1 /* 2 * Copyright (c) 2003,2004 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 * $DragonFly: src/sys/kern/lwkt_thread.c,v 1.120 2008/10/26 04:29:19 sephe Exp $ 35 */ 36 37 /* 38 * Each cpu in a system has its own self-contained light weight kernel 39 * thread scheduler, which means that generally speaking we only need 40 * to use a critical section to avoid problems. Foreign thread 41 * scheduling is queued via (async) IPIs. 42 */ 43 #include "opt_ddb.h" 44 45 #include <sys/param.h> 46 #include <sys/systm.h> 47 #include <sys/kernel.h> 48 #include <sys/proc.h> 49 #include <sys/rtprio.h> 50 #include <sys/queue.h> 51 #include <sys/sysctl.h> 52 #include <sys/kthread.h> 53 #include <machine/cpu.h> 54 #include <sys/lock.h> 55 #include <sys/caps.h> 56 #include <sys/spinlock.h> 57 #include <sys/ktr.h> 58 59 #include <sys/thread2.h> 60 #include <sys/spinlock2.h> 61 62 #include <vm/vm.h> 63 #include <vm/vm_param.h> 64 #include <vm/vm_kern.h> 65 #include <vm/vm_object.h> 66 #include <vm/vm_page.h> 67 #include <vm/vm_map.h> 68 #include <vm/vm_pager.h> 69 #include <vm/vm_extern.h> 70 71 #include <machine/stdarg.h> 72 #include <machine/smp.h> 73 74 #ifdef DDB 75 #include <ddb/ddb.h> 76 #endif 77 78 static MALLOC_DEFINE(M_THREAD, "thread", "lwkt threads"); 79 80 static int untimely_switch = 0; 81 #ifdef INVARIANTS 82 static int panic_on_cscount = 0; 83 #endif 84 static __int64_t switch_count = 0; 85 static __int64_t preempt_hit = 0; 86 static __int64_t preempt_miss = 0; 87 static __int64_t preempt_weird = 0; 88 static __int64_t token_contention_count = 0; 89 static __int64_t mplock_contention_count = 0; 90 static int lwkt_use_spin_port; 91 #ifdef SMP 92 static int chain_mplock = 0; 93 #endif 94 static struct objcache *thread_cache; 95 96 volatile cpumask_t mp_lock_contention_mask; 97 98 extern void cpu_heavy_restore(void); 99 extern void cpu_lwkt_restore(void); 100 extern void cpu_kthread_restore(void); 101 extern void cpu_idle_restore(void); 102 103 int 104 jg_tos_ok(struct thread *td) 105 { 106 if (td == NULL) { 107 return 1; 108 } 109 KKASSERT(td->td_sp != NULL); 110 unsigned long tos = ((unsigned long *)td->td_sp)[0]; 111 int tos_ok = 0; 112 if ((tos == cpu_heavy_restore) || (tos == cpu_lwkt_restore) 113 || (tos == cpu_kthread_restore) || (tos == cpu_idle_restore)) { 114 tos_ok = 1; 115 } 116 return tos_ok; 117 } 118 119 /* 120 * We can make all thread ports use the spin backend instead of the thread 121 * backend. This should only be set to debug the spin backend. 122 */ 123 TUNABLE_INT("lwkt.use_spin_port", &lwkt_use_spin_port); 124 125 SYSCTL_INT(_lwkt, OID_AUTO, untimely_switch, CTLFLAG_RW, &untimely_switch, 0, ""); 126 #ifdef INVARIANTS 127 SYSCTL_INT(_lwkt, OID_AUTO, panic_on_cscount, CTLFLAG_RW, &panic_on_cscount, 0, ""); 128 #endif 129 #ifdef SMP 130 SYSCTL_INT(_lwkt, OID_AUTO, chain_mplock, CTLFLAG_RW, &chain_mplock, 0, ""); 131 #endif 132 SYSCTL_QUAD(_lwkt, OID_AUTO, switch_count, CTLFLAG_RW, &switch_count, 0, ""); 133 SYSCTL_QUAD(_lwkt, OID_AUTO, preempt_hit, CTLFLAG_RW, &preempt_hit, 0, ""); 134 SYSCTL_QUAD(_lwkt, OID_AUTO, preempt_miss, CTLFLAG_RW, &preempt_miss, 0, ""); 135 SYSCTL_QUAD(_lwkt, OID_AUTO, preempt_weird, CTLFLAG_RW, &preempt_weird, 0, ""); 136 #ifdef INVARIANTS 137 SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count, CTLFLAG_RW, 138 &token_contention_count, 0, "spinning due to token contention"); 139 SYSCTL_QUAD(_lwkt, OID_AUTO, mplock_contention_count, CTLFLAG_RW, 140 &mplock_contention_count, 0, "spinning due to MPLOCK contention"); 141 #endif 142 143 /* 144 * Kernel Trace 145 */ 146 #if !defined(KTR_GIANT_CONTENTION) 147 #define KTR_GIANT_CONTENTION KTR_ALL 148 #endif 149 150 KTR_INFO_MASTER(giant); 151 KTR_INFO(KTR_GIANT_CONTENTION, giant, beg, 0, "thread=%p", sizeof(void *)); 152 KTR_INFO(KTR_GIANT_CONTENTION, giant, end, 1, "thread=%p", sizeof(void *)); 153 154 #define loggiant(name) KTR_LOG(giant_ ## name, curthread) 155 156 /* 157 * These helper procedures handle the runq, they can only be called from 158 * within a critical section. 159 * 160 * WARNING! Prior to SMP being brought up it is possible to enqueue and 161 * dequeue threads belonging to other cpus, so be sure to use td->td_gd 162 * instead of 'mycpu' when referencing the globaldata structure. Once 163 * SMP live enqueuing and dequeueing only occurs on the current cpu. 164 */ 165 static __inline 166 void 167 _lwkt_dequeue(thread_t td) 168 { 169 if (td->td_flags & TDF_RUNQ) { 170 int nq = td->td_pri & TDPRI_MASK; 171 struct globaldata *gd = td->td_gd; 172 173 td->td_flags &= ~TDF_RUNQ; 174 TAILQ_REMOVE(&gd->gd_tdrunq[nq], td, td_threadq); 175 /* runqmask is passively cleaned up by the switcher */ 176 } 177 } 178 179 static __inline 180 void 181 _lwkt_enqueue(thread_t td) 182 { 183 if ((td->td_flags & (TDF_RUNQ|TDF_MIGRATING|TDF_TSLEEPQ|TDF_BLOCKQ)) == 0) { 184 int nq = td->td_pri & TDPRI_MASK; 185 struct globaldata *gd = td->td_gd; 186 187 td->td_flags |= TDF_RUNQ; 188 TAILQ_INSERT_TAIL(&gd->gd_tdrunq[nq], td, td_threadq); 189 gd->gd_runqmask |= 1 << nq; 190 } 191 } 192 193 static __boolean_t 194 _lwkt_thread_ctor(void *obj, void *privdata, int ocflags) 195 { 196 struct thread *td = (struct thread *)obj; 197 198 td->td_kstack = NULL; 199 td->td_kstack_size = 0; 200 td->td_flags = TDF_ALLOCATED_THREAD; 201 return (1); 202 } 203 204 static void 205 _lwkt_thread_dtor(void *obj, void *privdata) 206 { 207 struct thread *td = (struct thread *)obj; 208 209 KASSERT(td->td_flags & TDF_ALLOCATED_THREAD, 210 ("_lwkt_thread_dtor: not allocated from objcache")); 211 KASSERT((td->td_flags & TDF_ALLOCATED_STACK) && td->td_kstack && 212 td->td_kstack_size > 0, 213 ("_lwkt_thread_dtor: corrupted stack")); 214 kmem_free(&kernel_map, (vm_offset_t)td->td_kstack, td->td_kstack_size); 215 } 216 217 /* 218 * Initialize the lwkt s/system. 