2 * Copyright (c) 2003 Matthew Dillon <dillon@backplane.com>
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
8 * 1. Redistributions of source code must retain the above copyright
9 * notice, this list of conditions and the following disclaimer.
10 * 2. Redistributions in binary form must reproduce the above copyright
11 * notice, this list of conditions and the following disclaimer in the
12 * documentation and/or other materials provided with the distribution.
14 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
15 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
16 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
17 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
18 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
19 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
20 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
21 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
22 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
23 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
26 * Each cpu in a system has its own self-contained light weight kernel
27 * thread scheduler, which means that generally speaking we only need
28 * to use a critical section to avoid problems. Foreign thread
29 * scheduling is queued via (async) IPIs.
31 * $DragonFly: src/sys/kern/lwkt_thread.c,v 1.28 2003/07/25 05:51:19 dillon Exp $
34 #include <sys/param.h>
35 #include <sys/systm.h>
36 #include <sys/kernel.h>
38 #include <sys/rtprio.h>
39 #include <sys/queue.h>
40 #include <sys/thread2.h>
41 #include <sys/sysctl.h>
42 #include <sys/kthread.h>
43 #include <machine/cpu.h>
47 #include <vm/vm_param.h>
48 #include <vm/vm_kern.h>
49 #include <vm/vm_object.h>
50 #include <vm/vm_page.h>
51 #include <vm/vm_map.h>
52 #include <vm/vm_pager.h>
53 #include <vm/vm_extern.h>
54 #include <vm/vm_zone.h>
56 #include <machine/stdarg.h>
57 #include <machine/ipl.h>
59 #include <machine/smp.h>
62 static int untimely_switch = 0;
63 SYSCTL_INT(_lwkt, OID_AUTO, untimely_switch, CTLFLAG_RW, &untimely_switch, 0, "");
65 static int token_debug = 0;
66 SYSCTL_INT(_lwkt, OID_AUTO, token_debug, CTLFLAG_RW, &token_debug, 0, "");
68 static quad_t switch_count = 0;
69 SYSCTL_QUAD(_lwkt, OID_AUTO, switch_count, CTLFLAG_RW, &switch_count, 0, "");
70 static quad_t preempt_hit = 0;
71 SYSCTL_QUAD(_lwkt, OID_AUTO, preempt_hit, CTLFLAG_RW, &preempt_hit, 0, "");
72 static quad_t preempt_miss = 0;
73 SYSCTL_QUAD(_lwkt, OID_AUTO, preempt_miss, CTLFLAG_RW, &preempt_miss, 0, "");
74 static quad_t preempt_weird = 0;
75 SYSCTL_QUAD(_lwkt, OID_AUTO, preempt_weird, CTLFLAG_RW, &preempt_weird, 0, "");
76 static quad_t ipiq_count = 0;
77 SYSCTL_QUAD(_lwkt, OID_AUTO, ipiq_count, CTLFLAG_RW, &ipiq_count, 0, "");
78 static quad_t ipiq_fifofull = 0;
79 SYSCTL_QUAD(_lwkt, OID_AUTO, ipiq_fifofull, CTLFLAG_RW, &ipiq_fifofull, 0, "");
82 * These helper procedures handle the runq, they can only be called from
83 * within a critical section.
87 _lwkt_dequeue(thread_t td)
89 if (td->td_flags & TDF_RUNQ) {
90 int nq = td->td_pri & TDPRI_MASK;
91 struct globaldata *gd = mycpu;
93 td->td_flags &= ~TDF_RUNQ;
94 TAILQ_REMOVE(&gd->gd_tdrunq[nq], td, td_threadq);
95 /* runqmask is passively cleaned up by the switcher */
101 _lwkt_enqueue(thread_t td)
103 if ((td->td_flags & TDF_RUNQ) == 0) {
104 int nq = td->td_pri & TDPRI_MASK;
105 struct globaldata *gd = mycpu;
107 td->td_flags |= TDF_RUNQ;
108 TAILQ_INSERT_TAIL(&gd->gd_tdrunq[nq], td, td_threadq);
109 gd->gd_runqmask |= 1 << nq;
115 _lwkt_wantresched(thread_t ntd, thread_t cur)
117 return((ntd->td_pri & TDPRI_MASK) > (cur->td_pri & TDPRI_MASK));
121 * LWKTs operate on a per-cpu basis
123 * WARNING! Called from early boot, 'mycpu' may not work yet.
126 lwkt_gdinit(struct globaldata *gd)
130 for (i = 0; i < sizeof(gd->gd_tdrunq)/sizeof(gd->gd_tdrunq[0]); ++i)
131 TAILQ_INIT(&gd->gd_tdrunq[i]);
133 TAILQ_INIT(&gd->gd_tdallq);
137 * Initialize a thread wait structure prior to first use.
139 * NOTE! called from low level boot code, we cannot do anything fancy!
