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 __debugvar = 0; 91 static __int64_t mplock_contention_count __debugvar = 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 __x86_64__ 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 __x86_64__ 784 { 785 int tos_ok __debugvar = jg_tos_ok(ntd); 786 KKASSERT(tos_ok); 787 } 788 #endif 789 KTR_LOG(ctxsw_sw, td, ntd); 790 td->td_switch(ntd); 791 } 792 /* NOTE: current cpu may have changed after switch */ 793 crit_exit_quick(td); 794 } 795 796 /* 797 * Request that the target thread preempt the current thread. Preemption 798 * only works under a specific set of conditions: 799 * 800 * - We are not preempting ourselves 801 * - The target thread is owned by the current cpu 802 * - We are not currently being preempted 803 * - The target is not currently being preempted 804 * - We are not holding any spin locks 805 * - The target thread is not holding any tokens 806 * - We are able to satisfy the target's MP lock requirements (if any). 807 * 808 * THE CALLER OF LWKT_PREEMPT() MUST BE IN A CRITICAL SECTION. Typically 809 * this is called via lwkt_schedule() through the td_preemptable callback. 810 * critpri is the managed critical priority that we should ignore in order 811 * to determine whether preemption is possible (aka usually just the crit 812 * priority of lwkt_schedule() itself). 813 * 814 * XXX at the moment we run the target thread in a critical section during 815 * the preemption in order to prevent the target from taking interrupts 816 * that *WE* can't. Preemption is strictly limited to interrupt threads 817 * and interrupt-like threads, outside of a critical section, and the 818 * preempted source thread will be resumed the instant the target blocks 819 * whether or not the source is scheduled (i.e. preemption is supposed to 820 * be as transparent as possible). 821 * 822 * The target thread inherits our MP count (added to its own) for the 823 * duration of the preemption in order to preserve the atomicy of the 824 * MP lock during the preemption. Therefore, any preempting targets must be 825 * careful in regards to MP assertions. Note that the MP count may be 826 * out of sync with the physical mp_lock, but we do not have to preserve 827 * the original ownership of the lock if it was out of synch (that is, we 828 * can leave it synchronized on return). 829 */ 830 void 831 lwkt_preempt(thread_t ntd, int critpri) 832 { 833 struct globaldata *gd = mycpu; 834 thread_t td; 835 #ifdef SMP 836 int mpheld; 837 int savecnt; 838 #endif 839 840 /* 841 * The caller has put us in a critical section. We can only preempt 842 * if the caller of the caller was not in a critical section (basically 843 * a local interrupt), as determined by the 'critpri' parameter. We 844 * also can't preempt if the caller is holding any spinlocks (even if 845 * he isn't in a critical section). This also handles the tokens test. 846 * 847 * YYY The target thread must be in a critical section (else it must 848 * inherit our critical section? I dunno yet). 