219 */ 220 void 221 lwkt_init(void) 222 { 223 /* An objcache has 2 magazines per CPU so divide cache size by 2. */ 224 thread_cache = objcache_create_mbacked(M_THREAD, sizeof(struct thread), 225 NULL, CACHE_NTHREADS/2, 226 _lwkt_thread_ctor, _lwkt_thread_dtor, NULL); 227 } 228 229 /* 230 * Schedule a thread to run. As the current thread we can always safely 231 * schedule ourselves, and a shortcut procedure is provided for that 232 * function. 233 * 234 * (non-blocking, self contained on a per cpu basis) 235 */ 236 void 237 lwkt_schedule_self(thread_t td) 238 { 239 crit_enter_quick(td); 240 KASSERT(td != &td->td_gd->gd_idlethread, ("lwkt_schedule_self(): scheduling gd_idlethread is illegal!")); 241 KKASSERT(td->td_lwp == NULL || (td->td_lwp->lwp_flag & LWP_ONRUNQ) == 0); 242 _lwkt_enqueue(td); 243 crit_exit_quick(td); 244 } 245 246 /* 247 * Deschedule a thread. 248 * 249 * (non-blocking, self contained on a per cpu basis) 250 */ 251 void 252 lwkt_deschedule_self(thread_t td) 253 { 254 crit_enter_quick(td); 255 _lwkt_dequeue(td); 256 crit_exit_quick(td); 257 } 258 259 /* 260 * LWKTs operate on a per-cpu basis 261 * 262 * WARNING! Called from early boot, 'mycpu' may not work yet. 263 */ 264 void 265 lwkt_gdinit(struct globaldata *gd) 266 { 267 int i; 268 269 for (i = 0; i < sizeof(gd->gd_tdrunq)/sizeof(gd->gd_tdrunq[0]); ++i) 270 TAILQ_INIT(&gd->gd_tdrunq[i]); 271 gd->gd_runqmask = 0; 272 TAILQ_INIT(&gd->gd_tdallq); 273 } 274 275 /* 276 * Create a new thread. The thread must be associated with a process context 277 * or LWKT start address before it can be scheduled. If the target cpu is 278 * -1 the thread will be created on the current cpu. 279 * 280 * If you intend to create a thread without a process context this function 281 * does everything except load the startup and switcher function. 282 */ 283 thread_t 284 lwkt_alloc_thread(struct thread *td, int stksize, int cpu, int flags) 285 { 286 globaldata_t gd = mycpu; 287 void *stack; 288 289 /* 290 * If static thread storage is not supplied allocate a thread. Reuse 291 * a cached free thread if possible. gd_freetd is used to keep an exiting 292 * thread intact through the exit. 293 */ 294 if (td == NULL) { 295 if ((td = gd->gd_freetd) != NULL) 296 gd->gd_freetd = NULL; 297 else 298 td = objcache_get(thread_cache, M_WAITOK); 299 KASSERT((td->td_flags & 300 (TDF_ALLOCATED_THREAD|TDF_RUNNING)) == TDF_ALLOCATED_THREAD, 301 ("lwkt_alloc_thread: corrupted td flags 0x%X", td->td_flags)); 302 flags |= td->td_flags & (TDF_ALLOCATED_THREAD|TDF_ALLOCATED_STACK); 303 } 304 305 /* 306 * Try to reuse cached stack. 307 */ 308 if ((stack = td->td_kstack) != NULL && td->td_kstack_size != stksize) { 309 if (flags & TDF_ALLOCATED_STACK) { 310 kmem_free(&kernel_map, (vm_offset_t)stack, td->td_kstack_size); 311 stack = NULL; 312 } 313 } 314 if (stack == NULL) { 315 stack = (void *)kmem_alloc(&kernel_map, stksize); 316 flags |= TDF_ALLOCATED_STACK; 317 } 318 if (cpu < 0) 319 lwkt_init_thread(td, stack, stksize, flags, gd); 320 else 321 lwkt_init_thread(td, stack, stksize, flags, globaldata_find(cpu)); 322 return(td); 323 } 324 325 /* 326 * Initialize a preexisting thread structure. This function is used by 327 * lwkt_alloc_thread() and also used to initialize the per-cpu idlethread. 328 * 329 * All threads start out in a critical section at a priority of 330 * TDPRI_KERN_DAEMON. Higher level code will modify the priority as 331 * appropriate. This function may send an IPI message when the 332 * requested cpu is not the current cpu and consequently gd_tdallq may 333 * not be initialized synchronously from the point of view of the originating 334 * cpu. 335 * 336 * NOTE! we have to be careful in regards to creating threads for other cpus 337 * if SMP has not yet been activated. 338 */ 339 #ifdef SMP 340 341 static void 342 lwkt_init_thread_remote(void *arg) 343 { 344 thread_t td = arg; 345 346 /* 347 * Protected by critical section held by IPI dispatch 348 */ 349 TAILQ_INSERT_TAIL(&td->td_gd->gd_tdallq, td, td_allq); 350 } 351 352 #endif 353 354 void 355 lwkt_init_thread(thread_t td, void *stack, int stksize, int flags, 356 struct globaldata *gd) 357 { 358 globaldata_t mygd = mycpu; 359 360 bzero(td, sizeof(struct thread)); 361 td->td_kstack = stack; 362 td->td_kstack_size = stksize; 363 td->td_flags = flags; 364 td->td_gd = gd; 365 td->td_pri = TDPRI_KERN_DAEMON + TDPRI_CRIT; 366 #ifdef SMP 367 if ((flags & TDF_MPSAFE) == 0) 368 td->td_mpcount = 1; 369 #endif 370 if (lwkt_use_spin_port) 371 lwkt_initport_spin(&td->td_msgport); 372 else 373 lwkt_initport_thread(&td->td_msgport, td); 374 pmap_init_thread(td); 375 #ifdef SMP 376 /* 377 * Normally initializing a thread for a remote cpu requires sending an 378 * IPI. However, the idlethread is setup before the other cpus are 379 * activated so we have to treat it as a special case. XXX manipulation 380 * of gd_tdallq requires the BGL. 381 */ 382 if (gd == mygd || td == &gd->gd_idlethread) { 383 crit_enter_gd(mygd); 384 TAILQ_INSERT_TAIL(&gd->gd_tdallq, td, td_allq); 385 crit_exit_gd(mygd); 386 } else { 387 lwkt_send_ipiq(gd, lwkt_init_thread_remote, td); 388 } 389 #else 390 crit_enter_gd(mygd); 391 TAILQ_INSERT_TAIL(&gd->gd_tdallq, td, td_allq); 392 crit_exit_gd(mygd); 393 #endif 394 } 395 396 void 397 lwkt_set_comm(thread_t td, const char *ctl, ...) 