142 lwkt_init_wait(lwkt_wait_t w)
144 TAILQ_INIT(&w->wa_waitq);
148 * Create a new thread. The thread must be associated with a process context
149 * or LWKT start address before it can be scheduled.
151 * If you intend to create a thread without a process context this function
152 * does everything except load the startup and switcher function.
155 lwkt_alloc_thread(struct thread *td)
162 if (mycpu->gd_tdfreecount > 0) {
163 --mycpu->gd_tdfreecount;
164 td = TAILQ_FIRST(&mycpu->gd_tdfreeq);
165 KASSERT(td != NULL && (td->td_flags & TDF_RUNNING) == 0,
166 ("lwkt_alloc_thread: unexpected NULL or corrupted td"));
167 TAILQ_REMOVE(&mycpu->gd_tdfreeq, td, td_threadq);
169 stack = td->td_kstack;
170 flags = td->td_flags & (TDF_ALLOCATED_STACK|TDF_ALLOCATED_THREAD);
173 td = zalloc(thread_zone);
174 td->td_kstack = NULL;
175 flags |= TDF_ALLOCATED_THREAD;
178 if ((stack = td->td_kstack) == NULL) {
179 stack = (void *)kmem_alloc(kernel_map, UPAGES * PAGE_SIZE);
180 flags |= TDF_ALLOCATED_STACK;
182 lwkt_init_thread(td, stack, flags, mycpu);
187 * Initialize a preexisting thread structure. This function is used by
188 * lwkt_alloc_thread() and also used to initialize the per-cpu idlethread.
190 * NOTE! called from low level boot code, we cannot do anything fancy!
191 * Only the low level boot code will call this function with gd != mycpu.
194 lwkt_init_thread(thread_t td, void *stack, int flags, struct globaldata *gd)
196 bzero(td, sizeof(struct thread));
197 td->td_kstack = stack;
198 td->td_flags |= flags;
200 td->td_pri = TDPRI_CRIT;
201 lwkt_init_port(&td->td_msgport, td);
202 pmap_init_thread(td);
204 TAILQ_INSERT_TAIL(&gd->gd_tdallq, td, td_allq);
209 lwkt_set_comm(thread_t td, const char *ctl, ...)
214 vsnprintf(td->td_comm, sizeof(td->td_comm), ctl, va);
219 lwkt_hold(thread_t td)
225 lwkt_rele(thread_t td)
227 KKASSERT(td->td_refs > 0);
232 lwkt_wait_free(thread_t td)
235 tsleep(td, 0, "tdreap", hz);
239 lwkt_free_thread(thread_t td)
241 struct globaldata *gd = mycpu;
243 KASSERT((td->td_flags & TDF_RUNNING) == 0,
244 ("lwkt_free_thread: did not exit! %p", td));
247 TAILQ_REMOVE(&gd->gd_tdallq, td, td_allq);
248 if (gd->gd_tdfreecount < CACHE_NTHREADS &&
249 (td->td_flags & TDF_ALLOCATED_THREAD)
251 ++gd->gd_tdfreecount;
252 TAILQ_INSERT_HEAD(&gd->gd_tdfreeq, td, td_threadq);
256 if (td->td_kstack && (td->td_flags & TDF_ALLOCATED_STACK)) {
257 kmem_free(kernel_map,
258 (vm_offset_t)td->td_kstack, UPAGES * PAGE_SIZE);
260 td->td_kstack = NULL;
262 if (td->td_flags & TDF_ALLOCATED_THREAD)
263 zfree(thread_zone, td);
269 * Switch to the next runnable lwkt. If no LWKTs are runnable then
270 * switch to the idlethread. Switching must occur within a critical
271 * section to avoid races with the scheduling queue.
273 * We always have full control over our cpu's run queue. Other cpus
274 * that wish to manipulate our queue must use the cpu_*msg() calls to
275 * talk to our cpu, so a critical section is all that is needed and
276 * the result is very, very fast thread switching.
278 * The LWKT scheduler uses a fixed priority model and round-robins at
279 * each priority level. User process scheduling is a totally
280 * different beast and LWKT priorities should not be confused with
281 * user process priorities.
283 * The MP lock may be out of sync with the thread's td_mpcount. lwkt_switch()
284 * cleans it up. Note that the td_switch() function cannot do anything that
285 * requires the MP lock since the MP lock will have already been setup for
286 * the target thread (not the current thread).
292 struct globaldata *gd;
293 thread_t td = curthread;
299 if (mycpu->gd_intr_nesting_level &&
300 td->td_preempted == NULL && panicstr == NULL
302 panic("lwkt_switch: cannot switch from within an interrupt, yet\n");
306 * Passive release (used to transition from user to kernel mode
307 * when we block or switch rather then when we enter the kernel).
308 * This function is NOT called if we are switching into a preemption
309 * or returning from a preemption. Typically this causes us to lose
310 * our P_CURPROC designation (if we have one) and become a true LWKT
311 * thread, and may also hand P_CURPROC to another process and schedule
322 * td_mpcount cannot be used to determine if we currently hold the
323 * MP lock because get_mplock() will increment it prior to attempting
324 * to get the lock, and switch out if it can't. Look at the actual lock.
