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 35 /* 36 * Each cpu in a system has its own self-contained light weight kernel 37 * thread scheduler, which means that generally speaking we only need 38 * to use a critical section to avoid problems. Foreign thread 39 * scheduling is queued via (async) IPIs. 40 */ 41 42 #include <sys/param.h> 43 #include <sys/systm.h> 44 #include <sys/kernel.h> 45 #include <sys/proc.h> 46 #include <sys/rtprio.h> 47 #include <sys/queue.h> 48 #include <sys/sysctl.h> 49 #include <sys/kthread.h> 50 #include <machine/cpu.h> 51 #include <sys/lock.h> 52 #include <sys/caps.h> 53 #include <sys/spinlock.h> 54 #include <sys/ktr.h> 55 56 #include <sys/thread2.h> 57 #include <sys/spinlock2.h> 58 59 #include <vm/vm.h> 60 #include <vm/vm_param.h> 61 #include <vm/vm_kern.h> 62 #include <vm/vm_object.h> 63 #include <vm/vm_page.h> 64 #include <vm/vm_map.h> 65 #include <vm/vm_pager.h> 66 #include <vm/vm_extern.h> 67 68 #include <machine/stdarg.h> 69 #include <machine/smp.h> 70 71 72 static MALLOC_DEFINE(M_THREAD, "thread", "lwkt threads"); 73 74 #ifdef SMP 75 static int mplock_countx = 0; 76 #endif 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 static int bgl_yield = 10; 90 #endif 91 static struct objcache *thread_cache; 92 93 volatile cpumask_t mp_lock_contention_mask; 94 95 static void lwkt_schedule_remote(void *arg, int arg2, struct intrframe *frame); 96 97 extern void cpu_heavy_restore(void); 98 extern void cpu_lwkt_restore(void); 99 extern void cpu_kthread_restore(void); 100 extern void cpu_idle_restore(void); 101 102 #ifdef __amd64__ 103 104 static int 105 jg_tos_ok(struct thread *td) 106 { 107 void *tos; 108 int tos_ok; 109 110 if (td == NULL) { 111 return 1; 112 } 113 KKASSERT(td->td_sp != NULL); 114 tos = ((void **)td->td_sp)[0]; 115 tos_ok = 0; 116 if ((tos == cpu_heavy_restore) || (tos == cpu_lwkt_restore) || 117 (tos == cpu_kthread_restore) || (tos == cpu_idle_restore)) { 118 tos_ok = 1; 119 } 120 return tos_ok; 121 } 122 123 #endif 124 125 /* 126 * We can make all thread ports use the spin backend instead of the thread 127 * backend. This should only be set to debug the spin backend. 128 */ 129 TUNABLE_INT("lwkt.use_spin_port", &lwkt_use_spin_port); 130 131 #ifdef INVARIANTS 132 SYSCTL_INT(_lwkt, OID_AUTO, panic_on_cscount, CTLFLAG_RW, &panic_on_cscount, 0, ""); 133 #endif 134 #ifdef SMP 135 SYSCTL_INT(_lwkt, OID_AUTO, chain_mplock, CTLFLAG_RW, &chain_mplock, 0, ""); 136 SYSCTL_INT(_lwkt, OID_AUTO, bgl_yield_delay, CTLFLAG_RW, &bgl_yield, 0, ""); 137 #endif 138 SYSCTL_QUAD(_lwkt, OID_AUTO, switch_count, CTLFLAG_RW, &switch_count, 0, ""); 139 SYSCTL_QUAD(_lwkt, OID_AUTO, preempt_hit, CTLFLAG_RW, &preempt_hit, 0, ""); 140 SYSCTL_QUAD(_lwkt, OID_AUTO, preempt_miss, CTLFLAG_RW, &preempt_miss, 0, ""); 141 SYSCTL_QUAD(_lwkt, OID_AUTO, preempt_weird, CTLFLAG_RW, &preempt_weird, 0, ""); 142 #ifdef INVARIANTS 143 SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count, CTLFLAG_RW, 144 &token_contention_count, 0, "spinning due to token contention"); 145 SYSCTL_QUAD(_lwkt, OID_AUTO, mplock_contention_count, CTLFLAG_RW, 146 &mplock_contention_count, 0, "spinning due to MPLOCK contention"); 147 #endif 148 149 /* 150 * Kernel Trace 151 */ 152 #if !defined(KTR_GIANT_CONTENTION) 153 #define KTR_GIANT_CONTENTION KTR_ALL 154 #endif 155 156 KTR_INFO_MASTER(giant); 157 KTR_INFO(KTR_GIANT_CONTENTION, giant, beg, 0, "thread=%p", sizeof(void *)); 158 KTR_INFO(KTR_GIANT_CONTENTION, giant, end, 1, "thread=%p", sizeof(void *)); 159 160 #define loggiant(name) KTR_LOG(giant_ ## name, curthread) 161 162 /* 163 * These helper procedures handle the runq, they can only be called from 164 * within a critical section. 165 * 166 * WARNING! Prior to SMP being brought up it is possible to enqueue and 167 * dequeue threads belonging to other cpus, so be sure to use td->td_gd 168 * instead of 'mycpu' when referencing the globaldata structure. Once 169 * SMP live enqueuing and dequeueing only occurs on the current cpu. 170 */ 171 static __inline 172 void 173 _lwkt_dequeue(thread_t td) 174 { 175 if (td->td_flags & TDF_RUNQ) { 176 int nq = td->td_pri & TDPRI_MASK; 177 struct globaldata *gd = td->td_gd; 178 179 td->td_flags &= ~TDF_RUNQ; 180 TAILQ_REMOVE(&gd->gd_tdrunq[nq], td, td_threadq); 181 /* runqmask is passively cleaned up by the switcher */ 182 } 183 } 184 185 static __inline 186 void 187 _lwkt_enqueue(thread_t td) 188 { 189 if ((td->td_flags & (TDF_RUNQ|TDF_MIGRATING|TDF_BLOCKQ)) == 0) { 190 int nq = td->td_pri & TDPRI_MASK; 191 struct globaldata *gd = td->td_gd; 192 193 td->td_flags |= TDF_RUNQ; 194 TAILQ_INSERT_TAIL(&gd->gd_tdrunq[nq], td, td_threadq); 195 gd->gd_runqmask |= 1 << nq; 196 } 197 } 198 199 static __boolean_t 200 _lwkt_thread_ctor(void *obj, void *privdata, int ocflags) 201 { 202 struct thread *td = (struct thread *)obj; 203 204 td->td_kstack = NULL; 205 td->td_kstack_size = 0; 206 td->td_flags = TDF_ALLOCATED_THREAD; 207 return (1); 208 } 209 210 static void 211 _lwkt_thread_dtor(void *obj, void *privdata) 212 { 213 struct thread *td = (struct thread *)obj; 214 215 KASSERT(td->td_flags & TDF_ALLOCATED_THREAD, 216 ("_lwkt_thread_dtor: not allocated from objcache")); 217 KASSERT((td->td_flags & TDF_ALLOCATED_STACK) && td->td_kstack && 218 td->td_kstack_size > 0, 219 ("_lwkt_thread_dtor: corrupted stack")); 220 kmem_free(&kernel_map, (vm_offset_t)td->td_kstack, td->td_kstack_size); 221 } 222 223 /* 224 * Initialize the lwkt s/system. 225 */ 226 void 227 lwkt_init(void) 228 { 229 /* An objcache has 2 magazines per CPU so divide cache size by 2. */ 230 thread_cache = objcache_create_mbacked(M_THREAD, sizeof(struct thread), 231 NULL, CACHE_NTHREADS/2, 232 _lwkt_thread_ctor, _lwkt_thread_dtor, NULL); 233 } 234 235 /* 236 * Schedule a thread to run. As the current thread we can always safely 237 * schedule ourselves, and a shortcut procedure is provided for that 238 * function. 