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/malloc.h> 49 #include <sys/queue.h> 50 #include <sys/sysctl.h> 51 #include <sys/kthread.h> 52 #include <machine/cpu.h> 53 #include <sys/lock.h> 54 #include <sys/spinlock.h> 55 #include <sys/ktr.h> 56 #include <sys/indefinite.h> 57 58 #include <sys/thread2.h> 59 #include <sys/spinlock2.h> 60 #include <sys/indefinite2.h> 61 62 #include <sys/dsched.h> 63 64 #include <vm/vm.h> 65 #include <vm/vm_param.h> 66 #include <vm/vm_kern.h> 67 #include <vm/vm_object.h> 68 #include <vm/vm_page.h> 69 #include <vm/vm_map.h> 70 #include <vm/vm_pager.h> 71 #include <vm/vm_extern.h> 72 73 #include <machine/stdarg.h> 74 #include <machine/smp.h> 75 #include <machine/clock.h> 76 77 #define LOOPMASK 78 79 #if !defined(KTR_CTXSW) 80 #define KTR_CTXSW KTR_ALL 81 #endif 82 KTR_INFO_MASTER(ctxsw); 83 KTR_INFO(KTR_CTXSW, ctxsw, sw, 0, "#cpu[%d].td = %p", int cpu, struct thread *td); 84 KTR_INFO(KTR_CTXSW, ctxsw, pre, 1, "#cpu[%d].td = %p", int cpu, struct thread *td); 85 KTR_INFO(KTR_CTXSW, ctxsw, newtd, 2, "#threads[%p].name = %s", struct thread *td, char *comm); 86 KTR_INFO(KTR_CTXSW, ctxsw, deadtd, 3, "#threads[%p].name = <dead>", struct thread *td); 87 88 static MALLOC_DEFINE(M_THREAD, "thread", "lwkt threads"); 89 MALLOC_DEFINE(M_FPUCTX, "fpuctx", "kernel FPU contexts"); 90 91 #ifdef INVARIANTS 92 static int panic_on_cscount = 0; 93 #endif 94 #ifdef DEBUG_LWKT_THREAD 95 static int64_t switch_count = 0; 96 static int64_t preempt_hit = 0; 97 static int64_t preempt_miss = 0; 98 static int64_t preempt_weird = 0; 99 #endif 100 static int lwkt_use_spin_port; 101 __read_mostly static struct objcache *thread_cache; 102 int cpu_mwait_spin = 0; 103 104 static void lwkt_schedule_remote(void *arg, int arg2, struct intrframe *frame); 105 static void lwkt_setcpu_remote(void *arg); 106 107 /* 108 * We can make all thread ports use the spin backend instead of the thread 109 * backend. This should only be set to debug the spin backend. 110 */ 111 TUNABLE_INT("lwkt.use_spin_port", &lwkt_use_spin_port); 112 113 #ifdef INVARIANTS 114 SYSCTL_INT(_lwkt, OID_AUTO, panic_on_cscount, CTLFLAG_RW, &panic_on_cscount, 0, 115 "Panic if attempting to switch lwkt's while mastering cpusync"); 116 #endif 117 #ifdef DEBUG_LWKT_THREAD 118 SYSCTL_QUAD(_lwkt, OID_AUTO, switch_count, CTLFLAG_RW, &switch_count, 0, 119 "Number of switched threads"); 120 SYSCTL_QUAD(_lwkt, OID_AUTO, preempt_hit, CTLFLAG_RW, &preempt_hit, 0, 121 "Successful preemption events"); 122 SYSCTL_QUAD(_lwkt, OID_AUTO, preempt_miss, CTLFLAG_RW, &preempt_miss, 0, 123 "Failed preemption events"); 124 SYSCTL_QUAD(_lwkt, OID_AUTO, preempt_weird, CTLFLAG_RW, &preempt_weird, 0, 125 "Number of preempted threads."); 126 #endif 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 __read_mostly static u_int lwkt_spin_loops = 10; 132 SYSCTL_UINT(_lwkt, OID_AUTO, spin_loops, CTLFLAG_RW, 133 &lwkt_spin_loops, 0, "Scheduler spin loops until sorted decon"); 134 __read_mostly 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 * We scan the queue in both directions to help deal with degenerate 174 * situations when hundreds or thousands (or more) threads are runnable. 175 * 176 * NOTE: lwkt_schedulerclock() will force a round-robin based on td_pri and 177 * will ignore user priority. This is to ensure that user threads in 178 * kernel mode get cpu at some point regardless of what the user 179 * scheduler thinks. 180 */ 181 static __inline 182 void 183 _lwkt_enqueue(thread_t td) 184 { 185 thread_t xtd; /* forward scan */ 186 thread_t rtd; /* reverse scan */ 187 188 if ((td->td_flags & (TDF_RUNQ|TDF_MIGRATING|TDF_BLOCKQ)) == 0) { 189 struct globaldata *gd = td->td_gd; 190 191 td->td_flags |= TDF_RUNQ; 192 xtd = TAILQ_FIRST(&gd->gd_tdrunq); 193 if (xtd == NULL) { 194 TAILQ_INSERT_TAIL(&gd->gd_tdrunq, td, td_threadq); 195 atomic_set_int(&gd->gd_reqflags, RQF_RUNNING); 196 } else { 197 /* 198 * NOTE: td_upri - higher numbers more desireable, same sense 199 * as td_pri (typically reversed from lwp_upri). 200 * 201 * In the equal priority case we want the best selection 202 * at the beginning so the less desireable selections know 203 * that they have to setrunqueue/go-to-another-cpu, even 204 * though it means switching back to the 'best' selection. 205 * This also avoids degenerate situations when many threads 206 * are runnable or waking up at the same time. 207 * 208 * If upri matches exactly place at end/round-robin. 209 */ 210 rtd = TAILQ_LAST(&gd->gd_tdrunq, lwkt_queue); 211 212 while (xtd && 213 (xtd->td_pri > td->td_pri || 214 (xtd->td_pri == td->td_pri && 215 xtd->td_upri >= td->td_upri))) { 216 xtd = TAILQ_NEXT(xtd, td_threadq); 217 218 /* 219 * Doing a reverse scan at the same time is an optimization 220 * for the insert-closer-to-tail case that avoids having to 221 * scan the entire list. This situation can occur when 222 * thousands of threads are woken up at the same time. 223 */ 224 if (rtd->td_pri > td->td_pri || 225 (rtd->td_pri == td->td_pri && 226 rtd->td_upri >= td->td_upri)) { 227 TAILQ_INSERT_AFTER(&gd->gd_tdrunq, rtd, td, td_threadq); 228 goto skip; 229 } 230 rtd = TAILQ_PREV(rtd, lwkt_queue, td_threadq); 231 } 232 if (xtd) 233 TAILQ_INSERT_BEFORE(xtd, td, td_threadq); 234 else 235 TAILQ_INSERT_TAIL(&gd->gd_tdrunq, td, td_threadq); 236 } 237 skip: 238 ++gd->gd_tdrunqcount; 239 240 /* 241 * Request a LWKT reschedule if we are now at the head of the queue. 242 */ 243 if (TAILQ_FIRST(&gd->gd_tdrunq) == td) 244 need_lwkt_resched(); 245 } 246 } 247 248 static boolean_t 249 _lwkt_thread_ctor(void *obj, void *privdata, int ocflags) 250 { 251 struct thread *td = (struct thread *)obj; 252 253 td->td_kstack = NULL; 254 td->td_kstack_size = 0; 255 td->td_flags = TDF_ALLOCATED_THREAD; 256 td->td_mpflags = 0; 257 return (1); 258 } 259 260 static void 261 _lwkt_thread_dtor(void *obj, void *privdata) 262 { 263 struct thread *td = (struct thread *)obj; 264 265 KASSERT(td->td_flags & TDF_ALLOCATED_THREAD, 266 ("_lwkt_thread_dtor: not allocated from objcache")); 267 KASSERT((td->td_flags & TDF_ALLOCATED_STACK) && td->td_kstack && 268 td->td_kstack_size > 0, 269 ("_lwkt_thread_dtor: corrupted stack")); 270 kmem_free(kernel_map, (vm_offset_t)td->td_kstack, td->td_kstack_size); 271 td->td_kstack = NULL; 272 td->td_flags = 0; 273 } 274 275 /* 276 * Initialize the lwkt s/system. 277 * 278 * Nominally cache up to 32 thread + kstack structures. Cache more on 279 * systems with a lot of cpu cores. 