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
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/queue.h>
48 #include <sys/sysctl.h>
49 #include <sys/kthread.h>
50 #include <machine/cpu.h>
53 #include <sys/spinlock.h>
56 #include <sys/thread2.h>
57 #include <sys/spinlock2.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>
68 #include <machine/stdarg.h>
69 #include <machine/smp.h>
71 #if !defined(KTR_CTXSW)
72 #define KTR_CTXSW KTR_ALL
74 KTR_INFO_MASTER(ctxsw
);
75 KTR_INFO(KTR_CTXSW
, ctxsw
, sw
, 0, "sw %p > %p", 2 * sizeof(struct thread
*));
76 KTR_INFO(KTR_CTXSW
, ctxsw
, pre
, 1, "pre %p > %p", 2 * sizeof(struct thread
*));
78 static MALLOC_DEFINE(M_THREAD
, "thread", "lwkt threads");
81 static int mplock_countx
= 0;
84 static int panic_on_cscount
= 0;
86 static __int64_t switch_count
= 0;
87 static __int64_t preempt_hit
= 0;
88 static __int64_t preempt_miss
= 0;
89 static __int64_t preempt_weird
= 0;
90 static __int64_t token_contention_count
= 0;
91 static __int64_t mplock_contention_count
= 0;
92 static int lwkt_use_spin_port
;
94 static int chain_mplock
= 0;
95 static int bgl_yield
= 10;
97 static struct objcache
*thread_cache
;
99 volatile cpumask_t mp_lock_contention_mask
;
102 static void lwkt_schedule_remote(void *arg
, int arg2
, struct intrframe
*frame
);
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, "");
143 SYSCTL_INT(_lwkt
, OID_AUTO
, chain_mplock
, CTLFLAG_RW
, &chain_mplock
, 0, "");
144 SYSCTL_INT(_lwkt
, OID_AUTO
, bgl_yield_delay
, CTLFLAG_RW
, &bgl_yield
, 0, "");
146 SYSCTL_QUAD(_lwkt
, OID_AUTO
, switch_count
, CTLFLAG_RW
, &switch_count
, 0, "");
147 SYSCTL_QUAD(_lwkt
, OID_AUTO
, preempt_hit
, CTLFLAG_RW
, &preempt_hit
, 0, "");
148 SYSCTL_QUAD(_lwkt
, OID_AUTO
, preempt_miss
, CTLFLAG_RW
, &preempt_miss
, 0, "");
149 SYSCTL_QUAD(_lwkt
, OID_AUTO
, preempt_weird
, CTLFLAG_RW
, &preempt_weird
, 0, "");
151 SYSCTL_QUAD(_lwkt
, OID_AUTO
, token_contention_count
, CTLFLAG_RW
,
152 &token_contention_count
, 0, "spinning due to token contention");
153 SYSCTL_QUAD(_lwkt
, OID_AUTO
, mplock_contention_count
, CTLFLAG_RW
,
154 &mplock_contention_count
, 0, "spinning due to MPLOCK contention");
160 #if !defined(KTR_GIANT_CONTENTION)
161 #define KTR_GIANT_CONTENTION KTR_ALL
164 KTR_INFO_MASTER(giant
);
165 KTR_INFO(KTR_GIANT_CONTENTION
, giant
, beg
, 0, "thread=%p", sizeof(void *));
166 KTR_INFO(KTR_GIANT_CONTENTION
, giant
, end
, 1, "thread=%p", sizeof(void *));
168 #define loggiant(name) KTR_LOG(giant_ ## name, curthread)
171 * These helper procedures handle the runq, they can only be called from
172 * within a critical section.
174 * WARNING! Prior to SMP being brought up it is possible to enqueue and
175 * dequeue threads belonging to other cpus, so be sure to use td->td_gd
176 * instead of 'mycpu' when referencing the globaldata structure. Once
177 * SMP live enqueuing and dequeueing only occurs on the current cpu.
