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>
53 #include <sys/spinlock.h>
56 #include <sys/thread2.h>
57 #include <sys/spinlock2.h>
58 #include <sys/mplock2.h>
60 #include <sys/dsched.h>
63 #include <vm/vm_param.h>
64 #include <vm/vm_kern.h>
65 #include <vm/vm_object.h>
66 #include <vm/vm_page.h>
67 #include <vm/vm_map.h>
68 #include <vm/vm_pager.h>
69 #include <vm/vm_extern.h>
71 #include <machine/stdarg.h>
72 #include <machine/smp.h>
74 #if !defined(KTR_CTXSW)
75 #define KTR_CTXSW KTR_ALL
77 KTR_INFO_MASTER(ctxsw);
78 KTR_INFO(KTR_CTXSW, ctxsw, sw, 0, "#cpu[%d].td = %p", int cpu, struct thread *td);
79 KTR_INFO(KTR_CTXSW, ctxsw, pre, 1, "#cpu[%d].td = %p", int cpu, struct thread *td);
80 KTR_INFO(KTR_CTXSW, ctxsw, newtd, 2, "#threads[%p].name = %s", struct thread *td, char *comm);
81 KTR_INFO(KTR_CTXSW, ctxsw, deadtd, 3, "#threads[%p].name = <dead>", struct thread *td);
83 static MALLOC_DEFINE(M_THREAD, "thread", "lwkt threads");
86 static int panic_on_cscount = 0;
88 static __int64_t switch_count = 0;
89 static __int64_t preempt_hit = 0;
90 static __int64_t preempt_miss = 0;
91 static __int64_t preempt_weird = 0;
92 static int lwkt_use_spin_port;
93 static struct objcache *thread_cache;
95 static void lwkt_schedule_remote(void *arg, int arg2, struct intrframe *frame);
96 static void lwkt_setcpu_remote(void *arg);
98 extern void cpu_heavy_restore(void);
99 extern void cpu_lwkt_restore(void);
100 extern void cpu_kthread_restore(void);
101 extern void cpu_idle_restore(void);
104 * We can make all thread ports use the spin backend instead of the thread
105 * backend. This should only be set to debug the spin backend.
107 TUNABLE_INT("lwkt.use_spin_port", &lwkt_use_spin_port);
110 SYSCTL_INT(_lwkt, OID_AUTO, panic_on_cscount, CTLFLAG_RW, &panic_on_cscount, 0,
111 "Panic if attempting to switch lwkt's while mastering cpusync");
113 SYSCTL_QUAD(_lwkt, OID_AUTO, switch_count, CTLFLAG_RW, &switch_count, 0,
114 "Number of switched threads");
115 SYSCTL_QUAD(_lwkt, OID_AUTO, preempt_hit, CTLFLAG_RW, &preempt_hit, 0,
116 "Successful preemption events");
117 SYSCTL_QUAD(_lwkt, OID_AUTO, preempt_miss, CTLFLAG_RW, &preempt_miss, 0,
118 "Failed preemption events");
119 SYSCTL_QUAD(_lwkt, OID_AUTO, preempt_weird, CTLFLAG_RW, &preempt_weird, 0,
120 "Number of preempted threads.");
121 static int fairq_enable = 0;
122 SYSCTL_INT(_lwkt, OID_AUTO, fairq_enable, CTLFLAG_RW,
123 &fairq_enable, 0, "Turn on fairq priority accumulators");
124 static int fairq_bypass = -1;
125 SYSCTL_INT(_lwkt, OID_AUTO, fairq_bypass, CTLFLAG_RW,
126 &fairq_bypass, 0, "Allow fairq to bypass td on token failure");
127 extern int lwkt_sched_debug;
128 int lwkt_sched_debug = 0;
129 SYSCTL_INT(_lwkt, OID_AUTO, sched_debug, CTLFLAG_RW,
130 &lwkt_sched_debug, 0, "Scheduler debug");
131 static int lwkt_spin_loops = 10;
132 SYSCTL_INT(_lwkt, OID_AUTO, spin_loops, CTLFLAG_RW,
133 &lwkt_spin_loops, 0, "Scheduler spin loops until sorted decon");
134 static int lwkt_spin_reseq = 0;
135 SYSCTL_INT(_lwkt, OID_AUTO, spin_reseq, CTLFLAG_RW,
136 &lwkt_spin_reseq, 0, "Scheduler resequencer enable");
137 static int lwkt_spin_monitor = 0;
138 SYSCTL_INT(_lwkt, OID_AUTO, spin_monitor, CTLFLAG_RW,
139 &lwkt_spin_monitor, 0, "Scheduler uses monitor/mwait");
140 static int lwkt_spin_fatal = 0; /* disabled */
141 SYSCTL_INT(_lwkt, OID_AUTO, spin_fatal, CTLFLAG_RW,
142 &lwkt_spin_fatal, 0, "LWKT scheduler spin loops till fatal panic");
143 static int preempt_enable = 1;
144 SYSCTL_INT(_lwkt, OID_AUTO, preempt_enable, CTLFLAG_RW,
145 &preempt_enable, 0, "Enable preemption");
146 static int lwkt_cache_threads = 0;
147 SYSCTL_INT(_lwkt, OID_AUTO, cache_threads, CTLFLAG_RD,
148 &lwkt_cache_threads, 0, "thread+kstack cache");
150 static __cachealign int lwkt_cseq_rindex;
151 static __cachealign int lwkt_cseq_windex;
154 * These helper procedures handle the runq, they can only be called from
155 * within a critical section.
157 * WARNING! Prior to SMP being brought up it is possible to enqueue and
158 * dequeue threads belonging to other cpus, so be sure to use td->td_gd
159 * instead of 'mycpu' when referencing the globaldata structure. Once
160 * SMP live enqueuing and dequeueing only occurs on the current cpu.
