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/malloc.h>
49 #include <sys/queue.h>
50 #include <sys/sysctl.h>
51 #include <sys/kthread.h>
52 #include <machine/cpu.h>
54 #include <sys/spinlock.h>
56 #include <sys/indefinite.h>
58 #include <sys/thread2.h>
59 #include <sys/spinlock2.h>
60 #include <sys/indefinite2.h>
62 #include <sys/dsched.h>
65 #include <vm/vm_param.h>
66 #include <vm/vm_kern.h>
67 #include <vm/vm_object.h>
68 #include <vm/vm_page.h>
69 #include <vm/vm_map.h>
70 #include <vm/vm_pager.h>
71 #include <vm/vm_extern.h>
73 #include <machine/stdarg.h>
74 #include <machine/smp.h>
75 #include <machine/clock.h>
79 #if !defined(KTR_CTXSW)
80 #define KTR_CTXSW KTR_ALL
82 KTR_INFO_MASTER(ctxsw);
83 KTR_INFO(KTR_CTXSW, ctxsw, sw, 0, "#cpu[%d].td = %p", int cpu, struct thread *td);
84 KTR_INFO(KTR_CTXSW, ctxsw, pre, 1, "#cpu[%d].td = %p", int cpu, struct thread *td);
85 KTR_INFO(KTR_CTXSW, ctxsw, newtd, 2, "#threads[%p].name = %s", struct thread *td, char *comm);
86 KTR_INFO(KTR_CTXSW, ctxsw, deadtd, 3, "#threads[%p].name = <dead>", struct thread *td);
88 static MALLOC_DEFINE(M_THREAD, "thread", "lwkt threads");
91 static int panic_on_cscount = 0;
93 #ifdef DEBUG_LWKT_THREAD
94 static int64_t switch_count = 0;
95 static int64_t preempt_hit = 0;
96 static int64_t preempt_miss = 0;
97 static int64_t preempt_weird = 0;
99 static int lwkt_use_spin_port;
100 __read_mostly static struct objcache *thread_cache;
101 int cpu_mwait_spin = 0;
103 static void lwkt_schedule_remote(void *arg, int arg2, struct intrframe *frame);
104 static void lwkt_setcpu_remote(void *arg);
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 #ifdef DEBUG_LWKT_THREAD
117 SYSCTL_QUAD(_lwkt, OID_AUTO, switch_count, CTLFLAG_RW, &switch_count, 0,
118 "Number of switched threads");
119 SYSCTL_QUAD(_lwkt, OID_AUTO, preempt_hit, CTLFLAG_RW, &preempt_hit, 0,
120 "Successful preemption events");
121 SYSCTL_QUAD(_lwkt, OID_AUTO, preempt_miss, CTLFLAG_RW, &preempt_miss, 0,
122 "Failed preemption events");
123 SYSCTL_QUAD(_lwkt, OID_AUTO, preempt_weird, CTLFLAG_RW, &preempt_weird, 0,
124 "Number of preempted threads.");
126 extern int lwkt_sched_debug;
127 int lwkt_sched_debug = 0;
128 SYSCTL_INT(_lwkt, OID_AUTO, sched_debug, CTLFLAG_RW,
129 &lwkt_sched_debug, 0, "Scheduler debug");
130 __read_mostly static u_int lwkt_spin_loops = 10;
131 SYSCTL_UINT(_lwkt, OID_AUTO, spin_loops, CTLFLAG_RW,
132 &lwkt_spin_loops, 0, "Scheduler spin loops until sorted decon");
133 __read_mostly static int preempt_enable = 1;
134 SYSCTL_INT(_lwkt, OID_AUTO, preempt_enable, CTLFLAG_RW,
135 &preempt_enable, 0, "Enable preemption");
136 static int lwkt_cache_threads = 0;
137 SYSCTL_INT(_lwkt, OID_AUTO, cache_threads, CTLFLAG_RD,
138 &lwkt_cache_threads, 0, "thread+kstack cache");
141 * These helper procedures handle the runq, they can only be called from
142 * within a critical section.
144 * WARNING! Prior to SMP being brought up it is possible to enqueue and
145 * dequeue threads belonging to other cpus, so be sure to use td->td_gd
146 * instead of 'mycpu' when referencing the globaldata structure. Once
147 * SMP live enqueuing and dequeueing only occurs on the current cpu.
151 _lwkt_dequeue(thread_t td)
153 if (td->td_flags & TDF_RUNQ) {
154 struct globaldata *gd = td->td_gd;
156 td->td_flags &= ~TDF_RUNQ;
157 TAILQ_REMOVE(&gd->gd_tdrunq, td, td_threadq);
158 --gd->gd_tdrunqcount;
159 if (TAILQ_FIRST(&gd->gd_tdrunq) == NULL)
160 atomic_clear_int(&gd->gd_reqflags, RQF_RUNNING);
167 * There are a limited number of lwkt threads runnable since user
168 * processes only schedule one at a time per cpu. However, there can
169 * be many user processes in kernel mode exiting from a tsleep() which
172 * We scan the queue in both directions to help deal with degenerate
173 * situations when hundreds or thousands (or more) threads are runnable.
175 * NOTE: lwkt_schedulerclock() will force a round-robin based on td_pri and
176 * will ignore user priority. This is to ensure that user threads in
177 * kernel mode get cpu at some point regardless of what the user
182 _lwkt_enqueue(thread_t td)
184 thread_t xtd; /* forward scan */
185 thread_t rtd; /* reverse scan */
187 if ((td->td_flags & (TDF_RUNQ|TDF_MIGRATING|TDF_BLOCKQ)) == 0) {
188 struct globaldata *gd = td->td_gd;
190 td->td_flags |= TDF_RUNQ;
191 xtd = TAILQ_FIRST(&gd->gd_tdrunq);
193 TAILQ_INSERT_TAIL(&gd->gd_tdrunq, td, td_threadq);
194 atomic_set_int(&gd->gd_reqflags, RQF_RUNNING);
197 * NOTE: td_upri - higher numbers more desireable, same sense
198 * as td_pri (typically reversed from lwp_upri).
200 * In the equal priority case we want the best selection
201 * at the beginning so the less desireable selections know
202 * that they have to setrunqueue/go-to-another-cpu, even
203 * though it means switching back to the 'best' selection.
204 * This also avoids degenerate situations when many threads
205 * are runnable or waking up at the same time.
207 * If upri matches exactly place at end/round-robin.
