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 #if !defined(KTR_CTXSW) 72 #define KTR_CTXSW KTR_ALL 73 #endif 74 KTR_INFO_MASTER(ctxsw); 75 KTR_INFO(KTR_CTXSW, ctxsw, sw, 0, "sw %p > %p", 2 * sizeof(struct thread *)); 76 KTR_INFO(KTR_CTXSW, ctxsw, pre, 1, "pre %p > %p", 2 * sizeof(struct thread *)); 77 78 static MALLOC_DEFINE(M_THREAD, "thread", "lwkt threads"); 79 80 #ifdef SMP 81 static int mplock_countx = 0; 82 #endif 83 #ifdef INVARIANTS 84 static int panic_on_cscount = 0; 85 #endif 86 static __int64_t switch_count = 0; 87 static __int64_t preempt_hit = 0; 88 static __int64_t preempt_miss = 0; 89 static __int64_t preempt_weird = 0; 90 static __int64_t token_contention_count = 0; 91 static __int64_t mplock_contention_count = 0; 92 static int lwkt_use_spin_port; 93 #ifdef SMP 94 static int chain_mplock = 0; 95 static int bgl_yield = 10; 96 #endif 97 static struct objcache *thread_cache; 98 99 volatile cpumask_t mp_lock_contention_mask; 100 101 #ifdef SMP 102 static void lwkt_schedule_remote(void *arg, int arg2, struct intrframe *frame); 103 #endif 104 105 extern void cpu_heavy_restore(void); 106 extern void cpu_lwkt_restore(void); 107 extern void cpu_kthread_restore(void); 108 extern void cpu_idle_restore(void); 109 110 #ifdef __amd64__ 111 112 static int 113 jg_tos_ok(struct thread *td) 114 { 115 void *tos; 116 int tos_ok; 117 118 if (td == NULL) { 119 return 1; 120 } 121 KKASSERT(td->td_sp != NULL); 122 tos = ((void **)td->td_sp)[0]; 123 tos_ok = 0; 124 if ((tos == cpu_heavy_restore) || (tos == cpu_lwkt_restore) || 125 (tos == cpu_kthread_restore) || (tos == cpu_idle_restore)) { 126 tos_ok = 1; 127 } 128 return tos_ok; 129 } 130 131 #endif 132 133 /* 134 * We can make all thread ports use the spin backend instead of the thread 135 * backend. This should only be set to debug the spin backend. 136 */ 137 TUNABLE_INT("lwkt.use_spin_port", &lwkt_use_spin_port); 138 139 #ifdef INVARIANTS 140 SYSCTL_INT(_lwkt, OID_AUTO, panic_on_cscount, CTLFLAG_RW, &panic_on_cscount, 0, ""); 141 #endif 142 #ifdef SMP 143 SYSCTL_INT(_lwkt, OID_AUTO, chain_mplock, CTLFLAG_RW, &chain_mplock, 0, ""); 144 SYSCTL_INT(_lwkt, OID_AUTO, bgl_yield_delay, CTLFLAG_RW, &bgl_yield, 0, ""); 145 #endif 146 SYSCTL_QUAD(_lwkt, OID_AUTO, switch_count, CTLFLAG_RW, &switch_count, 0, ""); 147 SYSCTL_QUAD(_lwkt, OID_AUTO, preempt_hit, CTLFLAG_RW, &preempt_hit, 0, ""); 148 SYSCTL_QUAD(_lwkt, OID_AUTO, preempt_miss, CTLFLAG_RW, &preempt_miss, 0, ""); 149 SYSCTL_QUAD(_lwkt, OID_AUTO, preempt_weird, CTLFLAG_RW, &preempt_weird, 0, ""); 150 #ifdef INVARIANTS 151 SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count, CTLFLAG_RW, 152 &token_contention_count, 0, "spinning due to token contention"); 153 SYSCTL_QUAD(_lwkt, OID_AUTO, mplock_contention_count, CTLFLAG_RW, 154 &mplock_contention_count, 0, "spinning due to MPLOCK contention"); 155 #endif 156 157 /* 158 * Kernel Trace 159 */ 160 #if !defined(KTR_GIANT_CONTENTION) 161 #define KTR_GIANT_CONTENTION KTR_ALL 162 #endif 163 164 KTR_INFO_MASTER(giant); 165 KTR_INFO(KTR_GIANT_CONTENTION, giant, beg, 0, "thread=%p", sizeof(void *)); 166 KTR_INFO(KTR_GIANT_CONTENTION, giant, end, 1, "thread=%p", sizeof(void *)); 167 168 #define loggiant(name) KTR_LOG(giant_ ## name, curthread) 169 170 /* 171 * These helper procedures handle the runq, they can only be called from 172 * within a critical section. 173 * 174 * WARNING! Prior to SMP being brought up it is possible to enqueue and 175 * dequeue threads belonging to other cpus, so be sure to use td->td_gd 176 * instead of 'mycpu' when referencing the globaldata structure. Once 177 * SMP live enqueuing and dequeueing only occurs on the current cpu. 178 */ 179 static __inline 180 void 181 _lwkt_dequeue(thread_t td) 182 { 183 if (td->td_flags & TDF_RUNQ) { 184 int nq = td->td_pri & TDPRI_MASK; 185 struct globaldata *gd = td->td_gd; 186 187 td->td_flags &= ~TDF_RUNQ; 188 TAILQ_REMOVE(&gd->gd_tdrunq[nq], td, td_threadq); 189 /* runqmask is passively cleaned up by the switcher */ 190 } 191 } 192 193 static __inline 194 void 195 _lwkt_enqueue(thread_t td) 196 { 197 if ((td->td_flags & (TDF_RUNQ|TDF_MIGRATING|TDF_BLOCKQ)) == 0) { 198 int nq = td->td_pri & TDPRI_MASK; 199 struct globaldata *gd = td->td_gd; 200 201 td->td_flags |= TDF_RUNQ; 202 TAILQ_INSERT_TAIL(&gd->gd_tdrunq[nq], td, td_threadq); 203 gd->gd_runqmask |= 1 << nq; 204 } 205 } 206 207 static __boolean_t 208 _lwkt_thread_ctor(void *obj, void *privdata, int ocflags) 209 { 210 struct thread *td = (struct thread *)obj; 211 212 td->td_kstack = NULL; 213 td->td_kstack_size = 0; 214 td->td_flags = TDF_ALLOCATED_THREAD; 215 return (1); 216 } 217 218 static void 219 _lwkt_thread_dtor(void *obj, void *privdata) 220 { 221 struct thread *td = (struct thread *)obj; 222 223 KASSERT(td->td_flags & TDF_ALLOCATED_THREAD, 224 ("_lwkt_thread_dtor: not allocated from objcache")); 225 KASSERT((td->td_flags & TDF_ALLOCATED_STACK) && td->td_kstack && 226 td->td_kstack_size > 0, 227 ("_lwkt_thread_dtor: corrupted stack")); 228 kmem_free(&kernel_map, (vm_offset_t)td->td_kstack, td->td_kstack_size); 229 } 230 231 /* 232 * Initialize the lwkt s/system. 233 */ 234 void 235 lwkt_init(void) 236 { 237 /* An objcache has 2 magazines per CPU so divide cache size by 2. */ 238 thread_cache = objcache_create_mbacked(M_THREAD, sizeof(struct thread), 239 NULL, CACHE_NTHREADS/2, 240 _lwkt_thread_ctor, _lwkt_thread_dtor, NULL); 241 } 242 243 /* 244 * Schedule a thread to run. As the current thread we can always safely 245 * schedule ourselves, and a shortcut procedure is provided for that 246 * function. 247 * 248 * (non-blocking, self contained on a per cpu basis) 249 */ 250 void 251 lwkt_schedule_self(thread_t td) 252 { 253 crit_enter_quick(td); 254 KASSERT(td != &td->td_gd->gd_idlethread, ("lwkt_schedule_self(): scheduling gd_idlethread is illegal!")); 255 KKASSERT(td->td_lwp == NULL || (td->td_lwp->lwp_flag & LWP_ONRUNQ) == 0); 256 _lwkt_enqueue(td); 257 crit_exit_quick(td); 258 } 259 260 /* 261 * Deschedule a thread. 