2 * Copyright (c) 2003-2011 The DragonFly Project. All rights reserved.
4 * This code is derived from software contributed to The DragonFly Project
5 * by Matthew Dillon <dillon@backplane.com>
7 * Redistribution and use in source and binary forms, with or without
8 * modification, are permitted provided that the following conditions
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
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.
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
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.
42 #include <sys/param.h>
43 #include <sys/systm.h>
44 #include <sys/kernel.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>
54 #include <sys/spinlock.h>
57 #include <sys/thread2.h>
58 #include <sys/spinlock2.h>
59 #include <sys/mplock2.h>
61 #include <sys/dsched.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>
72 #include <machine/stdarg.h>
73 #include <machine/smp.h>
75 #if !defined(KTR_CTXSW)
76 #define KTR_CTXSW KTR_ALL
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 *));
87 static MALLOC_DEFINE(M_THREAD, "thread", "lwkt threads");
90 static int panic_on_cscount = 0;
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[TDPRI_MAX+1] __debugvar;
97 static int lwkt_use_spin_port;
98 static struct objcache *thread_cache;
101 static void lwkt_schedule_remote(void *arg, int arg2, struct intrframe *frame);
102 static void lwkt_setcpu_remote(void *arg);
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);
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.
114 TUNABLE_INT("lwkt.use_spin_port", &lwkt_use_spin_port);
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");
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.");
129 SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count_00, CTLFLAG_RW,
130 &token_contention_count[0], 0, "spinning due to token contention");
131 SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count_01, CTLFLAG_RW,
132 &token_contention_count[1], 0, "spinning due to token contention");
133 SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count_02, CTLFLAG_RW,
134 &token_contention_count[2], 0, "spinning due to token contention");
135 SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count_03, CTLFLAG_RW,
136 &token_contention_count[3], 0, "spinning due to token contention");
137 SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count_04, CTLFLAG_RW,
138 &token_contention_count[4], 0, "spinning due to token contention");
139 SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count_05, CTLFLAG_RW,
140 &token_contention_count[5], 0, "spinning due to token contention");
141 SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count_06, CTLFLAG_RW,
142 &token_contention_count[6], 0, "spinning due to token contention");
143 SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count_07, CTLFLAG_RW,
144 &token_contention_count[7], 0, "spinning due to token contention");
145 SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count_08, CTLFLAG_RW,
146 &token_contention_count[8], 0, "spinning due to token contention");
147 SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count_09, CTLFLAG_RW,
148 &token_contention_count[9], 0, "spinning due to token contention");
149 SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count_10, CTLFLAG_RW,
150 &token_contention_count[10], 0, "spinning due to token contention");
151 SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count_11, CTLFLAG_RW,
152 &token_contention_count[11], 0, "spinning due to token contention");
153 SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count_12, CTLFLAG_RW,
154 &token_contention_count[12], 0, "spinning due to token contention");
155 SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count_13, CTLFLAG_RW,
156 &token_contention_count[13], 0, "spinning due to token contention");
157 SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count_14, CTLFLAG_RW,
158 &token_contention_count[14], 0, "spinning due to token contention");
159 SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count_15, CTLFLAG_RW,
160 &token_contention_count[15], 0, "spinning due to token contention");
161 SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count_16, CTLFLAG_RW,
162 &token_contention_count[16], 0, "spinning due to token contention");
163 SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count_17, CTLFLAG_RW,
164 &token_contention_count[17], 0, "spinning due to token contention");
165 SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count_18, CTLFLAG_RW,
166 &token_contention_count[18], 0, "spinning due to token contention");
167 SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count_19, CTLFLAG_RW,
168 &token_contention_count[19], 0, "spinning due to token contention");
169 SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count_20, CTLFLAG_RW,
170 &token_contention_count[20], 0, "spinning due to token contention");
171 SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count_21, CTLFLAG_RW,
172 &token_contention_count[21], 0, "spinning due to token contention");
173 SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count_22, CTLFLAG_RW,
174 &token_contention_count[22], 0, "spinning due to token contention");
175 SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count_23, CTLFLAG_RW,
176 &token_contention_count[23], 0, "spinning due to token contention");
177 SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count_24, CTLFLAG_RW,
178 &token_contention_count[24], 0, "spinning due to token contention");
179 SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count_25, CTLFLAG_RW,
180 &token_contention_count[25], 0, "spinning due to token contention");
181 SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count_26, CTLFLAG_RW,
182 &token_contention_count[26], 0, "spinning due to token contention");
183 SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count_27, CTLFLAG_RW,
184 &token_contention_count[27], 0, "spinning due to token contention");
185 SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count_28, CTLFLAG_RW,
186 &token_contention_count[28], 0, "spinning due to token contention");
187 SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count_29, CTLFLAG_RW,
188 &token_contention_count[29], 0, "spinning due to token contention");
189 SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count_30, CTLFLAG_RW,
190 &token_contention_count[30], 0, "spinning due to token contention");
191 SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count_31, CTLFLAG_RW,
192 &token_contention_count[31], 0, "spinning due to token contention");
194 static int fairq_enable = 0;
195 SYSCTL_INT(_lwkt, OID_AUTO, fairq_enable, CTLFLAG_RW,
196 &fairq_enable, 0, "Turn on fairq priority accumulators");
197 static int fairq_bypass = -1;
198 SYSCTL_INT(_lwkt, OID_AUTO, fairq_bypass, CTLFLAG_RW,
199 &fairq_bypass, 0, "Allow fairq to bypass td on token failure");
200 extern int lwkt_sched_debug;
201 int lwkt_sched_debug = 0;
202 SYSCTL_INT(_lwkt, OID_AUTO, sched_debug, CTLFLAG_RW,
203 &lwkt_sched_debug, 0, "Scheduler debug");
204 static int lwkt_spin_loops = 10;
205 SYSCTL_INT(_lwkt, OID_AUTO, spin_loops, CTLFLAG_RW,
206 &lwkt_spin_loops, 0, "Scheduler spin loops until sorted decon");
207 static int lwkt_spin_reseq = 0;
208 SYSCTL_INT(_lwkt, OID_AUTO, spin_reseq, CTLFLAG_RW,
209 &lwkt_spin_reseq, 0, "Scheduler resequencer enable");
210 static int lwkt_spin_monitor = 0;
211 SYSCTL_INT(_lwkt, OID_AUTO, spin_monitor, CTLFLAG_RW,
212 &lwkt_spin_monitor, 0, "Scheduler uses monitor/mwait");
213 static int lwkt_spin_fatal = 0; /* disabled */
214 SYSCTL_INT(_lwkt, OID_AUTO, spin_fatal, CTLFLAG_RW,
215 &lwkt_spin_fatal, 0, "LWKT scheduler spin loops till fatal panic");
216 static int preempt_enable = 1;
217 SYSCTL_INT(_lwkt, OID_AUTO, preempt_enable, CTLFLAG_RW,
218 &preempt_enable, 0, "Enable preemption");
219 static int lwkt_cache_threads = 32;
220 SYSCTL_INT(_lwkt, OID_AUTO, cache_threads, CTLFLAG_RD,
221 &lwkt_cache_threads, 0, "thread+kstack cache");
223 static __cachealign int lwkt_cseq_rindex;
224 static __cachealign int lwkt_cseq_windex;
227 * These helper procedures handle the runq, they can only be called from
228 * within a critical section.
