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", int cpu, struct thread *td);
80 KTR_INFO(KTR_CTXSW, ctxsw, pre, 1, "#cpu[%d].td = %p", int cpu, struct thread *td);
81 KTR_INFO(KTR_CTXSW, ctxsw, newtd, 2, "#threads[%p].name = %s", struct thread *td, char *comm);
82 KTR_INFO(KTR_CTXSW, ctxsw, deadtd, 3, "#threads[%p].name = <dead>", struct thread *td);
84 static MALLOC_DEFINE(M_THREAD, "thread", "lwkt threads");
87 static int panic_on_cscount = 0;
89 static __int64_t switch_count = 0;
90 static __int64_t preempt_hit = 0;
91 static __int64_t preempt_miss = 0;
92 static __int64_t preempt_weird = 0;
93 static int lwkt_use_spin_port;
94 static struct objcache *thread_cache;
97 static void lwkt_schedule_remote(void *arg, int arg2, struct intrframe *frame);
98 static void lwkt_setcpu_remote(void *arg);
101 extern void cpu_heavy_restore(void);
102 extern void cpu_lwkt_restore(void);
103 extern void cpu_kthread_restore(void);
104 extern void cpu_idle_restore(void);
107 * We can make all thread ports use the spin backend instead of the thread
108 * backend. This should only be set to debug the spin backend.
110 TUNABLE_INT("lwkt.use_spin_port", &lwkt_use_spin_port);
113 SYSCTL_INT(_lwkt, OID_AUTO, panic_on_cscount, CTLFLAG_RW, &panic_on_cscount, 0,
114 "Panic if attempting to switch lwkt's while mastering cpusync");
116 SYSCTL_QUAD(_lwkt, OID_AUTO, switch_count, CTLFLAG_RW, &switch_count, 0,
117 "Number of switched threads");
118 SYSCTL_QUAD(_lwkt, OID_AUTO, preempt_hit, CTLFLAG_RW, &preempt_hit, 0,
119 "Successful preemption events");
120 SYSCTL_QUAD(_lwkt, OID_AUTO, preempt_miss, CTLFLAG_RW, &preempt_miss, 0,
121 "Failed preemption events");
122 SYSCTL_QUAD(_lwkt, OID_AUTO, preempt_weird, CTLFLAG_RW, &preempt_weird, 0,
123 "Number of preempted threads.");
124 static int fairq_enable = 0;
125 SYSCTL_INT(_lwkt, OID_AUTO, fairq_enable, CTLFLAG_RW,
126 &fairq_enable, 0, "Turn on fairq priority accumulators");
127 static int fairq_bypass = -1;
128 SYSCTL_INT(_lwkt, OID_AUTO, fairq_bypass, CTLFLAG_RW,
129 &fairq_bypass, 0, "Allow fairq to bypass td on token failure");
130 extern int lwkt_sched_debug;
131 int lwkt_sched_debug = 0;
132 SYSCTL_INT(_lwkt, OID_AUTO, sched_debug, CTLFLAG_RW,
133 &lwkt_sched_debug, 0, "Scheduler debug");
134 static int lwkt_spin_loops = 10;
135 SYSCTL_INT(_lwkt, OID_AUTO, spin_loops, CTLFLAG_RW,
136 &lwkt_spin_loops, 0, "Scheduler spin loops until sorted decon");
137 static int lwkt_spin_reseq = 0;
138 SYSCTL_INT(_lwkt, OID_AUTO, spin_reseq, CTLFLAG_RW,
139 &lwkt_spin_reseq, 0, "Scheduler resequencer enable");
140 static int lwkt_spin_monitor = 0;
141 SYSCTL_INT(_lwkt, OID_AUTO, spin_monitor, CTLFLAG_RW,
142 &lwkt_spin_monitor, 0, "Scheduler uses monitor/mwait");
143 static int lwkt_spin_fatal = 0; /* disabled */
144 SYSCTL_INT(_lwkt, OID_AUTO, spin_fatal, CTLFLAG_RW,
145 &lwkt_spin_fatal, 0, "LWKT scheduler spin loops till fatal panic");
146 static int preempt_enable = 1;
147 SYSCTL_INT(_lwkt, OID_AUTO, preempt_enable, CTLFLAG_RW,
148 &preempt_enable, 0, "Enable preemption");
149 static int lwkt_cache_threads = 0;
150 SYSCTL_INT(_lwkt, OID_AUTO, cache_threads, CTLFLAG_RD,
151 &lwkt_cache_threads, 0, "thread+kstack cache");
153 static __cachealign int lwkt_cseq_rindex;
154 static __cachealign int lwkt_cseq_windex;
157 * These helper procedures handle the runq, they can only be called from
158 * within a critical section.
160 * WARNING! Prior to SMP being brought up it is possible to enqueue and
161 * dequeue threads belonging to other cpus, so be sure to use td->td_gd
162 * instead of 'mycpu' when referencing the globaldata structure. Once
163 * SMP live enqueuing and dequeueing only occurs on the current cpu.
167 _lwkt_dequeue(thread_t td)
169 if (td->td_flags & TDF_RUNQ) {
170 struct globaldata *gd = td->td_gd;
172 td->td_flags &= ~TDF_RUNQ;
173 TAILQ_REMOVE(&gd->gd_tdrunq, td, td_threadq);
174 --gd->gd_tdrunqcount;
175 if (TAILQ_FIRST(&gd->gd_tdrunq) == NULL)
176 atomic_clear_int(&gd->gd_reqflags, RQF_RUNNING);
183 * There are a limited number of lwkt threads runnable since user
184 * processes only schedule one at a time per cpu. However, there can
185 * be many user processes in kernel mode exiting from a tsleep() which
188 * NOTE: lwkt_schedulerclock() will force a round-robin based on td_pri and
189 * will ignore user priority. This is to ensure that user threads in
190 * kernel mode get cpu at some point regardless of what the user
195 _lwkt_enqueue(thread_t td)
199 if ((td->td_flags & (TDF_RUNQ|TDF_MIGRATING|TDF_BLOCKQ)) == 0) {
200 struct globaldata *gd = td->td_gd;
202 td->td_flags |= TDF_RUNQ;
203 xtd = TAILQ_FIRST(&gd->gd_tdrunq);
205 TAILQ_INSERT_TAIL(&gd->gd_tdrunq, td, td_threadq);
206 atomic_set_int(&gd->gd_reqflags, RQF_RUNNING);
209 * NOTE: td_upri - higher numbers more desireable, same sense
210 * as td_pri (typically reversed from lwp_upri).