209 rtd = TAILQ_LAST(&gd->gd_tdrunq, lwkt_queue);
212 (xtd->td_pri > td->td_pri ||
213 (xtd->td_pri == td->td_pri &&
214 xtd->td_upri >= td->td_upri))) {
215 xtd = TAILQ_NEXT(xtd, td_threadq);
218 * Doing a reverse scan at the same time is an optimization
219 * for the insert-closer-to-tail case that avoids having to
220 * scan the entire list. This situation can occur when
221 * thousands of threads are woken up at the same time.
223 if (rtd->td_pri > td->td_pri ||
224 (rtd->td_pri == td->td_pri &&
225 rtd->td_upri >= td->td_upri)) {
226 TAILQ_INSERT_AFTER(&gd->gd_tdrunq, rtd, td, td_threadq);
229 rtd = TAILQ_PREV(rtd, lwkt_queue, td_threadq);
232 TAILQ_INSERT_BEFORE(xtd, td, td_threadq);
234 TAILQ_INSERT_TAIL(&gd->gd_tdrunq, td, td_threadq);
237 ++gd->gd_tdrunqcount;
240 * Request a LWKT reschedule if we are now at the head of the queue.
242 if (TAILQ_FIRST(&gd->gd_tdrunq) == td)
248 _lwkt_thread_ctor(void *obj, void *privdata, int ocflags)
250 struct thread *td = (struct thread *)obj;
252 td->td_kstack = NULL;
253 td->td_kstack_size = 0;
254 td->td_flags = TDF_ALLOCATED_THREAD;
260 _lwkt_thread_dtor(void *obj, void *privdata)
262 struct thread *td = (struct thread *)obj;
264 KASSERT(td->td_flags & TDF_ALLOCATED_THREAD,
265 ("_lwkt_thread_dtor: not allocated from objcache"));
266 KASSERT((td->td_flags & TDF_ALLOCATED_STACK) && td->td_kstack &&
267 td->td_kstack_size > 0,
268 ("_lwkt_thread_dtor: corrupted stack"));
269 kmem_free(&kernel_map, (vm_offset_t)td->td_kstack, td->td_kstack_size);
270 td->td_kstack = NULL;
275 * Initialize the lwkt s/system.
277 * Nominally cache up to 32 thread + kstack structures. Cache more on
278 * systems with a lot of cpu cores.
283 TUNABLE_INT("lwkt.cache_threads", &lwkt_cache_threads);
284 if (lwkt_cache_threads == 0) {
285 lwkt_cache_threads = ncpus * 4;
286 if (lwkt_cache_threads < 32)
287 lwkt_cache_threads = 32;
289 thread_cache = objcache_create_mbacked(
290 M_THREAD, sizeof(struct thread),
291 0, lwkt_cache_threads,
292 _lwkt_thread_ctor, _lwkt_thread_dtor, NULL);
294 SYSINIT(lwkt_init, SI_BOOT2_LWKT_INIT, SI_ORDER_FIRST, lwkt_init, NULL);
297 * Schedule a thread to run. As the current thread we can always safely
298 * schedule ourselves, and a shortcut procedure is provided for that
301 * (non-blocking, self contained on a per cpu basis)
304 lwkt_schedule_self(thread_t td)
306 KKASSERT((td->td_flags & TDF_MIGRATING) == 0);
307 crit_enter_quick(td);
308 KASSERT(td != &td->td_gd->gd_idlethread,
309 ("lwkt_schedule_self(): scheduling gd_idlethread is illegal!"));
310 KKASSERT(td->td_lwp == NULL ||
311 (td->td_lwp->lwp_mpflags & LWP_MP_ONRUNQ) == 0);
317 * Deschedule a thread.
319 * (non-blocking, self contained on a per cpu basis)
322 lwkt_deschedule_self(thread_t td)
324 crit_enter_quick(td);
330 * LWKTs operate on a per-cpu basis
332 * WARNING! Called from early boot, 'mycpu' may not work yet.
335 lwkt_gdinit(struct globaldata *gd)
337 TAILQ_INIT(&gd->gd_tdrunq);
338 TAILQ_INIT(&gd->gd_tdallq);
339 lockinit(&gd->gd_sysctllock, "sysctl", 0, LK_CANRECURSE);
343 * Create a new thread. The thread must be associated with a process context
344 * or LWKT start address before it can be scheduled. If the target cpu is
345 * -1 the thread will be created on the current cpu.
347 * If you intend to create a thread without a process context this function
348 * does everything except load the startup and switcher function.
351 lwkt_alloc_thread(struct thread *td, int stksize, int cpu, int flags)
353 static int cpu_rotator;
354 globaldata_t gd = mycpu;
358 * If static thread storage is not supplied allocate a thread. Reuse
359 * a cached free thread if possible. gd_freetd is used to keep an exiting
360 * thread intact through the exit.
364 if ((td = gd->gd_freetd) != NULL) {
365 KKASSERT((td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK|
367 gd->gd_freetd = NULL;
369 td = objcache_get(thread_cache, M_WAITOK);
370 KKASSERT((td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK|
374 KASSERT((td->td_flags &
375 (TDF_ALLOCATED_THREAD|TDF_RUNNING|TDF_PREEMPT_LOCK)) ==
376 TDF_ALLOCATED_THREAD,
377 ("lwkt_alloc_thread: corrupted td flags 0x%X", td->td_flags));
378 flags |= td->td_flags & (TDF_ALLOCATED_THREAD|TDF_ALLOCATED_STACK);
382 * Try to reuse cached stack.
384 if ((stack = td->td_kstack) != NULL && td->td_kstack_size != stksize) {
385 if (flags & TDF_ALLOCATED_STACK) {
386 kmem_free(&kernel_map, (vm_offset_t)stack, td->td_kstack_size);
392 stack = (void *)kmem_alloc_stack(&kernel_map, stksize, 0);
394 stack = (void *)kmem_alloc_stack(&kernel_map, stksize,
396 flags |= TDF_ALLOCATED_STACK;
401 cpu = (uint32_t)cpu % (uint32_t)ncpus;
403 lwkt_init_thread(td, stack, stksize, flags, globaldata_find(cpu));
408 * Initialize a preexisting thread structure. This function is used by
409 * lwkt_alloc_thread() and also used to initialize the per-cpu idlethread.