230 * WARNING! Prior to SMP being brought up it is possible to enqueue and
231 * dequeue threads belonging to other cpus, so be sure to use td->td_gd
232 * instead of 'mycpu' when referencing the globaldata structure. Once
233 * SMP live enqueuing and dequeueing only occurs on the current cpu.
237 _lwkt_dequeue(thread_t td)
239 if (td->td_flags & TDF_RUNQ) {
240 struct globaldata *gd = td->td_gd;
242 td->td_flags &= ~TDF_RUNQ;
243 TAILQ_REMOVE(&gd->gd_tdrunq, td, td_threadq);
244 if (TAILQ_FIRST(&gd->gd_tdrunq) == NULL)
245 atomic_clear_int(&gd->gd_reqflags, RQF_RUNNING);
252 * NOTE: There are a limited number of lwkt threads runnable since user
253 * processes only schedule one at a time per cpu.
257 _lwkt_enqueue(thread_t td)
261 if ((td->td_flags & (TDF_RUNQ|TDF_MIGRATING|TDF_BLOCKQ)) == 0) {
262 struct globaldata *gd = td->td_gd;
264 td->td_flags |= TDF_RUNQ;
265 xtd = TAILQ_FIRST(&gd->gd_tdrunq);
267 TAILQ_INSERT_TAIL(&gd->gd_tdrunq, td, td_threadq);
268 atomic_set_int(&gd->gd_reqflags, RQF_RUNNING);
270 while (xtd && xtd->td_pri >= td->td_pri)
271 xtd = TAILQ_NEXT(xtd, td_threadq);
273 TAILQ_INSERT_BEFORE(xtd, td, td_threadq);
275 TAILQ_INSERT_TAIL(&gd->gd_tdrunq, td, td_threadq);
279 * Request a LWKT reschedule if we are now at the head of the queue.
281 if (TAILQ_FIRST(&gd->gd_tdrunq) == td)
287 _lwkt_thread_ctor(void *obj, void *privdata, int ocflags)
289 struct thread *td = (struct thread *)obj;
291 td->td_kstack = NULL;
292 td->td_kstack_size = 0;
293 td->td_flags = TDF_ALLOCATED_THREAD;
298 _lwkt_thread_dtor(void *obj, void *privdata)
300 struct thread *td = (struct thread *)obj;
302 KASSERT(td->td_flags & TDF_ALLOCATED_THREAD,
303 ("_lwkt_thread_dtor: not allocated from objcache"));
304 KASSERT((td->td_flags & TDF_ALLOCATED_STACK) && td->td_kstack &&
305 td->td_kstack_size > 0,
306 ("_lwkt_thread_dtor: corrupted stack"));
307 kmem_free(&kernel_map, (vm_offset_t)td->td_kstack, td->td_kstack_size);
311 * Initialize the lwkt s/system.
313 * Nominally cache up to 32 thread + kstack structures.
318 TUNABLE_INT("lwkt.cache_threads", &lwkt_cache_threads);
319 thread_cache = objcache_create_mbacked(
320 M_THREAD, sizeof(struct thread),
321 NULL, lwkt_cache_threads,
322 _lwkt_thread_ctor, _lwkt_thread_dtor, NULL);
326 * Schedule a thread to run. As the current thread we can always safely
327 * schedule ourselves, and a shortcut procedure is provided for that
330 * (non-blocking, self contained on a per cpu basis)
333 lwkt_schedule_self(thread_t td)
335 KKASSERT((td->td_flags & TDF_MIGRATING) == 0);
336 crit_enter_quick(td);
337 KASSERT(td != &td->td_gd->gd_idlethread,
338 ("lwkt_schedule_self(): scheduling gd_idlethread is illegal!"));
339 KKASSERT(td->td_lwp == NULL || (td->td_lwp->lwp_flag & LWP_ONRUNQ) == 0);
345 * Deschedule a thread.
347 * (non-blocking, self contained on a per cpu basis)
350 lwkt_deschedule_self(thread_t td)
352 crit_enter_quick(td);
358 * LWKTs operate on a per-cpu basis
360 * WARNING! Called from early boot, 'mycpu' may not work yet.
363 lwkt_gdinit(struct globaldata *gd)
365 TAILQ_INIT(&gd->gd_tdrunq);
366 TAILQ_INIT(&gd->gd_tdallq);
370 * Create a new thread. The thread must be associated with a process context
371 * or LWKT start address before it can be scheduled. If the target cpu is
372 * -1 the thread will be created on the current cpu.
374 * If you intend to create a thread without a process context this function
375 * does everything except load the startup and switcher function.
378 lwkt_alloc_thread(struct thread *td, int stksize, int cpu, int flags)
380 static int cpu_rotator;
381 globaldata_t gd = mycpu;
385 * If static thread storage is not supplied allocate a thread. Reuse
386 * a cached free thread if possible. gd_freetd is used to keep an exiting
387 * thread intact through the exit.
391 if ((td = gd->gd_freetd) != NULL) {
392 KKASSERT((td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK|
394 gd->gd_freetd = NULL;
396 td = objcache_get(thread_cache, M_WAITOK);
397 KKASSERT((td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK|
401 KASSERT((td->td_flags &
402 (TDF_ALLOCATED_THREAD|TDF_RUNNING)) == TDF_ALLOCATED_THREAD,
403 ("lwkt_alloc_thread: corrupted td flags 0x%X", td->td_flags));
404 flags |= td->td_flags & (TDF_ALLOCATED_THREAD|TDF_ALLOCATED_STACK);
408 * Try to reuse cached stack.