212 * In the equal priority case we want the best selection
213 * at the beginning so the less desireable selections know
214 * that they have to setrunqueue/go-to-another-cpu, even
215 * though it means switching back to the 'best' selection.
216 * This also avoids degenerate situations when many threads
217 * are runnable or waking up at the same time.
219 * If upri matches exactly place at end/round-robin.
222 (xtd->td_pri >= td->td_pri ||
223 (xtd->td_pri == td->td_pri &&
224 xtd->td_upri >= td->td_upri))) {
225 xtd = TAILQ_NEXT(xtd, td_threadq);
228 TAILQ_INSERT_BEFORE(xtd, td, td_threadq);
230 TAILQ_INSERT_TAIL(&gd->gd_tdrunq, td, td_threadq);
232 ++gd->gd_tdrunqcount;
235 * Request a LWKT reschedule if we are now at the head of the queue.
237 if (TAILQ_FIRST(&gd->gd_tdrunq) == td)
243 _lwkt_thread_ctor(void *obj, void *privdata, int ocflags)
245 struct thread *td = (struct thread *)obj;
247 td->td_kstack = NULL;
248 td->td_kstack_size = 0;
249 td->td_flags = TDF_ALLOCATED_THREAD;
255 _lwkt_thread_dtor(void *obj, void *privdata)
257 struct thread *td = (struct thread *)obj;
259 KASSERT(td->td_flags & TDF_ALLOCATED_THREAD,
260 ("_lwkt_thread_dtor: not allocated from objcache"));
261 KASSERT((td->td_flags & TDF_ALLOCATED_STACK) && td->td_kstack &&
262 td->td_kstack_size > 0,
263 ("_lwkt_thread_dtor: corrupted stack"));
264 kmem_free(&kernel_map, (vm_offset_t)td->td_kstack, td->td_kstack_size);
265 td->td_kstack = NULL;
270 * Initialize the lwkt s/system.
272 * Nominally cache up to 32 thread + kstack structures. Cache more on
273 * systems with a lot of cpu cores.
278 TUNABLE_INT("lwkt.cache_threads", &lwkt_cache_threads);
279 if (lwkt_cache_threads == 0) {
280 lwkt_cache_threads = ncpus * 4;
281 if (lwkt_cache_threads < 32)
282 lwkt_cache_threads = 32;
284 thread_cache = objcache_create_mbacked(
285 M_THREAD, sizeof(struct thread),
286 0, lwkt_cache_threads,
287 _lwkt_thread_ctor, _lwkt_thread_dtor, NULL);
291 * Schedule a thread to run. As the current thread we can always safely
292 * schedule ourselves, and a shortcut procedure is provided for that
295 * (non-blocking, self contained on a per cpu basis)
298 lwkt_schedule_self(thread_t td)
300 KKASSERT((td->td_flags & TDF_MIGRATING) == 0);
301 crit_enter_quick(td);
302 KASSERT(td != &td->td_gd->gd_idlethread,
303 ("lwkt_schedule_self(): scheduling gd_idlethread is illegal!"));
304 KKASSERT(td->td_lwp == NULL ||
305 (td->td_lwp->lwp_mpflags & LWP_MP_ONRUNQ) == 0);
311 * Deschedule a thread.
313 * (non-blocking, self contained on a per cpu basis)
316 lwkt_deschedule_self(thread_t td)
318 crit_enter_quick(td);
324 * LWKTs operate on a per-cpu basis
326 * WARNING! Called from early boot, 'mycpu' may not work yet.
329 lwkt_gdinit(struct globaldata *gd)
331 TAILQ_INIT(&gd->gd_tdrunq);
332 TAILQ_INIT(&gd->gd_tdallq);
336 * Create a new thread. The thread must be associated with a process context
337 * or LWKT start address before it can be scheduled. If the target cpu is
338 * -1 the thread will be created on the current cpu.
340 * If you intend to create a thread without a process context this function
341 * does everything except load the startup and switcher function.
344 lwkt_alloc_thread(struct thread *td, int stksize, int cpu, int flags)
346 static int cpu_rotator;
347 globaldata_t gd = mycpu;
351 * If static thread storage is not supplied allocate a thread. Reuse
352 * a cached free thread if possible. gd_freetd is used to keep an exiting
353 * thread intact through the exit.
357 if ((td = gd->gd_freetd) != NULL) {
358 KKASSERT((td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK|
360 gd->gd_freetd = NULL;
362 td = objcache_get(thread_cache, M_WAITOK);
363 KKASSERT((td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK|
367 KASSERT((td->td_flags &
368 (TDF_ALLOCATED_THREAD|TDF_RUNNING|TDF_PREEMPT_LOCK)) ==
369 TDF_ALLOCATED_THREAD,
370 ("lwkt_alloc_thread: corrupted td flags 0x%X", td->td_flags));
371 flags |= td->td_flags & (TDF_ALLOCATED_THREAD|TDF_ALLOCATED_STACK);
375 * Try to reuse cached stack.
377 if ((stack = td->td_kstack) != NULL && td->td_kstack_size != stksize) {
378 if (flags & TDF_ALLOCATED_STACK) {
379 kmem_free(&kernel_map, (vm_offset_t)stack, td->td_kstack_size);
384 stack = (void *)kmem_alloc_stack(&kernel_map, stksize);
385 flags |= TDF_ALLOCATED_STACK;
392 lwkt_init_thread(td, stack, stksize, flags, globaldata_find(cpu));
397 * Initialize a preexisting thread structure. This function is used by
398 * lwkt_alloc_thread() and also used to initialize the per-cpu idlethread.
400 * All threads start out in a critical section at a priority of
401 * TDPRI_KERN_DAEMON. Higher level code will modify the priority as
402 * appropriate. This function may send an IPI message when the
403 * requested cpu is not the current cpu and consequently gd_tdallq may
404 * not be initialized synchronously from the point of view of the originating
407 * NOTE! we have to be careful in regards to creating threads for other cpus
408 * if SMP has not yet been activated.
413 lwkt_init_thread_remote(void *arg)
418 * Protected by critical section held by IPI dispatch
420 TAILQ_INSERT_TAIL(&td->td_gd->gd_tdallq, td, td_allq);
426 * lwkt core thread structural initialization.