398 { 399 __va_list va; 400 401 __va_start(va, ctl); 402 kvsnprintf(td->td_comm, sizeof(td->td_comm), ctl, va); 403 __va_end(va); 404 } 405 406 void 407 lwkt_hold(thread_t td) 408 { 409 ++td->td_refs; 410 } 411 412 void 413 lwkt_rele(thread_t td) 414 { 415 KKASSERT(td->td_refs > 0); 416 --td->td_refs; 417 } 418 419 void 420 lwkt_wait_free(thread_t td) 421 { 422 while (td->td_refs) 423 tsleep(td, 0, "tdreap", hz); 424 } 425 426 void 427 lwkt_free_thread(thread_t td) 428 { 429 KASSERT((td->td_flags & TDF_RUNNING) == 0, 430 ("lwkt_free_thread: did not exit! %p", td)); 431 432 if (td->td_flags & TDF_ALLOCATED_THREAD) { 433 objcache_put(thread_cache, td); 434 } else if (td->td_flags & TDF_ALLOCATED_STACK) { 435 /* client-allocated struct with internally allocated stack */ 436 KASSERT(td->td_kstack && td->td_kstack_size > 0, 437 ("lwkt_free_thread: corrupted stack")); 438 kmem_free(&kernel_map, (vm_offset_t)td->td_kstack, td->td_kstack_size); 439 td->td_kstack = NULL; 440 td->td_kstack_size = 0; 441 } 442 } 443 444 445 /* 446 * Switch to the next runnable lwkt. If no LWKTs are runnable then 447 * switch to the idlethread. Switching must occur within a critical 448 * section to avoid races with the scheduling queue. 449 * 450 * We always have full control over our cpu's run queue. Other cpus 451 * that wish to manipulate our queue must use the cpu_*msg() calls to 452 * talk to our cpu, so a critical section is all that is needed and 453 * the result is very, very fast thread switching. 454 * 455 * The LWKT scheduler uses a fixed priority model and round-robins at 456 * each priority level. User process scheduling is a totally 457 * different beast and LWKT priorities should not be confused with 458 * user process priorities. 459 * 460 * The MP lock may be out of sync with the thread's td_mpcount. lwkt_switch() 461 * cleans it up. Note that the td_switch() function cannot do anything that 462 * requires the MP lock since the MP lock will have already been setup for 463 * the target thread (not the current thread). It's nice to have a scheduler 464 * that does not need the MP lock to work because it allows us to do some 465 * really cool high-performance MP lock optimizations. 466 * 467 * PREEMPTION NOTE: Preemption occurs via lwkt_preempt(). lwkt_switch() 468 * is not called by the current thread in the preemption case, only when 469 * the preempting thread blocks (in order to return to the original thread). 470 */ 471 void 472 lwkt_switch(void) 473 { 474 globaldata_t gd = mycpu; 475 thread_t td = gd->gd_curthread; 476 thread_t ntd; 477 #ifdef SMP 478 int mpheld; 479 #endif 480 481 /* 482 * Switching from within a 'fast' (non thread switched) interrupt or IPI 483 * is illegal. However, we may have to do it anyway if we hit a fatal 484 * kernel trap or we have paniced. 485 * 486 * If this case occurs save and restore the interrupt nesting level. 487 */ 488 if (gd->gd_intr_nesting_level) { 489 int savegdnest; 490 int savegdtrap; 491 492 if (gd->gd_trap_nesting_level == 0 && panicstr == NULL) { 493 panic("lwkt_switch: cannot switch from within " 494 "a fast interrupt, yet, td %p\n", td); 495 } else { 496 savegdnest = gd->gd_intr_nesting_level; 497 savegdtrap = gd->gd_trap_nesting_level; 498 gd->gd_intr_nesting_level = 0; 499 gd->gd_trap_nesting_level = 0; 500 if ((td->td_flags & TDF_PANICWARN) == 0) { 501 td->td_flags |= TDF_PANICWARN; 502 kprintf("Warning: thread switch from interrupt or IPI, " 503 "thread %p (%s)\n", td, td->td_comm); 504 #ifdef DDB 505 db_print_backtrace(); 506 #endif 507 } 508 lwkt_switch(); 509 gd->gd_intr_nesting_level = savegdnest; 510 gd->gd_trap_nesting_level = savegdtrap; 511 return; 512 } 513 } 514 515 /* 516 * Passive release (used to transition from user to kernel mode 517 * when we block or switch rather then when we enter the kernel). 518 * This function is NOT called if we are switching into a preemption 519 * or returning from a preemption. Typically this causes us to lose 520 * our current process designation (if we have one) and become a true 521 * LWKT thread, and may also hand the current process designation to 522 * another process and schedule thread. 523 */ 524 if (td->td_release) 525 td->td_release(td); 526 527 crit_enter_gd(gd); 528 if (td->td_toks) 529 lwkt_relalltokens(td); 530 531 /* 532 * We had better not be holding any spin locks, but don't get into an 533 * endless panic loop. 534 */ 535 KASSERT(gd->gd_spinlock_rd == NULL || panicstr != NULL, 536 ("lwkt_switch: still holding a shared spinlock %p!", 537 gd->gd_spinlock_rd)); 538 KASSERT(gd->gd_spinlocks_wr == 0 || panicstr != NULL, 539 ("lwkt_switch: still holding %d exclusive spinlocks!", 540 gd->gd_spinlocks_wr)); 541 542 543 #ifdef SMP 544 /* 545 * td_mpcount cannot be used to determine if we currently hold the 546 * MP lock because get_mplock() will increment it prior to attempting 547 * to get the lock, and switch out if it can't. Our ownership of 548 * the actual lock will remain stable while we are in a critical section 549 * (but, of course, another cpu may own or release the lock so the 550 * actual value of mp_lock is not stable). 551 */ 552 mpheld = MP_LOCK_HELD(); 553 #ifdef INVARIANTS 554 if (td->td_cscount) { 555 kprintf("Diagnostic: attempt to switch while mastering cpusync: %p\n", 556 td); 557 if (panic_on_cscount) 558 panic("switching while mastering cpusync"); 559 } 560 #endif 561 #endif 562 if ((ntd = td->td_preempted) != NULL) { 563 /* 564 * We had preempted another thread on this cpu, resume the preempted 565 * thread. This occurs transparently, whether the preempted thread 566 * was scheduled or not (it may have been preempted after descheduling 567 * itself). 568 * 569 * We have to setup the MP lock for the original thread after backing 570 * out the adjustment that was made to curthread when the original 571 * was preempted. 572 */ 573 KKASSERT(ntd->td_flags & TDF_PREEMPT_LOCK); 574 #ifdef SMP 575 if (ntd->td_mpcount && mpheld == 0) { 576 panic("MPLOCK NOT HELD ON RETURN: %p %p %d %d", 577 td, ntd, td->td_mpcount, ntd->td_mpcount); 578 } 579 if (ntd->td_mpcount) { 580 td->td_mpcount -= ntd->td_mpcount; 581 KKASSERT(td->td_mpcount >= 0); 582 } 583 #endif 584 ntd->td_flags |= TDF_PREEMPT_DONE; 585 586 /* 587 * The interrupt may have woken a thread up, we need to properly 588 * set the reschedule flag if the originally interrupted thread is 589 * at a lower priority. 