181 _lwkt_dequeue(thread_t td
)
183 if (td
->td_flags
& TDF_RUNQ
) {
184 int nq
= td
->td_pri
& TDPRI_MASK
;
185 struct globaldata
*gd
= td
->td_gd
;
187 td
->td_flags
&= ~TDF_RUNQ
;
188 TAILQ_REMOVE(&gd
->gd_tdrunq
[nq
], td
, td_threadq
);
189 /* runqmask is passively cleaned up by the switcher */
195 _lwkt_enqueue(thread_t td
)
197 if ((td
->td_flags
& (TDF_RUNQ
|TDF_MIGRATING
|TDF_BLOCKQ
)) == 0) {
198 int nq
= td
->td_pri
& TDPRI_MASK
;
199 struct globaldata
*gd
= td
->td_gd
;
201 td
->td_flags
|= TDF_RUNQ
;
202 TAILQ_INSERT_TAIL(&gd
->gd_tdrunq
[nq
], td
, td_threadq
);
203 gd
->gd_runqmask
|= 1 << nq
;
208 _lwkt_thread_ctor(void *obj
, void *privdata
, int ocflags
)
210 struct thread
*td
= (struct thread
*)obj
;
212 td
->td_kstack
= NULL
;
213 td
->td_kstack_size
= 0;
214 td
->td_flags
= TDF_ALLOCATED_THREAD
;
219 _lwkt_thread_dtor(void *obj
, void *privdata
)
221 struct thread
*td
= (struct thread
*)obj
;
223 KASSERT(td
->td_flags
& TDF_ALLOCATED_THREAD
,
224 ("_lwkt_thread_dtor: not allocated from objcache"));
225 KASSERT((td
->td_flags
& TDF_ALLOCATED_STACK
) && td
->td_kstack
&&
226 td
->td_kstack_size
> 0,
227 ("_lwkt_thread_dtor: corrupted stack"));
228 kmem_free(&kernel_map
, (vm_offset_t
)td
->td_kstack
, td
->td_kstack_size
);
232 * Initialize the lwkt s/system.
237 /* An objcache has 2 magazines per CPU so divide cache size by 2. */
238 thread_cache
= objcache_create_mbacked(M_THREAD
, sizeof(struct thread
),
239 NULL
, CACHE_NTHREADS
/2,
240 _lwkt_thread_ctor
, _lwkt_thread_dtor
, NULL
);
244 * Schedule a thread to run. As the current thread we can always safely
245 * schedule ourselves, and a shortcut procedure is provided for that
248 * (non-blocking, self contained on a per cpu basis)
251 lwkt_schedule_self(thread_t td
)
253 crit_enter_quick(td
);
254 KASSERT(td
!= &td
->td_gd
->gd_idlethread
, ("lwkt_schedule_self(): scheduling gd_idlethread is illegal!"));
255 KKASSERT(td
->td_lwp
== NULL
|| (td
->td_lwp
->lwp_flag
& LWP_ONRUNQ
) == 0);
261 * Deschedule a thread.
263 * (non-blocking, self contained on a per cpu basis)
266 lwkt_deschedule_self(thread_t td
)
268 crit_enter_quick(td
);
274 * LWKTs operate on a per-cpu basis
276 * WARNING! Called from early boot, 'mycpu' may not work yet.
279 lwkt_gdinit(struct globaldata
*gd
)
283 for (i
= 0; i
< sizeof(gd
->gd_tdrunq
)/sizeof(gd
->gd_tdrunq
[0]); ++i
)
284 TAILQ_INIT(&gd
->gd_tdrunq
[i
]);
286 TAILQ_INIT(&gd
->gd_tdallq
);
290 * Create a new thread. The thread must be associated with a process context
291 * or LWKT start address before it can be scheduled. If the target cpu is
292 * -1 the thread will be created on the current cpu.
294 * If you intend to create a thread without a process context this function
295 * does everything except load the startup and switcher function.
298 lwkt_alloc_thread(struct thread
*td
, int stksize
, int cpu
, int flags
)
300 globaldata_t gd
= mycpu
;
304 * If static thread storage is not supplied allocate a thread. Reuse
305 * a cached free thread if possible. gd_freetd is used to keep an exiting
306 * thread intact through the exit.
