1 /* 2 * Copyright (c) 2003-2010 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/queue.h> 48 #include <sys/sysctl.h> 49 #include <sys/kthread.h> 50 #include <machine/cpu.h> 51 #include <sys/lock.h> 52 #include <sys/caps.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 #if !defined(KTR_CTXSW) 75 #define KTR_CTXSW KTR_ALL 76 #endif 77 KTR_INFO_MASTER(ctxsw); 78 KTR_INFO(KTR_CTXSW, ctxsw, sw, 0, "#cpu[%d].td = %p", 79 sizeof(int) + sizeof(struct thread *)); 80 KTR_INFO(KTR_CTXSW, ctxsw, pre, 1, "#cpu[%d].td = %p", 81 sizeof(int) + sizeof(struct thread *)); 82 KTR_INFO(KTR_CTXSW, ctxsw, newtd, 2, "#threads[%p].name = %s", 83 sizeof (struct thread *) + sizeof(char *)); 84 KTR_INFO(KTR_CTXSW, ctxsw, deadtd, 3, "#threads[%p].name = <dead>", sizeof (struct thread *)); 85 86 static MALLOC_DEFINE(M_THREAD, "thread", "lwkt threads"); 87 88 #ifdef INVARIANTS 89 static int panic_on_cscount = 0; 90 #endif 91 static __int64_t switch_count = 0; 92 static __int64_t preempt_hit = 0; 93 static __int64_t preempt_miss = 0; 94 static __int64_t preempt_weird = 0; 95 static __int64_t token_contention_count __debugvar = 0; 96 static int lwkt_use_spin_port; 97 static struct objcache *thread_cache; 98 99 #ifdef SMP 100 static void lwkt_schedule_remote(void *arg, int arg2, struct intrframe *frame); 101 #endif 102 103 extern void cpu_heavy_restore(void); 104 extern void cpu_lwkt_restore(void); 105 extern void cpu_kthread_restore(void); 106 extern void cpu_idle_restore(void); 107 108 #ifdef __x86_64__ 109 110 static int 111 jg_tos_ok(struct thread *td) 112 { 113 void *tos; 114 int tos_ok; 115 116 if (td == NULL) { 117 return 1; 118 } 119 KKASSERT(td->td_sp != NULL); 120 tos = ((void **)td->td_sp)[0]; 121 tos_ok = 0; 122 if ((tos == cpu_heavy_restore) || (tos == cpu_lwkt_restore) || 123 (tos == cpu_kthread_restore) || (tos == cpu_idle_restore)) { 124 tos_ok = 1; 125 } 126 return tos_ok; 127 } 128 129 #endif 130 131 /* 132 * We can make all thread ports use the spin backend instead of the thread 133 * backend. This should only be set to debug the spin backend. 134 */ 135 TUNABLE_INT("lwkt.use_spin_port", &lwkt_use_spin_port); 136 137 #ifdef INVARIANTS 138 SYSCTL_INT(_lwkt, OID_AUTO, panic_on_cscount, CTLFLAG_RW, &panic_on_cscount, 0, ""); 139 #endif 140 SYSCTL_QUAD(_lwkt, OID_AUTO, switch_count, CTLFLAG_RW, &switch_count, 0, ""); 141 SYSCTL_QUAD(_lwkt, OID_AUTO, preempt_hit, CTLFLAG_RW, &preempt_hit, 0, ""); 142 SYSCTL_QUAD(_lwkt, OID_AUTO, preempt_miss, CTLFLAG_RW, &preempt_miss, 0, ""); 143 SYSCTL_QUAD(_lwkt, OID_AUTO, preempt_weird, CTLFLAG_RW, &preempt_weird, 0, ""); 144 #ifdef INVARIANTS 145 SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count, CTLFLAG_RW, 146 &token_contention_count, 0, "spinning due to token contention"); 147 #endif 148 149 /* 150 * These helper procedures handle the runq, they can only be called from 151 * within a critical section. 152 * 153 * WARNING! Prior to SMP being brought up it is possible to enqueue and 154 * dequeue threads belonging to other cpus, so be sure to use td->td_gd 155 * instead of 'mycpu' when referencing the globaldata structure. Once 156 * SMP live enqueuing and dequeueing only occurs on the current cpu. 157 */ 158 static __inline 159 void 160 _lwkt_dequeue(thread_t td) 161 { 162 if (td->td_flags & TDF_RUNQ) { 163 int nq = td->td_pri & TDPRI_MASK; 164 struct globaldata *gd = td->td_gd; 165 166 td->td_flags &= ~TDF_RUNQ; 167 TAILQ_REMOVE(&gd->gd_tdrunq[nq], td, td_threadq); 168 /* runqmask is passively cleaned up by the switcher */ 169 } 170 } 171 172 static __inline 173 void 174 _lwkt_enqueue(thread_t td) 175 { 176 if ((td->td_flags & (TDF_RUNQ|TDF_MIGRATING|TDF_BLOCKQ)) == 0) { 177 int nq = td->td_pri & TDPRI_MASK; 178 struct globaldata *gd = td->td_gd; 179 180 td->td_flags |= TDF_RUNQ; 181 TAILQ_INSERT_TAIL(&gd->gd_tdrunq[nq], td, td_threadq); 182 gd->gd_runqmask |= 1 << nq; 183 } 184 } 185 186 static __boolean_t 187 _lwkt_thread_ctor(void *obj, void *privdata, int ocflags) 188 { 189 struct thread *td = (struct thread *)obj; 190 191 td->td_kstack = NULL; 192 td->td_kstack_size = 0; 193 td->td_flags = TDF_ALLOCATED_THREAD; 194 return (1); 195 } 196 197 static void 198 _lwkt_thread_dtor(void *obj, void *privdata) 199 { 200 struct thread *td = (struct thread *)obj; 201 202 KASSERT(td->td_flags & TDF_ALLOCATED_THREAD, 203 ("_lwkt_thread_dtor: not allocated from objcache")); 204 KASSERT((td->td_flags & TDF_ALLOCATED_STACK) && td->td_kstack && 205 td->td_kstack_size > 0, 206 ("_lwkt_thread_dtor: corrupted stack")); 207 kmem_free(&kernel_map, (vm_offset_t)td->td_kstack, td->td_kstack_size); 208 } 209 210 /* 211 * Initialize the lwkt s/system. 212 */ 213 void 214 lwkt_init(void) 215 { 216 /* An objcache has 2 magazines per CPU so divide cache size by 2. */ 217 thread_cache = objcache_create_mbacked(M_THREAD, sizeof(struct thread), 218 NULL, CACHE_NTHREADS/2, 219 _lwkt_thread_ctor, _lwkt_thread_dtor, NULL); 220 } 221 222 /* 223 * Schedule a thread to run. As the current thread we can always safely 224 * schedule ourselves, and a shortcut procedure is provided for that 225 * function. 226 * 227 * (non-blocking, self contained on a per cpu basis) 228 */ 229 void 230 lwkt_schedule_self(thread_t td) 231 { 232 crit_enter_quick(td); 233 KASSERT(td != &td->td_gd->gd_idlethread, ("lwkt_schedule_self(): scheduling gd_idlethread is illegal!")); 234 KKASSERT(td->td_lwp == NULL || (td->td_lwp->lwp_flag & LWP_ONRUNQ) == 0); 235 _lwkt_enqueue(td); 236 crit_exit_quick(td); 237 } 238 239 /* 240 * Deschedule a thread. 