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 44 #include <sys/param.h> 45 #include <sys/systm.h> 46 #include <sys/kernel.h> 47 #include <sys/proc.h> 48 #include <sys/rtprio.h> 49 #include <sys/queue.h> 50 #include <sys/sysctl.h> 51 #include <sys/kthread.h> 52 #include <machine/cpu.h> 53 #include <sys/lock.h> 54 #include <sys/caps.h> 55 #include <sys/spinlock.h> 56 #include <sys/ktr.h> 57 58 #include <sys/thread2.h> 59 #include <sys/spinlock2.h> 60 61 #include <vm/vm.h> 62 #include <vm/vm_param.h> 63 #include <vm/vm_kern.h> 64 #include <vm/vm_object.h> 65 #include <vm/vm_page.h> 66 #include <vm/vm_map.h> 67 #include <vm/vm_pager.h> 68 #include <vm/vm_extern.h> 69 70 #include <machine/stdarg.h> 71 #include <machine/smp.h> 72 73 74 static MALLOC_DEFINE(M_THREAD, "thread", "lwkt threads"); 75 76 static int untimely_switch = 0; 77 #ifdef INVARIANTS 78 static int panic_on_cscount = 0; 79 #endif 80 static __int64_t switch_count = 0; 81 static __int64_t preempt_hit = 0; 82 static __int64_t preempt_miss = 0; 83 static __int64_t preempt_weird = 0; 84 static __int64_t token_contention_count = 0; 85 static __int64_t mplock_contention_count = 0; 86 static int lwkt_use_spin_port; 87 #ifdef SMP 88 static int chain_mplock = 0; 89 #endif 90 static struct objcache *thread_cache; 91 92 volatile cpumask_t mp_lock_contention_mask; 93 94 extern void cpu_heavy_restore(void); 95 extern void cpu_lwkt_restore(void); 96 extern void cpu_kthread_restore(void); 97 extern void cpu_idle_restore(void); 98 99 #ifdef __amd64__ 100 101 static int 102 jg_tos_ok(struct thread *td) 103 { 104 void *tos; 105 int tos_ok; 106 107 if (td == NULL) { 108 return 1; 109 } 110 KKASSERT(td->td_sp != NULL); 111 tos = ((void **)td->td_sp)[0]; 112 tos_ok = 0; 113 if ((tos == cpu_heavy_restore) || (tos == cpu_lwkt_restore) || 114 (tos == cpu_kthread_restore) || (tos == cpu_idle_restore)) { 115 tos_ok = 1; 116 } 117 return tos_ok; 118 } 119 120 #endif 121 122 /* 123 * We can make all thread ports use the spin backend instead of the thread 124 * backend. This should only be set to debug the spin backend. 125 */ 126 TUNABLE_INT("lwkt.use_spin_port", &lwkt_use_spin_port); 127 128 SYSCTL_INT(_lwkt, OID_AUTO, untimely_switch, CTLFLAG_RW, &untimely_switch, 0, ""); 129 #ifdef INVARIANTS 130 SYSCTL_INT(_lwkt, OID_AUTO, panic_on_cscount, CTLFLAG_RW, &panic_on_cscount, 0, ""); 131 #endif 132 #ifdef SMP 133 SYSCTL_INT(_lwkt, OID_AUTO, chain_mplock, CTLFLAG_RW, &chain_mplock, 0, ""); 134 #endif 135 SYSCTL_QUAD(_lwkt, OID_AUTO, switch_count, CTLFLAG_RW, &switch_count, 0, ""); 136 SYSCTL_QUAD(_lwkt, OID_AUTO, preempt_hit, CTLFLAG_RW, &preempt_hit, 0, ""); 137 SYSCTL_QUAD(_lwkt, OID_AUTO, preempt_miss, CTLFLAG_RW, &preempt_miss, 0, ""); 138 SYSCTL_QUAD(_lwkt, OID_AUTO, preempt_weird, CTLFLAG_RW, &preempt_weird, 0, ""); 139 #ifdef INVARIANTS 140 SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count, CTLFLAG_RW, 141 &token_contention_count, 0, "spinning due to token contention"); 142 SYSCTL_QUAD(_lwkt, OID_AUTO, mplock_contention_count, CTLFLAG_RW, 143 &mplock_contention_count, 0, "spinning due to MPLOCK contention"); 144 #endif 145 146 /* 147 * Kernel Trace 148 */ 149 #if !defined(KTR_GIANT_CONTENTION) 150 #define KTR_GIANT_CONTENTION KTR_ALL 151 #endif 152 153 KTR_INFO_MASTER(giant); 154 KTR_INFO(KTR_GIANT_CONTENTION, giant, beg, 0, "thread=%p", sizeof(void *)); 155 KTR_INFO(KTR_GIANT_CONTENTION, giant, end, 1, "thread=%p", sizeof(void *)); 156 157 #define loggiant(name) KTR_LOG(giant_ ## name, curthread) 158 159 /* 160 * These helper procedures handle the runq, they can only be called from 161 * within a critical section. 162 * 163 * WARNING! Prior to SMP being brought up it is possible to enqueue and 164 * dequeue threads belonging to other cpus, so be sure to use td->td_gd 165 * instead of 'mycpu' when referencing the globaldata structure. Once 166 * SMP live enqueuing and dequeueing only occurs on the current cpu. 167 */ 168 static __inline 169 void 170 _lwkt_dequeue(thread_t td) 171 { 172 if (td->td_flags & TDF_RUNQ) { 173 int nq = td->td_pri & TDPRI_MASK; 174 struct globaldata *gd = td->td_gd; 175 176 td->td_flags &= ~TDF_RUNQ; 177 TAILQ_REMOVE(&gd->gd_tdrunq[nq], td, td_threadq); 178 /* runqmask is passively cleaned up by the switcher */ 179 } 180 } 181 182 static __inline 183 void 184 _lwkt_enqueue(thread_t td) 185 { 186 if ((td->td_flags & (TDF_RUNQ|TDF_MIGRATING|TDF_TSLEEPQ|TDF_BLOCKQ)) == 0) { 187 int nq = td->td_pri & TDPRI_MASK; 188 struct globaldata *gd = td->td_gd; 189 190 td->td_flags |= TDF_RUNQ; 191 TAILQ_INSERT_TAIL(&gd->gd_tdrunq[nq], td, td_threadq); 192 gd->gd_runqmask |= 1 << nq; 193 } 194 } 195 196 static __boolean_t 197 _lwkt_thread_ctor(void *obj, void *privdata, int ocflags) 198 { 199 struct thread *td = (struct thread *)obj; 200 201 td->td_kstack = NULL; 202 td->td_kstack_size = 0; 203 td->td_flags = TDF_ALLOCATED_THREAD; 204 return (1); 205 } 206 207 static void 208 _lwkt_thread_dtor(void *obj, void *privdata) 209 { 210 struct thread *td = (struct thread *)obj; 211 212 KASSERT(td->td_flags & TDF_ALLOCATED_THREAD, 213 ("_lwkt_thread_dtor: not allocated from objcache")); 214 KASSERT((td->td_flags & TDF_ALLOCATED_STACK) && td->td_kstack && 215 td->td_kstack_size > 0, 216 ("_lwkt_thread_dtor: corrupted stack")); 217 kmem_free(&kernel_map, (vm_offset_t)td->td_kstack, td->td_kstack_size); 218 } 219 220 /* 221 * Initialize the lwkt s/system. 222 */ 223 void 224 lwkt_init(void) 225 { 226 /* An objcache has 2 magazines per CPU so divide cache size by 2. */ 227 thread_cache = objcache_create_mbacked(M_THREAD, sizeof(struct thread), 228 NULL, CACHE_NTHREADS/2, 229 _lwkt_thread_ctor, _lwkt_thread_dtor, NULL); 230 } 231 232 /* 233 * Schedule a thread to run. As the current thread we can always safely 234 * schedule ourselves, and a shortcut procedure is provided for that 235 * function. 