1 /*
2 * Copyright (c) 2003-2011 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/spinlock.h>
54 #include <sys/ktr.h>
55
56 #include <sys/thread2.h>
57 #include <sys/spinlock2.h>
58 #include <sys/mplock2.h>
59
60 #include <sys/dsched.h>
61
62 #include <vm/vm.h>
63 #include <vm/vm_param.h>
64 #include <vm/vm_kern.h>
65 #include <vm/vm_object.h>
66 #include <vm/vm_page.h>
67 #include <vm/vm_map.h>
68 #include <vm/vm_pager.h>
69 #include <vm/vm_extern.h>
70
71 #include <machine/stdarg.h>
72 #include <machine/smp.h>
73
74 #ifdef _KERNEL_VIRTUAL
75 #include <pthread.h>
76 #endif
77
78 #if !defined(KTR_CTXSW)
79 #define KTR_CTXSW KTR_ALL
80 #endif
81 KTR_INFO_MASTER(ctxsw);
82 KTR_INFO(KTR_CTXSW, ctxsw, sw, 0, "#cpu[%d].td = %p", int cpu, struct thread *td);
83 KTR_INFO(KTR_CTXSW, ctxsw, pre, 1, "#cpu[%d].td = %p", int cpu, struct thread *td);
84 KTR_INFO(KTR_CTXSW, ctxsw, newtd, 2, "#threads[%p].name = %s", struct thread *td, char *comm);
85 KTR_INFO(KTR_CTXSW, ctxsw, deadtd, 3, "#threads[%p].name = <dead>", struct thread *td);
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 int lwkt_use_spin_port;
97 static struct objcache *thread_cache;
98 int cpu_mwait_spin = 0;
99
100 static void lwkt_schedule_remote(void *arg, int arg2, struct intrframe *frame);
101 static void lwkt_setcpu_remote(void *arg);
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 /*
109 * We can make all thread ports use the spin backend instead of the thread
110 * backend. This should only be set to debug the spin backend.
111 */
112 TUNABLE_INT("lwkt.use_spin_port", &lwkt_use_spin_port);
113
114 #ifdef INVARIANTS
115 SYSCTL_INT(_lwkt, OID_AUTO, panic_on_cscount, CTLFLAG_RW, &panic_on_cscount, 0,
116 "Panic if attempting to switch lwkt's while mastering cpusync");
117 #endif
118 SYSCTL_INT(_hw, OID_AUTO, cpu_mwait_spin, CTLFLAG_RW, &cpu_mwait_spin, 0,
119 "monitor/mwait target state");
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 static int fairq_enable = 0;
129 SYSCTL_INT(_lwkt, OID_AUTO, fairq_enable, CTLFLAG_RW,
130 &fairq_enable, 0, "Turn on fairq priority accumulators");
131 static int fairq_bypass = -1;
132 SYSCTL_INT(_lwkt, OID_AUTO, fairq_bypass, CTLFLAG_RW,
133 &fairq_bypass, 0, "Allow fairq to bypass td on token failure");
134 extern int lwkt_sched_debug;
135 int lwkt_sched_debug = 0;
136 SYSCTL_INT(_lwkt, OID_AUTO, sched_debug, CTLFLAG_RW,
137 &lwkt_sched_debug, 0, "Scheduler debug");
138 static int lwkt_spin_loops = 10;
139 SYSCTL_INT(_lwkt, OID_AUTO, spin_loops, CTLFLAG_RW,
140 &lwkt_spin_loops, 0, "Scheduler spin loops until sorted decon");
141 static int lwkt_spin_reseq = 0;
142 SYSCTL_INT(_lwkt, OID_AUTO, spin_reseq, CTLFLAG_RW,
143 &lwkt_spin_reseq, 0, "Scheduler resequencer enable");
144 static int lwkt_spin_monitor = 0;
145 SYSCTL_INT(_lwkt, OID_AUTO, spin_monitor, CTLFLAG_RW,
146 &lwkt_spin_monitor, 0, "Scheduler uses monitor/mwait");
147 static int lwkt_spin_fatal = 0; /* disabled */
148 SYSCTL_INT(_lwkt, OID_AUTO, spin_fatal, CTLFLAG_RW,
149 &lwkt_spin_fatal, 0, "LWKT scheduler spin loops till fatal panic");
150 static int preempt_enable = 1;
151 SYSCTL_INT(_lwkt, OID_AUTO, preempt_enable, CTLFLAG_RW,
152 &preempt_enable, 0, "Enable preemption");
153 static int lwkt_cache_threads = 0;
154 SYSCTL_INT(_lwkt, OID_AUTO, cache_threads, CTLFLAG_RD,
155 &lwkt_cache_threads, 0, "thread+kstack cache");
156
157 #ifndef _KERNEL_VIRTUAL
158 static __cachealign int lwkt_cseq_rindex;
159 static __cachealign int lwkt_cseq_windex;
160 #endif
161
162 /*
163 * These helper procedures handle the runq, they can only be called from
164 * within a critical section.
165 *
166 * WARNING! Prior to SMP being brought up it is possible to enqueue and
167 * dequeue threads belonging to other cpus, so be sure to use td->td_gd
168 * instead of 'mycpu' when referencing the globaldata structure. Once
169 * SMP live enqueuing and dequeueing only occurs on the current cpu.
170 */
171 static __inline
172 void
173 _lwkt_dequeue(thread_t td)
174 {
175 if (td->td_flags & TDF_RUNQ) {
176 struct globaldata *gd = td->td_gd;
177
178 td->td_flags &= ~TDF_RUNQ;
179 TAILQ_REMOVE(&gd->gd_tdrunq, td, td_threadq);
180 --gd->gd_tdrunqcount;
181 if (TAILQ_FIRST(&gd->gd_tdrunq) == NULL)
182 atomic_clear_int(&gd->gd_reqflags, RQF_RUNNING);
183 }
184 }
185
186 /*
187 * Priority enqueue.
188 *
189 * There are a limited number of lwkt threads runnable since user
190 * processes only schedule one at a time per cpu. However, there can
191 * be many user processes in kernel mode exiting from a tsleep() which
192 * become runnable.
193 *
194 * NOTE: lwkt_schedulerclock() will force a round-robin based on td_pri and
195 * will ignore user priority. This is to ensure that user threads in
196 * kernel mode get cpu at some point regardless of what the user
197 * scheduler thinks.
198 */
199 static __inline
200 void
201 _lwkt_enqueue(thread_t td)
202 {
203 thread_t xtd;
204
205 if ((td->td_flags & (TDF_RUNQ|TDF_MIGRATING|TDF_BLOCKQ)) == 0) {
206 struct globaldata *gd = td->td_gd;
207
208 td->td_flags |= TDF_RUNQ;
209 xtd = TAILQ_FIRST(&gd->gd_tdrunq);
210 if (xtd == NULL) {
211 TAILQ_INSERT_TAIL(&gd->gd_tdrunq, td, td_threadq);
212 atomic_set_int(&gd->gd_reqflags, RQF_RUNNING);
213 } else {
214 /*
215 * NOTE: td_upri - higher numbers more desireable, same sense
216 * as td_pri (typically reversed from lwp_upri).
217 *
218 * In the equal priority case we want the best selection
219 * at the beginning so the less desireable selections know
220 * that they have to setrunqueue/go-to-another-cpu, even
221 * though it means switching back to the 'best' selection.
222 * This also avoids degenerate situations when many threads
223 * are runnable or waking up at the same time.
224 *
225 * If upri matches exactly place at end/round-robin.
226 */
227 while (xtd &&
228 (xtd->td_pri >= td->td_pri ||
229 (xtd->td_pri == td->td_pri &&
230 xtd->td_upri >= td->td_upri))) {
231 xtd = TAILQ_NEXT(xtd, td_threadq);
232 }
233 if (xtd)
234 TAILQ_INSERT_BEFORE(xtd, td, td_threadq);
235 else
236 TAILQ_INSERT_TAIL(&gd->gd_tdrunq, td, td_threadq);
237 }
238 ++gd->gd_tdrunqcount;
239
240 /*
241 * Request a LWKT reschedule if we are now at the head of the queue.