164 _lwkt_dequeue(thread_t td)
166 if (td->td_flags & TDF_RUNQ) {
167 struct globaldata *gd = td->td_gd;
169 td->td_flags &= ~TDF_RUNQ;
170 TAILQ_REMOVE(&gd->gd_tdrunq, td, td_threadq);
171 --gd->gd_tdrunqcount;
172 if (TAILQ_FIRST(&gd->gd_tdrunq) == NULL)
173 atomic_clear_int(&gd->gd_reqflags, RQF_RUNNING);
180 * There are a limited number of lwkt threads runnable since user
181 * processes only schedule one at a time per cpu. However, there can
182 * be many user processes in kernel mode exiting from a tsleep() which
185 * NOTE: lwkt_schedulerclock() will force a round-robin based on td_pri and
186 * will ignore user priority. This is to ensure that user threads in
187 * kernel mode get cpu at some point regardless of what the user
192 _lwkt_enqueue(thread_t td)
196 if ((td->td_flags & (TDF_RUNQ|TDF_MIGRATING|TDF_BLOCKQ)) == 0) {
197 struct globaldata *gd = td->td_gd;
199 td->td_flags |= TDF_RUNQ;
200 xtd = TAILQ_FIRST(&gd->gd_tdrunq);
202 TAILQ_INSERT_TAIL(&gd->gd_tdrunq, td, td_threadq);
203 atomic_set_int(&gd->gd_reqflags, RQF_RUNNING);
206 * NOTE: td_upri - higher numbers more desireable, same sense
207 * as td_pri (typically reversed from lwp_upri).
209 * In the equal priority case we want the best selection
210 * at the beginning so the less desireable selections know
211 * that they have to setrunqueue/go-to-another-cpu, even
212 * though it means switching back to the 'best' selection.
213 * This also avoids degenerate situations when many threads
214 * are runnable or waking up at the same time.
216 * If upri matches exactly place at end/round-robin.
219 (xtd->td_pri >= td->td_pri ||
220 (xtd->td_pri == td->td_pri &&
221 xtd->td_upri >= td->td_upri))) {
222 xtd = TAILQ_NEXT(xtd, td_threadq);
225 TAILQ_INSERT_BEFORE(xtd, td, td_threadq);
227 TAILQ_INSERT_TAIL(&gd->gd_tdrunq, td, td_threadq);
229 ++gd->gd_tdrunqcount;
232 * Request a LWKT reschedule if we are now at the head of the queue.
234 if (TAILQ_FIRST(&gd->gd_tdrunq) == td)
240 _lwkt_thread_ctor(void *obj, void *privdata, int ocflags)
242 struct thread *td = (struct thread *)obj;
244 td->td_kstack = NULL;
245 td->td_kstack_size = 0;
246 td->td_flags = TDF_ALLOCATED_THREAD;
252 _lwkt_thread_dtor(void *obj, void *privdata)
254 struct thread *td = (struct thread *)obj;
256 KASSERT(td->td_flags & TDF_ALLOCATED_THREAD,
257 ("_lwkt_thread_dtor: not allocated from objcache"));
258 KASSERT((td->td_flags & TDF_ALLOCATED_STACK) && td->td_kstack &&
259 td->td_kstack_size > 0,
260 ("_lwkt_thread_dtor: corrupted stack"));
261 kmem_free(&kernel_map, (vm_offset_t)td->td_kstack, td->td_kstack_size);
262 td->td_kstack = NULL;
267 * Initialize the lwkt s/system.
269 * Nominally cache up to 32 thread + kstack structures. Cache more on
270 * systems with a lot of cpu cores.
275 TUNABLE_INT("lwkt.cache_threads", &lwkt_cache_threads);
276 if (lwkt_cache_threads == 0) {
277 lwkt_cache_threads = ncpus * 4;
278 if (lwkt_cache_threads < 32)
279 lwkt_cache_threads = 32;
281 thread_cache = objcache_create_mbacked(
282 M_THREAD, sizeof(struct thread),
283 0, lwkt_cache_threads,
284 _lwkt_thread_ctor, _lwkt_thread_dtor, NULL);
288 * Schedule a thread to run. As the current thread we can always safely
289 * schedule ourselves, and a shortcut procedure is provided for that
292 * (non-blocking, self contained on a per cpu basis)
295 lwkt_schedule_self(thread_t td)
297 KKASSERT((td->td_flags & TDF_MIGRATING) == 0);
298 crit_enter_quick(td);
299 KASSERT(td != &td->td_gd->gd_idlethread,
300 ("lwkt_schedule_self(): scheduling gd_idlethread is illegal!"));
301 KKASSERT(td->td_lwp == NULL ||
302 (td->td_lwp->lwp_mpflags & LWP_MP_ONRUNQ) == 0);
308 * Deschedule a thread.
310 * (non-blocking, self contained on a per cpu basis)
313 lwkt_deschedule_self(thread_t td)
315 crit_enter_quick(td);
321 * LWKTs operate on a per-cpu basis
323 * WARNING! Called from early boot, 'mycpu' may not work yet.
326 lwkt_gdinit(struct globaldata *gd)
328 TAILQ_INIT(&gd->gd_tdrunq);
329 TAILQ_INIT(&gd->gd_tdallq);
333 * Create a new thread. The thread must be associated with a process context
334 * or LWKT start address before it can be scheduled. If the target cpu is
335 * -1 the thread will be created on the current cpu.
337 * If you intend to create a thread without a process context this function
338 * does everything except load the startup and switcher function.
341 lwkt_alloc_thread(struct thread *td, int stksize, int cpu, int flags)
343 static int cpu_rotator;
344 globaldata_t gd = mycpu;
348 * If static thread storage is not supplied allocate a thread. Reuse
349 * a cached free thread if possible. gd_freetd is used to keep an exiting
350 * thread intact through the exit.
354 if ((td = gd->gd_freetd) != NULL) {
355 KKASSERT((td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK|
357 gd->gd_freetd = NULL;
359 td = objcache_get(thread_cache, M_WAITOK);
360 KKASSERT((td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK|
364 KASSERT((td->td_flags &
365 (TDF_ALLOCATED_THREAD|TDF_RUNNING|TDF_PREEMPT_LOCK)) ==
366 TDF_ALLOCATED_THREAD,
367 ("lwkt_alloc_thread: corrupted td flags 0x%X", td->td_flags));
368 flags |= td->td_flags & (TDF_ALLOCATED_THREAD|TDF_ALLOCATED_STACK);
372 * Try to reuse cached stack.
374 if ((stack = td->td_kstack) != NULL && td->td_kstack_size != stksize) {
375 if (flags & TDF_ALLOCATED_STACK) {
376 kmem_free(&kernel_map, (vm_offset_t)stack, td->td_kstack_size);
381 stack = (void *)kmem_alloc_stack(&kernel_map, stksize);
382 flags |= TDF_ALLOCATED_STACK;
389 lwkt_init_thread(td, stack, stksize, flags, globaldata_find(cpu));
394 * Initialize a preexisting thread structure. This function is used by
395 * lwkt_alloc_thread() and also used to initialize the per-cpu idlethread.