849 * 850 * Set need_lwkt_resched() unconditionally for now YYY. 851 */ 852 KASSERT(ntd->td_pri >= TDPRI_CRIT, ("BADCRIT0 %d", ntd->td_pri)); 853 854 td = gd->gd_curthread; 855 if ((ntd->td_pri & TDPRI_MASK) <= (td->td_pri & TDPRI_MASK)) { 856 ++preempt_miss; 857 return; 858 } 859 if ((td->td_pri & ~TDPRI_MASK) > critpri) { 860 ++preempt_miss; 861 need_lwkt_resched(); 862 return; 863 } 864 #ifdef SMP 865 if (ntd->td_gd != gd) { 866 ++preempt_miss; 867 need_lwkt_resched(); 868 return; 869 } 870 #endif 871 /* 872 * Take the easy way out and do not preempt if we are holding 873 * any spinlocks. We could test whether the thread(s) being 874 * preempted interlock against the target thread's tokens and whether 875 * we can get all the target thread's tokens, but this situation 876 * should not occur very often so its easier to simply not preempt. 877 * Also, plain spinlocks are impossible to figure out at this point so 878 * just don't preempt. 879 * 880 * Do not try to preempt if the target thread is holding any tokens. 881 * We could try to acquire the tokens but this case is so rare there 882 * is no need to support it. 883 */ 884 if (gd->gd_spinlock_rd || gd->gd_spinlocks_wr) { 885 ++preempt_miss; 886 need_lwkt_resched(); 887 return; 888 } 889 if (ntd->td_toks) { 890 ++preempt_miss; 891 need_lwkt_resched(); 892 return; 893 } 894 if (td == ntd || ((td->td_flags | ntd->td_flags) & TDF_PREEMPT_LOCK)) { 895 ++preempt_weird; 896 need_lwkt_resched(); 897 return; 898 } 899 if (ntd->td_preempted) { 900 ++preempt_hit; 901 need_lwkt_resched(); 902 return; 903 } 904 #ifdef SMP 905 /* 906 * note: an interrupt might have occured just as we were transitioning 907 * to or from the MP lock. In this case td_mpcount will be pre-disposed 908 * (non-zero) but not actually synchronized with the actual state of the 909 * lock. We can use it to imply an MP lock requirement for the 910 * preemption but we cannot use it to test whether we hold the MP lock 911 * or not. 912 */ 913 savecnt = td->td_mpcount; 914 mpheld = MP_LOCK_HELD(); 915 ntd->td_mpcount += td->td_mpcount; 916 if (mpheld == 0 && ntd->td_mpcount && !cpu_try_mplock()) { 917 ntd->td_mpcount -= td->td_mpcount; 918 ++preempt_miss; 919 need_lwkt_resched(); 920 return; 921 } 922 #endif 923 924 /* 925 * Since we are able to preempt the current thread, there is no need to 926 * call need_lwkt_resched(). 927 */ 928 ++preempt_hit; 929 ntd->td_preempted = td; 930 td->td_flags |= TDF_PREEMPT_LOCK; 931 KTR_LOG(ctxsw_pre, td, ntd); 932 td->td_switch(ntd); 933 934 KKASSERT(ntd->td_preempted && (td->td_flags & TDF_PREEMPT_DONE)); 935 #ifdef SMP 936 KKASSERT(savecnt == td->td_mpcount); 937 mpheld = MP_LOCK_HELD(); 938 if (mpheld && td->td_mpcount == 0) 939 cpu_rel_mplock(); 940 else if (mpheld == 0 && td->td_mpcount) 941 panic("lwkt_preempt(): MP lock was not held through"); 942 #endif 943 ntd->td_preempted = NULL; 944 td->td_flags &= ~(TDF_PREEMPT_LOCK|TDF_PREEMPT_DONE); 945 } 946 947 /* 948 * Conditionally call splz() if gd_reqflags indicates work is pending. 949 * 950 * td_nest_count prevents deep nesting via splz() or doreti() which 951 * might otherwise blow out the kernel stack. Note that except for 952 * this special case, we MUST call splz() here to handle any 953 * pending ints, particularly after we switch, or we might accidently 954 * halt the cpu with interrupts pending. 