2 * Copyright (c) 2003,2004 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,
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27 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
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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
34 * $DragonFly: src/sys/kern/lwkt_thread.c,v 1.65 2004/07/16 05:51:10 dillon Exp $
38 * Each cpu in a system has its own self-contained light weight kernel
39 * thread scheduler, which means that generally speaking we only need
40 * to use a critical section to avoid problems. Foreign thread
41 * scheduling is queued via (async) IPIs.
46 #include <sys/param.h>
47 #include <sys/systm.h>
48 #include <sys/kernel.h>
50 #include <sys/rtprio.h>
51 #include <sys/queue.h>
52 #include <sys/thread2.h>
53 #include <sys/sysctl.h>
54 #include <sys/kthread.h>
55 #include <machine/cpu.h>
60 #include <vm/vm_param.h>
61 #include <vm/vm_kern.h>
62 #include <vm/vm_object.h>
63 #include <vm/vm_page.h>
64 #include <vm/vm_map.h>
65 #include <vm/vm_pager.h>
66 #include <vm/vm_extern.h>
67 #include <vm/vm_zone.h>
69 #include <machine/stdarg.h>
70 #include <machine/ipl.h>
71 #include <machine/smp.h>
73 #define THREAD_STACK (UPAGES * PAGE_SIZE)
77 #include <sys/stdint.h>
78 #include <libcaps/thread.h>
79 #include <sys/thread.h>
80 #include <sys/msgport.h>
81 #include <sys/errno.h>
82 #include <libcaps/globaldata.h>
83 #include <machine/cpufunc.h>
84 #include <sys/thread2.h>
85 #include <sys/msgport2.h>
89 #include <machine/lock.h>
93 static int untimely_switch = 0;
95 static int panic_on_cscount = 0;
97 static __int64_t switch_count = 0;
98 static __int64_t preempt_hit = 0;
99 static __int64_t preempt_miss = 0;
100 static __int64_t preempt_weird = 0;
104 SYSCTL_INT(_lwkt, OID_AUTO, untimely_switch, CTLFLAG_RW, &untimely_switch, 0, "");
106 SYSCTL_INT(_lwkt, OID_AUTO, panic_on_cscount, CTLFLAG_RW, &panic_on_cscount, 0, "");
108 SYSCTL_QUAD(_lwkt, OID_AUTO, switch_count, CTLFLAG_RW, &switch_count, 0, "");
109 SYSCTL_QUAD(_lwkt, OID_AUTO, preempt_hit, CTLFLAG_RW, &preempt_hit, 0, "");
110 SYSCTL_QUAD(_lwkt, OID_AUTO, preempt_miss, CTLFLAG_RW, &preempt_miss, 0, "");
111 SYSCTL_QUAD(_lwkt, OID_AUTO, preempt_weird, CTLFLAG_RW, &preempt_weird, 0, "");
116 * These helper procedures handle the runq, they can only be called from
117 * within a critical section.
119 * WARNING! Prior to SMP being brought up it is possible to enqueue and
120 * dequeue threads belonging to other cpus, so be sure to use td->td_gd
121 * instead of 'mycpu' when referencing the globaldata structure. Once
122 * SMP live enqueuing and dequeueing only occurs on the current cpu.
126 _lwkt_dequeue(thread_t td)
128 if (td->td_flags & TDF_RUNQ) {
129 int nq = td->td_pri & TDPRI_MASK;
130 struct globaldata *gd = td->td_gd;
132 td->td_flags &= ~TDF_RUNQ;
133 TAILQ_REMOVE(&gd->gd_tdrunq[nq], td, td_threadq);
134 /* runqmask is passively cleaned up by the switcher */
140 _lwkt_enqueue(thread_t td)
142 if ((td->td_flags & (TDF_RUNQ|TDF_MIGRATING)) == 0) {
143 int nq = td->td_pri & TDPRI_MASK;
144 struct globaldata *gd = td->td_gd;
146 td->td_flags |= TDF_RUNQ;
147 TAILQ_INSERT_TAIL(&gd->gd_tdrunq[nq], td, td_threadq);
148 gd->gd_runqmask |= 1 << nq;
153 * Schedule a thread to run. As the current thread we can always safely
154 * schedule ourselves, and a shortcut procedure is provided for that
157 * (non-blocking, self contained on a per cpu basis)
160 lwkt_schedule_self(thread_t td)
162 crit_enter_quick(td);
163 KASSERT(td->td_wait == NULL, ("lwkt_schedule_self(): td_wait not NULL!"));
164 KASSERT(td != &td->td_gd->gd_idlethread, ("lwkt_schedule_self(): scheduling gd_idlethread is illegal!"));
167 if (td->td_proc && td->td_proc->p_stat == SSLEEP)
168 panic("SCHED SELF PANIC");
174 * Deschedule a thread.
