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 #ifdef _KERNEL_VIRTUAL
78 #if !defined(KTR_CTXSW)
79 #define KTR_CTXSW KTR_ALL
81 KTR_INFO_MASTER(ctxsw);
82 KTR_INFO(KTR_CTXSW, ctxsw, sw, 0, "#cpu[%d].td = %p", int cpu, struct thread *td);
83 KTR_INFO(KTR_CTXSW, ctxsw, pre, 1, "#cpu[%d].td = %p", int cpu, struct thread *td);
84 KTR_INFO(KTR_CTXSW, ctxsw, newtd, 2, "#threads[%p].name = %s", struct thread *td, char *comm);
85 KTR_INFO(KTR_CTXSW, ctxsw, deadtd, 3, "#threads[%p].name = <dead>", struct thread *td);
87 static MALLOC_DEFINE(M_THREAD, "thread", "lwkt threads");
90 static int panic_on_cscount = 0;
92 static __int64_t switch_count = 0;
93 static __int64_t preempt_hit = 0;
94 static __int64_t preempt_miss = 0;
95 static __int64_t preempt_weird = 0;
96 static int lwkt_use_spin_port;
97 static struct objcache *thread_cache;
98 int cpu_mwait_spin = 0;
100 static void lwkt_schedule_remote(void *arg, int arg2, struct intrframe *frame);
101 static void lwkt_setcpu_remote(void *arg);
103 extern void cpu_heavy_restore(void);
104 extern void cpu_lwkt_restore(void);
105 extern void cpu_kthread_restore(void);
106 extern void cpu_idle_restore(void);
109 * We can make all thread ports use the spin backend instead of the thread
110 * backend. This should only be set to debug the spin backend.
112 TUNABLE_INT("lwkt.use_spin_port", &lwkt_use_spin_port);
115 SYSCTL_INT(_lwkt, OID_AUTO, panic_on_cscount, CTLFLAG_RW, &panic_on_cscount, 0,
116 "Panic if attempting to switch lwkt's while mastering cpusync");
118 SYSCTL_INT(_hw, OID_AUTO, cpu_mwait_spin, CTLFLAG_RW, &cpu_mwait_spin, 0,
119 "monitor/mwait target state");
120 SYSCTL_QUAD(_lwkt, OID_AUTO, switch_count, CTLFLAG_RW, &switch_count, 0,
121 "Number of switched threads");
122 SYSCTL_QUAD(_lwkt, OID_AUTO, preempt_hit, CTLFLAG_RW, &preempt_hit, 0,
123 "Successful preemption events");
124 SYSCTL_QUAD(_lwkt, OID_AUTO, preempt_miss, CTLFLAG_RW, &preempt_miss, 0,
125 "Failed preemption events");
126 SYSCTL_QUAD(_lwkt, OID_AUTO, preempt_weird, CTLFLAG_RW, &preempt_weird, 0,
127 "Number of preempted threads.");
128 static int fairq_enable = 0;
129 SYSCTL_INT(_lwkt, OID_AUTO, fairq_enable, CTLFLAG_RW,
130 &fairq_enable, 0, "Turn on fairq priority accumulators");
131 static int fairq_bypass = -1;
132 SYSCTL_INT(_lwkt, OID_AUTO, fairq_bypass, CTLFLAG_RW,
133 &fairq_bypass, 0, "Allow fairq to bypass td on token failure");
134 extern int lwkt_sched_debug;
135 int lwkt_sched_debug = 0;
136 SYSCTL_INT(_lwkt, OID_AUTO, sched_debug, CTLFLAG_RW,
137 &lwkt_sched_debug, 0, "Scheduler debug");
138 static int lwkt_spin_loops = 10;
139 SYSCTL_INT(_lwkt, OID_AUTO, spin_loops, CTLFLAG_RW,
140 &lwkt_spin_loops, 0, "Scheduler spin loops until sorted decon");
141 static int lwkt_spin_reseq = 0;
142 SYSCTL_INT(_lwkt, OID_AUTO, spin_reseq, CTLFLAG_RW,
143 &lwkt_spin_reseq, 0, "Scheduler resequencer enable");
144 static int lwkt_spin_monitor = 0;
145 SYSCTL_INT(_lwkt, OID_AUTO, spin_monitor, CTLFLAG_RW,
146 &lwkt_spin_monitor, 0, "Scheduler uses monitor/mwait");
147 static int lwkt_spin_fatal = 0; /* disabled */
148 SYSCTL_INT(_lwkt, OID_AUTO, spin_fatal, CTLFLAG_RW,
149 &lwkt_spin_fatal, 0, "LWKT scheduler spin loops till fatal panic");
150 static int preempt_enable = 1;
151 SYSCTL_INT(_lwkt, OID_AUTO, preempt_enable, CTLFLAG_RW,
152 &preempt_enable, 0, "Enable preemption");
153 static int lwkt_cache_threads = 0;
154 SYSCTL_INT(_lwkt, OID_AUTO, cache_threads, CTLFLAG_RD,
155 &lwkt_cache_threads, 0, "thread+kstack cache");
157 #ifndef _KERNEL_VIRTUAL
158 static __cachealign int lwkt_cseq_rindex;
159 static __cachealign int lwkt_cseq_windex;
163 * These helper procedures handle the runq, they can only be called from
164 * within a critical section.
166 * WARNING! Prior to SMP being brought up it is possible to enqueue and
167 * dequeue threads belonging to other cpus, so be sure to use td->td_gd
168 * instead of 'mycpu' when referencing the globaldata structure. Once
169 * SMP live enqueuing and dequeueing only occurs on the current cpu.