428 * NOTE: All threads are initialized as mpsafe threads.
431 lwkt_init_thread(thread_t td, void *stack, int stksize, int flags,
432 struct globaldata *gd)
434 globaldata_t mygd = mycpu;
436 bzero(td, sizeof(struct thread));
437 td->td_kstack = stack;
438 td->td_kstack_size = stksize;
439 td->td_flags = flags;
442 td->td_pri = TDPRI_KERN_DAEMON;
443 td->td_critcount = 1;
444 td->td_toks_have = NULL;
445 td->td_toks_stop = &td->td_toks_base;
446 if (lwkt_use_spin_port || (flags & TDF_FORCE_SPINPORT))
447 lwkt_initport_spin(&td->td_msgport, td);
449 lwkt_initport_thread(&td->td_msgport, td);
450 pmap_init_thread(td);
453 * Normally initializing a thread for a remote cpu requires sending an
454 * IPI. However, the idlethread is setup before the other cpus are
455 * activated so we have to treat it as a special case. XXX manipulation
456 * of gd_tdallq requires the BGL.
458 if (gd == mygd || td == &gd->gd_idlethread) {
460 TAILQ_INSERT_TAIL(&gd->gd_tdallq, td, td_allq);
463 lwkt_send_ipiq(gd, lwkt_init_thread_remote, td);
467 TAILQ_INSERT_TAIL(&gd->gd_tdallq, td, td_allq);
471 dsched_new_thread(td);
475 lwkt_set_comm(thread_t td, const char *ctl, ...)
480 kvsnprintf(td->td_comm, sizeof(td->td_comm), ctl, va);
482 KTR_LOG(ctxsw_newtd, td, td->td_comm);
486 * Prevent the thread from getting destroyed. Note that unlike PHOLD/PRELE
487 * this does not prevent the thread from migrating to another cpu so the
488 * gd_tdallq state is not protected by this.
491 lwkt_hold(thread_t td)
493 atomic_add_int(&td->td_refs, 1);
497 lwkt_rele(thread_t td)
499 KKASSERT(td->td_refs > 0);
500 atomic_add_int(&td->td_refs, -1);
504 lwkt_free_thread(thread_t td)
506 KKASSERT(td->td_refs == 0);
507 KKASSERT((td->td_flags & (TDF_RUNNING | TDF_PREEMPT_LOCK |
508 TDF_RUNQ | TDF_TSLEEPQ)) == 0);
509 if (td->td_flags & TDF_ALLOCATED_THREAD) {
510 objcache_put(thread_cache, td);
511 } else if (td->td_flags & TDF_ALLOCATED_STACK) {
512 /* client-allocated struct with internally allocated stack */
513 KASSERT(td->td_kstack && td->td_kstack_size > 0,
514 ("lwkt_free_thread: corrupted stack"));
515 kmem_free(&kernel_map, (vm_offset_t)td->td_kstack, td->td_kstack_size);
516 td->td_kstack = NULL;
517 td->td_kstack_size = 0;
519 KTR_LOG(ctxsw_deadtd, td);
524 * Switch to the next runnable lwkt. If no LWKTs are runnable then
525 * switch to the idlethread. Switching must occur within a critical
526 * section to avoid races with the scheduling queue.
528 * We always have full control over our cpu's run queue. Other cpus
529 * that wish to manipulate our queue must use the cpu_*msg() calls to
530 * talk to our cpu, so a critical section is all that is needed and
531 * the result is very, very fast thread switching.
533 * The LWKT scheduler uses a fixed priority model and round-robins at
534 * each priority level. User process scheduling is a totally
535 * different beast and LWKT priorities should not be confused with
536 * user process priorities.
538 * PREEMPTION NOTE: Preemption occurs via lwkt_preempt(). lwkt_switch()
539 * is not called by the current thread in the preemption case, only when
540 * the preempting thread blocks (in order to return to the original thread).
542 * SPECIAL NOTE ON SWITCH ATOMICY: Certain operations such as thread
543 * migration and tsleep deschedule the current lwkt thread and call
544 * lwkt_switch(). In particular, the target cpu of the migration fully
545 * expects the thread to become non-runnable and can deadlock against
546 * cpusync operations if we run any IPIs prior to switching the thread out.
548 * WE MUST BE VERY CAREFUL NOT TO RUN SPLZ DIRECTLY OR INDIRECTLY IF
549 * THE CURRENT THREAD HAS BEEN DESCHEDULED!
554 globaldata_t gd = mycpu;
555 thread_t td = gd->gd_curthread;
559 KKASSERT(gd->gd_processing_ipiq == 0);
560 KKASSERT(td->td_flags & TDF_RUNNING);
563 * Switching from within a 'fast' (non thread switched) interrupt or IPI
564 * is illegal. However, we may have to do it anyway if we hit a fatal
565 * kernel trap or we have paniced.
567 * If this case occurs save and restore the interrupt nesting level.
569 if (gd->gd_intr_nesting_level) {
573 if (gd->gd_trap_nesting_level == 0 && panic_cpu_gd != mycpu) {
574 panic("lwkt_switch: Attempt to switch from a "
575 "fast interrupt, ipi, or hard code section, "
579 savegdnest = gd->gd_intr_nesting_level;
580 savegdtrap = gd->gd_trap_nesting_level;
581 gd->gd_intr_nesting_level = 0;
582 gd->gd_trap_nesting_level = 0;
583 if ((td->td_flags & TDF_PANICWARN) == 0) {
584 td->td_flags |= TDF_PANICWARN;
585 kprintf("Warning: thread switch from interrupt, IPI, "
586 "or hard code section.\n"
587 "thread %p (%s)\n", td, td->td_comm);
591 gd->gd_intr_nesting_level = savegdnest;
592 gd->gd_trap_nesting_level = savegdtrap;
598 * Release our current user process designation if we are blocking
599 * or if a user reschedule was requested.
601 * NOTE: This function is NOT called if we are switching into or
602 * returning from a preemption.
604 * NOTE: Releasing our current user process designation may cause
605 * it to be assigned to another thread, which in turn will
606 * cause us to block in the usched acquire code when we attempt
607 * to return to userland.
609 * NOTE: On SMP systems this can be very nasty when heavy token
610 * contention is present so we want to be careful not to
611 * release the designation gratuitously.