411 * All threads start out in a critical section at a priority of
412 * TDPRI_KERN_DAEMON. Higher level code will modify the priority as
413 * appropriate. This function may send an IPI message when the
414 * requested cpu is not the current cpu and consequently gd_tdallq may
415 * not be initialized synchronously from the point of view of the originating
418 * NOTE! we have to be careful in regards to creating threads for other cpus
419 * if SMP has not yet been activated.
422 lwkt_init_thread_remote(void *arg)
427 * Protected by critical section held by IPI dispatch
429 TAILQ_INSERT_TAIL(&td->td_gd->gd_tdallq, td, td_allq);
433 * lwkt core thread structural initialization.
435 * NOTE: All threads are initialized as mpsafe threads.
438 lwkt_init_thread(thread_t td, void *stack, int stksize, int flags,
439 struct globaldata *gd)
441 globaldata_t mygd = mycpu;
443 bzero(td, sizeof(struct thread));
444 td->td_kstack = stack;
445 td->td_kstack_size = stksize;
446 td->td_flags = flags;
448 td->td_type = TD_TYPE_GENERIC;
450 td->td_pri = TDPRI_KERN_DAEMON;
451 td->td_critcount = 1;
452 td->td_toks_have = NULL;
453 td->td_toks_stop = &td->td_toks_base;
454 if (lwkt_use_spin_port || (flags & TDF_FORCE_SPINPORT)) {
455 lwkt_initport_spin(&td->td_msgport, td,
456 (flags & TDF_FIXEDCPU) ? TRUE : FALSE);
458 lwkt_initport_thread(&td->td_msgport, td);
460 pmap_init_thread(td);
462 * Normally initializing a thread for a remote cpu requires sending an
463 * IPI. However, the idlethread is setup before the other cpus are
464 * activated so we have to treat it as a special case. XXX manipulation
465 * of gd_tdallq requires the BGL.
467 if (gd == mygd || td == &gd->gd_idlethread) {
469 TAILQ_INSERT_TAIL(&gd->gd_tdallq, td, td_allq);
472 lwkt_send_ipiq(gd, lwkt_init_thread_remote, td);
474 dsched_enter_thread(td);
478 lwkt_set_comm(thread_t td, const char *ctl, ...)
483 kvsnprintf(td->td_comm, sizeof(td->td_comm), ctl, va);
485 KTR_LOG(ctxsw_newtd, td, td->td_comm);
489 * Prevent the thread from getting destroyed. Note that unlike PHOLD/PRELE
490 * this does not prevent the thread from migrating to another cpu so the
491 * gd_tdallq state is not protected by this.
494 lwkt_hold(thread_t td)
496 atomic_add_int(&td->td_refs, 1);
500 lwkt_rele(thread_t td)
502 KKASSERT(td->td_refs > 0);
503 atomic_add_int(&td->td_refs, -1);
507 lwkt_free_thread(thread_t td)
509 KKASSERT(td->td_refs == 0);
510 KKASSERT((td->td_flags & (TDF_RUNNING | TDF_PREEMPT_LOCK |
511 TDF_RUNQ | TDF_TSLEEPQ)) == 0);
512 if (td->td_flags & TDF_ALLOCATED_THREAD) {
513 objcache_put(thread_cache, td);
514 } else if (td->td_flags & TDF_ALLOCATED_STACK) {
515 /* client-allocated struct with internally allocated stack */
516 KASSERT(td->td_kstack && td->td_kstack_size > 0,
517 ("lwkt_free_thread: corrupted stack"));
518 kmem_free(&kernel_map, (vm_offset_t)td->td_kstack, td->td_kstack_size);
519 td->td_kstack = NULL;
520 td->td_kstack_size = 0;
523 KTR_LOG(ctxsw_deadtd, td);
528 * Switch to the next runnable lwkt. If no LWKTs are runnable then
529 * switch to the idlethread. Switching must occur within a critical
530 * section to avoid races with the scheduling queue.
532 * We always have full control over our cpu's run queue. Other cpus
533 * that wish to manipulate our queue must use the cpu_*msg() calls to
534 * talk to our cpu, so a critical section is all that is needed and
535 * the result is very, very fast thread switching.
537 * The LWKT scheduler uses a fixed priority model and round-robins at
538 * each priority level. User process scheduling is a totally
539 * different beast and LWKT priorities should not be confused with
540 * user process priorities.
542 * PREEMPTION NOTE: Preemption occurs via lwkt_preempt(). lwkt_switch()
543 * is not called by the current thread in the preemption case, only when
544 * the preempting thread blocks (in order to return to the original thread).
546 * SPECIAL NOTE ON SWITCH ATOMICY: Certain operations such as thread
547 * migration and tsleep deschedule the current lwkt thread and call
548 * lwkt_switch(). In particular, the target cpu of the migration fully
549 * expects the thread to become non-runnable and can deadlock against
550 * cpusync operations if we run any IPIs prior to switching the thread out.
552 * WE MUST BE VERY CAREFUL NOT TO RUN SPLZ DIRECTLY OR INDIRECTLY IF
553 * THE CURRENT THREAD HAS BEEN DESCHEDULED!
558 globaldata_t gd = mycpu;
559 thread_t td = gd->gd_curthread;
564 uint64_t tsc_base = rdtsc();
567 KKASSERT(gd->gd_processing_ipiq == 0);
568 KKASSERT(td->td_flags & TDF_RUNNING);
571 * Switching from within a 'fast' (non thread switched) interrupt or IPI
572 * is illegal. However, we may have to do it anyway if we hit a fatal
573 * kernel trap or we have paniced.
575 * If this case occurs save and restore the interrupt nesting level.
577 if (gd->gd_intr_nesting_level) {
581 if (gd->gd_trap_nesting_level == 0 && panic_cpu_gd != mycpu) {
582 panic("lwkt_switch: Attempt to switch from a "
583 "fast interrupt, ipi, or hard code section, "
587 savegdnest = gd->gd_intr_nesting_level;
588 savegdtrap = gd->gd_trap_nesting_level;
589 gd->gd_intr_nesting_level = 0;
590 gd->gd_trap_nesting_level = 0;
591 if ((td->td_flags & TDF_PANICWARN) == 0) {
592 td->td_flags |= TDF_PANICWARN;
593 kprintf("Warning: thread switch from interrupt, IPI, "
594 "or hard code section.\n"
595 "thread %p (%s)\n", td, td->td_comm);
599 gd->gd_intr_nesting_level = savegdnest;
600 gd->gd_trap_nesting_level = savegdtrap;
606 * Release our current user process designation if we are blocking
607 * or if a user reschedule was requested.
