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 1.21 2003/07/11 17:42:10 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;
112 * YYY needs cli/sti protection? gd_reqpri set by interrupt
113 * when made pending. need better mechanism.
115 if (gd->gd_reqpri < (td->td_pri & TDPRI_MASK))
116 gd->gd_reqpri = (td->td_pri & TDPRI_MASK);
123 _lwkt_wantresched(thread_t ntd, thread_t cur)
125 return((ntd->td_pri & TDPRI_MASK) > (cur->td_pri & TDPRI_MASK));
129 * LWKTs operate on a per-cpu basis
131 * WARNING! Called from early boot, 'mycpu' may not work yet.
134 lwkt_gdinit(struct globaldata *gd)
138 for (i = 0; i < sizeof(gd->gd_tdrunq)/sizeof(gd->gd_tdrunq[0]); ++i)
139 TAILQ_INIT(&gd->gd_tdrunq[i]);
141 TAILQ_INIT(&gd->gd_tdallq);
145 * Initialize a thread wait structure prior to first use.
147 * NOTE! called from low level boot code, we cannot do anything fancy!
150 lwkt_init_wait(lwkt_wait_t w)
152 TAILQ_INIT(&w->wa_waitq);
156 * Create a new thread. The thread must be associated with a process context
157 * or LWKT start address before it can be scheduled.
159 * If you intend to create a thread without a process context this function
160 * does everything except load the startup and switcher function.
163 lwkt_alloc_thread(struct thread *td)
170 if (mycpu->gd_tdfreecount > 0) {
171 --mycpu->gd_tdfreecount;
172 td = TAILQ_FIRST(&mycpu->gd_tdfreeq);
173 KASSERT(td != NULL && (td->td_flags & TDF_RUNNING) == 0,
174 ("lwkt_alloc_thread: unexpected NULL or corrupted td"));
175 TAILQ_REMOVE(&mycpu->gd_tdfreeq, td, td_threadq);
177 stack = td->td_kstack;
178 flags = td->td_flags & (TDF_ALLOCATED_STACK|TDF_ALLOCATED_THREAD);
181 td = zalloc(thread_zone);
182 td->td_kstack = NULL;
183 flags |= TDF_ALLOCATED_THREAD;
186 if ((stack = td->td_kstack) == NULL) {
187 stack = (void *)kmem_alloc(kernel_map, UPAGES * PAGE_SIZE);
188 flags |= TDF_ALLOCATED_STACK;
190 lwkt_init_thread(td, stack, flags, mycpu);
195 * Initialize a preexisting thread structure. This function is used by
196 * lwkt_alloc_thread() and also used to initialize the per-cpu idlethread.
198 * NOTE! called from low level boot code, we cannot do anything fancy!
201 lwkt_init_thread(thread_t td, void *stack, int flags, struct globaldata *gd)
203 bzero(td, sizeof(struct thread));
204 td->td_kstack = stack;
205 td->td_flags |= flags;
207 td->td_pri = TDPRI_CRIT;
208 td->td_cpu = gd->gd_cpuid; /* YYY don't really need this if have td_gd */
209 pmap_init_thread(td);
211 TAILQ_INSERT_TAIL(&mycpu->gd_tdallq, td, td_allq);
216 lwkt_set_comm(thread_t td, const char *ctl, ...)
221 vsnprintf(td->td_comm, sizeof(td->td_comm), ctl, va);
226 lwkt_hold(thread_t td)
232 lwkt_rele(thread_t td)
234 KKASSERT(td->td_refs > 0);
239 lwkt_wait_free(thread_t td)
242 tsleep(td, PWAIT, "tdreap", hz);
246 lwkt_free_thread(thread_t td)
248 struct globaldata *gd = mycpu;
250 KASSERT((td->td_flags & TDF_RUNNING) == 0,
251 ("lwkt_free_thread: did not exit! %p", td));
254 TAILQ_REMOVE(&gd->gd_tdallq, td, td_allq);
255 if (gd->gd_tdfreecount < CACHE_NTHREADS &&
256 (td->td_flags & TDF_ALLOCATED_THREAD)
258 ++gd->gd_tdfreecount;
259 TAILQ_INSERT_HEAD(&gd->gd_tdfreeq, td, td_threadq);
263 if (td->td_kstack && (td->td_flags & TDF_ALLOCATED_STACK)) {
264 kmem_free(kernel_map,
265 (vm_offset_t)td->td_kstack, UPAGES * PAGE_SIZE);
267 td->td_kstack = NULL;
269 if (td->td_flags & TDF_ALLOCATED_THREAD)
270 zfree(thread_zone, td);
276 * Switch to the next runnable lwkt. If no LWKTs are runnable then
277 * switch to the idlethread. Switching must occur within a critical
278 * section to avoid races with the scheduling queue.
