| 1 | /* |
| 2 | * Copyright (c) 2003-2010 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/kinfo.h> |
| 48 | #include <sys/queue.h> |
| 49 | #include <sys/sysctl.h> |
| 50 | #include <sys/kthread.h> |
| 51 | #include <machine/cpu.h> |
| 52 | #include <sys/lock.h> |
| 53 | #include <sys/caps.h> |
| 54 | #include <sys/spinlock.h> |
| 55 | #include <sys/ktr.h> |
| 56 | |
| 57 | #include <sys/thread2.h> |
| 58 | #include <sys/spinlock2.h> |
| 59 | #include <sys/mplock2.h> |
| 60 | |
| 61 | #include <sys/dsched.h> |
| 62 | |
| 63 | #include <vm/vm.h> |
| 64 | #include <vm/vm_param.h> |
| 65 | #include <vm/vm_kern.h> |
| 66 | #include <vm/vm_object.h> |
| 67 | #include <vm/vm_page.h> |
| 68 | #include <vm/vm_map.h> |
| 69 | #include <vm/vm_pager.h> |
| 70 | #include <vm/vm_extern.h> |
| 71 | |
| 72 | #include <machine/stdarg.h> |
| 73 | #include <machine/smp.h> |
| 74 | |
| 75 | #if !defined(KTR_CTXSW) |
| 76 | #define KTR_CTXSW KTR_ALL |
| 77 | #endif |
| 78 | KTR_INFO_MASTER(ctxsw); |
| 79 | KTR_INFO(KTR_CTXSW, ctxsw, sw, 0, "#cpu[%d].td = %p", |
| 80 | sizeof(int) + sizeof(struct thread *)); |
| 81 | KTR_INFO(KTR_CTXSW, ctxsw, pre, 1, "#cpu[%d].td = %p", |
| 82 | sizeof(int) + sizeof(struct thread *)); |
| 83 | KTR_INFO(KTR_CTXSW, ctxsw, newtd, 2, "#threads[%p].name = %s", |
| 84 | sizeof (struct thread *) + sizeof(char *)); |
| 85 | KTR_INFO(KTR_CTXSW, ctxsw, deadtd, 3, "#threads[%p].name = <dead>", sizeof (struct thread *)); |
| 86 | |
| 87 | static MALLOC_DEFINE(M_THREAD, "thread", "lwkt threads"); |
| 88 | |
| 89 | #ifdef INVARIANTS |
| 90 | static int panic_on_cscount = 0; |
| 91 | #endif |
| 92 | static __int64_t switch_count = 0; |
| 93 | static __int64_t preempt_hit = 0; |
| 94 | static __int64_t preempt_miss = 0; |
| 95 | static __int64_t preempt_weird = 0; |
| 96 | static __int64_t token_contention_count __debugvar = 0; |
| 97 | static int lwkt_use_spin_port; |
| 98 | static struct objcache *thread_cache; |
| 99 | |
| 100 | #ifdef SMP |
| 101 | static void lwkt_schedule_remote(void *arg, int arg2, struct intrframe *frame); |
| 102 | #endif |
| 103 | static void lwkt_fairq_accumulate(globaldata_t gd, thread_t td); |
| 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 | /* |
| 111 | * We can make all thread ports use the spin backend instead of the thread |
| 112 | * backend. This should only be set to debug the spin backend. |
| 113 | */ |
| 114 | TUNABLE_INT("lwkt.use_spin_port", &lwkt_use_spin_port); |
| 115 | |
| 116 | #ifdef INVARIANTS |
| 117 | SYSCTL_INT(_lwkt, OID_AUTO, panic_on_cscount, CTLFLAG_RW, &panic_on_cscount, 0, |
| 118 | "Panic if attempting to switch lwkt's while mastering cpusync"); |
| 119 | #endif |
| 120 | SYSCTL_QUAD(_lwkt, OID_AUTO, switch_count, CTLFLAG_RW, &switch_count, 0, |
| 121 | "Number of switched threads"); |
| 122 | SYSCTL_QUAD(_lwkt, OID_AUTO, preempt_hit, CTLFLAG_RW, &preempt_hit, 0, |
| 123 | "Successful preemption events"); |
| 124 | SYSCTL_QUAD(_lwkt, OID_AUTO, preempt_miss, CTLFLAG_RW, &preempt_miss, 0, |
| 125 | "Failed preemption events"); |
| 126 | SYSCTL_QUAD(_lwkt, OID_AUTO, preempt_weird, CTLFLAG_RW, &preempt_weird, 0, |
| 127 | "Number of preempted threads."); |
| 128 | #ifdef INVARIANTS |
| 129 | SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count, CTLFLAG_RW, |
| 130 | &token_contention_count, 0, "spinning due to token contention"); |
| 131 | #endif |
| 132 | static int fairq_enable = 1; |
| 133 | SYSCTL_INT(_lwkt, OID_AUTO, fairq_enable, CTLFLAG_RW, |
| 134 | &fairq_enable, 0, "Turn on fairq priority accumulators"); |
| 135 | static int lwkt_spin_loops = 10; |
| 136 | SYSCTL_INT(_lwkt, OID_AUTO, spin_loops, CTLFLAG_RW, |
| 137 | &lwkt_spin_loops, 0, ""); |
| 138 | static int lwkt_spin_delay = 1; |
| 139 | SYSCTL_INT(_lwkt, OID_AUTO, spin_delay, CTLFLAG_RW, |
| 140 | &lwkt_spin_delay, 0, "Scheduler spin delay in microseconds 0=auto"); |
| 141 | static int lwkt_spin_method = 1; |
| 142 | SYSCTL_INT(_lwkt, OID_AUTO, spin_method, CTLFLAG_RW, |
| 143 | &lwkt_spin_method, 0, "LWKT scheduler behavior when contended"); |
| 144 | static int lwkt_spin_fatal = 0; /* disabled */ |
| 145 | SYSCTL_INT(_lwkt, OID_AUTO, spin_fatal, CTLFLAG_RW, |
| 146 | &lwkt_spin_fatal, 0, "LWKT scheduler spin loops till fatal panic"); |
| 147 | static int preempt_enable = 1; |
| 148 | SYSCTL_INT(_lwkt, OID_AUTO, preempt_enable, CTLFLAG_RW, |
| 149 | &preempt_enable, 0, "Enable preemption"); |
| 150 | |
| 151 | static __cachealign int lwkt_cseq_rindex; |
| 152 | static __cachealign int lwkt_cseq_windex; |
| 153 | |
| 154 | /* |
| 155 | * These helper procedures handle the runq, they can only be called from |
| 156 | * within a critical section. |
| 157 | * |
| 158 | * WARNING! Prior to SMP being brought up it is possible to enqueue and |
| 159 | * dequeue threads belonging to other cpus, so be sure to use td->td_gd |
| 160 | * instead of 'mycpu' when referencing the globaldata structure. Once |
| 161 | * SMP live enqueuing and dequeueing only occurs on the current cpu. |
| 162 | */ |
| 163 | static __inline |
| 164 | void |
| 165 | _lwkt_dequeue(thread_t td) |
| 166 | { |
| 167 | if (td->td_flags & TDF_RUNQ) { |
| 168 | struct globaldata *gd = td->td_gd; |
| 169 | |
| 170 | td->td_flags &= ~TDF_RUNQ; |
| 171 | TAILQ_REMOVE(&gd->gd_tdrunq, td, td_threadq); |
| 172 | gd->gd_fairq_total_pri -= td->td_pri; |
| 173 | if (TAILQ_FIRST(&gd->gd_tdrunq) == NULL) |
| 174 | atomic_clear_int(&gd->gd_reqflags, RQF_RUNNING); |
| 175 | } |
| 176 | } |
| 177 | |
| 178 | /* |
| 179 | * Priority enqueue. |
| 180 | * |
| 181 | * NOTE: There are a limited number of lwkt threads runnable since user |
| 182 | * processes only schedule one at a time per cpu. |
| 183 | */ |
| 184 | static __inline |
| 185 | void |
| 186 | _lwkt_enqueue(thread_t td) |
| 187 | { |
| 188 | thread_t xtd; |
| 189 | |
| 190 | if ((td->td_flags & (TDF_RUNQ|TDF_MIGRATING|TDF_BLOCKQ)) == 0) { |
| 191 | struct globaldata *gd = td->td_gd; |
| 192 | |
| 193 | td->td_flags |= TDF_RUNQ; |
| 194 | xtd = TAILQ_FIRST(&gd->gd_tdrunq); |
| 195 | if (xtd == NULL) { |
| 196 | TAILQ_INSERT_TAIL(&gd->gd_tdrunq, td, td_threadq); |
| 197 | atomic_set_int(&gd->gd_reqflags, RQF_RUNNING); |
| 198 | } else { |
| 199 | while (xtd && xtd->td_pri > td->td_pri) |
| 200 | xtd = TAILQ_NEXT(xtd, td_threadq); |
| 201 | if (xtd) |
| 202 | TAILQ_INSERT_BEFORE(xtd, td, td_threadq); |
| 203 | else |
| 204 | TAILQ_INSERT_TAIL(&gd->gd_tdrunq, td, td_threadq); |
| 205 | } |
| 206 | gd->gd_fairq_total_pri += td->td_pri; |
| 207 | } |
| 208 | } |
| 209 | |
| 210 | static __boolean_t |
| 211 | _lwkt_thread_ctor(void *obj, void *privdata, int ocflags) |
| 212 | { |
| 213 | struct thread *td = (struct thread *)obj; |
| 214 | |
| 215 | td->td_kstack = NULL; |
| 216 | td->td_kstack_size = 0; |
| 217 | td->td_flags = TDF_ALLOCATED_THREAD; |
| 218 | return (1); |
| 219 | } |
| 220 | |
| 221 | static void |
| 222 | _lwkt_thread_dtor(void *obj, void *privdata) |
| 223 | { |
| 224 | struct thread *td = (struct thread *)obj; |
| 225 | |
| 226 | KASSERT(td->td_flags & TDF_ALLOCATED_THREAD, |
| 227 | ("_lwkt_thread_dtor: not allocated from objcache")); |
| 228 | KASSERT((td->td_flags & TDF_ALLOCATED_STACK) && td->td_kstack && |
| 229 | td->td_kstack_size > 0, |
| 230 | ("_lwkt_thread_dtor: corrupted stack")); |
| 231 | kmem_free(&kernel_map, (vm_offset_t)td->td_kstack, td->td_kstack_size); |
| 232 | } |
| 233 | |
| 234 | /* |
| 235 | * Initialize the lwkt s/system. |
| 236 | */ |
| 237 | void |
| 238 | lwkt_init(void) |
| 239 | { |
| 240 | /* An objcache has 2 magazines per CPU so divide cache size by 2. */ |
| 241 | thread_cache = objcache_create_mbacked(M_THREAD, sizeof(struct thread), |
| 242 | NULL, CACHE_NTHREADS/2, |
| 243 | _lwkt_thread_ctor, _lwkt_thread_dtor, NULL); |
| 244 | } |
| 245 | |
| 246 | /* |
| 247 | * Schedule a thread to run. As the current thread we can always safely |