609 * NOTE: This function is NOT called if we are switching into or
610 * returning from a preemption.
612 * NOTE: Releasing our current user process designation may cause
613 * it to be assigned to another thread, which in turn will
614 * cause us to block in the usched acquire code when we attempt
615 * to return to userland.
617 * NOTE: On SMP systems this can be very nasty when heavy token
618 * contention is present so we want to be careful not to
619 * release the designation gratuitously.
621 if (td->td_release &&
622 (user_resched_wanted() || (td->td_flags & TDF_RUNQ) == 0)) {
627 * Release all tokens. Once we do this we must remain in the critical
628 * section and cannot run IPIs or other interrupts until we switch away
629 * because they may implode if they try to get a token using our thread
633 if (TD_TOKS_HELD(td))
634 lwkt_relalltokens(td);
637 * We had better not be holding any spin locks, but don't get into an
638 * endless panic loop.
640 KASSERT(gd->gd_spinlocks == 0 || panicstr != NULL,
641 ("lwkt_switch: still holding %d exclusive spinlocks!",
645 if (td->td_cscount) {
646 kprintf("Diagnostic: attempt to switch while mastering cpusync: %p\n",
648 if (panic_on_cscount)
649 panic("switching while mastering cpusync");
654 * If we had preempted another thread on this cpu, resume the preempted
655 * thread. This occurs transparently, whether the preempted thread
656 * was scheduled or not (it may have been preempted after descheduling
659 * We have to setup the MP lock for the original thread after backing
660 * out the adjustment that was made to curthread when the original
663 if ((ntd = td->td_preempted) != NULL) {
664 KKASSERT(ntd->td_flags & TDF_PREEMPT_LOCK);
665 ntd->td_flags |= TDF_PREEMPT_DONE;
666 ntd->td_contended = 0; /* reset contended */
669 * The interrupt may have woken a thread up, we need to properly
670 * set the reschedule flag if the originally interrupted thread is
671 * at a lower priority.
673 * NOTE: The interrupt may not have descheduled ntd.
675 * NOTE: We do not reschedule if there are no threads on the runq.
676 * (ntd could be the idlethread).
678 xtd = TAILQ_FIRST(&gd->gd_tdrunq);
679 if (xtd && xtd != ntd)
681 goto havethread_preempted;
685 * Figure out switch target. If we cannot switch to our desired target
686 * look for a thread that we can switch to.
688 * NOTE! The limited spin loop and related parameters are extremely
689 * important for system performance, particularly for pipes and
690 * concurrent conflicting VM faults.
692 clear_lwkt_resched();
693 ntd = TAILQ_FIRST(&gd->gd_tdrunq);
697 if (TD_TOKS_NOT_HELD(ntd) ||
698 lwkt_getalltokens(ntd, (ntd->td_contended > lwkt_spin_loops)))
702 ++ntd->td_contended; /* overflow ok */
703 if (gd->gd_indefinite.type == 0)
704 indefinite_init(&gd->gd_indefinite, NULL, 0, 't');
706 if (tsc_frequency && rdtsc() - tsc_base > tsc_frequency) {
707 kprintf("lwkt_switch: excessive contended %d "
708 "thread %p\n", ntd->td_contended, ntd);
712 } while (ntd->td_contended < (lwkt_spin_loops >> 1));
716 * Bleh, the thread we wanted to switch to has a contended token.
717 * See if we can switch to another thread.
719 * We generally don't want to do this because it represents a
720 * priority inversion, but contending tokens on the same cpu can
721 * cause real problems if we don't now that we have an exclusive
722 * priority mechanism over shared for tokens.
724 * The solution is to allow threads with pending tokens to compete
725 * for them (a lower priority thread will get less cpu once it
726 * returns from the kernel anyway). If a thread does not have
727 * any contending tokens, we go by td_pri and upri.
729 while ((ntd = TAILQ_NEXT(ntd, td_threadq)) != NULL) {
730 if (TD_TOKS_NOT_HELD(ntd) &&
731 ntd->td_pri < TDPRI_KERN_LPSCHED && upri > ntd->td_upri) {
734 if (upri < ntd->td_upri)
740 if (TD_TOKS_NOT_HELD(ntd) ||
741 lwkt_getalltokens(ntd, (ntd->td_contended > lwkt_spin_loops))) {
744 ++ntd->td_contended; /* overflow ok */
748 * Fall through, switch to idle thread to get us out of the current
749 * context. Since we were contended, prevent HLT by flagging a
756 * We either contended on ntd or the runq is empty. We must switch
757 * through the idle thread to get out of the current context.
759 ntd = &gd->gd_idlethread;
760 if (gd->gd_trap_nesting_level == 0 && panicstr == NULL)
761 ASSERT_NO_TOKENS_HELD(ntd);
762 cpu_time.cp_msg[0] = 0;
767 * Clear gd_idle_repeat when doing a normal switch to a non-idle
770 ntd->td_wmesg = NULL;
771 ntd->td_contended = 0; /* reset once scheduled */
772 ++gd->gd_cnt.v_swtch;
773 gd->gd_idle_repeat = 0;
776 * If we were busy waiting record final disposition
778 if (gd->gd_indefinite.type)
779 indefinite_done(&gd->gd_indefinite);
781 havethread_preempted:
783 * If the new target does not need the MP lock and we are holding it,
784 * release the MP lock. If the new target requires the MP lock we have
785 * already acquired it for the target.
789 KASSERT(ntd->td_critcount,
790 ("priority problem in lwkt_switch %d %d",
791 td->td_critcount, ntd->td_critcount));
795 * Execute the actual thread switch operation. This function
796 * returns to the current thread and returns the previous thread
797 * (which may be different from the thread we switched to).
799 * We are responsible for marking ntd as TDF_RUNNING.
801 KKASSERT((ntd->td_flags & TDF_RUNNING) == 0);
802 #ifdef DEBUG_LWKT_THREAD
805 KTR_LOG(ctxsw_sw, gd->gd_cpuid, ntd);
806 ntd->td_flags |= TDF_RUNNING;
807 lwkt_switch_return(td->td_switch(ntd));
808 /* ntd invalid, td_switch() can return a different thread_t */
812 * catch-all. XXX is this strictly needed?
816 /* NOTE: current cpu may have changed after switch */
821 * Called by assembly in the td_switch (thread restore path) for thread
822 * bootstrap cases which do not 'return' to lwkt_switch().