280 */ 281 static void 282 lwkt_init(void) 283 { 284 TUNABLE_INT("lwkt.cache_threads", &lwkt_cache_threads); 285 if (lwkt_cache_threads == 0) { 286 lwkt_cache_threads = ncpus * 4; 287 if (lwkt_cache_threads < 32) 288 lwkt_cache_threads = 32; 289 } 290 thread_cache = objcache_create_mbacked( 291 M_THREAD, sizeof(struct thread), 292 0, lwkt_cache_threads, 293 _lwkt_thread_ctor, _lwkt_thread_dtor, NULL); 294 } 295 SYSINIT(lwkt_init, SI_BOOT2_LWKT_INIT, SI_ORDER_FIRST, lwkt_init, NULL); 296 297 /* 298 * Schedule a thread to run. As the current thread we can always safely 299 * schedule ourselves, and a shortcut procedure is provided for that 300 * function. 301 * 302 * (non-blocking, self contained on a per cpu basis) 303 */ 304 void 305 lwkt_schedule_self(thread_t td) 306 { 307 KKASSERT((td->td_flags & TDF_MIGRATING) == 0); 308 crit_enter_quick(td); 309 KASSERT(td != &td->td_gd->gd_idlethread, 310 ("lwkt_schedule_self(): scheduling gd_idlethread is illegal!")); 311 KKASSERT(td->td_lwp == NULL || 312 (td->td_lwp->lwp_mpflags & LWP_MP_ONRUNQ) == 0); 313 _lwkt_enqueue(td); 314 crit_exit_quick(td); 315 } 316 317 /* 318 * Deschedule a thread. 319 * 320 * (non-blocking, self contained on a per cpu basis) 321 */ 322 void 323 lwkt_deschedule_self(thread_t td) 324 { 325 crit_enter_quick(td); 326 _lwkt_dequeue(td); 327 crit_exit_quick(td); 328 } 329 330 /* 331 * LWKTs operate on a per-cpu basis 332 * 333 * WARNING! Called from early boot, 'mycpu' may not work yet. 334 */ 335 void 336 lwkt_gdinit(struct globaldata *gd) 337 { 338 TAILQ_INIT(&gd->gd_tdrunq); 339 TAILQ_INIT(&gd->gd_tdallq); 340 lockinit(&gd->gd_sysctllock, "sysctl", 0, LK_CANRECURSE); 341 } 342 343 /* 344 * Create a new thread. The thread must be associated with a process context 345 * or LWKT start address before it can be scheduled. If the target cpu is 346 * -1 the thread will be created on the current cpu. 347 * 348 * If you intend to create a thread without a process context this function 349 * does everything except load the startup and switcher function. 350 */ 351 thread_t 352 lwkt_alloc_thread(struct thread *td, int stksize, int cpu, int flags) 353 { 354 static int cpu_rotator; 355 globaldata_t gd = mycpu; 356 void *stack; 357 358 /* 359 * If static thread storage is not supplied allocate a thread. Reuse 360 * a cached free thread if possible. gd_freetd is used to keep an exiting 361 * thread intact through the exit. 362 */ 363 if (td == NULL) { 364 crit_enter_gd(gd); 365 if ((td = gd->gd_freetd) != NULL) { 366 KKASSERT((td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK| 367 TDF_RUNQ)) == 0); 368 gd->gd_freetd = NULL; 369 } else { 370 td = objcache_get(thread_cache, M_WAITOK); 371 KKASSERT((td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK| 372 TDF_RUNQ)) == 0); 373 } 374 crit_exit_gd(gd); 375 KASSERT((td->td_flags & 376 (TDF_ALLOCATED_THREAD|TDF_RUNNING|TDF_PREEMPT_LOCK)) == 377 TDF_ALLOCATED_THREAD, 378 ("lwkt_alloc_thread: corrupted td flags 0x%X", td->td_flags)); 379 flags |= td->td_flags & (TDF_ALLOCATED_THREAD|TDF_ALLOCATED_STACK); 380 } 381 382 /* 383 * Try to reuse cached stack. 384 */ 385 if ((stack = td->td_kstack) != NULL && td->td_kstack_size != stksize) { 386 if (flags & TDF_ALLOCATED_STACK) { 387 kmem_free(kernel_map, (vm_offset_t)stack, td->td_kstack_size); 388 stack = NULL; 389 } 390 } 391 if (stack == NULL) { 392 if (cpu < 0) { 393 stack = (void *)kmem_alloc_stack(kernel_map, stksize, 0); 394 } else { 395 stack = (void *)kmem_alloc_stack(kernel_map, stksize, 396 KM_CPU(cpu)); 397 } 398 flags |= TDF_ALLOCATED_STACK; 399 } 400 if (cpu < 0) { 401 cpu = ++cpu_rotator; 402 cpu_ccfence(); 403 cpu = (uint32_t)cpu % (uint32_t)ncpus; 404 } 405 lwkt_init_thread(td, stack, stksize, flags, globaldata_find(cpu)); 406 return(td); 407 } 408 409 /* 410 * Initialize a preexisting thread structure. This function is used by 411 * lwkt_alloc_thread() and also used to initialize the per-cpu idlethread. 412 * 413 * All threads start out in a critical section at a priority of 414 * TDPRI_KERN_DAEMON. Higher level code will modify the priority as 415 * appropriate. This function may send an IPI message when the 416 * requested cpu is not the current cpu and consequently gd_tdallq may 417 * not be initialized synchronously from the point of view of the originating 418 * cpu. 419 * 420 * NOTE! we have to be careful in regards to creating threads for other cpus 421 * if SMP has not yet been activated. 422 */ 423 static void 424 lwkt_init_thread_remote(void *arg) 425 { 426 thread_t td = arg; 427 428 /* 429 * Protected by critical section held by IPI dispatch 430 */ 431 TAILQ_INSERT_TAIL(&td->td_gd->gd_tdallq, td, td_allq); 432 } 433 434 /* 435 * lwkt core thread structural initialization. 436 * 437 * NOTE: All threads are initialized as mpsafe threads. 438 */ 439 void 440 lwkt_init_thread(thread_t td, void *stack, int stksize, int flags, 441 struct globaldata *gd) 442 { 443 globaldata_t mygd = mycpu; 444 445 bzero(td, sizeof(struct thread)); 446 td->td_kstack = stack; 447 td->td_kstack_size = stksize; 448 td->td_flags = flags; 449 td->td_mpflags = 0; 450 td->td_type = TD_TYPE_GENERIC; 451 td->td_gd = gd; 452 td->td_pri = TDPRI_KERN_DAEMON; 453 td->td_critcount = 1; 454 td->td_toks_have = NULL; 455 td->td_toks_stop = &td->td_toks_base; 456 if (lwkt_use_spin_port || (flags & TDF_FORCE_SPINPORT)) { 457 lwkt_initport_spin(&td->td_msgport, td, 458 (flags & TDF_FIXEDCPU) ? TRUE : FALSE); 459 } else { 460 lwkt_initport_thread(&td->td_msgport, td); 461 } 462 pmap_init_thread(td); 463 464 /* 465 * Normally initializing a thread for a remote cpu requires sending an 466 * IPI. However, the idlethread is setup before the other cpus are 467 * activated so we have to treat it as a special case. XXX manipulation 468 * of gd_tdallq requires the BGL. 469 */ 470 if (gd == mygd || td == &gd->gd_idlethread) { 471 crit_enter_gd(mygd); 472 TAILQ_INSERT_TAIL(&gd->gd_tdallq, td, td_allq); 473 crit_exit_gd(mygd); 474 } else { 475 lwkt_send_ipiq(gd, lwkt_init_thread_remote, td); 476 } 477 dsched_enter_thread(td); 478 } 479 480 void 481 lwkt_set_comm(thread_t td, const char *ctl, ...) 