326 mpheld = MP_LOCK_HELD();
328 if ((ntd = td->td_preempted) != NULL) {
330 * We had preempted another thread on this cpu, resume the preempted
331 * thread. This occurs transparently, whether the preempted thread
332 * was scheduled or not (it may have been preempted after descheduling
335 * We have to setup the MP lock for the original thread after backing
336 * out the adjustment that was made to curthread when the original
339 KKASSERT(ntd->td_flags & TDF_PREEMPT_LOCK);
341 if (ntd->td_mpcount && mpheld == 0) {
342 panic("MPLOCK NOT HELD ON RETURN: %p %p %d %d\n",
343 td, ntd, td->td_mpcount, ntd->td_mpcount);
345 if (ntd->td_mpcount) {
346 td->td_mpcount -= ntd->td_mpcount;
347 KKASSERT(td->td_mpcount >= 0);
350 ntd->td_flags |= TDF_PREEMPT_DONE;
351 /* YYY release mp lock on switchback if original doesn't need it */
354 * Priority queue / round-robin at each priority. Note that user
355 * processes run at a fixed, low priority and the user process
356 * scheduler deals with interactions between user processes
357 * by scheduling and descheduling them from the LWKT queue as
360 * We have to adjust the MP lock for the target thread. If we
361 * need the MP lock and cannot obtain it we try to locate a
362 * thread that does not need the MP lock.
366 if (gd->gd_runqmask) {
367 int nq = bsrl(gd->gd_runqmask);
368 if ((ntd = TAILQ_FIRST(&gd->gd_tdrunq[nq])) == NULL) {
369 gd->gd_runqmask &= ~(1 << nq);
373 if (ntd->td_mpcount && mpheld == 0 && !cpu_try_mplock()) {
375 * Target needs MP lock and we couldn't get it, try
376 * to locate a thread which does not need the MP lock
377 * to run. If we cannot locate a thread spin in idle.
379 u_int32_t rqmask = gd->gd_runqmask;
381 TAILQ_FOREACH(ntd, &gd->gd_tdrunq[nq], td_threadq) {
382 if (ntd->td_mpcount == 0)
387 rqmask &= ~(1 << nq);
391 ntd = &gd->gd_idlethread;
392 ntd->td_flags |= TDF_IDLE_NOHLT;
394 TAILQ_REMOVE(&gd->gd_tdrunq[nq], ntd, td_threadq);
395 TAILQ_INSERT_TAIL(&gd->gd_tdrunq[nq], ntd, td_threadq);
398 TAILQ_REMOVE(&gd->gd_tdrunq[nq], ntd, td_threadq);
399 TAILQ_INSERT_TAIL(&gd->gd_tdrunq[nq], ntd, td_threadq);
402 TAILQ_REMOVE(&gd->gd_tdrunq[nq], ntd, td_threadq);
403 TAILQ_INSERT_TAIL(&gd->gd_tdrunq[nq], ntd, td_threadq);
407 * Nothing to run but we may still need the BGL to deal with
408 * pending interrupts, spin in idle if so.
410 ntd = &gd->gd_idlethread;
412 ntd->td_flags |= TDF_IDLE_NOHLT;
415 KASSERT(ntd->td_pri >= TDPRI_CRIT,
416 ("priority problem in lwkt_switch %d %d", td->td_pri, ntd->td_pri));
419 * Do the actual switch. If the new target does not need the MP lock
420 * and we are holding it, release the MP lock. If the new target requires
421 * the MP lock we have already acquired it for the target.
424 if (ntd->td_mpcount == 0 ) {
428 ASSERT_MP_LOCK_HELD();
439 * Switch if another thread has a higher priority. Do not switch to other
440 * threads at the same priority.
445 struct globaldata *gd = mycpu;
446 struct thread *td = gd->gd_curthread;
448 if ((td->td_pri & TDPRI_MASK) < bsrl(gd->gd_runqmask)) {
454 * Request that the target thread preempt the current thread. Preemption
455 * only works under a specific set of conditions:
457 * - We are not preempting ourselves
458 * - The target thread is owned by the current cpu
459 * - We are not currently being preempted
460 * - The target is not currently being preempted
461 * - We are able to satisfy the target's MP lock requirements (if any).
463 * THE CALLER OF LWKT_PREEMPT() MUST BE IN A CRITICAL SECTION. Typically
464 * this is called via lwkt_schedule() through the td_preemptable callback.
465 * critpri is the managed critical priority that we should ignore in order
466 * to determine whether preemption is possible (aka usually just the crit
467 * priority of lwkt_schedule() itself).
469 * XXX at the moment we run the target thread in a critical section during
470 * the preemption in order to prevent the target from taking interrupts
471 * that *WE* can't. Preemption is strictly limited to interrupt threads
472 * and interrupt-like threads, outside of a critical section, and the
473 * preempted source thread will be resumed the instant the target blocks
474 * whether or not the source is scheduled (i.e. preemption is supposed to
475 * be as transparent as possible).