236 * 237 * (non-blocking, self contained on a per cpu basis) 238 */ 239 void 240 lwkt_schedule_self(thread_t td) 241 { 242 crit_enter_quick(td); 243 KASSERT(td != &td->td_gd->gd_idlethread, ("lwkt_schedule_self(): scheduling gd_idlethread is illegal!")); 244 KKASSERT(td->td_lwp == NULL || (td->td_lwp->lwp_flag & LWP_ONRUNQ) == 0); 245 _lwkt_enqueue(td); 246 crit_exit_quick(td); 247 } 248 249 /* 250 * Deschedule a thread. 251 * 252 * (non-blocking, self contained on a per cpu basis) 253 */ 254 void 255 lwkt_deschedule_self(thread_t td) 256 { 257 crit_enter_quick(td); 258 _lwkt_dequeue(td); 259 crit_exit_quick(td); 260 } 261 262 /* 263 * LWKTs operate on a per-cpu basis 264 * 265 * WARNING! Called from early boot, 'mycpu' may not work yet. 266 */ 267 void 268 lwkt_gdinit(struct globaldata *gd) 269 { 270 int i; 271 272 for (i = 0; i < sizeof(gd->gd_tdrunq)/sizeof(gd->gd_tdrunq[0]); ++i) 273 TAILQ_INIT(&gd->gd_tdrunq[i]); 274 gd->gd_runqmask = 0; 275 TAILQ_INIT(&gd->gd_tdallq); 276 } 277 278 /* 279 * Create a new thread. The thread must be associated with a process context 280 * or LWKT start address before it can be scheduled. If the target cpu is 281 * -1 the thread will be created on the current cpu. 282 * 283 * If you intend to create a thread without a process context this function 284 * does everything except load the startup and switcher function. 285 */ 286 thread_t 287 lwkt_alloc_thread(struct thread *td, int stksize, int cpu, int flags) 288 { 289 globaldata_t gd = mycpu; 290 void *stack; 291 292 /* 293 * If static thread storage is not supplied allocate a thread. Reuse 294 * a cached free thread if possible. gd_freetd is used to keep an exiting 295 * thread intact through the exit. 296 */ 297 if (td == NULL) { 298 if ((td = gd->gd_freetd) != NULL) 299 gd->gd_freetd = NULL; 300 else 301 td = objcache_get(thread_cache, M_WAITOK); 302 KASSERT((td->td_flags & 303 (TDF_ALLOCATED_THREAD|TDF_RUNNING)) == TDF_ALLOCATED_THREAD, 304 ("lwkt_alloc_thread: corrupted td flags 0x%X", td->td_flags)); 305 flags |= td->td_flags & (TDF_ALLOCATED_THREAD|TDF_ALLOCATED_STACK); 306 } 307 308 /* 309 * Try to reuse cached stack. 310 */ 311 if ((stack = td->td_kstack) != NULL && td->td_kstack_size != stksize) { 312 if (flags & TDF_ALLOCATED_STACK) { 313 kmem_free(&kernel_map, (vm_offset_t)stack, td->td_kstack_size); 314 stack = NULL; 315 } 316 } 317 if (stack == NULL) { 318 stack = (void *)kmem_alloc(&kernel_map, stksize); 319 flags |= TDF_ALLOCATED_STACK; 320 } 321 if (cpu < 0) 322 lwkt_init_thread(td, stack, stksize, flags, gd); 323 else 324 lwkt_init_thread(td, stack, stksize, flags, globaldata_find(cpu)); 325 return(td); 326 } 327 328 /* 329 * Initialize a preexisting thread structure. This function is used by 330 * lwkt_alloc_thread() and also used to initialize the per-cpu idlethread. 331 * 332 * All threads start out in a critical section at a priority of 333 * TDPRI_KERN_DAEMON. Higher level code will modify the priority as 334 * appropriate. This function may send an IPI message when the 335 * requested cpu is not the current cpu and consequently gd_tdallq may 336 * not be initialized synchronously from the point of view of the originating 337 * cpu. 338 * 339 * NOTE! we have to be careful in regards to creating threads for other cpus 340 * if SMP has not yet been activated. 341 */ 342 #ifdef SMP 343 344 static void 345 lwkt_init_thread_remote(void *arg) 346 { 347 thread_t td = arg; 348 349 /* 350 * Protected by critical section held by IPI dispatch 351 */ 352 TAILQ_INSERT_TAIL(&td->td_gd->gd_tdallq, td, td_allq); 353 } 354 355 #endif 356 357 void 358 lwkt_init_thread(thread_t td, void *stack, int stksize, int flags, 359 struct globaldata *gd) 360 { 361 globaldata_t mygd = mycpu; 362 363 bzero(td, sizeof(struct thread)); 364 td->td_kstack = stack; 365 td->td_kstack_size = stksize; 366 td->td_flags = flags; 367 td->td_gd = gd; 368 td->td_pri = TDPRI_KERN_DAEMON + TDPRI_CRIT; 369 #ifdef SMP 370 if ((flags & TDF_MPSAFE) == 0) 371 td->td_mpcount = 1; 372 #endif 373 if (lwkt_use_spin_port) 374 lwkt_initport_spin(&td->td_msgport); 375 else 376 lwkt_initport_thread(&td->td_msgport, td); 377 pmap_init_thread(td); 378 #ifdef SMP 379 /* 380 * Normally initializing a thread for a remote cpu requires sending an 381 * IPI. However, the idlethread is setup before the other cpus are 382 * activated so we have to treat it as a special case. XXX manipulation 383 * of gd_tdallq requires the BGL. 384 */ 385 if (gd == mygd || td == &gd->gd_idlethread) { 386 crit_enter_gd(mygd); 387 TAILQ_INSERT_TAIL(&gd->gd_tdallq, td, td_allq); 388 crit_exit_gd(mygd); 389 } else { 390 lwkt_send_ipiq(gd, lwkt_init_thread_remote, td); 391 } 392 #else 393 crit_enter_gd(mygd); 394 TAILQ_INSERT_TAIL(&gd->gd_tdallq, td, td_allq); 395 crit_exit_gd(mygd); 396 #endif 397 } 398 399 void 400 lwkt_set_comm(thread_t td, const char *ctl, ...) 401 { 402 __va_list va; 403 404 __va_start(va, ctl); 405 kvsnprintf(td->td_comm, sizeof(td->td_comm), ctl, va); 406 __va_end(va); 407 } 408 409 void 410 lwkt_hold(thread_t td) 411 { 412 ++td->td_refs; 413 } 414 415 void 416 lwkt_rele(thread_t td) 417 { 418 KKASSERT(td->td_refs > 0); 419 --td->td_refs; 420 } 421 422 void 423 lwkt_wait_free(thread_t td) 424 { 425 while (td->td_refs) 426 tsleep(td, 0, "tdreap", hz); 427 } 428 429 void 430 lwkt_free_thread(thread_t td) 431 { 432 KASSERT((td->td_flags & TDF_RUNNING) == 0, 433 ("lwkt_free_thread: did not exit! %p", td)); 434 435 if (td->td_flags & TDF_ALLOCATED_THREAD) { 436 objcache_put(thread_cache, td); 437 } else if (td->td_flags & TDF_ALLOCATED_STACK) { 438 /* client-allocated struct with internally allocated stack */ 439 KASSERT(td->td_kstack && td->td_kstack_size > 0, 440 ("lwkt_free_thread: corrupted stack")); 441 kmem_free(&kernel_map, (vm_offset_t)td->td_kstack, td->td_kstack_size); 442 td->td_kstack = NULL; 443 td->td_kstack_size = 0; 444 } 445 } 446 447 448 /* 449 * Switch to the next runnable lwkt. If no LWKTs are runnable then 450 * switch to the idlethread. Switching must occur within a critical 451 * section to avoid races with the scheduling queue. 