825 lwkt_switch_return(thread_t otd)
829 uint64_t tsc_base = rdtsc();
833 exiting = otd->td_flags & TDF_EXITING;
837 * Check if otd was migrating. Now that we are on ntd we can finish
838 * up the migration. This is a bit messy but it is the only place
839 * where td is known to be fully descheduled.
841 * We can only activate the migration if otd was migrating but not
842 * held on the cpu due to a preemption chain. We still have to
843 * clear TDF_RUNNING on the old thread either way.
845 * We are responsible for clearing the previously running thread's
848 if ((rgd = otd->td_migrate_gd) != NULL &&
849 (otd->td_flags & TDF_PREEMPT_LOCK) == 0) {
850 KKASSERT((otd->td_flags & (TDF_MIGRATING | TDF_RUNNING)) ==
851 (TDF_MIGRATING | TDF_RUNNING));
852 otd->td_migrate_gd = NULL;
853 otd->td_flags &= ~TDF_RUNNING;
854 lwkt_send_ipiq(rgd, lwkt_setcpu_remote, otd);
856 otd->td_flags &= ~TDF_RUNNING;
860 * Final exit validations (see lwp_wait()). Note that otd becomes
861 * invalid the *instant* we set TDF_MP_EXITSIG.
863 * Use the EXITING status loaded from before we clear TDF_RUNNING,
864 * because if it is not set otd becomes invalid the instant we clear
865 * TDF_RUNNING on it (otherwise, if the system is fast enough, we
866 * might 'steal' TDF_EXITING from another switch-return!).
871 mpflags = otd->td_mpflags;
874 if (mpflags & TDF_MP_EXITWAIT) {
875 if (atomic_cmpset_int(&otd->td_mpflags, mpflags,
876 mpflags | TDF_MP_EXITSIG)) {
881 if (atomic_cmpset_int(&otd->td_mpflags, mpflags,
882 mpflags | TDF_MP_EXITSIG)) {
889 if (tsc_frequency && rdtsc() - tsc_base > tsc_frequency) {
890 kprintf("lwkt_switch_return: excessive TDF_EXITING "
899 * Request that the target thread preempt the current thread. Preemption
900 * can only occur only:
902 * - If our critical section is the one that we were called with
903 * - The relative priority of the target thread is higher
904 * - The target is not excessively interrupt-nested via td_nest_count
905 * - The target thread holds no tokens.
906 * - The target thread is not already scheduled and belongs to the
908 * - The current thread is not holding any spin-locks.
910 * THE CALLER OF LWKT_PREEMPT() MUST BE IN A CRITICAL SECTION. Typically
911 * this is called via lwkt_schedule() through the td_preemptable callback.
912 * critcount is the managed critical priority that we should ignore in order
913 * to determine whether preemption is possible (aka usually just the crit
914 * priority of lwkt_schedule() itself).
916 * Preemption is typically limited to interrupt threads.
918 * Operation works in a fairly straight-forward manner. The normal
919 * scheduling code is bypassed and we switch directly to the target
920 * thread. When the target thread attempts to block or switch away
921 * code at the base of lwkt_switch() will switch directly back to our
922 * thread. Our thread is able to retain whatever tokens it holds and
923 * if the target needs one of them the target will switch back to us
924 * and reschedule itself normally.
927 lwkt_preempt(thread_t ntd, int critcount)
929 struct globaldata *gd = mycpu;
932 int save_gd_intr_nesting_level;
935 * The caller has put us in a critical section. We can only preempt
936 * if the caller of the caller was not in a critical section (basically
937 * a local interrupt), as determined by the 'critcount' parameter. We
938 * also can't preempt if the caller is holding any spinlocks (even if
939 * he isn't in a critical section). This also handles the tokens test.
941 * YYY The target thread must be in a critical section (else it must
942 * inherit our critical section? I dunno yet).
944 KASSERT(ntd->td_critcount, ("BADCRIT0 %d", ntd->td_pri));
946 td = gd->gd_curthread;
947 if (preempt_enable == 0) {
948 #ifdef DEBUG_LWKT_THREAD
953 if (ntd->td_pri <= td->td_pri) {
954 #ifdef DEBUG_LWKT_THREAD
959 if (td->td_critcount > critcount) {
960 #ifdef DEBUG_LWKT_THREAD
965 if (td->td_nest_count >= 2) {
966 #ifdef DEBUG_LWKT_THREAD
971 if (td->td_cscount) {
972 #ifdef DEBUG_LWKT_THREAD
977 if (ntd->td_gd != gd) {
978 #ifdef DEBUG_LWKT_THREAD
985 * We don't have to check spinlocks here as they will also bump
988 * Do not try to preempt if the target thread is holding any tokens.
989 * We could try to acquire the tokens but this case is so rare there
990 * is no need to support it.
992 KKASSERT(gd->gd_spinlocks == 0);
994 if (TD_TOKS_HELD(ntd)) {
995 #ifdef DEBUG_LWKT_THREAD
1000 if (td == ntd || ((td->td_flags | ntd->td_flags) & TDF_PREEMPT_LOCK)) {
1001 #ifdef DEBUG_LWKT_THREAD
1006 if (ntd->td_preempted) {
1007 #ifdef DEBUG_LWKT_THREAD
1012 KKASSERT(gd->gd_processing_ipiq == 0);
1015 * Since we are able to preempt the current thread, there is no need to
1016 * call need_lwkt_resched().
1018 * We must temporarily clear gd_intr_nesting_level around the switch
1019 * since switchouts from the target thread are allowed (they will just
1020 * return to our thread), and since the target thread has its own stack.
1022 * A preemption must switch back to the original thread, assert the
1025 #ifdef DEBUG_LWKT_THREAD
1028 ntd->td_preempted = td;
1029 td->td_flags |= TDF_PREEMPT_LOCK;
1030 KTR_LOG(ctxsw_pre, gd->gd_cpuid, ntd);
1031 save_gd_intr_nesting_level = gd->gd_intr_nesting_level;
1032 gd->gd_intr_nesting_level = 0;
1034 KKASSERT((ntd->td_flags & TDF_RUNNING) == 0);
1035 ntd->td_flags |= TDF_RUNNING;
1036 xtd = td->td_switch(ntd);
1037 KKASSERT(xtd == ntd);
1038 lwkt_switch_return(xtd);
1039 gd->gd_intr_nesting_level = save_gd_intr_nesting_level;
1041 KKASSERT(ntd->td_preempted && (td->td_flags & TDF_PREEMPT_DONE));
1042 ntd->td_preempted = NULL;
1043 td->td_flags &= ~(TDF_PREEMPT_LOCK|TDF_PREEMPT_DONE);
1047 * Conditionally call splz() if gd_reqflags indicates work is pending.
