifunc1_t)lwkt_deschedule, td); 1293 } 1294 } 1295 crit_exit(); 1296 } 1297 1298 /* 1299 * Set the target thread's priority. This routine does not automatically 1300 * switch to a higher priority thread, LWKT threads are not designed for 1301 * continuous priority changes. Yield if you want to switch. 1302 */ 1303 void 1304 lwkt_setpri(thread_t td, int pri) 1305 { 1306 if (td->td_pri != pri) { 1307 KKASSERT(pri >= 0); 1308 crit_enter(); 1309 if (td->td_flags & TDF_RUNQ) { 1310 KKASSERT(td->td_gd == mycpu); 1311 _lwkt_dequeue(td); 1312 td->td_pri = pri; 1313 _lwkt_enqueue(td); 1314 } else { 1315 td->td_pri = pri; 1316 } 1317 crit_exit(); 1318 } 1319 } 1320 1321 /* 1322 * Set the initial priority for a thread prior to it being scheduled for 1323 * the first time. The thread MUST NOT be scheduled before or during 1324 * this call. The thread may be assigned to a cpu other then the current 1325 * cpu. 1326 * 1327 * Typically used after a thread has been created with TDF_STOPPREQ, 1328 * and before the thread is initially scheduled. 1329 */ 1330 void 1331 lwkt_setpri_initial(thread_t td, int pri) 1332 { 1333 KKASSERT(pri >= 0); 1334 KKASSERT((td->td_flags & TDF_RUNQ) == 0); 1335 td->td_pri = pri; 1336 } 1337 1338 void 1339 lwkt_setpri_self(int pri) 1340 { 1341 thread_t td = curthread; 1342 1343 KKASSERT(pri >= 0 && pri <= TDPRI_MAX); 1344 crit_enter(); 1345 if (td->td_flags & TDF_RUNQ) { 1346 _lwkt_dequeue(td); 1347 td->td_pri = pri; 1348 _lwkt_enqueue(td); 1349 } else { 1350 td->td_pri = pri; 1351 } 1352 crit_exit(); 1353 } 1354 1355 /* 1356 * hz tick scheduler clock for LWKT threads 1357 */ 1358 void 1359 lwkt_schedulerclock(thread_t td) 1360 { 1361 globaldata_t gd = td->td_gd; 1362 thread_t xtd; 1363 1364 if (TAILQ_FIRST(&gd->gd_tdrunq) == td) { 1365 /* 1366 * If the current thread is at the head of the runq shift it to the 1367 * end of any equal-priority threads and request a LWKT reschedule 1368 * if it moved. 1369 * 1370 * Ignore upri in this situation. There will only be one user thread 1371 * in user mode, all others will be user threads running in kernel 1372 * mode and we have to make sure they get some cpu. 1373 */ 1374 xtd = TAILQ_NEXT(td, td_threadq); 1375 if (xtd && xtd->td_pri == td->td_pri) { 1376 TAILQ_REMOVE(&gd->gd_tdrunq, td, td_threadq); 1377 while (xtd && xtd->td_pri == td->td_pri) 1378 xtd = TAILQ_NEXT(xtd, td_threadq); 1379 if (xtd) 1380 TAILQ_INSERT_BEFORE(xtd, td, td_threadq); 1381 else 1382 TAILQ_INSERT_TAIL(&gd->gd_tdrunq, td, td_threadq); 1383 need_lwkt_resched(); 1384 } 1385 } else { 1386 /* 1387 * If we scheduled a thread other than the one at the head of the 1388 * queue always request a reschedule every tick. 1389 */ 1390 need_lwkt_resched(); 1391 } 1392 } 1393 1394 /* 1395 * Migrate the current thread to the specified cpu. 1396 * 1397 * This is accomplished by descheduling ourselves from the current cpu 1398 * and setting td_migrate_gd. The lwkt_switch() code will detect that the 1399 * 'old' thread wants to migrate after it has been completely switched out 1400 * and will complete the migration. 1401 * 1402 * TDF_MIGRATING prevents scheduling races while the thread is being migrated. 1403 * 1404 * We must be sure to release our current process designation (if a user 1405 * process) before clearing out any tsleepq we are on because the release 1406 * code may re-add us. 1407 * 1408 * We must be sure to remove ourselves from the current cpu's tsleepq 1409 * before potentially moving to another queue. The thread can be on 1410 * a tsleepq due to a left-over tsleep_interlock(). 