452 * 453 * We always have full control over our cpu's run queue. Other cpus 454 * that wish to manipulate our queue must use the cpu_*msg() calls to 455 * talk to our cpu, so a critical section is all that is needed and 456 * the result is very, very fast thread switching. 457 * 458 * The LWKT scheduler uses a fixed priority model and round-robins at 459 * each priority level. User process scheduling is a totally 460 * different beast and LWKT priorities should not be confused with 461 * user process priorities. 462 * 463 * The MP lock may be out of sync with the thread's td_mpcount. lwkt_switch() 464 * cleans it up. Note that the td_switch() function cannot do anything that 465 * requires the MP lock since the MP lock will have already been setup for 466 * the target thread (not the current thread). It's nice to have a scheduler 467 * that does not need the MP lock to work because it allows us to do some 468 * really cool high-performance MP lock optimizations. 469 * 470 * PREEMPTION NOTE: Preemption occurs via lwkt_preempt(). lwkt_switch() 471 * is not called by the current thread in the preemption case, only when 472 * the preempting thread blocks (in order to return to the original thread). 473 */ 474 void 475 lwkt_switch(void) 476 { 477 globaldata_t gd = mycpu; 478 thread_t td = gd->gd_curthread; 479 thread_t ntd; 480 #ifdef SMP 481 int mpheld; 482 #endif 483 484 /* 485 * Switching from within a 'fast' (non thread switched) interrupt or IPI 486 * is illegal. However, we may have to do it anyway if we hit a fatal 487 * kernel trap or we have paniced. 488 * 489 * If this case occurs save and restore the interrupt nesting level. 490 */ 491 if (gd->gd_intr_nesting_level) { 492 int savegdnest; 493 int savegdtrap; 494 495 if (gd->gd_trap_nesting_level == 0 && panicstr == NULL) { 496 panic("lwkt_switch: cannot switch from within " 497 "a fast interrupt, yet, td %p\n", td); 498 } else { 499 savegdnest = gd->gd_intr_nesting_level; 500 savegdtrap = gd->gd_trap_nesting_level; 501 gd->gd_intr_nesting_level = 0; 502 gd->gd_trap_nesting_level = 0; 503 if ((td->td_flags & TDF_PANICWARN) == 0) { 504 td->td_flags |= TDF_PANICWARN; 505 kprintf("Warning: thread switch from interrupt or IPI, " 506 "thread %p (%s)\n", td, td->td_comm); 507 print_backtrace(); 508 } 509 lwkt_switch(); 510 gd->gd_intr_nesting_level = savegdnest; 511 gd->gd_trap_nesting_level = savegdtrap; 512 return; 513 } 514 } 515 516 /* 517 * Passive release (used to transition from user to kernel mode 518 * when we block or switch rather then when we enter the kernel). 519 * This function is NOT called if we are switching into a preemption 520 * or returning from a preemption. Typically this causes us to lose 521 * our current process designation (if we have one) and become a true 522 * LWKT thread, and may also hand the current process designation to 523 * another process and schedule thread. 524 */ 525 if (td->td_release) 526 td->td_release(td); 527 528 crit_enter_gd(gd); 529 if (td->td_toks) 530 lwkt_relalltokens(td); 531 532 /* 533 * We had better not be holding any spin locks, but don't get into an 534 * endless panic loop. 535 */ 536 KASSERT(gd->gd_spinlock_rd == NULL || panicstr != NULL, 537 ("lwkt_switch: still holding a shared spinlock %p!", 538 gd->gd_spinlock_rd)); 539 KASSERT(gd->gd_spinlocks_wr == 0 || panicstr != NULL, 540 ("lwkt_switch: still holding %d exclusive spinlocks!", 541 gd->gd_spinlocks_wr)); 542 543 544 #ifdef SMP 545 /* 546 * td_mpcount cannot be used to determine if we currently hold the 547 * MP lock because get_mplock() will increment it prior to attempting 548 * to get the lock, and switch out if it can't. Our ownership of 549 * the actual lock will remain stable while we are in a critical section 550 * (but, of course, another cpu may own or release the lock so the 551 * actual value of mp_lock is not stable). 552 */ 553 mpheld = MP_LOCK_HELD(); 554 #ifdef INVARIANTS 555 if (td->td_cscount) { 556 kprintf("Diagnostic: attempt to switch while mastering cpusync: %p\n", 557 td); 558 if (panic_on_cscount) 559 panic("switching while mastering cpusync"); 560 } 561 #endif 562 #endif 563 if ((ntd = td->td_preempted) != NULL) { 564 /* 565 * We had preempted another thread on this cpu, resume the preempted 566 * thread. This occurs transparently, whether the preempted thread 567 * was scheduled or not (it may have been preempted after descheduling 568 * itself). 569 * 570 * We have to setup the MP lock for the original thread after backing 571 * out the adjustment that was made to curthread when the original 572 * was preempted. 573 */ 574 KKASSERT(ntd->td_flags & TDF_PREEMPT_LOCK); 575 #ifdef SMP 576 if (ntd->td_mpcount && mpheld == 0) { 577 panic("MPLOCK NOT HELD ON RETURN: %p %p %d %d", 578 td, ntd, td->td_mpcount, ntd->td_mpcount); 579 } 580 if (ntd->td_mpcount) { 581 td->td_mpcount -= ntd->td_mpcount; 582 KKASSERT(td->td_mpcount >= 0); 583 } 584 #endif 585 ntd->td_flags |= TDF_PREEMPT_DONE; 586 587 /* 588 * The interrupt may have woken a thread up, we need to properly 589 * set the reschedule flag if the originally interrupted thread is 590 * at a lower priority. 