613 if (td->td_release &&
614 (user_resched_wanted() || (td->td_flags & TDF_RUNQ) == 0)) {
622 if (TD_TOKS_HELD(td))
623 lwkt_relalltokens(td);
626 * We had better not be holding any spin locks, but don't get into an
627 * endless panic loop.
629 KASSERT(gd->gd_spinlocks == 0 || panicstr != NULL,
630 ("lwkt_switch: still holding %d exclusive spinlocks!",
636 if (td->td_cscount) {
637 kprintf("Diagnostic: attempt to switch while mastering cpusync: %p\n",
639 if (panic_on_cscount)
640 panic("switching while mastering cpusync");
646 * If we had preempted another thread on this cpu, resume the preempted
647 * thread. This occurs transparently, whether the preempted thread
648 * was scheduled or not (it may have been preempted after descheduling
651 * We have to setup the MP lock for the original thread after backing
652 * out the adjustment that was made to curthread when the original
655 if ((ntd = td->td_preempted) != NULL) {
656 KKASSERT(ntd->td_flags & TDF_PREEMPT_LOCK);
657 ntd->td_flags |= TDF_PREEMPT_DONE;
660 * The interrupt may have woken a thread up, we need to properly
661 * set the reschedule flag if the originally interrupted thread is
662 * at a lower priority.
664 * The interrupt may not have descheduled.
666 if (TAILQ_FIRST(&gd->gd_tdrunq) != ntd)
668 goto havethread_preempted;
672 * If we cannot obtain ownership of the tokens we cannot immediately
673 * schedule the target thread.
675 * Reminder: Again, we cannot afford to run any IPIs in this path if
676 * the current thread has been descheduled.
679 clear_lwkt_resched();
682 * Hotpath - pull the head of the run queue and attempt to schedule
685 ntd = TAILQ_FIRST(&gd->gd_tdrunq);
689 * Runq is empty, switch to idle to allow it to halt.
691 ntd = &gd->gd_idlethread;
693 if (gd->gd_trap_nesting_level == 0 && panicstr == NULL)
694 ASSERT_NO_TOKENS_HELD(ntd);
696 cpu_time.cp_msg[0] = 0;
697 cpu_time.cp_stallpc = 0;
702 * Hotpath - schedule ntd.
704 * NOTE: For UP there is no mplock and lwkt_getalltokens()
707 if (TD_TOKS_NOT_HELD(ntd) ||
708 lwkt_getalltokens(ntd, (spinning >= lwkt_spin_loops)))
714 * Coldpath (SMP only since tokens always succeed on UP)
716 * We had some contention on the thread we wanted to schedule.
717 * What we do now is try to find a thread that we can schedule
720 * The coldpath scan does NOT rearrange threads in the run list.
721 * The lwkt_schedulerclock() will assert need_lwkt_resched() on
722 * the next tick whenever the current head is not the current thread.
727 ++gd->gd_cnt.v_token_colls;
729 if (fairq_bypass > 0)
732 while ((ntd = TAILQ_NEXT(ntd, td_threadq)) != NULL) {
733 #ifndef NO_LWKT_SPLIT_USERPRI
735 * Never schedule threads returning to userland or the
736 * user thread scheduler helper thread when higher priority
737 * threads are present. The runq is sorted by priority
738 * so we can give up traversing it when we find the first
739 * low priority thread.
741 if (ntd->td_pri < TDPRI_KERN_LPSCHED) {
750 if (TD_TOKS_NOT_HELD(ntd) ||
751 lwkt_getalltokens(ntd, (spinning >= lwkt_spin_loops))) {
757 ++gd->gd_cnt.v_token_colls;
762 * We exhausted the run list, meaning that all runnable threads
766 ntd = &gd->gd_idlethread;
768 if (gd->gd_trap_nesting_level == 0 && panicstr == NULL)
769 ASSERT_NO_TOKENS_HELD(ntd);
770 /* contention case, do not clear contention mask */
774 * We are going to have to retry but if the current thread is not
775 * on the runq we instead switch through the idle thread to get away
776 * from the current thread. We have to flag for lwkt reschedule
777 * to prevent the idle thread from halting.
779 * NOTE: A non-zero spinning is passed to lwkt_getalltokens() to
780 * instruct it to deal with the potential for deadlocks by
781 * ordering the tokens by address.
783 if ((td->td_flags & TDF_RUNQ) == 0) {
784 need_lwkt_resched(); /* prevent hlt */
787 #if defined(INVARIANTS) && defined(__amd64__)
788 if ((read_rflags() & PSL_I) == 0) {
790 panic("lwkt_switch() called with interrupts disabled");
795 * Number iterations so far. After a certain point we switch to
796 * a sorted-address/monitor/mwait version of lwkt_getalltokens()
798 if (spinning < 0x7FFFFFFF)
803 * lwkt_getalltokens() failed in sorted token mode, we can use
804 * monitor/mwait in this case.
806 if (spinning >= lwkt_spin_loops &&
807 (cpu_mi_feature & CPU_MI_MONITOR) &&
810 cpu_mmw_pause_int(&gd->gd_reqflags,
811 (gd->gd_reqflags | RQF_SPINNING) &
812 ~RQF_IDLECHECK_WK_MASK);
817 * We already checked that td is still scheduled so this should be
823 * This experimental resequencer is used as a fall-back to reduce
824 * hw cache line contention by placing each core's scheduler into a
825 * time-domain-multplexed slot.
827 * The resequencer is disabled by default. It's functionality has
828 * largely been superceeded by the token algorithm which limits races
829 * to a subset of cores.
831 * The resequencer algorithm tends to break down when more than
832 * 20 cores are contending. What appears to happen is that new
833 * tokens can be obtained out of address-sorted order by new cores
834 * while existing cores languish in long delays between retries and
835 * wind up being starved-out of the token acquisition.
837 if (lwkt_spin_reseq && spinning >= lwkt_spin_reseq) {
838 int cseq = atomic_fetchadd_int(&lwkt_cseq_windex, 1);
841 while ((oseq = lwkt_cseq_rindex) != cseq) {
844 if (cpu_mi_feature & CPU_MI_MONITOR) {
845 cpu_mmw_pause_int(&lwkt_cseq_rindex, oseq);
855 atomic_add_int(&lwkt_cseq_rindex, 1);
857 /* highest level for(;;) loop */
862 * Clear gd_idle_repeat when doing a normal switch to a non-idle
865 ntd->td_wmesg = NULL;
866 ++gd->gd_cnt.v_swtch;
867 gd->gd_idle_repeat = 0;
869 havethread_preempted:
871 * If the new target does not need the MP lock and we are holding it,
872 * release the MP lock. If the new target requires the MP lock we have
873 * already acquired it for the target.