241 * 242 * (non-blocking, self contained on a per cpu basis) 243 */ 244 void 245 lwkt_deschedule_self(thread_t td) 246 { 247 crit_enter_quick(td); 248 _lwkt_dequeue(td); 249 crit_exit_quick(td); 250 } 251 252 /* 253 * LWKTs operate on a per-cpu basis 254 * 255 * WARNING! Called from early boot, 'mycpu' may not work yet. 256 */ 257 void 258 lwkt_gdinit(struct globaldata *gd) 259 { 260 int i; 261 262 for (i = 0; i < sizeof(gd->gd_tdrunq)/sizeof(gd->gd_tdrunq[0]); ++i) 263 TAILQ_INIT(&gd->gd_tdrunq[i]); 264 gd->gd_runqmask = 0; 265 TAILQ_INIT(&gd->gd_tdallq); 266 } 267 268 /* 269 * Create a new thread. The thread must be associated with a process context 270 * or LWKT start address before it can be scheduled. If the target cpu is 271 * -1 the thread will be created on the current cpu. 272 * 273 * If you intend to create a thread without a process context this function 274 * does everything except load the startup and switcher function. 275 */ 276 thread_t 277 lwkt_alloc_thread(struct thread *td, int stksize, int cpu, int flags) 278 { 279 globaldata_t gd = mycpu; 280 void *stack; 281 282 /* 283 * If static thread storage is not supplied allocate a thread. Reuse 284 * a cached free thread if possible. gd_freetd is used to keep an exiting 285 * thread intact through the exit. 286 */ 287 if (td == NULL) { 288 if ((td = gd->gd_freetd) != NULL) 289 gd->gd_freetd = NULL; 290 else 291 td = objcache_get(thread_cache, M_WAITOK); 292 KASSERT((td->td_flags & 293 (TDF_ALLOCATED_THREAD|TDF_RUNNING)) == TDF_ALLOCATED_THREAD, 294 ("lwkt_alloc_thread: corrupted td flags 0x%X", td->td_flags)); 295 flags |= td->td_flags & (TDF_ALLOCATED_THREAD|TDF_ALLOCATED_STACK); 296 } 297 298 /* 299 * Try to reuse cached stack. 300 */ 301 if ((stack = td->td_kstack) != NULL && td->td_kstack_size != stksize) { 302 if (flags & TDF_ALLOCATED_STACK) { 303 kmem_free(&kernel_map, (vm_offset_t)stack, td->td_kstack_size); 304 stack = NULL; 305 } 306 } 307 if (stack == NULL) { 308 stack = (void *)kmem_alloc(&kernel_map, stksize); 309 flags |= TDF_ALLOCATED_STACK; 310 } 311 if (cpu < 0) 312 lwkt_init_thread(td, stack, stksize, flags, gd); 313 else 314 lwkt_init_thread(td, stack, stksize, flags, globaldata_find(cpu)); 315 return(td); 316 } 317 318 /* 319 * Initialize a preexisting thread structure. This function is used by 320 * lwkt_alloc_thread() and also used to initialize the per-cpu idlethread. 321 * 322 * All threads start out in a critical section at a priority of 323 * TDPRI_KERN_DAEMON. Higher level code will modify the priority as 324 * appropriate. This function may send an IPI message when the 325 * requested cpu is not the current cpu and consequently gd_tdallq may 326 * not be initialized synchronously from the point of view of the originating 327 * cpu. 328 * 329 * NOTE! we have to be careful in regards to creating threads for other cpus 330 * if SMP has not yet been activated. 331 */ 332 #ifdef SMP 333 334 static void 335 lwkt_init_thread_remote(void *arg) 336 { 337 thread_t td = arg; 338 339 /* 340 * Protected by critical section held by IPI dispatch 341 */ 342 TAILQ_INSERT_TAIL(&td->td_gd->gd_tdallq, td, td_allq); 343 } 344 345 #endif 346 347 void 348 lwkt_init_thread(thread_t td, void *stack, int stksize, int flags, 349 struct globaldata *gd) 350 { 351 globaldata_t mygd = mycpu; 352 353 bzero(td, sizeof(struct thread)); 354 td->td_kstack = stack; 355 td->td_kstack_size = stksize; 356 td->td_flags = flags; 357 td->td_gd = gd; 358 td->td_pri = TDPRI_KERN_DAEMON + TDPRI_CRIT; 359 td->td_toks_stop = &td->td_toks_base; 360 #ifdef SMP 361 if ((flags & TDF_MPSAFE) == 0) 362 td->td_mpcount = 1; 363 #endif 364 if (lwkt_use_spin_port) 365 lwkt_initport_spin(&td->td_msgport); 366 else 367 lwkt_initport_thread(&td->td_msgport, td); 368 pmap_init_thread(td); 369 #ifdef SMP 370 /* 371 * Normally initializing a thread for a remote cpu requires sending an 372 * IPI. However, the idlethread is setup before the other cpus are 373 * activated so we have to treat it as a special case. XXX manipulation 374 * of gd_tdallq requires the BGL. 375 */ 376 if (gd == mygd || td == &gd->gd_idlethread) { 377 crit_enter_gd(mygd); 378 TAILQ_INSERT_TAIL(&gd->gd_tdallq, td, td_allq); 379 crit_exit_gd(mygd); 380 } else { 381 lwkt_send_ipiq(gd, lwkt_init_thread_remote, td); 382 } 383 #else 384 crit_enter_gd(mygd); 385 TAILQ_INSERT_TAIL(&gd->gd_tdallq, td, td_allq); 386 crit_exit_gd(mygd); 387 #endif 388 389 dsched_new_thread(td); 390 } 391 392 void 393 lwkt_set_comm(thread_t td, const char *ctl, ...) 394 { 395 __va_list va; 396 397 __va_start(va, ctl); 398 kvsnprintf(td->td_comm, sizeof(td->td_comm), ctl, va); 399 __va_end(va); 400 KTR_LOG(ctxsw_newtd, td, &td->td_comm[0]); 401 } 402 403 void 404 lwkt_hold(thread_t td) 405 { 406 ++td->td_refs; 407 } 408 409 void 410 lwkt_rele(thread_t td) 411 { 412 KKASSERT(td->td_refs > 0); 413 --td->td_refs; 414 } 415 416 void 417 lwkt_wait_free(thread_t td) 418 { 419 while (td->td_refs) 420 tsleep(td, 0, "tdreap", hz); 421 } 422 423 void 424 lwkt_free_thread(thread_t td) 425 { 426 KASSERT((td->td_flags & TDF_RUNNING) == 0, 427 ("lwkt_free_thread: did not exit! %p", td)); 428 429 if (td->td_flags & TDF_ALLOCATED_THREAD) { 430 objcache_put(thread_cache, td); 431 } else if (td->td_flags & TDF_ALLOCATED_STACK) { 432 /* client-allocated struct with internally allocated stack */ 433 KASSERT(td->td_kstack && td->td_kstack_size > 0, 434 ("lwkt_free_thread: corrupted stack")); 435 kmem_free(&kernel_map, (vm_offset_t)td->td_kstack, td->td_kstack_size); 436 td->td_kstack = NULL; 437 td->td_kstack_size = 0; 438 } 439 KTR_LOG(ctxsw_deadtd, td); 440 } 441 442 443 /* 444 * Switch to the next runnable lwkt. If no LWKTs are runnable then 445 * switch to the idlethread. Switching must occur within a critical 446 * section to avoid races with the scheduling queue. 