280 * We always have full control over our cpu's run queue. Other cpus
281 * that wish to manipulate our queue must use the cpu_*msg() calls to
282 * talk to our cpu, so a critical section is all that is needed and
283 * the result is very, very fast thread switching.
285 * The LWKT scheduler uses a fixed priority model and round-robins at
286 * each priority level. User process scheduling is a totally
287 * different beast and LWKT priorities should not be confused with
288 * user process priorities.
290 * The MP lock may be out of sync with the thread's td_mpcount. lwkt_switch()
291 * cleans it up. Note that the td_switch() function cannot do anything that
292 * requires the MP lock since the MP lock will have already been setup for
293 * the target thread (not the current thread).
299 struct globaldata *gd;
300 thread_t td = curthread;
306 if (mycpu->gd_intr_nesting_level &&
307 td->td_preempted == NULL && panicstr == NULL
309 panic("lwkt_switch: cannot switch from within an interrupt, yet\n");
313 * Passive release (used to transition from user to kernel mode
314 * when we block or switch rather then when we enter the kernel).
315 * This function is NOT called if we are switching into a preemption
316 * or returning from a preemption. Typically this causes us to lose
317 * our P_CURPROC designation (if we have one) and become a true LWKT
318 * thread, and may also hand P_CURPROC to another process and schedule
329 * td_mpcount cannot be used to determine if we currently hold the
330 * MP lock because get_mplock() will increment it prior to attempting
331 * to get the lock, and switch out if it can't. Look at the actual lock.
333 mpheld = MP_LOCK_HELD();
335 if ((ntd = td->td_preempted) != NULL) {
337 * We had preempted another thread on this cpu, resume the preempted
338 * thread. This occurs transparently, whether the preempted thread
339 * was scheduled or not (it may have been preempted after descheduling
342 * We have to setup the MP lock for the original thread after backing
343 * out the adjustment that was made to curthread when the original
346 KKASSERT(ntd->td_flags & TDF_PREEMPT_LOCK);
348 if (ntd->td_mpcount && mpheld == 0) {
349 panic("MPLOCK NOT HELD ON RETURN: %p %p %d %d\n",
350 td, ntd, td->td_mpcount, ntd->td_mpcount);
352 if (ntd->td_mpcount) {
353 td->td_mpcount -= ntd->td_mpcount;
354 KKASSERT(td->td_mpcount >= 0);
357 ntd->td_flags |= TDF_PREEMPT_DONE;
358 /* YYY release mp lock on switchback if original doesn't need it */
361 * Priority queue / round-robin at each priority. Note that user
362 * processes run at a fixed, low priority and the user process
363 * scheduler deals with interactions between user processes
364 * by scheduling and descheduling them from the LWKT queue as
367 * We have to adjust the MP lock for the target thread. If we
368 * need the MP lock and cannot obtain it we try to locate a
369 * thread that does not need the MP lock.
373 if (gd->gd_runqmask) {
374 int nq = bsrl(gd->gd_runqmask);
375 if ((ntd = TAILQ_FIRST(&gd->gd_tdrunq[nq])) == NULL) {
376 gd->gd_runqmask &= ~(1 << nq);
380 if (ntd->td_mpcount && mpheld == 0 && !cpu_try_mplock()) {
382 * Target needs MP lock and we couldn't get it, try
383 * to locate a thread which does not need the MP lock
386 u_int32_t rqmask = gd->gd_runqmask;
388 TAILQ_FOREACH(ntd, &gd->gd_tdrunq[nq], td_threadq) {
389 if (ntd->td_mpcount == 0)
394 rqmask &= ~(1 << nq);
398 ntd = &gd->gd_idlethread;
399 ntd->td_flags |= TDF_IDLE_NOHLT;
401 TAILQ_REMOVE(&gd->gd_tdrunq[nq], ntd, td_threadq);
402 TAILQ_INSERT_TAIL(&gd->gd_tdrunq[nq], ntd, td_threadq);
405 TAILQ_REMOVE(&gd->gd_tdrunq[nq], ntd, td_threadq);
406 TAILQ_INSERT_TAIL(&gd->gd_tdrunq[nq], ntd, td_threadq);
409 TAILQ_REMOVE(&gd->gd_tdrunq[nq], ntd, td_threadq);
410 TAILQ_INSERT_TAIL(&gd->gd_tdrunq[nq], ntd, td_threadq);
413 ntd = &gd->gd_idlethread;
416 KASSERT(ntd->td_pri >= TDPRI_CRIT,
417 ("priority problem in lwkt_switch %d %d", td->td_pri, ntd->td_pri));
420 * Do the actual switch. If the new target does not need the MP lock
421 * and we are holding it, release the MP lock. If the new target requires
422 * the MP lock we have already acquired it for the target.