262 * 263 * (non-blocking, self contained on a per cpu basis) 264 */ 265 void 266 lwkt_deschedule_self(thread_t td) 267 { 268 crit_enter_quick(td); 269 _lwkt_dequeue(td); 270 crit_exit_quick(td); 271 } 272 273 /* 274 * LWKTs operate on a per-cpu basis 275 * 276 * WARNING! Called from early boot, 'mycpu' may not work yet. 277 */ 278 void 279 lwkt_gdinit(struct globaldata *gd) 280 { 281 int i; 282 283 for (i = 0; i < sizeof(gd->gd_tdrunq)/sizeof(gd->gd_tdrunq[0]); ++i) 284 TAILQ_INIT(&gd->gd_tdrunq[i]); 285 gd->gd_runqmask = 0; 286 TAILQ_INIT(&gd->gd_tdallq); 287 } 288 289 /* 290 * Create a new thread. The thread must be associated with a process context 291 * or LWKT start address before it can be scheduled. If the target cpu is 292 * -1 the thread will be created on the current cpu. 293 * 294 * If you intend to create a thread without a process context this function 295 * does everything except load the startup and switcher function. 296 */ 297 thread_t 298 lwkt_alloc_thread(struct thread *td, int stksize, int cpu, int flags) 299 { 300 globaldata_t gd = mycpu; 301 void *stack; 302 303 /* 304 * If static thread storage is not supplied allocate a thread. Reuse 305 * a cached free thread if possible. gd_freetd is used to keep an exiting 306 * thread intact through the exit. 307 */ 308 if (td == NULL) { 309 if ((td = gd->gd_freetd) != NULL) 310 gd->gd_freetd = NULL; 311 else 312 td = objcache_get(thread_cache, M_WAITOK); 313 KASSERT((td->td_flags & 314 (TDF_ALLOCATED_THREAD|TDF_RUNNING)) == TDF_ALLOCATED_THREAD, 315 ("lwkt_alloc_thread: corrupted td flags 0x%X", td->td_flags)); 316 flags |= td->td_flags & (TDF_ALLOCATED_THREAD|TDF_ALLOCATED_STACK); 317 } 318 319 /* 320 * Try to reuse cached stack. 321 */ 322 if ((stack = td->td_kstack) != NULL && td->td_kstack_size != stksize) { 323 if (flags & TDF_ALLOCATED_STACK) { 324 kmem_free(&kernel_map, (vm_offset_t)stack, td->td_kstack_size); 325 stack = NULL; 326 } 327 } 328 if (stack == NULL) { 329 stack = (void *)kmem_alloc(&kernel_map, stksize); 330 flags |= TDF_ALLOCATED_STACK; 331 } 332 if (cpu < 0) 333 lwkt_init_thread(td, stack, stksize, flags, gd); 334 else 335 lwkt_init_thread(td, stack, stksize, flags, globaldata_find(cpu)); 336 return(td); 337 } 338 339 /* 340 * Initialize a preexisting thread structure. This function is used by 341 * lwkt_alloc_thread() and also used to initialize the per-cpu idlethread. 342 * 343 * All threads start out in a critical section at a priority of 344 * TDPRI_KERN_DAEMON. Higher level code will modify the priority as 345 * appropriate. This function may send an IPI message when the 346 * requested cpu is not the current cpu and consequently gd_tdallq may 347 * not be initialized synchronously from the point of view of the originating 348 * cpu. 349 * 350 * NOTE! we have to be careful in regards to creating threads for other cpus 351 * if SMP has not yet been activated. 352 */ 353 #ifdef SMP 354 355 static void 356 lwkt_init_thread_remote(void *arg) 357 { 358 thread_t td = arg; 359 360 /* 361 * Protected by critical section held by IPI dispatch 362 */ 363 TAILQ_INSERT_TAIL(&td->td_gd->gd_tdallq, td, td_allq); 364 } 365 366 #endif 367 368 void 369 lwkt_init_thread(thread_t td, void *stack, int stksize, int flags, 370 struct globaldata *gd) 371 { 372 globaldata_t mygd = mycpu; 373 374 bzero(td, sizeof(struct thread)); 375 td->td_kstack = stack; 376 td->td_kstack_size = stksize; 377 td->td_flags = flags; 378 td->td_gd = gd; 379 td->td_pri = TDPRI_KERN_DAEMON + TDPRI_CRIT; 380 #ifdef SMP 381 if ((flags & TDF_MPSAFE) == 0) 382 td->td_mpcount = 1; 383 #endif 384 if (lwkt_use_spin_port) 385 lwkt_initport_spin(&td->td_msgport); 386 else 387 lwkt_initport_thread(&td->td_msgport, td); 388 pmap_init_thread(td); 389 #ifdef SMP 390 /* 391 * Normally initializing a thread for a remote cpu requires sending an 392 * IPI. However, the idlethread is setup before the other cpus are 393 * activated so we have to treat it as a special case. XXX manipulation 394 * of gd_tdallq requires the BGL. 395 */ 396 if (gd == mygd || td == &gd->gd_idlethread) { 397 crit_enter_gd(mygd); 398 TAILQ_INSERT_TAIL(&gd->gd_tdallq, td, td_allq); 399 crit_exit_gd(mygd); 400 } else { 401 lwkt_send_ipiq(gd, lwkt_init_thread_remote, td); 402 } 403 #else 404 crit_enter_gd(mygd); 405 TAILQ_INSERT_TAIL(&gd->gd_tdallq, td, td_allq); 406 crit_exit_gd(mygd); 407 #endif 408 } 409 410 void 411 lwkt_set_comm(thread_t td, const char *ctl, ...) 412 { 413 __va_list va; 414 415 __va_start(va, ctl); 416 kvsnprintf(td->td_comm, sizeof(td->td_comm), ctl, va); 417 __va_end(va); 418 } 419 420 void 421 lwkt_hold(thread_t td) 422 { 423 ++td->td_refs; 424 } 425 426 void 427 lwkt_rele(thread_t td) 428 { 429 KKASSERT(td->td_refs > 0); 430 --td->td_refs; 431 } 432 433 void 434 lwkt_wait_free(thread_t td) 435 { 436 while (td->td_refs) 437 tsleep(td, 0, "tdreap", hz); 438 } 439 440 void 441 lwkt_free_thread(thread_t td) 442 { 443 KASSERT((td->td_flags & TDF_RUNNING) == 0, 444 ("lwkt_free_thread: did not exit! %p", td)); 445 446 if (td->td_flags & TDF_ALLOCATED_THREAD) { 447 objcache_put(thread_cache, td); 448 } else if (td->td_flags & TDF_ALLOCATED_STACK) { 449 /* client-allocated struct with internally allocated stack */ 450 KASSERT(td->td_kstack && td->td_kstack_size > 0, 451 ("lwkt_free_thread: corrupted stack")); 452 kmem_free(&kernel_map, (vm_offset_t)td->td_kstack, td->td_kstack_size); 453 td->td_kstack = NULL; 454 td->td_kstack_size = 0; 455 } 456 } 457 458 459 /* 460 * Switch to the next runnable lwkt. If no LWKTs are runnable then 461 * switch to the idlethread. Switching must occur within a critical 462 * section to avoid races with the scheduling queue. 463 * 464 * We always have full control over our cpu's run queue. Other cpus 465 * that wish to manipulate our queue must use the cpu_*msg() calls to 466 * talk to our cpu, so a critical section is all that is needed and 467 * the result is very, very fast thread switching. 