242 */
243 if (TAILQ_FIRST(&gd->gd_tdrunq) == td)
244 need_lwkt_resched();
245 }
246 }
247
248 static __boolean_t
249 _lwkt_thread_ctor(void *obj, void *privdata, int ocflags)
250 {
251 struct thread *td = (struct thread *)obj;
252
253 td->td_kstack = NULL;
254 td->td_kstack_size = 0;
255 td->td_flags = TDF_ALLOCATED_THREAD;
256 td->td_mpflags = 0;
257 return (1);
258 }
259
260 static void
261 _lwkt_thread_dtor(void *obj, void *privdata)
262 {
263 struct thread *td = (struct thread *)obj;
264
265 KASSERT(td->td_flags & TDF_ALLOCATED_THREAD,
266 ("_lwkt_thread_dtor: not allocated from objcache"));
267 KASSERT((td->td_flags & TDF_ALLOCATED_STACK) && td->td_kstack &&
268 td->td_kstack_size > 0,
269 ("_lwkt_thread_dtor: corrupted stack"));
270 kmem_free(&kernel_map, (vm_offset_t)td->td_kstack, td->td_kstack_size);
271 td->td_kstack = NULL;
272 td->td_flags = 0;
273 }
274
275 /*
276 * Initialize the lwkt s/system.
277 *
278 * Nominally cache up to 32 thread + kstack structures. Cache more on
279 * systems with a lot of cpu cores.
280 */
281 void
282 lwkt_init(void)
283 {
284 TUNABLE_INT("lwkt.cache_threads", &lwkt_cache_threads);
285 if (lwkt_cache_threads == 0) {
286 lwkt_cache_threads = ncpus * 4;
287 if (lwkt_cache_threads < 32)
288 lwkt_cache_threads = 32;
289 }
290 thread_cache = objcache_create_mbacked(
291 M_THREAD, sizeof(struct thread),
292 0, lwkt_cache_threads,
293 _lwkt_thread_ctor, _lwkt_thread_dtor, NULL);
294 }
295
296 /*
297 * Schedule a thread to run. As the current thread we can always safely
298 * schedule ourselves, and a shortcut procedure is provided for that
299 * function.
300 *
301 * (non-blocking, self contained on a per cpu basis)
302 */
303 void
304 lwkt_schedule_self(thread_t td)
305 {
306 KKASSERT((td->td_flags & TDF_MIGRATING) == 0);
307 crit_enter_quick(td);
308 KASSERT(td != &td->td_gd->gd_idlethread,
309 ("lwkt_schedule_self(): scheduling gd_idlethread is illegal!"));
310 KKASSERT(td->td_lwp == NULL ||
311 (td->td_lwp->lwp_mpflags & LWP_MP_ONRUNQ) == 0);
312 _lwkt_enqueue(td);
313 crit_exit_quick(td);
314 }
315
316 /*
317 * Deschedule a thread.
318 *
319 * (non-blocking, self contained on a per cpu basis)
320 */
321 void
322 lwkt_deschedule_self(thread_t td)
323 {
324 crit_enter_quick(td);
325 _lwkt_dequeue(td);
326 crit_exit_quick(td);
327 }
328
329 /*
330 * LWKTs operate on a per-cpu basis
331 *
332 * WARNING! Called from early boot, 'mycpu' may not work yet.
333 */
334 void
335 lwkt_gdinit(struct globaldata *gd)
336 {
337 TAILQ_INIT(&gd->gd_tdrunq);
338 TAILQ_INIT(&gd->gd_tdallq);
339 }
340
341 /*
342 * Create a new thread. The thread must be associated with a process context
343 * or LWKT start address before it can be scheduled. If the target cpu is
344 * -1 the thread will be created on the current cpu.
345 *
346 * If you intend to create a thread without a process context this function
347 * does everything except load the startup and switcher function.
348 */
349 thread_t
350 lwkt_alloc_thread(struct thread *td, int stksize, int cpu, int flags)
351 {
352 static int cpu_rotator;
353 globaldata_t gd = mycpu;
354 void *stack;
355
356 /*
357 * If static thread storage is not supplied allocate a thread. Reuse
358 * a cached free thread if possible. gd_freetd is used to keep an exiting
359 * thread intact through the exit.
360 */
361 if (td == NULL) {
362 crit_enter_gd(gd);
363 if ((td = gd->gd_freetd) != NULL) {
364 KKASSERT((td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK|
365 TDF_RUNQ)) == 0);
366 gd->gd_freetd = NULL;
367 } else {
368 td = objcache_get(thread_cache, M_WAITOK);
369 KKASSERT((td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK|
370 TDF_RUNQ)) == 0);
371 }
372 crit_exit_gd(gd);
373 KASSERT((td->td_flags &
374 (TDF_ALLOCATED_THREAD|TDF_RUNNING|TDF_PREEMPT_LOCK)) ==
375 TDF_ALLOCATED_THREAD,
376 ("lwkt_alloc_thread: corrupted td flags 0x%X", td->td_flags));
377 flags |= td->td_flags & (TDF_ALLOCATED_THREAD|TDF_ALLOCATED_STACK);
378 }
379
380 /*
381 * Try to reuse cached stack.
382 */
383 if ((stack = td->td_kstack) != NULL && td->td_kstack_size != stksize) {
384 if (flags & TDF_ALLOCATED_STACK) {
385 kmem_free(&kernel_map, (vm_offset_t)stack, td->td_kstack_size);
386 stack = NULL;
387 }
388 }
389 if (stack == NULL) {
390 stack = (void *)kmem_alloc_stack(&kernel_map, stksize);
391 flags |= TDF_ALLOCATED_STACK;
392 }
393 if (cpu < 0) {
394 cpu = ++cpu_rotator;
395 cpu_ccfence();
396 cpu %= ncpus;
397 }
398 lwkt_init_thread(td, stack, stksize, flags, globaldata_find(cpu));
399 return(td);
400 }
401
402 /*
403 * Initialize a preexisting thread structure. This function is used by
404 * lwkt_alloc_thread() and also used to initialize the per-cpu idlethread.
405 *
406 * All threads start out in a critical section at a priority of
407 * TDPRI_KERN_DAEMON. Higher level code will modify the priority as
408 * appropriate. This function may send an IPI message when the
409 * requested cpu is not the current cpu and consequently gd_tdallq may
410 * not be initialized synchronously from the point of view of the originating
411 * cpu.
412 *
413 * NOTE! we have to be careful in regards to creating threads for other cpus
414 * if SMP has not yet been activated.
415 */
416 static void
417 lwkt_init_thread_remote(void *arg)
418 {
419 thread_t td = arg;
420
421 /*
422 * Protected by critical section held by IPI dispatch
423 */
424 TAILQ_INSERT_TAIL(&td->td_gd->gd_tdallq, td, td_allq);
425 }
426
427 /*
428 * lwkt core thread structural initialization.
429 *
430 * NOTE: All threads are initialized as mpsafe threads.
431 */
432 void
433 lwkt_init_thread(thread_t td, void *stack, int stksize, int flags,
434 struct globaldata *gd)
435 {
436 globaldata_t mygd = mycpu;
437
438 bzero(td, sizeof(struct thread));
439 td->td_kstack = stack;
440 td->td_kstack_size = stksize;
441 td->td_flags = flags;
442 td->td_mpflags = 0;
443 td->td_type = TD_TYPE_GENERIC;
444 td->td_gd = gd;
445 td->td_pri = TDPRI_KERN_DAEMON;
446 td->td_critcount = 1;
447 td->td_toks_have = NULL;
448 td->td_toks_stop = &td->td_toks_base;
449 if (lwkt_use_spin_port || (flags & TDF_FORCE_SPINPORT)) {
450 lwkt_initport_spin(&td->td_msgport, td,
451 (flags & TDF_FIXEDCPU) ? TRUE : FALSE);
452 } else {
453 lwkt_initport_thread(&td->td_msgport, td);
454 }
455 pmap_init_thread(td);
456 /*
457 * Normally initializing a thread for a remote cpu requires sending an
458 * IPI. However, the idlethread is setup before the other cpus are
459 * activated so we have to treat it as a special case. XXX manipulation
460 * of gd_tdallq requires the BGL.
