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,
26 * INCIDENTAL, SPECIAL, EXEMPLARY OR CONSEQUENTIAL DAMAGES (INCLUDING,
27 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
28 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
29 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
30 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
31 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
34 * $DragonFly: src/sys/kern/lwkt_thread.c,v 1.72 2005/04/22 17:41:15 joerg 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>
75 #include <sys/stdint.h>
76 #include <libcaps/thread.h>
77 #include <sys/thread.h>
78 #include <sys/msgport.h>
79 #include <sys/errno.h>
80 #include <libcaps/globaldata.h>
81 #include <machine/cpufunc.h>
82 #include <sys/thread2.h>
83 #include <sys/msgport2.h>
87 #include <machine/lock.h>
88 #include <machine/atomic.h>
89 #include <machine/cpu.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 stksize
, 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 flags
= td
->td_flags
& (TDF_ALLOCATED_STACK
|TDF_ALLOCATED_THREAD
);
249 td
= zalloc(thread_zone
);
251 td
= malloc(sizeof(struct thread
));
253 td
->td_kstack
= NULL
;
254 td
->td_kstack_size
= 0;
255 flags
|= TDF_ALLOCATED_THREAD
;
258 if ((stack
= td
->td_kstack
) != NULL
&& td
->td_kstack_size
!= stksize
) {
259 if (flags
& TDF_ALLOCATED_STACK
) {
261 kmem_free(kernel_map
, (vm_offset_t
)stack
, td
->td_kstack_size
);
263 libcaps_free_stack(stack
, td
->td_kstack_size
);
270 stack
= (void *)kmem_alloc(kernel_map
, stksize
);
272 stack
= libcaps_alloc_stack(stksize
);
274 flags
|= TDF_ALLOCATED_STACK
;
277 lwkt_init_thread(td
, stack
, stksize
, flags
, mycpu
);
279 lwkt_init_thread(td
, stack
, stksize
, flags
, globaldata_find(cpu
));
286 * Initialize a preexisting thread structure. This function is used by
287 * lwkt_alloc_thread() and also used to initialize the per-cpu idlethread.
289 * All threads start out in a critical section at a priority of
290 * TDPRI_KERN_DAEMON. Higher level code will modify the priority as
291 * appropriate. This function may send an IPI message when the
292 * requested cpu is not the current cpu and consequently gd_tdallq may
293 * not be initialized synchronously from the point of view of the originating
296 * NOTE! we have to be careful in regards to creating threads for other cpus
297 * if SMP has not yet been activated.
302 lwkt_init_thread_remote(void *arg
)
306 TAILQ_INSERT_TAIL(&td
->td_gd
->gd_tdallq
, td
, td_allq
);
312 lwkt_init_thread(thread_t td
, void *stack
, int stksize
, int flags
,
313 struct globaldata
*gd
)
315 globaldata_t mygd
= mycpu
;
317 bzero(td
, sizeof(struct thread
));
318 td
->td_kstack
= stack
;
319 td
->td_kstack_size
= stksize
;
320 td
->td_flags
|= flags
;
322 td
->td_pri
= TDPRI_KERN_DAEMON
+ TDPRI_CRIT
;
323 lwkt_initport(&td
->td_msgport
, td
);
324 pmap_init_thread(td
);
327 * Normally initializing a thread for a remote cpu requires sending an
328 * IPI. However, the idlethread is setup before the other cpus are
329 * activated so we have to treat it as a special case. XXX manipulation
330 * of gd_tdallq requires the BGL.
332 if (gd
== mygd
|| td
== &gd
->gd_idlethread
) {
334 TAILQ_INSERT_TAIL(&gd
->gd_tdallq
, td
, td_allq
);
337 lwkt_send_ipiq(gd
, lwkt_init_thread_remote
, td
);
341 TAILQ_INSERT_TAIL(&gd
->gd_tdallq
, td
, td_allq
);
349 lwkt_set_comm(thread_t td
, const char *ctl
, ...)
