2 * Copyright (c) 2003-2010 The DragonFly Project. All rights reserved.
4 * This code is derived from software contributed to The DragonFly Project
5 * by Matthew Dillon <dillon@backplane.com>
7 * Redistribution and use in source and binary forms, with or without
8 * modification, are permitted provided that the following conditions
11 * 1. Redistributions of source code must retain the above copyright
12 * notice, this list of conditions and the following disclaimer.
13 * 2. Redistributions in binary form must reproduce the above copyright
14 * notice, this list of conditions and the following disclaimer in
15 * the documentation and/or other materials provided with the
17 * 3. Neither the name of The DragonFly Project nor the names of its
18 * contributors may be used to endorse or promote products derived
19 * from this software without specific, prior written permission.
21 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
22 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
23 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
24 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
25 * COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
26 * INCIDENTAL, SPECIAL, EXEMPLARY OR CONSEQUENTIAL DAMAGES (INCLUDING,
27 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
28 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
29 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
30 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
31 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
36 * Each cpu in a system has its own self-contained light weight kernel
37 * thread scheduler, which means that generally speaking we only need
38 * to use a critical section to avoid problems. Foreign thread
39 * scheduling is queued via (async) IPIs.
42 #include <sys/param.h>
43 #include <sys/systm.h>
44 #include <sys/kernel.h>
46 #include <sys/rtprio.h>
47 #include <sys/kinfo.h>
48 #include <sys/queue.h>
49 #include <sys/sysctl.h>
50 #include <sys/kthread.h>
51 #include <machine/cpu.h>
54 #include <sys/spinlock.h>
57 #include <sys/thread2.h>
58 #include <sys/spinlock2.h>
59 #include <sys/mplock2.h>
61 #include <sys/dsched.h>
64 #include <vm/vm_param.h>
65 #include <vm/vm_kern.h>
66 #include <vm/vm_object.h>
67 #include <vm/vm_page.h>
68 #include <vm/vm_map.h>
69 #include <vm/vm_pager.h>
70 #include <vm/vm_extern.h>
72 #include <machine/stdarg.h>
73 #include <machine/smp.h>
75 #if !defined(KTR_CTXSW)
76 #define KTR_CTXSW KTR_ALL
78 KTR_INFO_MASTER(ctxsw
);
79 KTR_INFO(KTR_CTXSW
, ctxsw
, sw
, 0, "#cpu[%d].td = %p",
80 sizeof(int) + sizeof(struct thread
*));
81 KTR_INFO(KTR_CTXSW
, ctxsw
, pre
, 1, "#cpu[%d].td = %p",
82 sizeof(int) + sizeof(struct thread
*));
83 KTR_INFO(KTR_CTXSW
, ctxsw
, newtd
, 2, "#threads[%p].name = %s",
84 sizeof (struct thread
*) + sizeof(char *));
85 KTR_INFO(KTR_CTXSW
, ctxsw
, deadtd
, 3, "#threads[%p].name = <dead>", sizeof (struct thread
*));
87 static MALLOC_DEFINE(M_THREAD
, "thread", "lwkt threads");
90 static int panic_on_cscount
= 0;
92 static __int64_t switch_count
= 0;
93 static __int64_t preempt_hit
= 0;
94 static __int64_t preempt_miss
= 0;
95 static __int64_t preempt_weird
= 0;
96 static __int64_t token_contention_count __debugvar
= 0;
97 static int lwkt_use_spin_port
;
98 static struct objcache
*thread_cache
;
101 static void lwkt_schedule_remote(void *arg
, int arg2
, struct intrframe
*frame
);
103 static void lwkt_fairq_accumulate(globaldata_t gd
, thread_t td
);
105 extern void cpu_heavy_restore(void);
106 extern void cpu_lwkt_restore(void);
107 extern void cpu_kthread_restore(void);
108 extern void cpu_idle_restore(void);
113 jg_tos_ok(struct thread
*td
)
121 KKASSERT(td
->td_sp
!= NULL
);
122 tos
= ((void **)td
->td_sp
)[0];
124 if ((tos
== cpu_heavy_restore
) || (tos
== cpu_lwkt_restore
) ||
125 (tos
== cpu_kthread_restore
) || (tos
== cpu_idle_restore
)) {
134 * We can make all thread ports use the spin backend instead of the thread
135 * backend. This should only be set to debug the spin backend.
137 TUNABLE_INT("lwkt.use_spin_port", &lwkt_use_spin_port
);
140 SYSCTL_INT(_lwkt
, OID_AUTO
, panic_on_cscount
, CTLFLAG_RW
, &panic_on_cscount
, 0, "");
142 SYSCTL_QUAD(_lwkt
, OID_AUTO
, switch_count
, CTLFLAG_RW
, &switch_count
, 0, "");
143 SYSCTL_QUAD(_lwkt
, OID_AUTO
, preempt_hit
, CTLFLAG_RW
, &preempt_hit
, 0,
144 "Successful preemption events");
145 SYSCTL_QUAD(_lwkt
, OID_AUTO
, preempt_miss
, CTLFLAG_RW
, &preempt_miss
, 0,
146 "Failed preemption events");
147 SYSCTL_QUAD(_lwkt
, OID_AUTO
, preempt_weird
, CTLFLAG_RW
, &preempt_weird
, 0, "");
149 SYSCTL_QUAD(_lwkt
, OID_AUTO
, token_contention_count
, CTLFLAG_RW
,
150 &token_contention_count
, 0, "spinning due to token contention");
152 static int fairq_enable
= 1;
153 SYSCTL_INT(_lwkt
, OID_AUTO
, fairq_enable
, CTLFLAG_RW
, &fairq_enable
, 0, "");
154 static int user_pri_sched
= 0;
155 SYSCTL_INT(_lwkt
, OID_AUTO
, user_pri_sched
, CTLFLAG_RW
, &user_pri_sched
, 0, "");
158 * These helper procedures handle the runq, they can only be called from
159 * within a critical section.
161 * WARNING! Prior to SMP being brought up it is possible to enqueue and
162 * dequeue threads belonging to other cpus, so be sure to use td->td_gd
163 * instead of 'mycpu' when referencing the globaldata structure. Once
164 * SMP live enqueuing and dequeueing only occurs on the current cpu.
168 _lwkt_dequeue(thread_t td
)
170 if (td
->td_flags
& TDF_RUNQ
) {
171 struct globaldata
*gd
= td
->td_gd
;
173 td
->td_flags
&= ~TDF_RUNQ
;
174 TAILQ_REMOVE(&gd
->gd_tdrunq
, td
, td_threadq
);
175 gd
->gd_fairq_total_pri
-= td
->td_pri
;
176 if (TAILQ_FIRST(&gd
->gd_tdrunq
) == NULL
)
177 atomic_clear_int_nonlocked(&gd
->gd_reqflags
, RQF_RUNNING
);
184 * NOTE: There are a limited number of lwkt threads runnable since user
185 * processes only schedule one at a time per cpu.