425 if (ntd->td_mpcount == 0 ) {
429 ASSERT_MP_LOCK_HELD();
440 * Switch if another thread has a higher priority. Do not switch to other
441 * threads at the same priority.
446 struct globaldata *gd = mycpu;
447 struct thread *td = gd->gd_curthread;
449 if ((td->td_pri & TDPRI_MASK) < bsrl(gd->gd_runqmask)) {
455 * Request that the target thread preempt the current thread. Preemption
456 * only works under a specific set of conditions:
458 * - We are not preempting ourselves
459 * - The target thread is owned by the current cpu
460 * - We are not currently being preempted
461 * - The target is not currently being preempted
462 * - We are able to satisfy the target's MP lock requirements (if any).
464 * THE CALLER OF LWKT_PREEMPT() MUST BE IN A CRITICAL SECTION. Typically
465 * this is called via lwkt_schedule() through the td_preemptable callback.
466 * critpri is the managed critical priority that we should ignore in order
467 * to determine whether preemption is possible (aka usually just the crit
468 * priority of lwkt_schedule() itself).
470 * XXX at the moment we run the target thread in a critical section during
471 * the preemption in order to prevent the target from taking interrupts
472 * that *WE* can't. Preemption is strictly limited to interrupt threads
473 * and interrupt-like threads, outside of a critical section, and the
474 * preempted source thread will be resumed the instant the target blocks
475 * whether or not the source is scheduled (i.e. preemption is supposed to
476 * be as transparent as possible).
478 * The target thread inherits our MP count (added to its own) for the
479 * duration of the preemption in order to preserve the atomicy of the
480 * MP lock during the preemption. Therefore, any preempting targets must be
481 * careful in regards to MP assertions. Note that the MP count may be
482 * out of sync with the physical mp_lock. If we preempt we have to preserve
483 * the expected situation.
486 lwkt_preempt(thread_t ntd, int critpri)
488 thread_t td = curthread;
495 * The caller has put us in a critical section. We can only preempt
496 * if the caller of the caller was not in a critical section (basically
497 * a local interrupt), as determined by the 'critpri' parameter. If
498 * we are unable to preempt
500 * YYY The target thread must be in a critical section (else it must
501 * inherit our critical section? I dunno yet).
503 KASSERT(ntd->td_pri >= TDPRI_CRIT, ("BADCRIT0 %d", ntd->td_pri));
506 if (!_lwkt_wantresched(ntd, td)) {
510 if ((td->td_pri & ~TDPRI_MASK) > critpri) {
515 if (ntd->td_cpu != mycpu->gd_cpuid) {
520 if (td == ntd || ((td->td_flags | ntd->td_flags) & TDF_PREEMPT_LOCK)) {
524 if (ntd->td_preempted) {
530 * note: an interrupt might have occured just as we were transitioning
531 * to the MP lock. In this case td_mpcount will be pre-disposed but
532 * not actually synchronized with the actual state of the lock. We
533 * can use it to imply an MP lock requirement for the preemption but
534 * we cannot use it to test whether we hold the MP lock or not.
536 mpheld = MP_LOCK_HELD();
537 if (mpheld && td->td_mpcount == 0)
538 panic("lwkt_preempt(): held and no count");
539 savecnt = td->td_mpcount;
540 ntd->td_mpcount += td->td_mpcount;
541 if (mpheld == 0 && ntd->td_mpcount && !cpu_try_mplock()) {
542 ntd->td_mpcount -= td->td_mpcount;
549 ntd->td_preempted = td;
550 td->td_flags |= TDF_PREEMPT_LOCK;
552 KKASSERT(ntd->td_preempted && (td->td_flags & TDF_PREEMPT_DONE));
554 KKASSERT(savecnt == td->td_mpcount);
555 if (mpheld == 0 && MP_LOCK_HELD())
557 else if (mpheld && !MP_LOCK_HELD())
558 panic("lwkt_preempt(): MP lock was not held through");
560 ntd->td_preempted = NULL;
561 td->td_flags &= ~(TDF_PREEMPT_LOCK|TDF_PREEMPT_DONE);
565 * Yield our thread while higher priority threads are pending. This is
566 * typically called when we leave a critical section but it can be safely
567 * called while we are in a critical section.