354 vsnprintf(td
->td_comm
, sizeof(td
->td_comm
), ctl
, va
);
359 lwkt_hold(thread_t td
)
365 lwkt_rele(thread_t td
)
367 KKASSERT(td
->td_refs
> 0);
374 lwkt_wait_free(thread_t td
)
377 tsleep(td
, 0, "tdreap", hz
);
383 lwkt_free_thread(thread_t td
)
385 struct globaldata
*gd
= mycpu
;
387 KASSERT((td
->td_flags
& TDF_RUNNING
) == 0,
388 ("lwkt_free_thread: did not exit! %p", td
));
391 TAILQ_REMOVE(&gd
->gd_tdallq
, td
, td_allq
);
392 if (gd
->gd_tdfreecount
< CACHE_NTHREADS
&&
393 (td
->td_flags
& TDF_ALLOCATED_THREAD
)
395 ++gd
->gd_tdfreecount
;
396 TAILQ_INSERT_HEAD(&gd
->gd_tdfreeq
, td
, td_threadq
);
400 if (td
->td_kstack
&& (td
->td_flags
& TDF_ALLOCATED_STACK
)) {
402 kmem_free(kernel_map
, (vm_offset_t
)td
->td_kstack
, td
->td_kstack_size
);
404 libcaps_free_stack(td
->td_kstack
, td
->td_kstack_size
);
407 td
->td_kstack
= NULL
;
408 td
->td_kstack_size
= 0;
410 if (td
->td_flags
& TDF_ALLOCATED_THREAD
) {
412 zfree(thread_zone
, td
);
422 * Switch to the next runnable lwkt. If no LWKTs are runnable then
423 * switch to the idlethread. Switching must occur within a critical
424 * section to avoid races with the scheduling queue.
426 * We always have full control over our cpu's run queue. Other cpus
427 * that wish to manipulate our queue must use the cpu_*msg() calls to
428 * talk to our cpu, so a critical section is all that is needed and
429 * the result is very, very fast thread switching.
431 * The LWKT scheduler uses a fixed priority model and round-robins at
432 * each priority level. User process scheduling is a totally
433 * different beast and LWKT priorities should not be confused with
434 * user process priorities.
436 * The MP lock may be out of sync with the thread's td_mpcount. lwkt_switch()
437 * cleans it up. Note that the td_switch() function cannot do anything that
438 * requires the MP lock since the MP lock will have already been setup for
439 * the target thread (not the current thread). It's nice to have a scheduler
440 * that does not need the MP lock to work because it allows us to do some
441 * really cool high-performance MP lock optimizations.
447 globaldata_t gd
= mycpu
;
448 thread_t td
= gd
->gd_curthread
;
455 * Switching from within a 'fast' (non thread switched) interrupt is
458 if (gd
->gd_intr_nesting_level
&& panicstr
== NULL
) {
459 panic("lwkt_switch: cannot switch from within a fast interrupt, yet");
463 * Passive release (used to transition from user to kernel mode
464 * when we block or switch rather then when we enter the kernel).
465 * This function is NOT called if we are switching into a preemption
466 * or returning from a preemption. Typically this causes us to lose
467 * our current process designation (if we have one) and become a true
468 * LWKT thread, and may also hand the current process designation to
469 * another process and schedule thread.
478 * td_mpcount cannot be used to determine if we currently hold the
479 * MP lock because get_mplock() will increment it prior to attempting
480 * to get the lock, and switch out if it can't. Our ownership of
481 * the actual lock will remain stable while we are in a critical section
482 * (but, of course, another cpu may own or release the lock so the
483 * actual value of mp_lock is not stable).