397 * All threads start out in a critical section at a priority of
398 * TDPRI_KERN_DAEMON. Higher level code will modify the priority as
399 * appropriate. This function may send an IPI message when the
400 * requested cpu is not the current cpu and consequently gd_tdallq may
401 * not be initialized synchronously from the point of view of the originating
404 * NOTE! we have to be careful in regards to creating threads for other cpus
405 * if SMP has not yet been activated.
408 lwkt_init_thread_remote(void *arg)
413 * Protected by critical section held by IPI dispatch
415 TAILQ_INSERT_TAIL(&td->td_gd->gd_tdallq, td, td_allq);
419 * lwkt core thread structural initialization.
421 * NOTE: All threads are initialized as mpsafe threads.
424 lwkt_init_thread(thread_t td, void *stack, int stksize, int flags,
425 struct globaldata *gd)
427 globaldata_t mygd = mycpu;
429 bzero(td, sizeof(struct thread));
430 td->td_kstack = stack;
431 td->td_kstack_size = stksize;
432 td->td_flags = flags;
435 td->td_pri = TDPRI_KERN_DAEMON;
436 td->td_critcount = 1;
437 td->td_toks_have = NULL;
438 td->td_toks_stop = &td->td_toks_base;
439 if (lwkt_use_spin_port || (flags & TDF_FORCE_SPINPORT))
440 lwkt_initport_spin(&td->td_msgport, td);
442 lwkt_initport_thread(&td->td_msgport, td);
443 pmap_init_thread(td);
445 * Normally initializing a thread for a remote cpu requires sending an
446 * IPI. However, the idlethread is setup before the other cpus are
447 * activated so we have to treat it as a special case. XXX manipulation
448 * of gd_tdallq requires the BGL.
450 if (gd == mygd || td == &gd->gd_idlethread) {
452 TAILQ_INSERT_TAIL(&gd->gd_tdallq, td, td_allq);
455 lwkt_send_ipiq(gd, lwkt_init_thread_remote, td);
457 dsched_new_thread(td);
461 lwkt_set_comm(thread_t td, const char *ctl, ...)
466 kvsnprintf(td->td_comm, sizeof(td->td_comm), ctl, va);
468 KTR_LOG(ctxsw_newtd, td, td->td_comm);
472 * Prevent the thread from getting destroyed. Note that unlike PHOLD/PRELE
473 * this does not prevent the thread from migrating to another cpu so the
474 * gd_tdallq state is not protected by this.
477 lwkt_hold(thread_t td)
479 atomic_add_int(&td->td_refs, 1);
483 lwkt_rele(thread_t td)
485 KKASSERT(td->td_refs > 0);
486 atomic_add_int(&td->td_refs, -1);
490 lwkt_free_thread(thread_t td)
492 KKASSERT(td->td_refs == 0);
493 KKASSERT((td->td_flags & (TDF_RUNNING | TDF_PREEMPT_LOCK |
494 TDF_RUNQ | TDF_TSLEEPQ)) == 0);
495 if (td->td_flags & TDF_ALLOCATED_THREAD) {
496 objcache_put(thread_cache, td);
497 } else if (td->td_flags & TDF_ALLOCATED_STACK) {
498 /* client-allocated struct with internally allocated stack */
499 KASSERT(td->td_kstack && td->td_kstack_size > 0,
500 ("lwkt_free_thread: corrupted stack"));
501 kmem_free(&kernel_map, (vm_offset_t)td->td_kstack, td->td_kstack_size);
502 td->td_kstack = NULL;
503 td->td_kstack_size = 0;
505 KTR_LOG(ctxsw_deadtd, td);
510 * Switch to the next runnable lwkt. If no LWKTs are runnable then
511 * switch to the idlethread. Switching must occur within a critical
512 * section to avoid races with the scheduling queue.
514 * We always have full control over our cpu's run queue. Other cpus
515 * that wish to manipulate our queue must use the cpu_*msg() calls to
516 * talk to our cpu, so a critical section is all that is needed and
517 * the result is very, very fast thread switching.
519 * The LWKT scheduler uses a fixed priority model and round-robins at
520 * each priority level. User process scheduling is a totally
521 * different beast and LWKT priorities should not be confused with
522 * user process priorities.
524 * PREEMPTION NOTE: Preemption occurs via lwkt_preempt(). lwkt_switch()
525 * is not called by the current thread in the preemption case, only when
526 * the preempting thread blocks (in order to return to the original thread).
528 * SPECIAL NOTE ON SWITCH ATOMICY: Certain operations such as thread
529 * migration and tsleep deschedule the current lwkt thread and call
530 * lwkt_switch(). In particular, the target cpu of the migration fully
531 * expects the thread to become non-runnable and can deadlock against
532 * cpusync operations if we run any IPIs prior to switching the thread out.
534 * WE MUST BE VERY CAREFUL NOT TO RUN SPLZ DIRECTLY OR INDIRECTLY IF
535 * THE CURRENT THREAD HAS BEEN DESCHEDULED!
540 globaldata_t gd = mycpu;
541 thread_t td = gd->gd_curthread;
545 KKASSERT(gd->gd_processing_ipiq == 0);
546 KKASSERT(td->td_flags & TDF_RUNNING);
549 * Switching from within a 'fast' (non thread switched) interrupt or IPI
550 * is illegal. However, we may have to do it anyway if we hit a fatal
551 * kernel trap or we have paniced.
553 * If this case occurs save and restore the interrupt nesting level.
555 if (gd->gd_intr_nesting_level) {
559 if (gd->gd_trap_nesting_level == 0 && panic_cpu_gd != mycpu) {
560 panic("lwkt_switch: Attempt to switch from a "
561 "fast interrupt, ipi, or hard code section, "
565 savegdnest = gd->gd_intr_nesting_level;
566 savegdtrap = gd->gd_trap_nesting_level;
567 gd->gd_intr_nesting_level = 0;
568 gd->gd_trap_nesting_level = 0;
569 if ((td->td_flags & TDF_PANICWARN) == 0) {
570 td->td_flags |= TDF_PANICWARN;
571 kprintf("Warning: thread switch from interrupt, IPI, "
572 "or hard code section.\n"
573 "thread %p (%s)\n", td, td->td_comm);
577 gd->gd_intr_nesting_level = savegdnest;
578 gd->gd_trap_nesting_level = savegdtrap;
584 * Release our current user process designation if we are blocking
585 * or if a user reschedule was requested.