955 * 956 * (self contained on a per cpu basis) 957 */ 958 void 959 splz_check(void) 960 { 961 globaldata_t gd = mycpu; 962 thread_t td = gd->gd_curthread; 963 964 if (gd->gd_reqflags && td->td_nest_count < 2) 965 splz(); 966 } 967 968 /* 969 * This implements a normal yield which will yield to equal priority 970 * threads as well as higher priority threads. Note that gd_reqflags 971 * tests will be handled by the crit_exit() call in lwkt_switch(). 972 * 973 * (self contained on a per cpu basis) 974 */ 975 void 976 lwkt_yield(void) 977 { 978 lwkt_schedule_self(curthread); 979 lwkt_switch(); 980 } 981 982 /* 983 * This function is used along with the lwkt_passive_recover() inline 984 * by the trap code to negotiate a passive release of the current 985 * process/lwp designation with the user scheduler. 986 */ 987 void 988 lwkt_passive_release(struct thread *td) 989 { 990 struct lwp *lp = td->td_lwp; 991 992 td->td_release = NULL; 993 lwkt_setpri_self(TDPRI_KERN_USER); 994 lp->lwp_proc->p_usched->release_curproc(lp); 995 } 996 997 /* 998 * Make a kernel thread act as if it were in user mode with regards 999 * to scheduling, to avoid becoming cpu-bound in the kernel. Kernel 1000 * loops which may be potentially cpu-bound can call lwkt_user_yield(). 1001 * 1002 * The lwkt_user_yield() function is designed to have very low overhead 1003 * if no yield is determined to be needed. 1004 */ 1005 void 1006 lwkt_user_yield(void) 1007 { 1008 thread_t td = curthread; 1009 struct lwp *lp = td->td_lwp; 1010 1011 #ifdef SMP 1012 /* 1013 * XXX SEVERE TEMPORARY HACK. A cpu-bound operation running in the 1014 * kernel can prevent other cpus from servicing interrupt threads 1015 * which still require the MP lock (which is a lot of them). This 1016 * has a chaining effect since if the interrupt is blocked, so is 1017 * the event, so normal scheduling will not pick up on the problem. 1018 */ 1019 if (mplock_countx && td->td_mpcount) { 1020 int savecnt = td->td_mpcount; 1021 1022 td->td_mpcount = 1; 1023 mplock_countx = 0; 1024 rel_mplock(); 1025 DELAY(bgl_yield); 1026 get_mplock(); 1027 td->td_mpcount = savecnt; 1028 } 1029 #endif 1030 1031 /* 1032 * Another kernel thread wants the cpu 1033 */ 1034 if (lwkt_resched_wanted()) 1035 lwkt_switch(); 1036 1037 /* 1038 * If the user scheduler has asynchronously determined that the current 1039 * process (when running in user mode) needs to lose the cpu then make 1040 * sure we are released. 1041 */ 1042 if (user_resched_wanted()) { 1043 if (td->td_release) 1044 td->td_release(td); 1045 } 1046 1047 /* 1048 * If we are released reduce our priority 1049 */ 1050 if (td->td_release == NULL) { 1051 if (lwkt_check_resched(td) > 0) 1052 lwkt_switch(); 1053 if (lp) { 1054 lp->lwp_proc->p_usched->acquire_curproc(lp); 1055 td->td_release = lwkt_passive_release; 1056 lwkt_setpri_self(TDPRI_USER_NORM); 1057 } 1058 } 1059 } 1060 1061 /* 1062 * Return 0 if no runnable threads are pending at the same or higher 1063 * priority as the passed thread. 1064 * 1065 * Return 1 if runnable threads are pending at the same priority. 1066 * 1067 * Return 2 if runnable threads are pending at a higher priority. 