461 */
462 if (gd == mygd || td == &gd->gd_idlethread) {
463 crit_enter_gd(mygd);
464 TAILQ_INSERT_TAIL(&gd->gd_tdallq, td, td_allq);
465 crit_exit_gd(mygd);
466 } else {
467 lwkt_send_ipiq(gd, lwkt_init_thread_remote, td);
468 }
469 dsched_new_thread(td);
470 }
471
472 void
473 lwkt_set_comm(thread_t td, const char *ctl, ...)
474 {
475 __va_list va;
476
477 __va_start(va, ctl);
478 kvsnprintf(td->td_comm, sizeof(td->td_comm), ctl, va);
479 __va_end(va);
480 KTR_LOG(ctxsw_newtd, td, td->td_comm);
481 }
482
483 /*
484 * Prevent the thread from getting destroyed. Note that unlike PHOLD/PRELE
485 * this does not prevent the thread from migrating to another cpu so the
486 * gd_tdallq state is not protected by this.
487 */
488 void
489 lwkt_hold(thread_t td)
490 {
491 atomic_add_int(&td->td_refs, 1);
492 }
493
494 void
495 lwkt_rele(thread_t td)
496 {
497 KKASSERT(td->td_refs > 0);
498 atomic_add_int(&td->td_refs, -1);
499 }
500
501 void
502 lwkt_free_thread(thread_t td)
503 {
504 KKASSERT(td->td_refs == 0);
505 KKASSERT((td->td_flags & (TDF_RUNNING | TDF_PREEMPT_LOCK |
506 TDF_RUNQ | TDF_TSLEEPQ)) == 0);
507 if (td->td_flags & TDF_ALLOCATED_THREAD) {
508 objcache_put(thread_cache, td);
509 } else if (td->td_flags & TDF_ALLOCATED_STACK) {
510 /* client-allocated struct with internally allocated stack */
511 KASSERT(td->td_kstack && td->td_kstack_size > 0,
512 ("lwkt_free_thread: corrupted stack"));
513 kmem_free(&kernel_map, (vm_offset_t)td->td_kstack, td->td_kstack_size);
514 td->td_kstack = NULL;
515 td->td_kstack_size = 0;
516 }
517
518 KTR_LOG(ctxsw_deadtd, td);
519 }
520
521
522 /*
523 * Switch to the next runnable lwkt. If no LWKTs are runnable then
524 * switch to the idlethread. Switching must occur within a critical
525 * section to avoid races with the scheduling queue.
526 *
527 * We always have full control over our cpu's run queue. Other cpus
528 * that wish to manipulate our queue must use the cpu_*msg() calls to
529 * talk to our cpu, so a critical section is all that is needed and
530 * the result is very, very fast thread switching.
531 *
532 * The LWKT scheduler uses a fixed priority model and round-robins at
533 * each priority level. User process scheduling is a totally
534 * different beast and LWKT priorities should not be confused with
535 * user process priorities.
536 *
537 * PREEMPTION NOTE: Preemption occurs via lwkt_preempt(). lwkt_switch()
538 * is not called by the current thread in the preemption case, only when
539 * the preempting thread blocks (in order to return to the original thread).
540 *
541 * SPECIAL NOTE ON SWITCH ATOMICY: Certain operations such as thread
542 * migration and tsleep deschedule the current lwkt thread and call
543 * lwkt_switch(). In particular, the target cpu of the migration fully
544 * expects the thread to become non-runnable and can deadlock against
545 * cpusync operations if we run any IPIs prior to switching the thread out.
546 *
547 * WE MUST BE VERY CAREFUL NOT TO RUN SPLZ DIRECTLY OR INDIRECTLY IF
548 * THE CURRENT THREAD HAS BEEN DESCHEDULED!
549 */
550 void
551 lwkt_switch(void)
552 {
553 globaldata_t gd = mycpu;
554 thread_t td = gd->gd_curthread;
555 thread_t ntd;
556 int spinning = 0;
557
558 KKASSERT(gd->gd_processing_ipiq == 0);
559 KKASSERT(td->td_flags & TDF_RUNNING);
560
561 /*
562 * Switching from within a 'fast' (non thread switched) interrupt or IPI
563 * is illegal. However, we may have to do it anyway if we hit a fatal
564 * kernel trap or we have paniced.
565 *
566 * If this case occurs save and restore the interrupt nesting level.
567 */
568 if (gd->gd_intr_nesting_level) {
569 int savegdnest;
570 int savegdtrap;
571
572 if (gd->gd_trap_nesting_level == 0 && panic_cpu_gd != mycpu) {
573 panic("lwkt_switch: Attempt to switch from a "
574 "fast interrupt, ipi, or hard code section, "
575 "td %p\n",
576 td);
577 } else {
578 savegdnest = gd->gd_intr_nesting_level;
579 savegdtrap = gd->gd_trap_nesting_level;
580 gd->gd_intr_nesting_level = 0;
581 gd->gd_trap_nesting_level = 0;
582 if ((td->td_flags & TDF_PANICWARN) == 0) {
583 td->td_flags |= TDF_PANICWARN;
584 kprintf("Warning: thread switch from interrupt, IPI, "
585 "or hard code section.\n"
586 "thread %p (%s)\n", td, td->td_comm);
587 print_backtrace(-1);
588 }
589 lwkt_switch();
590 gd->gd_intr_nesting_level = savegdnest;
591 gd->gd_trap_nesting_level = savegdtrap;
592 return;
593 }
594 }
595
596 /*
597 * Release our current user process designation if we are blocking
598 * or if a user reschedule was requested.
599 *
600 * NOTE: This function is NOT called if we are switching into or
601 * returning from a preemption.
602 *
603 * NOTE: Releasing our current user process designation may cause
604 * it to be assigned to another thread, which in turn will
605 * cause us to block in the usched acquire code when we attempt
606 * to return to userland.
607 *
608 * NOTE: On SMP systems this can be very nasty when heavy token
609 * contention is present so we want to be careful not to
610 * release the designation gratuitously.
611 */
612 if (td->td_release &&
613 (user_resched_wanted() || (td->td_flags & TDF_RUNQ) == 0)) {
614 td->td_release(td);
615 }
616
617 /*
618 * Release all tokens
619 */
620 crit_enter_gd(gd);
621 if (TD_TOKS_HELD(td))
622 lwkt_relalltokens(td);
623
624 /*
625 * We had better not be holding any spin locks, but don't get into an
626 * endless panic loop.
627 */
628 KASSERT(gd->gd_spinlocks == 0 || panicstr != NULL,
629 ("lwkt_switch: still holding %d exclusive spinlocks!",
630 gd->gd_spinlocks));
631
632
633 #ifdef INVARIANTS
634 if (td->td_cscount) {
635 kprintf("Diagnostic: attempt to switch while mastering cpusync: %p\n",
636 td);
637 if (panic_on_cscount)
638 panic("switching while mastering cpusync");
639 }
640 #endif
641
642 /*
643 * If we had preempted another thread on this cpu, resume the preempted
644 * thread. This occurs transparently, whether the preempted thread
645 * was scheduled or not (it may have been preempted after descheduling
646 * itself).
647 *
648 * We have to setup the MP lock for the original thread after backing
649 * out the adjustment that was made to curthread when the original
650 * was preempted.
651 */
652 if ((ntd = td->td_preempted) != NULL) {
653 KKASSERT(ntd->td_flags & TDF_PREEMPT_LOCK);
654 ntd->td_flags |= TDF_PREEMPT_DONE;
655
656 /*
657 * The interrupt may have woken a thread up, we need to properly
658 * set the reschedule flag if the originally interrupted thread is
659 * at a lower priority.
660 *
661 * The interrupt may not have descheduled.
662 */
663 if (TAILQ_FIRST(&gd->gd_tdrunq) != ntd)
664 need_lwkt_resched();
665 goto havethread_preempted;
666 }
667
668 /*
669 * If we cannot obtain ownership of the tokens we cannot immediately
670 * schedule the target thread.