587 * NOTE: This function is NOT called if we are switching into or
588 * returning from a preemption.
590 * NOTE: Releasing our current user process designation may cause
591 * it to be assigned to another thread, which in turn will
592 * cause us to block in the usched acquire code when we attempt
593 * to return to userland.
595 * NOTE: On SMP systems this can be very nasty when heavy token
596 * contention is present so we want to be careful not to
597 * release the designation gratuitously.
599 if (td->td_release &&
600 (user_resched_wanted() || (td->td_flags & TDF_RUNQ) == 0)) {
608 if (TD_TOKS_HELD(td))
609 lwkt_relalltokens(td);
612 * We had better not be holding any spin locks, but don't get into an
613 * endless panic loop.
615 KASSERT(gd->gd_spinlocks == 0 || panicstr != NULL,
616 ("lwkt_switch: still holding %d exclusive spinlocks!",
621 if (td->td_cscount) {
622 kprintf("Diagnostic: attempt to switch while mastering cpusync: %p\n",
624 if (panic_on_cscount)
625 panic("switching while mastering cpusync");
630 * If we had preempted another thread on this cpu, resume the preempted
631 * thread. This occurs transparently, whether the preempted thread
632 * was scheduled or not (it may have been preempted after descheduling
635 * We have to setup the MP lock for the original thread after backing
636 * out the adjustment that was made to curthread when the original
639 if ((ntd = td->td_preempted) != NULL) {
640 KKASSERT(ntd->td_flags & TDF_PREEMPT_LOCK);
641 ntd->td_flags |= TDF_PREEMPT_DONE;
644 * The interrupt may have woken a thread up, we need to properly
645 * set the reschedule flag if the originally interrupted thread is
646 * at a lower priority.
648 * The interrupt may not have descheduled.
650 if (TAILQ_FIRST(&gd->gd_tdrunq) != ntd)
652 goto havethread_preempted;
656 * If we cannot obtain ownership of the tokens we cannot immediately
657 * schedule the target thread.
659 * Reminder: Again, we cannot afford to run any IPIs in this path if
660 * the current thread has been descheduled.
663 clear_lwkt_resched();
666 * Hotpath - pull the head of the run queue and attempt to schedule
669 ntd = TAILQ_FIRST(&gd->gd_tdrunq);
673 * Runq is empty, switch to idle to allow it to halt.
675 ntd = &gd->gd_idlethread;
676 if (gd->gd_trap_nesting_level == 0 && panicstr == NULL)
677 ASSERT_NO_TOKENS_HELD(ntd);
678 cpu_time.cp_msg[0] = 0;
679 cpu_time.cp_stallpc = 0;
684 * Hotpath - schedule ntd.
686 * NOTE: For UP there is no mplock and lwkt_getalltokens()
689 if (TD_TOKS_NOT_HELD(ntd) ||
690 lwkt_getalltokens(ntd, (spinning >= lwkt_spin_loops)))
696 * Coldpath (SMP only since tokens always succeed on UP)
698 * We had some contention on the thread we wanted to schedule.
699 * What we do now is try to find a thread that we can schedule
702 * The coldpath scan does NOT rearrange threads in the run list.
703 * The lwkt_schedulerclock() will assert need_lwkt_resched() on
704 * the next tick whenever the current head is not the current thread.
709 ++gd->gd_cnt.v_token_colls;
711 if (fairq_bypass > 0)
714 while ((ntd = TAILQ_NEXT(ntd, td_threadq)) != NULL) {
715 #ifndef NO_LWKT_SPLIT_USERPRI
717 * Never schedule threads returning to userland or the
718 * user thread scheduler helper thread when higher priority
719 * threads are present. The runq is sorted by priority
720 * so we can give up traversing it when we find the first
721 * low priority thread.
723 if (ntd->td_pri < TDPRI_KERN_LPSCHED) {
732 if (TD_TOKS_NOT_HELD(ntd) ||
733 lwkt_getalltokens(ntd, (spinning >= lwkt_spin_loops))) {
739 ++gd->gd_cnt.v_token_colls;
744 * We exhausted the run list, meaning that all runnable threads
748 ntd = &gd->gd_idlethread;
749 if (gd->gd_trap_nesting_level == 0 && panicstr == NULL)
750 ASSERT_NO_TOKENS_HELD(ntd);
751 /* contention case, do not clear contention mask */
754 * We are going to have to retry but if the current thread is not
755 * on the runq we instead switch through the idle thread to get away
756 * from the current thread. We have to flag for lwkt reschedule
757 * to prevent the idle thread from halting.
759 * NOTE: A non-zero spinning is passed to lwkt_getalltokens() to
760 * instruct it to deal with the potential for deadlocks by
761 * ordering the tokens by address.
763 if ((td->td_flags & TDF_RUNQ) == 0) {
764 need_lwkt_resched(); /* prevent hlt */
767 #if defined(INVARIANTS) && defined(__amd64__)
768 if ((read_rflags() & PSL_I) == 0) {
770 panic("lwkt_switch() called with interrupts disabled");
775 * Number iterations so far. After a certain point we switch to
776 * a sorted-address/monitor/mwait version of lwkt_getalltokens()
778 if (spinning < 0x7FFFFFFF)
782 * lwkt_getalltokens() failed in sorted token mode, we can use
783 * monitor/mwait in this case.
785 if (spinning >= lwkt_spin_loops &&
786 (cpu_mi_feature & CPU_MI_MONITOR) &&
789 cpu_mmw_pause_int(&gd->gd_reqflags,
790 (gd->gd_reqflags | RQF_SPINNING) &
791 ~RQF_IDLECHECK_WK_MASK);
795 * We already checked that td is still scheduled so this should be
801 * This experimental resequencer is used as a fall-back to reduce
802 * hw cache line contention by placing each core's scheduler into a
803 * time-domain-multplexed slot.
805 * The resequencer is disabled by default. It's functionality has
806 * largely been superceeded by the token algorithm which limits races
807 * to a subset of cores.
809 * The resequencer algorithm tends to break down when more than
810 * 20 cores are contending. What appears to happen is that new
811 * tokens can be obtained out of address-sorted order by new cores
812 * while existing cores languish in long delays between retries and
813 * wind up being starved-out of the token acquisition.