309 if ((td
= gd
->gd_freetd
) != NULL
)
310 gd
->gd_freetd
= NULL
;
312 td
= objcache_get(thread_cache
, M_WAITOK
);
313 KASSERT((td
->td_flags
&
314 (TDF_ALLOCATED_THREAD
|TDF_RUNNING
)) == TDF_ALLOCATED_THREAD
,
315 ("lwkt_alloc_thread: corrupted td flags 0x%X", td
->td_flags
));
316 flags
|= td
->td_flags
& (TDF_ALLOCATED_THREAD
|TDF_ALLOCATED_STACK
);
320 * Try to reuse cached stack.
322 if ((stack
= td
->td_kstack
) != NULL
&& td
->td_kstack_size
!= stksize
) {
323 if (flags
& TDF_ALLOCATED_STACK
) {
324 kmem_free(&kernel_map
, (vm_offset_t
)stack
, td
->td_kstack_size
);
329 stack
= (void *)kmem_alloc(&kernel_map
, stksize
);
330 flags
|= TDF_ALLOCATED_STACK
;
333 lwkt_init_thread(td
, stack
, stksize
, flags
, gd
);
335 lwkt_init_thread(td
, stack
, stksize
, flags
, globaldata_find(cpu
));
340 * Initialize a preexisting thread structure. This function is used by
341 * lwkt_alloc_thread() and also used to initialize the per-cpu idlethread.
343 * All threads start out in a critical section at a priority of
344 * TDPRI_KERN_DAEMON. Higher level code will modify the priority as
345 * appropriate. This function may send an IPI message when the
346 * requested cpu is not the current cpu and consequently gd_tdallq may
347 * not be initialized synchronously from the point of view of the originating
350 * NOTE! we have to be careful in regards to creating threads for other cpus
351 * if SMP has not yet been activated.
356 lwkt_init_thread_remote(void *arg
)
361 * Protected by critical section held by IPI dispatch
363 TAILQ_INSERT_TAIL(&td
->td_gd
->gd_tdallq
, td
, td_allq
);
369 lwkt_init_thread(thread_t td
, void *stack
, int stksize
, int flags
,
370 struct globaldata
*gd
)
372 globaldata_t mygd
= mycpu
;
374 bzero(td
, sizeof(struct thread
));
375 td
->td_kstack
= stack
;
376 td
->td_kstack_size
= stksize
;
377 td
->td_flags
= flags
;
379 td
->td_pri
= TDPRI_KERN_DAEMON
+ TDPRI_CRIT
;
381 if ((flags
& TDF_MPSAFE
) == 0)
384 if (lwkt_use_spin_port
)
385 lwkt_initport_spin(&td
->td_msgport
);
387 lwkt_initport_thread(&td
->td_msgport
, td
);
388 pmap_init_thread(td
);
391 * Normally initializing a thread for a remote cpu requires sending an
392 * IPI. However, the idlethread is setup before the other cpus are
393 * activated so we have to treat it as a special case. XXX manipulation
394 * of gd_tdallq requires the BGL.
396 if (gd
== mygd
|| td
== &gd
->gd_idlethread
) {
398 TAILQ_INSERT_TAIL(&gd
->gd_tdallq
, td
, td_allq
);
401 lwkt_send_ipiq(gd
, lwkt_init_thread_remote
, td
);
405 TAILQ_INSERT_TAIL(&gd
->gd_tdallq
, td
, td_allq
);
411 lwkt_set_comm(thread_t td
, const char *ctl
, ...)
416 kvsnprintf(td
->td_comm
, sizeof(td
->td_comm
), ctl
, va
);
421 lwkt_hold(thread_t td
)
427 lwkt_rele(thread_t td
)
429 KKASSERT(td
->td_refs
> 0);
434 lwkt_wait_free(thread_t td
)
437 tsleep(td
, 0, "tdreap", hz
);
441 lwkt_free_thread(thread_t td
)
443 KASSERT((td
->td_flags
& TDF_RUNNING
) == 0,
444 ("lwkt_free_thread: did not exit! %p", td
));
446 if (td
->td_flags
& TDF_ALLOCATED_THREAD
) {
447 objcache_put(thread_cache
, td
);
448 } else if (td
->td_flags
& TDF_ALLOCATED_STACK
) {
449 /* client-allocated struct with internally allocated stack */
450 KASSERT(td
->td_kstack
&& td
->td_kstack_size
> 0,
451 ("lwkt_free_thread: corrupted stack"));
452 kmem_free(&kernel_map
, (vm_offset_t
)td
->td_kstack
, td
->td_kstack_size
);
453 td
->td_kstack
= NULL
;
454 td
->td_kstack_size
= 0;
460 * Switch to the next runnable lwkt. If no LWKTs are runnable then
461 * switch to the idlethread. Switching must occur within a critical
462 * section to avoid races with the scheduling queue.