447 * 448 * We always have full control over our cpu's run queue. Other cpus 449 * that wish to manipulate our queue must use the cpu_*msg() calls to 450 * talk to our cpu, so a critical section is all that is needed and 451 * the result is very, very fast thread switching. 452 * 453 * The LWKT scheduler uses a fixed priority model and round-robins at 454 * each priority level. User process scheduling is a totally 455 * different beast and LWKT priorities should not be confused with 456 * user process priorities. 457 * 458 * The MP lock may be out of sync with the thread's td_mpcount. lwkt_switch() 459 * cleans it up. Note that the td_switch() function cannot do anything that 460 * requires the MP lock since the MP lock will have already been setup for 461 * the target thread (not the current thread). It's nice to have a scheduler 462 * that does not need the MP lock to work because it allows us to do some 463 * really cool high-performance MP lock optimizations. 464 * 465 * PREEMPTION NOTE: Preemption occurs via lwkt_preempt(). lwkt_switch() 466 * is not called by the current thread in the preemption case, only when 467 * the preempting thread blocks (in order to return to the original thread). 468 */ 469 void 470 lwkt_switch(void) 471 { 472 globaldata_t gd = mycpu; 473 thread_t td = gd->gd_curthread; 474 thread_t ntd; 475 #ifdef SMP 476 int mpheld; 477 #endif 478 479 /* 480 * Switching from within a 'fast' (non thread switched) interrupt or IPI 481 * is illegal. However, we may have to do it anyway if we hit a fatal 482 * kernel trap or we have paniced. 483 * 484 * If this case occurs save and restore the interrupt nesting level. 485 */ 486 if (gd->gd_intr_nesting_level) { 487 int savegdnest; 488 int savegdtrap; 489 490 if (gd->gd_trap_nesting_level == 0 && panicstr == NULL) { 491 panic("lwkt_switch: cannot switch from within " 492 "a fast interrupt, yet, td %p\n", td); 493 } else { 494 savegdnest = gd->gd_intr_nesting_level; 495 savegdtrap = gd->gd_trap_nesting_level; 496 gd->gd_intr_nesting_level = 0; 497 gd->gd_trap_nesting_level = 0; 498 if ((td->td_flags & TDF_PANICWARN) == 0) { 499 td->td_flags |= TDF_PANICWARN; 500 kprintf("Warning: thread switch from interrupt or IPI, " 501 "thread %p (%s)\n", td, td->td_comm); 502 print_backtrace(-1); 503 } 504 lwkt_switch(); 505 gd->gd_intr_nesting_level = savegdnest; 506 gd->gd_trap_nesting_level = savegdtrap; 507 return; 508 } 509 } 510 511 /* 512 * Passive release (used to transition from user to kernel mode 513 * when we block or switch rather then when we enter the kernel). 514 * This function is NOT called if we are switching into a preemption 515 * or returning from a preemption. Typically this causes us to lose 516 * our current process designation (if we have one) and become a true 517 * LWKT thread, and may also hand the current process designation to 518 * another process and schedule thread. 519 */ 520 if (td->td_release) 521 td->td_release(td); 522 523 crit_enter_gd(gd); 524 if (TD_TOKS_HELD(td)) 525 lwkt_relalltokens(td); 526 527 /* 528 * We had better not be holding any spin locks, but don't get into an 529 * endless panic loop. 530 */ 531 KASSERT(gd->gd_spinlock_rd == NULL || panicstr != NULL, 532 ("lwkt_switch: still holding a shared spinlock %p!", 533 gd->gd_spinlock_rd)); 534 KASSERT(gd->gd_spinlocks_wr == 0 || panicstr != NULL, 535 ("lwkt_switch: still holding %d exclusive spinlocks!", 536 gd->gd_spinlocks_wr)); 537 538 539 #ifdef SMP 540 /* 541 * td_mpcount cannot be used to determine if we currently hold the 542 * MP lock because get_mplock() will increment it prior to attempting 543 * to get the lock, and switch out if it can't. Our ownership of 544 * the actual lock will remain stable while we are in a critical section 545 * (but, of course, another cpu may own or release the lock so the 546 * actual value of mp_lock is not stable). 547 */ 548 mpheld = MP_LOCK_HELD(); 549 #ifdef INVARIANTS 550 if (td->td_cscount) { 551 kprintf("Diagnostic: attempt to switch while mastering cpusync: %p\n", 552 td); 553 if (panic_on_cscount) 554 panic("switching while mastering cpusync"); 555 } 556 #endif 557 #endif 558 if ((ntd = td->td_preempted) != NULL) { 559 /* 560 * We had preempted another thread on this cpu, resume the preempted 561 * thread. This occurs transparently, whether the preempted thread 562 * was scheduled or not (it may have been preempted after descheduling 563 * itself). 564 * 565 * We have to setup the MP lock for the original thread after backing 566 * out the adjustment that was made to curthread when the original 567 * was preempted. 568 */ 569 KKASSERT(ntd->td_flags & TDF_PREEMPT_LOCK); 570 #ifdef SMP 571 if (ntd->td_mpcount && mpheld == 0) { 572 panic("MPLOCK NOT HELD ON RETURN: %p %p %d %d", 573 td, ntd, td->td_mpcount, ntd->td_mpcount); 574 } 575 if (ntd->td_mpcount) { 576 td->td_mpcount -= ntd->td_mpcount; 577 KKASSERT(td->td_mpcount >= 0); 578 } 579 #endif 580 ntd->td_flags |= TDF_PREEMPT_DONE; 581 582 /* 583 * The interrupt may have woken a thread up, we need to properly 584 * set the reschedule flag if the originally interrupted thread is 585 * at a lower priority. 586 */ 587 if (gd->gd_runqmask > (2 << (ntd->td_pri & TDPRI_MASK)) - 1) 588 need_lwkt_resched(); 589 /* YYY release mp lock on switchback if original doesn't need it */ 590 } else { 591 /* 592 * Priority queue / round-robin at each priority. Note that user 593 * processes run at a fixed, low priority and the user process 594 * scheduler deals with interactions between user processes 595 * by scheduling and descheduling them from the LWKT queue as 596 * necessary. 