815 if (lwkt_spin_reseq && spinning >= lwkt_spin_reseq) {
816 int cseq = atomic_fetchadd_int(&lwkt_cseq_windex, 1);
819 while ((oseq = lwkt_cseq_rindex) != cseq) {
822 if (cpu_mi_feature & CPU_MI_MONITOR) {
823 cpu_mmw_pause_int(&lwkt_cseq_rindex, oseq);
833 atomic_add_int(&lwkt_cseq_rindex, 1);
835 /* highest level for(;;) loop */
840 * Clear gd_idle_repeat when doing a normal switch to a non-idle
843 ntd->td_wmesg = NULL;
844 ++gd->gd_cnt.v_swtch;
845 gd->gd_idle_repeat = 0;
847 havethread_preempted:
849 * If the new target does not need the MP lock and we are holding it,
850 * release the MP lock. If the new target requires the MP lock we have
851 * already acquired it for the target.
855 KASSERT(ntd->td_critcount,
856 ("priority problem in lwkt_switch %d %d",
857 td->td_critcount, ntd->td_critcount));
861 * Execute the actual thread switch operation. This function
862 * returns to the current thread and returns the previous thread
863 * (which may be different from the thread we switched to).
865 * We are responsible for marking ntd as TDF_RUNNING.
867 KKASSERT((ntd->td_flags & TDF_RUNNING) == 0);
869 KTR_LOG(ctxsw_sw, gd->gd_cpuid, ntd);
870 ntd->td_flags |= TDF_RUNNING;
871 lwkt_switch_return(td->td_switch(ntd));
872 /* ntd invalid, td_switch() can return a different thread_t */
876 * catch-all. XXX is this strictly needed?
880 /* NOTE: current cpu may have changed after switch */
885 * Called by assembly in the td_switch (thread restore path) for thread
886 * bootstrap cases which do not 'return' to lwkt_switch().
889 lwkt_switch_return(thread_t otd)
894 * Check if otd was migrating. Now that we are on ntd we can finish
895 * up the migration. This is a bit messy but it is the only place
896 * where td is known to be fully descheduled.
898 * We can only activate the migration if otd was migrating but not
899 * held on the cpu due to a preemption chain. We still have to
900 * clear TDF_RUNNING on the old thread either way.
902 * We are responsible for clearing the previously running thread's
905 if ((rgd = otd->td_migrate_gd) != NULL &&
906 (otd->td_flags & TDF_PREEMPT_LOCK) == 0) {
907 KKASSERT((otd->td_flags & (TDF_MIGRATING | TDF_RUNNING)) ==
908 (TDF_MIGRATING | TDF_RUNNING));
909 otd->td_migrate_gd = NULL;
910 otd->td_flags &= ~TDF_RUNNING;
911 lwkt_send_ipiq(rgd, lwkt_setcpu_remote, otd);
913 otd->td_flags &= ~TDF_RUNNING;
917 * Final exit validations (see lwp_wait()). Note that otd becomes
918 * invalid the *instant* we set TDF_MP_EXITSIG.
920 while (otd->td_flags & TDF_EXITING) {
923 mpflags = otd->td_mpflags;
926 if (mpflags & TDF_MP_EXITWAIT) {
927 if (atomic_cmpset_int(&otd->td_mpflags, mpflags,
928 mpflags | TDF_MP_EXITSIG)) {
933 if (atomic_cmpset_int(&otd->td_mpflags, mpflags,
934 mpflags | TDF_MP_EXITSIG)) {
943 * Request that the target thread preempt the current thread. Preemption
944 * can only occur if our only critical section is the one that we were called
945 * with, the relative priority of the target thread is higher, and the target
946 * thread holds no tokens. This also only works if we are not holding any
947 * spinlocks (obviously).
949 * THE CALLER OF LWKT_PREEMPT() MUST BE IN A CRITICAL SECTION. Typically
950 * this is called via lwkt_schedule() through the td_preemptable callback.
951 * critcount is the managed critical priority that we should ignore in order
952 * to determine whether preemption is possible (aka usually just the crit
953 * priority of lwkt_schedule() itself).
955 * Preemption is typically limited to interrupt threads.
957 * Operation works in a fairly straight-forward manner. The normal
958 * scheduling code is bypassed and we switch directly to the target
959 * thread. When the target thread attempts to block or switch away
960 * code at the base of lwkt_switch() will switch directly back to our
961 * thread. Our thread is able to retain whatever tokens it holds and
962 * if the target needs one of them the target will switch back to us
963 * and reschedule itself normally.
966 lwkt_preempt(thread_t ntd, int critcount)
968 struct globaldata *gd = mycpu;
971 int save_gd_intr_nesting_level;
974 * The caller has put us in a critical section. We can only preempt
975 * if the caller of the caller was not in a critical section (basically
976 * a local interrupt), as determined by the 'critcount' parameter. We
977 * also can't preempt if the caller is holding any spinlocks (even if
978 * he isn't in a critical section). This also handles the tokens test.
980 * YYY The target thread must be in a critical section (else it must
981 * inherit our critical section? I dunno yet).
983 KASSERT(ntd->td_critcount, ("BADCRIT0 %d", ntd->td_pri));
985 td = gd->gd_curthread;
986 if (preempt_enable == 0) {
990 if (ntd->td_pri <= td->td_pri) {
994 if (td->td_critcount > critcount) {
998 if (td->td_cscount) {
1002 if (ntd->td_gd != gd) {
1007 * We don't have to check spinlocks here as they will also bump
1010 * Do not try to preempt if the target thread is holding any tokens.
1011 * We could try to acquire the tokens but this case is so rare there
1012 * is no need to support it.
1014 KKASSERT(gd->gd_spinlocks == 0);
1016 if (TD_TOKS_HELD(ntd)) {
1020 if (td == ntd || ((td->td_flags | ntd->td_flags) & TDF_PREEMPT_LOCK)) {
1024 if (ntd->td_preempted) {
1028 KKASSERT(gd->gd_processing_ipiq == 0);
1031 * Since we are able to preempt the current thread, there is no need to
1032 * call need_lwkt_resched().
1034 * We must temporarily clear gd_intr_nesting_level around the switch
1035 * since switchouts from the target thread are allowed (they will just
1036 * return to our thread), and since the target thread has its own stack.