464 * We always have full control over our cpu's run queue. Other cpus
465 * that wish to manipulate our queue must use the cpu_*msg() calls to
466 * talk to our cpu, so a critical section is all that is needed and
467 * the result is very, very fast thread switching.
469 * The LWKT scheduler uses a fixed priority model and round-robins at
470 * each priority level. User process scheduling is a totally
471 * different beast and LWKT priorities should not be confused with
472 * user process priorities.
474 * The MP lock may be out of sync with the thread's td_mpcount. lwkt_switch()
475 * cleans it up. Note that the td_switch() function cannot do anything that
476 * requires the MP lock since the MP lock will have already been setup for
477 * the target thread (not the current thread). It's nice to have a scheduler
478 * that does not need the MP lock to work because it allows us to do some
479 * really cool high-performance MP lock optimizations.
481 * PREEMPTION NOTE: Preemption occurs via lwkt_preempt(). lwkt_switch()
482 * is not called by the current thread in the preemption case, only when
483 * the preempting thread blocks (in order to return to the original thread).
488 globaldata_t gd
= mycpu
;
489 thread_t td
= gd
->gd_curthread
;
496 * Switching from within a 'fast' (non thread switched) interrupt or IPI
497 * is illegal. However, we may have to do it anyway if we hit a fatal
498 * kernel trap or we have paniced.
500 * If this case occurs save and restore the interrupt nesting level.
502 if (gd
->gd_intr_nesting_level
) {
506 if (gd
->gd_trap_nesting_level
== 0 && panicstr
== NULL
) {
507 panic("lwkt_switch: cannot switch from within "
508 "a fast interrupt, yet, td %p\n", td
);
510 savegdnest
= gd
->gd_intr_nesting_level
;
511 savegdtrap
= gd
->gd_trap_nesting_level
;
512 gd
->gd_intr_nesting_level
= 0;
513 gd
->gd_trap_nesting_level
= 0;
514 if ((td
->td_flags
& TDF_PANICWARN
) == 0) {
515 td
->td_flags
|= TDF_PANICWARN
;
516 kprintf("Warning: thread switch from interrupt or IPI, "
517 "thread %p (%s)\n", td
, td
->td_comm
);
521 gd
->gd_intr_nesting_level
= savegdnest
;
522 gd
->gd_trap_nesting_level
= savegdtrap
;
528 * Passive release (used to transition from user to kernel mode
529 * when we block or switch rather then when we enter the kernel).
530 * This function is NOT called if we are switching into a preemption
531 * or returning from a preemption. Typically this causes us to lose
532 * our current process designation (if we have one) and become a true
533 * LWKT thread, and may also hand the current process designation to
534 * another process and schedule thread.
541 lwkt_relalltokens(td
);
544 * We had better not be holding any spin locks, but don't get into an
545 * endless panic loop.
547 KASSERT(gd
->gd_spinlock_rd
== NULL
|| panicstr
!= NULL
,
548 ("lwkt_switch: still holding a shared spinlock %p!",
549 gd
->gd_spinlock_rd
));
550 KASSERT(gd
->gd_spinlocks_wr
== 0 || panicstr
!= NULL
,
551 ("lwkt_switch: still holding %d exclusive spinlocks!",
552 gd
->gd_spinlocks_wr
));
557 * td_mpcount cannot be used to determine if we currently hold the
558 * MP lock because get_mplock() will increment it prior to attempting
559 * to get the lock, and switch out if it can't. Our ownership of
560 * the actual lock will remain stable while we are in a critical section
561 * (but, of course, another cpu may own or release the lock so the
562 * actual value of mp_lock is not stable).