176 * (non-blocking, self contained on a per cpu basis)
179 lwkt_deschedule_self(thread_t td)
181 crit_enter_quick(td);
182 KASSERT(td->td_wait == NULL, ("lwkt_schedule_self(): td_wait not NULL!"));
190 * LWKTs operate on a per-cpu basis
192 * WARNING! Called from early boot, 'mycpu' may not work yet.
195 lwkt_gdinit(struct globaldata *gd)
199 for (i = 0; i < sizeof(gd->gd_tdrunq)/sizeof(gd->gd_tdrunq[0]); ++i)
200 TAILQ_INIT(&gd->gd_tdrunq[i]);
202 TAILQ_INIT(&gd->gd_tdallq);
208 * Initialize a thread wait structure prior to first use.
210 * NOTE! called from low level boot code, we cannot do anything fancy!
213 lwkt_wait_init(lwkt_wait_t w)
215 lwkt_token_init(&w->wa_token);
216 TAILQ_INIT(&w->wa_waitq);
222 * Create a new thread. The thread must be associated with a process context
223 * or LWKT start address before it can be scheduled. If the target cpu is
224 * -1 the thread will be created on the current cpu.
226 * If you intend to create a thread without a process context this function
227 * does everything except load the startup and switcher function.
230 lwkt_alloc_thread(struct thread *td, int cpu)
234 globaldata_t gd = mycpu;
238 if (gd->gd_tdfreecount > 0) {
239 --gd->gd_tdfreecount;
240 td = TAILQ_FIRST(&gd->gd_tdfreeq);
241 KASSERT(td != NULL && (td->td_flags & TDF_RUNNING) == 0,
242 ("lwkt_alloc_thread: unexpected NULL or corrupted td"));
243 TAILQ_REMOVE(&gd->gd_tdfreeq, td, td_threadq);
245 stack = td->td_kstack;
246 flags = td->td_flags & (TDF_ALLOCATED_STACK|TDF_ALLOCATED_THREAD);
250 td = zalloc(thread_zone);
252 td = malloc(sizeof(struct thread));
254 td->td_kstack = NULL;
255 flags |= TDF_ALLOCATED_THREAD;
258 if ((stack = td->td_kstack) == NULL) {
260 stack = (void *)kmem_alloc(kernel_map, THREAD_STACK);
262 stack = libcaps_alloc_stack(THREAD_STACK);
264 flags |= TDF_ALLOCATED_STACK;
267 lwkt_init_thread(td, stack, flags, mycpu);
269 lwkt_init_thread(td, stack, flags, globaldata_find(cpu));
276 * Initialize a preexisting thread structure. This function is used by
277 * lwkt_alloc_thread() and also used to initialize the per-cpu idlethread.
279 * All threads start out in a critical section at a priority of
280 * TDPRI_KERN_DAEMON. Higher level code will modify the priority as
281 * appropriate. This function may send an IPI message when the
282 * requested cpu is not the current cpu and consequently gd_tdallq may
283 * not be initialized synchronously from the point of view of the originating
286 * NOTE! we have to be careful in regards to creating threads for other cpus
287 * if SMP has not yet been activated.
292 lwkt_init_thread_remote(void *arg)
296 TAILQ_INSERT_TAIL(&td->td_gd->gd_tdallq, td, td_allq);
302 lwkt_init_thread(thread_t td, void *stack, int flags, struct globaldata *gd)
304 globaldata_t mygd = mycpu;
306 bzero(td, sizeof(struct thread));
307 td->td_kstack = stack;
308 td->td_flags |= flags;
310 td->td_pri = TDPRI_KERN_DAEMON + TDPRI_CRIT;
311 lwkt_initport(&td->td_msgport, td);
312 pmap_init_thread(td);
315 * Normally initializing a thread for a remote cpu requires sending an
316 * IPI. However, the idlethread is setup before the other cpus are
317 * activated so we have to treat it as a special case. XXX manipulation
318 * of gd_tdallq requires the BGL.
320 if (gd == mygd || td == &gd->gd_idlethread) {
322 TAILQ_INSERT_TAIL(&gd->gd_tdallq, td, td_allq);
325 lwkt_send_ipiq(gd, lwkt_init_thread_remote, td);
329 TAILQ_INSERT_TAIL(&gd->gd_tdallq, td, td_allq);
337 lwkt_set_comm(thread_t td, const char *ctl, ...)