410 if ((stack = td->td_kstack) != NULL && td->td_kstack_size != stksize) {
411 if (flags & TDF_ALLOCATED_STACK) {
412 kmem_free(&kernel_map, (vm_offset_t)stack, td->td_kstack_size);
417 stack = (void *)kmem_alloc_stack(&kernel_map, stksize);
418 flags |= TDF_ALLOCATED_STACK;
425 lwkt_init_thread(td, stack, stksize, flags, globaldata_find(cpu));
430 * Initialize a preexisting thread structure. This function is used by
431 * lwkt_alloc_thread() and also used to initialize the per-cpu idlethread.
433 * All threads start out in a critical section at a priority of
434 * TDPRI_KERN_DAEMON. Higher level code will modify the priority as
435 * appropriate. This function may send an IPI message when the
436 * requested cpu is not the current cpu and consequently gd_tdallq may
437 * not be initialized synchronously from the point of view of the originating
440 * NOTE! we have to be careful in regards to creating threads for other cpus
441 * if SMP has not yet been activated.
446 lwkt_init_thread_remote(void *arg)
451 * Protected by critical section held by IPI dispatch
453 TAILQ_INSERT_TAIL(&td->td_gd->gd_tdallq, td, td_allq);
459 * lwkt core thread structural initialization.
461 * NOTE: All threads are initialized as mpsafe threads.
464 lwkt_init_thread(thread_t td, void *stack, int stksize, int flags,
465 struct globaldata *gd)
467 globaldata_t mygd = mycpu;
469 bzero(td, sizeof(struct thread));
470 td->td_kstack = stack;
471 td->td_kstack_size = stksize;
472 td->td_flags = flags;
474 td->td_pri = TDPRI_KERN_DAEMON;
475 td->td_critcount = 1;
476 td->td_toks_stop = &td->td_toks_base;
477 if (lwkt_use_spin_port || (flags & TDF_FORCE_SPINPORT))
478 lwkt_initport_spin(&td->td_msgport);
480 lwkt_initport_thread(&td->td_msgport, td);
481 pmap_init_thread(td);
484 * Normally initializing a thread for a remote cpu requires sending an
485 * IPI. However, the idlethread is setup before the other cpus are
486 * activated so we have to treat it as a special case. XXX manipulation
487 * of gd_tdallq requires the BGL.
489 if (gd == mygd || td == &gd->gd_idlethread) {
491 TAILQ_INSERT_TAIL(&gd->gd_tdallq, td, td_allq);
494 lwkt_send_ipiq(gd, lwkt_init_thread_remote, td);
498 TAILQ_INSERT_TAIL(&gd->gd_tdallq, td, td_allq);
502 dsched_new_thread(td);
506 lwkt_set_comm(thread_t td, const char *ctl, ...)
511 kvsnprintf(td->td_comm, sizeof(td->td_comm), ctl, va);
513 KTR_LOG(ctxsw_newtd, td, &td->td_comm[0]);
517 lwkt_hold(thread_t td)
519 atomic_add_int(&td->td_refs, 1);
523 lwkt_rele(thread_t td)
525 KKASSERT(td->td_refs > 0);
526 atomic_add_int(&td->td_refs, -1);
530 lwkt_wait_free(thread_t td)
533 tsleep(td, 0, "tdreap", hz);
537 lwkt_free_thread(thread_t td)
539 KKASSERT(td->td_refs == 0);
540 KKASSERT((td->td_flags & (TDF_RUNNING | TDF_PREEMPT_LOCK |
541 TDF_RUNQ | TDF_TSLEEPQ)) == 0);
542 if (td->td_flags & TDF_ALLOCATED_THREAD) {
543 objcache_put(thread_cache, td);
544 } else if (td->td_flags & TDF_ALLOCATED_STACK) {
545 /* client-allocated struct with internally allocated stack */
546 KASSERT(td->td_kstack && td->td_kstack_size > 0,
547 ("lwkt_free_thread: corrupted stack"));
548 kmem_free(&kernel_map, (vm_offset_t)td->td_kstack, td->td_kstack_size);
549 td->td_kstack = NULL;
550 td->td_kstack_size = 0;
552 KTR_LOG(ctxsw_deadtd, td);
557 * Switch to the next runnable lwkt. If no LWKTs are runnable then
558 * switch to the idlethread. Switching must occur within a critical
559 * section to avoid races with the scheduling queue.
561 * We always have full control over our cpu's run queue. Other cpus
562 * that wish to manipulate our queue must use the cpu_*msg() calls to
563 * talk to our cpu, so a critical section is all that is needed and
564 * the result is very, very fast thread switching.
566 * The LWKT scheduler uses a fixed priority model and round-robins at
567 * each priority level. User process scheduling is a totally
568 * different beast and LWKT priorities should not be confused with
569 * user process priorities.
571 * PREEMPTION NOTE: Preemption occurs via lwkt_preempt(). lwkt_switch()
572 * is not called by the current thread in the preemption case, only when
573 * the preempting thread blocks (in order to return to the original thread).
575 * SPECIAL NOTE ON SWITCH ATOMICY: Certain operations such as thread
576 * migration and tsleep deschedule the current lwkt thread and call
577 * lwkt_switch(). In particular, the target cpu of the migration fully
578 * expects the thread to become non-runnable and can deadlock against
579 * cpusync operations if we run any IPIs prior to switching the thread out.
581 * WE MUST BE VERY CAREFUL NOT TO RUN SPLZ DIRECTLY OR INDIRECTLY IF
582 * THE CURRENT THREAD HAS BEEN DESCHEDULED!
587 globaldata_t gd = mycpu;
588 thread_t td = gd->gd_curthread;
593 KKASSERT(gd->gd_processing_ipiq == 0);
596 * Switching from within a 'fast' (non thread switched) interrupt or IPI
597 * is illegal. However, we may have to do it anyway if we hit a fatal
598 * kernel trap or we have paniced.
600 * If this case occurs save and restore the interrupt nesting level.