189 _lwkt_enqueue(thread_t td
)
193 if ((td
->td_flags
& (TDF_RUNQ
|TDF_MIGRATING
|TDF_BLOCKQ
)) == 0) {
194 struct globaldata
*gd
= td
->td_gd
;
196 td
->td_flags
|= TDF_RUNQ
;
197 xtd
= TAILQ_FIRST(&gd
->gd_tdrunq
);
199 TAILQ_INSERT_TAIL(&gd
->gd_tdrunq
, td
, td_threadq
);
200 atomic_set_int_nonlocked(&gd
->gd_reqflags
, RQF_RUNNING
);
202 while (xtd
&& xtd
->td_pri
> td
->td_pri
)
203 xtd
= TAILQ_NEXT(xtd
, td_threadq
);
205 TAILQ_INSERT_BEFORE(xtd
, td
, td_threadq
);
207 TAILQ_INSERT_TAIL(&gd
->gd_tdrunq
, td
, td_threadq
);
209 gd
->gd_fairq_total_pri
+= td
->td_pri
;
214 _lwkt_thread_ctor(void *obj
, void *privdata
, int ocflags
)
216 struct thread
*td
= (struct thread
*)obj
;
218 td
->td_kstack
= NULL
;
219 td
->td_kstack_size
= 0;
220 td
->td_flags
= TDF_ALLOCATED_THREAD
;
225 _lwkt_thread_dtor(void *obj
, void *privdata
)
227 struct thread
*td
= (struct thread
*)obj
;
229 KASSERT(td
->td_flags
& TDF_ALLOCATED_THREAD
,
230 ("_lwkt_thread_dtor: not allocated from objcache"));
231 KASSERT((td
->td_flags
& TDF_ALLOCATED_STACK
) && td
->td_kstack
&&
232 td
->td_kstack_size
> 0,
233 ("_lwkt_thread_dtor: corrupted stack"));
234 kmem_free(&kernel_map
, (vm_offset_t
)td
->td_kstack
, td
->td_kstack_size
);
238 * Initialize the lwkt s/system.
243 /* An objcache has 2 magazines per CPU so divide cache size by 2. */
244 thread_cache
= objcache_create_mbacked(M_THREAD
, sizeof(struct thread
),
245 NULL
, CACHE_NTHREADS
/2,
246 _lwkt_thread_ctor
, _lwkt_thread_dtor
, NULL
);
250 * Schedule a thread to run. As the current thread we can always safely
251 * schedule ourselves, and a shortcut procedure is provided for that
254 * (non-blocking, self contained on a per cpu basis)
257 lwkt_schedule_self(thread_t td
)
259 crit_enter_quick(td
);
260 KASSERT(td
!= &td
->td_gd
->gd_idlethread
,
261 ("lwkt_schedule_self(): scheduling gd_idlethread is illegal!"));
262 KKASSERT(td
->td_lwp
== NULL
|| (td
->td_lwp
->lwp_flag
& LWP_ONRUNQ
) == 0);
268 * Deschedule a thread.
270 * (non-blocking, self contained on a per cpu basis)
273 lwkt_deschedule_self(thread_t td
)
275 crit_enter_quick(td
);
281 * LWKTs operate on a per-cpu basis
283 * WARNING! Called from early boot, 'mycpu' may not work yet.
286 lwkt_gdinit(struct globaldata
*gd
)
288 TAILQ_INIT(&gd
->gd_tdrunq
);
289 TAILQ_INIT(&gd
->gd_tdallq
);
293 * Create a new thread. The thread must be associated with a process context
294 * or LWKT start address before it can be scheduled. If the target cpu is
295 * -1 the thread will be created on the current cpu.
297 * If you intend to create a thread without a process context this function
298 * does everything except load the startup and switcher function.
301 lwkt_alloc_thread(struct thread
*td
, int stksize
, int cpu
, int flags
)
303 globaldata_t gd
= mycpu
;
307 * If static thread storage is not supplied allocate a thread. Reuse
308 * a cached free thread if possible. gd_freetd is used to keep an exiting
309 * thread intact through the exit.
312 if ((td
= gd
->gd_freetd
) != NULL
)
313 gd
->gd_freetd
= NULL
;
315 td
= objcache_get(thread_cache
, M_WAITOK
);
316 KASSERT((td
->td_flags
&
317 (TDF_ALLOCATED_THREAD
|TDF_RUNNING
)) == TDF_ALLOCATED_THREAD
,
318 ("lwkt_alloc_thread: corrupted td flags 0x%X", td
->td_flags
));
319 flags
|= td
->td_flags
& (TDF_ALLOCATED_THREAD
|TDF_ALLOCATED_STACK
);
323 * Try to reuse cached stack.
325 if ((stack
= td
->td_kstack
) != NULL
&& td
->td_kstack_size
!= stksize
) {
326 if (flags
& TDF_ALLOCATED_STACK
) {
327 kmem_free(&kernel_map
, (vm_offset_t
)stack
, td
->td_kstack_size
);
332 stack
= (void *)kmem_alloc(&kernel_map
, stksize
);
333 flags
|= TDF_ALLOCATED_STACK
;
336 lwkt_init_thread(td
, stack
, stksize
, flags
, gd
);
338 lwkt_init_thread(td
, stack
, stksize
, flags
, globaldata_find(cpu
));
343 * Initialize a preexisting thread structure. This function is used by
344 * lwkt_alloc_thread() and also used to initialize the per-cpu idlethread.
346 * All threads start out in a critical section at a priority of
347 * TDPRI_KERN_DAEMON. Higher level code will modify the priority as
348 * appropriate. This function may send an IPI message when the
349 * requested cpu is not the current cpu and consequently gd_tdallq may
350 * not be initialized synchronously from the point of view of the originating
353 * NOTE! we have to be careful in regards to creating threads for other cpus
354 * if SMP has not yet been activated.
359 lwkt_init_thread_remote(void *arg
)
364 * Protected by critical section held by IPI dispatch
366 TAILQ_INSERT_TAIL(&td
->td_gd
->gd_tdallq
, td
, td_allq
);
372 * lwkt core thread structural initialization.
374 * NOTE: All threads are initialized as mpsafe threads.