597 * 598 * We have to adjust the MP lock for the target thread. If we 599 * need the MP lock and cannot obtain it we try to locate a 600 * thread that does not need the MP lock. If we cannot, we spin 601 * instead of HLT. 602 * 603 * A similar issue exists for the tokens held by the target thread. 604 * If we cannot obtain ownership of the tokens we cannot immediately 605 * schedule the thread. 606 */ 607 608 /* 609 * If an LWKT reschedule was requested, well that is what we are 610 * doing now so clear it. 611 */ 612 clear_lwkt_resched(); 613 again: 614 if (gd->gd_runqmask) { 615 int nq = bsrl(gd->gd_runqmask); 616 if ((ntd = TAILQ_FIRST(&gd->gd_tdrunq[nq])) == NULL) { 617 gd->gd_runqmask &= ~(1 << nq); 618 goto again; 619 } 620 #ifdef SMP 621 /* 622 * THREAD SELECTION FOR AN SMP MACHINE BUILD 623 * 624 * If the target needs the MP lock and we couldn't get it, 625 * or if the target is holding tokens and we could not 626 * gain ownership of the tokens, continue looking for a 627 * thread to schedule and spin instead of HLT if we can't. 628 * 629 * NOTE: the mpheld variable invalid after this conditional, it 630 * can change due to both cpu_try_mplock() returning success 631 * AND interactions in lwkt_getalltokens() due to the fact that 632 * we are trying to check the mpcount of a thread other then 633 * the current thread. Because of this, if the current thread 634 * is not holding td_mpcount, an IPI indirectly run via 635 * lwkt_getalltokens() can obtain and release the MP lock and 636 * cause the core MP lock to be released. 637 */ 638 if ((ntd->td_mpcount && mpheld == 0 && !cpu_try_mplock()) || 639 (TD_TOKS_HELD(ntd) && lwkt_getalltokens(ntd) == 0) 640 ) { 641 u_int32_t rqmask = gd->gd_runqmask; 642 643 cpu_pause(); 644 645 mpheld = MP_LOCK_HELD(); 646 ntd = NULL; 647 while (rqmask) { 648 TAILQ_FOREACH(ntd, &gd->gd_tdrunq[nq], td_threadq) { 649 if (ntd->td_mpcount && !mpheld && !cpu_try_mplock()) { 650 /* spinning due to MP lock being held */ 651 continue; 652 } 653 654 /* 655 * mpheld state invalid after getalltokens call returns 656 * failure, but the variable is only needed for 657 * the loop. 658 */ 659 if (TD_TOKS_HELD(ntd) && !lwkt_getalltokens(ntd)) { 660 /* spinning due to token contention */ 661 #ifdef INVARIANTS 662 ++token_contention_count; 663 #endif 664 mpheld = MP_LOCK_HELD(); 665 continue; 666 } 667 break; 668 } 669 if (ntd) 670 break; 671 rqmask &= ~(1 << nq); 672 nq = bsrl(rqmask); 673 674 /* 675 * We have two choices. We can either refuse to run a 676 * user thread when a kernel thread needs the MP lock 677 * but could not get it, or we can allow it to run but 678 * then expect an IPI (hopefully) later on to force a 679 * reschedule when the MP lock might become available. 680 */ 681 if (nq < TDPRI_KERN_LPSCHED) { 682 break; /* for now refuse to run */ 683 #if 0 684 if (chain_mplock == 0) 685 break; 686 /* continue loop, allow user threads to be scheduled */ 687 #endif 688 } 689 } 690 691 /* 692 * Case where a (kernel) thread needed the MP lock and could 693 * not get one, and we may or may not have found another 694 * thread which does not need the MP lock to run while 695 * we wait (ntd). 696 */ 697 if (ntd == NULL) { 698 ntd = &gd->gd_idlethread; 699 ntd->td_flags |= TDF_IDLE_NOHLT; 700 set_mplock_contention_mask(gd); 701 cpu_mplock_contested(); 702 goto using_idle_thread; 703 } else { 704 clr_mplock_contention_mask(gd); 705 ++gd->gd_cnt.v_swtch; 706 TAILQ_REMOVE(&gd->gd_tdrunq[nq], ntd, td_threadq); 707 TAILQ_INSERT_TAIL(&gd->gd_tdrunq[nq], ntd, td_threadq); 708 } 709 } else { 710 clr_mplock_contention_mask(gd); 711 ++gd->gd_cnt.v_swtch; 712 TAILQ_REMOVE(&gd->gd_tdrunq[nq], ntd, td_threadq); 713 TAILQ_INSERT_TAIL(&gd->gd_tdrunq[nq], ntd, td_threadq); 714 } 715 #else 716 /* 717 * THREAD SELECTION FOR A UP MACHINE BUILD. We don't have to 718 * worry about tokens or the BGL. However, we still have 719 * to call lwkt_getalltokens() in order to properly detect 720 * stale tokens. This call cannot fail for a UP build! 721 */ 722 lwkt_getalltokens(ntd); 723 ++gd->gd_cnt.v_swtch; 724 TAILQ_REMOVE(&gd->gd_tdrunq[nq], ntd, td_threadq); 725 TAILQ_INSERT_TAIL(&gd->gd_tdrunq[nq], ntd, td_threadq); 726 #endif 727 } else { 728 /* 729 * We have nothing to run but only let the idle loop halt 730 * the cpu if there are no pending interrupts. 731 */ 732 ntd = &gd->gd_idlethread; 733 if (gd->gd_reqflags & RQF_IDLECHECK_MASK) 734 ntd->td_flags |= TDF_IDLE_NOHLT; 735 #ifdef SMP 736 using_idle_thread: 737 /* 738 * The idle thread should not be holding the MP lock unless we 739 * are trapping in the kernel or in a panic. Since we select the 740 * idle thread unconditionally when no other thread is available, 741 * if the MP lock is desired during a panic or kernel trap, we 742 * have to loop in the scheduler until we get it. 743 */ 744 if (ntd->td_mpcount) { 745 mpheld = MP_LOCK_HELD(); 746 if (gd->gd_trap_nesting_level == 0 && panicstr == NULL) 747 panic("Idle thread %p was holding the BGL!", ntd); 748 if (mpheld == 0) 749 goto again; 750 } 751 #endif 752 } 753 } 754 KASSERT(ntd->td_pri >= TDPRI_CRIT, 755 ("priority problem in lwkt_switch %d %d", td->td_pri, ntd->td_pri)); 756 757 /* 758 * Do the actual switch. If the new target does not need the MP lock 759 * and we are holding it, release the MP lock. If the new target requires 760 * the MP lock we have already acquired it for the target. 