| 248 | * schedule ourselves, and a shortcut procedure is provided for that |
| 249 | * function. |
| 250 | * |
| 251 | * (non-blocking, self contained on a per cpu basis) |
| 252 | */ |
| 253 | void |
| 254 | lwkt_schedule_self(thread_t td) |
| 255 | { |
| 256 | KKASSERT((td->td_flags & TDF_MIGRATING) == 0); |
| 257 | crit_enter_quick(td); |
| 258 | KASSERT(td != &td->td_gd->gd_idlethread, |
| 259 | ("lwkt_schedule_self(): scheduling gd_idlethread is illegal!")); |
| 260 | KKASSERT(td->td_lwp == NULL || (td->td_lwp->lwp_flag & LWP_ONRUNQ) == 0); |
| 261 | _lwkt_enqueue(td); |
| 262 | crit_exit_quick(td); |
| 263 | } |
| 264 | |
| 265 | /* |
| 266 | * Deschedule a thread. |
| 267 | * |
| 268 | * (non-blocking, self contained on a per cpu basis) |
| 269 | */ |
| 270 | void |
| 271 | lwkt_deschedule_self(thread_t td) |
| 272 | { |
| 273 | crit_enter_quick(td); |
| 274 | _lwkt_dequeue(td); |
| 275 | crit_exit_quick(td); |
| 276 | } |
| 277 | |
| 278 | /* |
| 279 | * LWKTs operate on a per-cpu basis |
| 280 | * |
| 281 | * WARNING! Called from early boot, 'mycpu' may not work yet. |
| 282 | */ |
| 283 | void |
| 284 | lwkt_gdinit(struct globaldata *gd) |
| 285 | { |
| 286 | TAILQ_INIT(&gd->gd_tdrunq); |
| 287 | TAILQ_INIT(&gd->gd_tdallq); |
| 288 | } |
| 289 | |
| 290 | /* |
| 291 | * Create a new thread. The thread must be associated with a process context |
| 292 | * or LWKT start address before it can be scheduled. If the target cpu is |
| 293 | * -1 the thread will be created on the current cpu. |
| 294 | * |
| 295 | * If you intend to create a thread without a process context this function |
| 296 | * does everything except load the startup and switcher function. |
| 297 | */ |
| 298 | thread_t |
| 299 | lwkt_alloc_thread(struct thread *td, int stksize, int cpu, int flags) |
| 300 | { |
| 301 | globaldata_t gd = mycpu; |
| 302 | void *stack; |
| 303 | |
| 304 | /* |
| 305 | * If static thread storage is not supplied allocate a thread. Reuse |
| 306 | * a cached free thread if possible. gd_freetd is used to keep an exiting |
| 307 | * thread intact through the exit. |
| 308 | */ |
| 309 | if (td == NULL) { |
| 310 | crit_enter_gd(gd); |
| 311 | if ((td = gd->gd_freetd) != NULL) { |
| 312 | KKASSERT((td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK| |
| 313 | TDF_RUNQ)) == 0); |
| 314 | gd->gd_freetd = NULL; |
| 315 | } else { |
| 316 | td = objcache_get(thread_cache, M_WAITOK); |
| 317 | KKASSERT((td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK| |
| 318 | TDF_RUNQ)) == 0); |
| 319 | } |
| 320 | crit_exit_gd(gd); |
| 321 | KASSERT((td->td_flags & |
| 322 | (TDF_ALLOCATED_THREAD|TDF_RUNNING)) == TDF_ALLOCATED_THREAD, |
| 323 | ("lwkt_alloc_thread: corrupted td flags 0x%X", td->td_flags)); |
| 324 | flags |= td->td_flags & (TDF_ALLOCATED_THREAD|TDF_ALLOCATED_STACK); |
| 325 | } |
| 326 | |
| 327 | /* |
| 328 | * Try to reuse cached stack. |
| 329 | */ |
| 330 | if ((stack = td->td_kstack) != NULL && td->td_kstack_size != stksize) { |
| 331 | if (flags & TDF_ALLOCATED_STACK) { |
| 332 | kmem_free(&kernel_map, (vm_offset_t)stack, td->td_kstack_size); |
| 333 | stack = NULL; |
| 334 | } |
| 335 | } |
| 336 | if (stack == NULL) { |
| 337 | stack = (void *)kmem_alloc_stack(&kernel_map, stksize); |
| 338 | flags |= TDF_ALLOCATED_STACK; |
| 339 | } |
| 340 | if (cpu < 0) |
| 341 | lwkt_init_thread(td, stack, stksize, flags, gd); |
| 342 | else |
| 343 | lwkt_init_thread(td, stack, stksize, flags, globaldata_find(cpu)); |
| 344 | return(td); |
| 345 | } |
| 346 | |
| 347 | /* |
| 348 | * Initialize a preexisting thread structure. This function is used by |
| 349 | * lwkt_alloc_thread() and also used to initialize the per-cpu idlethread. |
| 350 | * |
| 351 | * All threads start out in a critical section at a priority of |
| 352 | * TDPRI_KERN_DAEMON. Higher level code will modify the priority as |
| 353 | * appropriate. This function may send an IPI message when the |
| 354 | * requested cpu is not the current cpu and consequently gd_tdallq may |
| 355 | * not be initialized synchronously from the point of view of the originating |
| 356 | * cpu. |
| 357 | * |
| 358 | * NOTE! we have to be careful in regards to creating threads for other cpus |
| 359 | * if SMP has not yet been activated. |
| 360 | */ |
| 361 | #ifdef SMP |
| 362 | |
| 363 | static void |
| 364 | lwkt_init_thread_remote(void *arg) |
| 365 | { |
| 366 | thread_t td = arg; |
| 367 | |
| 368 | /* |
| 369 | * Protected by critical section held by IPI dispatch |
| 370 | */ |
| 371 | TAILQ_INSERT_TAIL(&td->td_gd->gd_tdallq, td, td_allq); |
| 372 | } |
| 373 | |
| 374 | #endif |
| 375 | |
| 376 | /* |
| 377 | * lwkt core thread structural initialization. |
| 378 | * |
| 379 | * NOTE: All threads are initialized as mpsafe threads. |
| 380 | */ |
| 381 | void |
| 382 | lwkt_init_thread(thread_t td, void *stack, int stksize, int flags, |
| 383 | struct globaldata *gd) |
| 384 | { |
| 385 | globaldata_t mygd = mycpu; |
| 386 | |
| 387 | bzero(td, sizeof(struct thread)); |
| 388 | td->td_kstack = stack; |
| 389 | td->td_kstack_size = stksize; |
| 390 | td->td_flags = flags; |
| 391 | td->td_gd = gd; |
| 392 | td->td_pri = TDPRI_KERN_DAEMON; |
| 393 | td->td_critcount = 1; |
| 394 | td->td_toks_stop = &td->td_toks_base; |
| 395 | if (lwkt_use_spin_port) |
| 396 | lwkt_initport_spin(&td->td_msgport); |
| 397 | else |
| 398 | lwkt_initport_thread(&td->td_msgport, td); |
| 399 | pmap_init_thread(td); |
| 400 | #ifdef SMP |
| 401 | /* |
| 402 | * Normally initializing a thread for a remote cpu requires sending an |
| 403 | * IPI. However, the idlethread is setup before the other cpus are |
| 404 | * activated so we have to treat it as a special case. XXX manipulation |
| 405 | * of gd_tdallq requires the BGL. |
| 406 | */ |
| 407 | if (gd == mygd || td == &gd->gd_idlethread) { |
| 408 | crit_enter_gd(mygd); |
| 409 | TAILQ_INSERT_TAIL(&gd->gd_tdallq, td, td_allq); |
| 410 | crit_exit_gd(mygd); |
| 411 | } else { |
| 412 | lwkt_send_ipiq(gd, lwkt_init_thread_remote, td); |
| 413 | } |
| 414 | #else |
| 415 | crit_enter_gd(mygd); |
| 416 | TAILQ_INSERT_TAIL(&gd->gd_tdallq, td, td_allq); |
| 417 | crit_exit_gd(mygd); |
| 418 | #endif |
| 419 | |
| 420 | dsched_new_thread(td); |
| 421 | } |
| 422 | |
| 423 | void |
| 424 | lwkt_set_comm(thread_t td, const char *ctl, ...) |
| 425 | { |
| 426 | __va_list va; |
| 427 | |
| 428 | __va_start(va, ctl); |
| 429 | kvsnprintf(td->td_comm, sizeof(td->td_comm), ctl, va); |
| 430 | __va_end(va); |
| 431 | KTR_LOG(ctxsw_newtd, td, &td->td_comm[0]); |
| 432 | } |
| 433 | |
| 434 | void |
| 435 | lwkt_hold(thread_t td) |
| 436 | { |
| 437 | atomic_add_int(&td->td_refs, 1); |
| 438 | } |
| 439 | |
| 440 | void |
| 441 | lwkt_rele(thread_t td) |
| 442 | { |
| 443 | KKASSERT(td->td_refs > 0); |
| 444 | atomic_add_int(&td->td_refs, -1); |
| 445 | } |
| 446 | |
| 447 | void |
| 448 | lwkt_wait_free(thread_t td) |
| 449 | { |
| 450 | while (td->td_refs) |
| 451 | tsleep(td, 0, "tdreap", hz); |
| 452 | } |
| 453 | |
| 454 | void |
| 455 | lwkt_free_thread(thread_t td) |
| 456 | { |
| 457 | KKASSERT(td->td_refs == 0); |
| 458 | KKASSERT((td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK|TDF_RUNQ)) == 0); |
| 459 | if (td->td_flags & TDF_ALLOCATED_THREAD) { |
| 460 | objcache_put(thread_cache, td); |
| 461 | } else if (td->td_flags & TDF_ALLOCATED_STACK) { |
| 462 | /* client-allocated struct with internally allocated stack */ |
| 463 | KASSERT(td->td_kstack && td->td_kstack_size > 0, |
| 464 | ("lwkt_free_thread: corrupted stack")); |
| 465 | kmem_free(&kernel_map, (vm_offset_t)td->td_kstack, td->td_kstack_size); |
| 466 | td->td_kstack = NULL; |
| 467 | td->td_kstack_size = 0; |
| 468 | } |
| 469 | KTR_LOG(ctxsw_deadtd, td); |
| 470 | } |
| 471 | |
| 472 | |
| 473 | /* |
| 474 | * Switch to the next runnable lwkt. If no LWKTs are runnable then |
| 475 | * switch to the idlethread. Switching must occur within a critical |