173 _lwkt_dequeue(thread_t td)
175 if (td->td_flags & TDF_RUNQ) {
176 struct globaldata *gd = td->td_gd;
178 td->td_flags &= ~TDF_RUNQ;
179 TAILQ_REMOVE(&gd->gd_tdrunq, td, td_threadq);
180 --gd->gd_tdrunqcount;
181 if (TAILQ_FIRST(&gd->gd_tdrunq) == NULL)
182 atomic_clear_int(&gd->gd_reqflags, RQF_RUNNING);
189 * There are a limited number of lwkt threads runnable since user
190 * processes only schedule one at a time per cpu. However, there can
191 * be many user processes in kernel mode exiting from a tsleep() which
194 * NOTE: lwkt_schedulerclock() will force a round-robin based on td_pri and
195 * will ignore user priority. This is to ensure that user threads in
196 * kernel mode get cpu at some point regardless of what the user
201 _lwkt_enqueue(thread_t td)
205 if ((td->td_flags & (TDF_RUNQ|TDF_MIGRATING|TDF_BLOCKQ)) == 0) {
206 struct globaldata *gd = td->td_gd;
208 td->td_flags |= TDF_RUNQ;
209 xtd = TAILQ_FIRST(&gd->gd_tdrunq);
211 TAILQ_INSERT_TAIL(&gd->gd_tdrunq, td, td_threadq);
212 atomic_set_int(&gd->gd_reqflags, RQF_RUNNING);
215 * NOTE: td_upri - higher numbers more desireable, same sense
216 * as td_pri (typically reversed from lwp_upri).
218 * In the equal priority case we want the best selection
219 * at the beginning so the less desireable selections know
220 * that they have to setrunqueue/go-to-another-cpu, even
221 * though it means switching back to the 'best' selection.
222 * This also avoids degenerate situations when many threads
223 * are runnable or waking up at the same time.
225 * If upri matches exactly place at end/round-robin.
228 (xtd->td_pri >= td->td_pri ||
229 (xtd->td_pri == td->td_pri &&
230 xtd->td_upri >= td->td_upri))) {
231 xtd = TAILQ_NEXT(xtd, td_threadq);
234 TAILQ_INSERT_BEFORE(xtd, td, td_threadq);
236 TAILQ_INSERT_TAIL(&gd->gd_tdrunq, td, td_threadq);
238 ++gd->gd_tdrunqcount;
241 * Request a LWKT reschedule if we are now at the head of the queue.
243 if (TAILQ_FIRST(&gd->gd_tdrunq) == td)
249 _lwkt_thread_ctor(void *obj, void *privdata, int ocflags)
251 struct thread *td = (struct thread *)obj;
253 td->td_kstack = NULL;
254 td->td_kstack_size = 0;
255 td->td_flags = TDF_ALLOCATED_THREAD;
261 _lwkt_thread_dtor(void *obj, void *privdata)
263 struct thread *td = (struct thread *)obj;
265 KASSERT(td->td_flags & TDF_ALLOCATED_THREAD,
266 ("_lwkt_thread_dtor: not allocated from objcache"));
267 KASSERT((td->td_flags & TDF_ALLOCATED_STACK) && td->td_kstack &&
268 td->td_kstack_size > 0,
269 ("_lwkt_thread_dtor: corrupted stack"));
270 kmem_free(&kernel_map, (vm_offset_t)td->td_kstack, td->td_kstack_size);
271 td->td_kstack = NULL;
276 * Initialize the lwkt s/system.
278 * Nominally cache up to 32 thread + kstack structures. Cache more on
279 * systems with a lot of cpu cores.
284 TUNABLE_INT("lwkt.cache_threads", &lwkt_cache_threads);
285 if (lwkt_cache_threads == 0) {
286 lwkt_cache_threads = ncpus * 4;
287 if (lwkt_cache_threads < 32)
288 lwkt_cache_threads = 32;
290 thread_cache = objcache_create_mbacked(
291 M_THREAD, sizeof(struct thread),
292 0, lwkt_cache_threads,
293 _lwkt_thread_ctor, _lwkt_thread_dtor, NULL);
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);
342 * Create a new thread. The thread must be associated with a process context
343 * or LWKT start address before it can be scheduled. If the target cpu is
344 * -1 the thread will be created on the current cpu.
346 * If you intend to create a thread without a process context this function
347 * does everything except load the startup and switcher function.
350 lwkt_alloc_thread(struct thread *td, int stksize, int cpu, int flags)
352 static int cpu_rotator;
353 globaldata_t gd = mycpu;
357 * If static thread storage is not supplied allocate a thread. Reuse
358 * a cached free thread if possible. gd_freetd is used to keep an exiting
359 * thread intact through the exit.
363 if ((td = gd->gd_freetd) != NULL) {
364 KKASSERT((td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK|
366 gd->gd_freetd = NULL;
368 td = objcache_get(thread_cache, M_WAITOK);
369 KKASSERT((td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK|
373 KASSERT((td->td_flags &
374 (TDF_ALLOCATED_THREAD|TDF_RUNNING|TDF_PREEMPT_LOCK)) ==
375 TDF_ALLOCATED_THREAD,
376 ("lwkt_alloc_thread: corrupted td flags 0x%X", td->td_flags));
377 flags |= td->td_flags & (TDF_ALLOCATED_THREAD|TDF_ALLOCATED_STACK);
381 * Try to reuse cached stack.
383 if ((stack = td->td_kstack) != NULL && td->td_kstack_size != stksize) {
384 if (flags & TDF_ALLOCATED_STACK) {
385 kmem_free(&kernel_map, (vm_offset_t)stack, td->td_kstack_size);
390 stack = (void *)kmem_alloc_stack(&kernel_map, stksize);
391 flags |= TDF_ALLOCATED_STACK;
398 lwkt_init_thread(td, stack, stksize, flags, globaldata_find(cpu));
403 * Initialize a preexisting thread structure. This function is used by
404 * lwkt_alloc_thread() and also used to initialize the per-cpu idlethread.
406 * All threads start out in a critical section at a priority of
407 * TDPRI_KERN_DAEMON. Higher level code will modify the priority as
408 * appropriate. This function may send an IPI message when the
409 * requested cpu is not the current cpu and consequently gd_tdallq may
410 * not be initialized synchronously from the point of view of the originating
413 * NOTE! we have to be careful in regards to creating threads for other cpus
414 * if SMP has not yet been activated.
417 lwkt_init_thread_remote(void *arg)
422 * Protected by critical section held by IPI dispatch
424 TAILQ_INSERT_TAIL(&td->td_gd->gd_tdallq, td, td_allq);
428 * lwkt core thread structural initialization.
430 * NOTE: All threads are initialized as mpsafe threads.