485 mpheld
= MP_LOCK_HELD();
487 if (td
->td_cscount
) {
488 printf("Diagnostic: attempt to switch while mastering cpusync: %p\n",
490 if (panic_on_cscount
)
491 panic("switching while mastering cpusync");
495 if ((ntd
= td
->td_preempted
) != NULL
) {
497 * We had preempted another thread on this cpu, resume the preempted
498 * thread. This occurs transparently, whether the preempted thread
499 * was scheduled or not (it may have been preempted after descheduling
502 * We have to setup the MP lock for the original thread after backing
503 * out the adjustment that was made to curthread when the original
506 KKASSERT(ntd
->td_flags
& TDF_PREEMPT_LOCK
);
508 if (ntd
->td_mpcount
&& mpheld
== 0) {
509 panic("MPLOCK NOT HELD ON RETURN: %p %p %d %d",
510 td
, ntd
, td
->td_mpcount
, ntd
->td_mpcount
);
512 if (ntd
->td_mpcount
) {
513 td
->td_mpcount
-= ntd
->td_mpcount
;
514 KKASSERT(td
->td_mpcount
>= 0);
517 ntd
->td_flags
|= TDF_PREEMPT_DONE
;
520 * XXX. The interrupt may have woken a thread up, we need to properly
521 * set the reschedule flag if the originally interrupted thread is at
524 if (gd
->gd_runqmask
> (2 << (ntd
->td_pri
& TDPRI_MASK
)) - 1)
526 /* YYY release mp lock on switchback if original doesn't need it */
529 * Priority queue / round-robin at each priority. Note that user
530 * processes run at a fixed, low priority and the user process
531 * scheduler deals with interactions between user processes
532 * by scheduling and descheduling them from the LWKT queue as
535 * We have to adjust the MP lock for the target thread. If we
536 * need the MP lock and cannot obtain it we try to locate a
537 * thread that does not need the MP lock. If we cannot, we spin
540 * A similar issue exists for the tokens held by the target thread.
541 * If we cannot obtain ownership of the tokens we cannot immediately
542 * schedule the thread.
546 * We are switching threads. If there are any pending requests for
547 * tokens we can satisfy all of them here.
550 if (gd
->gd_tokreqbase
)
551 lwkt_drain_token_requests();
555 * If an LWKT reschedule was requested, well that is what we are
556 * doing now so clear it.
558 clear_lwkt_resched();
560 if (gd
->gd_runqmask
) {
561 int nq
= bsrl(gd
->gd_runqmask
);
562 if ((ntd
= TAILQ_FIRST(&gd
->gd_tdrunq
[nq
])) == NULL
) {
563 gd
->gd_runqmask
&= ~(1 << nq
);
568 * If the target needs the MP lock and we couldn't get it,
569 * or if the target is holding tokens and we could not
570 * gain ownership of the tokens, continue looking for a
571 * thread to schedule and spin instead of HLT if we can't.
573 if ((ntd
->td_mpcount
&& mpheld
== 0 && !cpu_try_mplock()) ||
574 (ntd
->td_toks
&& lwkt_chktokens(ntd
) == 0)
576 u_int32_t rqmask
= gd
->gd_runqmask
;
578 TAILQ_FOREACH(ntd
, &gd
->gd_tdrunq
[nq
], td_threadq
) {
579 if (ntd
->td_mpcount
&& !mpheld
&& !cpu_try_mplock())
581 mpheld
= MP_LOCK_HELD();
582 if (ntd
->td_toks
&& !lwkt_chktokens(ntd
))
588 rqmask
&= ~(1 << nq
);
592 ntd
= &gd
->gd_idlethread
;
593 ntd
->td_flags
|= TDF_IDLE_NOHLT
;
595 TAILQ_REMOVE(&gd
->gd_tdrunq
[nq
], ntd
, td_threadq
);
596 TAILQ_INSERT_TAIL(&gd
->gd_tdrunq
[nq
], ntd
, td_threadq
);
599 TAILQ_REMOVE(&gd
->gd_tdrunq
[nq
], ntd
, td_threadq
);
600 TAILQ_INSERT_TAIL(&gd
->gd_tdrunq
[nq
], ntd
, td_threadq
);
603 TAILQ_REMOVE(&gd
->gd_tdrunq
[nq
], ntd
, td_threadq
);
604 TAILQ_INSERT_TAIL(&gd
->gd_tdrunq
[nq
], ntd
, td_threadq
);
608 * We have nothing to run but only let the idle loop halt
609 * the cpu if there are no pending interrupts.
611 ntd
= &gd
->gd_idlethread
;
612 if (gd
->gd_reqflags
& RQF_IDLECHECK_MASK
)
613 ntd
->td_flags
|= TDF_IDLE_NOHLT
;
616 KASSERT(ntd
->td_pri
>= TDPRI_CRIT
,
617 ("priority problem in lwkt_switch %d %d", td
->td_pri
, ntd
->td_pri
));
620 * Do the actual switch. If the new target does not need the MP lock
621 * and we are holding it, release the MP lock. If the new target requires
622 * the MP lock we have already acquired it for the target.