239 * 240 * (non-blocking, self contained on a per cpu basis) 241 */ 242 void 243 lwkt_schedule_self(thread_t td) 244 { 245 crit_enter_quick(td); 246 KASSERT(td != &td->td_gd->gd_idlethread, ("lwkt_schedule_self(): scheduling gd_idlethread is illegal!")); 247 KKASSERT(td->td_lwp == NULL || (td->td_lwp->lwp_flag & LWP_ONRUNQ) == 0); 248 _lwkt_enqueue(td); 249 crit_exit_quick(td); 250 } 251 252 /* 253 * Deschedule a thread. 254 * 255 * (non-blocking, self contained on a per cpu basis) 256 */ 257 void 258 lwkt_deschedule_self(thread_t td) 259 { 260 crit_enter_quick(td); 261 _lwkt_dequeue(td); 262 crit_exit_quick(td); 263 } 264 265 /* 266 * LWKTs operate on a per-cpu basis 267 * 268 * WARNING! Called from early boot, 'mycpu' may not work yet. 269 */ 270 void 271 lwkt_gdinit(struct globaldata *gd) 272 { 273 int i; 274 275 for (i = 0; i < sizeof(gd->gd_tdrunq)/sizeof(gd->gd_tdrunq[0]); ++i) 276 TAILQ_INIT(&gd->gd_tdrunq[i]); 277 gd->gd_runqmask = 0; 278 TAILQ_INIT(&gd->gd_tdallq); 279 } 280 281 /* 282 * Create a new thread. The thread must be associated with a process context 283 * or LWKT start address before it can be scheduled. If the target cpu is 284 * -1 the thread will be created on the current cpu. 285 * 286 * If you intend to create a thread without a process context this function 287 * does everything except load the startup and switcher function. 288 */ 289 thread_t 290 lwkt_alloc_thread(struct thread *td, int stksize, int cpu, int flags) 291 { 292 globaldata_t gd = mycpu; 293 void *stack; 294 295 /* 296 * If static thread storage is not supplied allocate a thread. Reuse 297 * a cached free thread if possible. gd_freetd is used to keep an exiting 298 * thread intact through the exit. 299 */ 300 if (td == NULL) { 301 if ((td = gd->gd_freetd) != NULL) 302 gd->gd_freetd = NULL; 303 else 304 td = objcache_get(thread_cache, M_WAITOK); 305 KASSERT((td->td_flags & 306 (TDF_ALLOCATED_THREAD|TDF_RUNNING)) == TDF_ALLOCATED_THREAD, 307 ("lwkt_alloc_thread: corrupted td flags 0x%X", td->td_flags)); 308 flags |= td->td_flags & (TDF_ALLOCATED_THREAD|TDF_ALLOCATED_STACK); 309 } 310 311 /* 312 * Try to reuse cached stack. 313 */ 314 if ((stack = td->td_kstack) != NULL && td->td_kstack_size != stksize) { 315 if (flags & TDF_ALLOCATED_STACK) { 316 kmem_free(&kernel_map, (vm_offset_t)stack, td->td_kstack_size); 317 stack = NULL; 318 } 319 } 320 if (stack == NULL) { 321 stack = (void *)kmem_alloc(&kernel_map, stksize); 322 flags |= TDF_ALLOCATED_STACK; 323 } 324 if (cpu < 0) 325 lwkt_init_thread(td, stack, stksize, flags, gd); 326 else 327 lwkt_init_thread(td, stack, stksize, flags, globaldata_find(cpu)); 328 return(td); 329 } 330 331 /* 332 * Initialize a preexisting thread structure. This function is used by 333 * lwkt_alloc_thread() and also used to initialize the per-cpu idlethread. 334 * 335 * All threads start out in a critical section at a priority of 336 * TDPRI_KERN_DAEMON. Higher level code will modify the priority as 337 * appropriate. This function may send an IPI message when the 338 * requested cpu is not the current cpu and consequently gd_tdallq may 339 * not be initialized synchronously from the point of view of the originating 340 * cpu. 341 * 342 * NOTE! we have to be careful in regards to creating threads for other cpus 343 * if SMP has not yet been activated. 344 */ 345 #ifdef SMP 346 347 static void 348 lwkt_init_thread_remote(void *arg) 349 { 350 thread_t td = arg; 351 352 /* 353 * Protected by critical section held by IPI dispatch 354 */ 355 TAILQ_INSERT_TAIL(&td->td_gd->gd_tdallq, td, td_allq); 356 } 357 358 #endif 359 360 void 361 lwkt_init_thread(thread_t td, void *stack, int stksize, int flags, 362 struct globaldata *gd) 363 { 364 globaldata_t mygd = mycpu; 365 366 bzero(td, sizeof(struct thread)); 367 td->td_kstack = stack; 368 td->td_kstack_size = stksize; 369 td->td_flags = flags; 370 td->td_gd = gd; 371 td->td_pri = TDPRI_KERN_DAEMON + TDPRI_CRIT; 372 #ifdef SMP 373 if ((flags & TDF_MPSAFE) == 0) 374 td->td_mpcount = 1; 375 #endif 376 if (lwkt_use_spin_port) 377 lwkt_initport_spin(&td->td_msgport); 378 else 379 lwkt_initport_thread(&td->td_msgport, td); 380 pmap_init_thread(td); 381 #ifdef SMP 382 /* 383 * Normally initializing a thread for a remote cpu requires sending an 384 * IPI. However, the idlethread is setup before the other cpus are 385 * activated so we have to treat it as a special case. XXX manipulation 386 * of gd_tdallq requires the BGL. 387 */ 388 if (gd == mygd || td == &gd->gd_idlethread) { 389 crit_enter_gd(mygd); 390 TAILQ_INSERT_TAIL(&gd->gd_tdallq, td, td_allq); 391 crit_exit_gd(mygd); 392 } else { 393 lwkt_send_ipiq(gd, lwkt_init_thread_remote, td); 394 } 395 #else 396 crit_enter_gd(mygd); 397 TAILQ_INSERT_TAIL(&gd->gd_tdallq, td, td_allq); 398 crit_exit_gd(mygd); 399 #endif 400 } 401 402 void 403 lwkt_set_comm(thread_t td, const char *ctl, ...) 404 { 405 __va_list va; 406 407 __va_start(va, ctl); 408 kvsnprintf(td->td_comm, sizeof(td->td_comm), ctl, va); 409 __va_end(va); 410 } 411 412 void 413 lwkt_hold(thread_t td) 414 { 415 ++td->td_refs; 416 } 417 418 void 419 lwkt_rele(thread_t td) 420 { 421 KKASSERT(td->td_refs > 0); 422 --td->td_refs; 423 } 424 425 void 426 lwkt_wait_free(thread_t td) 427 { 428 while (td->td_refs) 429 tsleep(td, 0, "tdreap", hz); 430 } 431 432 void 433 lwkt_free_thread(thread_t td) 434 { 435 KASSERT((td->td_flags & TDF_RUNNING) == 0, 436 ("lwkt_free_thread: did not exit! %p", td)); 437 438 if (td->td_flags & TDF_ALLOCATED_THREAD) { 439 objcache_put(thread_cache, td); 440 } else if (td->td_flags & TDF_ALLOCATED_STACK) { 441 /* client-allocated struct with internally allocated stack */ 442 KASSERT(td->td_kstack && td->td_kstack_size > 0, 443 ("lwkt_free_thread: corrupted stack")); 444 kmem_free(&kernel_map, (vm_offset_t)td->td_kstack, td->td_kstack_size); 445 td->td_kstack = NULL; 446 td->td_kstack_size = 0; 447 } 448 } 449 450 451 /* 452 * Switch to the next runnable lwkt. If no LWKTs are runnable then 453 * switch to the idlethread. Switching must occur within a critical 454 * section to avoid races with the scheduling queue. 