591 */ 592 if (gd->gd_runqmask > (2 << (ntd->td_pri & TDPRI_MASK)) - 1) 593 need_lwkt_resched(); 594 /* YYY release mp lock on switchback if original doesn't need it */ 595 } else { 596 /* 597 * Priority queue / round-robin at each priority. Note that user 598 * processes run at a fixed, low priority and the user process 599 * scheduler deals with interactions between user processes 600 * by scheduling and descheduling them from the LWKT queue as 601 * necessary. 602 * 603 * We have to adjust the MP lock for the target thread. If we 604 * need the MP lock and cannot obtain it we try to locate a 605 * thread that does not need the MP lock. If we cannot, we spin 606 * instead of HLT. 607 * 608 * A similar issue exists for the tokens held by the target thread. 609 * If we cannot obtain ownership of the tokens we cannot immediately 610 * schedule the thread. 611 */ 612 613 /* 614 * If an LWKT reschedule was requested, well that is what we are 615 * doing now so clear it. 616 */ 617 clear_lwkt_resched(); 618 again: 619 if (gd->gd_runqmask) { 620 int nq = bsrl(gd->gd_runqmask); 621 if ((ntd = TAILQ_FIRST(&gd->gd_tdrunq[nq])) == NULL) { 622 gd->gd_runqmask &= ~(1 << nq); 623 goto again; 624 } 625 #ifdef SMP 626 /* 627 * THREAD SELECTION FOR AN SMP MACHINE BUILD 628 * 629 * If the target needs the MP lock and we couldn't get it, 630 * or if the target is holding tokens and we could not 631 * gain ownership of the tokens, continue looking for a 632 * thread to schedule and spin instead of HLT if we can't. 633 * 634 * NOTE: the mpheld variable invalid after this conditional, it 635 * can change due to both cpu_try_mplock() returning success 636 * AND interactions in lwkt_getalltokens() due to the fact that 637 * we are trying to check the mpcount of a thread other then 638 * the current thread. Because of this, if the current thread 639 * is not holding td_mpcount, an IPI indirectly run via 640 * lwkt_getalltokens() can obtain and release the MP lock and 641 * cause the core MP lock to be released. 642 */ 643 if ((ntd->td_mpcount && mpheld == 0 && !cpu_try_mplock()) || 644 (ntd->td_toks && lwkt_getalltokens(ntd) == 0) 645 ) { 646 u_int32_t rqmask = gd->gd_runqmask; 647 648 mpheld = MP_LOCK_HELD(); 649 ntd = NULL; 650 while (rqmask) { 651 TAILQ_FOREACH(ntd, &gd->gd_tdrunq[nq], td_threadq) { 652 if (ntd->td_mpcount && !mpheld && !cpu_try_mplock()) { 653 /* spinning due to MP lock being held */ 654 #ifdef INVARIANTS 655 ++mplock_contention_count; 656 #endif 657 /* mplock still not held, 'mpheld' still valid */ 658 continue; 659 } 660 661 /* 662 * mpheld state invalid after getalltokens call returns 663 * failure, but the variable is only needed for 664 * the loop. 665 */ 666 if (ntd->td_toks && !lwkt_getalltokens(ntd)) { 667 /* spinning due to token contention */ 668 #ifdef INVARIANTS 669 ++token_contention_count; 670 #endif 671 mpheld = MP_LOCK_HELD(); 672 continue; 673 } 674 break; 675 } 676 if (ntd) 677 break; 678 rqmask &= ~(1 << nq); 679 nq = bsrl(rqmask); 680 681 /* 682 * We have two choices. We can either refuse to run a 683 * user thread when a kernel thread needs the MP lock 684 * but could not get it, or we can allow it to run but 685 * then expect an IPI (hopefully) later on to force a 686 * reschedule when the MP lock might become available. 687 */ 688 if (nq < TDPRI_KERN_LPSCHED) { 689 if (chain_mplock == 0) 690 break; 691 atomic_set_int(&mp_lock_contention_mask, 692 gd->gd_cpumask); 693 /* continue loop, allow user threads to be scheduled */ 694 } 695 } 696 if (ntd == NULL) { 697 cpu_mplock_contested(); 698 ntd = &gd->gd_idlethread; 699 ntd->td_flags |= TDF_IDLE_NOHLT; 700 goto using_idle_thread; 701 } else { 702 ++gd->gd_cnt.v_swtch; 703 TAILQ_REMOVE(&gd->gd_tdrunq[nq], ntd, td_threadq); 704 TAILQ_INSERT_TAIL(&gd->gd_tdrunq[nq], ntd, td_threadq); 705 } 706 } else { 707 ++gd->gd_cnt.v_swtch; 708 TAILQ_REMOVE(&gd->gd_tdrunq[nq], ntd, td_threadq); 709 TAILQ_INSERT_TAIL(&gd->gd_tdrunq[nq], ntd, td_threadq); 710 } 711 #else 712 /* 713 * THREAD SELECTION FOR A UP MACHINE BUILD. We don't have to 714 * worry about tokens or the BGL. However, we still have 715 * to call lwkt_getalltokens() in order to properly detect 716 * stale tokens. This call cannot fail for a UP build! 717 */ 718 lwkt_getalltokens(ntd); 719 ++gd->gd_cnt.v_swtch; 720 TAILQ_REMOVE(&gd->gd_tdrunq[nq], ntd, td_threadq); 721 TAILQ_INSERT_TAIL(&gd->gd_tdrunq[nq], ntd, td_threadq); 722 #endif 723 } else { 724 /* 725 * We have nothing to run but only let the idle loop halt 726 * the cpu if there are no pending interrupts. 727 */ 728 ntd = &gd->gd_idlethread; 729 if (gd->gd_reqflags & RQF_IDLECHECK_MASK) 730 ntd->td_flags |= TDF_IDLE_NOHLT; 731 #ifdef SMP 732 using_idle_thread: 733 /* 734 * The idle thread should not be holding the MP lock unless we 735 * are trapping in the kernel or in a panic. Since we select the 736 * idle thread unconditionally when no other thread is available, 737 * if the MP lock is desired during a panic or kernel trap, we 738 * have to loop in the scheduler until we get it. 739 */ 740 if (ntd->td_mpcount) { 741 mpheld = MP_LOCK_HELD(); 742 if (gd->gd_trap_nesting_level == 0 && panicstr == NULL) { 743 panic("Idle thread %p was holding the BGL!", ntd); 744 } else if (mpheld == 0) { 745 cpu_mplock_contested(); 746 goto again; 747 } 748 } 749 #endif 750 } 751 } 752 KASSERT(ntd->td_pri >= TDPRI_CRIT, 753 ("priority problem in lwkt_switch %d %d", td->td_pri, ntd->td_pri)); 754 755 /* 756 * Do the actual switch. If the new target does not need the MP lock 757 * and we are holding it, release the MP lock. If the new target requires 758 * the MP lock we have already acquired it for the target. 