564 mpheld
= MP_LOCK_HELD();
566 if (td
->td_cscount
) {
567 kprintf("Diagnostic: attempt to switch while mastering cpusync: %p\n",
569 if (panic_on_cscount
)
570 panic("switching while mastering cpusync");
574 if ((ntd
= td
->td_preempted
) != NULL
) {
576 * We had preempted another thread on this cpu, resume the preempted
577 * thread. This occurs transparently, whether the preempted thread
578 * was scheduled or not (it may have been preempted after descheduling
581 * We have to setup the MP lock for the original thread after backing
582 * out the adjustment that was made to curthread when the original
585 KKASSERT(ntd
->td_flags
& TDF_PREEMPT_LOCK
);
587 if (ntd
->td_mpcount
&& mpheld
== 0) {
588 panic("MPLOCK NOT HELD ON RETURN: %p %p %d %d",
589 td
, ntd
, td
->td_mpcount
, ntd
->td_mpcount
);
591 if (ntd
->td_mpcount
) {
592 td
->td_mpcount
-= ntd
->td_mpcount
;
593 KKASSERT(td
->td_mpcount
>= 0);
596 ntd
->td_flags
|= TDF_PREEMPT_DONE
;
599 * The interrupt may have woken a thread up, we need to properly
600 * set the reschedule flag if the originally interrupted thread is
601 * at a lower priority.
603 if (gd
->gd_runqmask
> (2 << (ntd
->td_pri
& TDPRI_MASK
)) - 1)
605 /* YYY release mp lock on switchback if original doesn't need it */
608 * Priority queue / round-robin at each priority. Note that user
609 * processes run at a fixed, low priority and the user process
610 * scheduler deals with interactions between user processes
611 * by scheduling and descheduling them from the LWKT queue as
614 * We have to adjust the MP lock for the target thread. If we
615 * need the MP lock and cannot obtain it we try to locate a
616 * thread that does not need the MP lock. If we cannot, we spin
619 * A similar issue exists for the tokens held by the target thread.
620 * If we cannot obtain ownership of the tokens we cannot immediately
621 * schedule the thread.
625 * If an LWKT reschedule was requested, well that is what we are
626 * doing now so clear it.
628 clear_lwkt_resched();
630 if (gd
->gd_runqmask
) {
631 int nq
= bsrl(gd
->gd_runqmask
);
632 if ((ntd
= TAILQ_FIRST(&gd
->gd_tdrunq
[nq
])) == NULL
) {
633 gd
->gd_runqmask
&= ~(1 << nq
);
638 * THREAD SELECTION FOR AN SMP MACHINE BUILD
640 * If the target needs the MP lock and we couldn't get it,
641 * or if the target is holding tokens and we could not
642 * gain ownership of the tokens, continue looking for a
643 * thread to schedule and spin instead of HLT if we can't.
645 * NOTE: the mpheld variable invalid after this conditional, it
646 * can change due to both cpu_try_mplock() returning success
647 * AND interactions in lwkt_getalltokens() due to the fact that
648 * we are trying to check the mpcount of a thread other then
649 * the current thread. Because of this, if the current thread
650 * is not holding td_mpcount, an IPI indirectly run via
651 * lwkt_getalltokens() can obtain and release the MP lock and
652 * cause the core MP lock to be released.
654 if ((ntd
->td_mpcount
&& mpheld
== 0 && !cpu_try_mplock()) ||
655 (ntd
->td_toks
&& lwkt_getalltokens(ntd
) == 0)
657 u_int32_t rqmask
= gd
->gd_runqmask
;
659 mpheld
= MP_LOCK_HELD();
662 TAILQ_FOREACH(ntd
, &gd
->gd_tdrunq
[nq
], td_threadq
) {
663 if (ntd
->td_mpcount
&& !mpheld
&& !cpu_try_mplock()) {
664 /* spinning due to MP lock being held */
666 ++mplock_contention_count
;
668 /* mplock still not held, 'mpheld' still valid */
673 * mpheld state invalid after getalltokens call returns
674 * failure, but the variable is only needed for
677 if (ntd
->td_toks
&& !lwkt_getalltokens(ntd
)) {
678 /* spinning due to token contention */
680 ++token_contention_count
;
682 mpheld
= MP_LOCK_HELD();
689 rqmask
&= ~(1 << nq
);
693 * We have two choices. We can either refuse to run a
694 * user thread when a kernel thread needs the MP lock
695 * but could not get it, or we can allow it to run but
696 * then expect an IPI (hopefully) later on to force a
697 * reschedule when the MP lock might become available.