455 * 456 * We always have full control over our cpu's run queue. Other cpus 457 * that wish to manipulate our queue must use the cpu_*msg() calls to 458 * talk to our cpu, so a critical section is all that is needed and 459 * the result is very, very fast thread switching. 460 * 461 * The LWKT scheduler uses a fixed priority model and round-robins at 462 * each priority level. User process scheduling is a totally 463 * different beast and LWKT priorities should not be confused with 464 * user process priorities. 465 * 466 * The MP lock may be out of sync with the thread's td_mpcount. lwkt_switch() 467 * cleans it up. Note that the td_switch() function cannot do anything that 468 * requires the MP lock since the MP lock will have already been setup for 469 * the target thread (not the current thread). It's nice to have a scheduler 470 * that does not need the MP lock to work because it allows us to do some 471 * really cool high-performance MP lock optimizations. 472 * 473 * PREEMPTION NOTE: Preemption occurs via lwkt_preempt(). lwkt_switch() 474 * is not called by the current thread in the preemption case, only when 475 * the preempting thread blocks (in order to return to the original thread). 476 */ 477 void 478 lwkt_switch(void) 479 { 480 globaldata_t gd = mycpu; 481 thread_t td = gd->gd_curthread; 482 thread_t ntd; 483 #ifdef SMP 484 int mpheld; 485 #endif 486 487 /* 488 * Switching from within a 'fast' (non thread switched) interrupt or IPI 489 * is illegal. However, we may have to do it anyway if we hit a fatal 490 * kernel trap or we have paniced. 491 * 492 * If this case occurs save and restore the interrupt nesting level. 493 */ 494 if (gd->gd_intr_nesting_level) { 495 int savegdnest; 496 int savegdtrap; 497 498 if (gd->gd_trap_nesting_level == 0 && panicstr == NULL) { 499 panic("lwkt_switch: cannot switch from within " 500 "a fast interrupt, yet, td %p\n", td); 501 } else { 502 savegdnest = gd->gd_intr_nesting_level; 503 savegdtrap = gd->gd_trap_nesting_level; 504 gd->gd_intr_nesting_level = 0; 505 gd->gd_trap_nesting_level = 0; 506 if ((td->td_flags & TDF_PANICWARN) == 0) { 507 td->td_flags |= TDF_PANICWARN; 508 kprintf("Warning: thread switch from interrupt or IPI, " 509 "thread %p (%s)\n", td, td->td_comm); 510 print_backtrace(); 511 } 512 lwkt_switch(); 513 gd->gd_intr_nesting_level = savegdnest; 514 gd->gd_trap_nesting_level = savegdtrap; 515 return; 516 } 517 } 518 519 /* 520 * Passive release (used to transition from user to kernel mode 521 * when we block or switch rather then when we enter the kernel). 522 * This function is NOT called if we are switching into a preemption 523 * or returning from a preemption. Typically this causes us to lose 524 * our current process designation (if we have one) and become a true 525 * LWKT thread, and may also hand the current process designation to 526 * another process and schedule thread. 527 */ 528 if (td->td_release) 529 td->td_release(td); 530 531 crit_enter_gd(gd); 532 if (td->td_toks) 533 lwkt_relalltokens(td); 534 535 /* 536 * We had better not be holding any spin locks, but don't get into an 537 * endless panic loop. 538 */ 539 KASSERT(gd->gd_spinlock_rd == NULL || panicstr != NULL, 540 ("lwkt_switch: still holding a shared spinlock %p!", 541 gd->gd_spinlock_rd)); 542 KASSERT(gd->gd_spinlocks_wr == 0 || panicstr != NULL, 543 ("lwkt_switch: still holding %d exclusive spinlocks!", 544 gd->gd_spinlocks_wr)); 545 546 547 #ifdef SMP 548 /* 549 * td_mpcount cannot be used to determine if we currently hold the 550 * MP lock because get_mplock() will increment it prior to attempting 551 * to get the lock, and switch out if it can't. Our ownership of 552 * the actual lock will remain stable while we are in a critical section 553 * (but, of course, another cpu may own or release the lock so the 554 * actual value of mp_lock is not stable). 555 */ 556 mpheld = MP_LOCK_HELD(); 557 #ifdef INVARIANTS 558 if (td->td_cscount) { 559 kprintf("Diagnostic: attempt to switch while mastering cpusync: %p\n", 560 td); 561 if (panic_on_cscount) 562 panic("switching while mastering cpusync"); 563 } 564 #endif 565 #endif 566 if ((ntd = td->td_preempted) != NULL) { 567 /* 568 * We had preempted another thread on this cpu, resume the preempted 569 * thread. This occurs transparently, whether the preempted thread 570 * was scheduled or not (it may have been preempted after descheduling 571 * itself). 572 * 573 * We have to setup the MP lock for the original thread after backing 574 * out the adjustment that was made to curthread when the original 575 * was preempted. 576 */ 577 KKASSERT(ntd->td_flags & TDF_PREEMPT_LOCK); 578 #ifdef SMP 579 if (ntd->td_mpcount && mpheld == 0) { 580 panic("MPLOCK NOT HELD ON RETURN: %p %p %d %d", 581 td, ntd, td->td_mpcount, ntd->td_mpcount); 582 } 583 if (ntd->td_mpcount) { 584 td->td_mpcount -= ntd->td_mpcount; 585 KKASSERT(td->td_mpcount >= 0); 586 } 587 #endif 588 ntd->td_flags |= TDF_PREEMPT_DONE; 589 590 /* 591 * The interrupt may have woken a thread up, we need to properly 592 * set the reschedule flag if the originally interrupted thread is 593 * at a lower priority. 594 */ 595 if (gd->gd_runqmask > (2 << (ntd->td_pri & TDPRI_MASK)) - 1) 596 need_lwkt_resched(); 597 /* YYY release mp lock on switchback if original doesn't need it */ 598 } else { 599 /* 600 * Priority queue / round-robin at each priority. Note that user 601 * processes run at a fixed, low priority and the user process 602 * scheduler deals with interactions between user processes 603 * by scheduling and descheduling them from the LWKT queue as 604 * necessary. 605 * 606 * We have to adjust the MP lock for the target thread. If we 607 * need the MP lock and cannot obtain it we try to locate a 608 * thread that does not need the MP lock. If we cannot, we spin 609 * instead of HLT. 610 * 611 * A similar issue exists for the tokens held by the target thread. 