625 if (ntd
->td_mpcount
== 0 ) {
629 ASSERT_MP_LOCK_HELD();
636 /* NOTE: current cpu may have changed after switch */
641 * Request that the target thread preempt the current thread. Preemption
642 * only works under a specific set of conditions:
644 * - We are not preempting ourselves
645 * - The target thread is owned by the current cpu
646 * - We are not currently being preempted
647 * - The target is not currently being preempted
648 * - We are able to satisfy the target's MP lock requirements (if any).
650 * THE CALLER OF LWKT_PREEMPT() MUST BE IN A CRITICAL SECTION. Typically
651 * this is called via lwkt_schedule() through the td_preemptable callback.
652 * critpri is the managed critical priority that we should ignore in order
653 * to determine whether preemption is possible (aka usually just the crit
654 * priority of lwkt_schedule() itself).
656 * XXX at the moment we run the target thread in a critical section during
657 * the preemption in order to prevent the target from taking interrupts
658 * that *WE* can't. Preemption is strictly limited to interrupt threads
659 * and interrupt-like threads, outside of a critical section, and the
660 * preempted source thread will be resumed the instant the target blocks
661 * whether or not the source is scheduled (i.e. preemption is supposed to
662 * be as transparent as possible).
664 * The target thread inherits our MP count (added to its own) for the
665 * duration of the preemption in order to preserve the atomicy of the
666 * MP lock during the preemption. Therefore, any preempting targets must be
667 * careful in regards to MP assertions. Note that the MP count may be
668 * out of sync with the physical mp_lock, but we do not have to preserve
669 * the original ownership of the lock if it was out of synch (that is, we
670 * can leave it synchronized on return).
673 lwkt_preempt(thread_t ntd
, int critpri
)
675 struct globaldata
*gd
= mycpu
;
683 * The caller has put us in a critical section. We can only preempt
684 * if the caller of the caller was not in a critical section (basically
685 * a local interrupt), as determined by the 'critpri' parameter.
687 * YYY The target thread must be in a critical section (else it must
688 * inherit our critical section? I dunno yet).
690 * Any tokens held by the target may not be held by thread(s) being
691 * preempted. We take the easy way out and do not preempt if
692 * the target is holding tokens.
694 * Set need_lwkt_resched() unconditionally for now YYY.
696 KASSERT(ntd
->td_pri
>= TDPRI_CRIT
, ("BADCRIT0 %d", ntd
->td_pri
));
698 td
= gd
->gd_curthread
;
699 if ((ntd
->td_pri
& TDPRI_MASK
) <= (td
->td_pri
& TDPRI_MASK
)) {
703 if ((td
->td_pri
& ~TDPRI_MASK
) > critpri
) {
709 if (ntd
->td_gd
!= gd
) {
716 * Take the easy way out and do not preempt if the target is holding
717 * one or more tokens. We could test whether the thread(s) being
718 * preempted interlock against the target thread's tokens and whether
719 * we can get all the target thread's tokens, but this situation
720 * should not occur very often so its easier to simply not preempt.
722 if (ntd
->td_toks
!= NULL
) {
727 if (td
== ntd
|| ((td
->td_flags
| ntd
->td_flags
) & TDF_PREEMPT_LOCK
)) {
732 if (ntd
->td_preempted
) {
739 * note: an interrupt might have occured just as we were transitioning
740 * to or from the MP lock. In this case td_mpcount will be pre-disposed
741 * (non-zero) but not actually synchronized with the actual state of the
742 * lock. We can use it to imply an MP lock requirement for the
743 * preemption but we cannot use it to test whether we hold the MP lock
746 savecnt
= td
->td_mpcount
;
747 mpheld
= MP_LOCK_HELD();
748 ntd
->td_mpcount
+= td
->td_mpcount
;
749 if (mpheld
== 0 && ntd
->td_mpcount
&& !cpu_try_mplock()) {
750 ntd
->td_mpcount
-= td
->td_mpcount
;
758 * Since we are able to preempt the current thread, there is no need to
759 * call need_lwkt_resched().