1068 */ 1069 int 1070 lwkt_check_resched(thread_t td) 1071 { 1072 int pri = td->td_pri & TDPRI_MASK; 1073 1074 if (td->td_gd->gd_runqmask > (2 << pri) - 1) 1075 return(2); 1076 if (TAILQ_NEXT(td, td_threadq)) 1077 return(1); 1078 return(0); 1079 } 1080 1081 /* 1082 * Generic schedule. Possibly schedule threads belonging to other cpus and 1083 * deal with threads that might be blocked on a wait queue. 1084 * 1085 * We have a little helper inline function which does additional work after 1086 * the thread has been enqueued, including dealing with preemption and 1087 * setting need_lwkt_resched() (which prevents the kernel from returning 1088 * to userland until it has processed higher priority threads). 1089 * 1090 * It is possible for this routine to be called after a failed _enqueue 1091 * (due to the target thread migrating, sleeping, or otherwise blocked). 1092 * We have to check that the thread is actually on the run queue! 1093 * 1094 * reschedok is an optimized constant propagated from lwkt_schedule() or 1095 * lwkt_schedule_noresched(). By default it is non-zero, causing a 1096 * reschedule to be requested if the target thread has a higher priority. 1097 * The port messaging code will set MSG_NORESCHED and cause reschedok to 1098 * be 0, prevented undesired reschedules. 1099 */ 1100 static __inline 1101 void 1102 _lwkt_schedule_post(globaldata_t gd, thread_t ntd, int cpri, int reschedok) 1103 { 1104 thread_t otd; 1105 1106 if (ntd->td_flags & TDF_RUNQ) { 1107 if (ntd->td_preemptable && reschedok) { 1108 ntd->td_preemptable(ntd, cpri); /* YYY +token */ 1109 } else if (reschedok) { 1110 otd = curthread; 1111 if ((ntd->td_pri & TDPRI_MASK) > (otd->td_pri & TDPRI_MASK)) 1112 need_lwkt_resched(); 1113 } 1114 } 1115 } 1116 1117 static __inline 1118 void 1119 _lwkt_schedule(thread_t td, int reschedok) 1120 { 1121 globaldata_t mygd = mycpu; 1122 1123 KASSERT(td != &td->td_gd->gd_idlethread, ("lwkt_schedule(): scheduling gd_idlethread is illegal!")); 1124 crit_enter_gd(mygd); 1125 KKASSERT(td->td_lwp == NULL || (td->td_lwp->lwp_flag & LWP_ONRUNQ) == 0); 1126 if (td == mygd->gd_curthread) { 1127 _lwkt_enqueue(td); 1128 } else { 1129 /* 1130 * If we own the thread, there is no race (since we are in a 1131 * critical section). If we do not own the thread there might 1132 * be a race but the target cpu will deal with it. 1133 */ 1134 #ifdef SMP 1135 if (td->td_gd == mygd) { 1136 _lwkt_enqueue(td); 1137 _lwkt_schedule_post(mygd, td, TDPRI_CRIT, reschedok); 1138 } else { 1139 lwkt_send_ipiq3(td->td_gd, lwkt_schedule_remote, td, 0); 1140 } 1141 #else 1142 _lwkt_enqueue(td); 1143 _lwkt_schedule_post(mygd, td, TDPRI_CRIT, reschedok); 1144 #endif 1145 } 1146 crit_exit_gd(mygd); 1147 } 1148 1149 void 1150 lwkt_schedule(thread_t td) 1151 { 1152 _lwkt_schedule(td, 1); 1153 } 1154 1155 void 1156 lwkt_schedule_noresched(thread_t td) 1157 { 1158 _lwkt_schedule(td, 0); 1159 } 1160 1161 #ifdef SMP 1162 1163 /* 1164 * When scheduled remotely if frame != NULL the IPIQ is being 1165 * run via doreti or an interrupt then preemption can be allowed. 