342 vsnprintf(td->td_comm, sizeof(td->td_comm), ctl, va);
347 lwkt_hold(thread_t td)
353 lwkt_rele(thread_t td)
355 KKASSERT(td->td_refs > 0);
362 lwkt_wait_free(thread_t td)
365 tsleep(td, 0, "tdreap", hz);
371 lwkt_free_thread(thread_t td)
373 struct globaldata *gd = mycpu;
375 KASSERT((td->td_flags & TDF_RUNNING) == 0,
376 ("lwkt_free_thread: did not exit! %p", td));
379 TAILQ_REMOVE(&gd->gd_tdallq, td, td_allq);
380 if (gd->gd_tdfreecount < CACHE_NTHREADS &&
381 (td->td_flags & TDF_ALLOCATED_THREAD)
383 ++gd->gd_tdfreecount;
384 TAILQ_INSERT_HEAD(&gd->gd_tdfreeq, td, td_threadq);
388 if (td->td_kstack && (td->td_flags & TDF_ALLOCATED_STACK)) {
390 kmem_free(kernel_map, (vm_offset_t)td->td_kstack, THREAD_STACK);
392 libcaps_free_stack(td->td_kstack, THREAD_STACK);
395 td->td_kstack = NULL;
397 if (td->td_flags & TDF_ALLOCATED_THREAD) {
399 zfree(thread_zone, td);
409 * Switch to the next runnable lwkt. If no LWKTs are runnable then
410 * switch to the idlethread. Switching must occur within a critical
411 * section to avoid races with the scheduling queue.
413 * We always have full control over our cpu's run queue. Other cpus
414 * that wish to manipulate our queue must use the cpu_*msg() calls to
415 * talk to our cpu, so a critical section is all that is needed and
416 * the result is very, very fast thread switching.
418 * The LWKT scheduler uses a fixed priority model and round-robins at
419 * each priority level. User process scheduling is a totally
420 * different beast and LWKT priorities should not be confused with
421 * user process priorities.
423 * The MP lock may be out of sync with the thread's td_mpcount. lwkt_switch()
424 * cleans it up. Note that the td_switch() function cannot do anything that
425 * requires the MP lock since the MP lock will have already been setup for
426 * the target thread (not the current thread). It's nice to have a scheduler
427 * that does not need the MP lock to work because it allows us to do some
428 * really cool high-performance MP lock optimizations.
434 globaldata_t gd = mycpu;
435 thread_t td = gd->gd_curthread;
442 * Switching from within a 'fast' (non thread switched) interrupt is
445 if (gd->gd_intr_nesting_level && panicstr == NULL) {
446 panic("lwkt_switch: cannot switch from within a fast interrupt, yet");
450 * Passive release (used to transition from user to kernel mode
451 * when we block or switch rather then when we enter the kernel).
452 * This function is NOT called if we are switching into a preemption
453 * or returning from a preemption. Typically this causes us to lose
454 * our current process designation (if we have one) and become a true
455 * LWKT thread, and may also hand the current process designation to
456 * another process and schedule thread.
466 * td_mpcount cannot be used to determine if we currently hold the
467 * MP lock because get_mplock() will increment it prior to attempting
468 * to get the lock, and switch out if it can't. Our ownership of
469 * the actual lock will remain stable while we are in a critical section
470 * (but, of course, another cpu may own or release the lock so the
471 * actual value of mp_lock is not stable).
473 mpheld = MP_LOCK_HELD();
475 if (td->td_cscount) {
476 printf("Diagnostic: attempt to switch while mastering cpusync: %p\n",
478 if (panic_on_cscount)
479 panic("switching while mastering cpusync");
483 if ((ntd = td->td_preempted) != NULL) {
485 * We had preempted another thread on this cpu, resume the preempted
486 * thread. This occurs transparently, whether the preempted thread
487 * was scheduled or not (it may have been preempted after descheduling
490 * We have to setup the MP lock for the original thread after backing
491 * out the adjustment that was made to curthread when the original
494 KKASSERT(ntd->td_flags & TDF_PREEMPT_LOCK);
496 if (ntd->td_mpcount && mpheld == 0) {
497 panic("MPLOCK NOT HELD ON RETURN: %p %p %d %d",
498 td, ntd, td->td_mpcount, ntd->td_mpcount);
500 if (ntd->td_mpcount) {
501 td->td_mpcount -= ntd->td_mpcount;
502 KKASSERT(td->td_mpcount >= 0);
505 ntd->td_flags |= TDF_PREEMPT_DONE;
506 /* YYY release mp lock on switchback if original doesn't need it */
509 * Priority queue / round-robin at each priority. Note that user
510 * processes run at a fixed, low priority and the user process
511 * scheduler deals with interactions between user processes
512 * by scheduling and descheduling them from the LWKT queue as
515 * We have to adjust the MP lock for the target thread. If we
516 * need the MP lock and cannot obtain it we try to locate a
517 * thread that does not need the MP lock. If we cannot, we spin
520 * A similar issue exists for the tokens held by the target thread.