699 if (nq
< TDPRI_KERN_LPSCHED
) {
700 if (chain_mplock
== 0)
702 atomic_set_int(&mp_lock_contention_mask
,
704 /* continue loop, allow user threads to be scheduled */
708 cpu_mplock_contested();
709 ntd
= &gd
->gd_idlethread
;
710 ntd
->td_flags
|= TDF_IDLE_NOHLT
;
711 goto using_idle_thread
;
713 ++gd
->gd_cnt
.v_swtch
;
714 TAILQ_REMOVE(&gd
->gd_tdrunq
[nq
], ntd
, td_threadq
);
715 TAILQ_INSERT_TAIL(&gd
->gd_tdrunq
[nq
], ntd
, td_threadq
);
720 ++gd
->gd_cnt
.v_swtch
;
721 TAILQ_REMOVE(&gd
->gd_tdrunq
[nq
], ntd
, td_threadq
);
722 TAILQ_INSERT_TAIL(&gd
->gd_tdrunq
[nq
], ntd
, td_threadq
);
726 * THREAD SELECTION FOR A UP MACHINE BUILD. We don't have to
727 * worry about tokens or the BGL. However, we still have
728 * to call lwkt_getalltokens() in order to properly detect
729 * stale tokens. This call cannot fail for a UP build!
731 lwkt_getalltokens(ntd
);
732 ++gd
->gd_cnt
.v_swtch
;
733 TAILQ_REMOVE(&gd
->gd_tdrunq
[nq
], ntd
, td_threadq
);
734 TAILQ_INSERT_TAIL(&gd
->gd_tdrunq
[nq
], ntd
, td_threadq
);
738 * We have nothing to run but only let the idle loop halt
739 * the cpu if there are no pending interrupts.
741 ntd
= &gd
->gd_idlethread
;
742 if (gd
->gd_reqflags
& RQF_IDLECHECK_MASK
)
743 ntd
->td_flags
|= TDF_IDLE_NOHLT
;
747 * The idle thread should not be holding the MP lock unless we
748 * are trapping in the kernel or in a panic. Since we select the
749 * idle thread unconditionally when no other thread is available,
750 * if the MP lock is desired during a panic or kernel trap, we
751 * have to loop in the scheduler until we get it.
753 if (ntd
->td_mpcount
) {
754 mpheld
= MP_LOCK_HELD();
755 if (gd
->gd_trap_nesting_level
== 0 && panicstr
== NULL
) {
756 panic("Idle thread %p was holding the BGL!", ntd
);
757 } else if (mpheld
== 0) {
758 cpu_mplock_contested();
765 KASSERT(ntd
->td_pri
>= TDPRI_CRIT
,
766 ("priority problem in lwkt_switch %d %d", td
->td_pri
, ntd
->td_pri
));
769 * Do the actual switch. If the new target does not need the MP lock
770 * and we are holding it, release the MP lock. If the new target requires
771 * the MP lock we have already acquired it for the target.
774 if (ntd
->td_mpcount
== 0 ) {
778 ASSERT_MP_LOCK_HELD(ntd
);
784 KKASSERT(jg_tos_ok(ntd
));
786 KTR_LOG(ctxsw_sw
, td
, ntd
);
789 /* NOTE: current cpu may have changed after switch */
794 * Request that the target thread preempt the current thread. Preemption
795 * only works under a specific set of conditions:
797 * - We are not preempting ourselves
798 * - The target thread is owned by the current cpu
799 * - We are not currently being preempted
800 * - The target is not currently being preempted
801 * - We are not holding any spin locks
802 * - The target thread is not holding any tokens
803 * - We are able to satisfy the target's MP lock requirements (if any).
805 * THE CALLER OF LWKT_PREEMPT() MUST BE IN A CRITICAL SECTION. Typically
806 * this is called via lwkt_schedule() through the td_preemptable callback.
807 * critpri is the managed critical priority that we should ignore in order
808 * to determine whether preemption is possible (aka usually just the crit
809 * priority of lwkt_schedule() itself).