590 */ 591 if (gd->gd_runqmask > (2 << (ntd->td_pri & TDPRI_MASK)) - 1) 592 need_lwkt_resched(); 593 /* YYY release mp lock on switchback if original doesn't need it */ 594 } else { 595 /* 596 * Priority queue / round-robin at each priority. Note that user 597 * processes run at a fixed, low priority and the user process 598 * scheduler deals with interactions between user processes 599 * by scheduling and descheduling them from the LWKT queue as 600 * necessary. 601 * 602 * We have to adjust the MP lock for the target thread. If we 603 * need the MP lock and cannot obtain it we try to locate a 604 * thread that does not need the MP lock. If we cannot, we spin 605 * instead of HLT. 606 * 607 * A similar issue exists for the tokens held by the target thread. 608 * If we cannot obtain ownership of the tokens we cannot immediately 609 * schedule the thread. 610 */ 611 612 /* 613 * If an LWKT reschedule was requested, well that is what we are 614 * doing now so clear it. 615 */ 616 clear_lwkt_resched(); 617 again: 618 if (gd->gd_runqmask) { 619 int nq = bsrl(gd->gd_runqmask); 620 if ((ntd = TAILQ_FIRST(&gd->gd_tdrunq[nq])) == NULL) { 621 gd->gd_runqmask &= ~(1 << nq); 622 goto again; 623 } 624 #ifdef SMP 625 /* 626 * THREAD SELECTION FOR AN SMP MACHINE BUILD 627 * 628 * If the target needs the MP lock and we couldn't get it, 629 * or if the target is holding tokens and we could not 630 * gain ownership of the tokens, continue looking for a 631 * thread to schedule and spin instead of HLT if we can't. 632 * 633 * NOTE: the mpheld variable invalid after this conditional, it 634 * can change due to both cpu_try_mplock() returning success 635 * AND interactions in lwkt_getalltokens() due to the fact that 636 * we are trying to check the mpcount of a thread other then 637 * the current thread. Because of this, if the current thread 638 * is not holding td_mpcount, an IPI indirectly run via 639 * lwkt_getalltokens() can obtain and release the MP lock and 640 * cause the core MP lock to be released. 641 */ 642 if ((ntd->td_mpcount && mpheld == 0 && !cpu_try_mplock()) || 643 (ntd->td_toks && lwkt_getalltokens(ntd) == 0) 644 ) { 645 u_int32_t rqmask = gd->gd_runqmask; 646 647 mpheld = MP_LOCK_HELD(); 648 ntd = NULL; 649 while (rqmask) { 650 TAILQ_FOREACH(ntd, &gd->gd_tdrunq[nq], td_threadq) { 651 if (ntd->td_mpcount && !mpheld && !cpu_try_mplock()) { 652 /* spinning due to MP lock being held */ 653 #ifdef INVARIANTS 654 ++mplock_contention_count; 655 #endif 656 /* mplock still not held, 'mpheld' still valid */ 657 continue; 658 } 659 660 /* 661 * mpheld state invalid after getalltokens call returns 662 * failure, but the variable is only needed for 663 * the loop. 664 */ 665 if (ntd->td_toks && !lwkt_getalltokens(ntd)) { 666 /* spinning due to token contention */ 667 #ifdef INVARIANTS 668 ++token_contention_count; 669 #endif 670 mpheld = MP_LOCK_HELD(); 671 continue; 672 } 673 break; 674 } 675 if (ntd) 676 break; 677 rqmask &= ~(1 << nq); 678 nq = bsrl(rqmask); 679 680 /* 681 * We have two choices. We can either refuse to run a 682 * user thread when a kernel thread needs the MP lock 683 * but could not get it, or we can allow it to run but 684 * then expect an IPI (hopefully) later on to force a 685 * reschedule when the MP lock might become available. 686 */ 687 if (nq < TDPRI_KERN_LPSCHED) { 688 if (chain_mplock == 0) 689 break; 690 atomic_set_int(&mp_lock_contention_mask, 691 gd->gd_cpumask); 692 /* continue loop, allow user threads to be scheduled */ 693 } 694 } 695 if (ntd == NULL) { 696 cpu_mplock_contested(); 697 ntd = &gd->gd_idlethread; 698 ntd->td_flags |= TDF_IDLE_NOHLT; 699 goto using_idle_thread; 700 } else { 701 ++gd->gd_cnt.v_swtch; 702 TAILQ_REMOVE(&gd->gd_tdrunq[nq], ntd, td_threadq); 703 TAILQ_INSERT_TAIL(&gd->gd_tdrunq[nq], ntd, td_threadq); 704 } 705 } else { 706 ++gd->gd_cnt.v_swtch; 707 TAILQ_REMOVE(&gd->gd_tdrunq[nq], ntd, td_threadq); 708 TAILQ_INSERT_TAIL(&gd->gd_tdrunq[nq], ntd, td_threadq); 709 } 710 #else 711 /* 712 * THREAD SELECTION FOR A UP MACHINE BUILD. We don't have to 713 * worry about tokens or the BGL. However, we still have 714 * to call lwkt_getalltokens() in order to properly detect 715 * stale tokens. This call cannot fail for a UP build! 716 */ 717 lwkt_getalltokens(ntd); 718 ++gd->gd_cnt.v_swtch; 719 TAILQ_REMOVE(&gd->gd_tdrunq[nq], ntd, td_threadq); 720 TAILQ_INSERT_TAIL(&gd->gd_tdrunq[nq], ntd, td_threadq); 721 #endif 722 } else { 723 /* 724 * We have nothing to run but only let the idle loop halt 725 * the cpu if there are no pending interrupts. 726 */ 727 ntd = &gd->gd_idlethread; 728 if (gd->gd_reqflags & RQF_IDLECHECK_MASK) 729 ntd->td_flags |= TDF_IDLE_NOHLT; 730 #ifdef SMP 731 using_idle_thread: 732 /* 733 * The idle thread should not be holding the MP lock unless we 734 * are trapping in the kernel or in a panic. Since we select the 735 * idle thread unconditionally when no other thread is available, 736 * if the MP lock is desired during a panic or kernel trap, we 737 * have to loop in the scheduler until we get it. 738 */ 739 if (ntd->td_mpcount) { 740 mpheld = MP_LOCK_HELD(); 741 if (gd->gd_trap_nesting_level == 0 && panicstr == NULL) { 742 panic("Idle thread %p was holding the BGL!", ntd); 743 } else if (mpheld == 0) { 744 cpu_mplock_contested(); 745 goto again; 746 } 747 } 748 #endif 749 } 750 } 751 KASSERT(ntd->td_pri >= TDPRI_CRIT, 752 ("priority problem in lwkt_switch %d %d", td->td_pri, ntd->td_pri)); 753 754 /* 755 * Do the actual switch. If the new target does not need the MP lock 756 * and we are holding it, release the MP lock. If the new target requires 757 * the MP lock we have already acquired it for the target. 