482 { 483 __va_list va; 484 485 __va_start(va, ctl); 486 kvsnprintf(td->td_comm, sizeof(td->td_comm), ctl, va); 487 __va_end(va); 488 KTR_LOG(ctxsw_newtd, td, td->td_comm); 489 } 490 491 /* 492 * Prevent the thread from getting destroyed. Note that unlike PHOLD/PRELE 493 * this does not prevent the thread from migrating to another cpu so the 494 * gd_tdallq state is not protected by this. 495 */ 496 void 497 lwkt_hold(thread_t td) 498 { 499 atomic_add_int(&td->td_refs, 1); 500 } 501 502 void 503 lwkt_rele(thread_t td) 504 { 505 KKASSERT(td->td_refs > 0); 506 atomic_add_int(&td->td_refs, -1); 507 } 508 509 void 510 lwkt_free_thread(thread_t td) 511 { 512 KKASSERT(td->td_refs == 0); 513 KKASSERT((td->td_flags & (TDF_RUNNING | TDF_PREEMPT_LOCK | 514 TDF_RUNQ | TDF_TSLEEPQ | TDF_KERNELFP)) == 0); 515 516 if (td->td_kfpuctx) { 517 kfree(td->td_kfpuctx, M_FPUCTX); 518 td->td_kfpuctx = NULL; 519 } 520 521 if (td->td_flags & TDF_ALLOCATED_THREAD) { 522 objcache_put(thread_cache, td); 523 } else if (td->td_flags & TDF_ALLOCATED_STACK) { 524 /* client-allocated struct with internally allocated stack */ 525 KASSERT(td->td_kstack && td->td_kstack_size > 0, 526 ("lwkt_free_thread: corrupted stack")); 527 kmem_free(kernel_map, (vm_offset_t)td->td_kstack, td->td_kstack_size); 528 td->td_kstack = NULL; 529 td->td_kstack_size = 0; 530 } 531 532 KTR_LOG(ctxsw_deadtd, td); 533 } 534 535 536 /* 537 * Switch to the next runnable lwkt. If no LWKTs are runnable then 538 * switch to the idlethread. Switching must occur within a critical 539 * section to avoid races with the scheduling queue. 540 * 541 * We always have full control over our cpu's run queue. Other cpus 542 * that wish to manipulate our queue must use the cpu_*msg() calls to 543 * talk to our cpu, so a critical section is all that is needed and 544 * the result is very, very fast thread switching. 545 * 546 * The LWKT scheduler uses a fixed priority model and round-robins at 547 * each priority level. User process scheduling is a totally 548 * different beast and LWKT priorities should not be confused with 549 * user process priorities. 550 * 551 * PREEMPTION NOTE: Preemption occurs via lwkt_preempt(). lwkt_switch() 552 * is not called by the current thread in the preemption case, only when 553 * the preempting thread blocks (in order to return to the original thread). 554 * 555 * SPECIAL NOTE ON SWITCH ATOMICY: Certain operations such as thread 556 * migration and tsleep deschedule the current lwkt thread and call 557 * lwkt_switch(). In particular, the target cpu of the migration fully 558 * expects the thread to become non-runnable and can deadlock against 559 * cpusync operations if we run any IPIs prior to switching the thread out. 560 * 561 * WE MUST BE VERY CAREFUL NOT TO RUN SPLZ DIRECTLY OR INDIRECTLY IF 562 * THE CURRENT THREAD HAS BEEN DESCHEDULED! 563 */ 564 void 565 lwkt_switch(void) 566 { 567 globaldata_t gd = mycpu; 568 thread_t td = gd->gd_curthread; 569 thread_t ntd; 570 thread_t xtd; 571 int upri; 572 #ifdef LOOPMASK 573 uint64_t tsc_base = rdtsc(); 574 #endif 575 576 KKASSERT(gd->gd_processing_ipiq == 0); 577 KKASSERT(td->td_flags & TDF_RUNNING); 578 579 /* 580 * Switching from within a 'fast' (non thread switched) interrupt or IPI 581 * is illegal. However, we may have to do it anyway if we hit a fatal 582 * kernel trap or we have paniced. 583 * 584 * If this case occurs save and restore the interrupt nesting level. 585 */ 586 if (gd->gd_intr_nesting_level) { 587 int savegdnest; 588 int savegdtrap; 589 590 if (gd->gd_trap_nesting_level == 0 && panic_cpu_gd != mycpu) { 591 panic("lwkt_switch: Attempt to switch from a " 592 "fast interrupt, ipi, or hard code section, " 593 "td %p\n", 594 td); 595 } else { 596 savegdnest = gd->gd_intr_nesting_level; 597 savegdtrap = gd->gd_trap_nesting_level; 598 gd->gd_intr_nesting_level = 0; 599 gd->gd_trap_nesting_level = 0; 600 if ((td->td_flags & TDF_PANICWARN) == 0) { 601 td->td_flags |= TDF_PANICWARN; 602 kprintf("Warning: thread switch from interrupt, IPI, " 603 "or hard code section.\n" 604 "thread %p (%s)\n", td, td->td_comm); 605 print_backtrace(-1); 606 } 607 lwkt_switch(); 608 gd->gd_intr_nesting_level = savegdnest; 609 gd->gd_trap_nesting_level = savegdtrap; 610 return; 611 } 612 } 613 614 /* 615 * Release our current user process designation if we are blocking 616 * or if a user reschedule was requested. 617 * 618 * NOTE: This function is NOT called if we are switching into or 619 * returning from a preemption. 620 * 621 * NOTE: Releasing our current user process designation may cause 622 * it to be assigned to another thread, which in turn will 623 * cause us to block in the usched acquire code when we attempt 624 * to return to userland. 625 * 626 * NOTE: On SMP systems this can be very nasty when heavy token 627 * contention is present so we want to be careful not to 628 * release the designation gratuitously. 629 */ 630 if (td->td_release && 631 (user_resched_wanted() || (td->td_flags & TDF_RUNQ) == 0)) { 632 td->td_release(td); 633 } 634 635 /* 636 * Release all tokens. Once we do this we must remain in the critical 637 * section and cannot run IPIs or other interrupts until we switch away 638 * because they may implode if they try to get a token using our thread 639 * context. 640 */ 641 crit_enter_gd(gd); 642 if (TD_TOKS_HELD(td)) 643 lwkt_relalltokens(td); 644 645 /* 646 * We had better not be holding any spin locks, but don't get into an 647 * endless panic loop. 648 */ 649 KASSERT(gd->gd_spinlocks == 0 || panicstr != NULL, 650 ("lwkt_switch: still holding %d exclusive spinlocks!", 651 gd->gd_spinlocks)); 652 653 #ifdef INVARIANTS 654 if (td->td_cscount) { 655 kprintf("Diagnostic: attempt to switch while mastering cpusync: %p\n", 656 td); 657 if (panic_on_cscount) 658 panic("switching while mastering cpusync"); 659 } 660 #endif 661 662 /* 663 * If we had preempted another thread on this cpu, resume the preempted 664 * thread. This occurs transparently, whether the preempted thread 665 * was scheduled or not (it may have been preempted after descheduling 666 * itself). 667 * 668 * We have to setup the MP lock for the original thread after backing 669 * out the adjustment that was made to curthread when the original 670 * was preempted. 671 */ 672 if ((ntd = td->td_preempted) != NULL) { 673 KKASSERT(ntd->td_flags & TDF_PREEMPT_LOCK); 674 ntd->td_flags |= TDF_PREEMPT_DONE; 675 ntd->td_contended = 0; /* reset contended */ 676 677 /* 678 * The interrupt may have woken a thread up, we need to properly 679 * set the reschedule flag if the originally interrupted thread is 680 * at a lower priority. 681 * 682 * NOTE: The interrupt may not have descheduled ntd. 683 * 684 * NOTE: We do not reschedule if there are no threads on the runq. 685 * (ntd could be the idlethread). 