| 476 | * section to avoid races with the scheduling queue. |
| 477 | * |
| 478 | * We always have full control over our cpu's run queue. Other cpus |
| 479 | * that wish to manipulate our queue must use the cpu_*msg() calls to |
| 480 | * talk to our cpu, so a critical section is all that is needed and |
| 481 | * the result is very, very fast thread switching. |
| 482 | * |
| 483 | * The LWKT scheduler uses a fixed priority model and round-robins at |
| 484 | * each priority level. User process scheduling is a totally |
| 485 | * different beast and LWKT priorities should not be confused with |
| 486 | * user process priorities. |
| 487 | * |
| 488 | * PREEMPTION NOTE: Preemption occurs via lwkt_preempt(). lwkt_switch() |
| 489 | * is not called by the current thread in the preemption case, only when |
| 490 | * the preempting thread blocks (in order to return to the original thread). |
| 491 | * |
| 492 | * SPECIAL NOTE ON SWITCH ATOMICY: Certain operations such as thread |
| 493 | * migration and tsleep deschedule the current lwkt thread and call |
| 494 | * lwkt_switch(). In particular, the target cpu of the migration fully |
| 495 | * expects the thread to become non-runnable and can deadlock against |
| 496 | * cpusync operations if we run any IPIs prior to switching the thread out. |
| 497 | * |
| 498 | * WE MUST BE VERY CAREFUL NOT TO RUN SPLZ DIRECTLY OR INDIRECTLY IF |
| 499 | * THE CURRENT THREAD HAS BEEN DESCHEDULED! |
| 500 | */ |
| 501 | void |
| 502 | lwkt_switch(void) |
| 503 | { |
| 504 | globaldata_t gd = mycpu; |
| 505 | thread_t td = gd->gd_curthread; |
| 506 | thread_t ntd; |
| 507 | thread_t xtd; |
| 508 | int spinning = lwkt_spin_loops; /* loops before HLTing */ |
| 509 | int reqflags; |
| 510 | int cseq; |
| 511 | int oseq; |
| 512 | int fatal_count; |
| 513 | |
| 514 | /* |
| 515 | * Switching from within a 'fast' (non thread switched) interrupt or IPI |
| 516 | * is illegal. However, we may have to do it anyway if we hit a fatal |
| 517 | * kernel trap or we have paniced. |
| 518 | * |
| 519 | * If this case occurs save and restore the interrupt nesting level. |
| 520 | */ |
| 521 | if (gd->gd_intr_nesting_level) { |
| 522 | int savegdnest; |
| 523 | int savegdtrap; |
| 524 | |
| 525 | if (gd->gd_trap_nesting_level == 0 && panic_cpu_gd != mycpu) { |
| 526 | panic("lwkt_switch: Attempt to switch from a " |
| 527 | "a fast interrupt, ipi, or hard code section, " |
| 528 | "td %p\n", |
| 529 | td); |
| 530 | } else { |
| 531 | savegdnest = gd->gd_intr_nesting_level; |
| 532 | savegdtrap = gd->gd_trap_nesting_level; |
| 533 | gd->gd_intr_nesting_level = 0; |
| 534 | gd->gd_trap_nesting_level = 0; |
| 535 | if ((td->td_flags & TDF_PANICWARN) == 0) { |
| 536 | td->td_flags |= TDF_PANICWARN; |
| 537 | kprintf("Warning: thread switch from interrupt, IPI, " |
| 538 | "or hard code section.\n" |
| 539 | "thread %p (%s)\n", td, td->td_comm); |
| 540 | print_backtrace(-1); |
| 541 | } |
| 542 | lwkt_switch(); |
| 543 | gd->gd_intr_nesting_level = savegdnest; |
| 544 | gd->gd_trap_nesting_level = savegdtrap; |
| 545 | return; |
| 546 | } |
| 547 | } |
| 548 | |
| 549 | /* |
| 550 | * Passive release (used to transition from user to kernel mode |
| 551 | * when we block or switch rather then when we enter the kernel). |
| 552 | * This function is NOT called if we are switching into a preemption |
| 553 | * or returning from a preemption. Typically this causes us to lose |
| 554 | * our current process designation (if we have one) and become a true |
| 555 | * LWKT thread, and may also hand the current process designation to |
| 556 | * another process and schedule thread. |
| 557 | */ |
| 558 | if (td->td_release) |
| 559 | td->td_release(td); |
| 560 | |
| 561 | crit_enter_gd(gd); |
| 562 | if (TD_TOKS_HELD(td)) |
| 563 | lwkt_relalltokens(td); |
| 564 | |
| 565 | /* |
| 566 | * We had better not be holding any spin locks, but don't get into an |
| 567 | * endless panic loop. |
| 568 | */ |
| 569 | KASSERT(gd->gd_spinlocks_wr == 0 || panicstr != NULL, |
| 570 | ("lwkt_switch: still holding %d exclusive spinlocks!", |
| 571 | gd->gd_spinlocks_wr)); |
| 572 | |
| 573 | |
| 574 | #ifdef SMP |
| 575 | #ifdef INVARIANTS |
| 576 | if (td->td_cscount) { |
| 577 | kprintf("Diagnostic: attempt to switch while mastering cpusync: %p\n", |
| 578 | td); |
| 579 | if (panic_on_cscount) |
| 580 | panic("switching while mastering cpusync"); |
| 581 | } |
| 582 | #endif |
| 583 | #endif |
| 584 | |
| 585 | /* |
| 586 | * If we had preempted another thread on this cpu, resume the preempted |
| 587 | * thread. This occurs transparently, whether the preempted thread |
| 588 | * was scheduled or not (it may have been preempted after descheduling |
| 589 | * itself). |
| 590 | * |
| 591 | * We have to setup the MP lock for the original thread after backing |
| 592 | * out the adjustment that was made to curthread when the original |
| 593 | * was preempted. |
| 594 | */ |
| 595 | if ((ntd = td->td_preempted) != NULL) { |
| 596 | KKASSERT(ntd->td_flags & TDF_PREEMPT_LOCK); |
| 597 | ntd->td_flags |= TDF_PREEMPT_DONE; |
| 598 | |
| 599 | /* |
| 600 | * The interrupt may have woken a thread up, we need to properly |
| 601 | * set the reschedule flag if the originally interrupted thread is |
| 602 | * at a lower priority. |
| 603 | */ |
| 604 | if (TAILQ_FIRST(&gd->gd_tdrunq) && |
| 605 | TAILQ_FIRST(&gd->gd_tdrunq)->td_pri > ntd->td_pri) { |
| 606 | need_lwkt_resched(); |
| 607 | } |
| 608 | /* YYY release mp lock on switchback if original doesn't need it */ |
| 609 | goto havethread_preempted; |
| 610 | } |
| 611 | |
| 612 | /* |
| 613 | * Implement round-robin fairq with priority insertion. The priority |
| 614 | * insertion is handled by _lwkt_enqueue() |
| 615 | * |
| 616 | * If we cannot obtain ownership of the tokens we cannot immediately |
| 617 | * schedule the target thread. |
| 618 | * |
| 619 | * Reminder: Again, we cannot afford to run any IPIs in this path if |
| 620 | * the current thread has been descheduled. |
| 621 | */ |
| 622 | for (;;) { |
| 623 | /* |
| 624 | * Clear RQF_AST_LWKT_RESCHED (we handle the reschedule request) |
| 625 | * and set RQF_WAKEUP (prevent unnecessary IPIs from being |
| 626 | * received). |
| 627 | */ |
| 628 | for (;;) { |
| 629 | reqflags = gd->gd_reqflags; |
| 630 | if (atomic_cmpset_int(&gd->gd_reqflags, reqflags, |
| 631 | (reqflags & ~RQF_AST_LWKT_RESCHED) | |
| 632 | RQF_WAKEUP)) { |
| 633 | break; |
| 634 | } |
| 635 | } |
| 636 | |
| 637 | /* |
| 638 | * Hotpath - pull the head of the run queue and attempt to schedule |
| 639 | * it. Fairq exhaustion moves the task to the end of the list. If |
| 640 | * no threads are runnable we switch to the idle thread. |
| 641 | */ |
| 642 | for (;;) { |
| 643 | ntd = TAILQ_FIRST(&gd->gd_tdrunq); |
| 644 | |
| 645 | if (ntd == NULL) { |
| 646 | /* |
| 647 | * Runq is empty, switch to idle and clear RQF_WAKEUP |
| 648 | * to allow it to halt. |
| 649 | */ |
| 650 | ntd = &gd->gd_idlethread; |
| 651 | #ifdef SMP |
| 652 | if (gd->gd_trap_nesting_level == 0 && panicstr == NULL) |
| 653 | ASSERT_NO_TOKENS_HELD(ntd); |
| 654 | #endif |
| 655 | cpu_time.cp_msg[0] = 0; |
| 656 | cpu_time.cp_stallpc = 0; |
| 657 | atomic_clear_int(&gd->gd_reqflags, RQF_WAKEUP); |
| 658 | goto haveidle; |
| 659 | } |
| 660 | |
| 661 | if (ntd->td_fairq_accum >= 0) |
| 662 | break; |
| 663 | |
| 664 | /*splz_check(); cannot do this here, see above */ |
| 665 | lwkt_fairq_accumulate(gd, ntd); |
| 666 | TAILQ_REMOVE(&gd->gd_tdrunq, ntd, td_threadq); |
| 667 | TAILQ_INSERT_TAIL(&gd->gd_tdrunq, ntd, td_threadq); |
| 668 | } |
| 669 | |
| 670 | /* |
| 671 | * Hotpath - schedule ntd. Leaves RQF_WAKEUP set to prevent |
| 672 | * unwanted decontention IPIs. |
| 673 | * |
| 674 | * NOTE: For UP there is no mplock and lwkt_getalltokens() |
| 675 | * always succeeds. |
| 676 | */ |