612 * If we cannot obtain ownership of the tokens we cannot immediately 613 * schedule the thread. 614 */ 615 616 /* 617 * If an LWKT reschedule was requested, well that is what we are 618 * doing now so clear it. 619 */ 620 clear_lwkt_resched(); 621 again: 622 if (gd->gd_runqmask) { 623 int nq = bsrl(gd->gd_runqmask); 624 if ((ntd = TAILQ_FIRST(&gd->gd_tdrunq[nq])) == NULL) { 625 gd->gd_runqmask &= ~(1 << nq); 626 goto again; 627 } 628 #ifdef SMP 629 /* 630 * THREAD SELECTION FOR AN SMP MACHINE BUILD 631 * 632 * If the target needs the MP lock and we couldn't get it, 633 * or if the target is holding tokens and we could not 634 * gain ownership of the tokens, continue looking for a 635 * thread to schedule and spin instead of HLT if we can't. 636 * 637 * NOTE: the mpheld variable invalid after this conditional, it 638 * can change due to both cpu_try_mplock() returning success 639 * AND interactions in lwkt_getalltokens() due to the fact that 640 * we are trying to check the mpcount of a thread other then 641 * the current thread. Because of this, if the current thread 642 * is not holding td_mpcount, an IPI indirectly run via 643 * lwkt_getalltokens() can obtain and release the MP lock and 644 * cause the core MP lock to be released. 645 */ 646 if ((ntd->td_mpcount && mpheld == 0 && !cpu_try_mplock()) || 647 (ntd->td_toks && lwkt_getalltokens(ntd) == 0) 648 ) { 649 u_int32_t rqmask = gd->gd_runqmask; 650 651 mpheld = MP_LOCK_HELD(); 652 ntd = NULL; 653 while (rqmask) { 654 TAILQ_FOREACH(ntd, &gd->gd_tdrunq[nq], td_threadq) { 655 if (ntd->td_mpcount && !mpheld && !cpu_try_mplock()) { 656 /* spinning due to MP lock being held */ 657 #ifdef INVARIANTS 658 ++mplock_contention_count; 659 #endif 660 /* mplock still not held, 'mpheld' still valid */ 661 continue; 662 } 663 664 /* 665 * mpheld state invalid after getalltokens call returns 666 * failure, but the variable is only needed for 667 * the loop. 668 */ 669 if (ntd->td_toks && !lwkt_getalltokens(ntd)) { 670 /* spinning due to token contention */ 671 #ifdef INVARIANTS 672 ++token_contention_count; 673 #endif 674 mpheld = MP_LOCK_HELD(); 675 continue; 676 } 677 break; 678 } 679 if (ntd) 680 break; 681 rqmask &= ~(1 << nq); 682 nq = bsrl(rqmask); 683 684 /* 685 * We have two choices. We can either refuse to run a 686 * user thread when a kernel thread needs the MP lock 687 * but could not get it, or we can allow it to run but 688 * then expect an IPI (hopefully) later on to force a 689 * reschedule when the MP lock might become available. 690 */ 691 if (nq < TDPRI_KERN_LPSCHED) { 692 if (chain_mplock == 0) 693 break; 694 atomic_set_int(&mp_lock_contention_mask, 695 gd->gd_cpumask); 696 /* continue loop, allow user threads to be scheduled */ 697 } 698 } 699 if (ntd == NULL) { 700 cpu_mplock_contested(); 701 ntd = &gd->gd_idlethread; 702 ntd->td_flags |= TDF_IDLE_NOHLT; 703 goto using_idle_thread; 704 } else { 705 ++gd->gd_cnt.v_swtch; 706 TAILQ_REMOVE(&gd->gd_tdrunq[nq], ntd, td_threadq); 707 TAILQ_INSERT_TAIL(&gd->gd_tdrunq[nq], ntd, td_threadq); 708 } 709 } else { 710 if (ntd->td_mpcount) 711 ++mplock_countx; 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 } 716 #else 717 /* 718 * THREAD SELECTION FOR A UP MACHINE BUILD. We don't have to 719 * worry about tokens or the BGL. However, we still have 720 * to call lwkt_getalltokens() in order to properly detect 721 * stale tokens. This call cannot fail for a UP build! 722 */ 723 lwkt_getalltokens(ntd); 724 ++gd->gd_cnt.v_swtch; 725 TAILQ_REMOVE(&gd->gd_tdrunq[nq], ntd, td_threadq); 726 TAILQ_INSERT_TAIL(&gd->gd_tdrunq[nq], ntd, td_threadq); 727 #endif 728 } else { 729 /* 730 * We have nothing to run but only let the idle loop halt 731 * the cpu if there are no pending interrupts. 732 */ 733 ntd = &gd->gd_idlethread; 734 if (gd->gd_reqflags & RQF_IDLECHECK_MASK) 735 ntd->td_flags |= TDF_IDLE_NOHLT; 736 #ifdef SMP 737 using_idle_thread: 738 /* 739 * The idle thread should not be holding the MP lock unless we 740 * are trapping in the kernel or in a panic. Since we select the 741 * idle thread unconditionally when no other thread is available, 742 * if the MP lock is desired during a panic or kernel trap, we 743 * have to loop in the scheduler until we get it. 744 */ 745 if (ntd->td_mpcount) { 746 mpheld = MP_LOCK_HELD(); 747 if (gd->gd_trap_nesting_level == 0 && panicstr == NULL) { 748 panic("Idle thread %p was holding the BGL!", ntd); 749 } else if (mpheld == 0) { 750 cpu_mplock_contested(); 751 goto again; 752 } 753 } 754 #endif 755 } 756 } 757 KASSERT(ntd->td_pri >= TDPRI_CRIT, 758 ("priority problem in lwkt_switch %d %d", td->td_pri, ntd->td_pri)); 759 760 /* 761 * Do the actual switch. If the new target does not need the MP lock 762 * and we are holding it, release the MP lock. If the new target requires 763 * the MP lock we have already acquired it for the target. 764 */ 765 #ifdef SMP 766 if (ntd->td_mpcount == 0 ) { 767 if (MP_LOCK_HELD()) 768 cpu_rel_mplock(); 769 } else { 770 ASSERT_MP_LOCK_HELD(ntd); 771 } 772 #endif 773 if (td != ntd) { 774 ++switch_count; 775 #ifdef __amd64__ 776 KKASSERT(jg_tos_ok(ntd)); 777 #endif 778 td->td_switch(ntd); 779 } 780 /* NOTE: current cpu may have changed after switch */ 781 crit_exit_quick(td); 782 } 783 784 /* 785 * Request that the target thread preempt the current thread. Preemption 786 * only works under a specific set of conditions: 787 * 788 * - We are not preempting ourselves 789 * - The target thread is owned by the current cpu 790 * - We are not currently being preempted 791 * - The target is not currently being preempted 792 * - We are not holding any spin locks 793 * - The target thread is not holding any tokens 794 * - We are able to satisfy the target's MP lock requirements (if any). 795 * 796 * THE CALLER OF LWKT_PREEMPT() MUST BE IN A CRITICAL SECTION. Typically 797 * this is called via lwkt_schedule() through the td_preemptable callback. 