477 * The target thread inherits our MP count (added to its own) for the
478 * duration of the preemption in order to preserve the atomicy of the
479 * MP lock during the preemption. Therefore, any preempting targets must be
480 * careful in regards to MP assertions. Note that the MP count may be
481 * out of sync with the physical mp_lock. If we preempt we have to preserve
482 * the expected situation.
485 lwkt_preempt(thread_t ntd, int critpri)
487 thread_t td = curthread;
494 * The caller has put us in a critical section. We can only preempt
495 * if the caller of the caller was not in a critical section (basically
496 * a local interrupt), as determined by the 'critpri' parameter. If
497 * we are unable to preempt
499 * YYY The target thread must be in a critical section (else it must
500 * inherit our critical section? I dunno yet).
502 KASSERT(ntd->td_pri >= TDPRI_CRIT, ("BADCRIT0 %d", ntd->td_pri));
505 if (!_lwkt_wantresched(ntd, td)) {
509 if ((td->td_pri & ~TDPRI_MASK) > critpri) {
514 if (ntd->td_gd != mycpu) {
519 if (td == ntd || ((td->td_flags | ntd->td_flags) & TDF_PREEMPT_LOCK)) {
523 if (ntd->td_preempted) {
529 * note: an interrupt might have occured just as we were transitioning
530 * to the MP lock. In this case td_mpcount will be pre-disposed but
531 * not actually synchronized with the actual state of the lock. We
532 * can use it to imply an MP lock requirement for the preemption but
533 * we cannot use it to test whether we hold the MP lock or not.
535 mpheld = MP_LOCK_HELD();
536 if (mpheld && td->td_mpcount == 0)
537 panic("lwkt_preempt(): held and no count");
538 savecnt = td->td_mpcount;
539 ntd->td_mpcount += td->td_mpcount;
540 if (mpheld == 0 && ntd->td_mpcount && !cpu_try_mplock()) {
541 ntd->td_mpcount -= td->td_mpcount;
548 ntd->td_preempted = td;
549 td->td_flags |= TDF_PREEMPT_LOCK;
551 KKASSERT(ntd->td_preempted && (td->td_flags & TDF_PREEMPT_DONE));
553 KKASSERT(savecnt == td->td_mpcount);
554 if (mpheld == 0 && MP_LOCK_HELD())
556 else if (mpheld && !MP_LOCK_HELD())
557 panic("lwkt_preempt(): MP lock was not held through");
559 ntd->td_preempted = NULL;
560 td->td_flags &= ~(TDF_PREEMPT_LOCK|TDF_PREEMPT_DONE);
564 * Yield our thread while higher priority threads are pending. This is
565 * typically called when we leave a critical section but it can be safely
566 * called while we are in a critical section.
568 * This function will not generally yield to equal priority threads but it
569 * can occur as a side effect. Note that lwkt_switch() is called from
570 * inside the critical section to pervent its own crit_exit() from reentering
571 * lwkt_yield_quick().
573 * gd_reqflags indicates that *something* changed, e.g. an interrupt or softint
574 * came along but was blocked and made pending.
576 * (self contained on a per cpu basis)
579 lwkt_yield_quick(void)
581 globaldata_t gd = mycpu;
582 thread_t td = gd->gd_curthread;
585 * gd_reqflags is cleared in splz if the cpl is 0. If we were to clear
586 * it with a non-zero cpl then we might not wind up calling splz after
587 * a task switch when the critical section is exited even though the
588 * new task could accept the interrupt. YYY alternative is to have
589 * lwkt_switch() just call splz unconditionally.
591 * XXX from crit_exit() only called after last crit section is released.
592 * If called directly will run splz() even if in a critical section.
598 * YYY enabling will cause wakeup() to task-switch, which really
599 * confused the old 4.x code. This is a good way to simulate
600 * preemption and MP without actually doing preemption or MP, because a
601 * lot of code assumes that wakeup() does not block.
603 if (untimely_switch && gd->gd_intr_nesting_level == 0) {
606 * YYY temporary hacks until we disassociate the userland scheduler
607 * from the LWKT scheduler.
609 if (td->td_flags & TDF_RUNQ) {
610 lwkt_switch(); /* will not reenter yield function */
612 lwkt_schedule_self(); /* make sure we are scheduled */
613 lwkt_switch(); /* will not reenter yield function */
614 lwkt_deschedule_self(); /* make sure we are descheduled */
616 crit_exit_noyield(td);
621 * This implements a normal yield which, unlike _quick, will yield to equal
622 * priority threads as well. Note that gd_reqflags tests will be handled by
623 * the crit_exit() call in lwkt_switch().