433 lwkt_init_thread(thread_t td, void *stack, int stksize, int flags,
434 struct globaldata *gd)
436 globaldata_t mygd = mycpu;
438 bzero(td, sizeof(struct thread));
439 td->td_kstack = stack;
440 td->td_kstack_size = stksize;
441 td->td_flags = flags;
443 td->td_type = TD_TYPE_GENERIC;
445 td->td_pri = TDPRI_KERN_DAEMON;
446 td->td_critcount = 1;
447 td->td_toks_have = NULL;
448 td->td_toks_stop = &td->td_toks_base;
449 if (lwkt_use_spin_port || (flags & TDF_FORCE_SPINPORT))
450 lwkt_initport_spin(&td->td_msgport, td);
452 lwkt_initport_thread(&td->td_msgport, td);
453 pmap_init_thread(td);
455 * Normally initializing a thread for a remote cpu requires sending an
456 * IPI. However, the idlethread is setup before the other cpus are
457 * activated so we have to treat it as a special case. XXX manipulation
458 * of gd_tdallq requires the BGL.
460 if (gd == mygd || td == &gd->gd_idlethread) {
462 TAILQ_INSERT_TAIL(&gd->gd_tdallq, td, td_allq);
465 lwkt_send_ipiq(gd, lwkt_init_thread_remote, td);
467 dsched_new_thread(td);
471 lwkt_set_comm(thread_t td, const char *ctl, ...)
476 kvsnprintf(td->td_comm, sizeof(td->td_comm), ctl, va);
478 KTR_LOG(ctxsw_newtd, td, td->td_comm);
482 * Prevent the thread from getting destroyed. Note that unlike PHOLD/PRELE
483 * this does not prevent the thread from migrating to another cpu so the
484 * gd_tdallq state is not protected by this.
487 lwkt_hold(thread_t td)
489 atomic_add_int(&td->td_refs, 1);
493 lwkt_rele(thread_t td)
495 KKASSERT(td->td_refs > 0);
496 atomic_add_int(&td->td_refs, -1);
500 lwkt_free_thread(thread_t td)
502 KKASSERT(td->td_refs == 0);
503 KKASSERT((td->td_flags & (TDF_RUNNING | TDF_PREEMPT_LOCK |
504 TDF_RUNQ | TDF_TSLEEPQ)) == 0);
505 if (td->td_flags & TDF_ALLOCATED_THREAD) {
506 objcache_put(thread_cache, td);
507 } else if (td->td_flags & TDF_ALLOCATED_STACK) {
508 /* client-allocated struct with internally allocated stack */
509 KASSERT(td->td_kstack && td->td_kstack_size > 0,
510 ("lwkt_free_thread: corrupted stack"));
511 kmem_free(&kernel_map, (vm_offset_t)td->td_kstack, td->td_kstack_size);
512 td->td_kstack = NULL;
513 td->td_kstack_size = 0;
516 KTR_LOG(ctxsw_deadtd, td);
521 * Switch to the next runnable lwkt. If no LWKTs are runnable then
522 * switch to the idlethread. Switching must occur within a critical
523 * section to avoid races with the scheduling queue.
525 * We always have full control over our cpu's run queue. Other cpus
526 * that wish to manipulate our queue must use the cpu_*msg() calls to
527 * talk to our cpu, so a critical section is all that is needed and
528 * the result is very, very fast thread switching.
530 * The LWKT scheduler uses a fixed priority model and round-robins at
531 * each priority level. User process scheduling is a totally
532 * different beast and LWKT priorities should not be confused with
533 * user process priorities.
535 * PREEMPTION NOTE: Preemption occurs via lwkt_preempt(). lwkt_switch()
536 * is not called by the current thread in the preemption case, only when
537 * the preempting thread blocks (in order to return to the original thread).
539 * SPECIAL NOTE ON SWITCH ATOMICY: Certain operations such as thread
540 * migration and tsleep deschedule the current lwkt thread and call
541 * lwkt_switch(). In particular, the target cpu of the migration fully
542 * expects the thread to become non-runnable and can deadlock against
543 * cpusync operations if we run any IPIs prior to switching the thread out.
545 * WE MUST BE VERY CAREFUL NOT TO RUN SPLZ DIRECTLY OR INDIRECTLY IF
546 * THE CURRENT THREAD HAS BEEN DESCHEDULED!
551 globaldata_t gd = mycpu;
552 thread_t td = gd->gd_curthread;
556 KKASSERT(gd->gd_processing_ipiq == 0);
557 KKASSERT(td->td_flags & TDF_RUNNING);
560 * Switching from within a 'fast' (non thread switched) interrupt or IPI
561 * is illegal. However, we may have to do it anyway if we hit a fatal
562 * kernel trap or we have paniced.
564 * If this case occurs save and restore the interrupt nesting level.
566 if (gd->gd_intr_nesting_level) {
570 if (gd->gd_trap_nesting_level == 0 && panic_cpu_gd != mycpu) {
571 panic("lwkt_switch: Attempt to switch from a "
572 "fast interrupt, ipi, or hard code section, "
576 savegdnest = gd->gd_intr_nesting_level;
577 savegdtrap = gd->gd_trap_nesting_level;
578 gd->gd_intr_nesting_level = 0;
579 gd->gd_trap_nesting_level = 0;
580 if ((td->td_flags & TDF_PANICWARN) == 0) {
581 td->td_flags |= TDF_PANICWARN;
582 kprintf("Warning: thread switch from interrupt, IPI, "
583 "or hard code section.\n"
584 "thread %p (%s)\n", td, td->td_comm);
588 gd->gd_intr_nesting_level = savegdnest;
589 gd->gd_trap_nesting_level = savegdtrap;
595 * Release our current user process designation if we are blocking
596 * or if a user reschedule was requested.
598 * NOTE: This function is NOT called if we are switching into or
599 * returning from a preemption.
601 * NOTE: Releasing our current user process designation may cause
602 * it to be assigned to another thread, which in turn will
603 * cause us to block in the usched acquire code when we attempt
604 * to return to userland.
606 * NOTE: On SMP systems this can be very nasty when heavy token
607 * contention is present so we want to be careful not to
608 * release the designation gratuitously.
610 if (td->td_release &&
611 (user_resched_wanted() || (td->td_flags & TDF_RUNQ) == 0)) {
619 if (TD_TOKS_HELD(td))
620 lwkt_relalltokens(td);
623 * We had better not be holding any spin locks, but don't get into an
624 * endless panic loop.