761 */ 762 #ifdef SMP 763 if (ntd->td_mpcount == 0 ) { 764 if (MP_LOCK_HELD()) 765 cpu_rel_mplock(); 766 } else { 767 ASSERT_MP_LOCK_HELD(ntd); 768 } 769 #endif 770 if (td != ntd) { 771 ++switch_count; 772 #ifdef __x86_64__ 773 { 774 int tos_ok __debugvar = jg_tos_ok(ntd); 775 KKASSERT(tos_ok); 776 } 777 #endif 778 KTR_LOG(ctxsw_sw, gd->gd_cpuid, ntd); 779 td->td_switch(ntd); 780 } 781 /* NOTE: current cpu may have changed after switch */ 782 crit_exit_quick(td); 783 } 784 785 /* 786 * Request that the target thread preempt the current thread. Preemption 787 * only works under a specific set of conditions: 788 * 789 * - We are not preempting ourselves 790 * - The target thread is owned by the current cpu 791 * - We are not currently being preempted 792 * - The target is not currently being preempted 793 * - We are not holding any spin locks 794 * - The target thread is not holding any tokens 795 * - We are able to satisfy the target's MP lock requirements (if any). 796 * 797 * THE CALLER OF LWKT_PREEMPT() MUST BE IN A CRITICAL SECTION. Typically 798 * this is called via lwkt_schedule() through the td_preemptable callback. 799 * critpri is the managed critical priority that we should ignore in order 800 * to determine whether preemption is possible (aka usually just the crit 801 * priority of lwkt_schedule() itself). 802 * 803 * XXX at the moment we run the target thread in a critical section during 804 * the preemption in order to prevent the target from taking interrupts 805 * that *WE* can't. Preemption is strictly limited to interrupt threads 806 * and interrupt-like threads, outside of a critical section, and the 807 * preempted source thread will be resumed the instant the target blocks 808 * whether or not the source is scheduled (i.e. preemption is supposed to 809 * be as transparent as possible). 810 * 811 * The target thread inherits our MP count (added to its own) for the 812 * duration of the preemption in order to preserve the atomicy of the 813 * MP lock during the preemption. Therefore, any preempting targets must be 814 * careful in regards to MP assertions. Note that the MP count may be 815 * out of sync with the physical mp_lock, but we do not have to preserve 816 * the original ownership of the lock if it was out of synch (that is, we 817 * can leave it synchronized on return). 818 */ 819 void 820 lwkt_preempt(thread_t ntd, int critpri) 821 { 822 struct globaldata *gd = mycpu; 823 thread_t td; 824 #ifdef SMP 825 int mpheld; 826 int savecnt; 827 #endif 828 829 /* 830 * The caller has put us in a critical section. We can only preempt 831 * if the caller of the caller was not in a critical section (basically 832 * a local interrupt), as determined by the 'critpri' parameter. We 833 * also can't preempt if the caller is holding any spinlocks (even if 834 * he isn't in a critical section). This also handles the tokens test. 835 * 836 * YYY The target thread must be in a critical section (else it must 837 * inherit our critical section? I dunno yet). 838 * 839 * Set need_lwkt_resched() unconditionally for now YYY. 840 */ 841 KASSERT(ntd->td_pri >= TDPRI_CRIT, ("BADCRIT0 %d", ntd->td_pri)); 842 843 td = gd->gd_curthread; 844 if ((ntd->td_pri & TDPRI_MASK) <= (td->td_pri & TDPRI_MASK)) { 845 ++preempt_miss; 846 return; 847 } 848 if ((td->td_pri & ~TDPRI_MASK) > critpri) { 849 ++preempt_miss; 850 need_lwkt_resched(); 851 return; 852 } 853 #ifdef SMP 854 if (ntd->td_gd != gd) { 855 ++preempt_miss; 856 need_lwkt_resched(); 857 return; 858 } 859 #endif 860 /* 861 * Take the easy way out and do not preempt if we are holding 862 * any spinlocks. We could test whether the thread(s) being 863 * preempted interlock against the target thread's tokens and whether 864 * we can get all the target thread's tokens, but this situation 865 * should not occur very often so its easier to simply not preempt. 866 * Also, plain spinlocks are impossible to figure out at this point so 867 * just don't preempt. 868 * 869 * Do not try to preempt if the target thread is holding any tokens. 870 * We could try to acquire the tokens but this case is so rare there 871 * is no need to support it. 872 */ 873 if (gd->gd_spinlock_rd || gd->gd_spinlocks_wr) { 874 ++preempt_miss; 875 need_lwkt_resched(); 876 return; 877 } 878 if (TD_TOKS_HELD(ntd)) { 879 ++preempt_miss; 880 need_lwkt_resched(); 881 return; 882 } 883 if (td == ntd || ((td->td_flags | ntd->td_flags) & TDF_PREEMPT_LOCK)) { 884 ++preempt_weird; 885 need_lwkt_resched(); 886 return; 887 } 888 if (ntd->td_preempted) { 889 ++preempt_hit; 890 need_lwkt_resched(); 891 return; 892 } 893 #ifdef SMP 894 /* 895 * note: an interrupt might have occured just as we were transitioning 896 * to or from the MP lock. In this case td_mpcount will be pre-disposed 897 * (non-zero) but not actually synchronized with the actual state of the 898 * lock. We can use it to imply an MP lock requirement for the 899 * preemption but we cannot use it to test whether we hold the MP lock 900 * or not. 901 */ 902 savecnt = td->td_mpcount; 903 mpheld = MP_LOCK_HELD(); 904 ntd->td_mpcount += td->td_mpcount; 905 if (mpheld == 0 && ntd->td_mpcount && !cpu_try_mplock()) { 906 ntd->td_mpcount -= td->td_mpcount; 907 ++preempt_miss; 908 need_lwkt_resched(); 909 return; 910 } 911 #endif 912 913 /* 914 * Since we are able to preempt the current thread, there is no need to 915 * call need_lwkt_resched(). 916 */ 917 ++preempt_hit; 918 ntd->td_preempted = td; 919 td->td_flags |= TDF_PREEMPT_LOCK; 920 KTR_LOG(ctxsw_pre, gd->gd_cpuid, ntd); 921 td->td_switch(ntd); 922 923 KKASSERT(ntd->td_preempted && (td->td_flags & TDF_PREEMPT_DONE)); 924 #ifdef SMP 925 KKASSERT(savecnt == td->td_mpcount); 926 mpheld = MP_LOCK_HELD(); 927 if (mpheld && td->td_mpcount == 0) 928 cpu_rel_mplock(); 929 else if (mpheld == 0 && td->td_mpcount) 930 panic("lwkt_preempt(): MP lock was not held through"); 931 #endif 932 ntd->td_preempted = NULL; 933 td->td_flags &= ~(TDF_PREEMPT_LOCK|TDF_PREEMPT_DONE); 934 } 935 936 /* 937 * Conditionally call splz() if gd_reqflags indicates work is pending. 