521 * If we cannot obtain ownership of the tokens we cannot immediately
522 * schedule the thread.
526 * We are switching threads. If there are any pending requests for
527 * tokens we can satisfy all of them here.
530 if (gd->gd_tokreqbase)
531 lwkt_drain_token_requests();
535 if (gd->gd_runqmask) {
536 int nq = bsrl(gd->gd_runqmask);
537 if ((ntd = TAILQ_FIRST(&gd->gd_tdrunq[nq])) == NULL) {
538 gd->gd_runqmask &= ~(1 << nq);
543 * If the target needs the MP lock and we couldn't get it,
544 * or if the target is holding tokens and we could not
545 * gain ownership of the tokens, continue looking for a
546 * thread to schedule and spin instead of HLT if we can't.
548 if ((ntd->td_mpcount && mpheld == 0 && !cpu_try_mplock()) ||
549 (ntd->td_toks && lwkt_chktokens(ntd) == 0)
551 u_int32_t rqmask = gd->gd_runqmask;
553 TAILQ_FOREACH(ntd, &gd->gd_tdrunq[nq], td_threadq) {
554 if (ntd->td_mpcount && !mpheld && !cpu_try_mplock())
556 mpheld = MP_LOCK_HELD();
557 if (ntd->td_toks && !lwkt_chktokens(ntd))
563 rqmask &= ~(1 << nq);
567 ntd = &gd->gd_idlethread;
568 ntd->td_flags |= TDF_IDLE_NOHLT;
570 TAILQ_REMOVE(&gd->gd_tdrunq[nq], ntd, td_threadq);
571 TAILQ_INSERT_TAIL(&gd->gd_tdrunq[nq], ntd, td_threadq);
574 TAILQ_REMOVE(&gd->gd_tdrunq[nq], ntd, td_threadq);
575 TAILQ_INSERT_TAIL(&gd->gd_tdrunq[nq], ntd, td_threadq);
578 TAILQ_REMOVE(&gd->gd_tdrunq[nq], ntd, td_threadq);
579 TAILQ_INSERT_TAIL(&gd->gd_tdrunq[nq], ntd, td_threadq);
583 * We have nothing to run but only let the idle loop halt
584 * the cpu if there are no pending interrupts.
586 ntd = &gd->gd_idlethread;
587 if (gd->gd_reqflags & RQF_IDLECHECK_MASK)
588 ntd->td_flags |= TDF_IDLE_NOHLT;
591 KASSERT(ntd->td_pri >= TDPRI_CRIT,
592 ("priority problem in lwkt_switch %d %d", td->td_pri, ntd->td_pri));
595 * Do the actual switch. If the new target does not need the MP lock
596 * and we are holding it, release the MP lock. If the new target requires
597 * the MP lock we have already acquired it for the target.
600 if (ntd->td_mpcount == 0 ) {
604 ASSERT_MP_LOCK_HELD();
609 /* NOTE: current cpu may have changed after switch */
614 * Request that the target thread preempt the current thread. Preemption
615 * only works under a specific set of conditions:
617 * - We are not preempting ourselves
618 * - The target thread is owned by the current cpu
619 * - We are not currently being preempted
620 * - The target is not currently being preempted
621 * - We are able to satisfy the target's MP lock requirements (if any).
623 * THE CALLER OF LWKT_PREEMPT() MUST BE IN A CRITICAL SECTION. Typically
624 * this is called via lwkt_schedule() through the td_preemptable callback.
625 * critpri is the managed critical priority that we should ignore in order
626 * to determine whether preemption is possible (aka usually just the crit
627 * priority of lwkt_schedule() itself).
629 * XXX at the moment we run the target thread in a critical section during
630 * the preemption in order to prevent the target from taking interrupts
631 * that *WE* can't. Preemption is strictly limited to interrupt threads
632 * and interrupt-like threads, outside of a critical section, and the
633 * preempted source thread will be resumed the instant the target blocks
634 * whether or not the source is scheduled (i.e. preemption is supposed to
635 * be as transparent as possible).
