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