1166 * 1167 * To allow preemption we have to drop the critical section so only 1168 * one is present in _lwkt_schedule_post. 1169 */ 1170 static void 1171 lwkt_schedule_remote(void *arg, int arg2, struct intrframe *frame) 1172 { 1173 thread_t td = curthread; 1174 thread_t ntd = arg; 1175 1176 if (frame && ntd->td_preemptable) { 1177 crit_exit_noyield(td); 1178 _lwkt_schedule(ntd, 1); 1179 crit_enter_quick(td); 1180 } else { 1181 _lwkt_schedule(ntd, 1); 1182 } 1183 } 1184 1185 /* 1186 * Thread migration using a 'Pull' method. The thread may or may not be 1187 * the current thread. It MUST be descheduled and in a stable state. 1188 * lwkt_giveaway() must be called on the cpu owning the thread. 1189 * 1190 * At any point after lwkt_giveaway() is called, the target cpu may 1191 * 'pull' the thread by calling lwkt_acquire(). 1192 * 1193 * We have to make sure the thread is not sitting on a per-cpu tsleep 1194 * queue or it will blow up when it moves to another cpu. 1195 * 1196 * MPSAFE - must be called under very specific conditions. 1197 */ 1198 void 1199 lwkt_giveaway(thread_t td) 1200 { 1201 globaldata_t gd = mycpu; 1202 1203 crit_enter_gd(gd); 1204 if (td->td_flags & TDF_TSLEEPQ) 1205 tsleep_remove(td); 1206 KKASSERT(td->td_gd == gd); 1207 TAILQ_REMOVE(&gd->gd_tdallq, td, td_allq); 1208 td->td_flags |= TDF_MIGRATING; 1209 crit_exit_gd(gd); 1210 } 1211 1212 void 1213 lwkt_acquire(thread_t td) 1214 { 1215 globaldata_t gd; 1216 globaldata_t mygd; 1217 1218 KKASSERT(td->td_flags & TDF_MIGRATING); 1219 gd = td->td_gd; 1220 mygd = mycpu; 1221 if (gd != mycpu) { 1222 cpu_lfence(); 1223 KKASSERT((td->td_flags & TDF_RUNQ) == 0); 1224 crit_enter_gd(mygd); 1225 while (td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK)) { 1226 #ifdef SMP 1227 lwkt_process_ipiq(); 1228 #endif 1229 cpu_lfence(); 1230 } 1231 td->td_gd = mygd; 1232 TAILQ_INSERT_TAIL(&mygd->gd_tdallq, td, td_allq); 1233 td->td_flags &= ~TDF_MIGRATING; 1234 crit_exit_gd(mygd); 1235 } else { 1236 crit_enter_gd(mygd); 1237 TAILQ_INSERT_TAIL(&mygd->gd_tdallq, td, td_allq); 1238 td->td_flags &= ~TDF_MIGRATING; 1239 crit_exit_gd(mygd); 1240 } 1241 } 1242 1243 #endif 1244 1245 /* 1246 * Generic deschedule. Descheduling threads other then your own should be 1247 * done only in carefully controlled circumstances. Descheduling is 1248 * asynchronous. 1249 * 1250 * This function may block if the cpu has run out of messages. 1251 */ 1252 void 1253 lwkt_deschedule(thread_t td) 1254 { 1255 crit_enter(); 1256 #ifdef SMP 1257 if (td == curthread) { 1258 _lwkt_dequeue(td); 1259 } else { 1260 if (td->td_gd == mycpu) { 1261 _lwkt_dequeue(td); 1262 } else { 1263 lwkt_send_ipiq(td->td_gd, (ipifunc1_t)lwkt_deschedule, td); 1264 } 1265 } 1266 #else 1267 _lwkt_dequeue(td); 1268 #endif 1269 crit_exit(); 1270 } 1271 1272 /* 1273 * Set the target thread's priority. This routine does not automatically 1274 * switch to a higher priority thread, LWKT threads are not designed for 1275 * continuous priority changes. Yield if you want to switch. 1276 * 1277 * We have to retain the critical section count which uses the high bits 1278 * of the td_pri field. The specified priority may also indicate zero or 1279 * more critical sections by adding TDPRI_CRIT*N. 1280 * 1281 * Note that we requeue the thread whether it winds up on a different runq 1282 * or not. uio_yield() depends on this and the routine is not normally 1283 * called with the same priority otherwise. 