377 lwkt_init_thread(thread_t td
, void *stack
, int stksize
, int flags
,
378 struct globaldata
*gd
)
380 globaldata_t mygd
= mycpu
;
382 bzero(td
, sizeof(struct thread
));
383 td
->td_kstack
= stack
;
384 td
->td_kstack_size
= stksize
;
385 td
->td_flags
= flags
;
387 td
->td_pri
= TDPRI_KERN_DAEMON
;
388 td
->td_critcount
= 1;
389 td
->td_toks_stop
= &td
->td_toks_base
;
390 if (lwkt_use_spin_port
)
391 lwkt_initport_spin(&td
->td_msgport
);
393 lwkt_initport_thread(&td
->td_msgport
, td
);
394 pmap_init_thread(td
);
397 * Normally initializing a thread for a remote cpu requires sending an
398 * IPI. However, the idlethread is setup before the other cpus are
399 * activated so we have to treat it as a special case. XXX manipulation
400 * of gd_tdallq requires the BGL.
402 if (gd
== mygd
|| td
== &gd
->gd_idlethread
) {
404 TAILQ_INSERT_TAIL(&gd
->gd_tdallq
, td
, td_allq
);
407 lwkt_send_ipiq(gd
, lwkt_init_thread_remote
, td
);
411 TAILQ_INSERT_TAIL(&gd
->gd_tdallq
, td
, td_allq
);
415 dsched_new_thread(td
);
419 lwkt_set_comm(thread_t td
, const char *ctl
, ...)
424 kvsnprintf(td
->td_comm
, sizeof(td
->td_comm
), ctl
, va
);
426 KTR_LOG(ctxsw_newtd
, td
, &td
->td_comm
[0]);
430 lwkt_hold(thread_t td
)
436 lwkt_rele(thread_t td
)
438 KKASSERT(td
->td_refs
> 0);
443 lwkt_wait_free(thread_t td
)
446 tsleep(td
, 0, "tdreap", hz
);
450 lwkt_free_thread(thread_t td
)
452 KASSERT((td
->td_flags
& TDF_RUNNING
) == 0,
453 ("lwkt_free_thread: did not exit! %p", td
));
455 if (td
->td_flags
& TDF_ALLOCATED_THREAD
) {
456 objcache_put(thread_cache
, td
);
457 } else if (td
->td_flags
& TDF_ALLOCATED_STACK
) {
458 /* client-allocated struct with internally allocated stack */
459 KASSERT(td
->td_kstack
&& td
->td_kstack_size
> 0,
460 ("lwkt_free_thread: corrupted stack"));
461 kmem_free(&kernel_map
, (vm_offset_t
)td
->td_kstack
, td
->td_kstack_size
);
462 td
->td_kstack
= NULL
;
463 td
->td_kstack_size
= 0;
465 KTR_LOG(ctxsw_deadtd
, td
);
470 * Switch to the next runnable lwkt. If no LWKTs are runnable then
471 * switch to the idlethread. Switching must occur within a critical
472 * section to avoid races with the scheduling queue.
474 * We always have full control over our cpu's run queue. Other cpus
475 * that wish to manipulate our queue must use the cpu_*msg() calls to
476 * talk to our cpu, so a critical section is all that is needed and
477 * the result is very, very fast thread switching.
479 * The LWKT scheduler uses a fixed priority model and round-robins at
480 * each priority level. User process scheduling is a totally
481 * different beast and LWKT priorities should not be confused with
482 * user process priorities.
484 * The MP lock may be out of sync with the thread's td_mpcount. lwkt_switch()
485 * cleans it up. Note that the td_switch() function cannot do anything that
486 * requires the MP lock since the MP lock will have already been setup for
487 * the target thread (not the current thread). It's nice to have a scheduler
488 * that does not need the MP lock to work because it allows us to do some
489 * really cool high-performance MP lock optimizations.
491 * PREEMPTION NOTE: Preemption occurs via lwkt_preempt(). lwkt_switch()
492 * is not called by the current thread in the preemption case, only when
493 * the preempting thread blocks (in order to return to the original thread).
498 globaldata_t gd
= mycpu
;
499 thread_t td
= gd
->gd_curthread
;
508 const char *lmsg
; /* diagnostic - 'systat -pv 1' */
512 * Switching from within a 'fast' (non thread switched) interrupt or IPI
513 * is illegal. However, we may have to do it anyway if we hit a fatal
514 * kernel trap or we have paniced.
516 * If this case occurs save and restore the interrupt nesting level.
518 if (gd
->gd_intr_nesting_level
) {
522 if (gd
->gd_trap_nesting_level
== 0 && panicstr
== NULL
) {
523 panic("lwkt_switch: Attempt to switch from a "
524 "a fast interrupt, ipi, or hard code section, "
528 savegdnest
= gd
->gd_intr_nesting_level
;
529 savegdtrap
= gd
->gd_trap_nesting_level
;
530 gd
->gd_intr_nesting_level
= 0;
531 gd
->gd_trap_nesting_level
= 0;
532 if ((td
->td_flags
& TDF_PANICWARN
) == 0) {
533 td
->td_flags
|= TDF_PANICWARN
;
534 kprintf("Warning: thread switch from interrupt, IPI, "
535 "or hard code section.\n"
536 "thread %p (%s)\n", td
, td
->td_comm
);
540 gd
->gd_intr_nesting_level
= savegdnest
;
541 gd
->gd_trap_nesting_level
= savegdtrap
;
547 * Passive release (used to transition from user to kernel mode
548 * when we block or switch rather then when we enter the kernel).
549 * This function is NOT called if we are switching into a preemption
550 * or returning from a preemption. Typically this causes us to lose
551 * our current process designation (if we have one) and become a true
552 * LWKT thread, and may also hand the current process designation to
553 * another process and schedule thread.
559 if (TD_TOKS_HELD(td
))
560 lwkt_relalltokens(td
);
563 * We had better not be holding any spin locks, but don't get into an
564 * endless panic loop.
566 KASSERT(gd
->gd_spinlock_rd
== NULL
|| panicstr
!= NULL
,
567 ("lwkt_switch: still holding a shared spinlock %p!",
568 gd
->gd_spinlock_rd
));
569 KASSERT(gd
->gd_spinlocks_wr
== 0 || panicstr
!= NULL
,
570 ("lwkt_switch: still holding %d exclusive spinlocks!",
571 gd
->gd_spinlocks_wr
));
576 * td_mpcount cannot be used to determine if we currently hold the
577 * MP lock because get_mplock() will increment it prior to attempting
578 * to get the lock, and switch out if it can't. Our ownership of
579 * the actual lock will remain stable while we are in a critical section
580 * (but, of course, another cpu may own or release the lock so the
581 * actual value of mp_lock is not stable).