671 *
672 * Reminder: Again, we cannot afford to run any IPIs in this path if
673 * the current thread has been descheduled.
674 */
675 for (;;) {
676 clear_lwkt_resched();
677
678 /*
679 * Hotpath - pull the head of the run queue and attempt to schedule
680 * it.
681 */
682 ntd = TAILQ_FIRST(&gd->gd_tdrunq);
683
684 if (ntd == NULL) {
685 /*
686 * Runq is empty, switch to idle to allow it to halt.
687 */
688 ntd = &gd->gd_idlethread;
689 if (gd->gd_trap_nesting_level == 0 && panicstr == NULL)
690 ASSERT_NO_TOKENS_HELD(ntd);
691 cpu_time.cp_msg[0] = 0;
692 cpu_time.cp_stallpc = 0;
693 goto haveidle;
694 }
695
696 /*
697 * Hotpath - schedule ntd.
698 *
699 * NOTE: For UP there is no mplock and lwkt_getalltokens()
700 * always succeeds.
701 */
702 if (TD_TOKS_NOT_HELD(ntd) ||
703 lwkt_getalltokens(ntd, (spinning >= lwkt_spin_loops)))
704 {
705 goto havethread;
706 }
707
708 /*
709 * Coldpath (SMP only since tokens always succeed on UP)
710 *
711 * We had some contention on the thread we wanted to schedule.
712 * What we do now is try to find a thread that we can schedule
713 * in its stead.
714 *
715 * The coldpath scan does NOT rearrange threads in the run list.
716 * The lwkt_schedulerclock() will assert need_lwkt_resched() on
717 * the next tick whenever the current head is not the current thread.
718 */
719 #ifdef INVARIANTS
720 ++ntd->td_contended;
721 #endif
722 ++gd->gd_cnt.v_lock_colls;
723
724 if (fairq_bypass > 0)
725 goto skip;
726
727 while ((ntd = TAILQ_NEXT(ntd, td_threadq)) != NULL) {
728 #ifndef NO_LWKT_SPLIT_USERPRI
729 /*
730 * Never schedule threads returning to userland or the
731 * user thread scheduler helper thread when higher priority
732 * threads are present. The runq is sorted by priority
733 * so we can give up traversing it when we find the first
734 * low priority thread.
735 */
736 if (ntd->td_pri < TDPRI_KERN_LPSCHED) {
737 ntd = NULL;
738 break;
739 }
740 #endif
741
742 /*
743 * Try this one.
744 */
745 if (TD_TOKS_NOT_HELD(ntd) ||
746 lwkt_getalltokens(ntd, (spinning >= lwkt_spin_loops))) {
747 goto havethread;
748 }
749 #ifdef INVARIANTS
750 ++ntd->td_contended;
751 #endif
752 ++gd->gd_cnt.v_lock_colls;
753 }
754
755 skip:
756 /*
757 * We exhausted the run list, meaning that all runnable threads
758 * are contested.
759 */
760 cpu_pause();
761 #ifdef _KERNEL_VIRTUAL
762 pthread_yield();
763 #endif
764 ntd = &gd->gd_idlethread;
765 if (gd->gd_trap_nesting_level == 0 && panicstr == NULL)
766 ASSERT_NO_TOKENS_HELD(ntd);
767 /* contention case, do not clear contention mask */
768
769 /*
770 * We are going to have to retry but if the current thread is not
771 * on the runq we instead switch through the idle thread to get away
772 * from the current thread. We have to flag for lwkt reschedule
773 * to prevent the idle thread from halting.
774 *
775 * NOTE: A non-zero spinning is passed to lwkt_getalltokens() to
776 * instruct it to deal with the potential for deadlocks by
777 * ordering the tokens by address.
778 */
779 if ((td->td_flags & TDF_RUNQ) == 0) {
780 need_lwkt_resched(); /* prevent hlt */
781 goto haveidle;
782 }
783 #if defined(INVARIANTS) && defined(__x86_64__)
784 if ((read_rflags() & PSL_I) == 0) {
785 cpu_enable_intr();
786 panic("lwkt_switch() called with interrupts disabled");
787 }
788 #endif
789
790 /*
791 * Number iterations so far. After a certain point we switch to
792 * a sorted-address/monitor/mwait version of lwkt_getalltokens()
793 */
794 if (spinning < 0x7FFFFFFF)
795 ++spinning;
796
797 #ifndef _KERNEL_VIRTUAL
798 /*
799 * lwkt_getalltokens() failed in sorted token mode, we can use
800 * monitor/mwait in this case.
801 */
802 if (spinning >= lwkt_spin_loops &&
803 (cpu_mi_feature & CPU_MI_MONITOR) &&
804 lwkt_spin_monitor)
805 {
806 cpu_mmw_pause_int(&gd->gd_reqflags,
807 (gd->gd_reqflags | RQF_SPINNING) &
808 ~RQF_IDLECHECK_WK_MASK,
809 cpu_mwait_spin);
810 }
811 #endif
812
813 /*
814 * We already checked that td is still scheduled so this should be
815 * safe.
816 */
817 splz_check();
818
819 #ifndef _KERNEL_VIRTUAL
820 /*
821 * This experimental resequencer is used as a fall-back to reduce
822 * hw cache line contention by placing each core's scheduler into a
823 * time-domain-multplexed slot.
824 *
825 * The resequencer is disabled by default. It's functionality has
826 * largely been superceeded by the token algorithm which limits races
827 * to a subset of cores.
828 *
829 * The resequencer algorithm tends to break down when more than
830 * 20 cores are contending. What appears to happen is that new
831 * tokens can be obtained out of address-sorted order by new cores
832 * while existing cores languish in long delays between retries and
833 * wind up being starved-out of the token acquisition.
834 */
835 if (lwkt_spin_reseq && spinning >= lwkt_spin_reseq) {
836 int cseq = atomic_fetchadd_int(&lwkt_cseq_windex, 1);
837 int oseq;
838
839 while ((oseq = lwkt_cseq_rindex) != cseq) {
840 cpu_ccfence();
841 #if 1
842 if (cpu_mi_feature & CPU_MI_MONITOR) {
843 cpu_mmw_pause_int(&lwkt_cseq_rindex, oseq, cpu_mwait_spin);
844 } else {
845 #endif
846 cpu_pause();
847 cpu_lfence();
848 #if 1
849 }
850 #endif
851 }
852 DELAY(1);
853 atomic_add_int(&lwkt_cseq_rindex, 1);
854 }
855 #endif
856 /* highest level for(;;) loop */
857 }
858
859 havethread:
860 /*
861 * Clear gd_idle_repeat when doing a normal switch to a non-idle
862 * thread.
863 */
864 ntd->td_wmesg = NULL;
865 ++gd->gd_cnt.v_swtch;
866 gd->gd_idle_repeat = 0;
867
868 havethread_preempted:
869 /*
870 * If the new target does not need the MP lock and we are holding it,
871 * release the MP lock. If the new target requires the MP lock we have
872 * already acquired it for the target.
873 */
874 ;
875 haveidle:
876 KASSERT(ntd->td_critcount,
877 ("priority problem in lwkt_switch %d %d",
878 td->td_critcount, ntd->td_critcount));
879
880 if (td != ntd) {
881 /*
882 * Execute the actual thread switch operation. This function
883 * returns to the current thread and returns the previous thread
884 * (which may be different from the thread we switched to).
885 *
886 * We are responsible for marking ntd as TDF_RUNNING.
887 */
888 KKASSERT((ntd->td_flags & TDF_RUNNING) == 0);
889 ++switch_count;
890 KTR_LOG(ctxsw_sw, gd->gd_cpuid, ntd);
891 ntd->td_flags |= TDF_RUNNING;
892 lwkt_switch_return(td->td_switch(ntd));
893 /* ntd invalid, td_switch() can return a different thread_t */
894 }
895
896 /*
897 * catch-all. XXX is this strictly needed?