938 * 939 * td_nest_count prevents deep nesting via splz() or doreti() which 940 * might otherwise blow out the kernel stack. Note that except for 941 * this special case, we MUST call splz() here to handle any 942 * pending ints, particularly after we switch, or we might accidently 943 * halt the cpu with interrupts pending. 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 && td->td_nest_count < 2) 954 splz(); 955 } 956 957 /* 958 * This implements a normal yield which will yield to equal priority 959 * threads as well as higher priority threads. Note that gd_reqflags 960 * tests will be handled by the crit_exit() call in lwkt_switch(). 961 * 962 * (self contained on a per cpu basis) 963 */ 964 void 965 lwkt_yield(void) 966 { 967 lwkt_schedule_self(curthread); 968 lwkt_switch(); 969 } 970 971 /* 972 * This function is used along with the lwkt_passive_recover() inline 973 * by the trap code to negotiate a passive release of the current 974 * process/lwp designation with the user scheduler. 975 */ 976 void 977 lwkt_passive_release(struct thread *td) 978 { 979 struct lwp *lp = td->td_lwp; 980 981 td->td_release = NULL; 982 lwkt_setpri_self(TDPRI_KERN_USER); 983 lp->lwp_proc->p_usched->release_curproc(lp); 984 } 985 986 /* 987 * Make a kernel thread act as if it were in user mode with regards 988 * to scheduling, to avoid becoming cpu-bound in the kernel. Kernel 989 * loops which may be potentially cpu-bound can call lwkt_user_yield(). 990 * 991 * The lwkt_user_yield() function is designed to have very low overhead 992 * if no yield is determined to be needed. 993 */ 994 void 995 lwkt_user_yield(void) 996 { 997 thread_t td = curthread; 998 struct lwp *lp = td->td_lwp; 999 1000 #ifdef SMP 1001 /* 1002 * XXX SEVERE TEMPORARY HACK. A cpu-bound operation running in the 1003 * kernel can prevent other cpus from servicing interrupt threads 1004 * which still require the MP lock (which is a lot of them). This 1005 * has a chaining effect since if the interrupt is blocked, so is 1006 * the event, so normal scheduling will not pick up on the problem. 1007 */ 1008 if (mp_lock_contention_mask && td->td_mpcount) { 1009 yield_mplock(td); 1010 } 1011 #endif 1012 1013 /* 1014 * Another kernel thread wants the cpu 1015 */ 1016 if (lwkt_resched_wanted()) 1017 lwkt_switch(); 1018 1019 /* 1020 * If the user scheduler has asynchronously determined that the current 1021 * process (when running in user mode) needs to lose the cpu then make 1022 * sure we are released. 1023 */ 1024 if (user_resched_wanted()) { 1025 if (td->td_release) 1026 td->td_release(td); 1027 } 1028 1029 /* 1030 * If we are released reduce our priority 1031 */ 1032 if (td->td_release == NULL) { 1033 if (lwkt_check_resched(td) > 0) 1034 lwkt_switch(); 1035 if (lp) { 1036 lp->lwp_proc->p_usched->acquire_curproc(lp); 1037 td->td_release = lwkt_passive_release; 1038 lwkt_setpri_self(TDPRI_USER_NORM); 1039 } 1040 } 1041 } 1042 1043 /* 1044 * Return 0 if no runnable threads are pending at the same or higher 1045 * priority as the passed thread. 1046 * 1047 * Return 1 if runnable threads are pending at the same priority. 1048 * 1049 * Return 2 if runnable threads are pending at a higher priority. 1050 */ 1051 int 1052 lwkt_check_resched(thread_t td) 1053 { 1054 int pri = td->td_pri & TDPRI_MASK; 1055 1056 if (td->td_gd->gd_runqmask > (2 << pri) - 1) 1057 return(2); 1058 if (TAILQ_NEXT(td, td_threadq)) 1059 return(1); 1060 return(0); 1061 } 1062 1063 /* 1064 * Generic schedule. Possibly schedule threads belonging to other cpus and 1065 * deal with threads that might be blocked on a wait queue. 1066 * 1067 * We have a little helper inline function which does additional work after 1068 * the thread has been enqueued, including dealing with preemption and 1069 * setting need_lwkt_resched() (which prevents the kernel from returning 1070 * to userland until it has processed higher priority threads). 1071 * 1072 * It is possible for this routine to be called after a failed _enqueue 1073 * (due to the target thread migrating, sleeping, or otherwise blocked). 1074 * We have to check that the thread is actually on the run queue! 1075 * 1076 * reschedok is an optimized constant propagated from lwkt_schedule() or 1077 * lwkt_schedule_noresched(). By default it is non-zero, causing a 1078 * reschedule to be requested if the target thread has a higher priority. 1079 * The port messaging code will set MSG_NORESCHED and cause reschedok to 1080 * be 0, prevented undesired reschedules. 1081 */ 1082 static __inline 1083 void 1084 _lwkt_schedule_post(globaldata_t gd, thread_t ntd, int cpri, int reschedok) 1085 { 1086 thread_t otd; 1087 1088 if (ntd->td_flags & TDF_RUNQ) { 1089 if (ntd->td_preemptable && reschedok) { 1090 ntd->td_preemptable(ntd, cpri); /* YYY +token */ 1091 } else if (reschedok) { 1092 otd = curthread; 1093 if ((ntd->td_pri & TDPRI_MASK) > (otd->td_pri & TDPRI_MASK)) 1094 need_lwkt_resched(); 1095 } 1096 } 1097 } 1098 1099 static __inline 1100 void 1101 _lwkt_schedule(thread_t td, int reschedok) 1102 { 1103 globaldata_t mygd = mycpu; 1104 1105 KASSERT(td != &td->td_gd->gd_idlethread, ("lwkt_schedule(): scheduling gd_idlethread is illegal!")); 1106 crit_enter_gd(mygd); 1107 KKASSERT(td->td_lwp == NULL || (td->td_lwp->lwp_flag & LWP_ONRUNQ) == 0); 1108 if (td == mygd->gd_curthread) { 1109 _lwkt_enqueue(td); 1110 } else { 1111 /* 1112 * If we own the thread, there is no race (since we are in a 1113 * critical section). If we do not own the thread there might 1114 * be a race but the target cpu will deal with it. 1115 */ 1116 #ifdef SMP 1117 if (td->td_gd == mygd) { 1118 _lwkt_enqueue(td); 1119 _lwkt_schedule_post(mygd, td, TDPRI_CRIT, reschedok); 1120 } else { 1121 lwkt_send_ipiq3(td->td_gd, lwkt_schedule_remote, td, 0); 1122 } 1123 #else 1124 _lwkt_enqueue(td); 1125 _lwkt_schedule_post(mygd, td, TDPRI_CRIT, reschedok); 1126 #endif 1127 } 1128 crit_exit_gd(mygd); 1129 } 1130 1131 void 1132 lwkt_schedule(thread_t td) 1133 { 1134 _lwkt_schedule(td, 1); 1135 } 1136 1137 void 1138 lwkt_schedule_noresched(thread_t td) 1139 { 1140 _lwkt_schedule(td, 0); 1141 } 1142 1143 #ifdef SMP 1144 1145 /* 1146 * When scheduled remotely if frame != NULL the IPIQ is being 1147 * run via doreti or an interrupt then preemption can be allowed. 