1284 */ 1285 void 1286 lwkt_setpri(thread_t td, int pri) 1287 { 1288 KKASSERT(pri >= 0); 1289 KKASSERT(td->td_gd == mycpu); 1290 crit_enter(); 1291 if (td->td_flags & TDF_RUNQ) { 1292 _lwkt_dequeue(td); 1293 td->td_pri = (td->td_pri & ~TDPRI_MASK) + pri; 1294 _lwkt_enqueue(td); 1295 } else { 1296 td->td_pri = (td->td_pri & ~TDPRI_MASK) + pri; 1297 } 1298 crit_exit(); 1299 } 1300 1301 /* 1302 * Set the initial priority for a thread prior to it being scheduled for 1303 * the first time. The thread MUST NOT be scheduled before or during 1304 * this call. The thread may be assigned to a cpu other then the current 1305 * cpu. 1306 * 1307 * Typically used after a thread has been created with TDF_STOPPREQ, 1308 * and before the thread is initially scheduled. 1309 */ 1310 void 1311 lwkt_setpri_initial(thread_t td, int pri) 1312 { 1313 KKASSERT(pri >= 0); 1314 KKASSERT((td->td_flags & TDF_RUNQ) == 0); 1315 td->td_pri = (td->td_pri & ~TDPRI_MASK) + pri; 1316 } 1317 1318 void 1319 lwkt_setpri_self(int pri) 1320 { 1321 thread_t td = curthread; 1322 1323 KKASSERT(pri >= 0 && pri <= TDPRI_MAX); 1324 crit_enter(); 1325 if (td->td_flags & TDF_RUNQ) { 1326 _lwkt_dequeue(td); 1327 td->td_pri = (td->td_pri & ~TDPRI_MASK) + pri; 1328 _lwkt_enqueue(td); 1329 } else { 1330 td->td_pri = (td->td_pri & ~TDPRI_MASK) + pri; 1331 } 1332 crit_exit(); 1333 } 1334 1335 /* 1336 * Migrate the current thread to the specified cpu. 1337 * 1338 * This is accomplished by descheduling ourselves from the current cpu, 1339 * moving our thread to the tdallq of the target cpu, IPI messaging the 1340 * target cpu, and switching out. TDF_MIGRATING prevents scheduling 1341 * races while the thread is being migrated. 1342 * 1343 * We must be sure to remove ourselves from the current cpu's tsleepq 1344 * before potentially moving to another queue. The thread can be on 1345 * a tsleepq due to a left-over tsleep_interlock(). 1346 */ 1347 #ifdef SMP 1348 static void lwkt_setcpu_remote(void *arg); 1349 #endif 1350 1351 void 1352 lwkt_setcpu_self(globaldata_t rgd) 1353 { 1354 #ifdef SMP 1355 thread_t td = curthread; 1356 1357 if (td->td_gd != rgd) { 1358 crit_enter_quick(td); 1359 if (td->td_flags & TDF_TSLEEPQ) 1360 tsleep_remove(td); 1361 td->td_flags |= TDF_MIGRATING; 1362 lwkt_deschedule_self(td); 1363 TAILQ_REMOVE(&td->td_gd->gd_tdallq, td, td_allq); 1364 lwkt_send_ipiq(rgd, (ipifunc1_t)lwkt_setcpu_remote, td); 1365 lwkt_switch(); 1366 /* we are now on the target cpu */ 1367 TAILQ_INSERT_TAIL(&rgd->gd_tdallq, td, td_allq); 1368 crit_exit_quick(td); 1369 } 1370 #endif 1371 } 1372 1373 void 1374 lwkt_migratecpu(int cpuid) 1375 { 1376 #ifdef SMP 1377 globaldata_t rgd; 1378 1379 rgd = globaldata_find(cpuid); 1380 lwkt_setcpu_self(rgd); 1381 #endif 1382 } 1383 1384 /* 1385 * Remote IPI for cpu migration (called while in a critical section so we 1386 * do not have to enter another one). The thread has already been moved to 1387 * our cpu's allq, but we must wait for the thread to be completely switched 1388 * out on the originating cpu before we schedule it on ours or the stack 1389 * state may be corrupt. We clear TDF_MIGRATING after flushing the GD 1390 * change to main memory. 