468 * 469 * The LWKT scheduler uses a fixed priority model and round-robins at 470 * each priority level. User process scheduling is a totally 471 * different beast and LWKT priorities should not be confused with 472 * user process priorities. 473 * 474 * The MP lock may be out of sync with the thread's td_mpcount. lwkt_switch() 475 * cleans it up. Note that the td_switch() function cannot do anything that 476 * requires the MP lock since the MP lock will have already been setup for 477 * the target thread (not the current thread). It's nice to have a scheduler 478 * that does not need the MP lock to work because it allows us to do some 479 * really cool high-performance MP lock optimizations. 480 * 481 * PREEMPTION NOTE: Preemption occurs via lwkt_preempt(). lwkt_switch() 482 * is not called by the current thread in the preemption case, only when 483 * the preempting thread blocks (in order to return to the original thread). 484 */ 485 void 486 lwkt_switch(void) 487 { 488 globaldata_t gd = mycpu; 489 thread_t td = gd->gd_curthread; 490 thread_t ntd; 491 #ifdef SMP 492 int mpheld; 493 #endif 494 495 /* 496 * Switching from within a 'fast' (non thread switched) interrupt or IPI 497 * is illegal. However, we may have to do it anyway if we hit a fatal 498 * kernel trap or we have paniced. 499 * 500 * If this case occurs save and restore the interrupt nesting level. 501 */ 502 if (gd->gd_intr_nesting_level) { 503 int savegdnest; 504 int savegdtrap; 505 506 if (gd->gd_trap_nesting_level == 0 && panicstr == NULL) { 507 panic("lwkt_switch: cannot switch from within " 508 "a fast interrupt, yet, td %p\n", td); 509 } else { 510 savegdnest = gd->gd_intr_nesting_level; 511 savegdtrap = gd->gd_trap_nesting_level; 512 gd->gd_intr_nesting_level = 0; 513 gd->gd_trap_nesting_level = 0; 514 if ((td->td_flags & TDF_PANICWARN) == 0) { 515 td->td_flags |= TDF_PANICWARN; 516 kprintf("Warning: thread switch from interrupt or IPI, " 517 "thread %p (%s)\n", td, td->td_comm); 518 print_backtrace(); 519 } 520 lwkt_switch(); 521 gd->gd_intr_nesting_level = savegdnest; 522 gd->gd_trap_nesting_level = savegdtrap; 523 return; 524 } 525 } 526 527 /* 528 * Passive release (used to transition from user to kernel mode 529 * when we block or switch rather then when we enter the kernel). 530 * This function is NOT called if we are switching into a preemption 531 * or returning from a preemption. Typically this causes us to lose 532 * our current process designation (if we have one) and become a true 533 * LWKT thread, and may also hand the current process designation to 534 * another process and schedule thread. 535 */ 536 if (td->td_release) 537 td->td_release(td); 538 539 crit_enter_gd(gd); 540 if (td->td_toks) 541 lwkt_relalltokens(td); 542 543 /* 544 * We had better not be holding any spin locks, but don't get into an 545 * endless panic loop. 546 */ 547 KASSERT(gd->gd_spinlock_rd == NULL || panicstr != NULL, 548 ("lwkt_switch: still holding a shared spinlock %p!", 549 gd->gd_spinlock_rd)); 550 KASSERT(gd->gd_spinlocks_wr == 0 || panicstr != NULL, 551 ("lwkt_switch: still holding %d exclusive spinlocks!", 552 gd->gd_spinlocks_wr)); 553 554 555 #ifdef SMP 556 /* 557 * td_mpcount cannot be used to determine if we currently hold the 558 * MP lock because get_mplock() will increment it prior to attempting 559 * to get the lock, and switch out if it can't. Our ownership of 560 * the actual lock will remain stable while we are in a critical section 561 * (but, of course, another cpu may own or release the lock so the 562 * actual value of mp_lock is not stable). 563 */ 564 mpheld = MP_LOCK_HELD(); 565 #ifdef INVARIANTS 566 if (td->td_cscount) { 567 kprintf("Diagnostic: attempt to switch while mastering cpusync: %p\n", 568 td); 569 if (panic_on_cscount) 570 panic("switching while mastering cpusync"); 571 } 572 #endif 573 #endif 574 if ((ntd = td->td_preempted) != NULL) { 575 /* 576 * We had preempted another thread on this cpu, resume the preempted 577 * thread. This occurs transparently, whether the preempted thread 578 * was scheduled or not (it may have been preempted after descheduling 579 * itself). 580 * 581 * We have to setup the MP lock for the original thread after backing 582 * out the adjustment that was made to curthread when the original 583 * was preempted. 584 */ 585 KKASSERT(ntd->td_flags & TDF_PREEMPT_LOCK); 586 #ifdef SMP 587 if (ntd->td_mpcount && mpheld == 0) { 588 panic("MPLOCK NOT HELD ON RETURN: %p %p %d %d", 589 td, ntd, td->td_mpcount, ntd->td_mpcount); 590 } 591 if (ntd->td_mpcount) { 592 td->td_mpcount -= ntd->td_mpcount; 593 KKASSERT(td->td_mpcount >= 0); 594 } 595 #endif 596 ntd->td_flags |= TDF_PREEMPT_DONE; 597 598 /* 599 * The interrupt may have woken a thread up, we need to properly 600 * set the reschedule flag if the originally interrupted thread is 601 * at a lower priority. 602 */ 603 if (gd->gd_runqmask > (2 << (ntd->td_pri & TDPRI_MASK)) - 1) 604 need_lwkt_resched(); 605 /* YYY release mp lock on switchback if original doesn't need it */ 606 } else { 607 /* 608 * Priority queue / round-robin at each priority. Note that user 609 * processes run at a fixed, low priority and the user process 610 * scheduler deals with interactions between user processes 611 * by scheduling and descheduling them from the LWKT queue as 612 * necessary. 613 * 614 * We have to adjust the MP lock for the target thread. If we 615 * need the MP lock and cannot obtain it we try to locate a 616 * thread that does not need the MP lock. If we cannot, we spin 617 * instead of HLT. 618 * 619 * A similar issue exists for the tokens held by the target thread. 620 * If we cannot obtain ownership of the tokens we cannot immediately 621 * schedule the thread. 