569 * This function will not generally yield to equal priority threads but it
570 * can occur as a side effect. Note that lwkt_switch() is called from
571 * inside the critical section to pervent its own crit_exit() from reentering
572 * lwkt_yield_quick().
574 * gd_reqpri indicates that *something* changed, e.g. an interrupt or softint
575 * came along but was blocked and made pending.
577 * (self contained on a per cpu basis)
580 lwkt_yield_quick(void)
582 thread_t td = curthread;
585 * gd_reqpri 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.
594 if ((td->td_pri & TDPRI_MASK) < mycpu->gd_reqpri) {
599 * YYY enabling will cause wakeup() to task-switch, which really
600 * confused the old 4.x code. This is a good way to simulate
601 * preemption and MP without actually doing preemption or MP, because a
602 * lot of code assumes that wakeup() does not block.
604 if (untimely_switch && mycpu->gd_intr_nesting_level == 0) {
607 * YYY temporary hacks until we disassociate the userland scheduler
608 * from the LWKT scheduler.
610 if (td->td_flags & TDF_RUNQ) {
611 lwkt_switch(); /* will not reenter yield function */
613 lwkt_schedule_self(); /* make sure we are scheduled */
614 lwkt_switch(); /* will not reenter yield function */
615 lwkt_deschedule_self(); /* make sure we are descheduled */
622 * This implements a normal yield which, unlike _quick, will yield to equal
623 * priority threads as well. Note that gd_reqpri tests will be handled by
624 * the crit_exit() call in lwkt_switch().
626 * (self contained on a per cpu basis)
631 lwkt_schedule_self();
636 * Schedule a thread to run. As the current thread we can always safely
637 * schedule ourselves, and a shortcut procedure is provided for that
640 * (non-blocking, self contained on a per cpu basis)
643 lwkt_schedule_self(void)
645 thread_t td = curthread;
648 KASSERT(td->td_wait == NULL, ("lwkt_schedule_self(): td_wait not NULL!"));
650 if (td->td_proc && td->td_proc->p_stat == SSLEEP)
651 panic("SCHED SELF PANIC");
656 * Generic schedule. Possibly schedule threads belonging to other cpus and
657 * deal with threads that might be blocked on a wait queue.
659 * YYY this is one of the best places to implement load balancing code.
660 * Load balancing can be accomplished by requesting other sorts of actions
661 * for the thread in question.
664 lwkt_schedule(thread_t td)
667 if ((td->td_flags & TDF_PREEMPT_LOCK) == 0 && td->td_proc
668 && td->td_proc->p_stat == SSLEEP
670 printf("PANIC schedule curtd = %p (%d %d) target %p (%d %d)\n",
672 curthread->td_proc ? curthread->td_proc->p_pid : -1,
673 curthread->td_proc ? curthread->td_proc->p_stat : -1,
675 td->td_proc ? curthread->td_proc->p_pid : -1,
676 td->td_proc ? curthread->td_proc->p_stat : -1
678 panic("SCHED PANIC");
682 if (td == curthread) {
688 * If the thread is on a wait list we have to send our scheduling
689 * request to the owner of the wait structure. Otherwise we send
690 * the scheduling request to the cpu owning the thread. Races
691 * are ok, the target will forward the message as necessary (the
692 * message may chase the thread around before it finally gets
695 * (remember, wait structures use stable storage)
697 if ((w = td->td_wait) != NULL) {
698 if (lwkt_trytoken(&w->wa_token)) {
699 TAILQ_REMOVE(&w->wa_waitq, td, td_threadq);
702 if (td->td_cpu == mycpu->gd_cpuid) {
704 if (td->td_preemptable) {
705 td->td_preemptable(td, TDPRI_CRIT*2); /* YYY +token */
706 } else if (_lwkt_wantresched(td, curthread)) {
710 lwkt_send_ipiq(td->td_cpu, (ipifunc_t)lwkt_schedule, td);
712 lwkt_reltoken(&w->wa_token);
714 lwkt_send_ipiq(w->wa_token.t_cpu, (ipifunc_t)lwkt_schedule, td);
718 * If the wait structure is NULL and we own the thread, there
719 * is no race (since we are in a critical section). If we
720 * do not own the thread there might be a race but the
721 * target cpu will deal with it.