1048 * This will work inside a critical section but not inside a hard code
1051 * (self contained on a per cpu basis)
1056 globaldata_t gd = mycpu;
1057 thread_t td = gd->gd_curthread;
1059 if ((gd->gd_reqflags & RQF_IDLECHECK_MASK) &&
1060 gd->gd_intr_nesting_level == 0 &&
1061 td->td_nest_count < 2)
1068 * This version is integrated into crit_exit, reqflags has already
1069 * been tested but td_critcount has not.
1071 * We only want to execute the splz() on the 1->0 transition of
1072 * critcount and not in a hard code section or if too deeply nested.
1074 * NOTE: gd->gd_spinlocks is implied to be 0 when td_critcount is 0.
1077 lwkt_maybe_splz(thread_t td)
1079 globaldata_t gd = td->td_gd;
1081 if (td->td_critcount == 0 &&
1082 gd->gd_intr_nesting_level == 0 &&
1083 td->td_nest_count < 2)
1090 * Drivers which set up processing co-threads can call this function to
1091 * run the co-thread at a higher priority and to allow it to preempt
1095 lwkt_set_interrupt_support_thread(void)
1097 thread_t td = curthread;
1099 lwkt_setpri_self(TDPRI_INT_SUPPORT);
1100 td->td_flags |= TDF_INTTHREAD;
1101 td->td_preemptable = lwkt_preempt;
1106 * This function is used to negotiate a passive release of the current
1107 * process/lwp designation with the user scheduler, allowing the user
1108 * scheduler to schedule another user thread. The related kernel thread
1109 * (curthread) continues running in the released state.
1112 lwkt_passive_release(struct thread *td)
1114 struct lwp *lp = td->td_lwp;
1116 td->td_release = NULL;
1117 lwkt_setpri_self(TDPRI_KERN_USER);
1119 lp->lwp_proc->p_usched->release_curproc(lp);
1124 * This implements a LWKT yield, allowing a kernel thread to yield to other
1125 * kernel threads at the same or higher priority. This function can be
1126 * called in a tight loop and will typically only yield once per tick.
1128 * Most kernel threads run at the same priority in order to allow equal
1131 * (self contained on a per cpu basis)
1136 globaldata_t gd = mycpu;
1137 thread_t td = gd->gd_curthread;
1140 * Should never be called with spinlocks held but there is a path
1141 * via ACPI where it might happen.
1143 if (gd->gd_spinlocks)
1147 * Safe to call splz if we are not too-heavily nested.
1149 if ((gd->gd_reqflags & RQF_IDLECHECK_MASK) && td->td_nest_count < 2)
1153 * Caller allows switching
1155 if (lwkt_resched_wanted()) {
1156 atomic_set_int(&td->td_mpflags, TDF_MP_DIDYIELD);
1157 lwkt_schedule_self(td);
1163 * The quick version processes pending interrupts and higher-priority
1164 * LWKT threads but will not round-robin same-priority LWKT threads.
1166 * When called while attempting to return to userland the only same-pri
1167 * threads are the ones which have already tried to become the current
1171 lwkt_yield_quick(void)
1173 globaldata_t gd = mycpu;
1174 thread_t td = gd->gd_curthread;
1176 if ((gd->gd_reqflags & RQF_IDLECHECK_MASK) && td->td_nest_count < 2)
1178 if (lwkt_resched_wanted()) {
1180 if (TAILQ_FIRST(&gd->gd_tdrunq) == td) {
1181 clear_lwkt_resched();
1183 atomic_set_int(&td->td_mpflags, TDF_MP_DIDYIELD);
1184 lwkt_schedule_self(curthread);
1192 * This yield is designed for kernel threads with a user context.
1194 * The kernel acting on behalf of the user is potentially cpu-bound,
1195 * this function will efficiently allow other threads to run and also
1196 * switch to other processes by releasing.
1198 * The lwkt_user_yield() function is designed to have very low overhead
1199 * if no yield is determined to be needed.
1202 lwkt_user_yield(void)
1204 globaldata_t gd = mycpu;
1205 thread_t td = gd->gd_curthread;
1208 * Should never be called with spinlocks held but there is a path
1209 * via ACPI where it might happen.
1211 if (gd->gd_spinlocks)
1215 * Always run any pending interrupts in case we are in a critical
1218 if ((gd->gd_reqflags & RQF_IDLECHECK_MASK) && td->td_nest_count < 2)
1222 * Switch (which forces a release) if another kernel thread needs
1223 * the cpu, if userland wants us to resched, or if our kernel
1224 * quantum has run out.
1226 if (lwkt_resched_wanted() ||
1227 user_resched_wanted())
1234 * Reacquire the current process if we are released.
1236 * XXX not implemented atm. The kernel may be holding locks and such,
1237 * so we want the thread to continue to receive cpu.
1239 if (td->td_release == NULL && lp) {
1240 lp->lwp_proc->p_usched->acquire_curproc(lp);
1241 td->td_release = lwkt_passive_release;
1242 lwkt_setpri_self(TDPRI_USER_NORM);
1248 * Generic schedule. Possibly schedule threads belonging to other cpus and
1249 * deal with threads that might be blocked on a wait queue.
1251 * We have a little helper inline function which does additional work after
1252 * the thread has been enqueued, including dealing with preemption and
1253 * setting need_lwkt_resched() (which prevents the kernel from returning
1254 * to userland until it has processed higher priority threads).
1256 * It is possible for this routine to be called after a failed _enqueue
1257 * (due to the target thread migrating, sleeping, or otherwise blocked).
1258 * We have to check that the thread is actually on the run queue!
1262 _lwkt_schedule_post(globaldata_t gd, thread_t ntd, int ccount)
1264 if (ntd->td_flags & TDF_RUNQ) {
1265 if (ntd->td_preemptable) {
1266 ntd->td_preemptable(ntd, ccount); /* YYY +token */
1273 _lwkt_schedule(thread_t td)
1275 globaldata_t mygd = mycpu;
1277 KASSERT(td != &td->td_gd->gd_idlethread,
1278 ("lwkt_schedule(): scheduling gd_idlethread is illegal!"));
1279 KKASSERT((td->td_flags & TDF_MIGRATING) == 0);
1280 crit_enter_gd(mygd);
1281 KKASSERT(td->td_lwp == NULL ||
1282 (td->td_lwp->lwp_mpflags & LWP_MP_ONRUNQ) == 0);
1284 if (td == mygd->gd_curthread) {
1288 * If we own the thread, there is no race (since we are in a
1289 * critical section). If we do not own the thread there might
1290 * be a race but the target cpu will deal with it.