686 */ 687 xtd = TAILQ_FIRST(&gd->gd_tdrunq); 688 if (xtd && xtd != ntd) 689 need_lwkt_resched(); 690 goto havethread_preempted; 691 } 692 693 /* 694 * Figure out switch target. If we cannot switch to our desired target 695 * look for a thread that we can switch to. 696 * 697 * NOTE! The limited spin loop and related parameters are extremely 698 * important for system performance, particularly for pipes and 699 * concurrent conflicting VM faults. 700 */ 701 clear_lwkt_resched(); 702 ntd = TAILQ_FIRST(&gd->gd_tdrunq); 703 704 if (ntd) { 705 do { 706 if (TD_TOKS_NOT_HELD(ntd) || 707 lwkt_getalltokens(ntd, (ntd->td_contended > lwkt_spin_loops))) 708 { 709 goto havethread; 710 } 711 ++ntd->td_contended; /* overflow ok */ 712 if (gd->gd_indefinite.type == 0) 713 indefinite_init(&gd->gd_indefinite, NULL, NULL, 0, 't'); 714 #ifdef LOOPMASK 715 if (tsc_frequency && rdtsc() - tsc_base > tsc_frequency) { 716 kprintf("lwkt_switch: WARNING, excessive token contention " 717 "cpu %d, %d sec, " 718 "td %p (%s)\n", 719 gd->gd_cpuid, 720 ntd->td_contended, 721 ntd, 722 ntd->td_comm); 723 tsc_base = rdtsc(); 724 } 725 #endif 726 } while (ntd->td_contended < (lwkt_spin_loops >> 1)); 727 upri = ntd->td_upri; 728 729 /* 730 * Bleh, the thread we wanted to switch to has a contended token. 731 * See if we can switch to another thread. 732 * 733 * We generally don't want to do this because it represents a 734 * priority inversion, but contending tokens on the same cpu can 735 * cause real problems if we don't now that we have an exclusive 736 * priority mechanism over shared for tokens. 737 * 738 * The solution is to allow threads with pending tokens to compete 739 * for them (a lower priority thread will get less cpu once it 740 * returns from the kernel anyway). If a thread does not have 741 * any contending tokens, we go by td_pri and upri. 742 */ 743 while ((ntd = TAILQ_NEXT(ntd, td_threadq)) != NULL) { 744 if (TD_TOKS_NOT_HELD(ntd) && 745 ntd->td_pri < TDPRI_KERN_LPSCHED && upri > ntd->td_upri) { 746 continue; 747 } 748 if (upri < ntd->td_upri) 749 upri = ntd->td_upri; 750 751 /* 752 * Try this one. 753 */ 754 if (TD_TOKS_NOT_HELD(ntd) || 755 lwkt_getalltokens(ntd, (ntd->td_contended > lwkt_spin_loops))) { 756 goto havethread; 757 } 758 ++ntd->td_contended; /* overflow ok */ 759 } 760 761 /* 762 * Fall through, switch to idle thread to get us out of the current 763 * context. Since we were contended, prevent HLT by flagging a 764 * LWKT reschedule. 765 */ 766 need_lwkt_resched(); 767 } 768 769 /* 770 * We either contended on ntd or the runq is empty. We must switch 771 * through the idle thread to get out of the current context. 772 */ 773 ntd = &gd->gd_idlethread; 774 if (gd->gd_trap_nesting_level == 0 && panicstr == NULL) 775 ASSERT_NO_TOKENS_HELD(ntd); 776 cpu_time.cp_msg[0] = 0; 777 goto haveidle; 778 779 havethread: 780 /* 781 * Clear gd_idle_repeat when doing a normal switch to a non-idle 782 * thread. 783 */ 784 ntd->td_wmesg = NULL; 785 ntd->td_contended = 0; /* reset once scheduled */ 786 ++gd->gd_cnt.v_swtch; 787 gd->gd_idle_repeat = 0; 788 789 /* 790 * If we were busy waiting record final disposition 791 */ 792 if (gd->gd_indefinite.type) 793 indefinite_done(&gd->gd_indefinite); 794 795 havethread_preempted: 796 /* 797 * If the new target does not need the MP lock and we are holding it, 798 * release the MP lock. If the new target requires the MP lock we have 799 * already acquired it for the target. 800 */ 801 ; 802 haveidle: 803 KASSERT(ntd->td_critcount, 804 ("priority problem in lwkt_switch %d %d", 805 td->td_critcount, ntd->td_critcount)); 806 807 if (td != ntd) { 808 /* 809 * Execute the actual thread switch operation. This function 810 * returns to the current thread and returns the previous thread 811 * (which may be different from the thread we switched to). 812 * 813 * We are responsible for marking ntd as TDF_RUNNING. 814 */ 815 KKASSERT((ntd->td_flags & TDF_RUNNING) == 0); 816 #ifdef DEBUG_LWKT_THREAD 817 ++switch_count; 818 #endif 819 KTR_LOG(ctxsw_sw, gd->gd_cpuid, ntd); 820 ntd->td_flags |= TDF_RUNNING; 821 lwkt_switch_return(td->td_switch(ntd)); 822 /* ntd invalid, td_switch() can return a different thread_t */ 823 } 824 825 /* 826 * catch-all. XXX is this strictly needed? 827 */ 828 splz_check(); 829 830 /* NOTE: current cpu may have changed after switch */ 831 crit_exit_quick(td); 832 } 833 834 /* 835 * Called by assembly in the td_switch (thread restore path) for thread 836 * bootstrap cases which do not 'return' to lwkt_switch(). 837 */ 838 void 839 lwkt_switch_return(thread_t otd) 840 { 841 globaldata_t rgd; 842 #ifdef LOOPMASK 843 uint64_t tsc_base = rdtsc(); 844 #endif 845 int exiting; 846 847 exiting = otd->td_flags & TDF_EXITING; 848 cpu_ccfence(); 849 850 /* 851 * Check if otd was migrating. Now that we are on ntd we can finish 852 * up the migration. This is a bit messy but it is the only place 853 * where td is known to be fully descheduled. 854 * 855 * We can only activate the migration if otd was migrating but not 856 * held on the cpu due to a preemption chain. We still have to 857 * clear TDF_RUNNING on the old thread either way. 858 * 859 * We are responsible for clearing the previously running thread's 860 * TDF_RUNNING. 861 */ 862 if ((rgd = otd->td_migrate_gd) != NULL && 863 (otd->td_flags & TDF_PREEMPT_LOCK) == 0) { 864 KKASSERT((otd->td_flags & (TDF_MIGRATING | TDF_RUNNING)) == 865 (TDF_MIGRATING | TDF_RUNNING)); 866 otd->td_migrate_gd = NULL; 867 otd->td_flags &= ~TDF_RUNNING; 868 lwkt_send_ipiq(rgd, lwkt_setcpu_remote, otd); 869 } else { 870 otd->td_flags &= ~TDF_RUNNING; 871 } 872 873 /* 874 * Final exit validations (see lwp_wait()). Note that otd becomes 875 * invalid the *instant* we set TDF_MP_EXITSIG. 876 * 877 * Use the EXITING status loaded from before we clear TDF_RUNNING, 878 * because if it is not set otd becomes invalid the instant we clear 879 * TDF_RUNNING on it (otherwise, if the system is fast enough, we 880 * might 'steal' TDF_EXITING from another switch-return!). 881 */ 882 while (exiting) { 883 u_int mpflags; 884 885 mpflags = otd->td_mpflags; 886 cpu_ccfence(); 887 888 if (mpflags & TDF_MP_EXITWAIT) { 889 if (atomic_cmpset_int(&otd->td_mpflags, mpflags, 890 mpflags | TDF_MP_EXITSIG)) { 891 wakeup(otd); 892 break; 893 } 894 } else { 895 if (atomic_cmpset_int(&otd->td_mpflags, mpflags, 896 mpflags | TDF_MP_EXITSIG)) { 897 wakeup(otd); 898 break; 899 } 900 } 901 902 #ifdef LOOPMASK 903 if (tsc_frequency && rdtsc() - tsc_base > tsc_frequency) { 904 kprintf("lwkt_switch_return: excessive TDF_EXITING " 905 "thread %p\n", otd); 906 tsc_base = rdtsc(); 907 } 908 #endif 909 } 910 } 911 912 /* 913 * Request that the target thread preempt the current thread. Preemption 914 * can only occur only: 915 * 916 * - If our critical section is the one that we were called with 917 * - The relative priority of the target thread is higher 918 * - The target is not excessively interrupt-nested via td_nest_count 919 * - The target thread holds no tokens. 