626 KASSERT(gd->gd_spinlocks == 0 || panicstr != NULL,
627 ("lwkt_switch: still holding %d exclusive spinlocks!",
632 if (td->td_cscount) {
633 kprintf("Diagnostic: attempt to switch while mastering cpusync: %p\n",
635 if (panic_on_cscount)
636 panic("switching while mastering cpusync");
641 * If we had preempted another thread on this cpu, resume the preempted
642 * thread. This occurs transparently, whether the preempted thread
643 * was scheduled or not (it may have been preempted after descheduling
646 * We have to setup the MP lock for the original thread after backing
647 * out the adjustment that was made to curthread when the original
650 if ((ntd = td->td_preempted) != NULL) {
651 KKASSERT(ntd->td_flags & TDF_PREEMPT_LOCK);
652 ntd->td_flags |= TDF_PREEMPT_DONE;
655 * The interrupt may have woken a thread up, we need to properly
656 * set the reschedule flag if the originally interrupted thread is
657 * at a lower priority.
659 * The interrupt may not have descheduled.
661 if (TAILQ_FIRST(&gd->gd_tdrunq) != ntd)
663 goto havethread_preempted;
667 * If we cannot obtain ownership of the tokens we cannot immediately
668 * schedule the target thread.
670 * Reminder: Again, we cannot afford to run any IPIs in this path if
671 * the current thread has been descheduled.
674 clear_lwkt_resched();
677 * Hotpath - pull the head of the run queue and attempt to schedule
680 ntd = TAILQ_FIRST(&gd->gd_tdrunq);
684 * Runq is empty, switch to idle to allow it to halt.
686 ntd = &gd->gd_idlethread;
687 if (gd->gd_trap_nesting_level == 0 && panicstr == NULL)
688 ASSERT_NO_TOKENS_HELD(ntd);
689 cpu_time.cp_msg[0] = 0;
690 cpu_time.cp_stallpc = 0;
695 * Hotpath - schedule ntd.
697 * NOTE: For UP there is no mplock and lwkt_getalltokens()
700 if (TD_TOKS_NOT_HELD(ntd) ||
701 lwkt_getalltokens(ntd, (spinning >= lwkt_spin_loops)))
707 * Coldpath (SMP only since tokens always succeed on UP)
709 * We had some contention on the thread we wanted to schedule.
710 * What we do now is try to find a thread that we can schedule
713 * The coldpath scan does NOT rearrange threads in the run list.
714 * The lwkt_schedulerclock() will assert need_lwkt_resched() on
715 * the next tick whenever the current head is not the current thread.
720 ++gd->gd_cnt.v_token_colls;
722 if (fairq_bypass > 0)
725 while ((ntd = TAILQ_NEXT(ntd, td_threadq)) != NULL) {
726 #ifndef NO_LWKT_SPLIT_USERPRI
728 * Never schedule threads returning to userland or the
729 * user thread scheduler helper thread when higher priority
730 * threads are present. The runq is sorted by priority
731 * so we can give up traversing it when we find the first
732 * low priority thread.
734 if (ntd->td_pri < TDPRI_KERN_LPSCHED) {
743 if (TD_TOKS_NOT_HELD(ntd) ||
744 lwkt_getalltokens(ntd, (spinning >= lwkt_spin_loops))) {
750 ++gd->gd_cnt.v_token_colls;
755 * We exhausted the run list, meaning that all runnable threads
759 #ifdef _KERNEL_VIRTUAL
762 ntd = &gd->gd_idlethread;
763 if (gd->gd_trap_nesting_level == 0 && panicstr == NULL)
764 ASSERT_NO_TOKENS_HELD(ntd);
765 /* contention case, do not clear contention mask */
768 * We are going to have to retry but if the current thread is not
769 * on the runq we instead switch through the idle thread to get away
770 * from the current thread. We have to flag for lwkt reschedule
771 * to prevent the idle thread from halting.
773 * NOTE: A non-zero spinning is passed to lwkt_getalltokens() to
774 * instruct it to deal with the potential for deadlocks by
775 * ordering the tokens by address.
777 if ((td->td_flags & TDF_RUNQ) == 0) {
778 need_lwkt_resched(); /* prevent hlt */
781 #if defined(INVARIANTS) && defined(__x86_64__)
782 if ((read_rflags() & PSL_I) == 0) {
784 panic("lwkt_switch() called with interrupts disabled");
789 * Number iterations so far. After a certain point we switch to
790 * a sorted-address/monitor/mwait version of lwkt_getalltokens()
792 if (spinning < 0x7FFFFFFF)
795 #ifndef _KERNEL_VIRTUAL
797 * lwkt_getalltokens() failed in sorted token mode, we can use
798 * monitor/mwait in this case.
800 if (spinning >= lwkt_spin_loops &&
801 (cpu_mi_feature & CPU_MI_MONITOR) &&
804 cpu_mmw_pause_int(&gd->gd_reqflags,
805 (gd->gd_reqflags | RQF_SPINNING) &
806 ~RQF_IDLECHECK_WK_MASK,
812 * We already checked that td is still scheduled so this should be
817 #ifndef _KERNEL_VIRTUAL
819 * This experimental resequencer is used as a fall-back to reduce
820 * hw cache line contention by placing each core's scheduler into a
821 * time-domain-multplexed slot.
823 * The resequencer is disabled by default. It's functionality has
824 * largely been superceeded by the token algorithm which limits races
825 * to a subset of cores.
827 * The resequencer algorithm tends to break down when more than
828 * 20 cores are contending. What appears to happen is that new
829 * tokens can be obtained out of address-sorted order by new cores
830 * while existing cores languish in long delays between retries and
831 * wind up being starved-out of the token acquisition.
833 if (lwkt_spin_reseq && spinning >= lwkt_spin_reseq) {
834 int cseq = atomic_fetchadd_int(&lwkt_cseq_windex, 1);
837 while ((oseq = lwkt_cseq_rindex) != cseq) {
840 if (cpu_mi_feature & CPU_MI_MONITOR) {
841 cpu_mmw_pause_int(&lwkt_cseq_rindex, oseq, cpu_mwait_spin);
851 atomic_add_int(&lwkt_cseq_rindex, 1);
854 /* highest level for(;;) loop */
859 * Clear gd_idle_repeat when doing a normal switch to a non-idle
862 ntd->td_wmesg = NULL;
863 ++gd->gd_cnt.v_swtch;
864 gd->gd_idle_repeat = 0;
866 havethread_preempted:
868 * If the new target does not need the MP lock and we are holding it,
869 * release the MP lock. If the new target requires the MP lock we have
870 * already acquired it for the target.