583 mpheld
= MP_LOCK_HELD(gd
);
585 if (td
->td_cscount
) {
586 kprintf("Diagnostic: attempt to switch while mastering cpusync: %p\n",
588 if (panic_on_cscount
)
589 panic("switching while mastering cpusync");
595 * If we had preempted another thread on this cpu, resume the preempted
596 * thread. This occurs transparently, whether the preempted thread
597 * was scheduled or not (it may have been preempted after descheduling
600 * We have to setup the MP lock for the original thread after backing
601 * out the adjustment that was made to curthread when the original
604 if ((ntd
= td
->td_preempted
) != NULL
) {
605 KKASSERT(ntd
->td_flags
& TDF_PREEMPT_LOCK
);
607 if (ntd
->td_mpcount
&& mpheld
== 0) {
608 panic("MPLOCK NOT HELD ON RETURN: %p %p %d %d",
609 td
, ntd
, td
->td_mpcount
, ntd
->td_mpcount
);
611 if (ntd
->td_mpcount
) {
612 td
->td_mpcount
-= ntd
->td_mpcount
;
613 KKASSERT(td
->td_mpcount
>= 0);
616 ntd
->td_flags
|= TDF_PREEMPT_DONE
;
619 * The interrupt may have woken a thread up, we need to properly
620 * set the reschedule flag if the originally interrupted thread is
621 * at a lower priority.
623 if (TAILQ_FIRST(&gd
->gd_tdrunq
) &&
624 TAILQ_FIRST(&gd
->gd_tdrunq
)->td_pri
> ntd
->td_pri
) {
627 /* YYY release mp lock on switchback if original doesn't need it */
628 goto havethread_preempted
;
632 * Implement round-robin fairq with priority insertion. The priority
633 * insertion is handled by _lwkt_enqueue()
635 * We have to adjust the MP lock for the target thread. If we
636 * need the MP lock and cannot obtain it we try to locate a
637 * thread that does not need the MP lock. If we cannot, we spin
640 * A similar issue exists for the tokens held by the target thread.
641 * If we cannot obtain ownership of the tokens we cannot immediately
642 * schedule the thread.
645 clear_lwkt_resched();
647 ntd
= TAILQ_FIRST(&gd
->gd_tdrunq
);
650 * Hotpath if we can get all necessary resources.
652 * If nothing is runnable switch to the idle thread
655 ntd
= &gd
->gd_idlethread
;
656 if (gd
->gd_reqflags
& RQF_IDLECHECK_MASK
)
657 ntd
->td_flags
|= TDF_IDLE_NOHLT
;
659 if (ntd
->td_mpcount
) {
660 if (gd
->gd_trap_nesting_level
== 0 && panicstr
== NULL
)
661 panic("Idle thread %p was holding the BGL!", ntd
);
663 set_cpu_contention_mask(gd
);
664 handle_cpu_contention_mask();
666 mpheld
= MP_LOCK_HELD(gd
);
671 clr_cpu_contention_mask(gd
);
673 cpu_time
.cp_msg
[0] = 0;
674 cpu_time
.cp_stallpc
= 0;
681 * NOTE: For UP there is no mplock and lwkt_getalltokens()
684 if (ntd
->td_fairq_accum
>= 0 &&
686 (ntd
->td_mpcount
== 0 || mpheld
|| cpu_try_mplock()) &&
688 (!TD_TOKS_HELD(ntd
) || lwkt_getalltokens(ntd
, &lmsg
, &laddr
))
691 clr_cpu_contention_mask(gd
);
700 if (ntd
->td_fairq_accum
>= 0)
701 set_cpu_contention_mask(gd
);
702 /* Reload mpheld (it become stale after mplock/token ops) */
703 mpheld
= MP_LOCK_HELD(gd
);
704 if (ntd
->td_mpcount
&& mpheld
== 0) {
706 laddr
= ntd
->td_mplock_stallpc
;
711 * Coldpath - unable to schedule ntd, continue looking for threads
712 * to schedule. This is only allowed of the (presumably) kernel
713 * thread exhausted its fair share. A kernel thread stuck on
714 * resources does not currently allow a user thread to get in
718 nquserok
= ((ntd
->td_pri
< TDPRI_KERN_LPSCHED
) ||
719 (ntd
->td_fairq_accum
< 0));
727 * If the fair-share scheduler ran out ntd gets moved to the
728 * end and its accumulator will be bumped, if it didn't we
729 * maintain the same queue position.
731 * nlast keeps track of the last element prior to any moves.
733 if (ntd
->td_fairq_accum
< 0) {
734 lwkt_fairq_accumulate(gd
, ntd
);
740 xtd
= TAILQ_NEXT(ntd
, td_threadq
);
741 TAILQ_REMOVE(&gd
->gd_tdrunq
, ntd
, td_threadq
);
742 TAILQ_INSERT_TAIL(&gd
->gd_tdrunq
, ntd
, td_threadq
);
745 * Set terminal element (nlast)
754 ntd
= TAILQ_NEXT(ntd
, td_threadq
);
758 * If we exhausted the run list switch to the idle thread.
759 * Since one or more threads had resource acquisition issues
760 * we do not allow the idle thread to halt.
762 * NOTE: nlast can be NULL.
766 ntd
= &gd
->gd_idlethread
;
767 ntd
->td_flags
|= TDF_IDLE_NOHLT
;
769 if (ntd
->td_mpcount
) {
770 mpheld
= MP_LOCK_HELD(gd
);
771 if (gd
->gd_trap_nesting_level
== 0 && panicstr
== NULL
)
772 panic("Idle thread %p was holding the BGL!", ntd
);
774 set_cpu_contention_mask(gd
);
775 handle_cpu_contention_mask();
777 mpheld
= MP_LOCK_HELD(gd
);
779 break; /* try again from the top, almost */
785 * If fairq accumulations occured we do not schedule the
786 * idle thread. This will cause us to try again from
790 break; /* try again from the top, almost */
792 strlcpy(cpu_time
.cp_msg
, lmsg
, sizeof(cpu_time
.cp_msg
));
793 cpu_time
.cp_stallpc
= (uintptr_t)laddr
;
798 * Try to switch to this thread.
800 * NOTE: For UP there is no mplock and lwkt_getalltokens()
803 if ((ntd
->td_pri
>= TDPRI_KERN_LPSCHED
|| nquserok
||
804 user_pri_sched
) && ntd
->td_fairq_accum
>= 0 &&
806 (ntd
->td_mpcount
== 0 || mpheld
|| cpu_try_mplock()) &&
808 (!TD_TOKS_HELD(ntd
) || lwkt_getalltokens(ntd
, &lmsg
, &laddr
))
811 clr_cpu_contention_mask(gd
);
816 if (ntd
->td_fairq_accum
>= 0)
817 set_cpu_contention_mask(gd
);
819 * Reload mpheld (it become stale after mplock/token ops).