798 * critpri is the managed critical priority that we should ignore in order 799 * to determine whether preemption is possible (aka usually just the crit 800 * priority of lwkt_schedule() itself). 801 * 802 * XXX at the moment we run the target thread in a critical section during 803 * the preemption in order to prevent the target from taking interrupts 804 * that *WE* can't. Preemption is strictly limited to interrupt threads 805 * and interrupt-like threads, outside of a critical section, and the 806 * preempted source thread will be resumed the instant the target blocks 807 * whether or not the source is scheduled (i.e. preemption is supposed to 808 * be as transparent as possible). 809 * 810 * The target thread inherits our MP count (added to its own) for the 811 * duration of the preemption in order to preserve the atomicy of the 812 * MP lock during the preemption. Therefore, any preempting targets must be 813 * careful in regards to MP assertions. Note that the MP count may be 814 * out of sync with the physical mp_lock, but we do not have to preserve 815 * the original ownership of the lock if it was out of synch (that is, we 816 * can leave it synchronized on return). 817 */ 818 void 819 lwkt_preempt(thread_t ntd, int critpri) 820 { 821 struct globaldata *gd = mycpu; 822 thread_t td; 823 #ifdef SMP 824 int mpheld; 825 int savecnt; 826 #endif 827 828 /* 829 * The caller has put us in a critical section. We can only preempt 830 * if the caller of the caller was not in a critical section (basically 831 * a local interrupt), as determined by the 'critpri' parameter. We 832 * also can't preempt if the caller is holding any spinlocks (even if 833 * he isn't in a critical section). This also handles the tokens test. 834 * 835 * YYY The target thread must be in a critical section (else it must 836 * inherit our critical section? I dunno yet). 837 * 838 * Set need_lwkt_resched() unconditionally for now YYY. 839 */ 840 KASSERT(ntd->td_pri >= TDPRI_CRIT, ("BADCRIT0 %d", ntd->td_pri)); 841 842 td = gd->gd_curthread; 843 if ((ntd->td_pri & TDPRI_MASK) <= (td->td_pri & TDPRI_MASK)) { 844 ++preempt_miss; 845 return; 846 } 847 if ((td->td_pri & ~TDPRI_MASK) > critpri) { 848 ++preempt_miss; 849 need_lwkt_resched(); 850 return; 851 } 852 #ifdef SMP 853 if (ntd->td_gd != gd) { 854 ++preempt_miss; 855 need_lwkt_resched(); 856 return; 857 } 858 #endif 859 /* 860 * Take the easy way out and do not preempt if we are holding 861 * any spinlocks. We could test whether the thread(s) being 862 * preempted interlock against the target thread's tokens and whether 863 * we can get all the target thread's tokens, but this situation 864 * should not occur very often so its easier to simply not preempt. 865 * Also, plain spinlocks are impossible to figure out at this point so 866 * just don't preempt. 867 * 868 * Do not try to preempt if the target thread is holding any tokens. 869 * We could try to acquire the tokens but this case is so rare there 870 * is no need to support it. 871 */ 872 if (gd->gd_spinlock_rd || gd->gd_spinlocks_wr) { 873 ++preempt_miss; 874 need_lwkt_resched(); 875 return; 876 } 877 if (ntd->td_toks) { 878 ++preempt_miss; 879 need_lwkt_resched(); 880 return; 881 } 882 if (td == ntd || ((td->td_flags | ntd->td_flags) & TDF_PREEMPT_LOCK)) { 883 ++preempt_weird; 884 need_lwkt_resched(); 885 return; 886 } 887 if (ntd->td_preempted) { 888 ++preempt_hit; 889 need_lwkt_resched(); 890 return; 891 } 892 #ifdef SMP 893 /* 894 * note: an interrupt might have occured just as we were transitioning 895 * to or from the MP lock. In this case td_mpcount will be pre-disposed 896 * (non-zero) but not actually synchronized with the actual state of the 897 * lock. We can use it to imply an MP lock requirement for the 898 * preemption but we cannot use it to test whether we hold the MP lock 899 * or not. 900 */ 901 savecnt = td->td_mpcount; 902 mpheld = MP_LOCK_HELD(); 903 ntd->td_mpcount += td->td_mpcount; 904 if (mpheld == 0 && ntd->td_mpcount && !cpu_try_mplock()) { 905 ntd->td_mpcount -= td->td_mpcount; 906 ++preempt_miss; 907 need_lwkt_resched(); 908 return; 909 } 910 #endif 911 912 /* 913 * Since we are able to preempt the current thread, there is no need to 914 * call need_lwkt_resched(). 915 */ 916 ++preempt_hit; 917 ntd->td_preempted = td; 918 td->td_flags |= TDF_PREEMPT_LOCK; 919 td->td_switch(ntd); 920 921 KKASSERT(ntd->td_preempted && (td->td_flags & TDF_PREEMPT_DONE)); 922 #ifdef SMP 923 KKASSERT(savecnt == td->td_mpcount); 924 mpheld = MP_LOCK_HELD(); 925 if (mpheld && td->td_mpcount == 0) 926 cpu_rel_mplock(); 927 else if (mpheld == 0 && td->td_mpcount) 928 panic("lwkt_preempt(): MP lock was not held through"); 929 #endif 930 ntd->td_preempted = NULL; 931 td->td_flags &= ~(TDF_PREEMPT_LOCK|TDF_PREEMPT_DONE); 932 } 933 934 /* 935 * Conditionally call splz() if gd_reqflags indicates work is pending. 936 * 937 * td_nest_count prevents deep nesting via splz() or doreti() which 938 * might otherwise blow out the kernel stack. Note that except for 939 * this special case, we MUST call splz() here to handle any 940 * pending ints, particularly after we switch, or we might accidently 941 * halt the cpu with interrupts pending. 942 * 943 * (self contained on a per cpu basis) 944 */ 945 void 946 splz_check(void) 947 { 948 globaldata_t gd = mycpu; 949 thread_t td = gd->gd_curthread; 950 951 if (gd->gd_reqflags && td->td_nest_count < 2) 952 splz(); 953 } 954 955 /* 956 * This implements a normal yield which will yield to equal priority 957 * threads as well as higher priority threads. Note that gd_reqflags 958 * tests will be handled by the crit_exit() call in lwkt_switch(). 959 * 960 * (self contained on a per cpu basis) 961 */ 962 void 963 lwkt_yield(void) 964 { 965 lwkt_schedule_self(curthread); 966 lwkt_switch(); 967 } 968 969 /* 970 * This function is used along with the lwkt_passive_recover() inline 971 * by the trap code to negotiate a passive release of the current 972 * process/lwp designation with the user scheduler. 