759 */ 760 #ifdef SMP 761 if (ntd->td_mpcount == 0 ) { 762 if (MP_LOCK_HELD()) 763 cpu_rel_mplock(); 764 } else { 765 ASSERT_MP_LOCK_HELD(ntd); 766 } 767 #endif 768 if (td != ntd) { 769 ++switch_count; 770 #ifdef __amd64__ 771 KKASSERT(jg_tos_ok(ntd)); 772 #endif 773 td->td_switch(ntd); 774 } 775 /* NOTE: current cpu may have changed after switch */ 776 crit_exit_quick(td); 777 } 778 779 /* 780 * Request that the target thread preempt the current thread. Preemption 781 * only works under a specific set of conditions: 782 * 783 * - We are not preempting ourselves 784 * - The target thread is owned by the current cpu 785 * - We are not currently being preempted 786 * - The target is not currently being preempted 787 * - We are not holding any spin locks 788 * - The target thread is not holding any tokens 789 * - We are able to satisfy the target's MP lock requirements (if any). 790 * 791 * THE CALLER OF LWKT_PREEMPT() MUST BE IN A CRITICAL SECTION. Typically 792 * this is called via lwkt_schedule() through the td_preemptable callback. 793 * critpri is the managed critical priority that we should ignore in order 794 * to determine whether preemption is possible (aka usually just the crit 795 * priority of lwkt_schedule() itself). 796 * 797 * XXX at the moment we run the target thread in a critical section during 798 * the preemption in order to prevent the target from taking interrupts 799 * that *WE* can't. Preemption is strictly limited to interrupt threads 800 * and interrupt-like threads, outside of a critical section, and the 801 * preempted source thread will be resumed the instant the target blocks 802 * whether or not the source is scheduled (i.e. preemption is supposed to 803 * be as transparent as possible). 804 * 805 * The target thread inherits our MP count (added to its own) for the 806 * duration of the preemption in order to preserve the atomicy of the 807 * MP lock during the preemption. Therefore, any preempting targets must be 808 * careful in regards to MP assertions. Note that the MP count may be 809 * out of sync with the physical mp_lock, but we do not have to preserve 810 * the original ownership of the lock if it was out of synch (that is, we 811 * can leave it synchronized on return). 812 */ 813 void 814 lwkt_preempt(thread_t ntd, int critpri) 815 { 816 struct globaldata *gd = mycpu; 817 thread_t td; 818 #ifdef SMP 819 int mpheld; 820 int savecnt; 821 #endif 822 823 /* 824 * The caller has put us in a critical section. We can only preempt 825 * if the caller of the caller was not in a critical section (basically 826 * a local interrupt), as determined by the 'critpri' parameter. We 827 * also can't preempt if the caller is holding any spinlocks (even if 828 * he isn't in a critical section). This also handles the tokens test. 829 * 830 * YYY The target thread must be in a critical section (else it must 831 * inherit our critical section? I dunno yet). 832 * 833 * Set need_lwkt_resched() unconditionally for now YYY. 834 */ 835 KASSERT(ntd->td_pri >= TDPRI_CRIT, ("BADCRIT0 %d", ntd->td_pri)); 836 837 td = gd->gd_curthread; 838 if ((ntd->td_pri & TDPRI_MASK) <= (td->td_pri & TDPRI_MASK)) { 839 ++preempt_miss; 840 return; 841 } 842 if ((td->td_pri & ~TDPRI_MASK) > critpri) { 843 ++preempt_miss; 844 need_lwkt_resched(); 845 return; 846 } 847 #ifdef SMP 848 if (ntd->td_gd != gd) { 849 ++preempt_miss; 850 need_lwkt_resched(); 851 return; 852 } 853 #endif 854 /* 855 * Take the easy way out and do not preempt if we are holding 856 * any spinlocks. We could test whether the thread(s) being 857 * preempted interlock against the target thread's tokens and whether 858 * we can get all the target thread's tokens, but this situation 859 * should not occur very often so its easier to simply not preempt. 860 * Also, plain spinlocks are impossible to figure out at this point so 861 * just don't preempt. 862 * 863 * Do not try to preempt if the target thread is holding any tokens. 864 * We could try to acquire the tokens but this case is so rare there 865 * is no need to support it. 866 */ 867 if (gd->gd_spinlock_rd || gd->gd_spinlocks_wr) { 868 ++preempt_miss; 869 need_lwkt_resched(); 870 return; 871 } 872 if (ntd->td_toks) { 873 ++preempt_miss; 874 need_lwkt_resched(); 875 return; 876 } 877 if (td == ntd || ((td->td_flags | ntd->td_flags) & TDF_PREEMPT_LOCK)) { 878 ++preempt_weird; 879 need_lwkt_resched(); 880 return; 881 } 882 if (ntd->td_preempted) { 883 ++preempt_hit; 884 need_lwkt_resched(); 885 return; 886 } 887 #ifdef SMP 888 /* 889 * note: an interrupt might have occured just as we were transitioning 890 * to or from the MP lock. In this case td_mpcount will be pre-disposed 891 * (non-zero) but not actually synchronized with the actual state of the 892 * lock. We can use it to imply an MP lock requirement for the 893 * preemption but we cannot use it to test whether we hold the MP lock 894 * or not. 895 */ 896 savecnt = td->td_mpcount; 897 mpheld = MP_LOCK_HELD(); 898 ntd->td_mpcount += td->td_mpcount; 899 if (mpheld == 0 && ntd->td_mpcount && !cpu_try_mplock()) { 900 ntd->td_mpcount -= td->td_mpcount; 901 ++preempt_miss; 902 need_lwkt_resched(); 903 return; 904 } 905 #endif 906 907 /* 908 * Since we are able to preempt the current thread, there is no need to 909 * call need_lwkt_resched(). 910 */ 911 ++preempt_hit; 912 ntd->td_preempted = td; 913 td->td_flags |= TDF_PREEMPT_LOCK; 914 td->td_switch(ntd); 915 916 KKASSERT(ntd->td_preempted && (td->td_flags & TDF_PREEMPT_DONE)); 917 #ifdef SMP 918 KKASSERT(savecnt == td->td_mpcount); 919 mpheld = MP_LOCK_HELD(); 920 if (mpheld && td->td_mpcount == 0) 921 cpu_rel_mplock(); 922 else if (mpheld == 0 && td->td_mpcount) 923 panic("lwkt_preempt(): MP lock was not held through"); 924 #endif 925 ntd->td_preempted = NULL; 926 td->td_flags &= ~(TDF_PREEMPT_LOCK|TDF_PREEMPT_DONE); 927 } 928 929 /* 930 * Yield our thread while higher priority threads are pending. This is 931 * typically called when we leave a critical section but it can be safely 932 * called while we are in a critical section. 