637 * The target thread inherits our MP count (added to its own) for the
638 * duration of the preemption in order to preserve the atomicy of the
639 * MP lock during the preemption. Therefore, any preempting targets must be
640 * careful in regards to MP assertions. Note that the MP count may be
641 * out of sync with the physical mp_lock, but we do not have to preserve
642 * the original ownership of the lock if it was out of synch (that is, we
643 * can leave it synchronized on return).
646 lwkt_preempt(thread_t ntd, int critpri)
648 struct globaldata *gd = mycpu;
656 * The caller has put us in a critical section. We can only preempt
657 * if the caller of the caller was not in a critical section (basically
658 * a local interrupt), as determined by the 'critpri' parameter.
660 * YYY The target thread must be in a critical section (else it must
661 * inherit our critical section? I dunno yet).
663 * Any tokens held by the target may not be held by thread(s) being
664 * preempted. We take the easy way out and do not preempt if
665 * the target is holding tokens.
667 * Set need_lwkt_resched() unconditionally for now YYY.
669 KASSERT(ntd->td_pri >= TDPRI_CRIT, ("BADCRIT0 %d", ntd->td_pri));
671 td = gd->gd_curthread;
673 if ((ntd->td_pri & TDPRI_MASK) <= (td->td_pri & TDPRI_MASK)) {
677 if ((td->td_pri & ~TDPRI_MASK) > critpri) {
682 if (ntd->td_gd != gd) {
688 * Take the easy way out and do not preempt if the target is holding
689 * one or more tokens. We could test whether the thread(s) being
690 * preempted interlock against the target thread's tokens and whether
691 * we can get all the target thread's tokens, but this situation
692 * should not occur very often so its easier to simply not preempt.
694 if (ntd->td_toks != NULL) {
698 if (td == ntd || ((td->td_flags | ntd->td_flags) & TDF_PREEMPT_LOCK)) {
702 if (ntd->td_preempted) {
708 * note: an interrupt might have occured just as we were transitioning
709 * to or from the MP lock. In this case td_mpcount will be pre-disposed
710 * (non-zero) but not actually synchronized with the actual state of the
711 * lock. We can use it to imply an MP lock requirement for the
712 * preemption but we cannot use it to test whether we hold the MP lock
715 savecnt = td->td_mpcount;
716 mpheld = MP_LOCK_HELD();
717 ntd->td_mpcount += td->td_mpcount;
718 if (mpheld == 0 && ntd->td_mpcount && !cpu_try_mplock()) {
719 ntd->td_mpcount -= td->td_mpcount;
726 ntd->td_preempted = td;
727 td->td_flags |= TDF_PREEMPT_LOCK;
729 KKASSERT(ntd->td_preempted && (td->td_flags & TDF_PREEMPT_DONE));
731 KKASSERT(savecnt == td->td_mpcount);
732 mpheld = MP_LOCK_HELD();
733 if (mpheld && td->td_mpcount == 0)
735 else if (mpheld == 0 && td->td_mpcount)
736 panic("lwkt_preempt(): MP lock was not held through");
738 ntd->td_preempted = NULL;
739 td->td_flags &= ~(TDF_PREEMPT_LOCK|TDF_PREEMPT_DONE);
743 * Yield our thread while higher priority threads are pending. This is
744 * typically called when we leave a critical section but it can be safely
745 * called while we are in a critical section.
747 * This function will not generally yield to equal priority threads but it
748 * can occur as a side effect. Note that lwkt_switch() is called from
749 * inside the critical section to prevent its own crit_exit() from reentering
750 * lwkt_yield_quick().
752 * gd_reqflags indicates that *something* changed, e.g. an interrupt or softint
753 * came along but was blocked and made pending.
755 * (self contained on a per cpu basis)
758 lwkt_yield_quick(void)
760 globaldata_t gd = mycpu;
761 thread_t td = gd->gd_curthread;
764 * gd_reqflags is cleared in splz if the cpl is 0. If we were to clear
765 * it with a non-zero cpl then we might not wind up calling splz after
766 * a task switch when the critical section is exited even though the
767 * new task could accept the interrupt.
769 * XXX from crit_exit() only called after last crit section is released.
770 * If called directly will run splz() even if in a critical section.
772 * td_nest_count prevent deep nesting via splz() or doreti(). Note that
773 * except for this special case, we MUST call splz() here to handle any
774 * pending ints, particularly after we switch, or we might accidently
775 * halt the cpu with interrupts pending.