874 KASSERT(ntd->td_critcount,
875 ("priority problem in lwkt_switch %d %d",
876 td->td_critcount, ntd->td_critcount));
880 * Execute the actual thread switch operation. This function
881 * returns to the current thread and returns the previous thread
882 * (which may be different from the thread we switched to).
884 * We are responsible for marking ntd as TDF_RUNNING.
886 KKASSERT((ntd->td_flags & TDF_RUNNING) == 0);
888 KTR_LOG(ctxsw_sw, gd->gd_cpuid, ntd);
889 ntd->td_flags |= TDF_RUNNING;
890 lwkt_switch_return(td->td_switch(ntd));
891 /* ntd invalid, td_switch() can return a different thread_t */
895 * catch-all. XXX is this strictly needed?
899 /* NOTE: current cpu may have changed after switch */
904 * Called by assembly in the td_switch (thread restore path) for thread
905 * bootstrap cases which do not 'return' to lwkt_switch().
908 lwkt_switch_return(thread_t otd)
913 * Check if otd was migrating. Now that we are on ntd we can finish
914 * up the migration. This is a bit messy but it is the only place
915 * where td is known to be fully descheduled.
917 * We can only activate the migration if otd was migrating but not
918 * held on the cpu due to a preemption chain. We still have to
919 * clear TDF_RUNNING on the old thread either way.
921 * We are responsible for clearing the previously running thread's
924 if ((rgd = otd->td_migrate_gd) != NULL &&
925 (otd->td_flags & TDF_PREEMPT_LOCK) == 0) {
926 KKASSERT((otd->td_flags & (TDF_MIGRATING | TDF_RUNNING)) ==
927 (TDF_MIGRATING | TDF_RUNNING));
928 otd->td_migrate_gd = NULL;
929 otd->td_flags &= ~TDF_RUNNING;
930 lwkt_send_ipiq(rgd, lwkt_setcpu_remote, otd);
932 otd->td_flags &= ~TDF_RUNNING;
936 * Final exit validations (see lwp_wait()). Note that otd becomes
937 * invalid the *instant* we set TDF_MP_EXITSIG.
939 while (otd->td_flags & TDF_EXITING) {
942 mpflags = otd->td_mpflags;
945 if (mpflags & TDF_MP_EXITWAIT) {
946 if (atomic_cmpset_int(&otd->td_mpflags, mpflags,
947 mpflags | TDF_MP_EXITSIG)) {
952 if (atomic_cmpset_int(&otd->td_mpflags, mpflags,
953 mpflags | TDF_MP_EXITSIG)) {
962 * Request that the target thread preempt the current thread. Preemption
963 * can only occur if our only critical section is the one that we were called
964 * with, the relative priority of the target thread is higher, and the target
965 * thread holds no tokens. This also only works if we are not holding any
966 * spinlocks (obviously).
968 * THE CALLER OF LWKT_PREEMPT() MUST BE IN A CRITICAL SECTION. Typically
969 * this is called via lwkt_schedule() through the td_preemptable callback.
970 * critcount is the managed critical priority that we should ignore in order
971 * to determine whether preemption is possible (aka usually just the crit
972 * priority of lwkt_schedule() itself).
974 * Preemption is typically limited to interrupt threads.
976 * Operation works in a fairly straight-forward manner. The normal
977 * scheduling code is bypassed and we switch directly to the target
978 * thread. When the target thread attempts to block or switch away
979 * code at the base of lwkt_switch() will switch directly back to our
980 * thread. Our thread is able to retain whatever tokens it holds and
981 * if the target needs one of them the target will switch back to us
982 * and reschedule itself normally.
985 lwkt_preempt(thread_t ntd, int critcount)
987 struct globaldata *gd = mycpu;
990 int save_gd_intr_nesting_level;
993 * The caller has put us in a critical section. We can only preempt
994 * if the caller of the caller was not in a critical section (basically
995 * a local interrupt), as determined by the 'critcount' parameter. We
996 * also can't preempt if the caller is holding any spinlocks (even if
997 * he isn't in a critical section). This also handles the tokens test.
999 * YYY The target thread must be in a critical section (else it must
1000 * inherit our critical section? I dunno yet).
1002 KASSERT(ntd->td_critcount, ("BADCRIT0 %d", ntd->td_pri));
1004 td = gd->gd_curthread;
1005 if (preempt_enable == 0) {
1009 if (ntd->td_pri <= td->td_pri) {
1013 if (td->td_critcount > critcount) {
1017 if (td->td_cscount) {
1021 if (ntd->td_gd != gd) {
1026 * We don't have to check spinlocks here as they will also bump
1029 * Do not try to preempt if the target thread is holding any tokens.
1030 * We could try to acquire the tokens but this case is so rare there
1031 * is no need to support it.
1033 KKASSERT(gd->gd_spinlocks == 0);
1035 if (TD_TOKS_HELD(ntd)) {
1039 if (td == ntd || ((td->td_flags | ntd->td_flags) & TDF_PREEMPT_LOCK)) {
1043 if (ntd->td_preempted) {
1047 KKASSERT(gd->gd_processing_ipiq == 0);
1050 * Since we are able to preempt the current thread, there is no need to
1051 * call need_lwkt_resched().
1053 * We must temporarily clear gd_intr_nesting_level around the switch
1054 * since switchouts from the target thread are allowed (they will just
1055 * return to our thread), and since the target thread has its own stack.
1057 * A preemption must switch back to the original thread, assert the
1061 ntd->td_preempted = td;
1062 td->td_flags |= TDF_PREEMPT_LOCK;
1063 KTR_LOG(ctxsw_pre, gd->gd_cpuid, ntd);
1064 save_gd_intr_nesting_level = gd->gd_intr_nesting_level;
1065 gd->gd_intr_nesting_level = 0;
1067 KKASSERT((ntd->td_flags & TDF_RUNNING) == 0);
1068 ntd->td_flags |= TDF_RUNNING;
1069 xtd = td->td_switch(ntd);
1070 KKASSERT(xtd == ntd);
1071 lwkt_switch_return(xtd);
1072 gd->gd_intr_nesting_level = save_gd_intr_nesting_level;
1074 KKASSERT(ntd->td_preempted && (td->td_flags & TDF_PREEMPT_DONE));
1075 ntd->td_preempted = NULL;
1076 td->td_flags &= ~(TDF_PREEMPT_LOCK|TDF_PREEMPT_DONE);
1080 * Conditionally call splz() if gd_reqflags indicates work is pending.