1411 */ 1412 1413 void 1414 lwkt_setcpu_self(globaldata_t rgd) 1415 { 1416 thread_t td = curthread; 1417 1418 if (td->td_gd != rgd) { 1419 crit_enter_quick(td); 1420 1421 if (td->td_release) 1422 td->td_release(td); 1423 if (td->td_flags & TDF_TSLEEPQ) 1424 tsleep_remove(td); 1425 1426 /* 1427 * Set TDF_MIGRATING to prevent a spurious reschedule while we are 1428 * trying to deschedule ourselves and switch away, then deschedule 1429 * ourself, remove us from tdallq, and set td_migrate_gd. Finally, 1430 * call lwkt_switch() to complete the operation. 1431 */ 1432 td->td_flags |= TDF_MIGRATING; 1433 lwkt_deschedule_self(td); 1434 TAILQ_REMOVE(&td->td_gd->gd_tdallq, td, td_allq); 1435 td->td_migrate_gd = rgd; 1436 lwkt_switch(); 1437 1438 /* 1439 * We are now on the target cpu 1440 */ 1441 KKASSERT(rgd == mycpu); 1442 TAILQ_INSERT_TAIL(&rgd->gd_tdallq, td, td_allq); 1443 crit_exit_quick(td); 1444 } 1445 } 1446 1447 void 1448 lwkt_migratecpu(int cpuid) 1449 { 1450 globaldata_t rgd; 1451 1452 rgd = globaldata_find(cpuid); 1453 lwkt_setcpu_self(rgd); 1454 } 1455 1456 /* 1457 * Remote IPI for cpu migration (called while in a critical section so we 1458 * do not have to enter another one). 1459 * 1460 * The thread (td) has already been completely descheduled from the 1461 * originating cpu and we can simply assert the case. The thread is 1462 * assigned to the new cpu and enqueued. 1463 * 1464 * The thread will re-add itself to tdallq when it resumes execution. 1465 */ 1466 static void 1467 lwkt_setcpu_remote(void *arg) 1468 { 1469 thread_t td = arg; 1470 globaldata_t gd = mycpu; 1471 1472 KKASSERT((td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK)) == 0); 1473 td->td_gd = gd; 1474 cpu_mfence(); 1475 td->td_flags &= ~TDF_MIGRATING; 1476 KKASSERT(td->td_migrate_gd == NULL); 1477 KKASSERT(td->td_lwp == NULL || 1478 (td->td_lwp->lwp_mpflags & LWP_MP_ONRUNQ) == 0); 1479 _lwkt_enqueue(td); 1480 } 1481 1482 struct lwp * 1483 lwkt_preempted_proc(void) 1484 { 1485 thread_t td = curthread; 1486 while (td->td_preempted) 1487 td = td->td_preempted; 1488 return(td->td_lwp); 1489 } 1490 1491 /* 1492 * Create a kernel process/thread/whatever. It shares it's address space 1493 * with proc0 - ie: kernel only. 1494 * 1495 * If the cpu is not specified one will be selected. In the future 1496 * specifying a cpu of -1 will enable kernel thread migration between 1497 * cpus. 1498 */ 1499 int 1500 lwkt_create(void (*func)(void *), void *arg, struct thread **tdp, 1501 thread_t template, int tdflags, int cpu, const char *fmt, ...) 1502 { 1503 thread_t td; 1504 __va_list ap; 1505 1506 td = lwkt_alloc_thread(template, LWKT_THREAD_STACK, cpu, 1507 tdflags); 1508 if (tdp) 1509 *tdp = td; 1510 cpu_set_thread_handler(td, lwkt_exit, func, arg); 1511 1512 /* 1513 * Set up arg0 for 'ps' etc 1514 */ 1515 __va_start(ap, fmt); 1516 kvsnprintf(td->td_comm, sizeof(td->td_comm), fmt, ap); 1517 __va_end(ap); 1518 1519 /* 1520 * Schedule the thread to run 1521 */ 1522 if (td->td_flags & TDF_NOSTART) 1523 td->td_flags &= ~TDF_NOSTART; 1524 else 1525 lwkt_schedule(td); 1526 return 0; 1527 } 1528 1529 /* 1530 * Destroy an LWKT thread. Warning! This function is not called when 1531 * a process exits, cpu_proc_exit() directly calls cpu_thread_exit() and 1532 * uses a different reaping mechanism. 