| 677 | if (TD_TOKS_NOT_HELD(ntd) || lwkt_getalltokens(ntd)) |
| 678 | goto havethread; |
| 679 | |
| 680 | /* |
| 681 | * Coldpath (SMP only since tokens always succeed on UP) |
| 682 | * |
| 683 | * We had some contention on the thread we wanted to schedule. |
| 684 | * What we do now is try to find a thread that we can schedule |
| 685 | * in its stead until decontention reschedules on our cpu. |
| 686 | * |
| 687 | * The coldpath scan does NOT rearrange threads in the run list |
| 688 | * and it also ignores the accumulator. |
| 689 | * |
| 690 | * We do not immediately schedule a user priority thread, instead |
| 691 | * we record it in xtd and continue looking for kernel threads. |
| 692 | * A cpu can only have one user priority thread (normally) so just |
| 693 | * record the first one. |
| 694 | * |
| 695 | * NOTE: This scan will also include threads whos fairq's were |
| 696 | * accumulated in the first loop. |
| 697 | */ |
| 698 | ++token_contention_count; |
| 699 | xtd = NULL; |
| 700 | while ((ntd = TAILQ_NEXT(ntd, td_threadq)) != NULL) { |
| 701 | /* |
| 702 | * Try to switch to this thread. If the thread is running at |
| 703 | * user priority we clear WAKEUP to allow decontention IPIs |
| 704 | * (since this thread is simply running until the one we wanted |
| 705 | * decontends), and we make sure that LWKT_RESCHED is not set. |
| 706 | * |
| 707 | * Otherwise for kernel threads we leave WAKEUP set to avoid |
| 708 | * unnecessary decontention IPIs. |
| 709 | */ |
| 710 | if (ntd->td_pri < TDPRI_KERN_LPSCHED) { |
| 711 | if (xtd == NULL) |
| 712 | xtd = ntd; |
| 713 | continue; |
| 714 | } |
| 715 | |
| 716 | /* |
| 717 | * Do not let the fairq get too negative. Even though we are |
| 718 | * ignoring it atm once the scheduler decontends a very negative |
| 719 | * thread will get moved to the end of the queue. |
| 720 | */ |
| 721 | if (TD_TOKS_NOT_HELD(ntd) || lwkt_getalltokens(ntd)) { |
| 722 | if (ntd->td_fairq_accum < -TDFAIRQ_MAX(gd)) |
| 723 | ntd->td_fairq_accum = -TDFAIRQ_MAX(gd); |
| 724 | goto havethread; |
| 725 | } |
| 726 | |
| 727 | /* |
| 728 | * Well fubar, this thread is contended as well, loop |
| 729 | */ |
| 730 | /* */ |
| 731 | } |
| 732 | |
| 733 | /* |
| 734 | * We exhausted the run list but we may have recorded a user |
| 735 | * thread to try. We have three choices based on |
| 736 | * lwkt.decontention_method. |
| 737 | * |
| 738 | * (0) Atomically clear RQF_WAKEUP in order to receive decontention |
| 739 | * IPIs (to interrupt the user process) and test |
| 740 | * RQF_AST_LWKT_RESCHED at the same time. |
| 741 | * |
| 742 | * This results in significant decontention IPI traffic but may |
| 743 | * be more responsive. |
| 744 | * |
| 745 | * (1) Leave RQF_WAKEUP set so we do not receive a decontention IPI. |
| 746 | * An automatic LWKT reschedule will occur on the next hardclock |
| 747 | * (typically 100hz). |
| 748 | * |
| 749 | * This results in no decontention IPI traffic but may be less |
| 750 | * responsive. This is the default. |
| 751 | * |
| 752 | * (2) Refuse to schedule the user process at this time. |
| 753 | * |
| 754 | * This is highly experimental and should not be used under |
| 755 | * normal circumstances. This can cause a user process to |
| 756 | * get starved out in situations where kernel threads are |
| 757 | * fighting each other for tokens. |
| 758 | */ |
| 759 | if (xtd) { |
| 760 | ntd = xtd; |
| 761 | |
| 762 | switch(lwkt_spin_method) { |
| 763 | case 0: |
| 764 | for (;;) { |
| 765 | reqflags = gd->gd_reqflags; |
| 766 | if (atomic_cmpset_int(&gd->gd_reqflags, |
| 767 | reqflags, |
| 768 | reqflags & ~RQF_WAKEUP)) { |
| 769 | break; |
| 770 | } |
| 771 | } |
| 772 | break; |
| 773 | case 1: |
| 774 | reqflags = gd->gd_reqflags; |
| 775 | break; |
| 776 | default: |
| 777 | goto skip; |
| 778 | break; |
| 779 | } |
| 780 | if ((reqflags & RQF_AST_LWKT_RESCHED) == 0 && |
| 781 | (TD_TOKS_NOT_HELD(ntd) || lwkt_getalltokens(ntd)) |
| 782 | ) { |
| 783 | if (ntd->td_fairq_accum < -TDFAIRQ_MAX(gd)) |
| 784 | ntd->td_fairq_accum = -TDFAIRQ_MAX(gd); |
| 785 | goto havethread; |
| 786 | } |
| 787 | |
| 788 | skip: |
| 789 | /* |
| 790 | * Make sure RQF_WAKEUP is set if we failed to schedule the |
| 791 | * user thread to prevent the idle thread from halting. |
| 792 | */ |
| 793 | atomic_set_int(&gd->gd_reqflags, RQF_WAKEUP); |
| 794 | } |
| 795 | |
| 796 | /* |
| 797 | * We exhausted the run list, meaning that all runnable threads |
| 798 | * are contended. |
| 799 | */ |
| 800 | cpu_pause(); |
| 801 | ntd = &gd->gd_idlethread; |
| 802 | #ifdef SMP |
| 803 | if (gd->gd_trap_nesting_level == 0 && panicstr == NULL) |
| 804 | ASSERT_NO_TOKENS_HELD(ntd); |
| 805 | /* contention case, do not clear contention mask */ |
| 806 | #endif |
| 807 | |
| 808 | /* |
| 809 | * Ok, we might want to spin a few times as some tokens are held for |
| 810 | * very short periods of time and IPI overhead is 1uS or worse |
| 811 | * (meaning it is usually better to spin). Regardless we have to |
| 812 | * call splz_check() to be sure to service any interrupts blocked |
| 813 | * by our critical section, otherwise we could livelock e.g. IPIs. |
| 814 | * |
| 815 | * The IPI mechanic is really a last resort. In nearly all other |
| 816 | * cases RQF_WAKEUP is left set to prevent decontention IPIs. |
| 817 | * |
| 818 | * When we decide not to spin we clear RQF_WAKEUP and switch to |
| 819 | * the idle thread. Clearing RQF_WEAKEUP allows the idle thread |
| 820 | * to halt and decontended tokens will issue an IPI to us. The |
| 821 | * idle thread will check for pending reschedules already set |
| 822 | * (RQF_AST_LWKT_RESCHED) before actually halting so we don't have |
| 823 | * to here. |
| 824 | * |
| 825 | * Also, if TDF_RUNQ is not set the current thread is trying to |
| 826 | * deschedule, possibly in an atomic fashion. We cannot afford to |
| 827 | * stay here. |
| 828 | */ |
| 829 | if (spinning <= 0 || (td->td_flags & TDF_RUNQ) == 0) { |
| 830 | atomic_clear_int(&gd->gd_reqflags, RQF_WAKEUP); |
| 831 | goto haveidle; |
| 832 | } |
| 833 | --spinning; |
| 834 | |
| 835 | /* |
| 836 | * When spinning a delay is required both to avoid livelocks from |
| 837 | * token order reversals (a thread may be trying to acquire multiple |
| 838 | * tokens), and also to reduce cpu cache management traffic. |
| 839 | * |
| 840 | * In order to scale to a large number of CPUs we use a time slot |
| 841 | * resequencer to force contending cpus into non-contending |
| 842 | * time-slots. The scheduler may still contend with the lock holder |
| 843 | * but will not (generally) contend with all the other cpus trying |
| 844 | * trying to get the same token. |
| 845 | * |
| 846 | * The resequencer uses a FIFO counter mechanic. The owner of the |
| 847 | * rindex at the head of the FIFO is allowed to pull itself off |
| 848 | * the FIFO and fetchadd is used to enter into the FIFO. This bit |
| 849 | * of code is VERY cache friendly and forces all spinning schedulers |
| 850 | * into their own time slots. |
| 851 | * |
| 852 | * This code has been tested to 48-cpus and caps the cache |
| 853 | * contention load at ~1uS intervals regardless of the number of |
| 854 | * cpus. Scaling beyond 64 cpus might require additional smarts |
| 855 | * (such as separate FIFOs for specific token cases). |
| 856 | * |
| 857 | * WARNING! We can't call splz_check() or anything else here as |
| 858 | * it could cause a deadlock. |
| 859 | */ |
| 860 | #if defined(INVARIANTS) && defined(__amd64__) |
| 861 | if ((read_rflags() & PSL_I) == 0) { |
| 862 | cpu_enable_intr(); |
| 863 | panic("lwkt_switch() called with interrupts disabled"); |
| 864 | } |
| 865 | #endif |
| 866 | cseq = atomic_fetchadd_int(&lwkt_cseq_windex, 1); |
| 867 | fatal_count = lwkt_spin_fatal; |
| 868 | while ((oseq = lwkt_cseq_rindex) != cseq) { |
| 869 | cpu_ccfence(); |
| 870 | #if !defined(_KERNEL_VIRTUAL) |