898 */
899 splz_check();
900
901 /* NOTE: current cpu may have changed after switch */
902 crit_exit_quick(td);
903 }
904
905 /*
906 * Called by assembly in the td_switch (thread restore path) for thread
907 * bootstrap cases which do not 'return' to lwkt_switch().
908 */
909 void
910 lwkt_switch_return(thread_t otd)
911 {
912 globaldata_t rgd;
913
914 /*
915 * Check if otd was migrating. Now that we are on ntd we can finish
916 * up the migration. This is a bit messy but it is the only place
917 * where td is known to be fully descheduled.
918 *
919 * We can only activate the migration if otd was migrating but not
920 * held on the cpu due to a preemption chain. We still have to
921 * clear TDF_RUNNING on the old thread either way.
922 *
923 * We are responsible for clearing the previously running thread's
924 * TDF_RUNNING.
925 */
926 if ((rgd = otd->td_migrate_gd) != NULL &&
927 (otd->td_flags & TDF_PREEMPT_LOCK) == 0) {
928 KKASSERT((otd->td_flags & (TDF_MIGRATING | TDF_RUNNING)) ==
929 (TDF_MIGRATING | TDF_RUNNING));
930 otd->td_migrate_gd = NULL;
931 otd->td_flags &= ~TDF_RUNNING;
932 lwkt_send_ipiq(rgd, lwkt_setcpu_remote, otd);
933 } else {
934 otd->td_flags &= ~TDF_RUNNING;
935 }
936
937 /*
938 * Final exit validations (see lwp_wait()). Note that otd becomes
939 * invalid the *instant* we set TDF_MP_EXITSIG.
940 */
941 while (otd->td_flags & TDF_EXITING) {
942 u_int mpflags;
943
944 mpflags = otd->td_mpflags;
945 cpu_ccfence();
946
947 if (mpflags & TDF_MP_EXITWAIT) {
948 if (atomic_cmpset_int(&otd->td_mpflags, mpflags,
949 mpflags | TDF_MP_EXITSIG)) {
950 wakeup(otd);
951 break;
952 }
953 } else {
954 if (atomic_cmpset_int(&otd->td_mpflags, mpflags,
955 mpflags | TDF_MP_EXITSIG)) {
956 wakeup(otd);
957 break;
958 }
959 }
960 }
961 }
962
963 /*
964 * Request that the target thread preempt the current thread. Preemption
965 * can only occur if our only critical section is the one that we were called
966 * with, the relative priority of the target thread is higher, and the target
967 * thread holds no tokens. This also only works if we are not holding any
968 * spinlocks (obviously).
969 *
970 * THE CALLER OF LWKT_PREEMPT() MUST BE IN A CRITICAL SECTION. Typically
971 * this is called via lwkt_schedule() through the td_preemptable callback.
972 * critcount is the managed critical priority that we should ignore in order
973 * to determine whether preemption is possible (aka usually just the crit
974 * priority of lwkt_schedule() itself).
975 *
976 * Preemption is typically limited to interrupt threads.
977 *
978 * Operation works in a fairly straight-forward manner. The normal
979 * scheduling code is bypassed and we switch directly to the target
980 * thread. When the target thread attempts to block or switch away
981 * code at the base of lwkt_switch() will switch directly back to our
982 * thread. Our thread is able to retain whatever tokens it holds and
983 * if the target needs one of them the target will switch back to us
984 * and reschedule itself normally.
985 */
986 void
987 lwkt_preempt(thread_t ntd, int critcount)
988 {
989 struct globaldata *gd = mycpu;
990 thread_t xtd;
991 thread_t td;
992 int save_gd_intr_nesting_level;
993
994 /*
995 * The caller has put us in a critical section. We can only preempt
996 * if the caller of the caller was not in a critical section (basically
997 * a local interrupt), as determined by the 'critcount' parameter. We
998 * also can't preempt if the caller is holding any spinlocks (even if
999 * he isn't in a critical section). This also handles the tokens test.
1000 *
1001 * YYY The target thread must be in a critical section (else it must
1002 * inherit our critical section? I dunno yet).
1003 */
1004 KASSERT(ntd->td_critcount, ("BADCRIT0 %d", ntd->td_pri));
1005
1006 td = gd->gd_curthread;
1007 if (preempt_enable == 0) {
1008 ++preempt_miss;
1009 return;
1010 }
1011 if (ntd->td_pri <= td->td_pri) {
1012 ++preempt_miss;
1013 return;
1014 }
1015 if (td->td_critcount > critcount) {
1016 ++preempt_miss;
1017 return;
1018 }
1019 if (td->td_cscount) {
1020 ++preempt_miss;
1021 return;
1022 }
1023 if (ntd->td_gd != gd) {
1024 ++preempt_miss;
1025 return;
1026 }
1027 /*
1028 * We don't have to check spinlocks here as they will also bump
1029 * td_critcount.
1030 *
1031 * Do not try to preempt if the target thread is holding any tokens.
1032 * We could try to acquire the tokens but this case is so rare there
1033 * is no need to support it.
1034 */
1035 KKASSERT(gd->gd_spinlocks == 0);
1036
1037 if (TD_TOKS_HELD(ntd)) {
1038 ++preempt_miss;
1039 return;
1040 }
1041 if (td == ntd || ((td->td_flags | ntd->td_flags) & TDF_PREEMPT_LOCK)) {
1042 ++preempt_weird;
1043 return;
1044 }
1045 if (ntd->td_preempted) {
1046 ++preempt_hit;
1047 return;
1048 }
1049 KKASSERT(gd->gd_processing_ipiq == 0);
1050
1051 /*
1052 * Since we are able to preempt the current thread, there is no need to
1053 * call need_lwkt_resched().
1054 *
1055 * We must temporarily clear gd_intr_nesting_level around the switch
1056 * since switchouts from the target thread are allowed (they will just
1057 * return to our thread), and since the target thread has its own stack.
1058 *
1059 * A preemption must switch back to the original thread, assert the
1060 * case.
1061 */
1062 ++preempt_hit;
1063 ntd->td_preempted = td;
1064 td->td_flags |= TDF_PREEMPT_LOCK;
1065 KTR_LOG(ctxsw_pre, gd->gd_cpuid, ntd);
1066 save_gd_intr_nesting_level = gd->gd_intr_nesting_level;
1067 gd->gd_intr_nesting_level = 0;
1068
1069 KKASSERT((ntd->td_flags & TDF_RUNNING) == 0);
1070 ntd->td_flags |= TDF_RUNNING;
1071 xtd = td->td_switch(ntd);
1072 KKASSERT(xtd == ntd);
1073 lwkt_switch_return(xtd);
1074 gd->gd_intr_nesting_level = save_gd_intr_nesting_level;
1075
1076 KKASSERT(ntd->td_preempted && (td->td_flags & TDF_PREEMPT_DONE));
1077 ntd->td_preempted = NULL;
1078 td->td_flags &= ~(TDF_PREEMPT_LOCK|TDF_PREEMPT_DONE);
1079 }
1080
1081 /*
1082 * Conditionally call splz() if gd_reqflags indicates work is pending.
1083 * This will work inside a critical section but not inside a hard code
1084 * section.
1085 *
1086 * (self contained on a per cpu basis)
1087 */
1088 void
1089 splz_check(void)
1090 {
1091 globaldata_t gd = mycpu;
1092 thread_t td = gd->gd_curthread;
1093
1094 if ((gd->gd_reqflags & RQF_IDLECHECK_MASK) &&
1095 gd->gd_intr_nesting_level == 0 &&
1096 td->td_nest_count < 2)
1097 {
1098 splz();
1099 }
1100 }
1101
1102 /*
1103 * This version is integrated into crit_exit, reqflags has already
1104 * been tested but td_critcount has not.
1105 *
1106 * We only want to execute the splz() on the 1->0 transition of
1107 * critcount and not in a hard code section or if too deeply nested.
1108 *
1109 * NOTE: gd->gd_spinlocks is implied to be 0 when td_critcount is 0.