602 if (gd->gd_intr_nesting_level) {
606 if (gd->gd_trap_nesting_level == 0 && panic_cpu_gd != mycpu) {
607 panic("lwkt_switch: Attempt to switch from a "
608 "a fast interrupt, ipi, or hard code section, "
612 savegdnest = gd->gd_intr_nesting_level;
613 savegdtrap = gd->gd_trap_nesting_level;
614 gd->gd_intr_nesting_level = 0;
615 gd->gd_trap_nesting_level = 0;
616 if ((td->td_flags & TDF_PANICWARN) == 0) {
617 td->td_flags |= TDF_PANICWARN;
618 kprintf("Warning: thread switch from interrupt, IPI, "
619 "or hard code section.\n"
620 "thread %p (%s)\n", td, td->td_comm);
624 gd->gd_intr_nesting_level = savegdnest;
625 gd->gd_trap_nesting_level = savegdtrap;
631 * Release our current user process designation if we are blocking
632 * or if a user reschedule was requested.
634 * NOTE: This function is NOT called if we are switching into or
635 * returning from a preemption.
637 * NOTE: Releasing our current user process designation may cause
638 * it to be assigned to another thread, which in turn will
639 * cause us to block in the usched acquire code when we attempt
640 * to return to userland.
642 * NOTE: On SMP systems this can be very nasty when heavy token
643 * contention is present so we want to be careful not to
644 * release the designation gratuitously.
646 if (td->td_release &&
647 (user_resched_wanted() || (td->td_flags & TDF_RUNQ) == 0)) {
655 if (TD_TOKS_HELD(td))
656 lwkt_relalltokens(td);
659 * We had better not be holding any spin locks, but don't get into an
660 * endless panic loop.
662 KASSERT(gd->gd_spinlocks_wr == 0 || panicstr != NULL,
663 ("lwkt_switch: still holding %d exclusive spinlocks!",
664 gd->gd_spinlocks_wr));
669 if (td->td_cscount) {
670 kprintf("Diagnostic: attempt to switch while mastering cpusync: %p\n",
672 if (panic_on_cscount)
673 panic("switching while mastering cpusync");
679 * If we had preempted another thread on this cpu, resume the preempted
680 * thread. This occurs transparently, whether the preempted thread
681 * was scheduled or not (it may have been preempted after descheduling
684 * We have to setup the MP lock for the original thread after backing
685 * out the adjustment that was made to curthread when the original
688 if ((ntd = td->td_preempted) != NULL) {
689 KKASSERT(ntd->td_flags & TDF_PREEMPT_LOCK);
690 ntd->td_flags |= TDF_PREEMPT_DONE;
693 * The interrupt may have woken a thread up, we need to properly
694 * set the reschedule flag if the originally interrupted thread is
695 * at a lower priority.
697 * The interrupt may not have descheduled.
699 if (TAILQ_FIRST(&gd->gd_tdrunq) != ntd)
701 goto havethread_preempted;
705 * If we cannot obtain ownership of the tokens we cannot immediately
706 * schedule the target thread.
708 * Reminder: Again, we cannot afford to run any IPIs in this path if
709 * the current thread has been descheduled.
712 clear_lwkt_resched();
715 * Hotpath - pull the head of the run queue and attempt to schedule
719 ntd = TAILQ_FIRST(&gd->gd_tdrunq);
723 * Runq is empty, switch to idle to allow it to halt.
725 ntd = &gd->gd_idlethread;
727 if (gd->gd_trap_nesting_level == 0 && panicstr == NULL)
728 ASSERT_NO_TOKENS_HELD(ntd);
730 cpu_time.cp_msg[0] = 0;
731 cpu_time.cp_stallpc = 0;
738 * Hotpath - schedule ntd.
740 * NOTE: For UP there is no mplock and lwkt_getalltokens()
743 if (TD_TOKS_NOT_HELD(ntd) ||
744 lwkt_getalltokens(ntd, (spinning >= lwkt_spin_loops)))
750 * Coldpath (SMP only since tokens always succeed on UP)
752 * We had some contention on the thread we wanted to schedule.
753 * What we do now is try to find a thread that we can schedule
756 * The coldpath scan does NOT rearrange threads in the run list.
757 * The lwkt_schedulerclock() will assert need_lwkt_resched() on
758 * the next tick whenever the current head is not the current thread.
761 ++token_contention_count[ntd->td_pri];
765 if (fairq_bypass > 0)
769 while ((ntd = TAILQ_NEXT(ntd, td_threadq)) != NULL) {
771 * Never schedule threads returning to userland or the
772 * user thread scheduler helper thread when higher priority
773 * threads are present.
775 if (ntd->td_pri < TDPRI_KERN_LPSCHED) {
783 if (TD_TOKS_NOT_HELD(ntd) ||
784 lwkt_getalltokens(ntd, (spinning >= lwkt_spin_loops))) {
788 ++token_contention_count[ntd->td_pri];
795 * We exhausted the run list, meaning that all runnable threads
799 ntd = &gd->gd_idlethread;
801 if (gd->gd_trap_nesting_level == 0 && panicstr == NULL)
802 ASSERT_NO_TOKENS_HELD(ntd);
803 /* contention case, do not clear contention mask */
807 * We are going to have to retry but if the current thread is not
808 * on the runq we instead switch through the idle thread to get away
809 * from the current thread. We have to flag for lwkt reschedule
810 * to prevent the idle thread from halting.
812 * NOTE: A non-zero spinning is passed to lwkt_getalltokens() to
813 * instruct it to deal with the potential for deadlocks by
814 * ordering the tokens by address.
816 if ((td->td_flags & TDF_RUNQ) == 0) {
817 need_lwkt_resched(); /* prevent hlt */
820 #if defined(INVARIANTS) && defined(__amd64__)
821 if ((read_rflags() & PSL_I) == 0) {
823 panic("lwkt_switch() called with interrupts disabled");
828 * Number iterations so far. After a certain point we switch to
829 * a sorted-address/monitor/mwait version of lwkt_getalltokens()
831 if (spinning < 0x7FFFFFFF)
836 * lwkt_getalltokens() failed in sorted token mode, we can use
837 * monitor/mwait in this case.
839 if (spinning >= lwkt_spin_loops &&
840 (cpu_mi_feature & CPU_MI_MONITOR) &&
843 cpu_mmw_pause_int(&gd->gd_reqflags,
844 (gd->gd_reqflags | RQF_SPINNING) &
845 ~RQF_IDLECHECK_WK_MASK);
850 * We already checked that td is still scheduled so this should be
856 * This experimental resequencer is used as a fall-back to reduce
857 * hw cache line contention by placing each core's scheduler into a
858 * time-domain-multplexed slot.