| 871 | if (cpu_mi_feature & CPU_MI_MONITOR) { |
| 872 | cpu_mmw_pause_int(&lwkt_cseq_rindex, oseq); |
| 873 | } else |
| 874 | #endif |
| 875 | { |
| 876 | DELAY(1); |
| 877 | cpu_lfence(); |
| 878 | } |
| 879 | if (fatal_count && --fatal_count == 0) |
| 880 | panic("lwkt_switch: fatal spin wait"); |
| 881 | } |
| 882 | cseq = lwkt_spin_delay; /* don't trust the system operator */ |
| 883 | cpu_ccfence(); |
| 884 | if (cseq < 1) |
| 885 | cseq = 1; |
| 886 | if (cseq > 1000) |
| 887 | cseq = 1000; |
| 888 | DELAY(cseq); |
| 889 | atomic_add_int(&lwkt_cseq_rindex, 1); |
| 890 | splz_check(); /* ok, we already checked that td is still scheduled */ |
| 891 | /* highest level for(;;) loop */ |
| 892 | } |
| 893 | |
| 894 | havethread: |
| 895 | /* |
| 896 | * We must always decrement td_fairq_accum on non-idle threads just |
| 897 | * in case a thread never gets a tick due to being in a continuous |
| 898 | * critical section. The page-zeroing code does this, for example. |
| 899 | * |
| 900 | * If the thread we came up with is a higher or equal priority verses |
| 901 | * the thread at the head of the queue we move our thread to the |
| 902 | * front. This way we can always check the front of the queue. |
| 903 | * |
| 904 | * Clear gd_idle_repeat when doing a normal switch to a non-idle |
| 905 | * thread. |
| 906 | */ |
| 907 | ++gd->gd_cnt.v_swtch; |
| 908 | --ntd->td_fairq_accum; |
| 909 | ntd->td_wmesg = NULL; |
| 910 | xtd = TAILQ_FIRST(&gd->gd_tdrunq); |
| 911 | if (ntd != xtd && ntd->td_pri >= xtd->td_pri) { |
| 912 | TAILQ_REMOVE(&gd->gd_tdrunq, ntd, td_threadq); |
| 913 | TAILQ_INSERT_HEAD(&gd->gd_tdrunq, ntd, td_threadq); |
| 914 | } |
| 915 | gd->gd_idle_repeat = 0; |
| 916 | |
| 917 | havethread_preempted: |
| 918 | /* |
| 919 | * If the new target does not need the MP lock and we are holding it, |
| 920 | * release the MP lock. If the new target requires the MP lock we have |
| 921 | * already acquired it for the target. |
| 922 | */ |
| 923 | ; |
| 924 | haveidle: |
| 925 | KASSERT(ntd->td_critcount, |
| 926 | ("priority problem in lwkt_switch %d %d", |
| 927 | td->td_critcount, ntd->td_critcount)); |
| 928 | |
| 929 | if (td != ntd) { |
| 930 | ++switch_count; |
| 931 | KTR_LOG(ctxsw_sw, gd->gd_cpuid, ntd); |
| 932 | td->td_switch(ntd); |
| 933 | } |
| 934 | /* NOTE: current cpu may have changed after switch */ |
| 935 | crit_exit_quick(td); |
| 936 | } |
| 937 | |
| 938 | /* |
| 939 | * Request that the target thread preempt the current thread. Preemption |
| 940 | * only works under a specific set of conditions: |
| 941 | * |
| 942 | * - We are not preempting ourselves |
| 943 | * - The target thread is owned by the current cpu |
| 944 | * - We are not currently being preempted |
| 945 | * - The target is not currently being preempted |
| 946 | * - We are not holding any spin locks |
| 947 | * - The target thread is not holding any tokens |
| 948 | * - We are able to satisfy the target's MP lock requirements (if any). |
| 949 | * |
| 950 | * THE CALLER OF LWKT_PREEMPT() MUST BE IN A CRITICAL SECTION. Typically |
| 951 | * this is called via lwkt_schedule() through the td_preemptable callback. |
| 952 | * critcount is the managed critical priority that we should ignore in order |
| 953 | * to determine whether preemption is possible (aka usually just the crit |
| 954 | * priority of lwkt_schedule() itself). |
| 955 | * |
| 956 | * XXX at the moment we run the target thread in a critical section during |
| 957 | * the preemption in order to prevent the target from taking interrupts |
| 958 | * that *WE* can't. Preemption is strictly limited to interrupt threads |
| 959 | * and interrupt-like threads, outside of a critical section, and the |
| 960 | * preempted source thread will be resumed the instant the target blocks |
| 961 | * whether or not the source is scheduled (i.e. preemption is supposed to |
| 962 | * be as transparent as possible). |
| 963 | */ |
| 964 | void |
| 965 | lwkt_preempt(thread_t ntd, int critcount) |
| 966 | { |
| 967 | struct globaldata *gd = mycpu; |
| 968 | thread_t td; |
| 969 | int save_gd_intr_nesting_level; |
| 970 | |
| 971 | /* |
| 972 | * The caller has put us in a critical section. We can only preempt |
| 973 | * if the caller of the caller was not in a critical section (basically |
| 974 | * a local interrupt), as determined by the 'critcount' parameter. We |
| 975 | * also can't preempt if the caller is holding any spinlocks (even if |
| 976 | * he isn't in a critical section). This also handles the tokens test. |
| 977 | * |
| 978 | * YYY The target thread must be in a critical section (else it must |
| 979 | * inherit our critical section? I dunno yet). |
| 980 | * |
| 981 | * Set need_lwkt_resched() unconditionally for now YYY. |
| 982 | */ |
| 983 | KASSERT(ntd->td_critcount, ("BADCRIT0 %d", ntd->td_pri)); |
| 984 | |
| 985 | if (preempt_enable == 0) { |
| 986 | ++preempt_miss; |
| 987 | return; |
| 988 | } |
| 989 | |
| 990 | td = gd->gd_curthread; |
| 991 | if (ntd->td_pri <= td->td_pri) { |
| 992 | ++preempt_miss; |
| 993 | return; |
| 994 | } |
| 995 | if (td->td_critcount > critcount) { |
| 996 | ++preempt_miss; |
| 997 | need_lwkt_resched(); |
| 998 | return; |
| 999 | } |
| 1000 | #ifdef SMP |
| 1001 | if (ntd->td_gd != gd) { |
| 1002 | ++preempt_miss; |
| 1003 | need_lwkt_resched(); |
| 1004 | return; |
| 1005 | } |
| 1006 | #endif |
| 1007 | /* |
| 1008 | * We don't have to check spinlocks here as they will also bump |
| 1009 | * td_critcount. |
| 1010 | * |
| 1011 | * Do not try to preempt if the target thread is holding any tokens. |
| 1012 | * We could try to acquire the tokens but this case is so rare there |
| 1013 | * is no need to support it. |
| 1014 | */ |
| 1015 | KKASSERT(gd->gd_spinlocks_wr == 0); |
| 1016 | |
| 1017 | if (TD_TOKS_HELD(ntd)) { |
| 1018 | ++preempt_miss; |
| 1019 | need_lwkt_resched(); |
| 1020 | return; |
| 1021 | } |
| 1022 | if (td == ntd || ((td->td_flags | ntd->td_flags) & TDF_PREEMPT_LOCK)) { |
| 1023 | ++preempt_weird; |
| 1024 | need_lwkt_resched(); |
| 1025 | return; |
| 1026 | } |
| 1027 | if (ntd->td_preempted) { |
| 1028 | ++preempt_hit; |
| 1029 | need_lwkt_resched(); |
| 1030 | return; |
| 1031 | } |
| 1032 | |
| 1033 | /* |
| 1034 | * Since we are able to preempt the current thread, there is no need to |
| 1035 | * call need_lwkt_resched(). |
| 1036 | * |
| 1037 | * We must temporarily clear gd_intr_nesting_level around the switch |
| 1038 | * since switchouts from the target thread are allowed (they will just |
| 1039 | * return to our thread), and since the target thread has its own stack. |
| 1040 | */ |
| 1041 | ++preempt_hit; |
| 1042 | ntd->td_preempted = td; |
| 1043 | td->td_flags |= TDF_PREEMPT_LOCK; |
| 1044 | KTR_LOG(ctxsw_pre, gd->gd_cpuid, ntd); |
| 1045 | save_gd_intr_nesting_level = gd->gd_intr_nesting_level; |
| 1046 | gd->gd_intr_nesting_level = 0; |
| 1047 | td->td_switch(ntd); |
| 1048 | gd->gd_intr_nesting_level = save_gd_intr_nesting_level; |
| 1049 | |
| 1050 | KKASSERT(ntd->td_preempted && (td->td_flags & TDF_PREEMPT_DONE)); |
| 1051 | ntd->td_preempted = NULL; |
| 1052 | td->td_flags &= ~(TDF_PREEMPT_LOCK|TDF_PREEMPT_DONE); |
| 1053 | } |
| 1054 | |
| 1055 | /* |
| 1056 | * Conditionally call splz() if gd_reqflags indicates work is pending. |
| 1057 | * This will work inside a critical section but not inside a hard code |
| 1058 | * section. |
| 1059 | * |
| 1060 | * (self contained on a per cpu basis) |
| 1061 | */ |
| 1062 | void |
| 1063 | splz_check(void) |
| 1064 | { |
| 1065 | globaldata_t gd = mycpu; |
| 1066 | thread_t td = gd->gd_curthread; |
| 1067 | |
| 1068 | if ((gd->gd_reqflags & RQF_IDLECHECK_MASK) && |
| 1069 | gd->gd_intr_nesting_level == 0 && |
| 1070 | td->td_nest_count < 2) |
| 1071 | { |
| 1072 | splz(); |
| 1073 | } |
| 1074 | } |
| 1075 | |
| 1076 | /* |
| 1077 | * This version is integrated into crit_exit, reqflags has already |