877 KASSERT(ntd->td_critcount,
878 ("priority problem in lwkt_switch %d %d",
879 td->td_critcount, ntd->td_critcount));
883 * Execute the actual thread switch operation. This function
884 * returns to the current thread and returns the previous thread
885 * (which may be different from the thread we switched to).
887 * We are responsible for marking ntd as TDF_RUNNING.
889 KKASSERT((ntd->td_flags & TDF_RUNNING) == 0);
891 KTR_LOG(ctxsw_sw, gd->gd_cpuid, ntd);
892 ntd->td_flags |= TDF_RUNNING;
893 lwkt_switch_return(td->td_switch(ntd));
894 /* ntd invalid, td_switch() can return a different thread_t */
898 * catch-all. XXX is this strictly needed?
902 /* NOTE: current cpu may have changed after switch */
907 * Called by assembly in the td_switch (thread restore path) for thread
908 * bootstrap cases which do not 'return' to lwkt_switch().
911 lwkt_switch_return(thread_t otd)
917 * Check if otd was migrating. Now that we are on ntd we can finish
918 * up the migration. This is a bit messy but it is the only place
919 * where td is known to be fully descheduled.
921 * We can only activate the migration if otd was migrating but not
922 * held on the cpu due to a preemption chain. We still have to
923 * clear TDF_RUNNING on the old thread either way.
925 * We are responsible for clearing the previously running thread's
928 if ((rgd = otd->td_migrate_gd) != NULL &&
929 (otd->td_flags & TDF_PREEMPT_LOCK) == 0) {
930 KKASSERT((otd->td_flags & (TDF_MIGRATING | TDF_RUNNING)) ==
931 (TDF_MIGRATING | TDF_RUNNING));
932 otd->td_migrate_gd = NULL;
933 otd->td_flags &= ~TDF_RUNNING;
934 lwkt_send_ipiq(rgd, lwkt_setcpu_remote, otd);
936 otd->td_flags &= ~TDF_RUNNING;
939 otd->td_flags &= ~TDF_RUNNING;
943 * Final exit validations (see lwp_wait()). Note that otd becomes
944 * invalid the *instant* we set TDF_MP_EXITSIG.
946 while (otd->td_flags & TDF_EXITING) {
949 mpflags = otd->td_mpflags;
952 if (mpflags & TDF_MP_EXITWAIT) {
953 if (atomic_cmpset_int(&otd->td_mpflags, mpflags,
954 mpflags | TDF_MP_EXITSIG)) {
959 if (atomic_cmpset_int(&otd->td_mpflags, mpflags,
960 mpflags | TDF_MP_EXITSIG)) {
969 * Request that the target thread preempt the current thread. Preemption
970 * can only occur if our only critical section is the one that we were called
971 * with, the relative priority of the target thread is higher, and the target
972 * thread holds no tokens. This also only works if we are not holding any
973 * spinlocks (obviously).
975 * THE CALLER OF LWKT_PREEMPT() MUST BE IN A CRITICAL SECTION. Typically
976 * this is called via lwkt_schedule() through the td_preemptable callback.
977 * critcount is the managed critical priority that we should ignore in order
978 * to determine whether preemption is possible (aka usually just the crit
979 * priority of lwkt_schedule() itself).
981 * Preemption is typically limited to interrupt threads.
983 * Operation works in a fairly straight-forward manner. The normal
984 * scheduling code is bypassed and we switch directly to the target
985 * thread. When the target thread attempts to block or switch away
986 * code at the base of lwkt_switch() will switch directly back to our
987 * thread. Our thread is able to retain whatever tokens it holds and
988 * if the target needs one of them the target will switch back to us
989 * and reschedule itself normally.
992 lwkt_preempt(thread_t ntd, int critcount)
994 struct globaldata *gd = mycpu;
997 int save_gd_intr_nesting_level;
1000 * The caller has put us in a critical section. We can only preempt
1001 * if the caller of the caller was not in a critical section (basically
1002 * a local interrupt), as determined by the 'critcount' parameter. We
1003 * also can't preempt if the caller is holding any spinlocks (even if
1004 * he isn't in a critical section). This also handles the tokens test.
1006 * YYY The target thread must be in a critical section (else it must
1007 * inherit our critical section? I dunno yet).
1009 KASSERT(ntd->td_critcount, ("BADCRIT0 %d", ntd->td_pri));
1011 td = gd->gd_curthread;
1012 if (preempt_enable == 0) {
1016 if (ntd->td_pri <= td->td_pri) {
1020 if (td->td_critcount > critcount) {
1025 if (td->td_cscount) {
1029 if (ntd->td_gd != gd) {
1035 * We don't have to check spinlocks here as they will also bump
1038 * Do not try to preempt if the target thread is holding any tokens.
1039 * We could try to acquire the tokens but this case is so rare there
1040 * is no need to support it.
1042 KKASSERT(gd->gd_spinlocks == 0);
1044 if (TD_TOKS_HELD(ntd)) {
1048 if (td == ntd || ((td->td_flags | ntd->td_flags) & TDF_PREEMPT_LOCK)) {
1052 if (ntd->td_preempted) {
1056 KKASSERT(gd->gd_processing_ipiq == 0);
1059 * Since we are able to preempt the current thread, there is no need to
1060 * call need_lwkt_resched().
1062 * We must temporarily clear gd_intr_nesting_level around the switch
1063 * since switchouts from the target thread are allowed (they will just
1064 * return to our thread), and since the target thread has its own stack.
1066 * A preemption must switch back to the original thread, assert the
1070 ntd->td_preempted = td;
1071 td->td_flags |= TDF_PREEMPT_LOCK;
1072 KTR_LOG(ctxsw_pre, gd->gd_cpuid, ntd);
1073 save_gd_intr_nesting_level = gd->gd_intr_nesting_level;
1074 gd->gd_intr_nesting_level = 0;
1076 KKASSERT((ntd->td_flags & TDF_RUNNING) == 0);
1077 ntd->td_flags |= TDF_RUNNING;
1078 xtd = td->td_switch(ntd);
1079 KKASSERT(xtd == ntd);
1080 lwkt_switch_return(xtd);
1081 gd->gd_intr_nesting_level = save_gd_intr_nesting_level;
1083 KKASSERT(ntd->td_preempted && (td->td_flags & TDF_PREEMPT_DONE));
1084 ntd->td_preempted = NULL;
1085 td->td_flags &= ~(TDF_PREEMPT_LOCK|TDF_PREEMPT_DONE);
1089 * Conditionally call splz() if gd_reqflags indicates work is pending.