933 * 934 * This function will not generally yield to equal priority threads but it 935 * can occur as a side effect. Note that lwkt_switch() is called from 936 * inside the critical section to prevent its own crit_exit() from reentering 937 * lwkt_yield_quick(). 938 * 939 * gd_reqflags indicates that *something* changed, e.g. an interrupt or softint 940 * came along but was blocked and made pending. 941 * 942 * (self contained on a per cpu basis) 943 */ 944 void 945 lwkt_yield_quick(void) 946 { 947 globaldata_t gd = mycpu; 948 thread_t td = gd->gd_curthread; 949 950 /* 951 * gd_reqflags is cleared in splz if the cpl is 0. If we were to clear 952 * it with a non-zero cpl then we might not wind up calling splz after 953 * a task switch when the critical section is exited even though the 954 * new task could accept the interrupt. 955 * 956 * XXX from crit_exit() only called after last crit section is released. 957 * If called directly will run splz() even if in a critical section. 958 * 959 * td_nest_count prevent deep nesting via splz() or doreti(). Note that 960 * except for this special case, we MUST call splz() here to handle any 961 * pending ints, particularly after we switch, or we might accidently 962 * halt the cpu with interrupts pending. 963 */ 964 if (gd->gd_reqflags && td->td_nest_count < 2) 965 splz(); 966 967 /* 968 * YYY enabling will cause wakeup() to task-switch, which really 969 * confused the old 4.x code. This is a good way to simulate 970 * preemption and MP without actually doing preemption or MP, because a 971 * lot of code assumes that wakeup() does not block. 972 */ 973 if (untimely_switch && td->td_nest_count == 0 && 974 gd->gd_intr_nesting_level == 0 975 ) { 976 crit_enter_quick(td); 977 /* 978 * YYY temporary hacks until we disassociate the userland scheduler 979 * from the LWKT scheduler. 980 */ 981 if (td->td_flags & TDF_RUNQ) { 982 lwkt_switch(); /* will not reenter yield function */ 983 } else { 984 lwkt_schedule_self(td); /* make sure we are scheduled */ 985 lwkt_switch(); /* will not reenter yield function */ 986 lwkt_deschedule_self(td); /* make sure we are descheduled */ 987 } 988 crit_exit_noyield(td); 989 } 990 } 991 992 /* 993 * This implements a normal yield which, unlike _quick, will yield to equal 994 * priority threads as well. Note that gd_reqflags tests will be handled by 995 * the crit_exit() call in lwkt_switch(). 996 * 997 * (self contained on a per cpu basis) 998 */ 999 void 1000 lwkt_yield(void) 1001 { 1002 lwkt_schedule_self(curthread); 1003 lwkt_switch(); 1004 } 1005 1006 /* 1007 * Return 0 if no runnable threads are pending at the same or higher 1008 * priority as the passed thread. 1009 * 1010 * Return 1 if runnable threads are pending at the same priority. 1011 * 1012 * Return 2 if runnable threads are pending at a higher priority. 1013 */ 1014 int 1015 lwkt_check_resched(thread_t td) 1016 { 1017 int pri = td->td_pri & TDPRI_MASK; 1018 1019 if (td->td_gd->gd_runqmask > (2 << pri) - 1) 1020 return(2); 1021 if (TAILQ_NEXT(td, td_threadq)) 1022 return(1); 1023 return(0); 1024 } 1025 1026 /* 1027 * Generic schedule. Possibly schedule threads belonging to other cpus and 1028 * deal with threads that might be blocked on a wait queue. 1029 * 1030 * We have a little helper inline function which does additional work after 1031 * the thread has been enqueued, including dealing with preemption and 1032 * setting need_lwkt_resched() (which prevents the kernel from returning 1033 * to userland until it has processed higher priority threads). 1034 * 1035 * It is possible for this routine to be called after a failed _enqueue 1036 * (due to the target thread migrating, sleeping, or otherwise blocked). 1037 * We have to check that the thread is actually on the run queue! 1038 * 1039 * reschedok is an optimized constant propagated from lwkt_schedule() or 1040 * lwkt_schedule_noresched(). By default it is non-zero, causing a 1041 * reschedule to be requested if the target thread has a higher priority. 1042 * The port messaging code will set MSG_NORESCHED and cause reschedok to 1043 * be 0, prevented undesired reschedules. 1044 */ 1045 static __inline 1046 void 1047 _lwkt_schedule_post(globaldata_t gd, thread_t ntd, int cpri, int reschedok) 1048 { 1049 thread_t otd; 1050 1051 if (ntd->td_flags & TDF_RUNQ) { 1052 if (ntd->td_preemptable && reschedok) { 1053 ntd->td_preemptable(ntd, cpri); /* YYY +token */ 1054 } else if (reschedok) { 1055 otd = curthread; 1056 if ((ntd->td_pri & TDPRI_MASK) > (otd->td_pri & TDPRI_MASK)) 1057 need_lwkt_resched(); 1058 } 1059 } 1060 } 1061 1062 static __inline 1063 void 1064 _lwkt_schedule(thread_t td, int reschedok) 1065 { 1066 globaldata_t mygd = mycpu; 1067 1068 KASSERT(td != &td->td_gd->gd_idlethread, ("lwkt_schedule(): scheduling gd_idlethread is illegal!")); 1069 crit_enter_gd(mygd); 1070 KKASSERT(td->td_lwp == NULL || (td->td_lwp->lwp_flag & LWP_ONRUNQ) == 0); 1071 if (td == mygd->gd_curthread) { 1072 _lwkt_enqueue(td); 1073 } else { 1074 /* 1075 * If we own the thread, there is no race (since we are in a 1076 * critical section). If we do not own the thread there might 1077 * be a race but the target cpu will deal with it. 1078 */ 1079 #ifdef SMP 1080 if (td->td_gd == mygd) { 1081 _lwkt_enqueue(td); 1082 _lwkt_schedule_post(mygd, td, TDPRI_CRIT, reschedok); 1083 } else { 1084 lwkt_send_ipiq(td->td_gd, (ipifunc1_t)lwkt_schedule, td); 1085 } 1086 #else 1087 _lwkt_enqueue(td); 1088 _lwkt_schedule_post(mygd, td, TDPRI_CRIT, reschedok); 1089 #endif 1090 } 1091 crit_exit_gd(mygd); 1092 } 1093 1094 void 1095 lwkt_schedule(thread_t td) 1096 { 1097 _lwkt_schedule(td, 1); 1098 } 1099 1100 void 1101 lwkt_schedule_noresched(thread_t td) 1102 { 1103 _lwkt_schedule(td, 0); 1104 } 1105 1106 #ifdef SMP 1107 1108 /* 1109 * Thread migration using a 'Pull' method. The thread may or may not be 1110 * the current thread. It MUST be descheduled and in a stable state. 