| 1078 | * been tested but td_critcount has not. |
| 1079 | * |
| 1080 | * We only want to execute the splz() on the 1->0 transition of |
| 1081 | * critcount and not in a hard code section or if too deeply nested. |
| 1082 | */ |
| 1083 | void |
| 1084 | lwkt_maybe_splz(thread_t td) |
| 1085 | { |
| 1086 | globaldata_t gd = td->td_gd; |
| 1087 | |
| 1088 | if (td->td_critcount == 0 && |
| 1089 | gd->gd_intr_nesting_level == 0 && |
| 1090 | td->td_nest_count < 2) |
| 1091 | { |
| 1092 | splz(); |
| 1093 | } |
| 1094 | } |
| 1095 | |
| 1096 | /* |
| 1097 | * This function is used to negotiate a passive release of the current |
| 1098 | * process/lwp designation with the user scheduler, allowing the user |
| 1099 | * scheduler to schedule another user thread. The related kernel thread |
| 1100 | * (curthread) continues running in the released state. |
| 1101 | */ |
| 1102 | void |
| 1103 | lwkt_passive_release(struct thread *td) |
| 1104 | { |
| 1105 | struct lwp *lp = td->td_lwp; |
| 1106 | |
| 1107 | td->td_release = NULL; |
| 1108 | lwkt_setpri_self(TDPRI_KERN_USER); |
| 1109 | lp->lwp_proc->p_usched->release_curproc(lp); |
| 1110 | } |
| 1111 | |
| 1112 | |
| 1113 | /* |
| 1114 | * This implements a normal yield. This routine is virtually a nop if |
| 1115 | * there is nothing to yield to but it will always run any pending interrupts |
| 1116 | * if called from a critical section. |
| 1117 | * |
| 1118 | * This yield is designed for kernel threads without a user context. |
| 1119 | * |
| 1120 | * (self contained on a per cpu basis) |
| 1121 | */ |
| 1122 | void |
| 1123 | lwkt_yield(void) |
| 1124 | { |
| 1125 | globaldata_t gd = mycpu; |
| 1126 | thread_t td = gd->gd_curthread; |
| 1127 | thread_t xtd; |
| 1128 | |
| 1129 | if ((gd->gd_reqflags & RQF_IDLECHECK_MASK) && td->td_nest_count < 2) |
| 1130 | splz(); |
| 1131 | if (td->td_fairq_accum < 0) { |
| 1132 | lwkt_schedule_self(curthread); |
| 1133 | lwkt_switch(); |
| 1134 | } else { |
| 1135 | xtd = TAILQ_FIRST(&gd->gd_tdrunq); |
| 1136 | if (xtd && xtd->td_pri > td->td_pri) { |
| 1137 | lwkt_schedule_self(curthread); |
| 1138 | lwkt_switch(); |
| 1139 | } |
| 1140 | } |
| 1141 | } |
| 1142 | |
| 1143 | /* |
| 1144 | * This yield is designed for kernel threads with a user context. |
| 1145 | * |
| 1146 | * The kernel acting on behalf of the user is potentially cpu-bound, |
| 1147 | * this function will efficiently allow other threads to run and also |
| 1148 | * switch to other processes by releasing. |
| 1149 | * |
| 1150 | * The lwkt_user_yield() function is designed to have very low overhead |
| 1151 | * if no yield is determined to be needed. |
| 1152 | */ |
| 1153 | void |
| 1154 | lwkt_user_yield(void) |
| 1155 | { |
| 1156 | globaldata_t gd = mycpu; |
| 1157 | thread_t td = gd->gd_curthread; |
| 1158 | |
| 1159 | /* |
| 1160 | * Always run any pending interrupts in case we are in a critical |
| 1161 | * section. |
| 1162 | */ |
| 1163 | if ((gd->gd_reqflags & RQF_IDLECHECK_MASK) && td->td_nest_count < 2) |
| 1164 | splz(); |
| 1165 | |
| 1166 | /* |
| 1167 | * Switch (which forces a release) if another kernel thread needs |
| 1168 | * the cpu, if userland wants us to resched, or if our kernel |
| 1169 | * quantum has run out. |
| 1170 | */ |
| 1171 | if (lwkt_resched_wanted() || |
| 1172 | user_resched_wanted() || |
| 1173 | td->td_fairq_accum < 0) |
| 1174 | { |
| 1175 | lwkt_switch(); |
| 1176 | } |
| 1177 | |
| 1178 | #if 0 |
| 1179 | /* |
| 1180 | * Reacquire the current process if we are released. |
| 1181 | * |
| 1182 | * XXX not implemented atm. The kernel may be holding locks and such, |
| 1183 | * so we want the thread to continue to receive cpu. |
| 1184 | */ |
| 1185 | if (td->td_release == NULL && lp) { |
| 1186 | lp->lwp_proc->p_usched->acquire_curproc(lp); |
| 1187 | td->td_release = lwkt_passive_release; |
| 1188 | lwkt_setpri_self(TDPRI_USER_NORM); |
| 1189 | } |
| 1190 | #endif |
| 1191 | } |
| 1192 | |
| 1193 | /* |
| 1194 | * Generic schedule. Possibly schedule threads belonging to other cpus and |
| 1195 | * deal with threads that might be blocked on a wait queue. |
| 1196 | * |
| 1197 | * We have a little helper inline function which does additional work after |
| 1198 | * the thread has been enqueued, including dealing with preemption and |
| 1199 | * setting need_lwkt_resched() (which prevents the kernel from returning |
| 1200 | * to userland until it has processed higher priority threads). |
| 1201 | * |
| 1202 | * It is possible for this routine to be called after a failed _enqueue |
| 1203 | * (due to the target thread migrating, sleeping, or otherwise blocked). |
| 1204 | * We have to check that the thread is actually on the run queue! |
| 1205 | * |
| 1206 | * reschedok is an optimized constant propagated from lwkt_schedule() or |
| 1207 | * lwkt_schedule_noresched(). By default it is non-zero, causing a |
| 1208 | * reschedule to be requested if the target thread has a higher priority. |
| 1209 | * The port messaging code will set MSG_NORESCHED and cause reschedok to |
| 1210 | * be 0, prevented undesired reschedules. |
| 1211 | */ |
| 1212 | static __inline |
| 1213 | void |
| 1214 | _lwkt_schedule_post(globaldata_t gd, thread_t ntd, int ccount, int reschedok) |
| 1215 | { |
| 1216 | thread_t otd; |
| 1217 | |
| 1218 | if (ntd->td_flags & TDF_RUNQ) { |
| 1219 | if (ntd->td_preemptable && reschedok) { |
| 1220 | ntd->td_preemptable(ntd, ccount); /* YYY +token */ |
| 1221 | } else if (reschedok) { |
| 1222 | otd = curthread; |
| 1223 | if (ntd->td_pri > otd->td_pri) |
| 1224 | need_lwkt_resched(); |
| 1225 | } |
| 1226 | |
| 1227 | /* |
| 1228 | * Give the thread a little fair share scheduler bump if it |
| 1229 | * has been asleep for a while. This is primarily to avoid |
| 1230 | * a degenerate case for interrupt threads where accumulator |
| 1231 | * crosses into negative territory unnecessarily. |
| 1232 | */ |
| 1233 | if (ntd->td_fairq_lticks != ticks) { |
| 1234 | ntd->td_fairq_lticks = ticks; |
| 1235 | ntd->td_fairq_accum += gd->gd_fairq_total_pri; |
| 1236 | if (ntd->td_fairq_accum > TDFAIRQ_MAX(gd)) |
| 1237 | ntd->td_fairq_accum = TDFAIRQ_MAX(gd); |
| 1238 | } |
| 1239 | } |
| 1240 | } |
| 1241 | |
| 1242 | static __inline |
| 1243 | void |
| 1244 | _lwkt_schedule(thread_t td, int reschedok) |
| 1245 | { |
| 1246 | globaldata_t mygd = mycpu; |
| 1247 | |
| 1248 | KASSERT(td != &td->td_gd->gd_idlethread, |
| 1249 | ("lwkt_schedule(): scheduling gd_idlethread is illegal!")); |
| 1250 | KKASSERT((td->td_flags & TDF_MIGRATING) == 0); |
| 1251 | crit_enter_gd(mygd); |
| 1252 | KKASSERT(td->td_lwp == NULL || (td->td_lwp->lwp_flag & LWP_ONRUNQ) == 0); |
| 1253 | if (td == mygd->gd_curthread) { |
| 1254 | _lwkt_enqueue(td); |
| 1255 | } else { |
| 1256 | /* |
| 1257 | * If we own the thread, there is no race (since we are in a |
| 1258 | * critical section). If we do not own the thread there might |
| 1259 | * be a race but the target cpu will deal with it. |
| 1260 | */ |
| 1261 | #ifdef SMP |
| 1262 | if (td->td_gd == mygd) { |
| 1263 | _lwkt_enqueue(td); |
| 1264 | _lwkt_schedule_post(mygd, td, 1, reschedok); |
| 1265 | } else { |
| 1266 | lwkt_send_ipiq3(td->td_gd, lwkt_schedule_remote, td, 0); |
| 1267 | } |
| 1268 | #else |
| 1269 | _lwkt_enqueue(td); |
| 1270 | _lwkt_schedule_post(mygd, td, 1, reschedok); |
| 1271 | #endif |
| 1272 | } |
| 1273 | crit_exit_gd(mygd); |
| 1274 | } |
| 1275 | |
| 1276 | void |
| 1277 | lwkt_schedule(thread_t td) |
| 1278 | { |
| 1279 | _lwkt_schedule(td, 1); |
| 1280 | } |
| 1281 | |
| 1282 | void |
| 1283 | lwkt_schedule_noresched(thread_t td) |
| 1284 | { |
| 1285 | _lwkt_schedule(td, 0); |
| 1286 | } |
| 1287 | |
| 1288 | #ifdef SMP |
| 1289 | |
| 1290 | /* |
| 1291 | * When scheduled remotely if frame != NULL the IPIQ is being |
| 1292 | * run via doreti or an interrupt then preemption can be allowed. |
| 1293 | * |