920 * - The target thread is not already scheduled and belongs to the 921 * current cpu. 922 * - The current thread is not holding any spin-locks. 923 * 924 * THE CALLER OF LWKT_PREEMPT() MUST BE IN A CRITICAL SECTION. Typically 925 * this is called via lwkt_schedule() through the td_preemptable callback. 926 * critcount is the managed critical priority that we should ignore in order 927 * to determine whether preemption is possible (aka usually just the crit 928 * priority of lwkt_schedule() itself). 929 * 930 * Preemption is typically limited to interrupt threads. 931 * 932 * Operation works in a fairly straight-forward manner. The normal 933 * scheduling code is bypassed and we switch directly to the target 934 * thread. When the target thread attempts to block or switch away 935 * code at the base of lwkt_switch() will switch directly back to our 936 * thread. Our thread is able to retain whatever tokens it holds and 937 * if the target needs one of them the target will switch back to us 938 * and reschedule itself normally. 939 */ 940 void 941 lwkt_preempt(thread_t ntd, int critcount) 942 { 943 struct globaldata *gd = mycpu; 944 thread_t xtd; 945 thread_t td; 946 int save_gd_intr_nesting_level; 947 948 /* 949 * The caller has put us in a critical section. We can only preempt 950 * if the caller of the caller was not in a critical section (basically 951 * a local interrupt), as determined by the 'critcount' parameter. We 952 * also can't preempt if the caller is holding any spinlocks (even if 953 * he isn't in a critical section). This also handles the tokens test. 954 * 955 * YYY The target thread must be in a critical section (else it must 956 * inherit our critical section? I dunno yet). 957 */ 958 KASSERT(ntd->td_critcount, ("BADCRIT0 %d", ntd->td_pri)); 959 960 td = gd->gd_curthread; 961 if (preempt_enable == 0) { 962 #ifdef DEBUG_LWKT_THREAD 963 ++preempt_miss; 964 #endif 965 return; 966 } 967 if (ntd->td_pri <= td->td_pri) { 968 #ifdef DEBUG_LWKT_THREAD 969 ++preempt_miss; 970 #endif 971 return; 972 } 973 if (td->td_critcount > critcount) { 974 #ifdef DEBUG_LWKT_THREAD 975 ++preempt_miss; 976 #endif 977 return; 978 } 979 if (td->td_nest_count >= 2) { 980 #ifdef DEBUG_LWKT_THREAD 981 ++preempt_miss; 982 #endif 983 return; 984 } 985 if (td->td_cscount) { 986 #ifdef DEBUG_LWKT_THREAD 987 ++preempt_miss; 988 #endif 989 return; 990 } 991 if (ntd->td_gd != gd) { 992 #ifdef DEBUG_LWKT_THREAD 993 ++preempt_miss; 994 #endif 995 return; 996 } 997 998 /* 999 * We don't have to check spinlocks here as they will also bump 1000 * td_critcount. 1001 * 1002 * Do not try to preempt if the target thread is holding any tokens. 1003 * We could try to acquire the tokens but this case is so rare there 1004 * is no need to support it. 1005 */ 1006 KKASSERT(gd->gd_spinlocks == 0); 1007 1008 if (TD_TOKS_HELD(ntd)) { 1009 #ifdef DEBUG_LWKT_THREAD 1010 ++preempt_miss; 1011 #endif 1012 return; 1013 } 1014 if (td == ntd || ((td->td_flags | ntd->td_flags) & TDF_PREEMPT_LOCK)) { 1015 #ifdef DEBUG_LWKT_THREAD 1016 ++preempt_weird; 1017 #endif 1018 return; 1019 } 1020 if (ntd->td_preempted) { 1021 #ifdef DEBUG_LWKT_THREAD 1022 ++preempt_hit; 1023 #endif 1024 return; 1025 } 1026 KKASSERT(gd->gd_processing_ipiq == 0); 1027 1028 /* 1029 * Since we are able to preempt the current thread, there is no need to 1030 * call need_lwkt_resched(). 1031 * 1032 * We must temporarily clear gd_intr_nesting_level around the switch 1033 * since switchouts from the target thread are allowed (they will just 1034 * return to our thread), and since the target thread has its own stack. 1035 * 1036 * A preemption must switch back to the original thread, assert the 1037 * case. 1038 */ 1039 #ifdef DEBUG_LWKT_THREAD 1040 ++preempt_hit; 1041 #endif 1042 ntd->td_preempted = td; 1043 td->td_flags |= TDF_PREEMPT_LOCK; 1044 KTR_LOG(ctxsw_pre, gd->gd_cpuid, ntd); 1045 save_gd_intr_nesting_level = gd->gd_intr_nesting_level; 1046 gd->gd_intr_nesting_level = 0; 1047 1048 KKASSERT((ntd->td_flags & TDF_RUNNING) == 0); 1049 ntd->td_flags |= TDF_RUNNING; 1050 xtd = td->td_switch(ntd); 1051 KKASSERT(xtd == ntd); 1052 lwkt_switch_return(xtd); 1053 gd->gd_intr_nesting_level = save_gd_intr_nesting_level; 1054 1055 KKASSERT(ntd->td_preempted && (td->td_flags & TDF_PREEMPT_DONE)); 1056 ntd->td_preempted = NULL; 1057 td->td_flags &= ~(TDF_PREEMPT_LOCK|TDF_PREEMPT_DONE); 1058 } 1059 1060 /* 1061 * Conditionally call splz() if gd_reqflags indicates work is pending. 1062 * This will work inside a critical section but not inside a hard code 1063 * section. 1064 * 1065 * (self contained on a per cpu basis) 1066 */ 1067 void 1068 splz_check(void) 1069 { 1070 globaldata_t gd = mycpu; 1071 thread_t td = gd->gd_curthread; 1072 1073 if ((gd->gd_reqflags & RQF_IDLECHECK_MASK) && 1074 gd->gd_intr_nesting_level == 0 && 1075 td->td_nest_count < 2) 1076 { 1077 splz(); 1078 } 1079 } 1080 1081 /* 1082 * This version is integrated into crit_exit, reqflags has already 1083 * been tested but td_critcount has not. 1084 * 1085 * We only want to execute the splz() on the 1->0 transition of 1086 * critcount and not in a hard code section or if too deeply nested. 1087 * 1088 * NOTE: gd->gd_spinlocks is implied to be 0 when td_critcount is 0. 1089 */ 1090 void 1091 lwkt_maybe_splz(thread_t td) 1092 { 1093 globaldata_t gd = td->td_gd; 1094 1095 if (td->td_critcount == 0 && 1096 gd->gd_intr_nesting_level == 0 && 1097 td->td_nest_count < 2) 1098 { 1099 splz(); 1100 } 1101 } 1102 1103 /* 1104 * Drivers which set up processing co-threads can call this function to 1105 * run the co-thread at a higher priority and to allow it to preempt 1106 * normal threads. 1107 */ 1108 void 1109 lwkt_set_interrupt_support_thread(void) 1110 { 1111 thread_t td = curthread; 1112 1113 lwkt_setpri_self(TDPRI_INT_SUPPORT); 1114 td->td_flags |= TDF_INTTHREAD; 1115 td->td_preemptable = lwkt_preempt; 1116 } 1117 1118 1119 /* 1120 * This function is used to negotiate a passive release of the current 1121 * process/lwp designation with the user scheduler, allowing the user 1122 * scheduler to schedule another user thread. The related kernel thread 1123 * (curthread) continues running in the released state. 