1292 if (td->td_gd == mygd) {
1294 _lwkt_schedule_post(mygd, td, 1);
1296 lwkt_send_ipiq3(td->td_gd, lwkt_schedule_remote, td, 0);
1303 lwkt_schedule(thread_t td)
1309 lwkt_schedule_noresched(thread_t td) /* XXX not impl */
1315 * When scheduled remotely if frame != NULL the IPIQ is being
1316 * run via doreti or an interrupt then preemption can be allowed.
1318 * To allow preemption we have to drop the critical section so only
1319 * one is present in _lwkt_schedule_post.
1322 lwkt_schedule_remote(void *arg, int arg2, struct intrframe *frame)
1324 thread_t td = curthread;
1327 if (frame && ntd->td_preemptable) {
1328 crit_exit_noyield(td);
1329 _lwkt_schedule(ntd);
1330 crit_enter_quick(td);
1332 _lwkt_schedule(ntd);
1337 * Thread migration using a 'Pull' method. The thread may or may not be
1338 * the current thread. It MUST be descheduled and in a stable state.
1339 * lwkt_giveaway() must be called on the cpu owning the thread.
1341 * At any point after lwkt_giveaway() is called, the target cpu may
1342 * 'pull' the thread by calling lwkt_acquire().
1344 * We have to make sure the thread is not sitting on a per-cpu tsleep
1345 * queue or it will blow up when it moves to another cpu.
1347 * MPSAFE - must be called under very specific conditions.
1350 lwkt_giveaway(thread_t td)
1352 globaldata_t gd = mycpu;
1355 if (td->td_flags & TDF_TSLEEPQ)
1357 KKASSERT(td->td_gd == gd);
1358 TAILQ_REMOVE(&gd->gd_tdallq, td, td_allq);
1359 td->td_flags |= TDF_MIGRATING;
1364 lwkt_acquire(thread_t td)
1369 KKASSERT(td->td_flags & TDF_MIGRATING);
1374 uint64_t tsc_base = rdtsc();
1377 KKASSERT((td->td_flags & TDF_RUNQ) == 0);
1378 crit_enter_gd(mygd);
1379 DEBUG_PUSH_INFO("lwkt_acquire");
1380 while (td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK)) {
1381 lwkt_process_ipiq();
1383 #ifdef _KERNEL_VIRTUAL
1387 if (tsc_frequency && rdtsc() - tsc_base > tsc_frequency) {
1388 kprintf("lwkt_acquire: stuck td %p td->td_flags %08x\n",
1397 TAILQ_INSERT_TAIL(&mygd->gd_tdallq, td, td_allq);
1398 td->td_flags &= ~TDF_MIGRATING;
1401 crit_enter_gd(mygd);
1402 TAILQ_INSERT_TAIL(&mygd->gd_tdallq, td, td_allq);
1403 td->td_flags &= ~TDF_MIGRATING;
1409 * Generic deschedule. Descheduling threads other then your own should be
1410 * done only in carefully controlled circumstances. Descheduling is
1413 * This function may block if the cpu has run out of messages.
1416 lwkt_deschedule(thread_t td)
1419 if (td == curthread) {
1422 if (td->td_gd == mycpu) {
1425 lwkt_send_ipiq(td->td_gd, (ipifunc1_t)lwkt_deschedule, td);
1432 * Set the target thread's priority. This routine does not automatically
1433 * switch to a higher priority thread, LWKT threads are not designed for
1434 * continuous priority changes. Yield if you want to switch.
1437 lwkt_setpri(thread_t td, int pri)
1439 if (td->td_pri != pri) {
1442 if (td->td_flags & TDF_RUNQ) {
1443 KKASSERT(td->td_gd == mycpu);
1455 * Set the initial priority for a thread prior to it being scheduled for
1456 * the first time. The thread MUST NOT be scheduled before or during
1457 * this call. The thread may be assigned to a cpu other then the current
1460 * Typically used after a thread has been created with TDF_STOPPREQ,
1461 * and before the thread is initially scheduled.
1464 lwkt_setpri_initial(thread_t td, int pri)
1467 KKASSERT((td->td_flags & TDF_RUNQ) == 0);
1472 lwkt_setpri_self(int pri)
1474 thread_t td = curthread;
1476 KKASSERT(pri >= 0 && pri <= TDPRI_MAX);
1478 if (td->td_flags & TDF_RUNQ) {
1489 * hz tick scheduler clock for LWKT threads
1492 lwkt_schedulerclock(thread_t td)
1494 globaldata_t gd = td->td_gd;
1497 xtd = TAILQ_FIRST(&gd->gd_tdrunq);
1500 * If the current thread is at the head of the runq shift it to the
1501 * end of any equal-priority threads and request a LWKT reschedule
1504 * Ignore upri in this situation. There will only be one user thread
1505 * in user mode, all others will be user threads running in kernel
1506 * mode and we have to make sure they get some cpu.
1508 xtd = TAILQ_NEXT(td, td_threadq);
1509 if (xtd && xtd->td_pri == td->td_pri) {
1510 TAILQ_REMOVE(&gd->gd_tdrunq, td, td_threadq);
1511 while (xtd && xtd->td_pri == td->td_pri)
1512 xtd = TAILQ_NEXT(xtd, td_threadq);
1514 TAILQ_INSERT_BEFORE(xtd, td, td_threadq);
1516 TAILQ_INSERT_TAIL(&gd->gd_tdrunq, td, td_threadq);
1517 need_lwkt_resched();
1521 * If we scheduled a thread other than the one at the head of the
1522 * queue always request a reschedule every tick.
1524 need_lwkt_resched();
1526 /* else curthread probably the idle thread, no need to reschedule */
1530 * Migrate the current thread to the specified cpu.
1532 * This is accomplished by descheduling ourselves from the current cpu
1533 * and setting td_migrate_gd. The lwkt_switch() code will detect that the
1534 * 'old' thread wants to migrate after it has been completely switched out
1535 * and will complete the migration.
1537 * TDF_MIGRATING prevents scheduling races while the thread is being migrated.