1110 */
1111 void
1112 lwkt_maybe_splz(thread_t td)
1113 {
1114 globaldata_t gd = td->td_gd;
1115
1116 if (td->td_critcount == 0 &&
1117 gd->gd_intr_nesting_level == 0 &&
1118 td->td_nest_count < 2)
1119 {
1120 splz();
1121 }
1122 }
1123
1124 /*
1125 * Drivers which set up processing co-threads can call this function to
1126 * run the co-thread at a higher priority and to allow it to preempt
1127 * normal threads.
1128 */
1129 void
1130 lwkt_set_interrupt_support_thread(void)
1131 {
1132 thread_t td = curthread;
1133
1134 lwkt_setpri_self(TDPRI_INT_SUPPORT);
1135 td->td_flags |= TDF_INTTHREAD;
1136 td->td_preemptable = lwkt_preempt;
1137 }
1138
1139
1140 /*
1141 * This function is used to negotiate a passive release of the current
1142 * process/lwp designation with the user scheduler, allowing the user
1143 * scheduler to schedule another user thread. The related kernel thread
1144 * (curthread) continues running in the released state.
1145 */
1146 void
1147 lwkt_passive_release(struct thread *td)
1148 {
1149 struct lwp *lp = td->td_lwp;
1150
1151 #ifndef NO_LWKT_SPLIT_USERPRI
1152 td->td_release = NULL;
1153 lwkt_setpri_self(TDPRI_KERN_USER);
1154 #endif
1155
1156 lp->lwp_proc->p_usched->release_curproc(lp);
1157 }
1158
1159
1160 /*
1161 * This implements a LWKT yield, allowing a kernel thread to yield to other
1162 * kernel threads at the same or higher priority. This function can be
1163 * called in a tight loop and will typically only yield once per tick.
1164 *
1165 * Most kernel threads run at the same priority in order to allow equal
1166 * sharing.
1167 *
1168 * (self contained on a per cpu basis)
1169 */
1170 void
1171 lwkt_yield(void)
1172 {
1173 globaldata_t gd = mycpu;
1174 thread_t td = gd->gd_curthread;
1175
1176 if ((gd->gd_reqflags & RQF_IDLECHECK_MASK) && td->td_nest_count < 2)
1177 splz();
1178 if (lwkt_resched_wanted()) {
1179 lwkt_schedule_self(curthread);
1180 lwkt_switch();
1181 }
1182 }
1183
1184 /*
1185 * The quick version processes pending interrupts and higher-priority
1186 * LWKT threads but will not round-robin same-priority LWKT threads.
1187 *
1188 * When called while attempting to return to userland the only same-pri
1189 * threads are the ones which have already tried to become the current
1190 * user process.
1191 */
1192 void
1193 lwkt_yield_quick(void)
1194 {
1195 globaldata_t gd = mycpu;
1196 thread_t td = gd->gd_curthread;
1197
1198 if ((gd->gd_reqflags & RQF_IDLECHECK_MASK) && td->td_nest_count < 2)
1199 splz();
1200 if (lwkt_resched_wanted()) {
1201 crit_enter();
1202 if (TAILQ_FIRST(&gd->gd_tdrunq) == td) {
1203 clear_lwkt_resched();
1204 } else {
1205 lwkt_schedule_self(curthread);
1206 lwkt_switch();
1207 }
1208 crit_exit();
1209 }
1210 }
1211
1212 /*
1213 * This yield is designed for kernel threads with a user context.
1214 *
1215 * The kernel acting on behalf of the user is potentially cpu-bound,
1216 * this function will efficiently allow other threads to run and also
1217 * switch to other processes by releasing.
1218 *
1219 * The lwkt_user_yield() function is designed to have very low overhead
1220 * if no yield is determined to be needed.
1221 */
1222 void
1223 lwkt_user_yield(void)
1224 {
1225 globaldata_t gd = mycpu;
1226 thread_t td = gd->gd_curthread;
1227
1228 /*
1229 * Always run any pending interrupts in case we are in a critical
1230 * section.
1231 */
1232 if ((gd->gd_reqflags & RQF_IDLECHECK_MASK) && td->td_nest_count < 2)
1233 splz();
1234
1235 /*
1236 * Switch (which forces a release) if another kernel thread needs
1237 * the cpu, if userland wants us to resched, or if our kernel
1238 * quantum has run out.
1239 */
1240 if (lwkt_resched_wanted() ||
1241 user_resched_wanted())
1242 {
1243 lwkt_switch();
1244 }
1245
1246 #if 0
1247 /*
1248 * Reacquire the current process if we are released.
1249 *
1250 * XXX not implemented atm. The kernel may be holding locks and such,
1251 * so we want the thread to continue to receive cpu.
1252 */
1253 if (td->td_release == NULL && lp) {
1254 lp->lwp_proc->p_usched->acquire_curproc(lp);
1255 td->td_release = lwkt_passive_release;
1256 lwkt_setpri_self(TDPRI_USER_NORM);
1257 }
1258 #endif
1259 }
1260
1261 /*
1262 * Generic schedule. Possibly schedule threads belonging to other cpus and
1263 * deal with threads that might be blocked on a wait queue.
1264 *
1265 * We have a little helper inline function which does additional work after
1266 * the thread has been enqueued, including dealing with preemption and
1267 * setting need_lwkt_resched() (which prevents the kernel from returning
1268 * to userland until it has processed higher priority threads).
1269 *
1270 * It is possible for this routine to be called after a failed _enqueue
1271 * (due to the target thread migrating, sleeping, or otherwise blocked).
1272 * We have to check that the thread is actually on the run queue!
1273 */
1274 static __inline
1275 void
1276 _lwkt_schedule_post(globaldata_t gd, thread_t ntd, int ccount)
1277 {
1278 if (ntd->td_flags & TDF_RUNQ) {
1279 if (ntd->td_preemptable) {
1280 ntd->td_preemptable(ntd, ccount); /* YYY +token */
1281 }
1282 }
1283 }
1284
1285 static __inline
1286 void
1287 _lwkt_schedule(thread_t td)
1288 {
1289 globaldata_t mygd = mycpu;
1290
1291 KASSERT(td != &td->td_gd->gd_idlethread,
1292 ("lwkt_schedule(): scheduling gd_idlethread is illegal!"));
1293 KKASSERT((td->td_flags & TDF_MIGRATING) == 0);
1294 crit_enter_gd(mygd);
1295 KKASSERT(td->td_lwp == NULL ||
1296 (td->td_lwp->lwp_mpflags & LWP_MP_ONRUNQ) == 0);
1297
1298 if (td == mygd->gd_curthread) {
1299 _lwkt_enqueue(td);
1300 } else {
1301 /*
1302 * If we own the thread, there is no race (since we are in a
1303 * critical section). If we do not own the thread there might
1304 * be a race but the target cpu will deal with it.
1305 */
1306 if (td->td_gd == mygd) {
1307 _lwkt_enqueue(td);
1308 _lwkt_schedule_post(mygd, td, 1);
1309 } else {
1310 lwkt_send_ipiq3(td->td_gd, lwkt_schedule_remote, td, 0);
1311 }
1312 }
1313 crit_exit_gd(mygd);
1314 }
1315
1316 void
1317 lwkt_schedule(thread_t td)
1318 {
1319 _lwkt_schedule(td);
1320 }
1321
1322 void
1323 lwkt_schedule_noresched(thread_t td) /* XXX not impl */
1324 {
1325 _lwkt_schedule(td);
1326 }
1327
1328 /*
1329 * When scheduled remotely if frame != NULL the IPIQ is being
1330 * run via doreti or an interrupt then preemption can be allowed.
1331 *
1332 * To allow preemption we have to drop the critical section so only
1333 * one is present in _lwkt_schedule_post.
1334 */
1335 static void
1336 lwkt_schedule_remote(void *arg, int arg2, struct intrframe *frame)
1337 {
1338 thread_t td = curthread;
1339 thread_t ntd = arg;
1340
1341 if (frame && ntd->td_preemptable) {
1342 crit_exit_noyield(td);
1343 _lwkt_schedule(ntd);
1344 crit_enter_quick(td);
1345 } else {
1346 _lwkt_schedule(ntd);
1347 }
1348 }
1349
1350 /*
1351 * Thread migration using a 'Pull' method. The thread may or may not be
1352 * the current thread. It MUST be descheduled and in a stable state.