1124 */ 1125 void 1126 lwkt_passive_release(struct thread *td) 1127 { 1128 struct lwp *lp = td->td_lwp; 1129 1130 td->td_release = NULL; 1131 lwkt_setpri_self(TDPRI_KERN_USER); 1132 1133 lp->lwp_proc->p_usched->release_curproc(lp); 1134 } 1135 1136 1137 /* 1138 * This implements a LWKT yield, allowing a kernel thread to yield to other 1139 * kernel threads at the same or higher priority. This function can be 1140 * called in a tight loop and will typically only yield once per tick. 1141 * 1142 * Most kernel threads run at the same priority in order to allow equal 1143 * sharing. 1144 * 1145 * (self contained on a per cpu basis) 1146 */ 1147 void 1148 lwkt_yield(void) 1149 { 1150 globaldata_t gd = mycpu; 1151 thread_t td = gd->gd_curthread; 1152 1153 /* 1154 * Should never be called with spinlocks held but there is a path 1155 * via ACPI where it might happen. 1156 */ 1157 if (gd->gd_spinlocks) 1158 return; 1159 1160 /* 1161 * Safe to call splz if we are not too-heavily nested. 1162 */ 1163 if ((gd->gd_reqflags & RQF_IDLECHECK_MASK) && td->td_nest_count < 2) 1164 splz(); 1165 1166 /* 1167 * Caller allows switching 1168 */ 1169 if (lwkt_resched_wanted()) { 1170 atomic_set_int(&td->td_mpflags, TDF_MP_DIDYIELD); 1171 lwkt_schedule_self(td); 1172 lwkt_switch(); 1173 } 1174 } 1175 1176 /* 1177 * The quick version processes pending interrupts and higher-priority 1178 * LWKT threads but will not round-robin same-priority LWKT threads. 1179 * 1180 * When called while attempting to return to userland the only same-pri 1181 * threads are the ones which have already tried to become the current 1182 * user process. 1183 */ 1184 void 1185 lwkt_yield_quick(void) 1186 { 1187 globaldata_t gd = mycpu; 1188 thread_t td = gd->gd_curthread; 1189 1190 if ((gd->gd_reqflags & RQF_IDLECHECK_MASK) && td->td_nest_count < 2) 1191 splz(); 1192 if (lwkt_resched_wanted()) { 1193 crit_enter(); 1194 if (TAILQ_FIRST(&gd->gd_tdrunq) == td) { 1195 clear_lwkt_resched(); 1196 } else { 1197 atomic_set_int(&td->td_mpflags, TDF_MP_DIDYIELD); 1198 lwkt_schedule_self(curthread); 1199 lwkt_switch(); 1200 } 1201 crit_exit(); 1202 } 1203 } 1204 1205 /* 1206 * This yield is designed for kernel threads with a user context. 1207 * 1208 * The kernel acting on behalf of the user is potentially cpu-bound, 1209 * this function will efficiently allow other threads to run and also 1210 * switch to other processes by releasing. 1211 * 1212 * The lwkt_user_yield() function is designed to have very low overhead 1213 * if no yield is determined to be needed. 1214 */ 1215 void 1216 lwkt_user_yield(void) 1217 { 1218 globaldata_t gd = mycpu; 1219 thread_t td = gd->gd_curthread; 1220 1221 /* 1222 * Should never be called with spinlocks held but there is a path 1223 * via ACPI where it might happen. 1224 */ 1225 if (gd->gd_spinlocks) 1226 return; 1227 1228 /* 1229 * Always run any pending interrupts in case we are in a critical 1230 * section. 1231 */ 1232 if ((gd->gd_reqflags & RQF_IDLECHECK_MASK) && td->td_nest_count < 2) 1233 splz(); 1234 1235 /* 1236 * Switch (which forces a release) if another kernel thread needs 1237 * the cpu, if userland wants us to resched, or if our kernel 1238 * quantum has run out. 1239 */ 1240 if (lwkt_resched_wanted() || 1241 user_resched_wanted()) 1242 { 1243 lwkt_switch(); 1244 } 1245 1246 #if 0 1247 /* 1248 * Reacquire the current process if we are released. 1249 * 1250 * XXX not implemented atm. The kernel may be holding locks and such, 1251 * so we want the thread to continue to receive cpu. 1252 */ 1253 if (td->td_release == NULL && lp) { 1254 lp->lwp_proc->p_usched->acquire_curproc(lp); 1255 td->td_release = lwkt_passive_release; 1256 lwkt_setpri_self(TDPRI_USER_NORM); 1257 } 1258 #endif 1259 } 1260 1261 /* 1262 * Generic schedule. Possibly schedule threads belonging to other cpus and 1263 * deal with threads that might be blocked on a wait queue. 1264 * 1265 * We have a little helper inline function which does additional work after 1266 * the thread has been enqueued, including dealing with preemption and 1267 * setting need_lwkt_resched() (which prevents the kernel from returning 1268 * to userland until it has processed higher priority threads). 1269 * 1270 * It is possible for this routine to be called after a failed _enqueue 1271 * (due to the target thread migrating, sleeping, or otherwise blocked). 1272 * We have to check that the thread is actually on the run queue! 1273 */ 1274 static __inline 1275 void 1276 _lwkt_schedule_post(globaldata_t gd, thread_t ntd, int ccount) 1277 { 1278 if (ntd->td_flags & TDF_RUNQ) { 1279 if (ntd->td_preemptable) { 1280 ntd->td_preemptable(ntd, ccount); /* YYY +token */ 1281 } 1282 } 1283 } 1284 1285 static __inline 1286 void 1287 _lwkt_schedule(thread_t td) 1288 { 1289 globaldata_t mygd = mycpu; 1290 1291 KASSERT(td != &td->td_gd->gd_idlethread, 1292 ("lwkt_schedule(): scheduling gd_idlethread is illegal!")); 1293 KKASSERT((td->td_flags & TDF_MIGRATING) == 0); 1294 crit_enter_gd(mygd); 1295 KKASSERT(td->td_lwp == NULL || 1296 (td->td_lwp->lwp_mpflags & LWP_MP_ONRUNQ) == 0); 1297 1298 if (td == mygd->gd_curthread) { 1299 _lwkt_enqueue(td); 1300 } else { 1301 /* 1302 * If we own the thread, there is no race (since we are in a 1303 * critical section). If we do not own the thread there might 1304 * be a race but the target cpu will deal with it. 1305 */ 1306 if (td->td_gd == mygd) { 1307 _lwkt_enqueue(td); 1308 _lwkt_schedule_post(mygd, td, 1); 1309 } else { 1310 lwkt_send_ipiq3(td->td_gd, lwkt_schedule_remote, td, 0); 1311 } 1312 } 1313 crit_exit_gd(mygd); 1314 } 1315 1316 void 1317 lwkt_schedule(thread_t td) 1318 { 1319 _lwkt_schedule(td); 1320 } 1321 1322 void 1323 lwkt_schedule_noresched(thread_t td) /* XXX not impl */ 1324 { 1325 _lwkt_schedule(td); 1326 } 1327 1328 /* 1329 * When scheduled remotely if frame != NULL the IPIQ is being 1330 * run via doreti or an interrupt then preemption can be allowed. 1331 * 1332 * To allow preemption we have to drop the critical section so only 1333 * one is present in _lwkt_schedule_post. 1334 */ 1335 static void 1336 lwkt_schedule_remote(void *arg, int arg2, struct intrframe *frame) 1337 { 1338 thread_t td = curthread; 1339 thread_t ntd = arg; 1340 1341 if (frame && ntd->td_preemptable) { 1342 crit_exit_noyield(td); 1343 _lwkt_schedule(ntd); 1344 crit_enter_quick(td); 1345 } else { 1346 _lwkt_schedule(ntd); 1347 } 1348 } 1349 1350 /* 1351 * Thread migration using a 'Pull' method. The thread may or may not be 1352 * the current thread. It MUST be descheduled and in a stable state. 