1111 * lwkt_giveaway() must be called on the cpu owning the thread. 1112 * 1113 * At any point after lwkt_giveaway() is called, the target cpu may 1114 * 'pull' the thread by calling lwkt_acquire(). 1115 * 1116 * MPSAFE - must be called under very specific conditions. 1117 */ 1118 void 1119 lwkt_giveaway(thread_t td) 1120 { 1121 globaldata_t gd = mycpu; 1122 1123 crit_enter_gd(gd); 1124 KKASSERT(td->td_gd == gd); 1125 TAILQ_REMOVE(&gd->gd_tdallq, td, td_allq); 1126 td->td_flags |= TDF_MIGRATING; 1127 crit_exit_gd(gd); 1128 } 1129 1130 void 1131 lwkt_acquire(thread_t td) 1132 { 1133 globaldata_t gd; 1134 globaldata_t mygd; 1135 1136 KKASSERT(td->td_flags & TDF_MIGRATING); 1137 gd = td->td_gd; 1138 mygd = mycpu; 1139 if (gd != mycpu) { 1140 cpu_lfence(); 1141 KKASSERT((td->td_flags & TDF_RUNQ) == 0); 1142 crit_enter_gd(mygd); 1143 while (td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK)) { 1144 #ifdef SMP 1145 lwkt_process_ipiq(); 1146 #endif 1147 cpu_lfence(); 1148 } 1149 td->td_gd = mygd; 1150 TAILQ_INSERT_TAIL(&mygd->gd_tdallq, td, td_allq); 1151 td->td_flags &= ~TDF_MIGRATING; 1152 crit_exit_gd(mygd); 1153 } else { 1154 crit_enter_gd(mygd); 1155 TAILQ_INSERT_TAIL(&mygd->gd_tdallq, td, td_allq); 1156 td->td_flags &= ~TDF_MIGRATING; 1157 crit_exit_gd(mygd); 1158 } 1159 } 1160 1161 #endif 1162 1163 /* 1164 * Generic deschedule. Descheduling threads other then your own should be 1165 * done only in carefully controlled circumstances. Descheduling is 1166 * asynchronous. 1167 * 1168 * This function may block if the cpu has run out of messages. 1169 */ 1170 void 1171 lwkt_deschedule(thread_t td) 1172 { 1173 crit_enter(); 1174 #ifdef SMP 1175 if (td == curthread) { 1176 _lwkt_dequeue(td); 1177 } else { 1178 if (td->td_gd == mycpu) { 1179 _lwkt_dequeue(td); 1180 } else { 1181 lwkt_send_ipiq(td->td_gd, (ipifunc1_t)lwkt_deschedule, td); 1182 } 1183 } 1184 #else 1185 _lwkt_dequeue(td); 1186 #endif 1187 crit_exit(); 1188 } 1189 1190 /* 1191 * Set the target thread's priority. This routine does not automatically 1192 * switch to a higher priority thread, LWKT threads are not designed for 1193 * continuous priority changes. Yield if you want to switch. 1194 * 1195 * We have to retain the critical section count which uses the high bits 1196 * of the td_pri field. The specified priority may also indicate zero or 1197 * more critical sections by adding TDPRI_CRIT*N. 1198 * 1199 * Note that we requeue the thread whether it winds up on a different runq 1200 * or not. uio_yield() depends on this and the routine is not normally 1201 * called with the same priority otherwise. 1202 */ 1203 void 1204 lwkt_setpri(thread_t td, int pri) 1205 { 1206 KKASSERT(pri >= 0); 1207 KKASSERT(td->td_gd == mycpu); 1208 crit_enter(); 1209 if (td->td_flags & TDF_RUNQ) { 1210 _lwkt_dequeue(td); 1211 td->td_pri = (td->td_pri & ~TDPRI_MASK) + pri; 1212 _lwkt_enqueue(td); 1213 } else { 1214 td->td_pri = (td->td_pri & ~TDPRI_MASK) + pri; 1215 } 1216 crit_exit(); 1217 } 1218 1219 void 1220 lwkt_setpri_self(int pri) 1221 { 1222 thread_t td = curthread; 1223 1224 KKASSERT(pri >= 0 && pri <= TDPRI_MAX); 1225 crit_enter(); 1226 if (td->td_flags & TDF_RUNQ) { 1227 _lwkt_dequeue(td); 1228 td->td_pri = (td->td_pri & ~TDPRI_MASK) + pri; 1229 _lwkt_enqueue(td); 1230 } else { 1231 td->td_pri = (td->td_pri & ~TDPRI_MASK) + pri; 1232 } 1233 crit_exit(); 1234 } 1235 1236 /* 1237 * Migrate the current thread to the specified cpu. 1238 * 1239 * This is accomplished by descheduling ourselves from the current cpu, 1240 * moving our thread to the tdallq of the target cpu, IPI messaging the 1241 * target cpu, and switching out. TDF_MIGRATING prevents scheduling 1242 * races while the thread is being migrated. 1243 */ 1244 #ifdef SMP 1245 static void lwkt_setcpu_remote(void *arg); 1246 #endif 1247 1248 void 1249 lwkt_setcpu_self(globaldata_t rgd) 1250 { 1251 #ifdef SMP 1252 thread_t td = curthread; 1253 1254 if (td->td_gd != rgd) { 1255 crit_enter_quick(td); 1256 td->td_flags |= TDF_MIGRATING; 1257 lwkt_deschedule_self(td); 1258 TAILQ_REMOVE(&td->td_gd->gd_tdallq, td, td_allq); 1259 lwkt_send_ipiq(rgd, (ipifunc1_t)lwkt_setcpu_remote, td); 1260 lwkt_switch(); 1261 /* we are now on the target cpu */ 1262 TAILQ_INSERT_TAIL(&rgd->gd_tdallq, td, td_allq); 1263 crit_exit_quick(td); 1264 } 1265 #endif 1266 } 1267 1268 void 1269 lwkt_migratecpu(int cpuid) 1270 { 1271 #ifdef SMP 1272 globaldata_t rgd; 1273 1274 rgd = globaldata_find(cpuid); 1275 lwkt_setcpu_self(rgd); 1276 #endif 1277 } 1278 1279 /* 1280 * Remote IPI for cpu migration (called while in a critical section so we 1281 * do not have to enter another one). The thread has already been moved to 1282 * our cpu's allq, but we must wait for the thread to be completely switched 1283 * out on the originating cpu before we schedule it on ours or the stack 1284 * state may be corrupt. We clear TDF_MIGRATING after flushing the GD 1285 * change to main memory. 1286 * 1287 * XXX The use of TDF_MIGRATING might not be sufficient to avoid races 1288 * against wakeups. It is best if this interface is used only when there 1289 * are no pending events that might try to schedule the thread. 