1090 * This will work inside a critical section but not inside a hard code
1093 * (self contained on a per cpu basis)
1098 globaldata_t gd = mycpu;
1099 thread_t td = gd->gd_curthread;
1101 if ((gd->gd_reqflags & RQF_IDLECHECK_MASK) &&
1102 gd->gd_intr_nesting_level == 0 &&
1103 td->td_nest_count < 2)
1110 * This version is integrated into crit_exit, reqflags has already
1111 * been tested but td_critcount has not.
1113 * We only want to execute the splz() on the 1->0 transition of
1114 * critcount and not in a hard code section or if too deeply nested.
1116 * NOTE: gd->gd_spinlocks is implied to be 0 when td_critcount is 0.
1119 lwkt_maybe_splz(thread_t td)
1121 globaldata_t gd = td->td_gd;
1123 if (td->td_critcount == 0 &&
1124 gd->gd_intr_nesting_level == 0 &&
1125 td->td_nest_count < 2)
1132 * Drivers which set up processing co-threads can call this function to
1133 * run the co-thread at a higher priority and to allow it to preempt
1137 lwkt_set_interrupt_support_thread(void)
1139 thread_t td = curthread;
1141 lwkt_setpri_self(TDPRI_INT_SUPPORT);
1142 td->td_flags |= TDF_INTTHREAD;
1143 td->td_preemptable = lwkt_preempt;
1148 * This function is used to negotiate a passive release of the current
1149 * process/lwp designation with the user scheduler, allowing the user
1150 * scheduler to schedule another user thread. The related kernel thread
1151 * (curthread) continues running in the released state.
1154 lwkt_passive_release(struct thread *td)
1156 struct lwp *lp = td->td_lwp;
1158 #ifndef NO_LWKT_SPLIT_USERPRI
1159 td->td_release = NULL;
1160 lwkt_setpri_self(TDPRI_KERN_USER);
1163 lp->lwp_proc->p_usched->release_curproc(lp);
1168 * This implements a LWKT yield, allowing a kernel thread to yield to other
1169 * kernel threads at the same or higher priority. This function can be
1170 * called in a tight loop and will typically only yield once per tick.
1172 * Most kernel threads run at the same priority in order to allow equal
1175 * (self contained on a per cpu basis)
1180 globaldata_t gd = mycpu;
1181 thread_t td = gd->gd_curthread;
1183 if ((gd->gd_reqflags & RQF_IDLECHECK_MASK) && td->td_nest_count < 2)
1185 if (lwkt_resched_wanted()) {
1186 lwkt_schedule_self(curthread);
1192 * The quick version processes pending interrupts and higher-priority
1193 * LWKT threads but will not round-robin same-priority LWKT threads.
1195 * When called while attempting to return to userland the only same-pri
1196 * threads are the ones which have already tried to become the current
1200 lwkt_yield_quick(void)
1202 globaldata_t gd = mycpu;
1203 thread_t td = gd->gd_curthread;
1205 if ((gd->gd_reqflags & RQF_IDLECHECK_MASK) && td->td_nest_count < 2)
1207 if (lwkt_resched_wanted()) {
1208 if (TAILQ_FIRST(&gd->gd_tdrunq) == td) {
1209 clear_lwkt_resched();
1211 lwkt_schedule_self(curthread);
1218 * This yield is designed for kernel threads with a user context.
1220 * The kernel acting on behalf of the user is potentially cpu-bound,
1221 * this function will efficiently allow other threads to run and also
1222 * switch to other processes by releasing.
1224 * The lwkt_user_yield() function is designed to have very low overhead
1225 * if no yield is determined to be needed.
1228 lwkt_user_yield(void)
1230 globaldata_t gd = mycpu;
1231 thread_t td = gd->gd_curthread;
1234 * Always run any pending interrupts in case we are in a critical
1237 if ((gd->gd_reqflags & RQF_IDLECHECK_MASK) && td->td_nest_count < 2)
1241 * Switch (which forces a release) if another kernel thread needs
1242 * the cpu, if userland wants us to resched, or if our kernel
1243 * quantum has run out.
1245 if (lwkt_resched_wanted() ||
1246 user_resched_wanted())
1253 * Reacquire the current process if we are released.
1255 * XXX not implemented atm. The kernel may be holding locks and such,
1256 * so we want the thread to continue to receive cpu.
1258 if (td->td_release == NULL && lp) {
1259 lp->lwp_proc->p_usched->acquire_curproc(lp);
1260 td->td_release = lwkt_passive_release;
1261 lwkt_setpri_self(TDPRI_USER_NORM);
1267 * Generic schedule. Possibly schedule threads belonging to other cpus and
1268 * deal with threads that might be blocked on a wait queue.
1270 * We have a little helper inline function which does additional work after
1271 * the thread has been enqueued, including dealing with preemption and
1272 * setting need_lwkt_resched() (which prevents the kernel from returning
1273 * to userland until it has processed higher priority threads).
1275 * It is possible for this routine to be called after a failed _enqueue
1276 * (due to the target thread migrating, sleeping, or otherwise blocked).
1277 * We have to check that the thread is actually on the run queue!
1281 _lwkt_schedule_post(globaldata_t gd, thread_t ntd, int ccount)
1283 if (ntd->td_flags & TDF_RUNQ) {
1284 if (ntd->td_preemptable) {
1285 ntd->td_preemptable(ntd, ccount); /* YYY +token */
1292 _lwkt_schedule(thread_t td)
1294 globaldata_t mygd = mycpu;
1296 KASSERT(td != &td->td_gd->gd_idlethread,
1297 ("lwkt_schedule(): scheduling gd_idlethread is illegal!"));
1298 KKASSERT((td->td_flags & TDF_MIGRATING) == 0);
1299 crit_enter_gd(mygd);
1300 KKASSERT(td->td_lwp == NULL ||
1301 (td->td_lwp->lwp_mpflags & LWP_MP_ONRUNQ) == 0);
1303 if (td == mygd->gd_curthread) {
1307 * If we own the thread, there is no race (since we are in a
1308 * critical section). If we do not own the thread there might
1309 * be a race but the target cpu will deal with it.