777 if (gd->gd_reqflags && td->td_nest_count < 2)
781 * YYY enabling will cause wakeup() to task-switch, which really
782 * confused the old 4.x code. This is a good way to simulate
783 * preemption and MP without actually doing preemption or MP, because a
784 * lot of code assumes that wakeup() does not block.
786 if (untimely_switch && td->td_nest_count == 0 &&
787 gd->gd_intr_nesting_level == 0
789 crit_enter_quick(td);
791 * YYY temporary hacks until we disassociate the userland scheduler
792 * from the LWKT scheduler.
794 if (td->td_flags & TDF_RUNQ) {
795 lwkt_switch(); /* will not reenter yield function */
797 lwkt_schedule_self(td); /* make sure we are scheduled */
798 lwkt_switch(); /* will not reenter yield function */
799 lwkt_deschedule_self(td); /* make sure we are descheduled */
801 crit_exit_noyield(td);
806 * This implements a normal yield which, unlike _quick, will yield to equal
807 * priority threads as well. Note that gd_reqflags tests will be handled by
808 * the crit_exit() call in lwkt_switch().
810 * (self contained on a per cpu basis)
815 lwkt_schedule_self(curthread);
820 * Generic schedule. Possibly schedule threads belonging to other cpus and
821 * deal with threads that might be blocked on a wait queue.
823 * We have a little helper inline function which does additional work after
824 * the thread has been enqueued, including dealing with preemption and
825 * setting need_lwkt_resched() (which prevents the kernel from returning
826 * to userland until it has processed higher priority threads).
830 _lwkt_schedule_post(thread_t ntd, int cpri)
832 if (ntd->td_preemptable) {
833 ntd->td_preemptable(ntd, cpri); /* YYY +token */
835 if ((ntd->td_flags & TDF_NORESCHED) == 0) {
836 if ((ntd->td_pri & TDPRI_MASK) >= TDPRI_KERN_USER)
843 lwkt_schedule(thread_t td)
845 globaldata_t mygd = mycpu;
848 KASSERT(td != &td->td_gd->gd_idlethread, ("lwkt_schedule(): scheduling gd_idlethread is illegal!"));
849 if ((td->td_flags & TDF_PREEMPT_LOCK) == 0 && td->td_proc
850 && td->td_proc->p_stat == SSLEEP
852 printf("PANIC schedule curtd = %p (%d %d) target %p (%d %d)\n",
854 curthread->td_proc ? curthread->td_proc->p_pid : -1,
855 curthread->td_proc ? curthread->td_proc->p_stat : -1,
857 td->td_proc ? curthread->td_proc->p_pid : -1,
858 td->td_proc ? curthread->td_proc->p_stat : -1
860 panic("SCHED PANIC");
864 if (td == mygd->gd_curthread) {
870 * If the thread is on a wait list we have to send our scheduling
871 * request to the owner of the wait structure. Otherwise we send
872 * the scheduling request to the cpu owning the thread. Races
873 * are ok, the target will forward the message as necessary (the
874 * message may chase the thread around before it finally gets
877 * (remember, wait structures use stable storage)
879 * NOTE: tokens no longer enter a critical section, so we only need
880 * to account for the crit_enter() above when calling
881 * _lwkt_schedule_post().
883 if ((w = td->td_wait) != NULL) {
886 if (lwkt_trytoken(&wref, &w->wa_token)) {
887 TAILQ_REMOVE(&w->wa_waitq, td, td_threadq);
891 if (td->td_gd == mycpu) {
893 _lwkt_schedule_post(td, TDPRI_CRIT);
895 lwkt_send_ipiq(td->td_gd, (ipifunc_t)lwkt_schedule, td);
899 _lwkt_schedule_post(td, TDPRI_CRIT);
901 lwkt_reltoken(&wref);
903 lwkt_send_ipiq(w->wa_token.t_cpu, (ipifunc_t)lwkt_schedule, td);
907 * If the wait structure is NULL and we own the thread, there
908 * is no race (since we are in a critical section). If we
909 * do not own the thread there might be a race but the
910 * target cpu will deal with it.
913 if (td->td_gd == mygd) {
915 _lwkt_schedule_post(td, TDPRI_CRIT);
917 lwkt_send_ipiq(td->td_gd, (ipifunc_t)lwkt_schedule, td);
921 _lwkt_schedule_post(td, TDPRI_CRIT);
929 * Managed acquisition. This code assumes that the MP lock is held for
930 * the tdallq operation and that the thread has been descheduled from its
931 * original cpu. We also have to wait for the thread to be entirely switched
932 * out on its original cpu (this is usually fast enough that we never loop)
933 * since the LWKT system does not have to hold the MP lock while switching
934 * and the target may have released it before switching.