1081 * This will work inside a critical section but not inside a hard code
1084 * (self contained on a per cpu basis)
1089 globaldata_t gd = mycpu;
1090 thread_t td = gd->gd_curthread;
1092 if ((gd->gd_reqflags & RQF_IDLECHECK_MASK) &&
1093 gd->gd_intr_nesting_level == 0 &&
1094 td->td_nest_count < 2)
1101 * This version is integrated into crit_exit, reqflags has already
1102 * been tested but td_critcount has not.
1104 * We only want to execute the splz() on the 1->0 transition of
1105 * critcount and not in a hard code section or if too deeply nested.
1107 * NOTE: gd->gd_spinlocks is implied to be 0 when td_critcount is 0.
1110 lwkt_maybe_splz(thread_t td)
1112 globaldata_t gd = td->td_gd;
1114 if (td->td_critcount == 0 &&
1115 gd->gd_intr_nesting_level == 0 &&
1116 td->td_nest_count < 2)
1123 * Drivers which set up processing co-threads can call this function to
1124 * run the co-thread at a higher priority and to allow it to preempt
1128 lwkt_set_interrupt_support_thread(void)
1130 thread_t td = curthread;
1132 lwkt_setpri_self(TDPRI_INT_SUPPORT);
1133 td->td_flags |= TDF_INTTHREAD;
1134 td->td_preemptable = lwkt_preempt;
1139 * This function is used to negotiate a passive release of the current
1140 * process/lwp designation with the user scheduler, allowing the user
1141 * scheduler to schedule another user thread. The related kernel thread
1142 * (curthread) continues running in the released state.
1145 lwkt_passive_release(struct thread *td)
1147 struct lwp *lp = td->td_lwp;
1149 #ifndef NO_LWKT_SPLIT_USERPRI
1150 td->td_release = NULL;
1151 lwkt_setpri_self(TDPRI_KERN_USER);
1154 lp->lwp_proc->p_usched->release_curproc(lp);
1159 * This implements a LWKT yield, allowing a kernel thread to yield to other
1160 * kernel threads at the same or higher priority. This function can be
1161 * called in a tight loop and will typically only yield once per tick.
1163 * Most kernel threads run at the same priority in order to allow equal
1166 * (self contained on a per cpu basis)
1171 globaldata_t gd = mycpu;
1172 thread_t td = gd->gd_curthread;
1174 if ((gd->gd_reqflags & RQF_IDLECHECK_MASK) && td->td_nest_count < 2)
1176 if (lwkt_resched_wanted()) {
1177 lwkt_schedule_self(curthread);
1183 * The quick version processes pending interrupts and higher-priority
1184 * LWKT threads but will not round-robin same-priority LWKT threads.
1186 * When called while attempting to return to userland the only same-pri
1187 * threads are the ones which have already tried to become the current
1191 lwkt_yield_quick(void)
1193 globaldata_t gd = mycpu;
1194 thread_t td = gd->gd_curthread;
1196 if ((gd->gd_reqflags & RQF_IDLECHECK_MASK) && td->td_nest_count < 2)
1198 if (lwkt_resched_wanted()) {
1200 if (TAILQ_FIRST(&gd->gd_tdrunq) == td) {
1201 clear_lwkt_resched();
1203 lwkt_schedule_self(curthread);
1211 * This yield is designed for kernel threads with a user context.
1213 * The kernel acting on behalf of the user is potentially cpu-bound,
1214 * this function will efficiently allow other threads to run and also
1215 * switch to other processes by releasing.
1217 * The lwkt_user_yield() function is designed to have very low overhead
1218 * if no yield is determined to be needed.
1221 lwkt_user_yield(void)
1223 globaldata_t gd = mycpu;
1224 thread_t td = gd->gd_curthread;
1227 * Always run any pending interrupts in case we are in a critical
1230 if ((gd->gd_reqflags & RQF_IDLECHECK_MASK) && td->td_nest_count < 2)
1234 * Switch (which forces a release) if another kernel thread needs
1235 * the cpu, if userland wants us to resched, or if our kernel
1236 * quantum has run out.
1238 if (lwkt_resched_wanted() ||
1239 user_resched_wanted())
1246 * Reacquire the current process if we are released.
1248 * XXX not implemented atm. The kernel may be holding locks and such,
1249 * so we want the thread to continue to receive cpu.
1251 if (td->td_release == NULL && lp) {
1252 lp->lwp_proc->p_usched->acquire_curproc(lp);
1253 td->td_release = lwkt_passive_release;
1254 lwkt_setpri_self(TDPRI_USER_NORM);
1260 * Generic schedule. Possibly schedule threads belonging to other cpus and
1261 * deal with threads that might be blocked on a wait queue.
1263 * We have a little helper inline function which does additional work after
1264 * the thread has been enqueued, including dealing with preemption and
1265 * setting need_lwkt_resched() (which prevents the kernel from returning
1266 * to userland until it has processed higher priority threads).
1268 * It is possible for this routine to be called after a failed _enqueue
1269 * (due to the target thread migrating, sleeping, or otherwise blocked).
1270 * We have to check that the thread is actually on the run queue!
1274 _lwkt_schedule_post(globaldata_t gd, thread_t ntd, int ccount)
1276 if (ntd->td_flags & TDF_RUNQ) {
1277 if (ntd->td_preemptable) {
1278 ntd->td_preemptable(ntd, ccount); /* YYY +token */
1285 _lwkt_schedule(thread_t td)
1287 globaldata_t mygd = mycpu;
1289 KASSERT(td != &td->td_gd->gd_idlethread,
1290 ("lwkt_schedule(): scheduling gd_idlethread is illegal!"));
1291 KKASSERT((td->td_flags & TDF_MIGRATING) == 0);
1292 crit_enter_gd(mygd);
1293 KKASSERT(td->td_lwp == NULL ||
1294 (td->td_lwp->lwp_mpflags & LWP_MP_ONRUNQ) == 0);
1296 if (td == mygd->gd_curthread) {
1300 * If we own the thread, there is no race (since we are in a
1301 * critical section). If we do not own the thread there might
1302 * be a race but the target cpu will deal with it.