1148 * 1149 * To allow preemption we have to drop the critical section so only 1150 * one is present in _lwkt_schedule_post. 1151 */ 1152 static void 1153 lwkt_schedule_remote(void *arg, int arg2, struct intrframe *frame) 1154 { 1155 thread_t td = curthread; 1156 thread_t ntd = arg; 1157 1158 if (frame && ntd->td_preemptable) { 1159 crit_exit_noyield(td); 1160 _lwkt_schedule(ntd, 1); 1161 crit_enter_quick(td); 1162 } else { 1163 _lwkt_schedule(ntd, 1); 1164 } 1165 } 1166 1167 /* 1168 * Thread migration using a 'Pull' method. The thread may or may not be 1169 * the current thread. It MUST be descheduled and in a stable state. 1170 * lwkt_giveaway() must be called on the cpu owning the thread. 1171 * 1172 * At any point after lwkt_giveaway() is called, the target cpu may 1173 * 'pull' the thread by calling lwkt_acquire(). 1174 * 1175 * We have to make sure the thread is not sitting on a per-cpu tsleep 1176 * queue or it will blow up when it moves to another cpu. 1177 * 1178 * MPSAFE - must be called under very specific conditions. 1179 */ 1180 void 1181 lwkt_giveaway(thread_t td) 1182 { 1183 globaldata_t gd = mycpu; 1184 1185 crit_enter_gd(gd); 1186 if (td->td_flags & TDF_TSLEEPQ) 1187 tsleep_remove(td); 1188 KKASSERT(td->td_gd == gd); 1189 TAILQ_REMOVE(&gd->gd_tdallq, td, td_allq); 1190 td->td_flags |= TDF_MIGRATING; 1191 crit_exit_gd(gd); 1192 } 1193 1194 void 1195 lwkt_acquire(thread_t td) 1196 { 1197 globaldata_t gd; 1198 globaldata_t mygd; 1199 1200 KKASSERT(td->td_flags & TDF_MIGRATING); 1201 gd = td->td_gd; 1202 mygd = mycpu; 1203 if (gd != mycpu) { 1204 cpu_lfence(); 1205 KKASSERT((td->td_flags & TDF_RUNQ) == 0); 1206 crit_enter_gd(mygd); 1207 while (td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK)) { 1208 #ifdef SMP 1209 lwkt_process_ipiq(); 1210 #endif 1211 cpu_lfence(); 1212 } 1213 td->td_gd = mygd; 1214 TAILQ_INSERT_TAIL(&mygd->gd_tdallq, td, td_allq); 1215 td->td_flags &= ~TDF_MIGRATING; 1216 crit_exit_gd(mygd); 1217 } else { 1218 crit_enter_gd(mygd); 1219 TAILQ_INSERT_TAIL(&mygd->gd_tdallq, td, td_allq); 1220 td->td_flags &= ~TDF_MIGRATING; 1221 crit_exit_gd(mygd); 1222 } 1223 } 1224 1225 #endif 1226 1227 /* 1228 * Generic deschedule. Descheduling threads other then your own should be 1229 * done only in carefully controlled circumstances. Descheduling is 1230 * asynchronous. 1231 * 1232 * This function may block if the cpu has run out of messages. 1233 */ 1234 void 1235 lwkt_deschedule(thread_t td) 1236 { 1237 crit_enter(); 1238 #ifdef SMP 1239 if (td == curthread) { 1240 _lwkt_dequeue(td); 1241 } else { 1242 if (td->td_gd == mycpu) { 1243 _lwkt_dequeue(td); 1244 } else { 1245 lwkt_send_ipiq(td->td_gd, (ipifunc1_t)lwkt_deschedule, td); 1246 } 1247 } 1248 #else 1249 _lwkt_dequeue(td); 1250 #endif 1251 crit_exit(); 1252 } 1253 1254 /* 1255 * Set the target thread's priority. This routine does not automatically 1256 * switch to a higher priority thread, LWKT threads are not designed for 1257 * continuous priority changes. Yield if you want to switch. 1258 * 1259 * We have to retain the critical section count which uses the high bits 1260 * of the td_pri field. The specified priority may also indicate zero or 1261 * more critical sections by adding TDPRI_CRIT*N. 1262 * 1263 * Note that we requeue the thread whether it winds up on a different runq 1264 * or not. uio_yield() depends on this and the routine is not normally 1265 * called with the same priority otherwise. 1266 */ 1267 void 1268 lwkt_setpri(thread_t td, int pri) 1269 { 1270 KKASSERT(pri >= 0); 1271 KKASSERT(td->td_gd == mycpu); 1272 crit_enter(); 1273 if (td->td_flags & TDF_RUNQ) { 1274 _lwkt_dequeue(td); 1275 td->td_pri = (td->td_pri & ~TDPRI_MASK) + pri; 1276 _lwkt_enqueue(td); 1277 } else { 1278 td->td_pri = (td->td_pri & ~TDPRI_MASK) + pri; 1279 } 1280 crit_exit(); 1281 } 1282 1283 /* 1284 * Set the initial priority for a thread prior to it being scheduled for 1285 * the first time. The thread MUST NOT be scheduled before or during 1286 * this call. The thread may be assigned to a cpu other then the current 1287 * cpu. 1288 * 1289 * Typically used after a thread has been created with TDF_STOPPREQ, 1290 * and before the thread is initially scheduled. 1291 */ 1292 void 1293 lwkt_setpri_initial(thread_t td, int pri) 1294 { 1295 KKASSERT(pri >= 0); 1296 KKASSERT((td->td_flags & TDF_RUNQ) == 0); 1297 td->td_pri = (td->td_pri & ~TDPRI_MASK) + pri; 1298 } 1299 1300 void 1301 lwkt_setpri_self(int pri) 1302 { 1303 thread_t td = curthread; 1304 1305 KKASSERT(pri >= 0 && pri <= TDPRI_MAX); 1306 crit_enter(); 1307 if (td->td_flags & TDF_RUNQ) { 1308 _lwkt_dequeue(td); 1309 td->td_pri = (td->td_pri & ~TDPRI_MASK) + pri; 1310 _lwkt_enqueue(td); 1311 } else { 1312 td->td_pri = (td->td_pri & ~TDPRI_MASK) + pri; 1313 } 1314 crit_exit(); 1315 } 1316 1317 /* 1318 * Migrate the current thread to the specified cpu. 1319 * 1320 * This is accomplished by descheduling ourselves from the current cpu, 1321 * moving our thread to the tdallq of the target cpu, IPI messaging the 1322 * target cpu, and switching out. TDF_MIGRATING prevents scheduling 1323 * races while the thread is being migrated. 