762 ntd
->td_preempted
= td
;
763 td
->td_flags
|= TDF_PREEMPT_LOCK
;
765 KKASSERT(ntd
->td_preempted
&& (td
->td_flags
& TDF_PREEMPT_DONE
));
767 KKASSERT(savecnt
== td
->td_mpcount
);
768 mpheld
= MP_LOCK_HELD();
769 if (mpheld
&& td
->td_mpcount
== 0)
771 else if (mpheld
== 0 && td
->td_mpcount
)
772 panic("lwkt_preempt(): MP lock was not held through");
774 ntd
->td_preempted
= NULL
;
775 td
->td_flags
&= ~(TDF_PREEMPT_LOCK
|TDF_PREEMPT_DONE
);
779 * Yield our thread while higher priority threads are pending. This is
780 * typically called when we leave a critical section but it can be safely
781 * called while we are in a critical section.
783 * This function will not generally yield to equal priority threads but it
784 * can occur as a side effect. Note that lwkt_switch() is called from
785 * inside the critical section to prevent its own crit_exit() from reentering
786 * lwkt_yield_quick().
788 * gd_reqflags indicates that *something* changed, e.g. an interrupt or softint
789 * came along but was blocked and made pending.
791 * (self contained on a per cpu basis)
794 lwkt_yield_quick(void)
796 globaldata_t gd
= mycpu
;
797 thread_t td
= gd
->gd_curthread
;
800 * gd_reqflags is cleared in splz if the cpl is 0. If we were to clear
801 * it with a non-zero cpl then we might not wind up calling splz after
802 * a task switch when the critical section is exited even though the
803 * new task could accept the interrupt.
805 * XXX from crit_exit() only called after last crit section is released.
806 * If called directly will run splz() even if in a critical section.
808 * td_nest_count prevent deep nesting via splz() or doreti(). Note that
809 * except for this special case, we MUST call splz() here to handle any
810 * pending ints, particularly after we switch, or we might accidently
811 * halt the cpu with interrupts pending.
813 if (gd
->gd_reqflags
&& td
->td_nest_count
< 2)
817 * YYY enabling will cause wakeup() to task-switch, which really
818 * confused the old 4.x code. This is a good way to simulate
819 * preemption and MP without actually doing preemption or MP, because a
820 * lot of code assumes that wakeup() does not block.
822 if (untimely_switch
&& td
->td_nest_count
== 0 &&
823 gd
->gd_intr_nesting_level
== 0
825 crit_enter_quick(td
);
827 * YYY temporary hacks until we disassociate the userland scheduler
828 * from the LWKT scheduler.
830 if (td
->td_flags
& TDF_RUNQ
) {
831 lwkt_switch(); /* will not reenter yield function */
833 lwkt_schedule_self(td
); /* make sure we are scheduled */
834 lwkt_switch(); /* will not reenter yield function */
835 lwkt_deschedule_self(td
); /* make sure we are descheduled */
837 crit_exit_noyield(td
);
842 * This implements a normal yield which, unlike _quick, will yield to equal
843 * priority threads as well. Note that gd_reqflags tests will be handled by
844 * the crit_exit() call in lwkt_switch().
846 * (self contained on a per cpu basis)
851 lwkt_schedule_self(curthread
);
856 * Generic schedule. Possibly schedule threads belonging to other cpus and
857 * deal with threads that might be blocked on a wait queue.
859 * We have a little helper inline function which does additional work after
860 * the thread has been enqueued, including dealing with preemption and
861 * setting need_lwkt_resched() (which prevents the kernel from returning
862 * to userland until it has processed higher priority threads).