758 */ 759 #ifdef SMP 760 if (ntd->td_mpcount == 0 ) { 761 if (MP_LOCK_HELD()) 762 cpu_rel_mplock(); 763 } else { 764 ASSERT_MP_LOCK_HELD(ntd); 765 } 766 #endif 767 if (td != ntd) { 768 ++switch_count; 769 KKASSERT(jg_tos_ok(ntd)); 770 td->td_switch(ntd); 771 } 772 /* NOTE: current cpu may have changed after switch */ 773 crit_exit_quick(td); 774 } 775 776 /* 777 * Request that the target thread preempt the current thread. Preemption 778 * only works under a specific set of conditions: 779 * 780 * - We are not preempting ourselves 781 * - The target thread is owned by the current cpu 782 * - We are not currently being preempted 783 * - The target is not currently being preempted 784 * - We are not holding any spin locks 785 * - The target thread is not holding any tokens 786 * - We are able to satisfy the target's MP lock requirements (if any). 787 * 788 * THE CALLER OF LWKT_PREEMPT() MUST BE IN A CRITICAL SECTION. Typically 789 * this is called via lwkt_schedule() through the td_preemptable callback. 790 * critpri is the managed critical priority that we should ignore in order 791 * to determine whether preemption is possible (aka usually just the crit 792 * priority of lwkt_schedule() itself). 793 * 794 * XXX at the moment we run the target thread in a critical section during 795 * the preemption in order to prevent the target from taking interrupts 796 * that *WE* can't. Preemption is strictly limited to interrupt threads 797 * and interrupt-like threads, outside of a critical section, and the 798 * preempted source thread will be resumed the instant the target blocks 799 * whether or not the source is scheduled (i.e. preemption is supposed to 800 * be as transparent as possible). 801 * 802 * The target thread inherits our MP count (added to its own) for the 803 * duration of the preemption in order to preserve the atomicy of the 804 * MP lock during the preemption. Therefore, any preempting targets must be 805 * careful in regards to MP assertions. Note that the MP count may be 806 * out of sync with the physical mp_lock, but we do not have to preserve 807 * the original ownership of the lock if it was out of synch (that is, we 808 * can leave it synchronized on return). 809 */ 810 void 811 lwkt_preempt(thread_t ntd, int critpri) 812 { 813 struct globaldata *gd = mycpu; 814 thread_t td; 815 #ifdef SMP 816 int mpheld; 817 int savecnt; 818 #endif 819 820 /* 821 * The caller has put us in a critical section. We can only preempt 822 * if the caller of the caller was not in a critical section (basically 823 * a local interrupt), as determined by the 'critpri' parameter. We 824 * also can't preempt if the caller is holding any spinlocks (even if 825 * he isn't in a critical section). This also handles the tokens test. 826 * 827 * YYY The target thread must be in a critical section (else it must 828 * inherit our critical section? I dunno yet). 829 * 830 * Set need_lwkt_resched() unconditionally for now YYY. 831 */ 832 KASSERT(ntd->td_pri >= TDPRI_CRIT, ("BADCRIT0 %d", ntd->td_pri)); 833 834 td = gd->gd_curthread; 835 if ((ntd->td_pri & TDPRI_MASK) <= (td->td_pri & TDPRI_MASK)) { 836 ++preempt_miss; 837 return; 838 } 839 if ((td->td_pri & ~TDPRI_MASK) > critpri) { 840 ++preempt_miss; 841 need_lwkt_resched(); 842 return; 843 } 844 #ifdef SMP 845 if (ntd->td_gd != gd) { 846 ++preempt_miss; 847 need_lwkt_resched(); 848 return; 849 } 850 #endif 851 /* 852 * Take the easy way out and do not preempt if we are holding 853 * any spinlocks. We could test whether the thread(s) being 854 * preempted interlock against the target thread's tokens and whether 855 * we can get all the target thread's tokens, but this situation 856 * should not occur very often so its easier to simply not preempt. 857 * Also, plain spinlocks are impossible to figure out at this point so 858 * just don't preempt. 859 * 860 * Do not try to preempt if the target thread is holding any tokens. 861 * We could try to acquire the tokens but this case is so rare there 862 * is no need to support it. 863 */ 864 if (gd->gd_spinlock_rd || gd->gd_spinlocks_wr) { 865 ++preempt_miss; 866 need_lwkt_resched(); 867 return; 868 } 869 if (ntd->td_toks) { 870 ++preempt_miss; 871 need_lwkt_resched(); 872 return; 873 } 874 if (td == ntd || ((td->td_flags | ntd->td_flags) & TDF_PREEMPT_LOCK)) { 875 ++preempt_weird; 876 need_lwkt_resched(); 877 return; 878 } 879 if (ntd->td_preempted) { 880 ++preempt_hit; 881 need_lwkt_resched(); 882 return; 883 } 884 #ifdef SMP 885 /* 886 * note: an interrupt might have occured just as we were transitioning 887 * to or from the MP lock. In this case td_mpcount will be pre-disposed 888 * (non-zero) but not actually synchronized with the actual state of the 889 * lock. We can use it to imply an MP lock requirement for the 890 * preemption but we cannot use it to test whether we hold the MP lock 891 * or not. 892 */ 893 savecnt = td->td_mpcount; 894 mpheld = MP_LOCK_HELD(); 895 ntd->td_mpcount += td->td_mpcount; 896 if (mpheld == 0 && ntd->td_mpcount && !cpu_try_mplock()) { 897 ntd->td_mpcount -= td->td_mpcount; 898 ++preempt_miss; 899 need_lwkt_resched(); 900 return; 901 } 902 #endif 903 904 /* 905 * Since we are able to preempt the current thread, there is no need to 906 * call need_lwkt_resched(). 907 */ 908 ++preempt_hit; 909 ntd->td_preempted = td; 910 td->td_flags |= TDF_PREEMPT_LOCK; 911 td->td_switch(ntd); 912 913 KKASSERT(ntd->td_preempted && (td->td_flags & TDF_PREEMPT_DONE)); 914 #ifdef SMP 915 KKASSERT(savecnt == td->td_mpcount); 916 mpheld = MP_LOCK_HELD(); 917 if (mpheld && td->td_mpcount == 0) 918 cpu_rel_mplock(); 919 else if (mpheld == 0 && td->td_mpcount) 920 panic("lwkt_preempt(): MP lock was not held through"); 921 #endif 922 ntd->td_preempted = NULL; 923 td->td_flags &= ~(TDF_PREEMPT_LOCK|TDF_PREEMPT_DONE); 924 } 925 926 /* 927 * Yield our thread while higher priority threads are pending. This is 928 * typically called when we leave a critical section but it can be safely 929 * called while we are in a critical section. 