625 * (self contained on a per cpu basis)
630 lwkt_schedule_self();
635 * Schedule a thread to run. As the current thread we can always safely
636 * schedule ourselves, and a shortcut procedure is provided for that
639 * (non-blocking, self contained on a per cpu basis)
642 lwkt_schedule_self(void)
644 thread_t td = curthread;
647 KASSERT(td->td_wait == NULL, ("lwkt_schedule_self(): td_wait not NULL!"));
649 if (td->td_proc && td->td_proc->p_stat == SSLEEP)
650 panic("SCHED SELF PANIC");
655 * Generic schedule. Possibly schedule threads belonging to other cpus and
656 * deal with threads that might be blocked on a wait queue.
658 * YYY this is one of the best places to implement load balancing code.
659 * Load balancing can be accomplished by requesting other sorts of actions
660 * for the thread in question.
663 lwkt_schedule(thread_t td)
666 if ((td->td_flags & TDF_PREEMPT_LOCK) == 0 && td->td_proc
667 && td->td_proc->p_stat == SSLEEP
669 printf("PANIC schedule curtd = %p (%d %d) target %p (%d %d)\n",
671 curthread->td_proc ? curthread->td_proc->p_pid : -1,
672 curthread->td_proc ? curthread->td_proc->p_stat : -1,
674 td->td_proc ? curthread->td_proc->p_pid : -1,
675 td->td_proc ? curthread->td_proc->p_stat : -1
677 panic("SCHED PANIC");
681 if (td == curthread) {
687 * If the thread is on a wait list we have to send our scheduling
688 * request to the owner of the wait structure. Otherwise we send
689 * the scheduling request to the cpu owning the thread. Races
690 * are ok, the target will forward the message as necessary (the
691 * message may chase the thread around before it finally gets
694 * (remember, wait structures use stable storage)
696 if ((w = td->td_wait) != NULL) {
697 if (lwkt_trytoken(&w->wa_token)) {
698 TAILQ_REMOVE(&w->wa_waitq, td, td_threadq);
701 if (td->td_gd == mycpu) {
703 if (td->td_preemptable) {
704 td->td_preemptable(td, TDPRI_CRIT*2); /* YYY +token */
705 } else if (_lwkt_wantresched(td, curthread)) {
709 lwkt_send_ipiq(td->td_gd->gd_cpuid, (ipifunc_t)lwkt_schedule, td);
711 lwkt_reltoken(&w->wa_token);
713 lwkt_send_ipiq(w->wa_token.t_cpu, (ipifunc_t)lwkt_schedule, td);
717 * If the wait structure is NULL and we own the thread, there
718 * is no race (since we are in a critical section). If we
719 * do not own the thread there might be a race but the
720 * target cpu will deal with it.
722 if (td->td_gd == mycpu) {
724 if (td->td_preemptable) {
725 td->td_preemptable(td, TDPRI_CRIT);
726 } else if (_lwkt_wantresched(td, curthread)) {
730 lwkt_send_ipiq(td->td_gd->gd_cpuid, (ipifunc_t)lwkt_schedule, td);
738 * Managed acquisition. This code assumes that the MP lock is held for
739 * the tdallq operation and that the thread has been descheduled from its
740 * original cpu. We also have to wait for the thread to be entirely switched
741 * out on its original cpu (this is usually fast enough that we never loop)
742 * since the LWKT system does not have to hold the MP lock while switching
743 * and the target may have released it before switching.
746 lwkt_acquire(thread_t td)
748 struct globaldata *gd;
751 KKASSERT((td->td_flags & TDF_RUNQ) == 0);
752 while (td->td_flags & TDF_RUNNING) /* XXX spin */
756 TAILQ_REMOVE(&gd->gd_tdallq, td, td_allq); /* protected by BGL */
759 TAILQ_INSERT_TAIL(&gd->gd_tdallq, td, td_allq); /* protected by BGL */
765 * Deschedule a thread.
767 * (non-blocking, self contained on a per cpu basis)
770 lwkt_deschedule_self(void)
772 thread_t td = curthread;
775 KASSERT(td->td_wait == NULL, ("lwkt_schedule_self(): td_wait not NULL!"));
781 * Generic deschedule. Descheduling threads other then your own should be
782 * done only in carefully controlled circumstances. Descheduling is
785 * This function may block if the cpu has run out of messages.
788 lwkt_deschedule(thread_t td)
791 if (td == curthread) {
794 if (td->td_gd == mycpu) {
797 lwkt_send_ipiq(td->td_gd->gd_cpuid, (ipifunc_t)lwkt_deschedule, td);
804 * Set the target thread's priority. This routine does not automatically
805 * switch to a higher priority thread, LWKT threads are not designed for
806 * continuous priority changes. Yield if you want to switch.
808 * We have to retain the critical section count which uses the high bits
809 * of the td_pri field. The specified priority may also indicate zero or
810 * more critical sections by adding TDPRI_CRIT*N.