866 _lwkt_schedule_post(globaldata_t gd
, thread_t ntd
, int cpri
)
868 if (ntd
->td_preemptable
) {
869 ntd
->td_preemptable(ntd
, cpri
); /* YYY +token */
870 } else if ((ntd
->td_flags
& TDF_NORESCHED
) == 0 &&
871 (ntd
->td_pri
& TDPRI_MASK
) > (gd
->gd_curthread
->td_pri
& TDPRI_MASK
)
878 lwkt_schedule(thread_t td
)
880 globaldata_t mygd
= mycpu
;
883 KASSERT(td
!= &td
->td_gd
->gd_idlethread
, ("lwkt_schedule(): scheduling gd_idlethread is illegal!"));
884 if ((td
->td_flags
& TDF_PREEMPT_LOCK
) == 0 && td
->td_proc
885 && td
->td_proc
->p_stat
== SSLEEP
887 printf("PANIC schedule curtd = %p (%d %d) target %p (%d %d)\n",
889 curthread
->td_proc
? curthread
->td_proc
->p_pid
: -1,
890 curthread
->td_proc
? curthread
->td_proc
->p_stat
: -1,
892 td
->td_proc
? curthread
->td_proc
->p_pid
: -1,
893 td
->td_proc
? curthread
->td_proc
->p_stat
: -1
895 panic("SCHED PANIC");
899 if (td
== mygd
->gd_curthread
) {
905 * If the thread is on a wait list we have to send our scheduling
906 * request to the owner of the wait structure. Otherwise we send
907 * the scheduling request to the cpu owning the thread. Races
908 * are ok, the target will forward the message as necessary (the
909 * message may chase the thread around before it finally gets
912 * (remember, wait structures use stable storage)
914 * NOTE: tokens no longer enter a critical section, so we only need
915 * to account for the crit_enter() above when calling
916 * _lwkt_schedule_post().
918 if ((w
= td
->td_wait
) != NULL
) {
921 if (lwkt_trytoken(&wref
, &w
->wa_token
)) {
922 TAILQ_REMOVE(&w
->wa_waitq
, td
, td_threadq
);
926 if (td
->td_gd
== mygd
) {
928 _lwkt_schedule_post(mygd
, td
, TDPRI_CRIT
);
930 lwkt_send_ipiq(td
->td_gd
, (ipifunc_t
)lwkt_schedule
, td
);
934 _lwkt_schedule_post(mygd
, td
, TDPRI_CRIT
);
936 lwkt_reltoken(&wref
);
938 lwkt_send_ipiq(w
->wa_token
.t_cpu
, (ipifunc_t
)lwkt_schedule
, td
);
942 * If the wait structure is NULL and we own the thread, there
943 * is no race (since we are in a critical section). If we
944 * do not own the thread there might be a race but the
945 * target cpu will deal with it.
948 if (td
->td_gd
== mygd
) {
950 _lwkt_schedule_post(mygd
, td
, TDPRI_CRIT
);
952 lwkt_send_ipiq(td
->td_gd
, (ipifunc_t
)lwkt_schedule
, td
);
956 _lwkt_schedule_post(mygd
, td
, TDPRI_CRIT
);
964 * Managed acquisition. This code assumes that the MP lock is held for
965 * the tdallq operation and that the thread has been descheduled from its
966 * original cpu. We also have to wait for the thread to be entirely switched
967 * out on its original cpu (this is usually fast enough that we never loop)
968 * since the LWKT system does not have to hold the MP lock while switching
969 * and the target may have released it before switching.
972 lwkt_acquire(thread_t td
)
979 KKASSERT((td
->td_flags
& TDF_RUNQ
) == 0);
980 while (td
->td_flags
& TDF_RUNNING
) /* XXX spin */
984 TAILQ_REMOVE(&gd
->gd_tdallq
, td
, td_allq
); /* protected by BGL */
986 TAILQ_INSERT_TAIL(&mygd
->gd_tdallq
, td
, td_allq
); /* protected by BGL */
992 * Generic deschedule. Descheduling threads other then your own should be
993 * done only in carefully controlled circumstances. Descheduling is
996 * This function may block if the cpu has run out of messages.
999 lwkt_deschedule(thread_t td
)
1002 if (td
== curthread
) {
1005 if (td
->td_gd
== mycpu
) {
1008 lwkt_send_ipiq(td
->td_gd
, (ipifunc_t
)lwkt_deschedule
, td
);
1015 * Set the target thread's priority. This routine does not automatically
1016 * switch to a higher priority thread, LWKT threads are not designed for
1017 * continuous priority changes. Yield if you want to switch.