1539 * We must be sure to release our current process designation (if a user
1540 * process) before clearing out any tsleepq we are on because the release
1541 * code may re-add us.
1543 * We must be sure to remove ourselves from the current cpu's tsleepq
1544 * before potentially moving to another queue. The thread can be on
1545 * a tsleepq due to a left-over tsleep_interlock().
1549 lwkt_setcpu_self(globaldata_t rgd)
1551 thread_t td = curthread;
1553 if (td->td_gd != rgd) {
1554 crit_enter_quick(td);
1558 if (td->td_flags & TDF_TSLEEPQ)
1562 * Set TDF_MIGRATING to prevent a spurious reschedule while we are
1563 * trying to deschedule ourselves and switch away, then deschedule
1564 * ourself, remove us from tdallq, and set td_migrate_gd. Finally,
1565 * call lwkt_switch() to complete the operation.
1567 td->td_flags |= TDF_MIGRATING;
1568 lwkt_deschedule_self(td);
1569 TAILQ_REMOVE(&td->td_gd->gd_tdallq, td, td_allq);
1570 td->td_migrate_gd = rgd;
1574 * We are now on the target cpu
1576 KKASSERT(rgd == mycpu);
1577 TAILQ_INSERT_TAIL(&rgd->gd_tdallq, td, td_allq);
1578 crit_exit_quick(td);
1583 lwkt_migratecpu(int cpuid)
1587 rgd = globaldata_find(cpuid);
1588 lwkt_setcpu_self(rgd);
1592 * Remote IPI for cpu migration (called while in a critical section so we
1593 * do not have to enter another one).
1595 * The thread (td) has already been completely descheduled from the
1596 * originating cpu and we can simply assert the case. The thread is
1597 * assigned to the new cpu and enqueued.
1599 * The thread will re-add itself to tdallq when it resumes execution.
1602 lwkt_setcpu_remote(void *arg)
1605 globaldata_t gd = mycpu;
1607 KKASSERT((td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK)) == 0);
1610 td->td_flags &= ~TDF_MIGRATING;
1611 KKASSERT(td->td_migrate_gd == NULL);
1612 KKASSERT(td->td_lwp == NULL ||
1613 (td->td_lwp->lwp_mpflags & LWP_MP_ONRUNQ) == 0);
1618 lwkt_preempted_proc(void)
1620 thread_t td = curthread;
1621 while (td->td_preempted)
1622 td = td->td_preempted;
1627 * Create a kernel process/thread/whatever. It shares it's address space
1628 * with proc0 - ie: kernel only.
1630 * If the cpu is not specified one will be selected. In the future
1631 * specifying a cpu of -1 will enable kernel thread migration between
1635 lwkt_create(void (*func)(void *), void *arg, struct thread **tdp,
1636 thread_t template, int tdflags, int cpu, const char *fmt, ...)
1641 td = lwkt_alloc_thread(template, LWKT_THREAD_STACK, cpu,
1645 cpu_set_thread_handler(td, lwkt_exit, func, arg);
1648 * Set up arg0 for 'ps' etc
1650 __va_start(ap, fmt);
1651 kvsnprintf(td->td_comm, sizeof(td->td_comm), fmt, ap);
1655 * Schedule the thread to run
1657 if (td->td_flags & TDF_NOSTART)
1658 td->td_flags &= ~TDF_NOSTART;
1665 * Destroy an LWKT thread. Warning! This function is not called when
1666 * a process exits, cpu_proc_exit() directly calls cpu_thread_exit() and
1667 * uses a different reaping mechanism.
1672 thread_t td = curthread;
1677 * Do any cleanup that might block here
1680 dsched_exit_thread(td);
1683 * Get us into a critical section to interlock gd_freetd and loop
1684 * until we can get it freed.
1686 * We have to cache the current td in gd_freetd because objcache_put()ing
1687 * it would rip it out from under us while our thread is still active.
1689 * We are the current thread so of course our own TDF_RUNNING bit will
1690 * be set, so unlike the lwp reap code we don't wait for it to clear.
1693 crit_enter_quick(td);
1696 tsleep(td, 0, "tdreap", 1);
1699 if ((std = gd->gd_freetd) != NULL) {
1700 KKASSERT((std->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK)) == 0);
1701 gd->gd_freetd = NULL;
1702 objcache_put(thread_cache, std);
1709 * Remove thread resources from kernel lists and deschedule us for
1710 * the last time. We cannot block after this point or we may end
1711 * up with a stale td on the tsleepq.
1713 * None of this may block, the critical section is the only thing
1714 * protecting tdallq and the only thing preventing new lwkt_hold()
1717 if (td->td_flags & TDF_TSLEEPQ)
1719 lwkt_deschedule_self(td);
1720 lwkt_remove_tdallq(td);
1721 KKASSERT(td->td_refs == 0);
1726 KKASSERT(gd->gd_freetd == NULL);
1727 if (td->td_flags & TDF_ALLOCATED_THREAD)
1733 lwkt_remove_tdallq(thread_t td)
1735 KKASSERT(td->td_gd == mycpu);
1736 TAILQ_REMOVE(&td->td_gd->gd_tdallq, td, td_allq);
1740 * Code reduction and branch prediction improvements. Call/return
1741 * overhead on modern cpus often degenerates into 0 cycles due to
1742 * the cpu's branch prediction hardware and return pc cache. We
1743 * can take advantage of this by not inlining medium-complexity
1744 * functions and we can also reduce the branch prediction impact
1745 * by collapsing perfectly predictable branches into a single
1746 * procedure instead of duplicating it.
1748 * Is any of this noticeable? Probably not, so I'll take the
1749 * smaller code size.
1752 crit_exit_wrapper(__DEBUG_CRIT_ARG__)
1754 _crit_exit(mycpu __DEBUG_CRIT_PASS_ARG__);
1760 thread_t td = curthread;
1761 int lcrit = td->td_critcount;
1763 td->td_critcount = 0;
1765 panic("td_critcount is/would-go negative! %p %d", td, lcrit);
1770 * Called from debugger/panic on cpus which have been stopped. We must still
1771 * process the IPIQ while stopped.
1773 * If we are dumping also try to process any pending interrupts. This may
1774 * or may not work depending on the state of the cpu at the point it was
1778 lwkt_smp_stopped(void)
1780 globaldata_t gd = mycpu;
1783 lwkt_process_ipiq();
1784 --gd->gd_intr_nesting_level;
1786 ++gd->gd_intr_nesting_level;
1788 lwkt_process_ipiq();