973 */ 974 void 975 lwkt_passive_release(struct thread *td) 976 { 977 struct lwp *lp = td->td_lwp; 978 979 td->td_release = NULL; 980 lwkt_setpri_self(TDPRI_KERN_USER); 981 lp->lwp_proc->p_usched->release_curproc(lp); 982 } 983 984 /* 985 * Make a kernel thread act as if it were in user mode with regards 986 * to scheduling, to avoid becoming cpu-bound in the kernel. Kernel 987 * loops which may be potentially cpu-bound can call lwkt_user_yield(). 988 * 989 * The lwkt_user_yield() function is designed to have very low overhead 990 * if no yield is determined to be needed. 991 */ 992 void 993 lwkt_user_yield(void) 994 { 995 thread_t td = curthread; 996 struct lwp *lp = td->td_lwp; 997 998 #ifdef SMP 999 /* 1000 * XXX SEVERE TEMPORARY HACK. A cpu-bound operation running in the 1001 * kernel can prevent other cpus from servicing interrupt threads 1002 * which still require the MP lock (which is a lot of them). This 1003 * has a chaining effect since if the interrupt is blocked, so is 1004 * the event, so normal scheduling will not pick up on the problem. 1005 */ 1006 if (mplock_countx && td->td_mpcount) { 1007 int savecnt = td->td_mpcount; 1008 1009 td->td_mpcount = 1; 1010 mplock_countx = 0; 1011 rel_mplock(); 1012 DELAY(bgl_yield); 1013 get_mplock(); 1014 td->td_mpcount = savecnt; 1015 } 1016 #endif 1017 1018 /* 1019 * Another kernel thread wants the cpu 1020 */ 1021 if (lwkt_resched_wanted()) 1022 lwkt_switch(); 1023 1024 /* 1025 * If the user scheduler has asynchronously determined that the current 1026 * process (when running in user mode) needs to lose the cpu then make 1027 * sure we are released. 1028 */ 1029 if (user_resched_wanted()) { 1030 if (td->td_release) 1031 td->td_release(td); 1032 } 1033 1034 /* 1035 * If we are released reduce our priority 1036 */ 1037 if (td->td_release == NULL) { 1038 if (lwkt_check_resched(td) > 0) 1039 lwkt_switch(); 1040 if (lp) { 1041 lp->lwp_proc->p_usched->acquire_curproc(lp); 1042 td->td_release = lwkt_passive_release; 1043 lwkt_setpri_self(TDPRI_USER_NORM); 1044 } 1045 } 1046 } 1047 1048 /* 1049 * Return 0 if no runnable threads are pending at the same or higher 1050 * priority as the passed thread. 1051 * 1052 * Return 1 if runnable threads are pending at the same priority. 1053 * 1054 * Return 2 if runnable threads are pending at a higher priority. 1055 */ 1056 int 1057 lwkt_check_resched(thread_t td) 1058 { 1059 int pri = td->td_pri & TDPRI_MASK; 1060 1061 if (td->td_gd->gd_runqmask > (2 << pri) - 1) 1062 return(2); 1063 if (TAILQ_NEXT(td, td_threadq)) 1064 return(1); 1065 return(0); 1066 } 1067 1068 /* 1069 * Generic schedule. Possibly schedule threads belonging to other cpus and 1070 * deal with threads that might be blocked on a wait queue. 1071 * 1072 * We have a little helper inline function which does additional work after 1073 * the thread has been enqueued, including dealing with preemption and 1074 * setting need_lwkt_resched() (which prevents the kernel from returning 1075 * to userland until it has processed higher priority threads). 1076 * 1077 * It is possible for this routine to be called after a failed _enqueue 1078 * (due to the target thread migrating, sleeping, or otherwise blocked). 1079 * We have to check that the thread is actually on the run queue! 1080 * 1081 * reschedok is an optimized constant propagated from lwkt_schedule() or 1082 * lwkt_schedule_noresched(). By default it is non-zero, causing a 1083 * reschedule to be requested if the target thread has a higher priority. 1084 * The port messaging code will set MSG_NORESCHED and cause reschedok to 1085 * be 0, prevented undesired reschedules. 1086 */ 1087 static __inline 1088 void 1089 _lwkt_schedule_post(globaldata_t gd, thread_t ntd, int cpri, int reschedok) 1090 { 1091 thread_t otd; 1092 1093 if (ntd->td_flags & TDF_RUNQ) { 1094 if (ntd->td_preemptable && reschedok) { 1095 ntd->td_preemptable(ntd, cpri); /* YYY +token */ 1096 } else if (reschedok) { 1097 otd = curthread; 1098 if ((ntd->td_pri & TDPRI_MASK) > (otd->td_pri & TDPRI_MASK)) 1099 need_lwkt_resched(); 1100 } 1101 } 1102 } 1103 1104 static __inline 1105 void 1106 _lwkt_schedule(thread_t td, int reschedok) 1107 { 1108 globaldata_t mygd = mycpu; 1109 1110 KASSERT(td != &td->td_gd->gd_idlethread, ("lwkt_schedule(): scheduling gd_idlethread is illegal!")); 1111 crit_enter_gd(mygd); 1112 KKASSERT(td->td_lwp == NULL || (td->td_lwp->lwp_flag & LWP_ONRUNQ) == 0); 1113 if (td == mygd->gd_curthread) { 1114 _lwkt_enqueue(td); 1115 } else { 1116 /* 1117 * If we own the thread, there is no race (since we are in a 1118 * critical section). If we do not own the thread there might 1119 * be a race but the target cpu will deal with it. 1120 */ 1121 #ifdef SMP 1122 if (td->td_gd == mygd) { 1123 _lwkt_enqueue(td); 1124 _lwkt_schedule_post(mygd, td, TDPRI_CRIT, reschedok); 1125 } else { 1126 lwkt_send_ipiq3(td->td_gd, lwkt_schedule_remote, td, 0); 1127 } 1128 #else 1129 _lwkt_enqueue(td); 1130 _lwkt_schedule_post(mygd, td, TDPRI_CRIT, reschedok); 1131 #endif 1132 } 1133 crit_exit_gd(mygd); 1134 } 1135 1136 void 1137 lwkt_schedule(thread_t td) 1138 { 1139 _lwkt_schedule(td, 1); 1140 } 1141 1142 void 1143 lwkt_schedule_noresched(thread_t td) 1144 { 1145 _lwkt_schedule(td, 0); 1146 } 1147 1148 /* 1149 * When scheduled remotely if frame != NULL the IPIQ is being 1150 * run via doreti or an interrupt then preemption can be allowed. 1151 * 1152 * To allow preemption we have to drop the critical section so only 1153 * one is present in _lwkt_schedule_post. 1154 */ 1155 static void 1156 lwkt_schedule_remote(void *arg, int arg2, struct intrframe *frame) 1157 { 1158 thread_t td = curthread; 1159 thread_t ntd = arg; 1160 1161 if (frame && ntd->td_preemptable) { 1162 crit_exit_noyield(td); 1163 _lwkt_schedule(ntd, 1); 1164 crit_enter_quick(td); 1165 } else { 1166 _lwkt_schedule(ntd, 1); 1167 } 1168 } 1169 1170 #ifdef SMP 1171 1172 /* 1173 * Thread migration using a 'Pull' method. The thread may or may not be 1174 * the current thread. It MUST be descheduled and in a stable state. 