930 * 931 * This function will not generally yield to equal priority threads but it 932 * can occur as a side effect. Note that lwkt_switch() is called from 933 * inside the critical section to prevent its own crit_exit() from reentering 934 * lwkt_yield_quick(). 935 * 936 * gd_reqflags indicates that *something* changed, e.g. an interrupt or softint 937 * came along but was blocked and made pending. 938 * 939 * (self contained on a per cpu basis) 940 */ 941 void 942 lwkt_yield_quick(void) 943 { 944 globaldata_t gd = mycpu; 945 thread_t td = gd->gd_curthread; 946 947 /* 948 * gd_reqflags is cleared in splz if the cpl is 0. If we were to clear 949 * it with a non-zero cpl then we might not wind up calling splz after 950 * a task switch when the critical section is exited even though the 951 * new task could accept the interrupt. 952 * 953 * XXX from crit_exit() only called after last crit section is released. 954 * If called directly will run splz() even if in a critical section. 955 * 956 * td_nest_count prevent deep nesting via splz() or doreti(). Note that 957 * except for this special case, we MUST call splz() here to handle any 958 * pending ints, particularly after we switch, or we might accidently 959 * halt the cpu with interrupts pending. 960 */ 961 if (gd->gd_reqflags && td->td_nest_count < 2) 962 splz(); 963 964 /* 965 * YYY enabling will cause wakeup() to task-switch, which really 966 * confused the old 4.x code. This is a good way to simulate 967 * preemption and MP without actually doing preemption or MP, because a 968 * lot of code assumes that wakeup() does not block. 969 */ 970 if (untimely_switch && td->td_nest_count == 0 && 971 gd->gd_intr_nesting_level == 0 972 ) { 973 crit_enter_quick(td); 974 /* 975 * YYY temporary hacks until we disassociate the userland scheduler 976 * from the LWKT scheduler. 977 */ 978 if (td->td_flags & TDF_RUNQ) { 979 lwkt_switch(); /* will not reenter yield function */ 980 } else { 981 lwkt_schedule_self(td); /* make sure we are scheduled */ 982 lwkt_switch(); /* will not reenter yield function */ 983 lwkt_deschedule_self(td); /* make sure we are descheduled */ 984 } 985 crit_exit_noyield(td); 986 } 987 } 988 989 /* 990 * This implements a normal yield which, unlike _quick, will yield to equal 991 * priority threads as well. Note that gd_reqflags tests will be handled by 992 * the crit_exit() call in lwkt_switch(). 993 * 994 * (self contained on a per cpu basis) 995 */ 996 void 997 lwkt_yield(void) 998 { 999 lwkt_schedule_self(curthread); 1000 lwkt_switch(); 1001 } 1002 1003 /* 1004 * Return 0 if no runnable threads are pending at the same or higher 1005 * priority as the passed thread. 1006 * 1007 * Return 1 if runnable threads are pending at the same priority. 1008 * 1009 * Return 2 if runnable threads are pending at a higher priority. 1010 */ 1011 int 1012 lwkt_check_resched(thread_t td) 1013 { 1014 int pri = td->td_pri & TDPRI_MASK; 1015 1016 if (td->td_gd->gd_runqmask > (2 << pri) - 1) 1017 return(2); 1018 if (TAILQ_NEXT(td, td_threadq)) 1019 return(1); 1020 return(0); 1021 } 1022 1023 /* 1024 * Generic schedule. Possibly schedule threads belonging to other cpus and 1025 * deal with threads that might be blocked on a wait queue. 1026 * 1027 * We have a little helper inline function which does additional work after 1028 * the thread has been enqueued, including dealing with preemption and 1029 * setting need_lwkt_resched() (which prevents the kernel from returning 1030 * to userland until it has processed higher priority threads). 1031 * 1032 * It is possible for this routine to be called after a failed _enqueue 1033 * (due to the target thread migrating, sleeping, or otherwise blocked). 1034 * We have to check that the thread is actually on the run queue! 1035 * 1036 * reschedok is an optimized constant propagated from lwkt_schedule() or 1037 * lwkt_schedule_noresched(). By default it is non-zero, causing a 1038 * reschedule to be requested if the target thread has a higher priority. 1039 * The port messaging code will set MSG_NORESCHED and cause reschedok to 1040 * be 0, prevented undesired reschedules. 1041 */ 1042 static __inline 1043 void 1044 _lwkt_schedule_post(globaldata_t gd, thread_t ntd, int cpri, int reschedok) 1045 { 1046 thread_t otd; 1047 1048 if (ntd->td_flags & TDF_RUNQ) { 1049 if (ntd->td_preemptable && reschedok) { 1050 ntd->td_preemptable(ntd, cpri); /* YYY +token */ 1051 } else if (reschedok) { 1052 otd = curthread; 1053 if ((ntd->td_pri & TDPRI_MASK) > (otd->td_pri & TDPRI_MASK)) 1054 need_lwkt_resched(); 1055 } 1056 } 1057 } 1058 1059 static __inline 1060 void 1061 _lwkt_schedule(thread_t td, int reschedok) 1062 { 1063 globaldata_t mygd = mycpu; 1064 1065 KASSERT(td != &td->td_gd->gd_idlethread, ("lwkt_schedule(): scheduling gd_idlethread is illegal!")); 1066 crit_enter_gd(mygd); 1067 KKASSERT(td->td_lwp == NULL || (td->td_lwp->lwp_flag & LWP_ONRUNQ) == 0); 1068 if (td == mygd->gd_curthread) { 1069 _lwkt_enqueue(td); 1070 } else { 1071 /* 1072 * If we own the thread, there is no race (since we are in a 1073 * critical section). If we do not own the thread there might 1074 * be a race but the target cpu will deal with it. 1075 */ 1076 #ifdef SMP 1077 if (td->td_gd == mygd) { 1078 _lwkt_enqueue(td); 1079 _lwkt_schedule_post(mygd, td, TDPRI_CRIT, reschedok); 1080 } else { 1081 lwkt_send_ipiq(td->td_gd, (ipifunc1_t)lwkt_schedule, td); 1082 } 1083 #else 1084 _lwkt_enqueue(td); 1085 _lwkt_schedule_post(mygd, td, TDPRI_CRIT, reschedok); 1086 #endif 1087 } 1088 crit_exit_gd(mygd); 1089 } 1090 1091 void 1092 lwkt_schedule(thread_t td) 1093 { 1094 _lwkt_schedule(td, 1); 1095 } 1096 1097 void 1098 lwkt_schedule_noresched(thread_t td) 1099 { 1100 _lwkt_schedule(td, 0); 1101 } 1102 1103 #ifdef SMP 1104 1105 /* 1106 * Thread migration using a 'Pull' method. The thread may or may not be 1107 * the current thread. It MUST be descheduled and in a stable state. 