1391 * 1392 * XXX The use of TDF_MIGRATING might not be sufficient to avoid races 1393 * against wakeups. It is best if this interface is used only when there 1394 * are no pending events that might try to schedule the thread. 1395 */ 1396 #ifdef SMP 1397 static void 1398 lwkt_setcpu_remote(void *arg) 1399 { 1400 thread_t td = arg; 1401 globaldata_t gd = mycpu; 1402 1403 while (td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK)) { 1404 #ifdef SMP 1405 lwkt_process_ipiq(); 1406 #endif 1407 cpu_lfence(); 1408 } 1409 td->td_gd = gd; 1410 cpu_sfence(); 1411 td->td_flags &= ~TDF_MIGRATING; 1412 KKASSERT(td->td_lwp == NULL || (td->td_lwp->lwp_flag & LWP_ONRUNQ) == 0); 1413 _lwkt_enqueue(td); 1414 } 1415 #endif 1416 1417 struct lwp * 1418 lwkt_preempted_proc(void) 1419 { 1420 thread_t td = curthread; 1421 while (td->td_preempted) 1422 td = td->td_preempted; 1423 return(td->td_lwp); 1424 } 1425 1426 /* 1427 * Create a kernel process/thread/whatever. It shares it's address space 1428 * with proc0 - ie: kernel only. 1429 * 1430 * NOTE! By default new threads are created with the MP lock held. A 1431 * thread which does not require the MP lock should release it by calling 1432 * rel_mplock() at the start of the new thread. 1433 */ 1434 int 1435 lwkt_create(void (*func)(void *), void *arg, 1436 struct thread **tdp, thread_t template, int tdflags, int cpu, 1437 const char *fmt, ...) 1438 { 1439 thread_t td; 1440 __va_list ap; 1441 1442 td = lwkt_alloc_thread(template, LWKT_THREAD_STACK, cpu, 1443 tdflags); 1444 if (tdp) 1445 *tdp = td; 1446 cpu_set_thread_handler(td, lwkt_exit, func, arg); 1447 1448 /* 1449 * Set up arg0 for 'ps' etc 1450 */ 1451 __va_start(ap, fmt); 1452 kvsnprintf(td->td_comm, sizeof(td->td_comm), fmt, ap); 1453 __va_end(ap); 1454 1455 /* 1456 * Schedule the thread to run 1457 */ 1458 if ((td->td_flags & TDF_STOPREQ) == 0) 1459 lwkt_schedule(td); 1460 else 1461 td->td_flags &= ~TDF_STOPREQ; 1462 return 0; 1463 } 1464 1465 /* 1466 * Destroy an LWKT thread. Warning! This function is not called when 1467 * a process exits, cpu_proc_exit() directly calls cpu_thread_exit() and 1468 * uses a different reaping mechanism. 1469 */ 1470 void 1471 lwkt_exit(void) 1472 { 1473 thread_t td = curthread; 1474 thread_t std; 1475 globaldata_t gd; 1476 1477 if (td->td_flags & TDF_VERBOSE) 1478 kprintf("kthread %p %s has exited\n", td, td->td_comm); 1479 caps_exit(td); 1480 1481 /* 1482 * Get us into a critical section to interlock gd_freetd and loop 1483 * until we can get it freed. 1484 * 1485 * We have to cache the current td in gd_freetd because objcache_put()ing 1486 * it would rip it out from under us while our thread is still active. 1487 */ 1488 gd = mycpu; 1489 crit_enter_quick(td); 1490 while ((std = gd->gd_freetd) != NULL) { 1491 gd->gd_freetd = NULL; 1492 objcache_put(thread_cache, std); 1493 } 1494 1495 /* 1496 * Remove thread resources from kernel lists and deschedule us for 1497 * the last time. 1498 */ 1499 if (td->td_flags & TDF_TSLEEPQ) 1500 tsleep_remove(td); 1501 biosched_done(td); 1502 lwkt_deschedule_self(td); 1503 lwkt_remove_tdallq(td); 1504 if (td->td_flags & TDF_ALLOCATED_THREAD) 1505 gd->gd_freetd = td; 