1353 * lwkt_giveaway() must be called on the cpu owning the thread. 1354 * 1355 * At any point after lwkt_giveaway() is called, the target cpu may 1356 * 'pull' the thread by calling lwkt_acquire(). 1357 * 1358 * We have to make sure the thread is not sitting on a per-cpu tsleep 1359 * queue or it will blow up when it moves to another cpu. 1360 * 1361 * MPSAFE - must be called under very specific conditions. 1362 */ 1363 void 1364 lwkt_giveaway(thread_t td) 1365 { 1366 globaldata_t gd = mycpu; 1367 1368 crit_enter_gd(gd); 1369 if (td->td_flags & TDF_TSLEEPQ) 1370 tsleep_remove(td); 1371 KKASSERT(td->td_gd == gd); 1372 TAILQ_REMOVE(&gd->gd_tdallq, td, td_allq); 1373 td->td_flags |= TDF_MIGRATING; 1374 crit_exit_gd(gd); 1375 } 1376 1377 void 1378 lwkt_acquire(thread_t td) 1379 { 1380 globaldata_t gd; 1381 globaldata_t mygd; 1382 1383 KKASSERT(td->td_flags & TDF_MIGRATING); 1384 gd = td->td_gd; 1385 mygd = mycpu; 1386 if (gd != mycpu) { 1387 #ifdef LOOPMASK 1388 uint64_t tsc_base = rdtsc(); 1389 #endif 1390 cpu_lfence(); 1391 KKASSERT((td->td_flags & TDF_RUNQ) == 0); 1392 crit_enter_gd(mygd); 1393 DEBUG_PUSH_INFO("lwkt_acquire"); 1394 while (td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK)) { 1395 lwkt_process_ipiq(); 1396 cpu_lfence(); 1397 #ifdef _KERNEL_VIRTUAL 1398 vkernel_yield(); 1399 #endif 1400 #ifdef LOOPMASK 1401 if (tsc_frequency && rdtsc() - tsc_base > tsc_frequency) { 1402 kprintf("lwkt_acquire: stuck td %p td->td_flags %08x\n", 1403 td, td->td_flags); 1404 tsc_base = rdtsc(); 1405 } 1406 #endif 1407 } 1408 DEBUG_POP_INFO(); 1409 cpu_mfence(); 1410 td->td_gd = mygd; 1411 TAILQ_INSERT_TAIL(&mygd->gd_tdallq, td, td_allq); 1412 td->td_flags &= ~TDF_MIGRATING; 1413 crit_exit_gd(mygd); 1414 } else { 1415 crit_enter_gd(mygd); 1416 TAILQ_INSERT_TAIL(&mygd->gd_tdallq, td, td_allq); 1417 td->td_flags &= ~TDF_MIGRATING; 1418 crit_exit_gd(mygd); 1419 } 1420 } 1421 1422 /* 1423 * Generic deschedule. Descheduling threads other then your own should be 1424 * done only in carefully controlled circumstances. Descheduling is 1425 * asynchronous. 1426 * 1427 * This function may block if the cpu has run out of messages. 1428 */ 1429 void 1430 lwkt_deschedule(thread_t td) 1431 { 1432 crit_enter(); 1433 if (td == curthread) { 1434 _lwkt_dequeue(td); 1435 } else { 1436 if (td->td_gd == mycpu) { 1437 _lwkt_dequeue(td); 1438 } else { 1439 lwkt_send_ipiq(td->td_gd, (ipifunc1_t)lwkt_deschedule, td); 1440 } 1441 } 1442 crit_exit(); 1443 } 1444 1445 /* 1446 * Set the target thread's priority. This routine does not automatically 1447 * switch to a higher priority thread, LWKT threads are not designed for 1448 * continuous priority changes. Yield if you want to switch. 1449 */ 1450 void 1451 lwkt_setpri(thread_t td, int pri) 1452 { 1453 if (td->td_pri != pri) { 1454 KKASSERT(pri >= 0); 1455 crit_enter(); 1456 if (td->td_flags & TDF_RUNQ) { 1457 KKASSERT(td->td_gd == mycpu); 1458 _lwkt_dequeue(td); 1459 td->td_pri = pri; 1460 _lwkt_enqueue(td); 1461 } else { 1462 td->td_pri = pri; 1463 } 1464 crit_exit(); 1465 } 1466 } 1467 1468 /* 1469 * Set the initial priority for a thread prior to it being scheduled for 1470 * the first time. The thread MUST NOT be scheduled before or during 1471 * this call. The thread may be assigned to a cpu other then the current 1472 * cpu. 1473 * 1474 * Typically used after a thread has been created with TDF_STOPPREQ, 1475 * and before the thread is initially scheduled. 1476 */ 1477 void 1478 lwkt_setpri_initial(thread_t td, int pri) 1479 { 1480 KKASSERT(pri >= 0); 1481 KKASSERT((td->td_flags & TDF_RUNQ) == 0); 1482 td->td_pri = pri; 1483 } 1484 1485 void 1486 lwkt_setpri_self(int pri) 1487 { 1488 thread_t td = curthread; 1489 1490 KKASSERT(pri >= 0 && pri <= TDPRI_MAX); 1491 crit_enter(); 1492 if (td->td_flags & TDF_RUNQ) { 1493 _lwkt_dequeue(td); 1494 td->td_pri = pri; 1495 _lwkt_enqueue(td); 1496 } else { 1497 td->td_pri = pri; 1498 } 1499 crit_exit(); 1500 } 1501 1502 /* 1503 * hz tick scheduler clock for LWKT threads 1504 */ 1505 void 1506 lwkt_schedulerclock(thread_t td) 1507 { 1508 globaldata_t gd = td->td_gd; 1509 thread_t xtd; 1510 1511 xtd = TAILQ_FIRST(&gd->gd_tdrunq); 1512 if (xtd == td) { 1513 /* 1514 * If the current thread is at the head of the runq shift it to the 1515 * end of any equal-priority threads and request a LWKT reschedule 1516 * if it moved. 1517 * 1518 * Ignore upri in this situation. There will only be one user thread 1519 * in user mode, all others will be user threads running in kernel 1520 * mode and we have to make sure they get some cpu. 1521 */ 1522 xtd = TAILQ_NEXT(td, td_threadq); 1523 if (xtd && xtd->td_pri == td->td_pri) { 1524 TAILQ_REMOVE(&gd->gd_tdrunq, td, td_threadq); 1525 while (xtd && xtd->td_pri == td->td_pri) 1526 xtd = TAILQ_NEXT(xtd, td_threadq); 1527 if (xtd) 1528 TAILQ_INSERT_BEFORE(xtd, td, td_threadq); 1529 else 1530 TAILQ_INSERT_TAIL(&gd->gd_tdrunq, td, td_threadq); 1531 need_lwkt_resched(); 1532 } 1533 } else if (xtd) { 1534 /* 1535 * If we scheduled a thread other than the one at the head of the 1536 * queue always request a reschedule every tick. 1537 */ 1538 need_lwkt_resched(); 1539 } 1540 /* else curthread probably the idle thread, no need to reschedule */ 1541 } 1542 1543 /* 1544 * Migrate the current thread to the specified cpu. 1545 * 1546 * This is accomplished by descheduling ourselves from the current cpu 1547 * and setting td_migrate_gd. The lwkt_switch() code will detect that the 1548 * 'old' thread wants to migrate after it has been completely switched out 1549 * and will complete the migration. 1550 * 1551 * TDF_MIGRATING prevents scheduling races while the thread is being migrated. 1552 * 1553 * We must be sure to release our current process designation (if a user 1554 * process) before clearing out any tsleepq we are on because the release 1555 * code may re-add us. 1556 * 1557 * We must be sure to remove ourselves from the current cpu's tsleepq 1558 * before potentially moving to another queue. The thread can be on 1559 * a tsleepq due to a left-over tsleep_interlock(). 