| 1294 | * To allow preemption we have to drop the critical section so only |
| 1295 | * one is present in _lwkt_schedule_post. |
| 1296 | */ |
| 1297 | static void |
| 1298 | lwkt_schedule_remote(void *arg, int arg2, struct intrframe *frame) |
| 1299 | { |
| 1300 | thread_t td = curthread; |
| 1301 | thread_t ntd = arg; |
| 1302 | |
| 1303 | if (frame && ntd->td_preemptable) { |
| 1304 | crit_exit_noyield(td); |
| 1305 | _lwkt_schedule(ntd, 1); |
| 1306 | crit_enter_quick(td); |
| 1307 | } else { |
| 1308 | _lwkt_schedule(ntd, 1); |
| 1309 | } |
| 1310 | } |
| 1311 | |
| 1312 | /* |
| 1313 | * Thread migration using a 'Pull' method. The thread may or may not be |
| 1314 | * the current thread. It MUST be descheduled and in a stable state. |
| 1315 | * lwkt_giveaway() must be called on the cpu owning the thread. |
| 1316 | * |
| 1317 | * At any point after lwkt_giveaway() is called, the target cpu may |
| 1318 | * 'pull' the thread by calling lwkt_acquire(). |
| 1319 | * |
| 1320 | * We have to make sure the thread is not sitting on a per-cpu tsleep |
| 1321 | * queue or it will blow up when it moves to another cpu. |
| 1322 | * |
| 1323 | * MPSAFE - must be called under very specific conditions. |
| 1324 | */ |
| 1325 | void |
| 1326 | lwkt_giveaway(thread_t td) |
| 1327 | { |
| 1328 | globaldata_t gd = mycpu; |
| 1329 | |
| 1330 | crit_enter_gd(gd); |
| 1331 | if (td->td_flags & TDF_TSLEEPQ) |
| 1332 | tsleep_remove(td); |
| 1333 | KKASSERT(td->td_gd == gd); |
| 1334 | TAILQ_REMOVE(&gd->gd_tdallq, td, td_allq); |
| 1335 | td->td_flags |= TDF_MIGRATING; |
| 1336 | crit_exit_gd(gd); |
| 1337 | } |
| 1338 | |
| 1339 | void |
| 1340 | lwkt_acquire(thread_t td) |
| 1341 | { |
| 1342 | globaldata_t gd; |
| 1343 | globaldata_t mygd; |
| 1344 | |
| 1345 | KKASSERT(td->td_flags & TDF_MIGRATING); |
| 1346 | gd = td->td_gd; |
| 1347 | mygd = mycpu; |
| 1348 | if (gd != mycpu) { |
| 1349 | cpu_lfence(); |
| 1350 | KKASSERT((td->td_flags & TDF_RUNQ) == 0); |
| 1351 | crit_enter_gd(mygd); |
| 1352 | DEBUG_PUSH_INFO("lwkt_acquire"); |
| 1353 | while (td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK)) { |
| 1354 | #ifdef SMP |
| 1355 | lwkt_process_ipiq(); |
| 1356 | #endif |
| 1357 | cpu_lfence(); |
| 1358 | } |
| 1359 | DEBUG_POP_INFO(); |
| 1360 | cpu_mfence(); |
| 1361 | td->td_gd = mygd; |
| 1362 | TAILQ_INSERT_TAIL(&mygd->gd_tdallq, td, td_allq); |
| 1363 | td->td_flags &= ~TDF_MIGRATING; |
| 1364 | crit_exit_gd(mygd); |
| 1365 | } else { |
| 1366 | crit_enter_gd(mygd); |
| 1367 | TAILQ_INSERT_TAIL(&mygd->gd_tdallq, td, td_allq); |
| 1368 | td->td_flags &= ~TDF_MIGRATING; |
| 1369 | crit_exit_gd(mygd); |
| 1370 | } |
| 1371 | } |
| 1372 | |
| 1373 | #endif |
| 1374 | |
| 1375 | /* |
| 1376 | * Generic deschedule. Descheduling threads other then your own should be |
| 1377 | * done only in carefully controlled circumstances. Descheduling is |
| 1378 | * asynchronous. |
| 1379 | * |
| 1380 | * This function may block if the cpu has run out of messages. |
| 1381 | */ |
| 1382 | void |
| 1383 | lwkt_deschedule(thread_t td) |
| 1384 | { |
| 1385 | crit_enter(); |
| 1386 | #ifdef SMP |
| 1387 | if (td == curthread) { |
| 1388 | _lwkt_dequeue(td); |
| 1389 | } else { |
| 1390 | if (td->td_gd == mycpu) { |
| 1391 | _lwkt_dequeue(td); |
| 1392 | } else { |
| 1393 | lwkt_send_ipiq(td->td_gd, (ipifunc1_t)lwkt_deschedule, td); |
| 1394 | } |
| 1395 | } |
| 1396 | #else |
| 1397 | _lwkt_dequeue(td); |
| 1398 | #endif |
| 1399 | crit_exit(); |
| 1400 | } |
| 1401 | |
| 1402 | /* |
| 1403 | * Set the target thread's priority. This routine does not automatically |
| 1404 | * switch to a higher priority thread, LWKT threads are not designed for |
| 1405 | * continuous priority changes. Yield if you want to switch. |
| 1406 | */ |
| 1407 | void |
| 1408 | lwkt_setpri(thread_t td, int pri) |
| 1409 | { |
| 1410 | KKASSERT(td->td_gd == mycpu); |
| 1411 | if (td->td_pri != pri) { |
| 1412 | KKASSERT(pri >= 0); |
| 1413 | crit_enter(); |
| 1414 | if (td->td_flags & TDF_RUNQ) { |
| 1415 | _lwkt_dequeue(td); |
| 1416 | td->td_pri = pri; |
| 1417 | _lwkt_enqueue(td); |
| 1418 | } else { |
| 1419 | td->td_pri = pri; |
| 1420 | } |
| 1421 | crit_exit(); |
| 1422 | } |
| 1423 | } |
| 1424 | |
| 1425 | /* |
| 1426 | * Set the initial priority for a thread prior to it being scheduled for |
| 1427 | * the first time. The thread MUST NOT be scheduled before or during |
| 1428 | * this call. The thread may be assigned to a cpu other then the current |
| 1429 | * cpu. |
| 1430 | * |
| 1431 | * Typically used after a thread has been created with TDF_STOPPREQ, |
| 1432 | * and before the thread is initially scheduled. |
| 1433 | */ |
| 1434 | void |
| 1435 | lwkt_setpri_initial(thread_t td, int pri) |
| 1436 | { |
| 1437 | KKASSERT(pri >= 0); |
| 1438 | KKASSERT((td->td_flags & TDF_RUNQ) == 0); |
| 1439 | td->td_pri = pri; |
| 1440 | } |
| 1441 | |
| 1442 | void |
| 1443 | lwkt_setpri_self(int pri) |
| 1444 | { |
| 1445 | thread_t td = curthread; |
| 1446 | |
| 1447 | KKASSERT(pri >= 0 && pri <= TDPRI_MAX); |
| 1448 | crit_enter(); |
| 1449 | if (td->td_flags & TDF_RUNQ) { |
| 1450 | _lwkt_dequeue(td); |
| 1451 | td->td_pri = pri; |
| 1452 | _lwkt_enqueue(td); |
| 1453 | } else { |
| 1454 | td->td_pri = pri; |
| 1455 | } |
| 1456 | crit_exit(); |
| 1457 | } |
| 1458 | |
| 1459 | /* |
| 1460 | * 1/hz tick (typically 10ms) x TDFAIRQ_SCALE (typ 8) = 80ms full cycle. |
| 1461 | * |
| 1462 | * Example: two competing threads, same priority N. decrement by (2*N) |
| 1463 | * increment by N*8, each thread will get 4 ticks. |
| 1464 | */ |
| 1465 | void |
| 1466 | lwkt_fairq_schedulerclock(thread_t td) |
| 1467 | { |
| 1468 | globaldata_t gd; |
| 1469 | |
| 1470 | if (fairq_enable) { |
| 1471 | while (td) { |
| 1472 | gd = td->td_gd; |
| 1473 | if (td != &gd->gd_idlethread) { |
| 1474 | td->td_fairq_accum -= gd->gd_fairq_total_pri; |
| 1475 | if (td->td_fairq_accum < -TDFAIRQ_MAX(gd)) |
| 1476 | td->td_fairq_accum = -TDFAIRQ_MAX(gd); |
| 1477 | if (td->td_fairq_accum < 0) |
| 1478 | need_lwkt_resched(); |
| 1479 | td->td_fairq_lticks = ticks; |
| 1480 | } |
| 1481 | td = td->td_preempted; |
| 1482 | } |
| 1483 | } |
| 1484 | } |
| 1485 | |
| 1486 | static void |
| 1487 | lwkt_fairq_accumulate(globaldata_t gd, thread_t td) |
| 1488 | { |
| 1489 | td->td_fairq_accum += td->td_pri * TDFAIRQ_SCALE; |
| 1490 | if (td->td_fairq_accum > TDFAIRQ_MAX(td->td_gd)) |
| 1491 | td->td_fairq_accum = TDFAIRQ_MAX(td->td_gd); |
| 1492 | } |
| 1493 | |
| 1494 | /* |
| 1495 | * Migrate the current thread to the specified cpu. |
| 1496 | * |
| 1497 | * This is accomplished by descheduling ourselves from the current cpu, |
| 1498 | * moving our thread to the tdallq of the target cpu, IPI messaging the |
| 1499 | * target cpu, and switching out. TDF_MIGRATING prevents scheduling |
| 1500 | * races while the thread is being migrated. |
| 1501 | * |
| 1502 | * We must be sure to remove ourselves from the current cpu's tsleepq |
| 1503 | * before potentially moving to another queue. The thread can be on |
| 1504 | * a tsleepq due to a left-over tsleep_interlock(). |
| 1505 | * |
| 1506 | * We also have to make sure that the switch code doesn't allow an IPI |
| 1507 | * processing operation to leak in between our send and our switch, or |
| 1508 | * any other potential livelock such that might occur when we release the |
| 1509 | * current process designation, so do that first. |
| 1510 | */ |
| 1511 | #ifdef SMP |
| 1512 | static void lwkt_setcpu_remote(void *arg); |
| 1513 | #endif |
| 1514 | |
| 1515 | void |
| 1516 | lwkt_setcpu_self(globaldata_t rgd) |
| 1517 | { |
| 1518 | #ifdef SMP |
| 1519 | thread_t td = curthread; |
| 1520 | |
| 1521 | if (td->td_gd != rgd) { |
| 1522 | crit_enter_quick(td); |
| 1523 | if (td->td_release) |
| 1524 | td->td_release(td); |
| 1525 | if (td->td_flags & TDF_TSLEEPQ) |
| 1526 | tsleep_remove(td); |