1506 cpu_thread_exit(); 1507 } 1508 1509 void 1510 lwkt_remove_tdallq(thread_t td) 1511 { 1512 KKASSERT(td->td_gd == mycpu); 1513 TAILQ_REMOVE(&td->td_gd->gd_tdallq, td, td_allq); 1514 } 1515 1516 void 1517 crit_panic(void) 1518 { 1519 thread_t td = curthread; 1520 int lpri = td->td_pri; 1521 1522 td->td_pri = 0; 1523 panic("td_pri is/would-go negative! %p %d", td, lpri); 1524 } 1525 1526 #ifdef SMP 1527 1528 /* 1529 * Called from debugger/panic on cpus which have been stopped. We must still 1530 * process the IPIQ while stopped, even if we were stopped while in a critical 1531 * section (XXX). 1532 * 1533 * If we are dumping also try to process any pending interrupts. This may 1534 * or may not work depending on the state of the cpu at the point it was 1535 * stopped. 1536 */ 1537 void 1538 lwkt_smp_stopped(void) 1539 { 1540 globaldata_t gd = mycpu; 1541 1542 crit_enter_gd(gd); 1543 if (dumping) { 1544 lwkt_process_ipiq(); 1545 splz(); 1546 } else { 1547 lwkt_process_ipiq(); 1548 } 1549 crit_exit_gd(gd); 1550 } 1551 1552 /* 1553 * get_mplock() calls this routine if it is unable to obtain the MP lock. 1554 * get_mplock() has already incremented td_mpcount. We must block and 1555 * not return until giant is held. 1556 * 1557 * All we have to do is lwkt_switch() away. The LWKT scheduler will not 1558 * reschedule the thread until it can obtain the giant lock for it. 1559 */ 1560 void 1561 lwkt_mp_lock_contested(void) 1562 { 1563 ++mplock_countx; 1564 loggiant(beg); 1565 lwkt_switch(); 1566 loggiant(end); 1567 } 1568 1569 /* 1570 * The rel_mplock() code will call this function after releasing the 1571 * last reference on the MP lock if mp_lock_contention_mask is non-zero. 1572 * 1573 * We then chain an IPI to a single other cpu potentially needing the 1574 * lock. This is a bit heuristical and we can wind up with IPIs flying 1575 * all over the place. 1576 */ 1577 static void lwkt_mp_lock_uncontested_remote(void *arg __unused); 1578 1579 void 1580 lwkt_mp_lock_uncontested(void) 1581 { 1582 globaldata_t gd; 1583 globaldata_t dgd; 1584 cpumask_t mask; 1585 cpumask_t tmpmask; 1586 int cpuid; 1587 1588 if (chain_mplock) { 1589 gd = mycpu; 1590 atomic_clear_int(&mp_lock_contention_mask, gd->gd_cpumask); 1591 mask = mp_lock_contention_mask; 1592 tmpmask = ~((1 << gd->gd_cpuid) - 1); 1593 1594 if (mask) { 1595 if (mask & tmpmask) 1596 cpuid = bsfl(mask & tmpmask); 1597 else 1598 cpuid = bsfl(mask); 1599 atomic_clear_int(&mp_lock_contention_mask, 1 << cpuid); 1600 dgd = globaldata_find(cpuid); 1601 lwkt_send_ipiq(dgd, lwkt_mp_lock_uncontested_remote, NULL); 1602 } 1603 } 1604 } 1605 1606 /* 1607 * The idea is for this IPI to interrupt a potentially lower priority 1608 * thread, such as a user thread, to allow the scheduler to reschedule 1609 * a higher priority kernel thread that needs the MP lock. 1610 * 1611 * For now we set the LWKT reschedule flag which generates an AST in 1612 * doreti, though theoretically it is also possible to possibly preempt 1613 * here if the underlying thread was operating in user mode. Nah. 1614 */ 1615 static void 1616 lwkt_mp_lock_uncontested_remote(void *arg __unused) 1617 { 1618 need_lwkt_resched(); 1619 } 1620 1621 #endif 1622