821 mpheld
= MP_LOCK_HELD(gd
);
822 if (ntd
->td_mpcount
&& mpheld
== 0) {
824 laddr
= ntd
->td_mplock_stallpc
;
826 if (ntd
->td_pri
>= TDPRI_KERN_LPSCHED
&& ntd
->td_fairq_accum
>= 0)
832 * All threads exhausted but we can loop due to a negative
835 * While we are looping in the scheduler be sure to service
836 * any interrupts which were made pending due to our critical
837 * section, otherwise we could livelock (e.g.) IPIs.
839 * NOTE: splz can enter and exit the mplock so mpheld is
840 * stale after this call.
846 * Our mplock can be cached and cause other cpus to livelock
847 * if we loop due to e.g. not being able to acquire tokens.
849 if (MP_LOCK_HELD(gd
))
850 cpu_rel_mplock(gd
->gd_cpuid
);
856 * Do the actual switch. WARNING: mpheld is stale here.
858 * We must always decrement td_fairq_accum on non-idle threads just
859 * in case a thread never gets a tick due to being in a continuous
860 * critical section. The page-zeroing code does that.
862 * If the thread we came up with is a higher or equal priority verses
863 * the thread at the head of the queue we move our thread to the
864 * front. This way we can always check the front of the queue.
867 ++gd
->gd_cnt
.v_swtch
;
868 --ntd
->td_fairq_accum
;
869 xtd
= TAILQ_FIRST(&gd
->gd_tdrunq
);
870 if (ntd
!= xtd
&& ntd
->td_pri
>= xtd
->td_pri
) {
871 TAILQ_REMOVE(&gd
->gd_tdrunq
, ntd
, td_threadq
);
872 TAILQ_INSERT_HEAD(&gd
->gd_tdrunq
, ntd
, td_threadq
);
874 havethread_preempted
:
877 * If the new target does not need the MP lock and we are holding it,
878 * release the MP lock. If the new target requires the MP lock we have
879 * already acquired it for the target.
881 * WARNING: mpheld is stale here.
884 KASSERT(ntd
->td_critcount
,
885 ("priority problem in lwkt_switch %d %d", td
->td_pri
, ntd
->td_pri
));
887 if (ntd
->td_mpcount
== 0 ) {
888 if (MP_LOCK_HELD(gd
))
889 cpu_rel_mplock(gd
->gd_cpuid
);
891 ASSERT_MP_LOCK_HELD(ntd
);
898 int tos_ok __debugvar
= jg_tos_ok(ntd
);
902 KTR_LOG(ctxsw_sw
, gd
->gd_cpuid
, ntd
);
905 /* NOTE: current cpu may have changed after switch */
910 * Request that the target thread preempt the current thread. Preemption
911 * only works under a specific set of conditions:
913 * - We are not preempting ourselves
914 * - The target thread is owned by the current cpu
915 * - We are not currently being preempted
916 * - The target is not currently being preempted
917 * - We are not holding any spin locks
918 * - The target thread is not holding any tokens
919 * - We are able to satisfy the target's MP lock requirements (if any).
921 * THE CALLER OF LWKT_PREEMPT() MUST BE IN A CRITICAL SECTION. Typically
922 * this is called via lwkt_schedule() through the td_preemptable callback.
923 * critcount is the managed critical priority that we should ignore in order
924 * to determine whether preemption is possible (aka usually just the crit
925 * priority of lwkt_schedule() itself).
927 * XXX at the moment we run the target thread in a critical section during
928 * the preemption in order to prevent the target from taking interrupts
929 * that *WE* can't. Preemption is strictly limited to interrupt threads
930 * and interrupt-like threads, outside of a critical section, and the
931 * preempted source thread will be resumed the instant the target blocks
932 * whether or not the source is scheduled (i.e. preemption is supposed to
933 * be as transparent as possible).
935 * The target thread inherits our MP count (added to its own) for the
936 * duration of the preemption in order to preserve the atomicy of the
937 * MP lock during the preemption. Therefore, any preempting targets must be
938 * careful in regards to MP assertions. Note that the MP count may be
939 * out of sync with the physical mp_lock, but we do not have to preserve
940 * the original ownership of the lock if it was out of synch (that is, we
941 * can leave it synchronized on return).
944 lwkt_preempt(thread_t ntd
, int critcount
)
946 struct globaldata
*gd
= mycpu
;
954 * The caller has put us in a critical section. We can only preempt
955 * if the caller of the caller was not in a critical section (basically
956 * a local interrupt), as determined by the 'critcount' parameter. We
957 * also can't preempt if the caller is holding any spinlocks (even if
958 * he isn't in a critical section). This also handles the tokens test.
960 * YYY The target thread must be in a critical section (else it must
961 * inherit our critical section? I dunno yet).
963 * Set need_lwkt_resched() unconditionally for now YYY.
965 KASSERT(ntd
->td_critcount
, ("BADCRIT0 %d", ntd
->td_pri
));
967 td
= gd
->gd_curthread
;
968 if (ntd
->td_pri
<= td
->td_pri
) {
972 if (td
->td_critcount
> critcount
) {
978 if (ntd
->td_gd
!= gd
) {
985 * We don't have to check spinlocks here as they will also bump
988 * Do not try to preempt if the target thread is holding any tokens.
989 * We could try to acquire the tokens but this case is so rare there
990 * is no need to support it.
992 KKASSERT(gd
->gd_spinlock_rd
== NULL
);
993 KKASSERT(gd
->gd_spinlocks_wr
== 0);
995 if (TD_TOKS_HELD(ntd
)) {
1000 if (td
== ntd
|| ((td
->td_flags
| ntd
->td_flags
) & TDF_PREEMPT_LOCK
)) {
1002 need_lwkt_resched();
1005 if (ntd
->td_preempted
) {
1007 need_lwkt_resched();
1012 * note: an interrupt might have occured just as we were transitioning
1013 * to or from the MP lock. In this case td_mpcount will be pre-disposed
1014 * (non-zero) but not actually synchronized with the actual state of the
1015 * lock. We can use it to imply an MP lock requirement for the
1016 * preemption but we cannot use it to test whether we hold the MP lock
1019 savecnt
= td
->td_mpcount
;
1020 mpheld
= MP_LOCK_HELD(gd
);
1021 ntd
->td_mpcount
+= td
->td_mpcount
;
1022 if (mpheld
== 0 && ntd
->td_mpcount
&& !cpu_try_mplock()) {
1023 ntd
->td_mpcount
-= td
->td_mpcount
;
1025 need_lwkt_resched();
1031 * Since we are able to preempt the current thread, there is no need to
1032 * call need_lwkt_resched().