1312 if (td->td_gd == mygd) {
1314 _lwkt_schedule_post(mygd, td, 1);
1316 lwkt_send_ipiq3(td->td_gd, lwkt_schedule_remote, td, 0);
1320 _lwkt_schedule_post(mygd, td, 1);
1327 lwkt_schedule(thread_t td)
1333 lwkt_schedule_noresched(thread_t td) /* XXX not impl */
1341 * When scheduled remotely if frame != NULL the IPIQ is being
1342 * run via doreti or an interrupt then preemption can be allowed.
1344 * To allow preemption we have to drop the critical section so only
1345 * one is present in _lwkt_schedule_post.
1348 lwkt_schedule_remote(void *arg, int arg2, struct intrframe *frame)
1350 thread_t td = curthread;
1353 if (frame && ntd->td_preemptable) {
1354 crit_exit_noyield(td);
1355 _lwkt_schedule(ntd);
1356 crit_enter_quick(td);
1358 _lwkt_schedule(ntd);
1363 * Thread migration using a 'Pull' method. The thread may or may not be
1364 * the current thread. It MUST be descheduled and in a stable state.
1365 * lwkt_giveaway() must be called on the cpu owning the thread.
1367 * At any point after lwkt_giveaway() is called, the target cpu may
1368 * 'pull' the thread by calling lwkt_acquire().
1370 * We have to make sure the thread is not sitting on a per-cpu tsleep
1371 * queue or it will blow up when it moves to another cpu.
1373 * MPSAFE - must be called under very specific conditions.
1376 lwkt_giveaway(thread_t td)
1378 globaldata_t gd = mycpu;
1381 if (td->td_flags & TDF_TSLEEPQ)
1383 KKASSERT(td->td_gd == gd);
1384 TAILQ_REMOVE(&gd->gd_tdallq, td, td_allq);
1385 td->td_flags |= TDF_MIGRATING;
1390 lwkt_acquire(thread_t td)
1394 int retry = 10000000;
1396 KKASSERT(td->td_flags & TDF_MIGRATING);
1401 KKASSERT((td->td_flags & TDF_RUNQ) == 0);
1402 crit_enter_gd(mygd);
1403 DEBUG_PUSH_INFO("lwkt_acquire");
1404 while (td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK)) {
1406 lwkt_process_ipiq();
1410 kprintf("lwkt_acquire: stuck: td %p td->td_flags %08x\n",
1418 TAILQ_INSERT_TAIL(&mygd->gd_tdallq, td, td_allq);
1419 td->td_flags &= ~TDF_MIGRATING;
1422 crit_enter_gd(mygd);
1423 TAILQ_INSERT_TAIL(&mygd->gd_tdallq, td, td_allq);
1424 td->td_flags &= ~TDF_MIGRATING;
1432 * Generic deschedule. Descheduling threads other then your own should be
1433 * done only in carefully controlled circumstances. Descheduling is
1436 * This function may block if the cpu has run out of messages.
1439 lwkt_deschedule(thread_t td)
1443 if (td == curthread) {
1446 if (td->td_gd == mycpu) {
1449 lwkt_send_ipiq(td->td_gd, (ipifunc1_t)lwkt_deschedule, td);
1459 * Set the target thread's priority. This routine does not automatically
1460 * switch to a higher priority thread, LWKT threads are not designed for
1461 * continuous priority changes. Yield if you want to switch.
1464 lwkt_setpri(thread_t td, int pri)
1466 if (td->td_pri != pri) {
1469 if (td->td_flags & TDF_RUNQ) {
1470 KKASSERT(td->td_gd == mycpu);
1482 * Set the initial priority for a thread prior to it being scheduled for
1483 * the first time. The thread MUST NOT be scheduled before or during
1484 * this call. The thread may be assigned to a cpu other then the current
1487 * Typically used after a thread has been created with TDF_STOPPREQ,
1488 * and before the thread is initially scheduled.
1491 lwkt_setpri_initial(thread_t td, int pri)
1494 KKASSERT((td->td_flags & TDF_RUNQ) == 0);
1499 lwkt_setpri_self(int pri)
1501 thread_t td = curthread;
1503 KKASSERT(pri >= 0 && pri <= TDPRI_MAX);
1505 if (td->td_flags & TDF_RUNQ) {
1516 * hz tick scheduler clock for LWKT threads
1519 lwkt_schedulerclock(thread_t td)
1521 globaldata_t gd = td->td_gd;
1524 if (TAILQ_FIRST(&gd->gd_tdrunq) == td) {
1526 * If the current thread is at the head of the runq shift it to the
1527 * end of any equal-priority threads and request a LWKT reschedule
1530 * Ignore upri in this situation. There will only be one user thread
1531 * in user mode, all others will be user threads running in kernel
1532 * mode and we have to make sure they get some cpu.
1534 xtd = TAILQ_NEXT(td, td_threadq);
1535 if (xtd && xtd->td_pri == td->td_pri) {
1536 TAILQ_REMOVE(&gd->gd_tdrunq, td, td_threadq);
1537 while (xtd && xtd->td_pri == td->td_pri)
1538 xtd = TAILQ_NEXT(xtd, td_threadq);
1540 TAILQ_INSERT_BEFORE(xtd, td, td_threadq);
1542 TAILQ_INSERT_TAIL(&gd->gd_tdrunq, td, td_threadq);
1543 need_lwkt_resched();
1547 * If we scheduled a thread other than the one at the head of the
1548 * queue always request a reschedule every tick.
1550 need_lwkt_resched();
1555 * Migrate the current thread to the specified cpu.
1557 * This is accomplished by descheduling ourselves from the current cpu
1558 * and setting td_migrate_gd. The lwkt_switch() code will detect that the
1559 * 'old' thread wants to migrate after it has been completely switched out
1560 * and will complete the migration.
1562 * TDF_MIGRATING prevents scheduling races while the thread is being migrated.
1564 * We must be sure to release our current process designation (if a user
1565 * process) before clearing out any tsleepq we are on because the release
1566 * code may re-add us.