811 * XXX at the moment we run the target thread in a critical section during
812 * the preemption in order to prevent the target from taking interrupts
813 * that *WE* can't. Preemption is strictly limited to interrupt threads
814 * and interrupt-like threads, outside of a critical section, and the
815 * preempted source thread will be resumed the instant the target blocks
816 * whether or not the source is scheduled (i.e. preemption is supposed to
817 * be as transparent as possible).
819 * The target thread inherits our MP count (added to its own) for the
820 * duration of the preemption in order to preserve the atomicy of the
821 * MP lock during the preemption. Therefore, any preempting targets must be
822 * careful in regards to MP assertions. Note that the MP count may be
823 * out of sync with the physical mp_lock, but we do not have to preserve
824 * the original ownership of the lock if it was out of synch (that is, we
825 * can leave it synchronized on return).
828 lwkt_preempt(thread_t ntd
, int critpri
)
830 struct globaldata
*gd
= mycpu
;
838 * The caller has put us in a critical section. We can only preempt
839 * if the caller of the caller was not in a critical section (basically
840 * a local interrupt), as determined by the 'critpri' parameter. We
841 * also can't preempt if the caller is holding any spinlocks (even if
842 * he isn't in a critical section). This also handles the tokens test.
844 * YYY The target thread must be in a critical section (else it must
845 * inherit our critical section? I dunno yet).
847 * Set need_lwkt_resched() unconditionally for now YYY.
849 KASSERT(ntd
->td_pri
>= TDPRI_CRIT
, ("BADCRIT0 %d", ntd
->td_pri
));
851 td
= gd
->gd_curthread
;
852 if ((ntd
->td_pri
& TDPRI_MASK
) <= (td
->td_pri
& TDPRI_MASK
)) {
856 if ((td
->td_pri
& ~TDPRI_MASK
) > critpri
) {
862 if (ntd
->td_gd
!= gd
) {
869 * Take the easy way out and do not preempt if we are holding
870 * any spinlocks. We could test whether the thread(s) being
871 * preempted interlock against the target thread's tokens and whether
872 * we can get all the target thread's tokens, but this situation
873 * should not occur very often so its easier to simply not preempt.
874 * Also, plain spinlocks are impossible to figure out at this point so
875 * just don't preempt.
877 * Do not try to preempt if the target thread is holding any tokens.
878 * We could try to acquire the tokens but this case is so rare there
879 * is no need to support it.
881 if (gd
->gd_spinlock_rd
|| gd
->gd_spinlocks_wr
) {
891 if (td
== ntd
|| ((td
->td_flags
| ntd
->td_flags
) & TDF_PREEMPT_LOCK
)) {
896 if (ntd
->td_preempted
) {
903 * note: an interrupt might have occured just as we were transitioning
904 * to or from the MP lock. In this case td_mpcount will be pre-disposed
905 * (non-zero) but not actually synchronized with the actual state of the
906 * lock. We can use it to imply an MP lock requirement for the
907 * preemption but we cannot use it to test whether we hold the MP lock
910 savecnt
= td
->td_mpcount
;
911 mpheld
= MP_LOCK_HELD();
912 ntd
->td_mpcount
+= td
->td_mpcount
;
913 if (mpheld
== 0 && ntd
->td_mpcount
&& !cpu_try_mplock()) {
914 ntd
->td_mpcount
-= td
->td_mpcount
;
922 * Since we are able to preempt the current thread, there is no need to
923 * call need_lwkt_resched().
926 ntd
->td_preempted
= td
;
927 td
->td_flags
|= TDF_PREEMPT_LOCK
;
928 KTR_LOG(ctxsw_pre
, td
, ntd
);
931 KKASSERT(ntd
->td_preempted
&& (td
->td_flags
& TDF_PREEMPT_DONE
));
933 KKASSERT(savecnt
== td
->td_mpcount
);
934 mpheld
= MP_LOCK_HELD();
935 if (mpheld
&& td
->td_mpcount
== 0)
937 else if (mpheld
== 0 && td
->td_mpcount
)
938 panic("lwkt_preempt(): MP lock was not held through");
940 ntd
->td_preempted
= NULL
;
941 td
->td_flags
&= ~(TDF_PREEMPT_LOCK
|TDF_PREEMPT_DONE
);
945 * Conditionally call splz() if gd_reqflags indicates work is pending.