1035 ntd
->td_preempted
= td
;
1036 td
->td_flags
|= TDF_PREEMPT_LOCK
;
1037 KTR_LOG(ctxsw_pre
, gd
->gd_cpuid
, ntd
);
1040 KKASSERT(ntd
->td_preempted
&& (td
->td_flags
& TDF_PREEMPT_DONE
));
1042 KKASSERT(savecnt
== td
->td_mpcount
);
1043 mpheld
= MP_LOCK_HELD(gd
);
1044 if (mpheld
&& td
->td_mpcount
== 0)
1045 cpu_rel_mplock(gd
->gd_cpuid
);
1046 else if (mpheld
== 0 && td
->td_mpcount
)
1047 panic("lwkt_preempt(): MP lock was not held through");
1049 ntd
->td_preempted
= NULL
;
1050 td
->td_flags
&= ~(TDF_PREEMPT_LOCK
|TDF_PREEMPT_DONE
);
1054 * Conditionally call splz() if gd_reqflags indicates work is pending.
1055 * This will work inside a critical section but not inside a hard code
1058 * (self contained on a per cpu basis)
1063 globaldata_t gd
= mycpu
;
1064 thread_t td
= gd
->gd_curthread
;
1066 if ((gd
->gd_reqflags
& RQF_IDLECHECK_MASK
) &&
1067 gd
->gd_intr_nesting_level
== 0 &&
1068 td
->td_nest_count
< 2)
1075 * This version is integrated into crit_exit, reqflags has already
1076 * been tested but td_critcount has not.
1078 * We only want to execute the splz() on the 1->0 transition of
1079 * critcount and not in a hard code section or if too deeply nested.
1082 lwkt_maybe_splz(thread_t td
)
1084 globaldata_t gd
= td
->td_gd
;
1086 if (td
->td_critcount
== 0 &&
1087 gd
->gd_intr_nesting_level
== 0 &&
1088 td
->td_nest_count
< 2)
1095 * This function is used to negotiate a passive release of the current
1096 * process/lwp designation with the user scheduler, allowing the user
1097 * scheduler to schedule another user thread. The related kernel thread
1098 * (curthread) continues running in the released state.
1101 lwkt_passive_release(struct thread
*td
)
1103 struct lwp
*lp
= td
->td_lwp
;
1105 td
->td_release
= NULL
;
1106 lwkt_setpri_self(TDPRI_KERN_USER
);
1107 lp
->lwp_proc
->p_usched
->release_curproc(lp
);
1112 * This implements a normal yield. This routine is virtually a nop if
1113 * there is nothing to yield to but it will always run any pending interrupts
1114 * if called from a critical section.
1116 * This yield is designed for kernel threads without a user context.
1118 * (self contained on a per cpu basis)
1123 globaldata_t gd
= mycpu
;
1124 thread_t td
= gd
->gd_curthread
;
1127 if ((gd
->gd_reqflags
& RQF_IDLECHECK_MASK
) && td
->td_nest_count
< 2)
1129 if (td
->td_fairq_accum
< 0) {
1130 lwkt_schedule_self(curthread
);
1133 xtd
= TAILQ_FIRST(&gd
->gd_tdrunq
);
1134 if (xtd
&& xtd
->td_pri
> td
->td_pri
) {
1135 lwkt_schedule_self(curthread
);
1142 * This yield is designed for kernel threads with a user context.
1144 * The kernel acting on behalf of the user is potentially cpu-bound,
1145 * this function will efficiently allow other threads to run and also
1146 * switch to other processes by releasing.
1148 * The lwkt_user_yield() function is designed to have very low overhead
1149 * if no yield is determined to be needed.
1152 lwkt_user_yield(void)
1154 globaldata_t gd
= mycpu
;
1155 thread_t td
= gd
->gd_curthread
;
1158 * Always run any pending interrupts in case we are in a critical
1161 if ((gd
->gd_reqflags
& RQF_IDLECHECK_MASK
) && td
->td_nest_count
< 2)
1166 * XXX SEVERE TEMPORARY HACK. A cpu-bound operation running in the
1167 * kernel can prevent other cpus from servicing interrupt threads
1168 * which still require the MP lock (which is a lot of them). This
1169 * has a chaining effect since if the interrupt is blocked, so is
1170 * the event, so normal scheduling will not pick up on the problem.
1172 if (cpu_contention_mask
&& td
->td_mpcount
) {
1178 * Switch (which forces a release) if another kernel thread needs
1179 * the cpu, if userland wants us to resched, or if our kernel
1180 * quantum has run out.
1182 if (lwkt_resched_wanted() ||
1183 user_resched_wanted() ||
1184 td
->td_fairq_accum
< 0)
1191 * Reacquire the current process if we are released.
1193 * XXX not implemented atm. The kernel may be holding locks and such,
1194 * so we want the thread to continue to receive cpu.
1196 if (td
->td_release
== NULL
&& lp
) {
1197 lp
->lwp_proc
->p_usched
->acquire_curproc(lp
);
1198 td
->td_release
= lwkt_passive_release
;
1199 lwkt_setpri_self(TDPRI_USER_NORM
);
1205 * Generic schedule. Possibly schedule threads belonging to other cpus and
1206 * deal with threads that might be blocked on a wait queue.
1208 * We have a little helper inline function which does additional work after
1209 * the thread has been enqueued, including dealing with preemption and
1210 * setting need_lwkt_resched() (which prevents the kernel from returning
1211 * to userland until it has processed higher priority threads).
1213 * It is possible for this routine to be called after a failed _enqueue
1214 * (due to the target thread migrating, sleeping, or otherwise blocked).
1215 * We have to check that the thread is actually on the run queue!
1217 * reschedok is an optimized constant propagated from lwkt_schedule() or
1218 * lwkt_schedule_noresched(). By default it is non-zero, causing a
1219 * reschedule to be requested if the target thread has a higher priority.
1220 * The port messaging code will set MSG_NORESCHED and cause reschedok to
1221 * be 0, prevented undesired reschedules.
1225 _lwkt_schedule_post(globaldata_t gd
, thread_t ntd
, int ccount
, int reschedok
)
1229 if (ntd
->td_flags
& TDF_RUNQ
) {
1230 if (ntd
->td_preemptable
&& reschedok
) {
1231 ntd
->td_preemptable(ntd
, ccount
); /* YYY +token */
1232 } else if (reschedok
) {
1234 if (ntd
->td_pri
> otd
->td_pri
)
1235 need_lwkt_resched();
1239 * Give the thread a little fair share scheduler bump if it
1240 * has been asleep for a while. This is primarily to avoid
1241 * a degenerate case for interrupt threads where accumulator
1242 * crosses into negative territory unnecessarily.