1568 * We must be sure to remove ourselves from the current cpu's tsleepq
1569 * before potentially moving to another queue. The thread can be on
1570 * a tsleepq due to a left-over tsleep_interlock().
1574 lwkt_setcpu_self(globaldata_t rgd)
1577 thread_t td = curthread;
1579 if (td->td_gd != rgd) {
1580 crit_enter_quick(td);
1584 if (td->td_flags & TDF_TSLEEPQ)
1588 * Set TDF_MIGRATING to prevent a spurious reschedule while we are
1589 * trying to deschedule ourselves and switch away, then deschedule
1590 * ourself, remove us from tdallq, and set td_migrate_gd. Finally,
1591 * call lwkt_switch() to complete the operation.
1593 td->td_flags |= TDF_MIGRATING;
1594 lwkt_deschedule_self(td);
1595 TAILQ_REMOVE(&td->td_gd->gd_tdallq, td, td_allq);
1596 td->td_migrate_gd = rgd;
1600 * We are now on the target cpu
1602 KKASSERT(rgd == mycpu);
1603 TAILQ_INSERT_TAIL(&rgd->gd_tdallq, td, td_allq);
1604 crit_exit_quick(td);
1610 lwkt_migratecpu(int cpuid)
1615 rgd = globaldata_find(cpuid);
1616 lwkt_setcpu_self(rgd);
1622 * Remote IPI for cpu migration (called while in a critical section so we
1623 * do not have to enter another one).
1625 * The thread (td) has already been completely descheduled from the
1626 * originating cpu and we can simply assert the case. The thread is
1627 * assigned to the new cpu and enqueued.
1629 * The thread will re-add itself to tdallq when it resumes execution.
1632 lwkt_setcpu_remote(void *arg)
1635 globaldata_t gd = mycpu;
1637 KKASSERT((td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK)) == 0);
1640 td->td_flags &= ~TDF_MIGRATING;
1641 KKASSERT(td->td_migrate_gd == NULL);
1642 KKASSERT(td->td_lwp == NULL ||
1643 (td->td_lwp->lwp_mpflags & LWP_MP_ONRUNQ) == 0);
1649 lwkt_preempted_proc(void)
1651 thread_t td = curthread;
1652 while (td->td_preempted)
1653 td = td->td_preempted;
1658 * Create a kernel process/thread/whatever. It shares it's address space
1659 * with proc0 - ie: kernel only.
1661 * If the cpu is not specified one will be selected. In the future
1662 * specifying a cpu of -1 will enable kernel thread migration between
1666 lwkt_create(void (*func)(void *), void *arg, struct thread **tdp,
1667 thread_t template, int tdflags, int cpu, const char *fmt, ...)
1672 td = lwkt_alloc_thread(template, LWKT_THREAD_STACK, cpu,
1676 cpu_set_thread_handler(td, lwkt_exit, func, arg);
1679 * Set up arg0 for 'ps' etc
1681 __va_start(ap, fmt);
1682 kvsnprintf(td->td_comm, sizeof(td->td_comm), fmt, ap);
1686 * Schedule the thread to run
1688 if (td->td_flags & TDF_NOSTART)
1689 td->td_flags &= ~TDF_NOSTART;
1696 * Destroy an LWKT thread. Warning! This function is not called when
1697 * a process exits, cpu_proc_exit() directly calls cpu_thread_exit() and
1698 * uses a different reaping mechanism.
1703 thread_t td = curthread;
1708 * Do any cleanup that might block here
1710 if (td->td_flags & TDF_VERBOSE)
1711 kprintf("kthread %p %s has exited\n", td, td->td_comm);
1714 dsched_exit_thread(td);
1717 * Get us into a critical section to interlock gd_freetd and loop
1718 * until we can get it freed.
1720 * We have to cache the current td in gd_freetd because objcache_put()ing
1721 * it would rip it out from under us while our thread is still active.
1723 * We are the current thread so of course our own TDF_RUNNING bit will
1724 * be set, so unlike the lwp reap code we don't wait for it to clear.
1727 crit_enter_quick(td);
1730 tsleep(td, 0, "tdreap", 1);
1733 if ((std = gd->gd_freetd) != NULL) {
1734 KKASSERT((std->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK)) == 0);
1735 gd->gd_freetd = NULL;
1736 objcache_put(thread_cache, std);
1743 * Remove thread resources from kernel lists and deschedule us for
1744 * the last time. We cannot block after this point or we may end
1745 * up with a stale td on the tsleepq.
1747 * None of this may block, the critical section is the only thing
1748 * protecting tdallq and the only thing preventing new lwkt_hold()
1751 if (td->td_flags & TDF_TSLEEPQ)
1753 lwkt_deschedule_self(td);
1754 lwkt_remove_tdallq(td);
1755 KKASSERT(td->td_refs == 0);
1760 KKASSERT(gd->gd_freetd == NULL);
1761 if (td->td_flags & TDF_ALLOCATED_THREAD)
1767 lwkt_remove_tdallq(thread_t td)
1769 KKASSERT(td->td_gd == mycpu);
1770 TAILQ_REMOVE(&td->td_gd->gd_tdallq, td, td_allq);
1774 * Code reduction and branch prediction improvements. Call/return
1775 * overhead on modern cpus often degenerates into 0 cycles due to
1776 * the cpu's branch prediction hardware and return pc cache. We
1777 * can take advantage of this by not inlining medium-complexity
1778 * functions and we can also reduce the branch prediction impact
1779 * by collapsing perfectly predictable branches into a single
1780 * procedure instead of duplicating it.
1782 * Is any of this noticeable? Probably not, so I'll take the
1783 * smaller code size.
1786 crit_exit_wrapper(__DEBUG_CRIT_ARG__)
1788 _crit_exit(mycpu __DEBUG_CRIT_PASS_ARG__);
1794 thread_t td = curthread;
1795 int lcrit = td->td_critcount;
1797 td->td_critcount = 0;
1798 panic("td_critcount is/would-go negative! %p %d", td, lcrit);
1805 * Called from debugger/panic on cpus which have been stopped. We must still
1806 * process the IPIQ while stopped, even if we were stopped while in a critical
1809 * If we are dumping also try to process any pending interrupts. This may
1810 * or may not work depending on the state of the cpu at the point it was
1814 lwkt_smp_stopped(void)
1816 globaldata_t gd = mycpu;
1820 lwkt_process_ipiq();
1823 lwkt_process_ipiq();