622 */ 623 624 /* 625 * If an LWKT reschedule was requested, well that is what we are 626 * doing now so clear it. 627 */ 628 clear_lwkt_resched(); 629 again: 630 if (gd->gd_runqmask) { 631 int nq = bsrl(gd->gd_runqmask); 632 if ((ntd = TAILQ_FIRST(&gd->gd_tdrunq[nq])) == NULL) { 633 gd->gd_runqmask &= ~(1 << nq); 634 goto again; 635 } 636 #ifdef SMP 637 /* 638 * THREAD SELECTION FOR AN SMP MACHINE BUILD 639 * 640 * If the target needs the MP lock and we couldn't get it, 641 * or if the target is holding tokens and we could not 642 * gain ownership of the tokens, continue looking for a 643 * thread to schedule and spin instead of HLT if we can't. 644 * 645 * NOTE: the mpheld variable invalid after this conditional, it 646 * can change due to both cpu_try_mplock() returning success 647 * AND interactions in lwkt_getalltokens() due to the fact that 648 * we are trying to check the mpcount of a thread other then 649 * the current thread. Because of this, if the current thread 650 * is not holding td_mpcount, an IPI indirectly run via 651 * lwkt_getalltokens() can obtain and release the MP lock and 652 * cause the core MP lock to be released. 653 */ 654 if ((ntd->td_mpcount && mpheld == 0 && !cpu_try_mplock()) || 655 (ntd->td_toks && lwkt_getalltokens(ntd) == 0) 656 ) { 657 u_int32_t rqmask = gd->gd_runqmask; 658 659 mpheld = MP_LOCK_HELD(); 660 ntd = NULL; 661 while (rqmask) { 662 TAILQ_FOREACH(ntd, &gd->gd_tdrunq[nq], td_threadq) { 663 if (ntd->td_mpcount && !mpheld && !cpu_try_mplock()) { 664 /* spinning due to MP lock being held */ 665 #ifdef INVARIANTS 666 ++mplock_contention_count; 667 #endif 668 /* mplock still not held, 'mpheld' still valid */ 669 continue; 670 } 671 672 /* 673 * mpheld state invalid after getalltokens call returns 674 * failure, but the variable is only needed for 675 * the loop. 676 */ 677 if (ntd->td_toks && !lwkt_getalltokens(ntd)) { 678 /* spinning due to token contention */ 679 #ifdef INVARIANTS 680 ++token_contention_count; 681 #endif 682 mpheld = MP_LOCK_HELD(); 683 continue; 684 } 685 break; 686 } 687 if (ntd) 688 break; 689 rqmask &= ~(1 << nq); 690 nq = bsrl(rqmask); 691 692 /* 693 * We have two choices. We can either refuse to run a 694 * user thread when a kernel thread needs the MP lock 695 * but could not get it, or we can allow it to run but 696 * then expect an IPI (hopefully) later on to force a 697 * reschedule when the MP lock might become available. 698 */ 699 if (nq < TDPRI_KERN_LPSCHED) { 700 if (chain_mplock == 0) 701 break; 702 atomic_set_int(&mp_lock_contention_mask, 703 gd->gd_cpumask); 704 /* continue loop, allow user threads to be scheduled */ 705 } 706 } 707 if (ntd == NULL) { 708 cpu_mplock_contested(); 709 ntd = &gd->gd_idlethread; 710 ntd->td_flags |= TDF_IDLE_NOHLT; 711 goto using_idle_thread; 712 } else { 713 ++gd->gd_cnt.v_swtch; 714 TAILQ_REMOVE(&gd->gd_tdrunq[nq], ntd, td_threadq); 715 TAILQ_INSERT_TAIL(&gd->gd_tdrunq[nq], ntd, td_threadq); 716 } 717 } else { 718 if (ntd->td_mpcount) 719 ++mplock_countx; 720 ++gd->gd_cnt.v_swtch; 721 TAILQ_REMOVE(&gd->gd_tdrunq[nq], ntd, td_threadq); 722 TAILQ_INSERT_TAIL(&gd->gd_tdrunq[nq], ntd, td_threadq); 723 } 724 #else 725 /* 726 * THREAD SELECTION FOR A UP MACHINE BUILD. We don't have to 727 * worry about tokens or the BGL. However, we still have 728 * to call lwkt_getalltokens() in order to properly detect 729 * stale tokens. This call cannot fail for a UP build! 730 */ 731 lwkt_getalltokens(ntd); 732 ++gd->gd_cnt.v_swtch; 733 TAILQ_REMOVE(&gd->gd_tdrunq[nq], ntd, td_threadq); 734 TAILQ_INSERT_TAIL(&gd->gd_tdrunq[nq], ntd, td_threadq); 735 #endif 736 } else { 737 /* 738 * We have nothing to run but only let the idle loop halt 739 * the cpu if there are no pending interrupts. 740 */ 741 ntd = &gd->gd_idlethread; 742 if (gd->gd_reqflags & RQF_IDLECHECK_MASK) 743 ntd->td_flags |= TDF_IDLE_NOHLT; 744 #ifdef SMP 745 using_idle_thread: 746 /* 747 * The idle thread should not be holding the MP lock unless we 748 * are trapping in the kernel or in a panic. Since we select the 749 * idle thread unconditionally when no other thread is available, 750 * if the MP lock is desired during a panic or kernel trap, we 751 * have to loop in the scheduler until we get it. 752 */ 753 if (ntd->td_mpcount) { 754 mpheld = MP_LOCK_HELD(); 755 if (gd->gd_trap_nesting_level == 0 && panicstr == NULL) { 756 panic("Idle thread %p was holding the BGL!", ntd); 757 } else if (mpheld == 0) { 758 cpu_mplock_contested(); 759 goto again; 760 } 761 } 762 #endif 763 } 764 } 765 KASSERT(ntd->td_pri >= TDPRI_CRIT, 766 ("priority problem in lwkt_switch %d %d", td->td_pri, ntd->td_pri)); 767 768 /* 769 * Do the actual switch. If the new target does not need the MP lock 770 * and we are holding it, release the MP lock. If the new target requires 771 * the MP lock we have already acquired it for the target. 772 */ 773 #ifdef SMP 774 if (ntd->td_mpcount == 0 ) { 775 if (MP_LOCK_HELD()) 776 cpu_rel_mplock(); 777 } else { 778 ASSERT_MP_LOCK_HELD(ntd); 779 } 780 #endif 781 if (td != ntd) { 782 ++switch_count; 783 #ifdef __amd64__ 784 KKASSERT(jg_tos_ok(ntd)); 785 #endif 786 KTR_LOG(ctxsw_sw, td, ntd); 787 td->td_switch(ntd); 788 } 789 /* NOTE: current cpu may have changed after switch */ 790 crit_exit_quick(td); 791 } 792 793 /* 794 * Request that the target thread preempt the current thread. Preemption 795 * only works under a specific set of conditions: 796 * 797 * - We are not preempting ourselves 798 * - The target thread is owned by the current cpu 799 * - We are not currently being preempted 800 * - The target is not currently being preempted 801 * - We are not holding any spin locks 802 * - The target thread is not holding any tokens 803 * - We are able to satisfy the target's MP lock requirements (if any). 804 * 805 * THE CALLER OF LWKT_PREEMPT() MUST BE IN A CRITICAL SECTION. Typically 806 * this is called via lwkt_schedule() through the td_preemptable callback. 807 * critpri is the managed critical priority that we should ignore in order 808 * to determine whether preemption is possible (aka usually just the crit 809 * priority of lwkt_schedule() itself). 