1244 if (ntd
->td_fairq_lticks
!= ticks
) {
1245 ntd
->td_fairq_lticks
= ticks
;
1246 ntd
->td_fairq_accum
+= gd
->gd_fairq_total_pri
;
1247 if (ntd
->td_fairq_accum
> TDFAIRQ_MAX(gd
))
1248 ntd
->td_fairq_accum
= TDFAIRQ_MAX(gd
);
1255 _lwkt_schedule(thread_t td
, int reschedok
)
1257 globaldata_t mygd
= mycpu
;
1259 KASSERT(td
!= &td
->td_gd
->gd_idlethread
, ("lwkt_schedule(): scheduling gd_idlethread is illegal!"));
1260 crit_enter_gd(mygd
);
1261 KKASSERT(td
->td_lwp
== NULL
|| (td
->td_lwp
->lwp_flag
& LWP_ONRUNQ
) == 0);
1262 if (td
== mygd
->gd_curthread
) {
1266 * If we own the thread, there is no race (since we are in a
1267 * critical section). If we do not own the thread there might
1268 * be a race but the target cpu will deal with it.
1271 if (td
->td_gd
== mygd
) {
1273 _lwkt_schedule_post(mygd
, td
, 1, reschedok
);
1275 lwkt_send_ipiq3(td
->td_gd
, lwkt_schedule_remote
, td
, 0);
1279 _lwkt_schedule_post(mygd
, td
, 1, reschedok
);
1286 lwkt_schedule(thread_t td
)
1288 _lwkt_schedule(td
, 1);
1292 lwkt_schedule_noresched(thread_t td
)
1294 _lwkt_schedule(td
, 0);
1300 * When scheduled remotely if frame != NULL the IPIQ is being
1301 * run via doreti or an interrupt then preemption can be allowed.
1303 * To allow preemption we have to drop the critical section so only
1304 * one is present in _lwkt_schedule_post.
1307 lwkt_schedule_remote(void *arg
, int arg2
, struct intrframe
*frame
)
1309 thread_t td
= curthread
;
1312 if (frame
&& ntd
->td_preemptable
) {
1313 crit_exit_noyield(td
);
1314 _lwkt_schedule(ntd
, 1);
1315 crit_enter_quick(td
);
1317 _lwkt_schedule(ntd
, 1);
1322 * Thread migration using a 'Pull' method. The thread may or may not be
1323 * the current thread. It MUST be descheduled and in a stable state.
1324 * lwkt_giveaway() must be called on the cpu owning the thread.
1326 * At any point after lwkt_giveaway() is called, the target cpu may
1327 * 'pull' the thread by calling lwkt_acquire().
1329 * We have to make sure the thread is not sitting on a per-cpu tsleep
1330 * queue or it will blow up when it moves to another cpu.
1332 * MPSAFE - must be called under very specific conditions.
1335 lwkt_giveaway(thread_t td
)
1337 globaldata_t gd
= mycpu
;
1340 if (td
->td_flags
& TDF_TSLEEPQ
)
1342 KKASSERT(td
->td_gd
== gd
);
1343 TAILQ_REMOVE(&gd
->gd_tdallq
, td
, td_allq
);
1344 td
->td_flags
|= TDF_MIGRATING
;
1349 lwkt_acquire(thread_t td
)
1354 KKASSERT(td
->td_flags
& TDF_MIGRATING
);
1359 KKASSERT((td
->td_flags
& TDF_RUNQ
) == 0);
1360 crit_enter_gd(mygd
);
1361 while (td
->td_flags
& (TDF_RUNNING
|TDF_PREEMPT_LOCK
)) {
1363 lwkt_process_ipiq();
1368 TAILQ_INSERT_TAIL(&mygd
->gd_tdallq
, td
, td_allq
);
1369 td
->td_flags
&= ~TDF_MIGRATING
;
1372 crit_enter_gd(mygd
);
1373 TAILQ_INSERT_TAIL(&mygd
->gd_tdallq
, td
, td_allq
);
1374 td
->td_flags
&= ~TDF_MIGRATING
;
1382 * Generic deschedule. Descheduling threads other then your own should be
1383 * done only in carefully controlled circumstances. Descheduling is
1386 * This function may block if the cpu has run out of messages.
1389 lwkt_deschedule(thread_t td
)
1393 if (td
== curthread
) {
1396 if (td
->td_gd
== mycpu
) {
1399 lwkt_send_ipiq(td
->td_gd
, (ipifunc1_t
)lwkt_deschedule
, td
);
1409 * Set the target thread's priority. This routine does not automatically
1410 * switch to a higher priority thread, LWKT threads are not designed for
1411 * continuous priority changes. Yield if you want to switch.
1414 lwkt_setpri(thread_t td
, int pri
)
1416 KKASSERT(td
->td_gd
== mycpu
);
1417 if (td
->td_pri
!= pri
) {
1420 if (td
->td_flags
& TDF_RUNQ
) {
1432 * Set the initial priority for a thread prior to it being scheduled for
1433 * the first time. The thread MUST NOT be scheduled before or during
1434 * this call. The thread may be assigned to a cpu other then the current
1437 * Typically used after a thread has been created with TDF_STOPPREQ,
1438 * and before the thread is initially scheduled.
1441 lwkt_setpri_initial(thread_t td
, int pri
)
1444 KKASSERT((td
->td_flags
& TDF_RUNQ
) == 0);
1449 lwkt_setpri_self(int pri
)
1451 thread_t td
= curthread
;
1453 KKASSERT(pri
>= 0 && pri
<= TDPRI_MAX
);
1455 if (td
->td_flags
& TDF_RUNQ
) {
1466 * 1/hz tick (typically 10ms) x TDFAIRQ_SCALE (typ 8) = 80ms full cycle.
1468 * Example: two competing threads, same priority N. decrement by (2*N)
1469 * increment by N*8, each thread will get 4 ticks.
1472 lwkt_fairq_schedulerclock(thread_t td
)
1476 if (td
!= &td
->td_gd
->gd_idlethread
) {
1477 td
->td_fairq_accum
-= td
->td_gd
->gd_fairq_total_pri
;
1478 if (td
->td_fairq_accum
< -TDFAIRQ_MAX(td
->td_gd
))
1479 td
->td_fairq_accum
= -TDFAIRQ_MAX(td
->td_gd
);
1480 if (td
->td_fairq_accum
< 0)
1481 need_lwkt_resched();
1482 td
->td_fairq_lticks
= ticks
;
1484 td
= td
->td_preempted
;
1490 lwkt_fairq_accumulate(globaldata_t gd
, thread_t td
)
1492 td
->td_fairq_accum
+= td
->td_pri
* TDFAIRQ_SCALE
;
1493 if (td
->td_fairq_accum
> TDFAIRQ_MAX(td
->td_gd
))
1494 td
->td_fairq_accum
= TDFAIRQ_MAX(td
->td_gd
);
1498 * Migrate the current thread to the specified cpu.