1290 */ 1291 #ifdef SMP 1292 static void 1293 lwkt_setcpu_remote(void *arg) 1294 { 1295 thread_t td = arg; 1296 globaldata_t gd = mycpu; 1297 1298 while (td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK)) { 1299 #ifdef SMP 1300 lwkt_process_ipiq(); 1301 #endif 1302 cpu_lfence(); 1303 } 1304 td->td_gd = gd; 1305 cpu_sfence(); 1306 td->td_flags &= ~TDF_MIGRATING; 1307 KKASSERT(td->td_lwp == NULL || (td->td_lwp->lwp_flag & LWP_ONRUNQ) == 0); 1308 _lwkt_enqueue(td); 1309 } 1310 #endif 1311 1312 struct lwp * 1313 lwkt_preempted_proc(void) 1314 { 1315 thread_t td = curthread; 1316 while (td->td_preempted) 1317 td = td->td_preempted; 1318 return(td->td_lwp); 1319 } 1320 1321 /* 1322 * Create a kernel process/thread/whatever. It shares it's address space 1323 * with proc0 - ie: kernel only. 1324 * 1325 * NOTE! By default new threads are created with the MP lock held. A 1326 * thread which does not require the MP lock should release it by calling 1327 * rel_mplock() at the start of the new thread. 1328 */ 1329 int 1330 lwkt_create(void (*func)(void *), void *arg, 1331 struct thread **tdp, thread_t template, int tdflags, int cpu, 1332 const char *fmt, ...) 1333 { 1334 thread_t td; 1335 __va_list ap; 1336 1337 td = lwkt_alloc_thread(template, LWKT_THREAD_STACK, cpu, 1338 tdflags); 1339 if (tdp) 1340 *tdp = td; 1341 cpu_set_thread_handler(td, lwkt_exit, func, arg); 1342 1343 /* 1344 * Set up arg0 for 'ps' etc 1345 */ 1346 __va_start(ap, fmt); 1347 kvsnprintf(td->td_comm, sizeof(td->td_comm), fmt, ap); 1348 __va_end(ap); 1349 1350 /* 1351 * Schedule the thread to run 1352 */ 1353 if ((td->td_flags & TDF_STOPREQ) == 0) 1354 lwkt_schedule(td); 1355 else 1356 td->td_flags &= ~TDF_STOPREQ; 1357 return 0; 1358 } 1359 1360 /* 1361 * Destroy an LWKT thread. Warning! This function is not called when 1362 * a process exits, cpu_proc_exit() directly calls cpu_thread_exit() and 1363 * uses a different reaping mechanism. 1364 */ 1365 void 1366 lwkt_exit(void) 1367 { 1368 thread_t td = curthread; 1369 thread_t std; 1370 globaldata_t gd; 1371 1372 if (td->td_flags & TDF_VERBOSE) 1373 kprintf("kthread %p %s has exited\n", td, td->td_comm); 1374 caps_exit(td); 1375 1376 /* 1377 * Get us into a critical section to interlock gd_freetd and loop 1378 * until we can get it freed. 1379 * 1380 * We have to cache the current td in gd_freetd because objcache_put()ing 1381 * it would rip it out from under us while our thread is still active. 1382 */ 1383 gd = mycpu; 1384 crit_enter_quick(td); 1385 while ((std = gd->gd_freetd) != NULL) { 1386 gd->gd_freetd = NULL; 1387 objcache_put(thread_cache, std); 1388 } 1389 lwkt_deschedule_self(td); 1390 lwkt_remove_tdallq(td); 1391 if (td->td_flags & TDF_ALLOCATED_THREAD) 1392 gd->gd_freetd = td; 1393 cpu_thread_exit(); 1394 } 1395 1396 void 1397 lwkt_remove_tdallq(thread_t td) 1398 { 1399 KKASSERT(td->td_gd == mycpu); 1400 TAILQ_REMOVE(&td->td_gd->gd_tdallq, td, td_allq); 1401 } 1402 1403 void 1404 crit_panic(void) 1405 { 1406 thread_t td = curthread; 1407 int lpri = td->td_pri; 1408 1409 td->td_pri = 0; 1410 panic("td_pri is/would-go negative! %p %d", td, lpri); 1411 } 1412 1413 #ifdef SMP 1414 1415 /* 1416 * Called from debugger/panic on cpus which have been stopped. We must still 1417 * process the IPIQ while stopped, even if we were stopped while in a critical 1418 * section (XXX). 1419 * 1420 * If we are dumping also try to process any pending interrupts. This may 1421 * or may not work depending on the state of the cpu at the point it was 1422 * stopped. 1423 */ 1424 void 1425 lwkt_smp_stopped(void) 1426 { 1427 globaldata_t gd = mycpu; 1428 1429 crit_enter_gd(gd); 1430 if (dumping) { 1431 lwkt_process_ipiq(); 1432 splz(); 1433 } else { 1434 lwkt_process_ipiq(); 1435 } 1436 crit_exit_gd(gd); 1437 } 1438 1439 /* 1440 * get_mplock() calls this routine if it is unable to obtain the MP lock. 1441 * get_mplock() has already incremented td_mpcount. We must block and 1442 * not return until giant is held. 1443 * 1444 * All we have to do is lwkt_switch() away. The LWKT scheduler will not 1445 * reschedule the thread until it can obtain the giant lock for it. 1446 */ 1447 void 1448 lwkt_mp_lock_contested(void) 1449 { 1450 loggiant(beg); 1451 lwkt_switch(); 1452 loggiant(end); 1453 } 1454 1455 /* 1456 * The rel_mplock() code will call this function after releasing the 1457 * last reference on the MP lock if mp_lock_contention_mask is non-zero. 1458 * 1459 * We then chain an IPI to a single other cpu potentially needing the 1460 * lock. This is a bit heuristical and we can wind up with IPIs flying 1461 * all over the place. 1462 */ 1463 static void lwkt_mp_lock_uncontested_remote(void *arg __unused); 1464 1465 void 1466 lwkt_mp_lock_uncontested(void) 1467 { 1468 globaldata_t gd; 1469 globaldata_t dgd; 1470 cpumask_t mask; 1471 cpumask_t tmpmask; 1472 int cpuid; 1473 1474 if (chain_mplock) { 1475 gd = mycpu; 1476 atomic_clear_int(&mp_lock_contention_mask, gd->gd_cpumask); 1477 mask = mp_lock_contention_mask; 1478 tmpmask = ~((1 << gd->gd_cpuid) - 1); 1479 1480 if (mask) { 1481 if (mask & tmpmask) 1482 cpuid = bsfl(mask & tmpmask); 1483 else 1484 cpuid = bsfl(mask); 1485 atomic_clear_int(&mp_lock_contention_mask, 1 << cpuid); 1486 dgd = globaldata_find(cpuid); 1487 lwkt_send_ipiq(dgd, lwkt_mp_lock_uncontested_remote, NULL); 1488 } 1489 } 1490 } 1491 1492 /* 1493 * The idea is for this IPI to interrupt a potentially lower priority 1494 * thread, such as a user thread, to allow the scheduler to reschedule 1495 * a higher priority kernel thread that needs the MP lock. 1496 * 1497 * For now we set the LWKT reschedule flag which generates an AST in 1498 * doreti, though theoretically it is also possible to possibly preempt 1499 * here if the underlying thread was operating in user mode. Nah. 1500 */ 1501 static void 1502 lwkt_mp_lock_uncontested_remote(void *arg __unused) 1503 { 1504 need_lwkt_resched(); 1505 } 1506 1507 #endif 1508