810 * 811 * XXX at the moment we run the target thread in a critical section during 812 * the preemption in order to prevent the target from taking interrupts 813 * that *WE* can't. Preemption is strictly limited to interrupt threads 814 * and interrupt-like threads, outside of a critical section, and the 815 * preempted source thread will be resumed the instant the target blocks 816 * whether or not the source is scheduled (i.e. preemption is supposed to 817 * be as transparent as possible). 818 * 819 * The target thread inherits our MP count (added to its own) for the 820 * duration of the preemption in order to preserve the atomicy of the 821 * MP lock during the preemption. Therefore, any preempting targets must be 822 * careful in regards to MP assertions. Note that the MP count may be 823 * out of sync with the physical mp_lock, but we do not have to preserve 824 * the original ownership of the lock if it was out of synch (that is, we 825 * can leave it synchronized on return). 826 */ 827 void 828 lwkt_preempt(thread_t ntd, int critpri) 829 { 830 struct globaldata *gd = mycpu; 831 thread_t td; 832 #ifdef SMP 833 int mpheld; 834 int savecnt; 835 #endif 836 837 /* 838 * The caller has put us in a critical section. We can only preempt 839 * if the caller of the caller was not in a critical section (basically 840 * a local interrupt), as determined by the 'critpri' parameter. We 841 * also can't preempt if the caller is holding any spinlocks (even if 842 * he isn't in a critical section). This also handles the tokens test. 843 * 844 * YYY The target thread must be in a critical section (else it must 845 * inherit our critical section? I dunno yet). 846 * 847 * Set need_lwkt_resched() unconditionally for now YYY. 848 */ 849 KASSERT(ntd->td_pri >= TDPRI_CRIT, ("BADCRIT0 %d", ntd->td_pri)); 850 851 td = gd->gd_curthread; 852 if ((ntd->td_pri & TDPRI_MASK) <= (td->td_pri & TDPRI_MASK)) { 853 ++preempt_miss; 854 return; 855 } 856 if ((td->td_pri & ~TDPRI_MASK) > critpri) { 857 ++preempt_miss; 858 need_lwkt_resched(); 859 return; 860 } 861 #ifdef SMP 862 if (ntd->td_gd != gd) { 863 ++preempt_miss; 864 need_lwkt_resched(); 865 return; 866 } 867 #endif 868 /* 869 * Take the easy way out and do not preempt if we are holding 870 * any spinlocks. We could test whether the thread(s) being 871 * preempted interlock against the target thread's tokens and whether 872 * we can get all the target thread's tokens, but this situation 873 * should not occur very often so its easier to simply not preempt. 874 * Also, plain spinlocks are impossible to figure out at this point so 875 * just don't preempt. 876 * 877 * Do not try to preempt if the target thread is holding any tokens. 878 * We could try to acquire the tokens but this case is so rare there 879 * is no need to support it. 880 */ 881 if (gd->gd_spinlock_rd || gd->gd_spinlocks_wr) { 882 ++preempt_miss; 883 need_lwkt_resched(); 884 return; 885 } 886 if (ntd->td_toks) { 887 ++preempt_miss; 888 need_lwkt_resched(); 889 return; 890 } 891 if (td == ntd || ((td->td_flags | ntd->td_flags) & TDF_PREEMPT_LOCK)) { 892 ++preempt_weird; 893 need_lwkt_resched(); 894 return; 895 } 896 if (ntd->td_preempted) { 897 ++preempt_hit; 898 need_lwkt_resched(); 899 return; 900 } 901 #ifdef SMP 902 /* 903 * note: an interrupt might have occured just as we were transitioning 904 * to or from the MP lock. In this case td_mpcount will be pre-disposed 905 * (non-zero) but not actually synchronized with the actual state of the 906 * lock. We can use it to imply an MP lock requirement for the 907 * preemption but we cannot use it to test whether we hold the MP lock 908 * or not. 909 */ 910 savecnt = td->td_mpcount; 911 mpheld = MP_LOCK_HELD(); 912 ntd->td_mpcount += td->td_mpcount; 913 if (mpheld == 0 && ntd->td_mpcount && !cpu_try_mplock()) { 914 ntd->td_mpcount -= td->td_mpcount; 915 ++preempt_miss; 916 need_lwkt_resched(); 917 return; 918 } 919 #endif 920 921 /* 922 * Since we are able to preempt the current thread, there is no need to 923 * call need_lwkt_resched(). 924 */ 925 ++preempt_hit; 926 ntd->td_preempted = td; 927 td->td_flags |= TDF_PREEMPT_LOCK; 928 KTR_LOG(ctxsw_pre, td, ntd); 929 td->td_switch(ntd); 930 931 KKASSERT(ntd->td_preempted && (td->td_flags & TDF_PREEMPT_DONE)); 932 #ifdef SMP 933 KKASSERT(savecnt == td->td_mpcount); 934 mpheld = MP_LOCK_HELD(); 935 if (mpheld && td->td_mpcount == 0) 936 cpu_rel_mplock(); 937 else if (mpheld == 0 && td->td_mpcount) 938 panic("lwkt_preempt(): MP lock was not held through"); 939 #endif 940 ntd->td_preempted = NULL; 941 td->td_flags &= ~(TDF_PREEMPT_LOCK|TDF_PREEMPT_DONE); 942 } 943 944 /* 945 * Conditionally call splz() if gd_reqflags indicates work is pending. 946 * 947 * td_nest_count prevents deep nesting via splz() or doreti() which 948 * might otherwise blow out the kernel stack. Note that except for 949 * this special case, we MUST call splz() here to handle any 950 * pending ints, particularly after we switch, or we might accidently 951 * halt the cpu with interrupts pending. 952 * 953 * (self contained on a per cpu basis) 954 */ 955 void 956 splz_check(void) 957 { 958 globaldata_t gd = mycpu; 959 thread_t td = gd->gd_curthread; 960 961 if (gd->gd_reqflags && td->td_nest_count < 2) 962 splz(); 963 } 964 965 /* 966 * This implements a normal yield which will yield to equal priority 967 * threads as well as higher priority threads. Note that gd_reqflags 968 * tests will be handled by the crit_exit() call in lwkt_switch(). 969 * 970 * (self contained on a per cpu basis) 971 */ 972 void 973 lwkt_yield(void) 974 { 975 lwkt_schedule_self(curthread); 976 lwkt_switch(); 977 } 978 979 /* 980 * This function is used along with the lwkt_passive_recover() inline 981 * by the trap code to negotiate a passive release of the current 982 * process/lwp designation with the user scheduler. 