860 * The resequencer is disabled by default. It's functionality has
861 * largely been superceeded by the token algorithm which limits races
862 * to a subset of cores.
864 * The resequencer algorithm tends to break down when more than
865 * 20 cores are contending. What appears to happen is that new
866 * tokens can be obtained out of address-sorted order by new cores
867 * while existing cores languish in long delays between retries and
868 * wind up being starved-out of the token acquisition.
870 if (lwkt_spin_reseq && spinning >= lwkt_spin_reseq) {
871 int cseq = atomic_fetchadd_int(&lwkt_cseq_windex, 1);
874 while ((oseq = lwkt_cseq_rindex) != cseq) {
877 if (cpu_mi_feature & CPU_MI_MONITOR) {
878 cpu_mmw_pause_int(&lwkt_cseq_rindex, oseq);
888 atomic_add_int(&lwkt_cseq_rindex, 1);
890 /* highest level for(;;) loop */
895 * If the thread we came up with is a higher or equal priority verses
896 * the thread at the head of the queue we move our thread to the
897 * front. This way we can always check the front of the queue.
899 * Clear gd_idle_repeat when doing a normal switch to a non-idle
902 ntd->td_wmesg = NULL;
903 ++gd->gd_cnt.v_swtch;
905 xtd = TAILQ_FIRST(&gd->gd_tdrunq);
906 if (ntd != xtd && ntd->td_pri >= xtd->td_pri) {
907 TAILQ_REMOVE(&gd->gd_tdrunq, ntd, td_threadq);
908 TAILQ_INSERT_HEAD(&gd->gd_tdrunq, ntd, td_threadq);
911 gd->gd_idle_repeat = 0;
913 havethread_preempted:
915 * If the new target does not need the MP lock and we are holding it,
916 * release the MP lock. If the new target requires the MP lock we have
917 * already acquired it for the target.
921 KASSERT(ntd->td_critcount,
922 ("priority problem in lwkt_switch %d %d",
923 td->td_critcount, ntd->td_critcount));
927 * Execute the actual thread switch operation. This function
928 * returns to the current thread and returns the previous thread
929 * (which may be different from the thread we switched to).
931 * We are responsible for marking ntd as TDF_RUNNING.
934 KTR_LOG(ctxsw_sw, gd->gd_cpuid, ntd);
935 ntd->td_flags |= TDF_RUNNING;
936 lwkt_switch_return(td->td_switch(ntd));
937 /* ntd invalid, td_switch() can return a different thread_t */
946 /* NOTE: current cpu may have changed after switch */
951 * Called by assembly in the td_switch (thread restore path) for thread
952 * bootstrap cases which do not 'return' to lwkt_switch().
955 lwkt_switch_return(thread_t otd)
961 * Check if otd was migrating. Now that we are on ntd we can finish
962 * up the migration. This is a bit messy but it is the only place
963 * where td is known to be fully descheduled.
965 * We can only activate the migration if otd was migrating but not
966 * held on the cpu due to a preemption chain. We still have to
967 * clear TDF_RUNNING on the old thread either way.
969 * We are responsible for clearing the previously running thread's
972 if ((rgd = otd->td_migrate_gd) != NULL &&
973 (otd->td_flags & TDF_PREEMPT_LOCK) == 0) {
974 KKASSERT((otd->td_flags & (TDF_MIGRATING | TDF_RUNNING)) ==
975 (TDF_MIGRATING | TDF_RUNNING));
976 otd->td_migrate_gd = NULL;
977 otd->td_flags &= ~TDF_RUNNING;
978 lwkt_send_ipiq(rgd, lwkt_setcpu_remote, otd);
980 otd->td_flags &= ~TDF_RUNNING;
983 otd->td_flags &= ~TDF_RUNNING;
988 * Request that the target thread preempt the current thread. Preemption
989 * only works under a specific set of conditions:
991 * - We are not preempting ourselves
992 * - The target thread is owned by the current cpu
993 * - We are not currently being preempted
994 * - The target is not currently being preempted
995 * - We are not holding any spin locks
996 * - The target thread is not holding any tokens
997 * - We are able to satisfy the target's MP lock requirements (if any).
999 * THE CALLER OF LWKT_PREEMPT() MUST BE IN A CRITICAL SECTION. Typically
1000 * this is called via lwkt_schedule() through the td_preemptable callback.
1001 * critcount is the managed critical priority that we should ignore in order
1002 * to determine whether preemption is possible (aka usually just the crit
1003 * priority of lwkt_schedule() itself).
1005 * XXX at the moment we run the target thread in a critical section during
1006 * the preemption in order to prevent the target from taking interrupts
1007 * that *WE* can't. Preemption is strictly limited to interrupt threads
1008 * and interrupt-like threads, outside of a critical section, and the
1009 * preempted source thread will be resumed the instant the target blocks
1010 * whether or not the source is scheduled (i.e. preemption is supposed to
1011 * be as transparent as possible).
1014 lwkt_preempt(thread_t ntd, int critcount)
1016 struct globaldata *gd = mycpu;
1019 int save_gd_intr_nesting_level;
1022 * The caller has put us in a critical section. We can only preempt
1023 * if the caller of the caller was not in a critical section (basically
1024 * a local interrupt), as determined by the 'critcount' parameter. We
1025 * also can't preempt if the caller is holding any spinlocks (even if
1026 * he isn't in a critical section). This also handles the tokens test.
1028 * YYY The target thread must be in a critical section (else it must
1029 * inherit our critical section? I dunno yet).
1031 KASSERT(ntd->td_critcount, ("BADCRIT0 %d", ntd->td_pri));
1033 td = gd->gd_curthread;
1034 if (preempt_enable == 0) {
1036 if (ntd->td_pri > td->td_pri)
1037 need_lwkt_resched();
1042 if (ntd->td_pri <= td->td_pri) {
1046 if (td->td_critcount > critcount) {
1049 need_lwkt_resched();
1054 if (ntd->td_gd != gd) {
1057 need_lwkt_resched();
1063 * We don't have to check spinlocks here as they will also bump
1066 * Do not try to preempt if the target thread is holding any tokens.