1038 * A preemption must switch back to the original thread, assert the
1042 ntd->td_preempted = td;
1043 td->td_flags |= TDF_PREEMPT_LOCK;
1044 KTR_LOG(ctxsw_pre, gd->gd_cpuid, ntd);
1045 save_gd_intr_nesting_level = gd->gd_intr_nesting_level;
1046 gd->gd_intr_nesting_level = 0;
1048 KKASSERT((ntd->td_flags & TDF_RUNNING) == 0);
1049 ntd->td_flags |= TDF_RUNNING;
1050 xtd = td->td_switch(ntd);
1051 KKASSERT(xtd == ntd);
1052 lwkt_switch_return(xtd);
1053 gd->gd_intr_nesting_level = save_gd_intr_nesting_level;
1055 KKASSERT(ntd->td_preempted && (td->td_flags & TDF_PREEMPT_DONE));
1056 ntd->td_preempted = NULL;
1057 td->td_flags &= ~(TDF_PREEMPT_LOCK|TDF_PREEMPT_DONE);
1061 * Conditionally call splz() if gd_reqflags indicates work is pending.
1062 * This will work inside a critical section but not inside a hard code
1065 * (self contained on a per cpu basis)
1070 globaldata_t gd = mycpu;
1071 thread_t td = gd->gd_curthread;
1073 if ((gd->gd_reqflags & RQF_IDLECHECK_MASK) &&
1074 gd->gd_intr_nesting_level == 0 &&
1075 td->td_nest_count < 2)
1082 * This version is integrated into crit_exit, reqflags has already
1083 * been tested but td_critcount has not.
1085 * We only want to execute the splz() on the 1->0 transition of
1086 * critcount and not in a hard code section or if too deeply nested.
1088 * NOTE: gd->gd_spinlocks is implied to be 0 when td_critcount is 0.
1091 lwkt_maybe_splz(thread_t td)
1093 globaldata_t gd = td->td_gd;
1095 if (td->td_critcount == 0 &&
1096 gd->gd_intr_nesting_level == 0 &&
1097 td->td_nest_count < 2)
1104 * Drivers which set up processing co-threads can call this function to
1105 * run the co-thread at a higher priority and to allow it to preempt
1109 lwkt_set_interrupt_support_thread(void)
1111 thread_t td = curthread;
1113 lwkt_setpri_self(TDPRI_INT_SUPPORT);
1114 td->td_flags |= TDF_INTTHREAD;
1115 td->td_preemptable = lwkt_preempt;
1120 * This function is used to negotiate a passive release of the current
1121 * process/lwp designation with the user scheduler, allowing the user
1122 * scheduler to schedule another user thread. The related kernel thread
1123 * (curthread) continues running in the released state.
1126 lwkt_passive_release(struct thread *td)
1128 struct lwp *lp = td->td_lwp;
1130 #ifndef NO_LWKT_SPLIT_USERPRI
1131 td->td_release = NULL;
1132 lwkt_setpri_self(TDPRI_KERN_USER);
1135 lp->lwp_proc->p_usched->release_curproc(lp);
1140 * This implements a LWKT yield, allowing a kernel thread to yield to other
1141 * kernel threads at the same or higher priority. This function can be
1142 * called in a tight loop and will typically only yield once per tick.
1144 * Most kernel threads run at the same priority in order to allow equal
1147 * (self contained on a per cpu basis)
1152 globaldata_t gd = mycpu;
1153 thread_t td = gd->gd_curthread;
1155 if ((gd->gd_reqflags & RQF_IDLECHECK_MASK) && td->td_nest_count < 2)
1157 if (lwkt_resched_wanted()) {
1158 lwkt_schedule_self(curthread);
1164 * The quick version processes pending interrupts and higher-priority
1165 * LWKT threads but will not round-robin same-priority LWKT threads.
1167 * When called while attempting to return to userland the only same-pri
1168 * threads are the ones which have already tried to become the current
1172 lwkt_yield_quick(void)
1174 globaldata_t gd = mycpu;
1175 thread_t td = gd->gd_curthread;
1177 if ((gd->gd_reqflags & RQF_IDLECHECK_MASK) && td->td_nest_count < 2)
1179 if (lwkt_resched_wanted()) {
1180 if (TAILQ_FIRST(&gd->gd_tdrunq) == td) {
1181 clear_lwkt_resched();
1183 lwkt_schedule_self(curthread);
1190 * This yield is designed for kernel threads with a user context.
1192 * The kernel acting on behalf of the user is potentially cpu-bound,
1193 * this function will efficiently allow other threads to run and also
1194 * switch to other processes by releasing.
1196 * The lwkt_user_yield() function is designed to have very low overhead
1197 * if no yield is determined to be needed.
1200 lwkt_user_yield(void)
1202 globaldata_t gd = mycpu;
1203 thread_t td = gd->gd_curthread;
1206 * Always run any pending interrupts in case we are in a critical
1209 if ((gd->gd_reqflags & RQF_IDLECHECK_MASK) && td->td_nest_count < 2)
1213 * Switch (which forces a release) if another kernel thread needs
1214 * the cpu, if userland wants us to resched, or if our kernel
1215 * quantum has run out.
1217 if (lwkt_resched_wanted() ||
1218 user_resched_wanted())
1225 * Reacquire the current process if we are released.
1227 * XXX not implemented atm. The kernel may be holding locks and such,
1228 * so we want the thread to continue to receive cpu.
1230 if (td->td_release == NULL && lp) {
1231 lp->lwp_proc->p_usched->acquire_curproc(lp);
1232 td->td_release = lwkt_passive_release;
1233 lwkt_setpri_self(TDPRI_USER_NORM);
1239 * Generic schedule. Possibly schedule threads belonging to other cpus and
1240 * deal with threads that might be blocked on a wait queue.
1242 * We have a little helper inline function which does additional work after
1243 * the thread has been enqueued, including dealing with preemption and
1244 * setting need_lwkt_resched() (which prevents the kernel from returning
1245 * to userland until it has processed higher priority threads).
1247 * It is possible for this routine to be called after a failed _enqueue
1248 * (due to the target thread migrating, sleeping, or otherwise blocked).
1249 * We have to check that the thread is actually on the run queue!
1253 _lwkt_schedule_post(globaldata_t gd, thread_t ntd, int ccount)
1255 if (ntd->td_flags & TDF_RUNQ) {
1256 if (ntd->td_preemptable) {
1257 ntd->td_preemptable(ntd, ccount); /* YYY +token */
1264 _lwkt_schedule(thread_t td)
1266 globaldata_t mygd = mycpu;
1268 KASSERT(td != &td->td_gd->gd_idlethread,
1269 ("lwkt_schedule(): scheduling gd_idlethread is illegal!"));
1270 KKASSERT((td->td_flags & TDF_MIGRATING) == 0);
1271 crit_enter_gd(mygd);
1272 KKASSERT(td->td_lwp == NULL ||
1273 (td->td_lwp->lwp_mpflags & LWP_MP_ONRUNQ) == 0);
1275 if (td == mygd->gd_curthread) {
1279 * If we own the thread, there is no race (since we are in a
1280 * critical section). If we do not own the thread there might
1281 * be a race but the target cpu will deal with it.