1533 */ 1534 void 1535 lwkt_exit(void) 1536 { 1537 thread_t td = curthread; 1538 thread_t std; 1539 globaldata_t gd; 1540 1541 /* 1542 * Do any cleanup that might block here 1543 */ 1544 if (td->td_flags & TDF_VERBOSE) 1545 kprintf("kthread %p %s has exited\n", td, td->td_comm); 1546 biosched_done(td); 1547 dsched_exit_thread(td); 1548 1549 /* 1550 * Get us into a critical section to interlock gd_freetd and loop 1551 * until we can get it freed. 1552 * 1553 * We have to cache the current td in gd_freetd because objcache_put()ing 1554 * it would rip it out from under us while our thread is still active. 1555 * 1556 * We are the current thread so of course our own TDF_RUNNING bit will 1557 * be set, so unlike the lwp reap code we don't wait for it to clear. 1558 */ 1559 gd = mycpu; 1560 crit_enter_quick(td); 1561 for (;;) { 1562 if (td->td_refs) { 1563 tsleep(td, 0, "tdreap", 1); 1564 continue; 1565 } 1566 if ((std = gd->gd_freetd) != NULL) { 1567 KKASSERT((std->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK)) == 0); 1568 gd->gd_freetd = NULL; 1569 objcache_put(thread_cache, std); 1570 continue; 1571 } 1572 break; 1573 } 1574 1575 /* 1576 * Remove thread resources from kernel lists and deschedule us for 1577 * the last time. We cannot block after this point or we may end 1578 * up with a stale td on the tsleepq. 1579 * 1580 * None of this may block, the critical section is the only thing 1581 * protecting tdallq and the only thing preventing new lwkt_hold() 1582 * thread refs now. 1583 */ 1584 if (td->td_flags & TDF_TSLEEPQ) 1585 tsleep_remove(td); 1586 lwkt_deschedule_self(td); 1587 lwkt_remove_tdallq(td); 1588 KKASSERT(td->td_refs == 0); 1589 1590 /* 1591 * Final cleanup 1592 */ 1593 KKASSERT(gd->gd_freetd == NULL); 1594 if (td->td_flags & TDF_ALLOCATED_THREAD) 1595 gd->gd_freetd = td; 1596 cpu_thread_exit(); 1597 } 1598 1599 void 1600 lwkt_remove_tdallq(thread_t td) 1601 { 1602 KKASSERT(td->td_gd == mycpu); 1603 TAILQ_REMOVE(&td->td_gd->gd_tdallq, td, td_allq); 1604 } 1605 1606 /* 1607 * Code reduction and branch prediction improvements. Call/return 1608 * overhead on modern cpus often degenerates into 0 cycles due to 1609 * the cpu's branch prediction hardware and return pc cache. We 1610 * can take advantage of this by not inlining medium-complexity 1611 * functions and we can also reduce the branch prediction impact 1612 * by collapsing perfectly predictable branches into a single 1613 * procedure instead of duplicating it. 1614 * 1615 * Is any of this noticeable? Probably not, so I'll take the 1616 * smaller code size. 1617 */ 1618 void 1619 crit_exit_wrapper(__DEBUG_CRIT_ARG__) 1620 { 1621 _crit_exit(mycpu __DEBUG_CRIT_PASS_ARG__); 1622 } 1623 1624 void 1625 crit_panic(void) 1626 { 1627 thread_t td = curthread; 1628 int lcrit = td->td_critcount; 1629 1630 td->td_critcount = 0; 1631 panic("td_critcount is/would-go negative! %p %d", td, lcrit); 1632 /* NOT REACHED */ 1633 } 1634 1635 /* 1636 * Called from debugger/panic on cpus which have been stopped. We must still 1637 * process the IPIQ while stopped. 1638 * 1639 * If we are dumping also try to process any pending interrupts. This may 1640 * or may not work depending on the state of the cpu at the point it was 1641 * stopped. 1642 */ 1643 void 1644 lwkt_smp_stopped(void) 1645 { 1646 globaldata_t gd = mycpu; 1647 1648 if (dumping) { 1649 lwkt_process_ipiq(); 1650 --gd->gd_intr_nesting_level; 1651 splz(); 1652 ++gd->gd_intr_nesting_level; 1653 } else { 1654 lwkt_process_ipiq(); 1655 } 1656 } 1657