1175 * lwkt_giveaway() must be called on the cpu owning the thread. 1176 * 1177 * At any point after lwkt_giveaway() is called, the target cpu may 1178 * 'pull' the thread by calling lwkt_acquire(). 1179 * 1180 * We have to make sure the thread is not sitting on a per-cpu tsleep 1181 * queue or it will blow up when it moves to another cpu. 1182 * 1183 * MPSAFE - must be called under very specific conditions. 1184 */ 1185 void 1186 lwkt_giveaway(thread_t td) 1187 { 1188 globaldata_t gd = mycpu; 1189 1190 crit_enter_gd(gd); 1191 if (td->td_flags & TDF_TSLEEPQ) 1192 tsleep_remove(td); 1193 KKASSERT(td->td_gd == gd); 1194 TAILQ_REMOVE(&gd->gd_tdallq, td, td_allq); 1195 td->td_flags |= TDF_MIGRATING; 1196 crit_exit_gd(gd); 1197 } 1198 1199 void 1200 lwkt_acquire(thread_t td) 1201 { 1202 globaldata_t gd; 1203 globaldata_t mygd; 1204 1205 KKASSERT(td->td_flags & TDF_MIGRATING); 1206 gd = td->td_gd; 1207 mygd = mycpu; 1208 if (gd != mycpu) { 1209 cpu_lfence(); 1210 KKASSERT((td->td_flags & TDF_RUNQ) == 0); 1211 crit_enter_gd(mygd); 1212 while (td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK)) { 1213 #ifdef SMP 1214 lwkt_process_ipiq(); 1215 #endif 1216 cpu_lfence(); 1217 } 1218 td->td_gd = mygd; 1219 TAILQ_INSERT_TAIL(&mygd->gd_tdallq, td, td_allq); 1220 td->td_flags &= ~TDF_MIGRATING; 1221 crit_exit_gd(mygd); 1222 } else { 1223 crit_enter_gd(mygd); 1224 TAILQ_INSERT_TAIL(&mygd->gd_tdallq, td, td_allq); 1225 td->td_flags &= ~TDF_MIGRATING; 1226 crit_exit_gd(mygd); 1227 } 1228 } 1229 1230 #endif 1231 1232 /* 1233 * Generic deschedule. Descheduling threads other then your own should be 1234 * done only in carefully controlled circumstances. Descheduling is 1235 * asynchronous. 1236 * 1237 * This function may block if the cpu has run out of messages. 1238 */ 1239 void 1240 lwkt_deschedule(thread_t td) 1241 { 1242 crit_enter(); 1243 #ifdef SMP 1244 if (td == curthread) { 1245 _lwkt_dequeue(td); 1246 } else { 1247 if (td->td_gd == mycpu) { 1248 _lwkt_dequeue(td); 1249 } else { 1250 lwkt_send_ipiq(td->td_gd, (ipifunc1_t)lwkt_deschedule, td); 1251 } 1252 } 1253 #else 1254 _lwkt_dequeue(td); 1255 #endif 1256 crit_exit(); 1257 } 1258 1259 /* 1260 * Set the target thread's priority. This routine does not automatically 1261 * switch to a higher priority thread, LWKT threads are not designed for 1262 * continuous priority changes. Yield if you want to switch. 1263 * 1264 * We have to retain the critical section count which uses the high bits 1265 * of the td_pri field. The specified priority may also indicate zero or 1266 * more critical sections by adding TDPRI_CRIT*N. 1267 * 1268 * Note that we requeue the thread whether it winds up on a different runq 1269 * or not. uio_yield() depends on this and the routine is not normally 1270 * called with the same priority otherwise. 1271 */ 1272 void 1273 lwkt_setpri(thread_t td, int pri) 1274 { 1275 KKASSERT(pri >= 0); 1276 KKASSERT(td->td_gd == mycpu); 1277 crit_enter(); 1278 if (td->td_flags & TDF_RUNQ) { 1279 _lwkt_dequeue(td); 1280 td->td_pri = (td->td_pri & ~TDPRI_MASK) + pri; 1281 _lwkt_enqueue(td); 1282 } else { 1283 td->td_pri = (td->td_pri & ~TDPRI_MASK) + pri; 1284 } 1285 crit_exit(); 1286 } 1287 1288 void 1289 lwkt_setpri_self(int pri) 1290 { 1291 thread_t td = curthread; 1292 1293 KKASSERT(pri >= 0 && pri <= TDPRI_MAX); 1294 crit_enter(); 1295 if (td->td_flags & TDF_RUNQ) { 1296 _lwkt_dequeue(td); 1297 td->td_pri = (td->td_pri & ~TDPRI_MASK) + pri; 1298 _lwkt_enqueue(td); 1299 } else { 1300 td->td_pri = (td->td_pri & ~TDPRI_MASK) + pri; 1301 } 1302 crit_exit(); 1303 } 1304 1305 /* 1306 * Migrate the current thread to the specified cpu. 1307 * 1308 * This is accomplished by descheduling ourselves from the current cpu, 1309 * moving our thread to the tdallq of the target cpu, IPI messaging the 1310 * target cpu, and switching out. TDF_MIGRATING prevents scheduling 1311 * races while the thread is being migrated. 1312 * 1313 * We must be sure to remove ourselves from the current cpu's tsleepq 1314 * before potentially moving to another queue. The thread can be on 1315 * a tsleepq due to a left-over tsleep_interlock(). 1316 */ 1317 #ifdef SMP 1318 static void lwkt_setcpu_remote(void *arg); 1319 #endif 1320 1321 void 1322 lwkt_setcpu_self(globaldata_t rgd) 1323 { 1324 #ifdef SMP 1325 thread_t td = curthread; 1326 1327 if (td->td_gd != rgd) { 1328 crit_enter_quick(td); 1329 if (td->td_flags & TDF_TSLEEPQ) 1330 tsleep_remove(td); 1331 td->td_flags |= TDF_MIGRATING; 1332 lwkt_deschedule_self(td); 1333 TAILQ_REMOVE(&td->td_gd->gd_tdallq, td, td_allq); 1334 lwkt_send_ipiq(rgd, (ipifunc1_t)lwkt_setcpu_remote, td); 1335 lwkt_switch(); 1336 /* we are now on the target cpu */ 1337 TAILQ_INSERT_TAIL(&rgd->gd_tdallq, td, td_allq); 1338 crit_exit_quick(td); 1339 } 1340 #endif 1341 } 1342 1343 void 1344 lwkt_migratecpu(int cpuid) 1345 { 1346 #ifdef SMP 1347 globaldata_t rgd; 1348 1349 rgd = globaldata_find(cpuid); 1350 lwkt_setcpu_self(rgd); 1351 #endif 1352 } 1353 1354 /* 1355 * Remote IPI for cpu migration (called while in a critical section so we 1356 * do not have to enter another one). The thread has already been moved to 1357 * our cpu's allq, but we must wait for the thread to be completely switched 1358 * out on the originating cpu before we schedule it on ours or the stack 1359 * state may be corrupt. We clear TDF_MIGRATING after flushing the GD 1360 * change to main memory. 1361 * 1362 * XXX The use of TDF_MIGRATING might not be sufficient to avoid races 1363 * against wakeups. It is best if this interface is used only when there 1364 * are no pending events that might try to schedule the thread. 