1283 if (td->td_gd == mygd) {
1285 _lwkt_schedule_post(mygd, td, 1);
1287 lwkt_send_ipiq3(td->td_gd, lwkt_schedule_remote, td, 0);
1294 lwkt_schedule(thread_t td)
1300 lwkt_schedule_noresched(thread_t td) /* XXX not impl */
1306 * When scheduled remotely if frame != NULL the IPIQ is being
1307 * run via doreti or an interrupt then preemption can be allowed.
1309 * To allow preemption we have to drop the critical section so only
1310 * one is present in _lwkt_schedule_post.
1313 lwkt_schedule_remote(void *arg, int arg2, struct intrframe *frame)
1315 thread_t td = curthread;
1318 if (frame && ntd->td_preemptable) {
1319 crit_exit_noyield(td);
1320 _lwkt_schedule(ntd);
1321 crit_enter_quick(td);
1323 _lwkt_schedule(ntd);
1328 * Thread migration using a 'Pull' method. The thread may or may not be
1329 * the current thread. It MUST be descheduled and in a stable state.
1330 * lwkt_giveaway() must be called on the cpu owning the thread.
1332 * At any point after lwkt_giveaway() is called, the target cpu may
1333 * 'pull' the thread by calling lwkt_acquire().
1335 * We have to make sure the thread is not sitting on a per-cpu tsleep
1336 * queue or it will blow up when it moves to another cpu.
1338 * MPSAFE - must be called under very specific conditions.
1341 lwkt_giveaway(thread_t td)
1343 globaldata_t gd = mycpu;
1346 if (td->td_flags & TDF_TSLEEPQ)
1348 KKASSERT(td->td_gd == gd);
1349 TAILQ_REMOVE(&gd->gd_tdallq, td, td_allq);
1350 td->td_flags |= TDF_MIGRATING;
1355 lwkt_acquire(thread_t td)
1359 int retry = 10000000;
1361 KKASSERT(td->td_flags & TDF_MIGRATING);
1366 KKASSERT((td->td_flags & TDF_RUNQ) == 0);
1367 crit_enter_gd(mygd);
1368 DEBUG_PUSH_INFO("lwkt_acquire");
1369 while (td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK)) {
1370 lwkt_process_ipiq();
1373 kprintf("lwkt_acquire: stuck: td %p td->td_flags %08x\n",
1381 TAILQ_INSERT_TAIL(&mygd->gd_tdallq, td, td_allq);
1382 td->td_flags &= ~TDF_MIGRATING;
1385 crit_enter_gd(mygd);
1386 TAILQ_INSERT_TAIL(&mygd->gd_tdallq, td, td_allq);
1387 td->td_flags &= ~TDF_MIGRATING;
1393 * Generic deschedule. Descheduling threads other then your own should be
1394 * done only in carefully controlled circumstances. Descheduling is
1397 * This function may block if the cpu has run out of messages.
1400 lwkt_deschedule(thread_t td)
1403 if (td == curthread) {
1406 if (td->td_gd == mycpu) {
1409 lwkt_send_ipiq(td->td_gd, (ipifunc1_t)lwkt_deschedule, td);
1416 * Set the target thread's priority. This routine does not automatically
1417 * switch to a higher priority thread, LWKT threads are not designed for
1418 * continuous priority changes. Yield if you want to switch.
1421 lwkt_setpri(thread_t td, int pri)
1423 if (td->td_pri != pri) {
1426 if (td->td_flags & TDF_RUNQ) {
1427 KKASSERT(td->td_gd == mycpu);
1439 * Set the initial priority for a thread prior to it being scheduled for
1440 * the first time. The thread MUST NOT be scheduled before or during
1441 * this call. The thread may be assigned to a cpu other then the current
1444 * Typically used after a thread has been created with TDF_STOPPREQ,
1445 * and before the thread is initially scheduled.
1448 lwkt_setpri_initial(thread_t td, int pri)
1451 KKASSERT((td->td_flags & TDF_RUNQ) == 0);
1456 lwkt_setpri_self(int pri)
1458 thread_t td = curthread;
1460 KKASSERT(pri >= 0 && pri <= TDPRI_MAX);
1462 if (td->td_flags & TDF_RUNQ) {
1473 * hz tick scheduler clock for LWKT threads
1476 lwkt_schedulerclock(thread_t td)
1478 globaldata_t gd = td->td_gd;
1481 if (TAILQ_FIRST(&gd->gd_tdrunq) == td) {
1483 * If the current thread is at the head of the runq shift it to the
1484 * end of any equal-priority threads and request a LWKT reschedule
1487 * Ignore upri in this situation. There will only be one user thread
1488 * in user mode, all others will be user threads running in kernel
1489 * mode and we have to make sure they get some cpu.
1491 xtd = TAILQ_NEXT(td, td_threadq);
1492 if (xtd && xtd->td_pri == td->td_pri) {
1493 TAILQ_REMOVE(&gd->gd_tdrunq, td, td_threadq);
1494 while (xtd && xtd->td_pri == td->td_pri)
1495 xtd = TAILQ_NEXT(xtd, td_threadq);
1497 TAILQ_INSERT_BEFORE(xtd, td, td_threadq);
1499 TAILQ_INSERT_TAIL(&gd->gd_tdrunq, td, td_threadq);
1500 need_lwkt_resched();
1504 * If we scheduled a thread other than the one at the head of the
1505 * queue always request a reschedule every tick.
1507 need_lwkt_resched();
1512 * Migrate the current thread to the specified cpu.
1514 * This is accomplished by descheduling ourselves from the current cpu
1515 * and setting td_migrate_gd. The lwkt_switch() code will detect that the
1516 * 'old' thread wants to migrate after it has been completely switched out
1517 * and will complete the migration.
1519 * TDF_MIGRATING prevents scheduling races while the thread is being migrated.
1521 * We must be sure to release our current process designation (if a user
1522 * process) before clearing out any tsleepq we are on because the release
1523 * code may re-add us.