983 */ 984 void 985 lwkt_passive_release(struct thread *td) 986 { 987 struct lwp *lp = td->td_lwp; 988 989 td->td_release = NULL; 990 lwkt_setpri_self(TDPRI_KERN_USER); 991 lp->lwp_proc->p_usched->release_curproc(lp); 992 } 993 994 /* 995 * Make a kernel thread act as if it were in user mode with regards 996 * to scheduling, to avoid becoming cpu-bound in the kernel. Kernel 997 * loops which may be potentially cpu-bound can call lwkt_user_yield(). 998 * 999 * The lwkt_user_yield() function is designed to have very low overhead 1000 * if no yield is determined to be needed. 1001 */ 1002 void 1003 lwkt_user_yield(void) 1004 { 1005 thread_t td = curthread; 1006 struct lwp *lp = td->td_lwp; 1007 1008 #ifdef SMP 1009 /* 1010 * XXX SEVERE TEMPORARY HACK. A cpu-bound operation running in the 1011 * kernel can prevent other cpus from servicing interrupt threads 1012 * which still require the MP lock (which is a lot of them). This 1013 * has a chaining effect since if the interrupt is blocked, so is 1014 * the event, so normal scheduling will not pick up on the problem. 1015 */ 1016 if (mplock_countx && td->td_mpcount) { 1017 int savecnt = td->td_mpcount; 1018 1019 td->td_mpcount = 1; 1020 mplock_countx = 0; 1021 rel_mplock(); 1022 DELAY(bgl_yield); 1023 get_mplock(); 1024 td->td_mpcount = savecnt; 1025 } 1026 #endif 1027 1028 /* 1029 * Another kernel thread wants the cpu 1030 */ 1031 if (lwkt_resched_wanted()) 1032 lwkt_switch(); 1033 1034 /* 1035 * If the user scheduler has asynchronously determined that the current 1036 * process (when running in user mode) needs to lose the cpu then make 1037 * sure we are released. 1038 */ 1039 if (user_resched_wanted()) { 1040 if (td->td_release) 1041 td->td_release(td); 1042 } 1043 1044 /* 1045 * If we are released reduce our priority 1046 */ 1047 if (td->td_release == NULL) { 1048 if (lwkt_check_resched(td) > 0) 1049 lwkt_switch(); 1050 if (lp) { 1051 lp->lwp_proc->p_usched->acquire_curproc(lp); 1052 td->td_release = lwkt_passive_release; 1053 lwkt_setpri_self(TDPRI_USER_NORM); 1054 } 1055 } 1056 } 1057 1058 /* 1059 * Return 0 if no runnable threads are pending at the same or higher 1060 * priority as the passed thread. 1061 * 1062 * Return 1 if runnable threads are pending at the same priority. 1063 * 1064 * Return 2 if runnable threads are pending at a higher priority. 1065 */ 1066 int 1067 lwkt_check_resched(thread_t td) 1068 { 1069 int pri = td->td_pri & TDPRI_MASK; 1070 1071 if (td->td_gd->gd_runqmask > (2 << pri) - 1) 1072 return(2); 1073 if (TAILQ_NEXT(td, td_threadq)) 1074 return(1); 1075 return(0); 1076 } 1077 1078 /* 1079 * Generic schedule. Possibly schedule threads belonging to other cpus and 1080 * deal with threads that might be blocked on a wait queue. 1081 * 1082 * We have a little helper inline function which does additional work after 1083 * the thread has been enqueued, including dealing with preemption and 1084 * setting need_lwkt_resched() (which prevents the kernel from returning 1085 * to userland until it has processed higher priority threads). 1086 * 1087 * It is possible for this routine to be called after a failed _enqueue 1088 * (due to the target thread migrating, sleeping, or otherwise blocked). 1089 * We have to check that the thread is actually on the run queue! 1090 * 1091 * reschedok is an optimized constant propagated from lwkt_schedule() or 1092 * lwkt_schedule_noresched(). By default it is non-zero, causing a 1093 * reschedule to be requested if the target thread has a higher priority. 1094 * The port messaging code will set MSG_NORESCHED and cause reschedok to 1095 * be 0, prevented undesired reschedules. 1096 */ 1097 static __inline 1098 void 1099 _lwkt_schedule_post(globaldata_t gd, thread_t ntd, int cpri, int reschedok) 1100 { 1101 thread_t otd; 1102 1103 if (ntd->td_flags & TDF_RUNQ) { 1104 if (ntd->td_preemptable && reschedok) { 1105 ntd->td_preemptable(ntd, cpri); /* YYY +token */ 1106 } else if (reschedok) { 1107 otd = curthread; 1108 if ((ntd->td_pri & TDPRI_MASK) > (otd->td_pri & TDPRI_MASK)) 1109 need_lwkt_resched(); 1110 } 1111 } 1112 } 1113 1114 static __inline 1115 void 1116 _lwkt_schedule(thread_t td, int reschedok) 1117 { 1118 globaldata_t mygd = mycpu; 1119 1120 KASSERT(td != &td->td_gd->gd_idlethread, ("lwkt_schedule(): scheduling gd_idlethread is illegal!")); 1121 crit_enter_gd(mygd); 1122 KKASSERT(td->td_lwp == NULL || (td->td_lwp->lwp_flag & LWP_ONRUNQ) == 0); 1123 if (td == mygd->gd_curthread) { 1124 _lwkt_enqueue(td); 1125 } else { 1126 /* 1127 * If we own the thread, there is no race (since we are in a 1128 * critical section). If we do not own the thread there might 1129 * be a race but the target cpu will deal with it. 1130 */ 1131 #ifdef SMP 1132 if (td->td_gd == mygd) { 1133 _lwkt_enqueue(td); 1134 _lwkt_schedule_post(mygd, td, TDPRI_CRIT, reschedok); 1135 } else { 1136 lwkt_send_ipiq3(td->td_gd, lwkt_schedule_remote, td, 0); 1137 } 1138 #else 1139 _lwkt_enqueue(td); 1140 _lwkt_schedule_post(mygd, td, TDPRI_CRIT, reschedok); 1141 #endif 1142 } 1143 crit_exit_gd(mygd); 1144 } 1145 1146 void 1147 lwkt_schedule(thread_t td) 1148 { 1149 _lwkt_schedule(td, 1); 1150 } 1151 1152 void 1153 lwkt_schedule_noresched(thread_t td) 1154 { 1155 _lwkt_schedule(td, 0); 1156 } 1157 1158 #ifdef SMP 1159 1160 /* 1161 * When scheduled remotely if frame != NULL the IPIQ is being 1162 * run via doreti or an interrupt then preemption can be allowed. 1163 * 1164 * To allow preemption we have to drop the critical section so only 1165 * one is present in _lwkt_schedule_post. 1166 */ 1167 static void 1168 lwkt_schedule_remote(void *arg, int arg2, struct intrframe *frame) 1169 { 1170 thread_t td = curthread; 1171 thread_t ntd = arg; 1172 1173 if (frame && ntd->td_preemptable) { 1174 crit_exit_noyield(td); 1175 _lwkt_schedule(ntd, 1); 1176 crit_enter_quick(td); 1177 } else { 1178 _lwkt_schedule(ntd, 1); 1179 } 1180 } 1181 1182 /* 1183 * Thread migration using a 'Pull' method. The thread may or may not be 1184 * the current thread. It MUST be descheduled and in a stable state. 