1108 * lwkt_giveaway() must be called on the cpu owning the thread. 1109 * 1110 * At any point after lwkt_giveaway() is called, the target cpu may 1111 * 'pull' the thread by calling lwkt_acquire(). 1112 * 1113 * MPSAFE - must be called under very specific conditions. 1114 */ 1115 void 1116 lwkt_giveaway(thread_t td) 1117 { 1118 globaldata_t gd = mycpu; 1119 1120 crit_enter_gd(gd); 1121 KKASSERT(td->td_gd == gd); 1122 TAILQ_REMOVE(&gd->gd_tdallq, td, td_allq); 1123 td->td_flags |= TDF_MIGRATING; 1124 crit_exit_gd(gd); 1125 } 1126 1127 void 1128 lwkt_acquire(thread_t td) 1129 { 1130 globaldata_t gd; 1131 globaldata_t mygd; 1132 1133 KKASSERT(td->td_flags & TDF_MIGRATING); 1134 gd = td->td_gd; 1135 mygd = mycpu; 1136 if (gd != mycpu) { 1137 cpu_lfence(); 1138 KKASSERT((td->td_flags & TDF_RUNQ) == 0); 1139 crit_enter_gd(mygd); 1140 while (td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK)) { 1141 #ifdef SMP 1142 lwkt_process_ipiq(); 1143 #endif 1144 cpu_lfence(); 1145 } 1146 td->td_gd = mygd; 1147 TAILQ_INSERT_TAIL(&mygd->gd_tdallq, td, td_allq); 1148 td->td_flags &= ~TDF_MIGRATING; 1149 crit_exit_gd(mygd); 1150 } else { 1151 crit_enter_gd(mygd); 1152 TAILQ_INSERT_TAIL(&mygd->gd_tdallq, td, td_allq); 1153 td->td_flags &= ~TDF_MIGRATING; 1154 crit_exit_gd(mygd); 1155 } 1156 } 1157 1158 #endif 1159 1160 /* 1161 * Generic deschedule. Descheduling threads other then your own should be 1162 * done only in carefully controlled circumstances. Descheduling is 1163 * asynchronous. 1164 * 1165 * This function may block if the cpu has run out of messages. 1166 */ 1167 void 1168 lwkt_deschedule(thread_t td) 1169 { 1170 crit_enter(); 1171 #ifdef SMP 1172 if (td == curthread) { 1173 _lwkt_dequeue(td); 1174 } else { 1175 if (td->td_gd == mycpu) { 1176 _lwkt_dequeue(td); 1177 } else { 1178 lwkt_send_ipiq(td->td_gd, (ipifunc1_t)lwkt_deschedule, td); 1179 } 1180 } 1181 #else 1182 _lwkt_dequeue(td); 1183 #endif 1184 crit_exit(); 1185 } 1186 1187 /* 1188 * Set the target thread's priority. This routine does not automatically 1189 * switch to a higher priority thread, LWKT threads are not designed for 1190 * continuous priority changes. Yield if you want to switch. 1191 * 1192 * We have to retain the critical section count which uses the high bits 1193 * of the td_pri field. The specified priority may also indicate zero or 1194 * more critical sections by adding TDPRI_CRIT*N. 1195 * 1196 * Note that we requeue the thread whether it winds up on a different runq 1197 * or not. uio_yield() depends on this and the routine is not normally 1198 * called with the same priority otherwise. 1199 */ 1200 void 1201 lwkt_setpri(thread_t td, int pri) 1202 { 1203 KKASSERT(pri >= 0); 1204 KKASSERT(td->td_gd == mycpu); 1205 crit_enter(); 1206 if (td->td_flags & TDF_RUNQ) { 1207 _lwkt_dequeue(td); 1208 td->td_pri = (td->td_pri & ~TDPRI_MASK) + pri; 1209 _lwkt_enqueue(td); 1210 } else { 1211 td->td_pri = (td->td_pri & ~TDPRI_MASK) + pri; 1212 } 1213 crit_exit(); 1214 } 1215 1216 void 1217 lwkt_setpri_self(int pri) 1218 { 1219 thread_t td = curthread; 1220 1221 KKASSERT(pri >= 0 && pri <= TDPRI_MAX); 1222 crit_enter(); 1223 if (td->td_flags & TDF_RUNQ) { 1224 _lwkt_dequeue(td); 1225 td->td_pri = (td->td_pri & ~TDPRI_MASK) + pri; 1226 _lwkt_enqueue(td); 1227 } else { 1228 td->td_pri = (td->td_pri & ~TDPRI_MASK) + pri; 1229 } 1230 crit_exit(); 1231 } 1232 1233 /* 1234 * Migrate the current thread to the specified cpu. 1235 * 1236 * This is accomplished by descheduling ourselves from the current cpu, 1237 * moving our thread to the tdallq of the target cpu, IPI messaging the 1238 * target cpu, and switching out. TDF_MIGRATING prevents scheduling 1239 * races while the thread is being migrated. 1240 */ 1241 #ifdef SMP 1242 static void lwkt_setcpu_remote(void *arg); 1243 #endif 1244 1245 void 1246 lwkt_setcpu_self(globaldata_t rgd) 1247 { 1248 #ifdef SMP 1249 thread_t td = curthread; 1250 1251 if (td->td_gd != rgd) { 1252 crit_enter_quick(td); 1253 td->td_flags |= TDF_MIGRATING; 1254 lwkt_deschedule_self(td); 1255 TAILQ_REMOVE(&td->td_gd->gd_tdallq, td, td_allq); 1256 lwkt_send_ipiq(rgd, (ipifunc1_t)lwkt_setcpu_remote, td); 1257 lwkt_switch(); 1258 /* we are now on the target cpu */ 1259 TAILQ_INSERT_TAIL(&rgd->gd_tdallq, td, td_allq); 1260 crit_exit_quick(td); 1261 } 1262 #endif 1263 } 1264 1265 void 1266 lwkt_migratecpu(int cpuid) 1267 { 1268 #ifdef SMP 1269 globaldata_t rgd; 1270 1271 rgd = globaldata_find(cpuid); 1272 lwkt_setcpu_self(rgd); 1273 #endif 1274 } 1275 1276 /* 1277 * Remote IPI for cpu migration (called while in a critical section so we 1278 * do not have to enter another one). The thread has already been moved to 1279 * our cpu's allq, but we must wait for the thread to be completely switched 1280 * out on the originating cpu before we schedule it on ours or the stack 1281 * state may be corrupt. We clear TDF_MIGRATING after flushing the GD 1282 * change to main memory. 1283 * 1284 * XXX The use of TDF_MIGRATING might not be sufficient to avoid races 1285 * against wakeups. It is best if this interface is used only when there 1286 * are no pending events that might try to schedule the thread. 