1353 * lwkt_giveaway() must be called on the cpu owning the thread.
1354 *
1355 * At any point after lwkt_giveaway() is called, the target cpu may
1356 * 'pull' the thread by calling lwkt_acquire().
1357 *
1358 * We have to make sure the thread is not sitting on a per-cpu tsleep
1359 * queue or it will blow up when it moves to another cpu.
1360 *
1361 * MPSAFE - must be called under very specific conditions.
1362 */
1363 void
1364 lwkt_giveaway(thread_t td)
1365 {
1366 globaldata_t gd = mycpu;
1367
1368 crit_enter_gd(gd);
1369 if (td->td_flags & TDF_TSLEEPQ)
1370 tsleep_remove(td);
1371 KKASSERT(td->td_gd == gd);
1372 TAILQ_REMOVE(&gd->gd_tdallq, td, td_allq);
1373 td->td_flags |= TDF_MIGRATING;
1374 crit_exit_gd(gd);
1375 }
1376
1377 void
1378 lwkt_acquire(thread_t td)
1379 {
1380 globaldata_t gd;
1381 globaldata_t mygd;
1382 int retry = 10000000;
1383
1384 KKASSERT(td->td_flags & TDF_MIGRATING);
1385 gd = td->td_gd;
1386 mygd = mycpu;
1387 if (gd != mycpu) {
1388 cpu_lfence();
1389 KKASSERT((td->td_flags & TDF_RUNQ) == 0);
1390 crit_enter_gd(mygd);
1391 DEBUG_PUSH_INFO("lwkt_acquire");
1392 while (td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK)) {
1393 lwkt_process_ipiq();
1394 cpu_lfence();
1395 if (--retry == 0) {
1396 kprintf("lwkt_acquire: stuck: td %p td->td_flags %08x\n",
1397 td, td->td_flags);
1398 retry = 10000000;
1399 }
1400 #ifdef _KERNEL_VIRTUAL
1401 pthread_yield();
1402 #endif
1403 }
1404 DEBUG_POP_INFO();
1405 cpu_mfence();
1406 td->td_gd = mygd;
1407 TAILQ_INSERT_TAIL(&mygd->gd_tdallq, td, td_allq);
1408 td->td_flags &= ~TDF_MIGRATING;
1409 crit_exit_gd(mygd);
1410 } else {
1411 crit_enter_gd(mygd);
1412 TAILQ_INSERT_TAIL(&mygd->gd_tdallq, td, td_allq);
1413 td->td_flags &= ~TDF_MIGRATING;
1414 crit_exit_gd(mygd);
1415 }
1416 }
1417
1418 /*
1419 * Generic deschedule. Descheduling threads other then your own should be
1420 * done only in carefully controlled circumstances. Descheduling is
1421 * asynchronous.
1422 *
1423 * This function may block if the cpu has run out of messages.
1424 */
1425 void
1426 lwkt_deschedule(thread_t td)
1427 {
1428 crit_enter();
1429 if (td == curthread) {
1430 _lwkt_dequeue(td);
1431 } else {
1432 if (td->td_gd == mycpu) {
1433 _lwkt_dequeue(td);
1434 } else {
1435 lwkt_send_ipiq(td->td_gd, (ipifunc1_t)lwkt_deschedule, td);
1436 }
1437 }
1438 crit_exit();
1439 }
1440
1441 /*
1442 * Set the target thread's priority. This routine does not automatically
1443 * switch to a higher priority thread, LWKT threads are not designed for
1444 * continuous priority changes. Yield if you want to switch.
1445 */
1446 void
1447 lwkt_setpri(thread_t td, int pri)
1448 {
1449 if (td->td_pri != pri) {
1450 KKASSERT(pri >= 0);
1451 crit_enter();
1452 if (td->td_flags & TDF_RUNQ) {
1453 KKASSERT(td->td_gd == mycpu);
1454 _lwkt_dequeue(td);
1455 td->td_pri = pri;
1456 _lwkt_enqueue(td);
1457 } else {
1458 td->td_pri = pri;
1459 }
1460 crit_exit();
1461 }
1462 }
1463
1464 /*
1465 * Set the initial priority for a thread prior to it being scheduled for
1466 * the first time. The thread MUST NOT be scheduled before or during
1467 * this call. The thread may be assigned to a cpu other then the current
1468 * cpu.
1469 *
1470 * Typically used after a thread has been created with TDF_STOPPREQ,
1471 * and before the thread is initially scheduled.
1472 */
1473 void
1474 lwkt_setpri_initial(thread_t td, int pri)
1475 {
1476 KKASSERT(pri >= 0);
1477 KKASSERT((td->td_flags & TDF_RUNQ) == 0);
1478 td->td_pri = pri;
1479 }
1480
1481 void
1482 lwkt_setpri_self(int pri)
1483 {
1484 thread_t td = curthread;
1485
1486 KKASSERT(pri >= 0 && pri <= TDPRI_MAX);
1487 crit_enter();
1488 if (td->td_flags & TDF_RUNQ) {
1489 _lwkt_dequeue(td);
1490 td->td_pri = pri;
1491 _lwkt_enqueue(td);
1492 } else {
1493 td->td_pri = pri;
1494 }
1495 crit_exit();
1496 }
1497
1498 /*
1499 * hz tick scheduler clock for LWKT threads
1500 */
1501 void
1502 lwkt_schedulerclock(thread_t td)
1503 {
1504 globaldata_t gd = td->td_gd;
1505 thread_t xtd;
1506
1507 if (TAILQ_FIRST(&gd->gd_tdrunq) == td) {
1508 /*
1509 * If the current thread is at the head of the runq shift it to the
1510 * end of any equal-priority threads and request a LWKT reschedule
1511 * if it moved.
1512 *
1513 * Ignore upri in this situation. There will only be one user thread
1514 * in user mode, all others will be user threads running in kernel
1515 * mode and we have to make sure they get some cpu.
1516 */
1517 xtd = TAILQ_NEXT(td, td_threadq);
1518 if (xtd && xtd->td_pri == td->td_pri) {
1519 TAILQ_REMOVE(&gd->gd_tdrunq, td, td_threadq);
1520 while (xtd && xtd->td_pri == td->td_pri)
1521 xtd = TAILQ_NEXT(xtd, td_threadq);
1522 if (xtd)
1523 TAILQ_INSERT_BEFORE(xtd, td, td_threadq);
1524 else
1525 TAILQ_INSERT_TAIL(&gd->gd_tdrunq, td, td_threadq);
1526 need_lwkt_resched();
1527 }
1528 } else {
1529 /*
1530 * If we scheduled a thread other than the one at the head of the
1531 * queue always request a reschedule every tick.
1532 */
1533 need_lwkt_resched();
1534 }
1535 }
1536
1537 /*
1538 * Migrate the current thread to the specified cpu.
1539 *
1540 * This is accomplished by descheduling ourselves from the current cpu
1541 * and setting td_migrate_gd. The lwkt_switch() code will detect that the
1542 * 'old' thread wants to migrate after it has been completely switched out
1543 * and will complete the migration.
1544 *
1545 * TDF_MIGRATING prevents scheduling races while the thread is being migrated.
1546 *
1547 * We must be sure to release our current process designation (if a user
1548 * process) before clearing out any tsleepq we are on because the release
1549 * code may re-add us.
1550 *
1551 * We must be sure to remove ourselves from the current cpu's tsleepq
1552 * before potentially moving to another queue. The thread can be on
1553 * a tsleepq due to a left-over tsleep_interlock().
1554 */
1555
1556 void
1557 lwkt_setcpu_self(globaldata_t rgd)
1558 {
1559 thread_t td = curthread;
1560
1561 if (td->td_gd != rgd) {
1562 crit_enter_quick(td);
1563
1564 if (td->td_release)
1565 td->td_release(td);
1566 if (td->td_flags & TDF_TSLEEPQ)
1567 tsleep_remove(td);
1568
1569 /*
1570 * Set TDF_MIGRATING to prevent a spurious reschedule while we are
1571 * trying to deschedule ourselves and switch away, then deschedule
1572 * ourself, remove us from tdallq, and set td_migrate_gd. Finally,
1573 * call lwkt_switch() to complete the operation.