813 lwkt_setpri(thread_t td, int pri)
816 KKASSERT(td->td_gd == mycpu);
818 if (td->td_flags & TDF_RUNQ) {
820 td->td_pri = (td->td_pri & ~TDPRI_MASK) + pri;
823 td->td_pri = (td->td_pri & ~TDPRI_MASK) + pri;
829 lwkt_setpri_self(int pri)
831 thread_t td = curthread;
833 KKASSERT(pri >= 0 && pri <= TDPRI_MAX);
835 if (td->td_flags & TDF_RUNQ) {
837 td->td_pri = (td->td_pri & ~TDPRI_MASK) + pri;
840 td->td_pri = (td->td_pri & ~TDPRI_MASK) + pri;
846 lwkt_preempted_proc(void)
848 thread_t td = curthread;
849 while (td->td_preempted)
850 td = td->td_preempted;
854 typedef struct lwkt_gettoken_req {
862 * This function deschedules the current thread and blocks on the specified
863 * wait queue. We obtain ownership of the wait queue in order to block
864 * on it. A generation number is used to interlock the wait queue in case
865 * it gets signalled while we are blocked waiting on the token.
867 * Note: alternatively we could dequeue our thread and then message the
868 * target cpu owning the wait queue. YYY implement as sysctl.
870 * Note: wait queue signals normally ping-pong the cpu as an optimization.
874 lwkt_block(lwkt_wait_t w, const char *wmesg, int *gen)
876 thread_t td = curthread;
878 lwkt_gettoken(&w->wa_token);
879 if (w->wa_gen == *gen) {
881 TAILQ_INSERT_TAIL(&w->wa_waitq, td, td_threadq);
884 td->td_wmesg = wmesg;
887 lwkt_regettoken(&w->wa_token);
888 if (td->td_wmesg != NULL) {
893 /* token might be lost, doesn't matter for gen update */
895 lwkt_reltoken(&w->wa_token);
899 * Signal a wait queue. We gain ownership of the wait queue in order to
900 * signal it. Once a thread is removed from the wait queue we have to
901 * deal with the cpu owning the thread.
903 * Note: alternatively we could message the target cpu owning the wait
904 * queue. YYY implement as sysctl.
907 lwkt_signal(lwkt_wait_t w, int count)
912 lwkt_gettoken(&w->wa_token);
916 while ((td = TAILQ_FIRST(&w->wa_waitq)) != NULL && count) {
919 TAILQ_REMOVE(&w->wa_waitq, td, td_threadq);
922 if (td->td_gd == mycpu) {
925 lwkt_send_ipiq(td->td_gd->gd_cpuid, (ipifunc_t)lwkt_schedule, td);
927 lwkt_regettoken(&w->wa_token);
929 lwkt_reltoken(&w->wa_token);
935 * Acquire ownership of a token
937 * Acquire ownership of a token. The token may have spl and/or critical
938 * section side effects, depending on its purpose. These side effects
939 * guarentee that you will maintain ownership of the token as long as you
940 * do not block. If you block you may lose access to the token (but you
941 * must still release it even if you lose your access to it).
943 * YYY for now we use a critical section to prevent IPIs from taking away
944 * a token, but do we really only need to disable IPIs ?
946 * YYY certain tokens could be made to act like mutexes when performance
947 * would be better (e.g. t_cpu == -1). This is not yet implemented.
949 * YYY the tokens replace 4.x's simplelocks for the most part, but this
950 * means that 4.x does not expect a switch so for now we cannot switch
951 * when waiting for an IPI to be returned.
953 * YYY If the token is owned by another cpu we may have to send an IPI to
954 * it and then block. The IPI causes the token to be given away to the
955 * requesting cpu, unless it has already changed hands. Since only the
956 * current cpu can give away a token it owns we do not need a memory barrier.
957 * This needs serious optimization.
964 lwkt_gettoken_remote(void *arg)
966 lwkt_gettoken_req *req = arg;
967 if (req->tok->t_cpu == mycpu->gd_cpuid) {
970 printf("GT(%d,%d) ", req->tok->t_cpu, req->cpu);
972 req->tok->t_cpu = req->cpu;
973 req->tok->t_reqcpu = req->cpu; /* YYY leave owned by target cpu */
974 /* else set reqcpu to point to current cpu for release */
981 lwkt_gettoken(lwkt_token_t tok)
984 * Prevent preemption so the token can't be taken away from us once
985 * we gain ownership of it. Use a synchronous request which might
986 * block. The request will be forwarded as necessary playing catchup
992 if (curthread->td_pri > 2000) {
993 curthread->td_pri = 1000;
998 while (tok->t_cpu != mycpu->gd_cpuid) {
999 struct lwkt_gettoken_req req;
1003 req.cpu = mycpu->gd_cpuid;
1005 dcpu = (volatile int)tok->t_cpu;
1006 KKASSERT(dcpu >= 0 && dcpu < ncpus);
1009 printf("REQT%d ", dcpu);
1011 seq = lwkt_send_ipiq(dcpu, lwkt_gettoken_remote, &req);
1012 lwkt_wait_ipiq(dcpu, seq);
1015 printf("REQR%d ", tok->t_cpu);
1020 * leave us in a critical section on return. This will be undone
1021 * by lwkt_reltoken(). Bump the generation number.