1500 * This is accomplished by descheduling ourselves from the current cpu,
1501 * moving our thread to the tdallq of the target cpu, IPI messaging the
1502 * target cpu, and switching out. TDF_MIGRATING prevents scheduling
1503 * races while the thread is being migrated.
1505 * We must be sure to remove ourselves from the current cpu's tsleepq
1506 * before potentially moving to another queue. The thread can be on
1507 * a tsleepq due to a left-over tsleep_interlock().
1510 static void lwkt_setcpu_remote(void *arg
);
1514 lwkt_setcpu_self(globaldata_t rgd
)
1517 thread_t td
= curthread
;
1519 if (td
->td_gd
!= rgd
) {
1520 crit_enter_quick(td
);
1521 if (td
->td_flags
& TDF_TSLEEPQ
)
1523 td
->td_flags
|= TDF_MIGRATING
;
1524 lwkt_deschedule_self(td
);
1525 TAILQ_REMOVE(&td
->td_gd
->gd_tdallq
, td
, td_allq
);
1526 lwkt_send_ipiq(rgd
, (ipifunc1_t
)lwkt_setcpu_remote
, td
);
1528 /* we are now on the target cpu */
1529 TAILQ_INSERT_TAIL(&rgd
->gd_tdallq
, td
, td_allq
);
1530 crit_exit_quick(td
);
1536 lwkt_migratecpu(int cpuid
)
1541 rgd
= globaldata_find(cpuid
);
1542 lwkt_setcpu_self(rgd
);
1547 * Remote IPI for cpu migration (called while in a critical section so we
1548 * do not have to enter another one). The thread has already been moved to
1549 * our cpu's allq, but we must wait for the thread to be completely switched
1550 * out on the originating cpu before we schedule it on ours or the stack
1551 * state may be corrupt. We clear TDF_MIGRATING after flushing the GD
1552 * change to main memory.
1554 * XXX The use of TDF_MIGRATING might not be sufficient to avoid races
1555 * against wakeups. It is best if this interface is used only when there
1556 * are no pending events that might try to schedule the thread.
1560 lwkt_setcpu_remote(void *arg
)
1563 globaldata_t gd
= mycpu
;
1565 while (td
->td_flags
& (TDF_RUNNING
|TDF_PREEMPT_LOCK
)) {
1567 lwkt_process_ipiq();
1573 td
->td_flags
&= ~TDF_MIGRATING
;
1574 KKASSERT(td
->td_lwp
== NULL
|| (td
->td_lwp
->lwp_flag
& LWP_ONRUNQ
) == 0);
1580 lwkt_preempted_proc(void)
1582 thread_t td
= curthread
;
1583 while (td
->td_preempted
)
1584 td
= td
->td_preempted
;
1589 * Create a kernel process/thread/whatever. It shares it's address space
1590 * with proc0 - ie: kernel only.
1592 * NOTE! By default new threads are created with the MP lock held. A
1593 * thread which does not require the MP lock should release it by calling
1594 * rel_mplock() at the start of the new thread.
1597 lwkt_create(void (*func
)(void *), void *arg
, struct thread
**tdp
,
1598 thread_t
template, int tdflags
, int cpu
, const char *fmt
, ...)
1603 td
= lwkt_alloc_thread(template, LWKT_THREAD_STACK
, cpu
,
1607 cpu_set_thread_handler(td
, lwkt_exit
, func
, arg
);
1610 * Set up arg0 for 'ps' etc
1612 __va_start(ap
, fmt
);
1613 kvsnprintf(td
->td_comm
, sizeof(td
->td_comm
), fmt
, ap
);
1617 * Schedule the thread to run
1619 if ((td
->td_flags
& TDF_STOPREQ
) == 0)
1622 td
->td_flags
&= ~TDF_STOPREQ
;
1627 * Destroy an LWKT thread. Warning! This function is not called when
1628 * a process exits, cpu_proc_exit() directly calls cpu_thread_exit() and
1629 * uses a different reaping mechanism.
1634 thread_t td
= curthread
;
1638 if (td
->td_flags
& TDF_VERBOSE
)
1639 kprintf("kthread %p %s has exited\n", td
, td
->td_comm
);
1643 * Get us into a critical section to interlock gd_freetd and loop
1644 * until we can get it freed.
1646 * We have to cache the current td in gd_freetd because objcache_put()ing
1647 * it would rip it out from under us while our thread is still active.
1650 crit_enter_quick(td
);
1651 while ((std
= gd
->gd_freetd
) != NULL
) {
1652 gd
->gd_freetd
= NULL
;
1653 objcache_put(thread_cache
, std
);
1657 * Remove thread resources from kernel lists and deschedule us for
1660 if (td
->td_flags
& TDF_TSLEEPQ
)
1663 dsched_exit_thread(td
);
1664 lwkt_deschedule_self(td
);
1665 lwkt_remove_tdallq(td
);
1666 if (td
->td_flags
& TDF_ALLOCATED_THREAD
)
1672 lwkt_remove_tdallq(thread_t td
)
1674 KKASSERT(td
->td_gd
== mycpu
);
1675 TAILQ_REMOVE(&td
->td_gd
->gd_tdallq
, td
, td_allq
);
1679 * Code reduction and branch prediction improvements. Call/return
1680 * overhead on modern cpus often degenerates into 0 cycles due to
1681 * the cpu's branch prediction hardware and return pc cache. We
1682 * can take advantage of this by not inlining medium-complexity
1683 * functions and we can also reduce the branch prediction impact
1684 * by collapsing perfectly predictable branches into a single
1685 * procedure instead of duplicating it.
1687 * Is any of this noticeable? Probably not, so I'll take the
1688 * smaller code size.
1691 crit_exit_wrapper(void)
1699 thread_t td
= curthread
;
1700 int lcrit
= td
->td_critcount
;
1702 td
->td_critcount
= 0;
1703 panic("td_critcount is/would-go negative! %p %d", td
, lcrit
);
1710 * Called from debugger/panic on cpus which have been stopped. We must still
1711 * process the IPIQ while stopped, even if we were stopped while in a critical
1714 * If we are dumping also try to process any pending interrupts. This may
1715 * or may not work depending on the state of the cpu at the point it was
1719 lwkt_smp_stopped(void)
1721 globaldata_t gd
= mycpu
;
1725 lwkt_process_ipiq();
1728 lwkt_process_ipiq();