1019 * We have to retain the critical section count which uses the high bits
1020 * of the td_pri field. The specified priority may also indicate zero or
1021 * more critical sections by adding TDPRI_CRIT*N.
1023 * Note that we requeue the thread whether it winds up on a different runq
1024 * or not. uio_yield() depends on this and the routine is not normally
1025 * called with the same priority otherwise.
1028 lwkt_setpri(thread_t td
, int pri
)
1031 KKASSERT(td
->td_gd
== mycpu
);
1033 if (td
->td_flags
& TDF_RUNQ
) {
1035 td
->td_pri
= (td
->td_pri
& ~TDPRI_MASK
) + pri
;
1038 td
->td_pri
= (td
->td_pri
& ~TDPRI_MASK
) + pri
;
1044 lwkt_setpri_self(int pri
)
1046 thread_t td
= curthread
;
1048 KKASSERT(pri
>= 0 && pri
<= TDPRI_MAX
);
1050 if (td
->td_flags
& TDF_RUNQ
) {
1052 td
->td_pri
= (td
->td_pri
& ~TDPRI_MASK
) + pri
;
1055 td
->td_pri
= (td
->td_pri
& ~TDPRI_MASK
) + pri
;
1061 * Determine if there is a runnable thread at a higher priority then
1062 * the current thread. lwkt_setpri() does not check this automatically.
1063 * Return 1 if there is, 0 if there isn't.
1065 * Example: if bit 31 of runqmask is set and the current thread is priority
1066 * 30, then we wind up checking the mask: 0x80000000 against 0x7fffffff.
1068 * If nq reaches 31 the shift operation will overflow to 0 and we will wind
1069 * up comparing against 0xffffffff, a comparison that will always be false.
1072 lwkt_checkpri_self(void)
1074 globaldata_t gd
= mycpu
;
1075 thread_t td
= gd
->gd_curthread
;
1076 int nq
= td
->td_pri
& TDPRI_MASK
;
1078 while (gd
->gd_runqmask
> (__uint32_t
)(2 << nq
) - 1) {
1079 if (TAILQ_FIRST(&gd
->gd_tdrunq
[nq
+ 1]))
1087 * Migrate the current thread to the specified cpu. The BGL must be held
1088 * (for the gd_tdallq manipulation XXX). This is accomplished by
1089 * descheduling ourselves from the current cpu, moving our thread to the
1090 * tdallq of the target cpu, IPI messaging the target cpu, and switching out.
1091 * TDF_MIGRATING prevents scheduling races while the thread is being migrated.
1094 static void lwkt_setcpu_remote(void *arg
);
1098 lwkt_setcpu_self(globaldata_t rgd
)
1101 thread_t td
= curthread
;
1103 if (td
->td_gd
!= rgd
) {
1104 crit_enter_quick(td
);
1105 td
->td_flags
|= TDF_MIGRATING
;
1106 lwkt_deschedule_self(td
);
1107 TAILQ_REMOVE(&td
->td_gd
->gd_tdallq
, td
, td_allq
); /* protected by BGL */
1108 TAILQ_INSERT_TAIL(&rgd
->gd_tdallq
, td
, td_allq
); /* protected by BGL */
1109 lwkt_send_ipiq(rgd
, (ipifunc_t
)lwkt_setcpu_remote
, td
);
1111 /* we are now on the target cpu */
1112 crit_exit_quick(td
);
1119 * Remote IPI for cpu migration (called while in a critical section so we
1120 * do not have to enter another one). The thread has already been moved to
1121 * our cpu's allq, but we must wait for the thread to be completely switched
1122 * out on the originating cpu before we schedule it on ours or the stack
1123 * state may be corrupt. We clear TDF_MIGRATING after flushing the GD
1124 * change to main memory.
1126 * XXX The use of TDF_MIGRATING might not be sufficient to avoid races
1127 * against wakeups. It is best if this interface is used only when there
1128 * are no pending events that might try to schedule the thread.