937 lwkt_acquire(thread_t td)
944 KKASSERT((td->td_flags & TDF_RUNQ) == 0);
945 while (td->td_flags & TDF_RUNNING) /* XXX spin */
949 TAILQ_REMOVE(&gd->gd_tdallq, td, td_allq); /* protected by BGL */
951 TAILQ_INSERT_TAIL(&mygd->gd_tdallq, td, td_allq); /* protected by BGL */
957 * Generic deschedule. Descheduling threads other then your own should be
958 * done only in carefully controlled circumstances. Descheduling is
961 * This function may block if the cpu has run out of messages.
964 lwkt_deschedule(thread_t td)
967 if (td == curthread) {
970 if (td->td_gd == mycpu) {
973 lwkt_send_ipiq(td->td_gd, (ipifunc_t)lwkt_deschedule, td);
980 * Set the target thread's priority. This routine does not automatically
981 * switch to a higher priority thread, LWKT threads are not designed for
982 * continuous priority changes. Yield if you want to switch.
984 * We have to retain the critical section count which uses the high bits
985 * of the td_pri field. The specified priority may also indicate zero or
986 * more critical sections by adding TDPRI_CRIT*N.
988 * Note that we requeue the thread whether it winds up on a different runq
989 * or not. uio_yield() depends on this and the routine is not normally
990 * called with the same priority otherwise.
993 lwkt_setpri(thread_t td, int pri)
996 KKASSERT(td->td_gd == mycpu);
998 if (td->td_flags & TDF_RUNQ) {
1000 td->td_pri = (td->td_pri & ~TDPRI_MASK) + pri;
1003 td->td_pri = (td->td_pri & ~TDPRI_MASK) + pri;
1009 lwkt_setpri_self(int pri)
1011 thread_t td = curthread;
1013 KKASSERT(pri >= 0 && pri <= TDPRI_MAX);
1015 if (td->td_flags & TDF_RUNQ) {
1017 td->td_pri = (td->td_pri & ~TDPRI_MASK) + pri;
1020 td->td_pri = (td->td_pri & ~TDPRI_MASK) + pri;
1026 * Migrate the current thread to the specified cpu. The BGL must be held
1027 * (for the gd_tdallq manipulation XXX). This is accomplished by
1028 * descheduling ourselves from the current cpu, moving our thread to the
1029 * tdallq of the target cpu, IPI messaging the target cpu, and switching out.
1030 * TDF_MIGRATING prevents scheduling races while the thread is being migrated.
1033 static void lwkt_setcpu_remote(void *arg);
1037 lwkt_setcpu_self(globaldata_t rgd)
1040 thread_t td = curthread;
1042 if (td->td_gd != rgd) {
1043 crit_enter_quick(td);
1044 td->td_flags |= TDF_MIGRATING;
1045 lwkt_deschedule_self(td);
1046 TAILQ_REMOVE(&td->td_gd->gd_tdallq, td, td_allq); /* protected by BGL */
1047 TAILQ_INSERT_TAIL(&rgd->gd_tdallq, td, td_allq); /* protected by BGL */
1048 lwkt_send_ipiq(rgd, (ipifunc_t)lwkt_setcpu_remote, td);
1050 /* we are now on the target cpu */
1051 crit_exit_quick(td);
1057 * Remote IPI for cpu migration (called while in a critical section so we
1058 * do not have to enter another one). The thread has already been moved to
1059 * our cpu's allq, but we must wait for the thread to be completely switched
1060 * out on the originating cpu before we schedule it on ours or the stack
1061 * state may be corrupt. We clear TDF_MIGRATING after flushing the GD
1062 * change to main memory.
1064 * XXX The use of TDF_MIGRATING might not be sufficient to avoid races
1065 * against wakeups. It is best if this interface is used only when there
1066 * are no pending events that might try to schedule the thread.
1070 lwkt_setcpu_remote(void *arg)
1073 globaldata_t gd = mycpu;
1075 while (td->td_flags & TDF_RUNNING)
1079 td->td_flags &= ~TDF_MIGRATING;
1085 lwkt_preempted_proc(void)
1087 thread_t td = curthread;
1088 while (td->td_preempted)
1089 td = td->td_preempted;
1090 return(td->td_proc);
1094 * Block on the specified wait queue until signaled. A generation number
1095 * must be supplied to interlock the wait queue. The function will
1096 * return immediately if the generation number does not match the wait
1097 * structure's generation number.