1525 * We must be sure to remove ourselves from the current cpu's tsleepq
1526 * before potentially moving to another queue. The thread can be on
1527 * a tsleepq due to a left-over tsleep_interlock().
1531 lwkt_setcpu_self(globaldata_t rgd)
1533 thread_t td = curthread;
1535 if (td->td_gd != rgd) {
1536 crit_enter_quick(td);
1540 if (td->td_flags & TDF_TSLEEPQ)
1544 * Set TDF_MIGRATING to prevent a spurious reschedule while we are
1545 * trying to deschedule ourselves and switch away, then deschedule
1546 * ourself, remove us from tdallq, and set td_migrate_gd. Finally,
1547 * call lwkt_switch() to complete the operation.
1549 td->td_flags |= TDF_MIGRATING;
1550 lwkt_deschedule_self(td);
1551 TAILQ_REMOVE(&td->td_gd->gd_tdallq, td, td_allq);
1552 td->td_migrate_gd = rgd;
1556 * We are now on the target cpu
1558 KKASSERT(rgd == mycpu);
1559 TAILQ_INSERT_TAIL(&rgd->gd_tdallq, td, td_allq);
1560 crit_exit_quick(td);
1565 lwkt_migratecpu(int cpuid)
1569 rgd = globaldata_find(cpuid);
1570 lwkt_setcpu_self(rgd);
1574 * Remote IPI for cpu migration (called while in a critical section so we
1575 * do not have to enter another one).
1577 * The thread (td) has already been completely descheduled from the
1578 * originating cpu and we can simply assert the case. The thread is
1579 * assigned to the new cpu and enqueued.
1581 * The thread will re-add itself to tdallq when it resumes execution.
1584 lwkt_setcpu_remote(void *arg)
1587 globaldata_t gd = mycpu;
1589 KKASSERT((td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK)) == 0);
1592 td->td_flags &= ~TDF_MIGRATING;
1593 KKASSERT(td->td_migrate_gd == NULL);
1594 KKASSERT(td->td_lwp == NULL ||
1595 (td->td_lwp->lwp_mpflags & LWP_MP_ONRUNQ) == 0);
1600 lwkt_preempted_proc(void)
1602 thread_t td = curthread;
1603 while (td->td_preempted)
1604 td = td->td_preempted;
1609 * Create a kernel process/thread/whatever. It shares it's address space
1610 * with proc0 - ie: kernel only.
1612 * If the cpu is not specified one will be selected. In the future
1613 * specifying a cpu of -1 will enable kernel thread migration between
1617 lwkt_create(void (*func)(void *), void *arg, struct thread **tdp,
1618 thread_t template, int tdflags, int cpu, const char *fmt, ...)
1623 td = lwkt_alloc_thread(template, LWKT_THREAD_STACK, cpu,
1627 cpu_set_thread_handler(td, lwkt_exit, func, arg);
1630 * Set up arg0 for 'ps' etc
1632 __va_start(ap, fmt);
1633 kvsnprintf(td->td_comm, sizeof(td->td_comm), fmt, ap);
1637 * Schedule the thread to run
1639 if (td->td_flags & TDF_NOSTART)
1640 td->td_flags &= ~TDF_NOSTART;
1647 * Destroy an LWKT thread. Warning! This function is not called when
1648 * a process exits, cpu_proc_exit() directly calls cpu_thread_exit() and
1649 * uses a different reaping mechanism.
1654 thread_t td = curthread;
1659 * Do any cleanup that might block here
1661 if (td->td_flags & TDF_VERBOSE)
1662 kprintf("kthread %p %s has exited\n", td, td->td_comm);
1664 dsched_exit_thread(td);
1667 * Get us into a critical section to interlock gd_freetd and loop
1668 * until we can get it freed.
1670 * We have to cache the current td in gd_freetd because objcache_put()ing
1671 * it would rip it out from under us while our thread is still active.
1673 * We are the current thread so of course our own TDF_RUNNING bit will
1674 * be set, so unlike the lwp reap code we don't wait for it to clear.
1677 crit_enter_quick(td);
1680 tsleep(td, 0, "tdreap", 1);
1683 if ((std = gd->gd_freetd) != NULL) {
1684 KKASSERT((std->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK)) == 0);
1685 gd->gd_freetd = NULL;
1686 objcache_put(thread_cache, std);
1693 * Remove thread resources from kernel lists and deschedule us for
1694 * the last time. We cannot block after this point or we may end
1695 * up with a stale td on the tsleepq.
1697 * None of this may block, the critical section is the only thing
1698 * protecting tdallq and the only thing preventing new lwkt_hold()
1701 if (td->td_flags & TDF_TSLEEPQ)
1703 lwkt_deschedule_self(td);
1704 lwkt_remove_tdallq(td);
1705 KKASSERT(td->td_refs == 0);
1710 KKASSERT(gd->gd_freetd == NULL);
1711 if (td->td_flags & TDF_ALLOCATED_THREAD)
1717 lwkt_remove_tdallq(thread_t td)
1719 KKASSERT(td->td_gd == mycpu);
1720 TAILQ_REMOVE(&td->td_gd->gd_tdallq, td, td_allq);
1724 * Code reduction and branch prediction improvements. Call/return
1725 * overhead on modern cpus often degenerates into 0 cycles due to
1726 * the cpu's branch prediction hardware and return pc cache. We
1727 * can take advantage of this by not inlining medium-complexity
1728 * functions and we can also reduce the branch prediction impact
1729 * by collapsing perfectly predictable branches into a single
1730 * procedure instead of duplicating it.
1732 * Is any of this noticeable? Probably not, so I'll take the
1733 * smaller code size.
1736 crit_exit_wrapper(__DEBUG_CRIT_ARG__)
1738 _crit_exit(mycpu __DEBUG_CRIT_PASS_ARG__);
1744 thread_t td = curthread;
1745 int lcrit = td->td_critcount;
1747 td->td_critcount = 0;
1748 panic("td_critcount is/would-go negative! %p %d", td, lcrit);
1753 * Called from debugger/panic on cpus which have been stopped. We must still
1754 * process the IPIQ while stopped, even if we were stopped while in a critical
1757 * If we are dumping also try to process any pending interrupts. This may
1758 * or may not work depending on the state of the cpu at the point it was
1762 lwkt_smp_stopped(void)
1764 globaldata_t gd = mycpu;
1768 lwkt_process_ipiq();
1771 lwkt_process_ipiq();