1287 */ 1288 #ifdef SMP 1289 static void 1290 lwkt_setcpu_remote(void *arg) 1291 { 1292 thread_t td = arg; 1293 globaldata_t gd = mycpu; 1294 1295 while (td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK)) { 1296 #ifdef SMP 1297 lwkt_process_ipiq(); 1298 #endif 1299 cpu_lfence(); 1300 } 1301 td->td_gd = gd; 1302 cpu_sfence(); 1303 td->td_flags &= ~TDF_MIGRATING; 1304 KKASSERT(td->td_lwp == NULL || (td->td_lwp->lwp_flag & LWP_ONRUNQ) == 0); 1305 _lwkt_enqueue(td); 1306 } 1307 #endif 1308 1309 struct lwp * 1310 lwkt_preempted_proc(void) 1311 { 1312 thread_t td = curthread; 1313 while (td->td_preempted) 1314 td = td->td_preempted; 1315 return(td->td_lwp); 1316 } 1317 1318 /* 1319 * Create a kernel process/thread/whatever. It shares it's address space 1320 * with proc0 - ie: kernel only. 1321 * 1322 * NOTE! By default new threads are created with the MP lock held. A 1323 * thread which does not require the MP lock should release it by calling 1324 * rel_mplock() at the start of the new thread. 1325 */ 1326 int 1327 lwkt_create(void (*func)(void *), void *arg, 1328 struct thread **tdp, thread_t template, int tdflags, int cpu, 1329 const char *fmt, ...) 1330 { 1331 thread_t td; 1332 __va_list ap; 1333 1334 td = lwkt_alloc_thread(template, LWKT_THREAD_STACK, cpu, 1335 tdflags); 1336 if (tdp) 1337 *tdp = td; 1338 cpu_set_thread_handler(td, lwkt_exit, func, arg); 1339 1340 /* 1341 * Set up arg0 for 'ps' etc 1342 */ 1343 __va_start(ap, fmt); 1344 kvsnprintf(td->td_comm, sizeof(td->td_comm), fmt, ap); 1345 __va_end(ap); 1346 1347 /* 1348 * Schedule the thread to run 1349 */ 1350 if ((td->td_flags & TDF_STOPREQ) == 0) 1351 lwkt_schedule(td); 1352 else 1353 td->td_flags &= ~TDF_STOPREQ; 1354 return 0; 1355 } 1356 1357 /* 1358 * Destroy an LWKT thread. Warning! This function is not called when 1359 * a process exits, cpu_proc_exit() directly calls cpu_thread_exit() and 1360 * uses a different reaping mechanism. 1361 */ 1362 void 1363 lwkt_exit(void) 1364 { 1365 thread_t td = curthread; 1366 thread_t std; 1367 globaldata_t gd; 1368 1369 if (td->td_flags & TDF_VERBOSE) 1370 kprintf("kthread %p %s has exited\n", td, td->td_comm); 1371 caps_exit(td); 1372 1373 /* 1374 * Get us into a critical section to interlock gd_freetd and loop 1375 * until we can get it freed. 1376 * 1377 * We have to cache the current td in gd_freetd because objcache_put()ing 1378 * it would rip it out from under us while our thread is still active. 1379 */ 1380 gd = mycpu; 1381 crit_enter_quick(td); 1382 while ((std = gd->gd_freetd) != NULL) { 1383 gd->gd_freetd = NULL; 1384 objcache_put(thread_cache, std); 1385 } 1386 lwkt_deschedule_self(td); 1387 lwkt_remove_tdallq(td); 1388 if (td->td_flags & TDF_ALLOCATED_THREAD) 1389 gd->gd_freetd = td; 1390 cpu_thread_exit(); 1391 } 1392 1393 void 1394 lwkt_remove_tdallq(thread_t td) 1395 { 1396 KKASSERT(td->td_gd == mycpu); 1397 TAILQ_REMOVE(&td->td_gd->gd_tdallq, td, td_allq); 1398 } 1399 1400 void 1401 crit_panic(void) 1402 { 1403 thread_t td = curthread; 1404 int lpri = td->td_pri; 1405 1406 td->td_pri = 0; 1407 panic("td_pri is/would-go negative! %p %d", td, lpri); 1408 } 1409 1410 #ifdef SMP 1411 1412 /* 1413 * Called from debugger/panic on cpus which have been stopped. We must still 1414 * process the IPIQ while stopped, even if we were stopped while in a critical 1415 * section (XXX). 1416 * 1417 * If we are dumping also try to process any pending interrupts. This may 1418 * or may not work depending on the state of the cpu at the point it was 1419 * stopped. 1420 */ 1421 void 1422 lwkt_smp_stopped(void) 1423 { 1424 globaldata_t gd = mycpu; 1425 1426 crit_enter_gd(gd); 1427 if (dumping) { 1428 lwkt_process_ipiq(); 1429 splz(); 1430 } else { 1431 lwkt_process_ipiq(); 1432 } 1433 crit_exit_gd(gd); 1434 } 1435 1436 /* 1437 * get_mplock() calls this routine if it is unable to obtain the MP lock. 1438 * get_mplock() has already incremented td_mpcount. We must block and 1439 * not return until giant is held. 1440 * 1441 * All we have to do is lwkt_switch() away. The LWKT scheduler will not 1442 * reschedule the thread until it can obtain the giant lock for it. 1443 */ 1444 void 1445 lwkt_mp_lock_contested(void) 1446 { 1447 loggiant(beg); 1448 lwkt_switch(); 1449 loggiant(end); 1450 } 1451 1452 /* 1453 * The rel_mplock() code will call this function after releasing the 1454 * last reference on the MP lock if mp_lock_contention_mask is non-zero. 1455 * 1456 * We then chain an IPI to a single other cpu potentially needing the 1457 * lock. This is a bit heuristical and we can wind up with IPIs flying 1458 * all over the place. 1459 */ 1460 static void lwkt_mp_lock_uncontested_remote(void *arg __unused); 1461 1462 void 1463 lwkt_mp_lock_uncontested(void) 1464 { 1465 globaldata_t gd; 1466 globaldata_t dgd; 1467 cpumask_t mask; 1468 cpumask_t tmpmask; 1469 int cpuid; 1470 1471 if (chain_mplock) { 1472 gd = mycpu; 1473 atomic_clear_int(&mp_lock_contention_mask, gd->gd_cpumask); 1474 mask = mp_lock_contention_mask; 1475 tmpmask = ~((1 << gd->gd_cpuid) - 1); 1476 1477 if (mask) { 1478 if (mask & tmpmask) 1479 cpuid = bsfl(mask & tmpmask); 1480 else 1481 cpuid = bsfl(mask); 1482 atomic_clear_int(&mp_lock_contention_mask, 1 << cpuid); 1483 dgd = globaldata_find(cpuid); 1484 lwkt_send_ipiq(dgd, lwkt_mp_lock_uncontested_remote, NULL); 1485 } 1486 } 1487 } 1488 1489 /* 1490 * The idea is for this IPI to interrupt a potentially lower priority 1491 * thread, such as a user thread, to allow the scheduler to reschedule 1492 * a higher priority kernel thread that needs the MP lock. 1493 * 1494 * For now we set the LWKT reschedule flag which generates an AST in 1495 * doreti, though theoretically it is also possible to possibly preempt 1496 * here if the underlying thread was operating in user mode. Nah. 1497 */ 1498 static void 1499 lwkt_mp_lock_uncontested_remote(void *arg __unused) 1500 { 1501 need_lwkt_resched(); 1502 } 1503 1504 #endif 1505