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