1324 * 1325 * We must be sure to remove ourselves from the current cpu's tsleepq 1326 * before potentially moving to another queue. The thread can be on 1327 * a tsleepq due to a left-over tsleep_interlock(). 1328 */ 1329 #ifdef SMP 1330 static void lwkt_setcpu_remote(void *arg); 1331 #endif 1332 1333 void 1334 lwkt_setcpu_self(globaldata_t rgd) 1335 { 1336 #ifdef SMP 1337 thread_t td = curthread; 1338 1339 if (td->td_gd != rgd) { 1340 crit_enter_quick(td); 1341 if (td->td_flags & TDF_TSLEEPQ) 1342 tsleep_remove(td); 1343 td->td_flags |= TDF_MIGRATING; 1344 lwkt_deschedule_self(td); 1345 TAILQ_REMOVE(&td->td_gd->gd_tdallq, td, td_allq); 1346 lwkt_send_ipiq(rgd, (ipifunc1_t)lwkt_setcpu_remote, td); 1347 lwkt_switch(); 1348 /* we are now on the target cpu */ 1349 TAILQ_INSERT_TAIL(&rgd->gd_tdallq, td, td_allq); 1350 crit_exit_quick(td); 1351 } 1352 #endif 1353 } 1354 1355 void 1356 lwkt_migratecpu(int cpuid) 1357 { 1358 #ifdef SMP 1359 globaldata_t rgd; 1360 1361 rgd = globaldata_find(cpuid); 1362 lwkt_setcpu_self(rgd); 1363 #endif 1364 } 1365 1366 /* 1367 * Remote IPI for cpu migration (called while in a critical section so we 1368 * do not have to enter another one). The thread has already been moved to 1369 * our cpu's allq, but we must wait for the thread to be completely switched 1370 * out on the originating cpu before we schedule it on ours or the stack 1371 * state may be corrupt. We clear TDF_MIGRATING after flushing the GD 1372 * change to main memory. 1373 * 1374 * XXX The use of TDF_MIGRATING might not be sufficient to avoid races 1375 * against wakeups. It is best if this interface is used only when there 1376 * are no pending events that might try to schedule the thread. 1377 */ 1378 #ifdef SMP 1379 static void 1380 lwkt_setcpu_remote(void *arg) 1381 { 1382 thread_t td = arg; 1383 globaldata_t gd = mycpu; 1384 1385 while (td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK)) { 1386 #ifdef SMP 1387 lwkt_process_ipiq(); 1388 #endif 1389 cpu_lfence(); 1390 } 1391 td->td_gd = gd; 1392 cpu_sfence(); 1393 td->td_flags &= ~TDF_MIGRATING; 1394 KKASSERT(td->td_lwp == NULL || (td->td_lwp->lwp_flag & LWP_ONRUNQ) == 0); 1395 _lwkt_enqueue(td); 1396 } 1397 #endif 1398 1399 struct lwp * 1400 lwkt_preempted_proc(void) 1401 { 1402 thread_t td = curthread; 1403 while (td->td_preempted) 1404 td = td->td_preempted; 1405 return(td->td_lwp); 1406 } 1407 1408 /* 1409 * Create a kernel process/thread/whatever. It shares it's address space 1410 * with proc0 - ie: kernel only. 1411 * 1412 * NOTE! By default new threads are created with the MP lock held. A 1413 * thread which does not require the MP lock should release it by calling 1414 * rel_mplock() at the start of the new thread. 1415 */ 1416 int 1417 lwkt_create(void (*func)(void *), void *arg, 1418 struct thread **tdp, thread_t template, int tdflags, int cpu, 1419 const char *fmt, ...) 1420 { 1421 thread_t td; 1422 __va_list ap; 1423 1424 td = lwkt_alloc_thread(template, LWKT_THREAD_STACK, cpu, 1425 tdflags); 1426 if (tdp) 1427 *tdp = td; 1428 cpu_set_thread_handler(td, lwkt_exit, func, arg); 1429 1430 /* 1431 * Set up arg0 for 'ps' etc 1432 */ 1433 __va_start(ap, fmt); 1434 kvsnprintf(td->td_comm, sizeof(td->td_comm), fmt, ap); 1435 __va_end(ap); 1436 1437 /* 1438 * Schedule the thread to run 1439 */ 1440 if ((td->td_flags & TDF_STOPREQ) == 0) 1441 lwkt_schedule(td); 1442 else 1443 td->td_flags &= ~TDF_STOPREQ; 1444 return 0; 1445 } 1446 1447 /* 1448 * Destroy an LWKT thread. Warning! This function is not called when 1449 * a process exits, cpu_proc_exit() directly calls cpu_thread_exit() and 1450 * uses a different reaping mechanism. 1451 */ 1452 void 1453 lwkt_exit(void) 1454 { 1455 thread_t td = curthread; 1456 thread_t std; 1457 globaldata_t gd; 1458 1459 if (td->td_flags & TDF_VERBOSE) 1460 kprintf("kthread %p %s has exited\n", td, td->td_comm); 1461 caps_exit(td); 1462 1463 /* 1464 * Get us into a critical section to interlock gd_freetd and loop 1465 * until we can get it freed. 1466 * 1467 * We have to cache the current td in gd_freetd because objcache_put()ing 1468 * it would rip it out from under us while our thread is still active. 1469 */ 1470 gd = mycpu; 1471 crit_enter_quick(td); 1472 while ((std = gd->gd_freetd) != NULL) { 1473 gd->gd_freetd = NULL; 1474 objcache_put(thread_cache, std); 1475 } 1476 1477 /* 1478 * Remove thread resources from kernel lists and deschedule us for 1479 * the last time. 1480 */ 1481 if (td->td_flags & TDF_TSLEEPQ) 1482 tsleep_remove(td); 1483 biosched_done(td); 1484 dsched_exit_thread(td); 1485 lwkt_deschedule_self(td); 1486 lwkt_remove_tdallq(td); 1487 if (td->td_flags & TDF_ALLOCATED_THREAD) 1488 gd->gd_freetd = td; 1489 cpu_thread_exit(); 1490 } 1491 1492 void 1493 lwkt_remove_tdallq(thread_t td) 1494 { 1495 KKASSERT(td->td_gd == mycpu); 1496 TAILQ_REMOVE(&td->td_gd->gd_tdallq, td, td_allq); 1497 } 1498 1499 void 1500 crit_panic(void) 1501 { 1502 thread_t td = curthread; 1503 int lpri = td->td_pri; 1504 1505 td->td_pri = 0; 1506 panic("td_pri is/would-go negative! %p %d", td, lpri); 1507 } 1508 1509 #ifdef SMP 1510 1511 /* 1512 * Called from debugger/panic on cpus which have been stopped. We must still 1513 * process the IPIQ while stopped, even if we were stopped while in a critical 1514 * section (XXX). 1515 * 1516 * If we are dumping also try to process any pending interrupts. This may 1517 * or may not work depending on the state of the cpu at the point it was 1518 * stopped. 1519 */ 1520 void 1521 lwkt_smp_stopped(void) 1522 { 1523 globaldata_t gd = mycpu; 1524 1525 crit_enter_gd(gd); 1526 if (dumping) { 1527 lwkt_process_ipiq(); 1528 splz(); 1529 } else { 1530 lwkt_process_ipiq(); 1531 } 1532 crit_exit_gd(gd); 1533 } 1534 1535 #endif 1536