| 1527 | td->td_flags |= TDF_MIGRATING; |
| 1528 | lwkt_deschedule_self(td); |
| 1529 | TAILQ_REMOVE(&td->td_gd->gd_tdallq, td, td_allq); |
| 1530 | lwkt_send_ipiq(rgd, (ipifunc1_t)lwkt_setcpu_remote, td); |
| 1531 | lwkt_switch(); |
| 1532 | /* we are now on the target cpu */ |
| 1533 | TAILQ_INSERT_TAIL(&rgd->gd_tdallq, td, td_allq); |
| 1534 | crit_exit_quick(td); |
| 1535 | } |
| 1536 | #endif |
| 1537 | } |
| 1538 | |
| 1539 | void |
| 1540 | lwkt_migratecpu(int cpuid) |
| 1541 | { |
| 1542 | #ifdef SMP |
| 1543 | globaldata_t rgd; |
| 1544 | |
| 1545 | rgd = globaldata_find(cpuid); |
| 1546 | lwkt_setcpu_self(rgd); |
| 1547 | #endif |
| 1548 | } |
| 1549 | |
| 1550 | /* |
| 1551 | * Remote IPI for cpu migration (called while in a critical section so we |
| 1552 | * do not have to enter another one). The thread has already been moved to |
| 1553 | * our cpu's allq, but we must wait for the thread to be completely switched |
| 1554 | * out on the originating cpu before we schedule it on ours or the stack |
| 1555 | * state may be corrupt. We clear TDF_MIGRATING after flushing the GD |
| 1556 | * change to main memory. |
| 1557 | * |
| 1558 | * XXX The use of TDF_MIGRATING might not be sufficient to avoid races |
| 1559 | * against wakeups. It is best if this interface is used only when there |
| 1560 | * are no pending events that might try to schedule the thread. |
| 1561 | */ |
| 1562 | #ifdef SMP |
| 1563 | static void |
| 1564 | lwkt_setcpu_remote(void *arg) |
| 1565 | { |
| 1566 | thread_t td = arg; |
| 1567 | globaldata_t gd = mycpu; |
| 1568 | int retry = 10000000; |
| 1569 | |
| 1570 | DEBUG_PUSH_INFO("lwkt_setcpu_remote"); |
| 1571 | while (td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK)) { |
| 1572 | #ifdef SMP |
| 1573 | lwkt_process_ipiq(); |
| 1574 | #endif |
| 1575 | cpu_lfence(); |
| 1576 | cpu_pause(); |
| 1577 | if (--retry == 0) { |
| 1578 | kprintf("lwkt_setcpu_remote: td->td_flags %08x\n", |
| 1579 | td->td_flags); |
| 1580 | retry = 10000000; |
| 1581 | } |
| 1582 | } |
| 1583 | DEBUG_POP_INFO(); |
| 1584 | td->td_gd = gd; |
| 1585 | cpu_mfence(); |
| 1586 | td->td_flags &= ~TDF_MIGRATING; |
| 1587 | KKASSERT(td->td_lwp == NULL || (td->td_lwp->lwp_flag & LWP_ONRUNQ) == 0); |
| 1588 | _lwkt_enqueue(td); |
| 1589 | } |
| 1590 | #endif |
| 1591 | |
| 1592 | struct lwp * |
| 1593 | lwkt_preempted_proc(void) |
| 1594 | { |
| 1595 | thread_t td = curthread; |
| 1596 | while (td->td_preempted) |
| 1597 | td = td->td_preempted; |
| 1598 | return(td->td_lwp); |
| 1599 | } |
| 1600 | |
| 1601 | /* |
| 1602 | * Create a kernel process/thread/whatever. It shares it's address space |
| 1603 | * with proc0 - ie: kernel only. |
| 1604 | * |
| 1605 | * NOTE! By default new threads are created with the MP lock held. A |
| 1606 | * thread which does not require the MP lock should release it by calling |
| 1607 | * rel_mplock() at the start of the new thread. |
| 1608 | */ |
| 1609 | int |
| 1610 | lwkt_create(void (*func)(void *), void *arg, struct thread **tdp, |
| 1611 | thread_t template, int tdflags, int cpu, const char *fmt, ...) |
| 1612 | { |
| 1613 | thread_t td; |
| 1614 | __va_list ap; |
| 1615 | |
| 1616 | td = lwkt_alloc_thread(template, LWKT_THREAD_STACK, cpu, |
| 1617 | tdflags); |
| 1618 | if (tdp) |
| 1619 | *tdp = td; |
| 1620 | cpu_set_thread_handler(td, lwkt_exit, func, arg); |
| 1621 | |
| 1622 | /* |
| 1623 | * Set up arg0 for 'ps' etc |
| 1624 | */ |
| 1625 | __va_start(ap, fmt); |
| 1626 | kvsnprintf(td->td_comm, sizeof(td->td_comm), fmt, ap); |
| 1627 | __va_end(ap); |
| 1628 | |
| 1629 | /* |
| 1630 | * Schedule the thread to run |
| 1631 | */ |
| 1632 | if ((td->td_flags & TDF_STOPREQ) == 0) |
| 1633 | lwkt_schedule(td); |
| 1634 | else |
| 1635 | td->td_flags &= ~TDF_STOPREQ; |
| 1636 | return 0; |
| 1637 | } |
| 1638 | |
| 1639 | /* |
| 1640 | * Destroy an LWKT thread. Warning! This function is not called when |
| 1641 | * a process exits, cpu_proc_exit() directly calls cpu_thread_exit() and |
| 1642 | * uses a different reaping mechanism. |
| 1643 | */ |
| 1644 | void |
| 1645 | lwkt_exit(void) |
| 1646 | { |
| 1647 | thread_t td = curthread; |
| 1648 | thread_t std; |
| 1649 | globaldata_t gd; |
| 1650 | |
| 1651 | /* |
| 1652 | * Do any cleanup that might block here |
| 1653 | */ |
| 1654 | if (td->td_flags & TDF_VERBOSE) |
| 1655 | kprintf("kthread %p %s has exited\n", td, td->td_comm); |
| 1656 | caps_exit(td); |
| 1657 | biosched_done(td); |
| 1658 | dsched_exit_thread(td); |
| 1659 | |
| 1660 | /* |
| 1661 | * Get us into a critical section to interlock gd_freetd and loop |
| 1662 | * until we can get it freed. |
| 1663 | * |
| 1664 | * We have to cache the current td in gd_freetd because objcache_put()ing |
| 1665 | * it would rip it out from under us while our thread is still active. |
| 1666 | */ |
| 1667 | gd = mycpu; |
| 1668 | crit_enter_quick(td); |
| 1669 | while ((std = gd->gd_freetd) != NULL) { |
| 1670 | KKASSERT((std->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK)) == 0); |
| 1671 | gd->gd_freetd = NULL; |
| 1672 | objcache_put(thread_cache, std); |
| 1673 | } |
| 1674 | |
| 1675 | /* |
| 1676 | * Remove thread resources from kernel lists and deschedule us for |
| 1677 | * the last time. We cannot block after this point or we may end |
| 1678 | * up with a stale td on the tsleepq. |
| 1679 | */ |
| 1680 | if (td->td_flags & TDF_TSLEEPQ) |
| 1681 | tsleep_remove(td); |
| 1682 | lwkt_deschedule_self(td); |
| 1683 | lwkt_remove_tdallq(td); |
| 1684 | KKASSERT(td->td_refs == 0); |
| 1685 | |
| 1686 | /* |
| 1687 | * Final cleanup |
| 1688 | */ |
| 1689 | KKASSERT(gd->gd_freetd == NULL); |
| 1690 | if (td->td_flags & TDF_ALLOCATED_THREAD) |
| 1691 | gd->gd_freetd = td; |
| 1692 | cpu_thread_exit(); |
| 1693 | } |
| 1694 | |
| 1695 | void |
| 1696 | lwkt_remove_tdallq(thread_t td) |
| 1697 | { |
| 1698 | KKASSERT(td->td_gd == mycpu); |
| 1699 | TAILQ_REMOVE(&td->td_gd->gd_tdallq, td, td_allq); |
| 1700 | } |
| 1701 | |
| 1702 | /* |
| 1703 | * Code reduction and branch prediction improvements. Call/return |
| 1704 | * overhead on modern cpus often degenerates into 0 cycles due to |
| 1705 | * the cpu's branch prediction hardware and return pc cache. We |
| 1706 | * can take advantage of this by not inlining medium-complexity |
| 1707 | * functions and we can also reduce the branch prediction impact |
| 1708 | * by collapsing perfectly predictable branches into a single |
| 1709 | * procedure instead of duplicating it. |
| 1710 | * |
| 1711 | * Is any of this noticeable? Probably not, so I'll take the |
| 1712 | * smaller code size. |
| 1713 | */ |
| 1714 | void |
| 1715 | crit_exit_wrapper(__DEBUG_CRIT_ARG__) |
| 1716 | { |
| 1717 | _crit_exit(mycpu __DEBUG_CRIT_PASS_ARG__); |
| 1718 | } |
| 1719 | |
| 1720 | void |
| 1721 | crit_panic(void) |
| 1722 | { |
| 1723 | thread_t td = curthread; |
| 1724 | int lcrit = td->td_critcount; |
| 1725 | |
| 1726 | td->td_critcount = 0; |
| 1727 | panic("td_critcount is/would-go negative! %p %d", td, lcrit); |
| 1728 | /* NOT REACHED */ |
| 1729 | } |
| 1730 | |
| 1731 | #ifdef SMP |
| 1732 | |
| 1733 | /* |
| 1734 | * Called from debugger/panic on cpus which have been stopped. We must still |
| 1735 | * process the IPIQ while stopped, even if we were stopped while in a critical |
| 1736 | * section (XXX). |
| 1737 | * |
| 1738 | * If we are dumping also try to process any pending interrupts. This may |
| 1739 | * or may not work depending on the state of the cpu at the point it was |
| 1740 | * stopped. |
| 1741 | */ |
| 1742 | void |
| 1743 | lwkt_smp_stopped(void) |
| 1744 | { |
| 1745 | globaldata_t gd = mycpu; |
| 1746 | |
| 1747 | crit_enter_gd(gd); |
| 1748 | if (dumping) { |
| 1749 | lwkt_process_ipiq(); |
| 1750 | splz(); |
| 1751 | } else { |
| 1752 | lwkt_process_ipiq(); |
| 1753 | } |
| 1754 | crit_exit_gd(gd); |
| 1755 | } |
| 1756 | |
| 1757 | #endif |