1023 return(++tok->t_gen);
1027 * Attempt to acquire ownership of a token. Returns 1 on success, 0 on
1031 lwkt_trytoken(lwkt_token_t tok)
1035 if (tok->t_cpu != mycpu->gd_cpuid) {
1039 /* leave us in the critical section */
1045 * Release your ownership of a token. Releases must occur in reverse
1046 * order to aquisitions, eventually so priorities can be unwound properly
1047 * like SPLs. At the moment the actual implemention doesn't care.
1049 * We can safely hand a token that we own to another cpu without notifying
1050 * it, but once we do we can't get it back without requesting it (unless
1051 * the other cpu hands it back to us before we check).
1053 * We might have lost the token, so check that.
1056 lwkt_reltoken(lwkt_token_t tok)
1058 if (tok->t_cpu == mycpu->gd_cpuid) {
1059 tok->t_cpu = tok->t_reqcpu;
1065 * Reacquire a token that might have been lost and compare and update the
1066 * generation number. 0 is returned if the generation has not changed
1067 * (nobody else obtained the token while we were blocked, on this cpu or
1070 * This function returns with the token re-held whether the generation
1071 * number changed or not.
1074 lwkt_gentoken(lwkt_token_t tok, int *gen)
1076 if (lwkt_regettoken(tok) == *gen) {
1086 * Re-acquire a token that might have been lost. Returns the generation
1087 * number of the token.
1090 lwkt_regettoken(lwkt_token_t tok)
1092 /* assert we are in a critical section */
1093 if (tok->t_cpu != mycpu->gd_cpuid) {
1095 while (tok->t_cpu != mycpu->gd_cpuid) {
1096 struct lwkt_gettoken_req req;
1100 req.cpu = mycpu->gd_cpuid;
1102 dcpu = (volatile int)tok->t_cpu;
1103 KKASSERT(dcpu >= 0 && dcpu < ncpus);
1106 printf("REQT%d ", dcpu);
1108 seq = lwkt_send_ipiq(dcpu, lwkt_gettoken_remote, &req);
1109 lwkt_wait_ipiq(dcpu, seq);
1112 printf("REQR%d ", tok->t_cpu);
1122 lwkt_inittoken(lwkt_token_t tok)
1125 * Zero structure and set cpu owner and reqcpu to cpu 0.
1127 bzero(tok, sizeof(*tok));
1131 * Create a kernel process/thread/whatever. It shares it's address space
1132 * with proc0 - ie: kernel only.
1134 * XXX should be renamed to lwkt_create()
1136 * The thread will be entered with the MP lock held.
1139 lwkt_create(void (*func)(void *), void *arg,
1140 struct thread **tdp, thread_t template, int tdflags,
1141 const char *fmt, ...)
1146 td = lwkt_alloc_thread(template);
1149 cpu_set_thread_handler(td, kthread_exit, func, arg);
1150 td->td_flags |= TDF_VERBOSE | tdflags;
1156 * Set up arg0 for 'ps' etc
1159 vsnprintf(td->td_comm, sizeof(td->td_comm), fmt, ap);
1163 * Schedule the thread to run
1165 if ((td->td_flags & TDF_STOPREQ) == 0)
1168 td->td_flags &= ~TDF_STOPREQ;
1173 * Destroy an LWKT thread. Warning! This function is not called when
1174 * a process exits, cpu_proc_exit() directly calls cpu_thread_exit() and
1175 * uses a different reaping mechanism.
1180 thread_t td = curthread;
1182 if (td->td_flags & TDF_VERBOSE)
1183 printf("kthread %p %s has exited\n", td, td->td_comm);
1185 lwkt_deschedule_self();
1186 ++mycpu->gd_tdfreecount;
1187 TAILQ_INSERT_TAIL(&mycpu->gd_tdfreeq, td, td_threadq);
1192 * Create a kernel process/thread/whatever. It shares it's address space
1193 * with proc0 - ie: kernel only. 5.x compatible.
1196 kthread_create(void (*func)(void *), void *arg,
1197 struct thread **tdp, const char *fmt, ...)
1202 td = lwkt_alloc_thread(NULL);
1205 cpu_set_thread_handler(td, kthread_exit, func, arg);
1206 td->td_flags |= TDF_VERBOSE;
1212 * Set up arg0 for 'ps' etc
1215 vsnprintf(td->td_comm, sizeof(td->td_comm), fmt, ap);
1219 * Schedule the thread to run
1228 thread_t td = curthread;
1229 int lpri = td->td_pri;
1232 panic("td_pri is/would-go negative! %p %d", td, lpri);
1236 * Destroy an LWKT thread. Warning! This function is not called when
1237 * a process exits, cpu_proc_exit() directly calls cpu_thread_exit() and
1238 * uses a different reaping mechanism.