1574 */
1575 td->td_flags |= TDF_MIGRATING;
1576 lwkt_deschedule_self(td);
1577 TAILQ_REMOVE(&td->td_gd->gd_tdallq, td, td_allq);
1578 td->td_migrate_gd = rgd;
1579 lwkt_switch();
1580
1581 /*
1582 * We are now on the target cpu
1583 */
1584 KKASSERT(rgd == mycpu);
1585 TAILQ_INSERT_TAIL(&rgd->gd_tdallq, td, td_allq);
1586 crit_exit_quick(td);
1587 }
1588 }
1589
1590 void
1591 lwkt_migratecpu(int cpuid)
1592 {
1593 globaldata_t rgd;
1594
1595 rgd = globaldata_find(cpuid);
1596 lwkt_setcpu_self(rgd);
1597 }
1598
1599 /*
1600 * Remote IPI for cpu migration (called while in a critical section so we
1601 * do not have to enter another one).
1602 *
1603 * The thread (td) has already been completely descheduled from the
1604 * originating cpu and we can simply assert the case. The thread is
1605 * assigned to the new cpu and enqueued.
1606 *
1607 * The thread will re-add itself to tdallq when it resumes execution.
1608 */
1609 static void
1610 lwkt_setcpu_remote(void *arg)
1611 {
1612 thread_t td = arg;
1613 globaldata_t gd = mycpu;
1614
1615 KKASSERT((td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK)) == 0);
1616 td->td_gd = gd;
1617 cpu_mfence();
1618 td->td_flags &= ~TDF_MIGRATING;
1619 KKASSERT(td->td_migrate_gd == NULL);
1620 KKASSERT(td->td_lwp == NULL ||
1621 (td->td_lwp->lwp_mpflags & LWP_MP_ONRUNQ) == 0);
1622 _lwkt_enqueue(td);
1623 }
1624
1625 struct lwp *
1626 lwkt_preempted_proc(void)
1627 {
1628 thread_t td = curthread;
1629 while (td->td_preempted)
1630 td = td->td_preempted;
1631 return(td->td_lwp);
1632 }
1633
1634 /*
1635 * Create a kernel process/thread/whatever. It shares it's address space
1636 * with proc0 - ie: kernel only.
1637 *
1638 * If the cpu is not specified one will be selected. In the future
1639 * specifying a cpu of -1 will enable kernel thread migration between
1640 * cpus.
1641 */
1642 int
1643 lwkt_create(void (*func)(void *), void *arg, struct thread **tdp,
1644 thread_t template, int tdflags, int cpu, const char *fmt, ...)
1645 {
1646 thread_t td;
1647 __va_list ap;
1648
1649 td = lwkt_alloc_thread(template, LWKT_THREAD_STACK, cpu,
1650 tdflags);
1651 if (tdp)
1652 *tdp = td;
1653 cpu_set_thread_handler(td, lwkt_exit, func, arg);
1654
1655 /*
1656 * Set up arg0 for 'ps' etc
1657 */
1658 __va_start(ap, fmt);
1659 kvsnprintf(td->td_comm, sizeof(td->td_comm), fmt, ap);
1660 __va_end(ap);
1661
1662 /*
1663 * Schedule the thread to run
1664 */
1665 if (td->td_flags & TDF_NOSTART)
1666 td->td_flags &= ~TDF_NOSTART;
1667 else
1668 lwkt_schedule(td);
1669 return 0;
1670 }
1671
1672 /*
1673 * Destroy an LWKT thread. Warning! This function is not called when
1674 * a process exits, cpu_proc_exit() directly calls cpu_thread_exit() and
1675 * uses a different reaping mechanism.
1676 */
1677 void
1678 lwkt_exit(void)
1679 {
1680 thread_t td = curthread;
1681 thread_t std;
1682 globaldata_t gd;
1683
1684 /*
1685 * Do any cleanup that might block here
1686 */
1687 if (td->td_flags & TDF_VERBOSE)
1688 kprintf("kthread %p %s has exited\n", td, td->td_comm);
1689 biosched_done(td);
1690 dsched_exit_thread(td);
1691
1692 /*
1693 * Get us into a critical section to interlock gd_freetd and loop
1694 * until we can get it freed.
1695 *
1696 * We have to cache the current td in gd_freetd because objcache_put()ing
1697 * it would rip it out from under us while our thread is still active.
1698 *
1699 * We are the current thread so of course our own TDF_RUNNING bit will
1700 * be set, so unlike the lwp reap code we don't wait for it to clear.
1701 */
1702 gd = mycpu;
1703 crit_enter_quick(td);
1704 for (;;) {
1705 if (td->td_refs) {
1706 tsleep(td, 0, "tdreap", 1);
1707 continue;
1708 }
1709 if ((std = gd->gd_freetd) != NULL) {
1710 KKASSERT((std->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK)) == 0);
1711 gd->gd_freetd = NULL;
1712 objcache_put(thread_cache, std);
1713 continue;
1714 }
1715 break;
1716 }
1717
1718 /*
1719 * Remove thread resources from kernel lists and deschedule us for
1720 * the last time. We cannot block after this point or we may end
1721 * up with a stale td on the tsleepq.
1722 *
1723 * None of this may block, the critical section is the only thing
1724 * protecting tdallq and the only thing preventing new lwkt_hold()
1725 * thread refs now.
1726 */
1727 if (td->td_flags & TDF_TSLEEPQ)
1728 tsleep_remove(td);
1729 lwkt_deschedule_self(td);
1730 lwkt_remove_tdallq(td);
1731 KKASSERT(td->td_refs == 0);
1732
1733 /*
1734 * Final cleanup
1735 */
1736 KKASSERT(gd->gd_freetd == NULL);
1737 if (td->td_flags & TDF_ALLOCATED_THREAD)
1738 gd->gd_freetd = td;
1739 cpu_thread_exit();
1740 }
1741
1742 void
1743 lwkt_remove_tdallq(thread_t td)
1744 {
1745 KKASSERT(td->td_gd == mycpu);
1746 TAILQ_REMOVE(&td->td_gd->gd_tdallq, td, td_allq);
1747 }
1748
1749 /*
1750 * Code reduction and branch prediction improvements. Call/return
1751 * overhead on modern cpus often degenerates into 0 cycles due to
1752 * the cpu's branch prediction hardware and return pc cache. We
1753 * can take advantage of this by not inlining medium-complexity
1754 * functions and we can also reduce the branch prediction impact
1755 * by collapsing perfectly predictable branches into a single
1756 * procedure instead of duplicating it.
1757 *
1758 * Is any of this noticeable? Probably not, so I'll take the
1759 * smaller code size.
1760 */
1761 void
1762 crit_exit_wrapper(__DEBUG_CRIT_ARG__)
1763 {
1764 _crit_exit(mycpu __DEBUG_CRIT_PASS_ARG__);
1765 }
1766
1767 void
1768 crit_panic(void)
1769 {
1770 thread_t td = curthread;
1771 int lcrit = td->td_critcount;
1772
1773 td->td_critcount = 0;
1774 panic("td_critcount is/would-go negative! %p %d", td, lcrit);
1775 /* NOT REACHED */
1776 }
1777
1778 /*
1779 * Called from debugger/panic on cpus which have been stopped. We must still
1780 * process the IPIQ while stopped, even if we were stopped while in a critical
1781 * section (XXX).
1782 *
1783 * If we are dumping also try to process any pending interrupts. This may
1784 * or may not work depending on the state of the cpu at the point it was
1785 * stopped.
1786 */
1787 void
1788 lwkt_smp_stopped(void)
1789 {
1790 globaldata_t gd = mycpu;
1791
1792 crit_enter_gd(gd);
1793 if (dumping) {
1794 lwkt_process_ipiq();
1795 splz();
1796 } else {
1797 lwkt_process_ipiq();
1798 }
1799 crit_exit_gd(gd);
1800 }
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