1304 if (td->td_gd == mygd) {
1306 _lwkt_schedule_post(mygd, td, 1);
1308 lwkt_send_ipiq3(td->td_gd, lwkt_schedule_remote, td, 0);
1315 lwkt_schedule(thread_t td)
1321 lwkt_schedule_noresched(thread_t td) /* XXX not impl */
1327 * When scheduled remotely if frame != NULL the IPIQ is being
1328 * run via doreti or an interrupt then preemption can be allowed.
1330 * To allow preemption we have to drop the critical section so only
1331 * one is present in _lwkt_schedule_post.
1334 lwkt_schedule_remote(void *arg, int arg2, struct intrframe *frame)
1336 thread_t td = curthread;
1339 if (frame && ntd->td_preemptable) {
1340 crit_exit_noyield(td);
1341 _lwkt_schedule(ntd);
1342 crit_enter_quick(td);
1344 _lwkt_schedule(ntd);
1349 * Thread migration using a 'Pull' method. The thread may or may not be
1350 * the current thread. It MUST be descheduled and in a stable state.
1351 * lwkt_giveaway() must be called on the cpu owning the thread.
1353 * At any point after lwkt_giveaway() is called, the target cpu may
1354 * 'pull' the thread by calling lwkt_acquire().
1356 * We have to make sure the thread is not sitting on a per-cpu tsleep
1357 * queue or it will blow up when it moves to another cpu.
1359 * MPSAFE - must be called under very specific conditions.
1362 lwkt_giveaway(thread_t td)
1364 globaldata_t gd = mycpu;
1367 if (td->td_flags & TDF_TSLEEPQ)
1369 KKASSERT(td->td_gd == gd);
1370 TAILQ_REMOVE(&gd->gd_tdallq, td, td_allq);
1371 td->td_flags |= TDF_MIGRATING;
1376 lwkt_acquire(thread_t td)
1380 int retry = 10000000;
1382 KKASSERT(td->td_flags & TDF_MIGRATING);
1387 KKASSERT((td->td_flags & TDF_RUNQ) == 0);
1388 crit_enter_gd(mygd);
1389 DEBUG_PUSH_INFO("lwkt_acquire");
1390 while (td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK)) {
1391 lwkt_process_ipiq();
1394 kprintf("lwkt_acquire: stuck: td %p td->td_flags %08x\n",
1398 #ifdef _KERNEL_VIRTUAL
1405 TAILQ_INSERT_TAIL(&mygd->gd_tdallq, td, td_allq);
1406 td->td_flags &= ~TDF_MIGRATING;
1409 crit_enter_gd(mygd);
1410 TAILQ_INSERT_TAIL(&mygd->gd_tdallq, td, td_allq);
1411 td->td_flags &= ~TDF_MIGRATING;
1417 * Generic deschedule. Descheduling threads other then your own should be
1418 * done only in carefully controlled circumstances. Descheduling is
1421 * This function may block if the cpu has run out of messages.
1424 lwkt_deschedule(thread_t td)
1427 if (td == curthread) {
1430 if (td->td_gd == mycpu) {
1433 lwkt_send_ipiq(td->td_gd, (ipifunc1_t)lwkt_deschedule, td);
1440 * Set the target thread's priority. This routine does not automatically
1441 * switch to a higher priority thread, LWKT threads are not designed for
1442 * continuous priority changes. Yield if you want to switch.
1445 lwkt_setpri(thread_t td, int pri)
1447 if (td->td_pri != pri) {
1450 if (td->td_flags & TDF_RUNQ) {
1451 KKASSERT(td->td_gd == mycpu);
1463 * Set the initial priority for a thread prior to it being scheduled for
1464 * the first time. The thread MUST NOT be scheduled before or during
1465 * this call. The thread may be assigned to a cpu other then the current
1468 * Typically used after a thread has been created with TDF_STOPPREQ,
1469 * and before the thread is initially scheduled.
1472 lwkt_setpri_initial(thread_t td, int pri)
1475 KKASSERT((td->td_flags & TDF_RUNQ) == 0);
1480 lwkt_setpri_self(int pri)
1482 thread_t td = curthread;
1484 KKASSERT(pri >= 0 && pri <= TDPRI_MAX);
1486 if (td->td_flags & TDF_RUNQ) {
1497 * hz tick scheduler clock for LWKT threads
1500 lwkt_schedulerclock(thread_t td)
1502 globaldata_t gd = td->td_gd;
1505 if (TAILQ_FIRST(&gd->gd_tdrunq) == td) {
1507 * If the current thread is at the head of the runq shift it to the
1508 * end of any equal-priority threads and request a LWKT reschedule
1511 * Ignore upri in this situation. There will only be one user thread
1512 * in user mode, all others will be user threads running in kernel
1513 * mode and we have to make sure they get some cpu.
1515 xtd = TAILQ_NEXT(td, td_threadq);
1516 if (xtd && xtd->td_pri == td->td_pri) {
1517 TAILQ_REMOVE(&gd->gd_tdrunq, td, td_threadq);
1518 while (xtd && xtd->td_pri == td->td_pri)
1519 xtd = TAILQ_NEXT(xtd, td_threadq);
1521 TAILQ_INSERT_BEFORE(xtd, td, td_threadq);
1523 TAILQ_INSERT_TAIL(&gd->gd_tdrunq, td, td_threadq);
1524 need_lwkt_resched();
1528 * If we scheduled a thread other than the one at the head of the
1529 * queue always request a reschedule every tick.
1531 need_lwkt_resched();
1536 * Migrate the current thread to the specified cpu.
1538 * This is accomplished by descheduling ourselves from the current cpu
1539 * and setting td_migrate_gd. The lwkt_switch() code will detect that the
1540 * 'old' thread wants to migrate after it has been completely switched out
1541 * and will complete the migration.
1543 * TDF_MIGRATING prevents scheduling races while the thread is being migrated.
1545 * We must be sure to release our current process designation (if a user
1546 * process) before clearing out any tsleepq we are on because the release
1547 * code may re-add us.
1549 * We must be sure to remove ourselves from the current cpu's tsleepq
1550 * before potentially moving to another queue. The thread can be on
1551 * a tsleepq due to a left-over tsleep_interlock().