1067 * We could try to acquire the tokens but this case is so rare there
1068 * is no need to support it.
1070 KKASSERT(gd->gd_spinlocks_wr == 0);
1072 if (TD_TOKS_HELD(ntd)) {
1075 need_lwkt_resched();
1079 if (td == ntd || ((td->td_flags | ntd->td_flags) & TDF_PREEMPT_LOCK)) {
1082 need_lwkt_resched();
1086 if (ntd->td_preempted) {
1089 need_lwkt_resched();
1093 KKASSERT(gd->gd_processing_ipiq == 0);
1096 * Since we are able to preempt the current thread, there is no need to
1097 * call need_lwkt_resched().
1099 * We must temporarily clear gd_intr_nesting_level around the switch
1100 * since switchouts from the target thread are allowed (they will just
1101 * return to our thread), and since the target thread has its own stack.
1103 * A preemption must switch back to the original thread, assert the
1107 ntd->td_preempted = td;
1108 td->td_flags |= TDF_PREEMPT_LOCK;
1109 KTR_LOG(ctxsw_pre, gd->gd_cpuid, ntd);
1110 save_gd_intr_nesting_level = gd->gd_intr_nesting_level;
1111 gd->gd_intr_nesting_level = 0;
1112 ntd->td_flags |= TDF_RUNNING;
1113 xtd = td->td_switch(ntd);
1114 KKASSERT(xtd == ntd);
1115 lwkt_switch_return(xtd);
1116 gd->gd_intr_nesting_level = save_gd_intr_nesting_level;
1118 KKASSERT(ntd->td_preempted && (td->td_flags & TDF_PREEMPT_DONE));
1119 ntd->td_preempted = NULL;
1120 td->td_flags &= ~(TDF_PREEMPT_LOCK|TDF_PREEMPT_DONE);
1124 * Conditionally call splz() if gd_reqflags indicates work is pending.
1125 * This will work inside a critical section but not inside a hard code
1128 * (self contained on a per cpu basis)
1133 globaldata_t gd = mycpu;
1134 thread_t td = gd->gd_curthread;
1136 if ((gd->gd_reqflags & RQF_IDLECHECK_MASK) &&
1137 gd->gd_intr_nesting_level == 0 &&
1138 td->td_nest_count < 2)
1145 * This version is integrated into crit_exit, reqflags has already
1146 * been tested but td_critcount has not.
1148 * We only want to execute the splz() on the 1->0 transition of
1149 * critcount and not in a hard code section or if too deeply nested.
1152 lwkt_maybe_splz(thread_t td)
1154 globaldata_t gd = td->td_gd;
1156 if (td->td_critcount == 0 &&
1157 gd->gd_intr_nesting_level == 0 &&
1158 td->td_nest_count < 2)
1165 * Drivers which set up processing co-threads can call this function to
1166 * run the co-thread at a higher priority and to allow it to preempt
1170 lwkt_set_interrupt_support_thread(void)
1172 thread_t td = curthread;
1174 lwkt_setpri_self(TDPRI_INT_SUPPORT);
1175 td->td_flags |= TDF_INTTHREAD;
1176 td->td_preemptable = lwkt_preempt;
1181 * This function is used to negotiate a passive release of the current
1182 * process/lwp designation with the user scheduler, allowing the user
1183 * scheduler to schedule another user thread. The related kernel thread
1184 * (curthread) continues running in the released state.
1187 lwkt_passive_release(struct thread *td)
1189 struct lwp *lp = td->td_lwp;
1191 td->td_release = NULL;
1192 lwkt_setpri_self(TDPRI_KERN_USER);
1193 lp->lwp_proc->p_usched->release_curproc(lp);
1198 * This implements a LWKT yield, allowing a kernel thread to yield to other
1199 * kernel threads at the same or higher priority. This function can be
1200 * called in a tight loop and will typically only yield once per tick.
1202 * Most kernel threads run at the same priority in order to allow equal
1205 * (self contained on a per cpu basis)
1210 globaldata_t gd = mycpu;
1211 thread_t td = gd->gd_curthread;
1213 if ((gd->gd_reqflags & RQF_IDLECHECK_MASK) && td->td_nest_count < 2)
1215 if (lwkt_resched_wanted()) {
1216 lwkt_schedule_self(curthread);
1222 * This yield is designed for kernel threads with a user context.
1224 * The kernel acting on behalf of the user is potentially cpu-bound,
1225 * this function will efficiently allow other threads to run and also
1226 * switch to other processes by releasing.
1228 * The lwkt_user_yield() function is designed to have very low overhead
1229 * if no yield is determined to be needed.
1232 lwkt_user_yield(void)
1234 globaldata_t gd = mycpu;
1235 thread_t td = gd->gd_curthread;
1238 * Always run any pending interrupts in case we are in a critical
1241 if ((gd->gd_reqflags & RQF_IDLECHECK_MASK) && td->td_nest_count < 2)
1245 * Switch (which forces a release) if another kernel thread needs
1246 * the cpu, if userland wants us to resched, or if our kernel
1247 * quantum has run out.
1249 if (lwkt_resched_wanted() ||
1250 user_resched_wanted())
1257 * Reacquire the current process if we are released.
1259 * XXX not implemented atm. The kernel may be holding locks and such,
1260 * so we want the thread to continue to receive cpu.
1262 if (td->td_release == NULL && lp) {
1263 lp->lwp_proc->p_usched->acquire_curproc(lp);
1264 td->td_release = lwkt_passive_release;
1265 lwkt_setpri_self(TDPRI_USER_NORM);
1271 * Generic schedule. Possibly schedule threads belonging to other cpus and
1272 * deal with threads that might be blocked on a wait queue.
1274 * We have a little helper inline function which does additional work after
1275 * the thread has been enqueued, including dealing with preemption and
1276 * setting need_lwkt_resched() (which prevents the kernel from returning
1277 * to userland until it has processed higher priority threads).
1279 * It is possible for this routine to be called after a failed _enqueue
1280 * (due to the target thread migrating, sleeping, or otherwise blocked).
1281 * We have to check that the thread is actually on the run queue!