1560 */ 1561 1562 void 1563 lwkt_setcpu_self(globaldata_t rgd) 1564 { 1565 thread_t td = curthread; 1566 1567 if (td->td_gd != rgd) { 1568 crit_enter_quick(td); 1569 1570 if (td->td_release) 1571 td->td_release(td); 1572 if (td->td_flags & TDF_TSLEEPQ) 1573 tsleep_remove(td); 1574 1575 /* 1576 * Set TDF_MIGRATING to prevent a spurious reschedule while we are 1577 * trying to deschedule ourselves and switch away, then deschedule 1578 * ourself, remove us from tdallq, and set td_migrate_gd. Finally, 1579 * call lwkt_switch() to complete the operation. 1580 */ 1581 td->td_flags |= TDF_MIGRATING; 1582 lwkt_deschedule_self(td); 1583 TAILQ_REMOVE(&td->td_gd->gd_tdallq, td, td_allq); 1584 td->td_migrate_gd = rgd; 1585 lwkt_switch(); 1586 1587 /* 1588 * We are now on the target cpu 1589 */ 1590 KKASSERT(rgd == mycpu); 1591 TAILQ_INSERT_TAIL(&rgd->gd_tdallq, td, td_allq); 1592 crit_exit_quick(td); 1593 } 1594 } 1595 1596 void 1597 lwkt_migratecpu(int cpuid) 1598 { 1599 globaldata_t rgd; 1600 1601 rgd = globaldata_find(cpuid); 1602 lwkt_setcpu_self(rgd); 1603 } 1604 1605 /* 1606 * Remote IPI for cpu migration (called while in a critical section so we 1607 * do not have to enter another one). 1608 * 1609 * The thread (td) has already been completely descheduled from the 1610 * originating cpu and we can simply assert the case. The thread is 1611 * assigned to the new cpu and enqueued. 1612 * 1613 * The thread will re-add itself to tdallq when it resumes execution. 1614 */ 1615 static void 1616 lwkt_setcpu_remote(void *arg) 1617 { 1618 thread_t td = arg; 1619 globaldata_t gd = mycpu; 1620 1621 KKASSERT((td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK)) == 0); 1622 td->td_gd = gd; 1623 cpu_mfence(); 1624 td->td_flags &= ~TDF_MIGRATING; 1625 KKASSERT(td->td_migrate_gd == NULL); 1626 KKASSERT(td->td_lwp == NULL || 1627 (td->td_lwp->lwp_mpflags & LWP_MP_ONRUNQ) == 0); 1628 _lwkt_enqueue(td); 1629 } 1630 1631 struct lwp * 1632 lwkt_preempted_proc(void) 1633 { 1634 thread_t td = curthread; 1635 while (td->td_preempted) 1636 td = td->td_preempted; 1637 return(td->td_lwp); 1638 } 1639 1640 /* 1641 * Create a kernel process/thread/whatever. It shares it's address space 1642 * with proc0 - ie: kernel only. 1643 * 1644 * If the cpu is not specified one will be selected. In the future 1645 * specifying a cpu of -1 will enable kernel thread migration between 1646 * cpus. 1647 */ 1648 int 1649 lwkt_create(void (*func)(void *), void *arg, struct thread **tdp, 1650 thread_t template, int tdflags, int cpu, const char *fmt, ...) 1651 { 1652 thread_t td; 1653 __va_list ap; 1654 1655 td = lwkt_alloc_thread(template, LWKT_THREAD_STACK, cpu, 1656 tdflags); 1657 if (tdp) 1658 *tdp = td; 1659 cpu_set_thread_handler(td, lwkt_exit, func, arg); 1660 1661 /* 1662 * Set up arg0 for 'ps' etc 1663 */ 1664 __va_start(ap, fmt); 1665 kvsnprintf(td->td_comm, sizeof(td->td_comm), fmt, ap); 1666 __va_end(ap); 1667 1668 /* 1669 * Schedule the thread to run 1670 */ 1671 if (td->td_flags & TDF_NOSTART) 1672 td->td_flags &= ~TDF_NOSTART; 1673 else 1674 lwkt_schedule(td); 1675 return 0; 1676 } 1677 1678 /* 1679 * Destroy an LWKT thread. Warning! This function is not called when 1680 * a process exits, cpu_proc_exit() directly calls cpu_thread_exit() and 1681 * uses a different reaping mechanism. 1682 */ 1683 void 1684 lwkt_exit(void) 1685 { 1686 thread_t td = curthread; 1687 thread_t std; 1688 globaldata_t gd; 1689 1690 /* 1691 * Do any cleanup that might block here 1692 */ 1693 biosched_done(td); 1694 dsched_exit_thread(td); 1695 1696 /* 1697 * Get us into a critical section to interlock gd_freetd and loop 1698 * until we can get it freed. 1699 * 1700 * We have to cache the current td in gd_freetd because objcache_put()ing 1701 * it would rip it out from under us while our thread is still active. 1702 * 1703 * We are the current thread so of course our own TDF_RUNNING bit will 1704 * be set, so unlike the lwp reap code we don't wait for it to clear. 1705 */ 1706 gd = mycpu; 1707 crit_enter_quick(td); 1708 for (;;) { 1709 if (td->td_refs) { 1710 tsleep(td, 0, "tdreap", 1); 1711 continue; 1712 } 1713 if ((std = gd->gd_freetd) != NULL) { 1714 KKASSERT((std->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK)) == 0); 1715 gd->gd_freetd = NULL; 1716 objcache_put(thread_cache, std); 1717 continue; 1718 } 1719 break; 1720 } 1721 1722 /* 1723 * Remove thread resources from kernel lists and deschedule us for 1724 * the last time. We cannot block after this point or we may end 1725 * up with a stale td on the tsleepq. 1726 * 1727 * None of this may block, the critical section is the only thing 1728 * protecting tdallq and the only thing preventing new lwkt_hold() 1729 * thread refs now. 1730 */ 1731 if (td->td_flags & TDF_TSLEEPQ) 1732 tsleep_remove(td); 1733 lwkt_deschedule_self(td); 1734 lwkt_remove_tdallq(td); 1735 KKASSERT(td->td_refs == 0); 1736 1737 /* 1738 * Final cleanup 1739 */ 1740 KKASSERT(gd->gd_freetd == NULL); 1741 if (td->td_flags & TDF_ALLOCATED_THREAD) 1742 gd->gd_freetd = td; 1743 cpu_thread_exit(); 1744 } 1745 1746 void 1747 lwkt_remove_tdallq(thread_t td) 1748 { 1749 KKASSERT(td->td_gd == mycpu); 1750 TAILQ_REMOVE(&td->td_gd->gd_tdallq, td, td_allq); 1751 } 1752 1753 /* 1754 * Code reduction and branch prediction improvements. Call/return 1755 * overhead on modern cpus often degenerates into 0 cycles due to 1756 * the cpu's branch prediction hardware and return pc cache. We 1757 * can take advantage of this by not inlining medium-complexity 1758 * functions and we can also reduce the branch prediction impact 1759 * by collapsing perfectly predictable branches into a single 1760 * procedure instead of duplicating it. 1761 * 1762 * Is any of this noticeable? Probably not, so I'll take the 1763 * smaller code size. 1764 */ 1765 void 1766 crit_exit_wrapper(__DEBUG_CRIT_ARG__) 1767 { 1768 _crit_exit(mycpu __DEBUG_CRIT_PASS_ARG__); 1769 } 1770 1771 void 1772 crit_panic(void) 1773 { 1774 thread_t td = curthread; 1775 int lcrit = td->td_critcount; 1776 1777 td->td_critcount = 0; 1778 cpu_ccfence(); 1779 panic("td_critcount is/would-go negative! %p %d", td, lcrit); 1780 /* NOT REACHED */ 1781 } 1782 1783 /* 1784 * Called from debugger/panic on cpus which have been stopped. We must still 1785 * process the IPIQ while stopped. 1786 * 1787 * If we are dumping also try to process any pending interrupts. This may 1788 * or may not work depending on the state of the cpu at the point it was 1789 * stopped. 1790 */ 1791 void 1792 lwkt_smp_stopped(void) 1793 { 1794 globaldata_t gd = mycpu; 1795 1796 if (dumping) { 1797 lwkt_process_ipiq(); 1798 --gd->gd_intr_nesting_level; 1799 splz(); 1800 ++gd->gd_intr_nesting_level; 1801 } else { 1802 lwkt_process_ipiq(); 1803 } 1804 cpu_smp_stopped(); 1805 } 1806