723 if (td->td_cpu == mycpu->gd_cpuid) {
725 if (td->td_preemptable) {
726 td->td_preemptable(td, TDPRI_CRIT);
727 } else if (_lwkt_wantresched(td, curthread)) {
731 lwkt_send_ipiq(td->td_cpu, (ipifunc_t)lwkt_schedule, td);
739 * Managed acquisition. This code assumes that the MP lock is held for
740 * the tdallq operation and that the thread has been descheduled from its
741 * original cpu. We also have to wait for the thread to be entirely switched
742 * out on its original cpu (this is usually fast enough that we never loop)
743 * since the LWKT system does not have to hold the MP lock while switching
744 * and the target may have released it before switching.
747 lwkt_acquire(thread_t td)
749 struct globaldata *gd;
753 KKASSERT((td->td_flags & TDF_RUNQ) == 0);
754 while (td->td_flags & TDF_RUNNING) /* XXX spin */
759 TAILQ_REMOVE(&gd->gd_tdallq, td, td_allq); /* protected by BGL */
762 td->td_cpu = gd->gd_cpuid;
763 TAILQ_INSERT_TAIL(&gd->gd_tdallq, td, td_allq); /* protected by BGL */
769 * Deschedule a thread.
771 * (non-blocking, self contained on a per cpu basis)
774 lwkt_deschedule_self(void)
776 thread_t td = curthread;
779 KASSERT(td->td_wait == NULL, ("lwkt_schedule_self(): td_wait not NULL!"));
785 * Generic deschedule. Descheduling threads other then your own should be
786 * done only in carefully controlled circumstances. Descheduling is
789 * This function may block if the cpu has run out of messages.
792 lwkt_deschedule(thread_t td)
795 if (td == curthread) {
798 if (td->td_cpu == mycpu->gd_cpuid) {
801 lwkt_send_ipiq(td->td_cpu, (ipifunc_t)lwkt_deschedule, td);
808 * Set the target thread's priority. This routine does not automatically
809 * switch to a higher priority thread, LWKT threads are not designed for
810 * continuous priority changes. Yield if you want to switch.
812 * We have to retain the critical section count which uses the high bits
813 * of the td_pri field. The specified priority may also indicate zero or
814 * more critical sections by adding TDPRI_CRIT*N.
817 lwkt_setpri(thread_t td, int pri)
820 KKASSERT(td->td_cpu == mycpu->gd_cpuid);
822 if (td->td_flags & TDF_RUNQ) {
824 td->td_pri = (td->td_pri & ~TDPRI_MASK) + pri;
827 td->td_pri = (td->td_pri & ~TDPRI_MASK) + pri;
833 lwkt_setpri_self(int pri)
835 thread_t td = curthread;
837 KKASSERT(pri >= 0 && pri <= TDPRI_MAX);
839 if (td->td_flags & TDF_RUNQ) {
841 td->td_pri = (td->td_pri & ~TDPRI_MASK) + pri;
844 td->td_pri = (td->td_pri & ~TDPRI_MASK) + pri;
850 lwkt_preempted_proc(void)
852 thread_t td = curthread;
853 while (td->td_preempted)
854 td = td->td_preempted;
860 * This function deschedules the current thread and blocks on the specified
861 * wait queue. We obtain ownership of the wait queue in order to block
862 * on it. A generation number is used to interlock the wait queue in case
863 * it gets signalled while we are blocked waiting on the token.
865 * Note: alternatively we could dequeue our thread and then message the
866 * target cpu owning the wait queue. YYY implement as sysctl.
868 * Note: wait queue signals normally ping-pong the cpu as an optimization.
870 typedef struct lwkt_gettoken_req {
876 lwkt_block(lwkt_wait_t w, const char *wmesg, int *gen)
878 thread_t td = curthread;
880 lwkt_gettoken(&w->wa_token);
881 if (w->wa_gen == *gen) {
883 TAILQ_INSERT_TAIL(&w->wa_waitq, td, td_threadq);
886 td->td_wmesg = wmesg;
889 /* token might be lost, doesn't matter for gen update */
891 lwkt_reltoken(&w->wa_token);
895 * Signal a wait queue. We gain ownership of the wait queue in order to
896 * signal it. Once a thread is removed from the wait queue we have to
897 * deal with the cpu owning the thread.