1132 lwkt_setcpu_remote(void *arg
)
1135 globaldata_t gd
= mycpu
;
1137 while (td
->td_flags
& TDF_RUNNING
)
1141 td
->td_flags
&= ~TDF_MIGRATING
;
1147 lwkt_preempted_proc(void)
1149 thread_t td
= curthread
;
1150 while (td
->td_preempted
)
1151 td
= td
->td_preempted
;
1152 return(td
->td_proc
);
1156 * Block on the specified wait queue until signaled. A generation number
1157 * must be supplied to interlock the wait queue. The function will
1158 * return immediately if the generation number does not match the wait
1159 * structure's generation number.
1162 lwkt_block(lwkt_wait_t w
, const char *wmesg
, int *gen
)
1164 thread_t td
= curthread
;
1167 lwkt_gettoken(&ilock
, &w
->wa_token
);
1169 if (w
->wa_gen
== *gen
) {
1171 TAILQ_INSERT_TAIL(&w
->wa_waitq
, td
, td_threadq
);
1174 td
->td_wmesg
= wmesg
;
1177 if (td
->td_wmesg
!= NULL
) {
1184 lwkt_reltoken(&ilock
);
1188 * Signal a wait queue. We gain ownership of the wait queue in order to
1189 * signal it. Once a thread is removed from the wait queue we have to
1190 * deal with the cpu owning the thread.
1192 * Note: alternatively we could message the target cpu owning the wait
1193 * queue. YYY implement as sysctl.
1196 lwkt_signal(lwkt_wait_t w
, int count
)
1201 lwkt_gettoken(&ilock
, &w
->wa_token
);
1205 count
= w
->wa_count
;
1206 while ((td
= TAILQ_FIRST(&w
->wa_waitq
)) != NULL
&& count
) {
1209 TAILQ_REMOVE(&w
->wa_waitq
, td
, td_threadq
);
1211 td
->td_wmesg
= NULL
;
1212 if (td
->td_gd
== mycpu
) {
1215 lwkt_send_ipiq(td
->td_gd
, (ipifunc_t
)lwkt_schedule
, td
);
1219 lwkt_reltoken(&ilock
);
1223 * Create a kernel process/thread/whatever. It shares it's address space
1224 * with proc0 - ie: kernel only.
1226 * NOTE! By default new threads are created with the MP lock held. A
1227 * thread which does not require the MP lock should release it by calling
1228 * rel_mplock() at the start of the new thread.
1231 lwkt_create(void (*func
)(void *), void *arg
,
1232 struct thread
**tdp
, thread_t
template, int tdflags
, int cpu
,
1233 const char *fmt
, ...)
1238 td
= lwkt_alloc_thread(template, LWKT_THREAD_STACK
, cpu
);
1241 cpu_set_thread_handler(td
, lwkt_exit
, func
, arg
);
1242 td
->td_flags
|= TDF_VERBOSE
| tdflags
;
1248 * Set up arg0 for 'ps' etc
1250 __va_start(ap
, fmt
);
1251 vsnprintf(td
->td_comm
, sizeof(td
->td_comm
), fmt
, ap
);
1255 * Schedule the thread to run
1257 if ((td
->td_flags
& TDF_STOPREQ
) == 0)
1260 td
->td_flags
&= ~TDF_STOPREQ
;
1265 * kthread_* is specific to the kernel and is not needed by userland.
1270 * Destroy an LWKT thread. Warning! This function is not called when
1271 * a process exits, cpu_proc_exit() directly calls cpu_thread_exit() and
1272 * uses a different reaping mechanism.
1277 thread_t td
= curthread
;
1280 if (td
->td_flags
& TDF_VERBOSE
)
1281 printf("kthread %p %s has exited\n", td
, td
->td_comm
);
1283 crit_enter_quick(td
);
1284 lwkt_deschedule_self(td
);
1286 KKASSERT(gd
== td
->td_gd
);
1287 TAILQ_REMOVE(&gd
->gd_tdallq
, td
, td_allq
);
1288 if (td
->td_flags
& TDF_ALLOCATED_THREAD
) {
1289 ++gd
->gd_tdfreecount
;
1290 TAILQ_INSERT_TAIL(&gd
->gd_tdfreeq
, td
, td_threadq
);
1295 #endif /* _KERNEL */
1300 thread_t td
= curthread
;
1301 int lpri
= td
->td_pri
;
1304 panic("td_pri is/would-go negative! %p %d", td
, lpri
);