1555 lwkt_setcpu_self(globaldata_t rgd)
1557 thread_t td = curthread;
1559 if (td->td_gd != rgd) {
1560 crit_enter_quick(td);
1564 if (td->td_flags & TDF_TSLEEPQ)
1568 * Set TDF_MIGRATING to prevent a spurious reschedule while we are
1569 * trying to deschedule ourselves and switch away, then deschedule
1570 * ourself, remove us from tdallq, and set td_migrate_gd. Finally,
1571 * call lwkt_switch() to complete the operation.
1573 td->td_flags |= TDF_MIGRATING;
1574 lwkt_deschedule_self(td);
1575 TAILQ_REMOVE(&td->td_gd->gd_tdallq, td, td_allq);
1576 td->td_migrate_gd = rgd;
1580 * We are now on the target cpu
1582 KKASSERT(rgd == mycpu);
1583 TAILQ_INSERT_TAIL(&rgd->gd_tdallq, td, td_allq);
1584 crit_exit_quick(td);
1589 lwkt_migratecpu(int cpuid)
1593 rgd = globaldata_find(cpuid);
1594 lwkt_setcpu_self(rgd);
1598 * Remote IPI for cpu migration (called while in a critical section so we
1599 * do not have to enter another one).
1601 * The thread (td) has already been completely descheduled from the
1602 * originating cpu and we can simply assert the case. The thread is
1603 * assigned to the new cpu and enqueued.
1605 * The thread will re-add itself to tdallq when it resumes execution.
1608 lwkt_setcpu_remote(void *arg)
1611 globaldata_t gd = mycpu;
1613 KKASSERT((td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK)) == 0);
1616 td->td_flags &= ~TDF_MIGRATING;
1617 KKASSERT(td->td_migrate_gd == NULL);
1618 KKASSERT(td->td_lwp == NULL ||
1619 (td->td_lwp->lwp_mpflags & LWP_MP_ONRUNQ) == 0);
1624 lwkt_preempted_proc(void)
1626 thread_t td = curthread;
1627 while (td->td_preempted)
1628 td = td->td_preempted;
1633 * Create a kernel process/thread/whatever. It shares it's address space
1634 * with proc0 - ie: kernel only.
1636 * If the cpu is not specified one will be selected. In the future
1637 * specifying a cpu of -1 will enable kernel thread migration between
1641 lwkt_create(void (*func)(void *), void *arg, struct thread **tdp,
1642 thread_t template, int tdflags, int cpu, const char *fmt, ...)
1647 td = lwkt_alloc_thread(template, LWKT_THREAD_STACK, cpu,
1651 cpu_set_thread_handler(td, lwkt_exit, func, arg);
1654 * Set up arg0 for 'ps' etc
1656 __va_start(ap, fmt);
1657 kvsnprintf(td->td_comm, sizeof(td->td_comm), fmt, ap);
1661 * Schedule the thread to run
1663 if (td->td_flags & TDF_NOSTART)
1664 td->td_flags &= ~TDF_NOSTART;
1671 * Destroy an LWKT thread. Warning! This function is not called when
1672 * a process exits, cpu_proc_exit() directly calls cpu_thread_exit() and
1673 * uses a different reaping mechanism.
1678 thread_t td = curthread;
1683 * Do any cleanup that might block here
1685 if (td->td_flags & TDF_VERBOSE)
1686 kprintf("kthread %p %s has exited\n", td, td->td_comm);
1688 dsched_exit_thread(td);
1691 * Get us into a critical section to interlock gd_freetd and loop
1692 * until we can get it freed.
1694 * We have to cache the current td in gd_freetd because objcache_put()ing
1695 * it would rip it out from under us while our thread is still active.
1697 * We are the current thread so of course our own TDF_RUNNING bit will
1698 * be set, so unlike the lwp reap code we don't wait for it to clear.
1701 crit_enter_quick(td);
1704 tsleep(td, 0, "tdreap", 1);
1707 if ((std = gd->gd_freetd) != NULL) {
1708 KKASSERT((std->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK)) == 0);
1709 gd->gd_freetd = NULL;
1710 objcache_put(thread_cache, std);
1717 * Remove thread resources from kernel lists and deschedule us for
1718 * the last time. We cannot block after this point or we may end
1719 * up with a stale td on the tsleepq.
1721 * None of this may block, the critical section is the only thing
1722 * protecting tdallq and the only thing preventing new lwkt_hold()
1725 if (td->td_flags & TDF_TSLEEPQ)
1727 lwkt_deschedule_self(td);
1728 lwkt_remove_tdallq(td);
1729 KKASSERT(td->td_refs == 0);
1734 KKASSERT(gd->gd_freetd == NULL);
1735 if (td->td_flags & TDF_ALLOCATED_THREAD)
1741 lwkt_remove_tdallq(thread_t td)
1743 KKASSERT(td->td_gd == mycpu);
1744 TAILQ_REMOVE(&td->td_gd->gd_tdallq, td, td_allq);
1748 * Code reduction and branch prediction improvements. Call/return
1749 * overhead on modern cpus often degenerates into 0 cycles due to
1750 * the cpu's branch prediction hardware and return pc cache. We
1751 * can take advantage of this by not inlining medium-complexity
1752 * functions and we can also reduce the branch prediction impact
1753 * by collapsing perfectly predictable branches into a single
1754 * procedure instead of duplicating it.
1756 * Is any of this noticeable? Probably not, so I'll take the
1757 * smaller code size.
1760 crit_exit_wrapper(__DEBUG_CRIT_ARG__)
1762 _crit_exit(mycpu __DEBUG_CRIT_PASS_ARG__);
1768 thread_t td = curthread;
1769 int lcrit = td->td_critcount;
1771 td->td_critcount = 0;
1772 panic("td_critcount is/would-go negative! %p %d", td, lcrit);
1777 * Called from debugger/panic on cpus which have been stopped. We must still
1778 * process the IPIQ while stopped, even if we were stopped while in a critical
1781 * If we are dumping also try to process any pending interrupts. This may
1782 * or may not work depending on the state of the cpu at the point it was
1786 lwkt_smp_stopped(void)
1788 globaldata_t gd = mycpu;
1792 lwkt_process_ipiq();
1795 lwkt_process_ipiq();