899 * Note: alternatively we could message the target cpu owning the wait
900 * queue. YYY implement as sysctl.
903 lwkt_signal(lwkt_wait_t w)
908 lwkt_gettoken(&w->wa_token);
911 while ((td = TAILQ_FIRST(&w->wa_waitq)) != NULL && count) {
914 TAILQ_REMOVE(&w->wa_waitq, td, td_threadq);
917 if (td->td_cpu == mycpu->gd_cpuid) {
920 lwkt_send_ipiq(td->td_cpu, (ipifunc_t)lwkt_schedule, td);
922 lwkt_regettoken(&w->wa_token);
924 lwkt_reltoken(&w->wa_token);
928 * Acquire ownership of a token
930 * Acquire ownership of a token. The token may have spl and/or critical
931 * section side effects, depending on its purpose. These side effects
932 * guarentee that you will maintain ownership of the token as long as you
933 * do not block. If you block you may lose access to the token (but you
934 * must still release it even if you lose your access to it).
936 * YYY for now we use a critical section to prevent IPIs from taking away
937 * a token, but do we really only need to disable IPIs ?
939 * YYY certain tokens could be made to act like mutexes when performance
940 * would be better (e.g. t_cpu == -1). This is not yet implemented.
942 * YYY the tokens replace 4.x's simplelocks for the most part, but this
943 * means that 4.x does not expect a switch so for now we cannot switch
944 * when waiting for an IPI to be returned.
946 * YYY If the token is owned by another cpu we may have to send an IPI to
947 * it and then block. The IPI causes the token to be given away to the
948 * requesting cpu, unless it has already changed hands. Since only the
949 * current cpu can give away a token it owns we do not need a memory barrier.
950 * This needs serious optimization.
957 lwkt_gettoken_remote(void *arg)
959 lwkt_gettoken_req *req = arg;
960 if (req->tok->t_cpu == mycpu->gd_cpuid) {
962 printf("GT(%d,%d) ", req->tok->t_cpu, req->cpu);
963 req->tok->t_cpu = req->cpu;
964 req->tok->t_reqcpu = req->cpu; /* YYY leave owned by target cpu */
965 /* else set reqcpu to point to current cpu for release */
972 lwkt_gettoken(lwkt_token_t tok)
975 * Prevent preemption so the token can't be taken away from us once
976 * we gain ownership of it. Use a synchronous request which might
977 * block. The request will be forwarded as necessary playing catchup
983 if (curthread->td_pri > 2000) {
984 curthread->td_pri = 1000;
989 while (tok->t_cpu != mycpu->gd_cpuid) {
990 struct lwkt_gettoken_req req;
994 req.cpu = mycpu->gd_cpuid;
996 dcpu = (volatile int)tok->t_cpu;
997 KKASSERT(dcpu >= 0 && dcpu < ncpus);
999 printf("REQT%d ", dcpu);
1000 seq = lwkt_send_ipiq(dcpu, lwkt_gettoken_remote, &req);
1001 lwkt_wait_ipiq(dcpu, seq);
1003 printf("REQR%d ", tok->t_cpu);
1007 * leave us in a critical section on return. This will be undone
1008 * by lwkt_reltoken(). Bump the generation number.
1010 return(++tok->t_gen);
1014 * Attempt to acquire ownership of a token. Returns 1 on success, 0 on
1018 lwkt_trytoken(lwkt_token_t tok)
1022 if (tok->t_cpu != mycpu->gd_cpuid) {
1026 /* leave us in the critical section */
1032 * Release your ownership of a token. Releases must occur in reverse
1033 * order to aquisitions, eventually so priorities can be unwound properly
1034 * like SPLs. At the moment the actual implemention doesn't care.
1036 * We can safely hand a token that we own to another cpu without notifying
1037 * it, but once we do we can't get it back without requesting it (unless
1038 * the other cpu hands it back to us before we check).
1040 * We might have lost the token, so check that.
1043 lwkt_reltoken(lwkt_token_t tok)
1045 if (tok->t_cpu == mycpu->gd_cpuid) {
1046 tok->t_cpu = tok->t_reqcpu;
1052 * Reacquire a token that might have been lost and compare and update the
1053 * generation number. 0 is returned if the generation has not changed
1054 * (nobody else obtained the token while we were blocked, on this cpu or
1057 * This function returns with the token re-held whether the generation
1058 * number changed or not.