1100 lwkt_block(lwkt_wait_t w, const char *wmesg, int *gen)
1102 thread_t td = curthread;
1105 lwkt_gettoken(&ilock, &w->wa_token);
1107 if (w->wa_gen == *gen) {
1109 TAILQ_INSERT_TAIL(&w->wa_waitq, td, td_threadq);
1112 td->td_wmesg = wmesg;
1115 if (td->td_wmesg != NULL) {
1122 lwkt_reltoken(&ilock);
1126 * Signal a wait queue. We gain ownership of the wait queue in order to
1127 * signal it. Once a thread is removed from the wait queue we have to
1128 * deal with the cpu owning the thread.
1130 * Note: alternatively we could message the target cpu owning the wait
1131 * queue. YYY implement as sysctl.
1134 lwkt_signal(lwkt_wait_t w, int count)
1139 lwkt_gettoken(&ilock, &w->wa_token);
1143 count = w->wa_count;
1144 while ((td = TAILQ_FIRST(&w->wa_waitq)) != NULL && count) {
1147 TAILQ_REMOVE(&w->wa_waitq, td, td_threadq);
1149 td->td_wmesg = NULL;
1150 if (td->td_gd == mycpu) {
1153 lwkt_send_ipiq(td->td_gd, (ipifunc_t)lwkt_schedule, td);
1157 lwkt_reltoken(&ilock);
1161 * Create a kernel process/thread/whatever. It shares it's address space
1162 * with proc0 - ie: kernel only.
1164 * NOTE! By default new threads are created with the MP lock held. A
1165 * thread which does not require the MP lock should release it by calling
1166 * rel_mplock() at the start of the new thread.
1169 lwkt_create(void (*func)(void *), void *arg,
1170 struct thread **tdp, thread_t template, int tdflags, int cpu,
1171 const char *fmt, ...)
1176 td = lwkt_alloc_thread(template, cpu);
1179 cpu_set_thread_handler(td, lwkt_exit, func, arg);
1180 td->td_flags |= TDF_VERBOSE | tdflags;
1186 * Set up arg0 for 'ps' etc
1188 __va_start(ap, fmt);
1189 vsnprintf(td->td_comm, sizeof(td->td_comm), fmt, ap);
1193 * Schedule the thread to run
1195 if ((td->td_flags & TDF_STOPREQ) == 0)
1198 td->td_flags &= ~TDF_STOPREQ;
1203 * kthread_* is specific to the kernel and is not needed by userland.
1208 * Destroy an LWKT thread. Warning! This function is not called when
1209 * a process exits, cpu_proc_exit() directly calls cpu_thread_exit() and
1210 * uses a different reaping mechanism.
1215 thread_t td = curthread;
1218 if (td->td_flags & TDF_VERBOSE)
1219 printf("kthread %p %s has exited\n", td, td->td_comm);
1221 crit_enter_quick(td);
1222 lwkt_deschedule_self(td);
1224 KKASSERT(gd == td->td_gd);
1225 TAILQ_REMOVE(&gd->gd_tdallq, td, td_allq);
1226 if (td->td_flags & TDF_ALLOCATED_THREAD) {
1227 ++gd->gd_tdfreecount;
1228 TAILQ_INSERT_TAIL(&gd->gd_tdfreeq, td, td_threadq);
1234 * Create a kernel process/thread/whatever. It shares it's address space
1235 * with proc0 - ie: kernel only. 5.x compatible.
1237 * NOTE! By default kthreads are created with the MP lock held. A
1238 * thread which does not require the MP lock should release it by calling
1239 * rel_mplock() at the start of the new thread.
1242 kthread_create(void (*func)(void *), void *arg,
1243 struct thread **tdp, const char *fmt, ...)
1248 td = lwkt_alloc_thread(NULL, -1);
1251 cpu_set_thread_handler(td, kthread_exit, func, arg);
1252 td->td_flags |= TDF_VERBOSE;
1258 * Set up arg0 for 'ps' etc
1260 __va_start(ap, fmt);
1261 vsnprintf(td->td_comm, sizeof(td->td_comm), fmt, ap);
1265 * Schedule the thread to run
1272 * Destroy an LWKT thread. Warning! This function is not called when
1273 * a process exits, cpu_proc_exit() directly calls cpu_thread_exit() and
1274 * uses a different reaping mechanism.
1276 * XXX duplicates lwkt_exit()
1284 #endif /* _KERNEL */
1289 thread_t td = curthread;
1290 int lpri = td->td_pri;
1293 panic("td_pri is/would-go negative! %p %d", td, lpri);