1285 _lwkt_schedule_post(globaldata_t gd, thread_t ntd, int ccount)
1287 if (ntd->td_flags & TDF_RUNQ) {
1288 if (ntd->td_preemptable) {
1289 ntd->td_preemptable(ntd, ccount); /* YYY +token */
1296 _lwkt_schedule(thread_t td)
1298 globaldata_t mygd = mycpu;
1300 KASSERT(td != &td->td_gd->gd_idlethread,
1301 ("lwkt_schedule(): scheduling gd_idlethread is illegal!"));
1302 KKASSERT((td->td_flags & TDF_MIGRATING) == 0);
1303 crit_enter_gd(mygd);
1304 KKASSERT(td->td_lwp == NULL || (td->td_lwp->lwp_flag & LWP_ONRUNQ) == 0);
1305 if (td == mygd->gd_curthread) {
1309 * If we own the thread, there is no race (since we are in a
1310 * critical section). If we do not own the thread there might
1311 * be a race but the target cpu will deal with it.
1314 if (td->td_gd == mygd) {
1316 _lwkt_schedule_post(mygd, td, 1);
1318 lwkt_send_ipiq3(td->td_gd, lwkt_schedule_remote, td, 0);
1322 _lwkt_schedule_post(mygd, td, 1);
1329 lwkt_schedule(thread_t td)
1335 lwkt_schedule_noresched(thread_t td) /* XXX not impl */
1343 * When scheduled remotely if frame != NULL the IPIQ is being
1344 * run via doreti or an interrupt then preemption can be allowed.
1346 * To allow preemption we have to drop the critical section so only
1347 * one is present in _lwkt_schedule_post.
1350 lwkt_schedule_remote(void *arg, int arg2, struct intrframe *frame)
1352 thread_t td = curthread;
1355 if (frame && ntd->td_preemptable) {
1356 crit_exit_noyield(td);
1357 _lwkt_schedule(ntd);
1358 crit_enter_quick(td);
1360 _lwkt_schedule(ntd);
1365 * Thread migration using a 'Pull' method. The thread may or may not be
1366 * the current thread. It MUST be descheduled and in a stable state.
1367 * lwkt_giveaway() must be called on the cpu owning the thread.
1369 * At any point after lwkt_giveaway() is called, the target cpu may
1370 * 'pull' the thread by calling lwkt_acquire().
1372 * We have to make sure the thread is not sitting on a per-cpu tsleep
1373 * queue or it will blow up when it moves to another cpu.
1375 * MPSAFE - must be called under very specific conditions.
1378 lwkt_giveaway(thread_t td)
1380 globaldata_t gd = mycpu;
1383 if (td->td_flags & TDF_TSLEEPQ)
1385 KKASSERT(td->td_gd == gd);
1386 TAILQ_REMOVE(&gd->gd_tdallq, td, td_allq);
1387 td->td_flags |= TDF_MIGRATING;
1392 lwkt_acquire(thread_t td)
1396 int retry = 10000000;
1398 KKASSERT(td->td_flags & TDF_MIGRATING);
1403 KKASSERT((td->td_flags & TDF_RUNQ) == 0);
1404 crit_enter_gd(mygd);
1405 DEBUG_PUSH_INFO("lwkt_acquire");
1406 while (td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK)) {
1408 lwkt_process_ipiq();
1412 kprintf("lwkt_acquire: stuck: td %p td->td_flags %08x\n",
1420 TAILQ_INSERT_TAIL(&mygd->gd_tdallq, td, td_allq);
1421 td->td_flags &= ~TDF_MIGRATING;
1424 crit_enter_gd(mygd);
1425 TAILQ_INSERT_TAIL(&mygd->gd_tdallq, td, td_allq);
1426 td->td_flags &= ~TDF_MIGRATING;
1434 * Generic deschedule. Descheduling threads other then your own should be
1435 * done only in carefully controlled circumstances. Descheduling is
1438 * This function may block if the cpu has run out of messages.
1441 lwkt_deschedule(thread_t td)
1445 if (td == curthread) {
1448 if (td->td_gd == mycpu) {
1451 lwkt_send_ipiq(td->td_gd, (ipifunc1_t)lwkt_deschedule, td);
1461 * Set the target thread's priority. This routine does not automatically
1462 * switch to a higher priority thread, LWKT threads are not designed for
1463 * continuous priority changes. Yield if you want to switch.
1466 lwkt_setpri(thread_t td, int pri)
1468 if (td->td_pri != pri) {
1471 if (td->td_flags & TDF_RUNQ) {
1472 KKASSERT(td->td_gd == mycpu);
1484 * Set the initial priority for a thread prior to it being scheduled for
1485 * the first time. The thread MUST NOT be scheduled before or during
1486 * this call. The thread may be assigned to a cpu other then the current
1489 * Typically used after a thread has been created with TDF_STOPPREQ,
1490 * and before the thread is initially scheduled.
1493 lwkt_setpri_initial(thread_t td, int pri)
1496 KKASSERT((td->td_flags & TDF_RUNQ) == 0);
1501 lwkt_setpri_self(int pri)
1503 thread_t td = curthread;
1505 KKASSERT(pri >= 0 && pri <= TDPRI_MAX);
1507 if (td->td_flags & TDF_RUNQ) {
1518 * hz tick scheduler clock for LWKT threads
1521 lwkt_schedulerclock(thread_t td)
1523 globaldata_t gd = td->td_gd;
1526 if (TAILQ_FIRST(&gd->gd_tdrunq) == td) {
1528 * If the current thread is at the head of the runq shift it to the
1529 * end of any equal-priority threads and request a LWKT reschedule
1532 xtd = TAILQ_NEXT(td, td_threadq);
1533 if (xtd && xtd->td_pri == td->td_pri) {
1534 TAILQ_REMOVE(&gd->gd_tdrunq, td, td_threadq);
1535 while (xtd && xtd->td_pri == td->td_pri)
1536 xtd = TAILQ_NEXT(xtd, td_threadq);
1538 TAILQ_INSERT_BEFORE(xtd, td, td_threadq);
1540 TAILQ_INSERT_TAIL(&gd->gd_tdrunq, td, td_threadq);
1541 need_lwkt_resched();
1545 * If we scheduled a thread other than the one at the head of the
1546 * queue always request a reschedule every tick.
1548 need_lwkt_resched();
1553 * Migrate the current thread to the specified cpu.
1555 * This is accomplished by descheduling ourselves from the current cpu
1556 * and setting td_migrate_gd. The lwkt_switch() code will detect that the
1557 * 'old' thread wants to migrate after it has been completely switched out
1558 * and will complete the migration.