1061 lwkt_gentoken(lwkt_token_t tok, int *gen)
1063 if (lwkt_regettoken(tok) == *gen) {
1073 * Re-acquire a token that might have been lost. Returns the generation
1074 * number of the token.
1077 lwkt_regettoken(lwkt_token_t tok)
1079 /* assert we are in a critical section */
1080 if (tok->t_cpu != mycpu->gd_cpuid) {
1082 while (tok->t_cpu != mycpu->gd_cpuid) {
1083 struct lwkt_gettoken_req req;
1087 req.cpu = mycpu->gd_cpuid;
1089 dcpu = (volatile int)tok->t_cpu;
1090 KKASSERT(dcpu >= 0 && dcpu < ncpus);
1092 printf("REQT%d ", dcpu);
1093 seq = lwkt_send_ipiq(dcpu, lwkt_gettoken_remote, &req);
1094 lwkt_wait_ipiq(dcpu, seq);
1096 printf("REQR%d ", tok->t_cpu);
1105 lwkt_inittoken(lwkt_token_t tok)
1108 * Zero structure and set cpu owner and reqcpu to cpu 0.
1110 bzero(tok, sizeof(*tok));
1114 * Create a kernel process/thread/whatever. It shares it's address space
1115 * with proc0 - ie: kernel only.
1117 * XXX should be renamed to lwkt_create()
1119 * The thread will be entered with the MP lock held.
1122 lwkt_create(void (*func)(void *), void *arg,
1123 struct thread **tdp, thread_t template, int tdflags,
1124 const char *fmt, ...)
1129 td = lwkt_alloc_thread(template);
1132 cpu_set_thread_handler(td, kthread_exit, func, arg);
1133 td->td_flags |= TDF_VERBOSE | tdflags;
1139 * Set up arg0 for 'ps' etc
1142 vsnprintf(td->td_comm, sizeof(td->td_comm), fmt, ap);
1146 * Schedule the thread to run
1148 if ((td->td_flags & TDF_STOPREQ) == 0)
1151 td->td_flags &= ~TDF_STOPREQ;
1156 * Destroy an LWKT thread. Warning! This function is not called when
1157 * a process exits, cpu_proc_exit() directly calls cpu_thread_exit() and
1158 * uses a different reaping mechanism.
1163 thread_t td = curthread;
1165 if (td->td_flags & TDF_VERBOSE)
1166 printf("kthread %p %s has exited\n", td, td->td_comm);
1168 lwkt_deschedule_self();
1169 ++mycpu->gd_tdfreecount;
1170 TAILQ_INSERT_TAIL(&mycpu->gd_tdfreeq, td, td_threadq);
1175 * Create a kernel process/thread/whatever. It shares it's address space
1176 * with proc0 - ie: kernel only. 5.x compatible.
1179 kthread_create(void (*func)(void *), void *arg,
1180 struct thread **tdp, const char *fmt, ...)
1185 td = lwkt_alloc_thread(NULL);
1188 cpu_set_thread_handler(td, kthread_exit, func, arg);
1189 td->td_flags |= TDF_VERBOSE;
1195 * Set up arg0 for 'ps' etc
1198 vsnprintf(td->td_comm, sizeof(td->td_comm), fmt, ap);
1202 * Schedule the thread to run
1211 thread_t td = curthread;
1212 int lpri = td->td_pri;
1215 panic("td_pri is/would-go negative! %p %d", td, lpri);
1219 * Destroy an LWKT thread. Warning! This function is not called when
1220 * a process exits, cpu_proc_exit() directly calls cpu_thread_exit() and
1221 * uses a different reaping mechanism.
1223 * XXX duplicates lwkt_exit()
1234 * Send a function execution request to another cpu. The request is queued
1235 * on the cpu<->cpu ipiq matrix. Each cpu owns a unique ipiq FIFO for every
1236 * possible target cpu. The FIFO can be written.
1238 * YYY If the FIFO fills up we have to enable interrupts and process the
1239 * IPIQ while waiting for it to empty or we may deadlock with another cpu.
1240 * Create a CPU_*() function to do this!
1242 * Must be called from a critical section.