1185 * lwkt_giveaway() must be called on the cpu owning the thread. 1186 * 1187 * At any point after lwkt_giveaway() is called, the target cpu may 1188 * 'pull' the thread by calling lwkt_acquire(). 1189 * 1190 * We have to make sure the thread is not sitting on a per-cpu tsleep 1191 * queue or it will blow up when it moves to another cpu. 1192 * 1193 * MPSAFE - must be called under very specific conditions. 1194 */ 1195 void 1196 lwkt_giveaway(thread_t td) 1197 { 1198 globaldata_t gd = mycpu; 1199 1200 crit_enter_gd(gd); 1201 if (td->td_flags & TDF_TSLEEPQ) 1202 tsleep_remove(td); 1203 KKASSERT(td->td_gd == gd); 1204 TAILQ_REMOVE(&gd->gd_tdallq, td, td_allq); 1205 td->td_flags |= TDF_MIGRATING; 1206 crit_exit_gd(gd); 1207 } 1208 1209 void 1210 lwkt_acquire(thread_t td) 1211 { 1212 globaldata_t gd; 1213 globaldata_t mygd; 1214 1215 KKASSERT(td->td_flags & TDF_MIGRATING); 1216 gd = td->td_gd; 1217 mygd = mycpu; 1218 if (gd != mycpu) { 1219 cpu_lfence(); 1220 KKASSERT((td->td_flags & TDF_RUNQ) == 0); 1221 crit_enter_gd(mygd); 1222 while (td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK)) { 1223 #ifdef SMP 1224 lwkt_process_ipiq(); 1225 #endif 1226 cpu_lfence(); 1227 } 1228 td->td_gd = mygd; 1229 TAILQ_INSERT_TAIL(&mygd->gd_tdallq, td, td_allq); 1230 td->td_flags &= ~TDF_MIGRATING; 1231 crit_exit_gd(mygd); 1232 } else { 1233 crit_enter_gd(mygd); 1234 TAILQ_INSERT_TAIL(&mygd->gd_tdallq, td, td_allq); 1235 td->td_flags &= ~TDF_MIGRATING; 1236 crit_exit_gd(mygd); 1237 } 1238 } 1239 1240 #endif 1241 1242 /* 1243 * Generic deschedule. Descheduling threads other then your own should be 1244 * done only in carefully controlled circumstances. Descheduling is 1245 * asynchronous. 1246 * 1247 * This function may block if the cpu has run out of messages. 1248 */ 1249 void 1250 lwkt_deschedule(thread_t td) 1251 { 1252 crit_enter(); 1253 #ifdef SMP 1254 if (td == curthread) { 1255 _lwkt_dequeue(td); 1256 } else { 1257 if (td->td_gd == mycpu) { 1258 _lwkt_dequeue(td); 1259 } else { 1260 lwkt_send_ipiq(td->td_gd, (ipifunc1_t)lwkt_deschedule, td); 1261 } 1262 } 1263 #else 1264 _lwkt_dequeue(td); 1265 #endif 1266 crit_exit(); 1267 } 1268 1269 /* 1270 * Set the target thread's priority. This routine does not automatically 1271 * switch to a higher priority thread, LWKT threads are not designed for 1272 * continuous priority changes. Yield if you want to switch. 1273 * 1274 * We have to retain the critical section count which uses the high bits 1275 * of the td_pri field. The specified priority may also indicate zero or 1276 * more critical sections by adding TDPRI_CRIT*N. 1277 * 1278 * Note that we requeue the thread whether it winds up on a different runq 1279 * or not. uio_yield() depends on this and the routine is not normally 1280 * called with the same priority otherwise. 1281 */ 1282 void 1283 lwkt_setpri(thread_t td, int pri) 1284 { 1285 KKASSERT(pri >= 0); 1286 KKASSERT(td->td_gd == mycpu); 1287 crit_enter(); 1288 if (td->td_flags & TDF_RUNQ) { 1289 _lwkt_dequeue(td); 1290 td->td_pri = (td->td_pri & ~TDPRI_MASK) + pri; 1291 _lwkt_enqueue(td); 1292 } else { 1293 td->td_pri = (td->td_pri & ~TDPRI_MASK) + pri; 1294 } 1295 crit_exit(); 1296 } 1297 1298 void 1299 lwkt_setpri_self(int pri) 1300 { 1301 thread_t td = curthread; 1302 1303 KKASSERT(pri >= 0 && pri <= TDPRI_MAX); 1304 crit_enter(); 1305 if (td->td_flags & TDF_RUNQ) { 1306 _lwkt_dequeue(td); 1307 td->td_pri = (td->td_pri & ~TDPRI_MASK) + pri; 1308 _lwkt_enqueue(td); 1309 } else { 1310 td->td_pri = (td->td_pri & ~TDPRI_MASK) + pri; 1311 } 1312 crit_exit(); 1313 } 1314 1315 /* 1316 * Migrate the current thread to the specified cpu. 1317 * 1318 * This is accomplished by descheduling ourselves from the current cpu, 1319 * moving our thread to the tdallq of the target cpu, IPI messaging the 1320 * target cpu, and switching out. TDF_MIGRATING prevents scheduling 1321 * races while the thread is being migrated. 1322 * 1323 * We must be sure to remove ourselves from the current cpu's tsleepq 1324 * before potentially moving to another queue. The thread can be on 1325 * a tsleepq due to a left-over tsleep_interlock(). 1326 */ 1327 #ifdef SMP 1328 static void lwkt_setcpu_remote(void *arg); 1329 #endif 1330 1331 void 1332 lwkt_setcpu_self(globaldata_t rgd) 1333 { 1334 #ifdef SMP 1335 thread_t td = curthread; 1336 1337 if (td->td_gd != rgd) { 1338 crit_enter_quick(td); 1339 if (td->td_flags & TDF_TSLEEPQ) 1340 tsleep_remove(td); 1341 td->td_flags |= TDF_MIGRATING; 1342 lwkt_deschedule_self(td); 1343 TAILQ_REMOVE(&td->td_gd->gd_tdallq, td, td_allq); 1344 lwkt_send_ipiq(rgd, (ipifunc1_t)lwkt_setcpu_remote, td); 1345 lwkt_switch(); 1346 /* we are now on the target cpu */ 1347 TAILQ_INSERT_TAIL(&rgd->gd_tdallq, td, td_allq); 1348 crit_exit_quick(td); 1349 } 1350 #endif 1351 } 1352 1353 void 1354 lwkt_migratecpu(int cpuid) 1355 { 1356 #ifdef SMP 1357 globaldata_t rgd; 1358 1359 rgd = globaldata_find(cpuid); 1360 lwkt_setcpu_self(rgd); 1361 #endif 1362 } 1363 1364 /* 1365 * Remote IPI for cpu migration (called while in a critical section so we 1366 * do not have to enter another one). The thread has already been moved to 1367 * our cpu's allq, but we must wait for the thread to be completely switched 1368 * out on the originating cpu before we schedule it on ours or the stack 1369 * state may be corrupt. We clear TDF_MIGRATING after flushing the GD 1370 * change to main memory. 1371 * 1372 * XXX The use of TDF_MIGRATING might not be sufficient to avoid races 1373 * against wakeups. It is best if this interface is used only when there 1374 * are no pending events that might try to schedule the thread. 