1560 * TDF_MIGRATING prevents scheduling races while the thread is being migrated.
1562 * We must be sure to release our current process designation (if a user
1563 * process) before clearing out any tsleepq we are on because the release
1564 * code may re-add us.
1566 * We must be sure to remove ourselves from the current cpu's tsleepq
1567 * before potentially moving to another queue. The thread can be on
1568 * a tsleepq due to a left-over tsleep_interlock().
1572 lwkt_setcpu_self(globaldata_t rgd)
1575 thread_t td = curthread;
1577 if (td->td_gd != rgd) {
1578 crit_enter_quick(td);
1582 if (td->td_flags & TDF_TSLEEPQ)
1586 * Set TDF_MIGRATING to prevent a spurious reschedule while we are
1587 * trying to deschedule ourselves and switch away, then deschedule
1588 * ourself, remove us from tdallq, and set td_migrate_gd. Finally,
1589 * call lwkt_switch() to complete the operation.
1591 td->td_flags |= TDF_MIGRATING;
1592 lwkt_deschedule_self(td);
1593 TAILQ_REMOVE(&td->td_gd->gd_tdallq, td, td_allq);
1594 td->td_migrate_gd = rgd;
1598 * We are now on the target cpu
1600 KKASSERT(rgd == mycpu);
1601 TAILQ_INSERT_TAIL(&rgd->gd_tdallq, td, td_allq);
1602 crit_exit_quick(td);
1608 lwkt_migratecpu(int cpuid)
1613 rgd = globaldata_find(cpuid);
1614 lwkt_setcpu_self(rgd);
1620 * Remote IPI for cpu migration (called while in a critical section so we
1621 * do not have to enter another one).
1623 * The thread (td) has already been completely descheduled from the
1624 * originating cpu and we can simply assert the case. The thread is
1625 * assigned to the new cpu and enqueued.
1627 * The thread will re-add itself to tdallq when it resumes execution.
1630 lwkt_setcpu_remote(void *arg)
1633 globaldata_t gd = mycpu;
1635 KKASSERT((td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK)) == 0);
1638 td->td_flags &= ~TDF_MIGRATING;
1639 KKASSERT(td->td_migrate_gd == NULL);
1640 KKASSERT(td->td_lwp == NULL || (td->td_lwp->lwp_flag & LWP_ONRUNQ) == 0);
1646 lwkt_preempted_proc(void)
1648 thread_t td = curthread;
1649 while (td->td_preempted)
1650 td = td->td_preempted;
1655 * Create a kernel process/thread/whatever. It shares it's address space
1656 * with proc0 - ie: kernel only.
1658 * If the cpu is not specified one will be selected. In the future
1659 * specifying a cpu of -1 will enable kernel thread migration between
1663 lwkt_create(void (*func)(void *), void *arg, struct thread **tdp,
1664 thread_t template, int tdflags, int cpu, const char *fmt, ...)
1669 td = lwkt_alloc_thread(template, LWKT_THREAD_STACK, cpu,
1673 cpu_set_thread_handler(td, lwkt_exit, func, arg);
1676 * Set up arg0 for 'ps' etc
1678 __va_start(ap, fmt);
1679 kvsnprintf(td->td_comm, sizeof(td->td_comm), fmt, ap);
1683 * Schedule the thread to run
1685 if ((td->td_flags & TDF_STOPREQ) == 0)
1688 td->td_flags &= ~TDF_STOPREQ;
1693 * Destroy an LWKT thread. Warning! This function is not called when
1694 * a process exits, cpu_proc_exit() directly calls cpu_thread_exit() and
1695 * uses a different reaping mechanism.
1700 thread_t td = curthread;
1705 * Do any cleanup that might block here
1707 if (td->td_flags & TDF_VERBOSE)
1708 kprintf("kthread %p %s has exited\n", td, td->td_comm);
1711 dsched_exit_thread(td);
1714 * Get us into a critical section to interlock gd_freetd and loop
1715 * until we can get it freed.
1717 * We have to cache the current td in gd_freetd because objcache_put()ing
1718 * it would rip it out from under us while our thread is still active.
1721 crit_enter_quick(td);
1722 while ((std = gd->gd_freetd) != NULL) {
1723 KKASSERT((std->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK)) == 0);
1724 gd->gd_freetd = NULL;
1725 objcache_put(thread_cache, std);
1729 * Remove thread resources from kernel lists and deschedule us for
1730 * the last time. We cannot block after this point or we may end
1731 * up with a stale td on the tsleepq.
1733 if (td->td_flags & TDF_TSLEEPQ)
1735 lwkt_deschedule_self(td);
1736 lwkt_remove_tdallq(td);
1737 KKASSERT(td->td_refs == 0);
1742 KKASSERT(gd->gd_freetd == NULL);
1743 if (td->td_flags & TDF_ALLOCATED_THREAD)
1749 lwkt_remove_tdallq(thread_t td)
1751 KKASSERT(td->td_gd == mycpu);
1752 TAILQ_REMOVE(&td->td_gd->gd_tdallq, td, td_allq);
1756 * Code reduction and branch prediction improvements. Call/return
1757 * overhead on modern cpus often degenerates into 0 cycles due to
1758 * the cpu's branch prediction hardware and return pc cache. We
1759 * can take advantage of this by not inlining medium-complexity
1760 * functions and we can also reduce the branch prediction impact
1761 * by collapsing perfectly predictable branches into a single
1762 * procedure instead of duplicating it.
1764 * Is any of this noticeable? Probably not, so I'll take the
1765 * smaller code size.
1768 crit_exit_wrapper(__DEBUG_CRIT_ARG__)
1770 _crit_exit(mycpu __DEBUG_CRIT_PASS_ARG__);
1776 thread_t td = curthread;
1777 int lcrit = td->td_critcount;
1779 td->td_critcount = 0;
1780 panic("td_critcount is/would-go negative! %p %d", td, lcrit);
1787 * Called from debugger/panic on cpus which have been stopped. We must still
1788 * process the IPIQ while stopped, even if we were stopped while in a critical
1791 * If we are dumping also try to process any pending interrupts. This may
1792 * or may not work depending on the state of the cpu at the point it was
1796 lwkt_smp_stopped(void)
1798 globaldata_t gd = mycpu;
1802 lwkt_process_ipiq();
1805 lwkt_process_ipiq();