1365 */ 1366 #ifdef SMP 1367 static void 1368 lwkt_setcpu_remote(void *arg) 1369 { 1370 thread_t td = arg; 1371 globaldata_t gd = mycpu; 1372 1373 while (td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK)) { 1374 #ifdef SMP 1375 lwkt_process_ipiq(); 1376 #endif 1377 cpu_lfence(); 1378 } 1379 td->td_gd = gd; 1380 cpu_sfence(); 1381 td->td_flags &= ~TDF_MIGRATING; 1382 KKASSERT(td->td_lwp == NULL || (td->td_lwp->lwp_flag & LWP_ONRUNQ) == 0); 1383 _lwkt_enqueue(td); 1384 } 1385 #endif 1386 1387 struct lwp * 1388 lwkt_preempted_proc(void) 1389 { 1390 thread_t td = curthread; 1391 while (td->td_preempted) 1392 td = td->td_preempted; 1393 return(td->td_lwp); 1394 } 1395 1396 /* 1397 * Create a kernel process/thread/whatever. It shares it's address space 1398 * with proc0 - ie: kernel only. 1399 * 1400 * NOTE! By default new threads are created with the MP lock held. A 1401 * thread which does not require the MP lock should release it by calling 1402 * rel_mplock() at the start of the new thread. 1403 */ 1404 int 1405 lwkt_create(void (*func)(void *), void *arg, 1406 struct thread **tdp, thread_t template, int tdflags, int cpu, 1407 const char *fmt, ...) 1408 { 1409 thread_t td; 1410 __va_list ap; 1411 1412 td = lwkt_alloc_thread(template, LWKT_THREAD_STACK, cpu, 1413 tdflags); 1414 if (tdp) 1415 *tdp = td; 1416 cpu_set_thread_handler(td, lwkt_exit, func, arg); 1417 1418 /* 1419 * Set up arg0 for 'ps' etc 1420 */ 1421 __va_start(ap, fmt); 1422 kvsnprintf(td->td_comm, sizeof(td->td_comm), fmt, ap); 1423 __va_end(ap); 1424 1425 /* 1426 * Schedule the thread to run 1427 */ 1428 if ((td->td_flags & TDF_STOPREQ) == 0) 1429 lwkt_schedule(td); 1430 else 1431 td->td_flags &= ~TDF_STOPREQ; 1432 return 0; 1433 } 1434 1435 /* 1436 * Destroy an LWKT thread. Warning! This function is not called when 1437 * a process exits, cpu_proc_exit() directly calls cpu_thread_exit() and 1438 * uses a different reaping mechanism. 1439 */ 1440 void 1441 lwkt_exit(void) 1442 { 1443 thread_t td = curthread; 1444 thread_t std; 1445 globaldata_t gd; 1446 1447 if (td->td_flags & TDF_VERBOSE) 1448 kprintf("kthread %p %s has exited\n", td, td->td_comm); 1449 caps_exit(td); 1450 1451 /* 1452 * Get us into a critical section to interlock gd_freetd and loop 1453 * until we can get it freed. 1454 * 1455 * We have to cache the current td in gd_freetd because objcache_put()ing 1456 * it would rip it out from under us while our thread is still active. 1457 */ 1458 gd = mycpu; 1459 crit_enter_quick(td); 1460 while ((std = gd->gd_freetd) != NULL) { 1461 gd->gd_freetd = NULL; 1462 objcache_put(thread_cache, std); 1463 } 1464 1465 /* 1466 * Remove thread resources from kernel lists and deschedule us for 1467 * the last time. 1468 */ 1469 if (td->td_flags & TDF_TSLEEPQ) 1470 tsleep_remove(td); 1471 lwkt_deschedule_self(td); 1472 lwkt_remove_tdallq(td); 1473 if (td->td_flags & TDF_ALLOCATED_THREAD) 1474 gd->gd_freetd = td; 1475 cpu_thread_exit(); 1476 } 1477 1478 void 1479 lwkt_remove_tdallq(thread_t td) 1480 { 1481 KKASSERT(td->td_gd == mycpu); 1482 TAILQ_REMOVE(&td->td_gd->gd_tdallq, td, td_allq); 1483 } 1484 1485 void 1486 crit_panic(void) 1487 { 1488 thread_t td = curthread; 1489 int lpri = td->td_pri; 1490 1491 td->td_pri = 0; 1492 panic("td_pri is/would-go negative! %p %d", td, lpri); 1493 } 1494 1495 #ifdef SMP 1496 1497 /* 1498 * Called from debugger/panic on cpus which have been stopped. We must still 1499 * process the IPIQ while stopped, even if we were stopped while in a critical 1500 * section (XXX). 1501 * 1502 * If we are dumping also try to process any pending interrupts. This may 1503 * or may not work depending on the state of the cpu at the point it was 1504 * stopped. 1505 */ 1506 void 1507 lwkt_smp_stopped(void) 1508 { 1509 globaldata_t gd = mycpu; 1510 1511 crit_enter_gd(gd); 1512 if (dumping) { 1513 lwkt_process_ipiq(); 1514 splz(); 1515 } else { 1516 lwkt_process_ipiq(); 1517 } 1518 crit_exit_gd(gd); 1519 } 1520 1521 /* 1522 * get_mplock() calls this routine if it is unable to obtain the MP lock. 1523 * get_mplock() has already incremented td_mpcount. We must block and 1524 * not return until giant is held. 1525 * 1526 * All we have to do is lwkt_switch() away. The LWKT scheduler will not 1527 * reschedule the thread until it can obtain the giant lock for it. 1528 */ 1529 void 1530 lwkt_mp_lock_contested(void) 1531 { 1532 ++mplock_countx; 1533 loggiant(beg); 1534 lwkt_switch(); 1535 loggiant(end); 1536 } 1537 1538 /* 1539 * The rel_mplock() code will call this function after releasing the 1540 * last reference on the MP lock if mp_lock_contention_mask is non-zero. 1541 * 1542 * We then chain an IPI to a single other cpu potentially needing the 1543 * lock. This is a bit heuristical and we can wind up with IPIs flying 1544 * all over the place. 1545 */ 1546 static void lwkt_mp_lock_uncontested_remote(void *arg __unused); 1547 1548 void 1549 lwkt_mp_lock_uncontested(void) 1550 { 1551 globaldata_t gd; 1552 globaldata_t dgd; 1553 cpumask_t mask; 1554 cpumask_t tmpmask; 1555 int cpuid; 1556 1557 if (chain_mplock) { 1558 gd = mycpu; 1559 atomic_clear_int(&mp_lock_contention_mask, gd->gd_cpumask); 1560 mask = mp_lock_contention_mask; 1561 tmpmask = ~((1 << gd->gd_cpuid) - 1); 1562 1563 if (mask) { 1564 if (mask & tmpmask) 1565 cpuid = bsfl(mask & tmpmask); 1566 else 1567 cpuid = bsfl(mask); 1568 atomic_clear_int(&mp_lock_contention_mask, 1 << cpuid); 1569 dgd = globaldata_find(cpuid); 1570 lwkt_send_ipiq(dgd, lwkt_mp_lock_uncontested_remote, NULL); 1571 } 1572 } 1573 } 1574 1575 /* 1576 * The idea is for this IPI to interrupt a potentially lower priority 1577 * thread, such as a user thread, to allow the scheduler to reschedule 1578 * a higher priority kernel thread that needs the MP lock. 1579 * 1580 * For now we set the LWKT reschedule flag which generates an AST in 1581 * doreti, though theoretically it is also possible to possibly preempt 1582 * here if the underlying thread was operating in user mode. Nah. 1583 */ 1584 static void 1585 lwkt_mp_lock_uncontested_remote(void *arg __unused) 1586 { 1587 need_lwkt_resched(); 1588 } 1589 1590 #endif 1591