1245 lwkt_send_ipiq(int dcpu, ipifunc_t func, void *arg)
1249 struct globaldata *gd = mycpu;
1251 if (dcpu == gd->gd_cpuid) {
1256 ++gd->gd_intr_nesting_level;
1258 if (gd->gd_intr_nesting_level > 20)
1259 panic("lwkt_send_ipiq: TOO HEAVILY NESTED!");
1261 KKASSERT(curthread->td_pri >= TDPRI_CRIT);
1262 KKASSERT(dcpu >= 0 && dcpu < ncpus);
1264 ip = &gd->gd_ipiq[dcpu];
1267 * We always drain before the FIFO becomes full so it should never
1268 * become full. We need to leave enough entries to deal with
1271 KKASSERT(ip->ip_windex - ip->ip_rindex != MAXCPUFIFO);
1272 windex = ip->ip_windex & MAXCPUFIFO_MASK;
1273 ip->ip_func[windex] = func;
1274 ip->ip_arg[windex] = arg;
1275 /* YYY memory barrier */
1277 if (ip->ip_windex - ip->ip_rindex > MAXCPUFIFO / 2) {
1278 unsigned int eflags = read_eflags();
1281 while (ip->ip_windex - ip->ip_rindex > MAXCPUFIFO / 4) {
1282 KKASSERT(ip->ip_windex - ip->ip_rindex != MAXCPUFIFO - 1);
1283 lwkt_process_ipiq();
1285 write_eflags(eflags);
1287 --gd->gd_intr_nesting_level;
1288 cpu_send_ipiq(dcpu); /* issues memory barrier if appropriate */
1290 return(ip->ip_windex);
1294 * Send a message to several target cpus. Typically used for scheduling.
1297 lwkt_send_ipiq_mask(u_int32_t mask, ipifunc_t func, void *arg)
1303 lwkt_send_ipiq(cpuid, func, arg);
1304 mask &= ~(1 << cpuid);
1309 * Wait for the remote cpu to finish processing a function.
1311 * YYY we have to enable interrupts and process the IPIQ while waiting
1312 * for it to empty or we may deadlock with another cpu. Create a CPU_*()
1313 * function to do this! YYY we really should 'block' here.
1315 * Must be called from a critical section. Thsi routine may be called
1316 * from an interrupt (for example, if an interrupt wakes a foreign thread
1320 lwkt_wait_ipiq(int dcpu, int seq)
1323 int maxc = 100000000;
1325 if (dcpu != mycpu->gd_cpuid) {
1326 KKASSERT(dcpu >= 0 && dcpu < ncpus);
1327 ip = &mycpu->gd_ipiq[dcpu];
1328 if ((int)(ip->ip_xindex - seq) < 0) {
1329 unsigned int eflags = read_eflags();
1331 while ((int)(ip->ip_xindex - seq) < 0) {
1332 lwkt_process_ipiq();
1334 printf("LWKT_WAIT_IPIQ WARNING! %d wait %d (%d)\n", mycpu->gd_cpuid, dcpu, ip->ip_xindex - seq);
1335 if (maxc < -1000000)
1336 panic("LWKT_WAIT_IPIQ");
1338 write_eflags(eflags);
1344 * Called from IPI interrupt (like a fast interrupt), which has placed
1345 * us in a critical section. The MP lock may or may not be held.
1346 * May also be called from doreti or splz, or be reentrantly called
1347 * indirectly through the ip_func[] we run.
1350 lwkt_process_ipiq(void)
1353 int cpuid = mycpu->gd_cpuid;
1355 for (n = 0; n < ncpus; ++n) {
1361 ip = globaldata_find(n)->gd_ipiq;
1367 * Note: xindex is only updated after we are sure the function has
1368 * finished execution. Beware lwkt_process_ipiq() reentrancy! The
1369 * function may send an IPI which may block/drain.
1371 while (ip->ip_rindex != ip->ip_windex) {
1372 ri = ip->ip_rindex & MAXCPUFIFO_MASK;
1374 ip->ip_func[ri](ip->ip_arg[ri]);
1375 /* YYY memory barrier */
1376 ip->ip_xindex = ip->ip_rindex;
1384 lwkt_send_ipiq(int dcpu, ipifunc_t func, void *arg)
1386 panic("lwkt_send_ipiq: UP box! (%d,%p,%p)", dcpu, func, arg);
1387 return(0); /* NOT REACHED */
1391 lwkt_wait_ipiq(int dcpu, int seq)
1393 panic("lwkt_wait_ipiq: UP box! (%d,%d)", dcpu, seq);