1240 * XXX duplicates lwkt_exit()
1251 * Send a function execution request to another cpu. The request is queued
1252 * on the cpu<->cpu ipiq matrix. Each cpu owns a unique ipiq FIFO for every
1253 * possible target cpu. The FIFO can be written.
1255 * YYY If the FIFO fills up we have to enable interrupts and process the
1256 * IPIQ while waiting for it to empty or we may deadlock with another cpu.
1257 * Create a CPU_*() function to do this!
1259 * Must be called from a critical section.
1262 lwkt_send_ipiq(int dcpu, ipifunc_t func, void *arg)
1266 struct globaldata *gd = mycpu;
1268 if (dcpu == gd->gd_cpuid) {
1273 ++gd->gd_intr_nesting_level;
1275 if (gd->gd_intr_nesting_level > 20)
1276 panic("lwkt_send_ipiq: TOO HEAVILY NESTED!");
1278 KKASSERT(curthread->td_pri >= TDPRI_CRIT);
1279 KKASSERT(dcpu >= 0 && dcpu < ncpus);
1281 ip = &gd->gd_ipiq[dcpu];
1284 * We always drain before the FIFO becomes full so it should never
1285 * become full. We need to leave enough entries to deal with
1288 KKASSERT(ip->ip_windex - ip->ip_rindex != MAXCPUFIFO);
1289 windex = ip->ip_windex & MAXCPUFIFO_MASK;
1290 ip->ip_func[windex] = func;
1291 ip->ip_arg[windex] = arg;
1292 /* YYY memory barrier */
1294 if (ip->ip_windex - ip->ip_rindex > MAXCPUFIFO / 2) {
1295 unsigned int eflags = read_eflags();
1298 while (ip->ip_windex - ip->ip_rindex > MAXCPUFIFO / 4) {
1299 KKASSERT(ip->ip_windex - ip->ip_rindex != MAXCPUFIFO - 1);
1300 lwkt_process_ipiq();
1302 write_eflags(eflags);
1304 --gd->gd_intr_nesting_level;
1305 cpu_send_ipiq(dcpu); /* issues memory barrier if appropriate */
1307 return(ip->ip_windex);
1311 * Send a message to several target cpus. Typically used for scheduling.
1314 lwkt_send_ipiq_mask(u_int32_t mask, ipifunc_t func, void *arg)
1320 lwkt_send_ipiq(cpuid, func, arg);
1321 mask &= ~(1 << cpuid);
1326 * Wait for the remote cpu to finish processing a function.
1328 * YYY we have to enable interrupts and process the IPIQ while waiting
1329 * for it to empty or we may deadlock with another cpu. Create a CPU_*()
1330 * function to do this! YYY we really should 'block' here.
1332 * Must be called from a critical section. Thsi routine may be called
1333 * from an interrupt (for example, if an interrupt wakes a foreign thread
1337 lwkt_wait_ipiq(int dcpu, int seq)
1340 int maxc = 100000000;
1342 if (dcpu != mycpu->gd_cpuid) {
1343 KKASSERT(dcpu >= 0 && dcpu < ncpus);
1344 ip = &mycpu->gd_ipiq[dcpu];
1345 if ((int)(ip->ip_xindex - seq) < 0) {
1346 unsigned int eflags = read_eflags();
1348 while ((int)(ip->ip_xindex - seq) < 0) {
1349 lwkt_process_ipiq();
1351 printf("LWKT_WAIT_IPIQ WARNING! %d wait %d (%d)\n", mycpu->gd_cpuid, dcpu, ip->ip_xindex - seq);
1352 if (maxc < -1000000)
1353 panic("LWKT_WAIT_IPIQ");
1355 write_eflags(eflags);
1361 * Called from IPI interrupt (like a fast interrupt), which has placed
1362 * us in a critical section. The MP lock may or may not be held.
1363 * May also be called from doreti or splz, or be reentrantly called
1364 * indirectly through the ip_func[] we run.
1367 lwkt_process_ipiq(void)
1370 int cpuid = mycpu->gd_cpuid;
1372 for (n = 0; n < ncpus; ++n) {
1378 ip = globaldata_find(n)->gd_ipiq;
1384 * Note: xindex is only updated after we are sure the function has
1385 * finished execution. Beware lwkt_process_ipiq() reentrancy! The
1386 * function may send an IPI which may block/drain.
1388 while (ip->ip_rindex != ip->ip_windex) {
1389 ri = ip->ip_rindex & MAXCPUFIFO_MASK;
1391 ip->ip_func[ri](ip->ip_arg[ri]);
1392 /* YYY memory barrier */
1393 ip->ip_xindex = ip->ip_rindex;
1401 lwkt_send_ipiq(int dcpu, ipifunc_t func, void *arg)
1403 panic("lwkt_send_ipiq: UP box! (%d,%p,%p)", dcpu, func, arg);
1404 return(0); /* NOT REACHED */
1408 lwkt_wait_ipiq(int dcpu, int seq)
1410 panic("lwkt_wait_ipiq: UP box! (%d,%d)", dcpu, seq);