1375 */ 1376 #ifdef SMP 1377 static void 1378 lwkt_setcpu_remote(void *arg) 1379 { 1380 thread_t td = arg; 1381 globaldata_t gd = mycpu; 1382 1383 while (td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK)) { 1384 #ifdef SMP 1385 lwkt_process_ipiq(); 1386 #endif 1387 cpu_lfence(); 1388 } 1389 td->td_gd = gd; 1390 cpu_sfence(); 1391 td->td_flags &= ~TDF_MIGRATING; 1392 KKASSERT(td->td_lwp == NULL || (td->td_lwp->lwp_flag & LWP_ONRUNQ) == 0); 1393 _lwkt_enqueue(td); 1394 } 1395 #endif 1396 1397 struct lwp * 1398 lwkt_preempted_proc(void) 1399 { 1400 thread_t td = curthread; 1401 while (td->td_preempted) 1402 td = td->td_preempted; 1403 return(td->td_lwp); 1404 } 1405 1406 /* 1407 * Create a kernel process/thread/whatever. It shares it's address space 1408 * with proc0 - ie: kernel only. 1409 * 1410 * NOTE! By default new threads are created with the MP lock held. A 1411 * thread which does not require the MP lock should release it by calling 1412 * rel_mplock() at the start of the new thread. 1413 */ 1414 int 1415 lwkt_create(void (*func)(void *), void *arg, 1416 struct thread **tdp, thread_t template, int tdflags, int cpu, 1417 const char *fmt, ...) 1418 { 1419 thread_t td; 1420 __va_list ap; 1421 1422 td = lwkt_alloc_thread(template, LWKT_THREAD_STACK, cpu, 1423 tdflags); 1424 if (tdp) 1425 *tdp = td; 1426 cpu_set_thread_handler(td, lwkt_exit, func, arg); 1427 1428 /* 1429 * Set up arg0 for 'ps' etc 1430 */ 1431 __va_start(ap, fmt); 1432 kvsnprintf(td->td_comm, sizeof(td->td_comm), fmt, ap); 1433 __va_end(ap); 1434 1435 /* 1436 * Schedule the thread to run 1437 */ 1438 if ((td->td_flags & TDF_STOPREQ) == 0) 1439 lwkt_schedule(td); 1440 else 1441 td->td_flags &= ~TDF_STOPREQ; 1442 return 0; 1443 } 1444 1445 /* 1446 * Destroy an LWKT thread. Warning! This function is not called when 1447 * a process exits, cpu_proc_exit() directly calls cpu_thread_exit() and 1448 * uses a different reaping mechanism. 1449 */ 1450 void 1451 lwkt_exit(void) 1452 { 1453 thread_t td = curthread; 1454 thread_t std; 1455 globaldata_t gd; 1456 1457 if (td->td_flags & TDF_VERBOSE) 1458 kprintf("kthread %p %s has exited\n", td, td->td_comm); 1459 caps_exit(td); 1460 1461 /* 1462 * Get us into a critical section to interlock gd_freetd and loop 1463 * until we can get it freed. 1464 * 1465 * We have to cache the current td in gd_freetd because objcache_put()ing 1466 * it would rip it out from under us while our thread is still active. 1467 */ 1468 gd = mycpu; 1469 crit_enter_quick(td); 1470 while ((std = gd->gd_freetd) != NULL) { 1471 gd->gd_freetd = NULL; 1472 objcache_put(thread_cache, std); 1473 } 1474 1475 /* 1476 * Remove thread resources from kernel lists and deschedule us for 1477 * the last time. 1478 */ 1479 if (td->td_flags & TDF_TSLEEPQ) 1480 tsleep_remove(td); 1481 biosched_done(td); 1482 lwkt_deschedule_self(td); 1483 lwkt_remove_tdallq(td); 1484 if (td->td_flags & TDF_ALLOCATED_THREAD) 1485 gd->gd_freetd = td; 1486 cpu_thread_exit(); 1487 } 1488 1489 void 1490 lwkt_remove_tdallq(thread_t td) 1491 { 1492 KKASSERT(td->td_gd == mycpu); 1493 TAILQ_REMOVE(&td->td_gd->gd_tdallq, td, td_allq); 1494 } 1495 1496 void 1497 crit_panic(void) 1498 { 1499 thread_t td = curthread; 1500 int lpri = td->td_pri; 1501 1502 td->td_pri = 0; 1503 panic("td_pri is/would-go negative! %p %d", td, lpri); 1504 } 1505 1506 #ifdef SMP 1507 1508 /* 1509 * Called from debugger/panic on cpus which have been stopped. We must still 1510 * process the IPIQ while stopped, even if we were stopped while in a critical 1511 * section (XXX). 1512 * 1513 * If we are dumping also try to process any pending interrupts. This may 1514 * or may not work depending on the state of the cpu at the point it was 1515 * stopped. 1516 */ 1517 void 1518 lwkt_smp_stopped(void) 1519 { 1520 globaldata_t gd = mycpu; 1521 1522 crit_enter_gd(gd); 1523 if (dumping) { 1524 lwkt_process_ipiq(); 1525 splz(); 1526 } else { 1527 lwkt_process_ipiq(); 1528 } 1529 crit_exit_gd(gd); 1530 } 1531 1532 /* 1533 * get_mplock() calls this routine if it is unable to obtain the MP lock. 1534 * get_mplock() has already incremented td_mpcount. We must block and 1535 * not return until giant is held. 1536 * 1537 * All we have to do is lwkt_switch() away. The LWKT scheduler will not 1538 * reschedule the thread until it can obtain the giant lock for it. 1539 */ 1540 void 1541 lwkt_mp_lock_contested(void) 1542 { 1543 ++mplock_countx; 1544 loggiant(beg); 1545 lwkt_switch(); 1546 loggiant(end); 1547 } 1548 1549 /* 1550 * The rel_mplock() code will call this function after releasing the 1551 * last reference on the MP lock if mp_lock_contention_mask is non-zero. 1552 * 1553 * We then chain an IPI to a single other cpu potentially needing the 1554 * lock. This is a bit heuristical and we can wind up with IPIs flying 1555 * all over the place. 1556 */ 1557 static void lwkt_mp_lock_uncontested_remote(void *arg __unused); 1558 1559 void 1560 lwkt_mp_lock_uncontested(void) 1561 { 1562 globaldata_t gd; 1563 globaldata_t dgd; 1564 cpumask_t mask; 1565 cpumask_t tmpmask; 1566 int cpuid; 1567 1568 if (chain_mplock) { 1569 gd = mycpu; 1570 atomic_clear_int(&mp_lock_contention_mask, gd->gd_cpumask); 1571 mask = mp_lock_contention_mask; 1572 tmpmask = ~((1 << gd->gd_cpuid) - 1); 1573 1574 if (mask) { 1575 if (mask & tmpmask) 1576 cpuid = bsfl(mask & tmpmask); 1577 else 1578 cpuid = bsfl(mask); 1579 atomic_clear_int(&mp_lock_contention_mask, 1 << cpuid); 1580 dgd = globaldata_find(cpuid); 1581 lwkt_send_ipiq(dgd, lwkt_mp_lock_uncontested_remote, NULL); 1582 } 1583 } 1584 } 1585 1586 /* 1587 * The idea is for this IPI to interrupt a potentially lower priority 1588 * thread, such as a user thread, to allow the scheduler to reschedule 1589 * a higher priority kernel thread that needs the MP lock. 1590 * 1591 * For now we set the LWKT reschedule flag which generates an AST in 1592 * doreti, though theoretically it is also possible to possibly preempt 1593 * here if the underlying thread was operating in user mode. Nah. 1594 */ 1595 static void 1596 lwkt_mp_lock_uncontested_remote(void *arg __unused) 1597 { 1598 need_lwkt_resched(); 1599 } 1600 1601 #endif 1602