947 * td_nest_count prevents deep nesting via splz() or doreti() which
948 * might otherwise blow out the kernel stack. Note that except for
949 * this special case, we MUST call splz() here to handle any
950 * pending ints, particularly after we switch, or we might accidently
951 * halt the cpu with interrupts pending.
953 * (self contained on a per cpu basis)
958 globaldata_t gd
= mycpu
;
959 thread_t td
= gd
->gd_curthread
;
961 if (gd
->gd_reqflags
&& td
->td_nest_count
< 2)
966 * This implements a normal yield which will yield to equal priority
967 * threads as well as higher priority threads. Note that gd_reqflags
968 * tests will be handled by the crit_exit() call in lwkt_switch().
970 * (self contained on a per cpu basis)
975 lwkt_schedule_self(curthread
);
980 * This function is used along with the lwkt_passive_recover() inline
981 * by the trap code to negotiate a passive release of the current
982 * process/lwp designation with the user scheduler.
985 lwkt_passive_release(struct thread
*td
)
987 struct lwp
*lp
= td
->td_lwp
;
989 td
->td_release
= NULL
;
990 lwkt_setpri_self(TDPRI_KERN_USER
);
991 lp
->lwp_proc
->p_usched
->release_curproc(lp
);
995 * Make a kernel thread act as if it were in user mode with regards
996 * to scheduling, to avoid becoming cpu-bound in the kernel. Kernel
997 * loops which may be potentially cpu-bound can call lwkt_user_yield().
999 * The lwkt_user_yield() function is designed to have very low overhead
1000 * if no yield is determined to be needed.
1003 lwkt_user_yield(void)
1005 thread_t td
= curthread
;
1006 struct lwp
*lp
= td
->td_lwp
;
1010 * XXX SEVERE TEMPORARY HACK. A cpu-bound operation running in the
1011 * kernel can prevent other cpus from servicing interrupt threads
1012 * which still require the MP lock (which is a lot of them). This
1013 * has a chaining effect since if the interrupt is blocked, so is
1014 * the event, so normal scheduling will not pick up on the problem.
1016 if (mplock_countx
&& td
->td_mpcount
) {
1017 int savecnt
= td
->td_mpcount
;
1024 td
->td_mpcount
= savecnt
;
1029 * Another kernel thread wants the cpu
1031 if (lwkt_resched_wanted())
1035 * If the user scheduler has asynchronously determined that the current
1036 * process (when running in user mode) needs to lose the cpu then make
1037 * sure we are released.
1039 if (user_resched_wanted()) {
1045 * If we are released reduce our priority
1047 if (td
->td_release
== NULL
) {
1048 if (lwkt_check_resched(td
) > 0)
1051 lp
->lwp_proc
->p_usched
->acquire_curproc(lp
);
1052 td
->td_release
= lwkt_passive_release
;
1053 lwkt_setpri_self(TDPRI_USER_NORM
);
1059 * Return 0 if no runnable threads are pending at the same or higher
1060 * priority as the passed thread.
1062 * Return 1 if runnable threads are pending at the same priority.
1064 * Return 2 if runnable threads are pending at a higher priority.
1067 lwkt_check_resched(thread_t td
)
1069 int pri
= td
->td_pri
& TDPRI_MASK
;
1071 if (td
->td_gd
->gd_runqmask
> (2 << pri
) - 1)
1073 if (TAILQ_NEXT(td
, td_threadq
))
1079 * Generic schedule. Possibly schedule threads belonging to other cpus and
1080 * deal with threads that might be blocked on a wait queue.
1082 * We have a little helper inline function which does additional work after
1083 * the thread has been enqueued, including dealing with preemption and
1084 * setting need_lwkt_resched() (which prevents the kernel from returning
1085 * to userland until it has processed higher priority threads).
1087 * It is possible for this routine to be called after a failed _enqueue
1088 * (due to the target thread migrating, sleeping, or otherwise blocked).
1089 * We have to check that the thread is actually on the run queue!
1091 * reschedok is an optimized constant propagated from lwkt_schedule() or
1092 * lwkt_schedule_noresched(). By default it is non-zero, causing a
1093 * reschedule to be requested if the target thread has a higher priority.
1094 * The port messaging code will set MSG_NORESCHED and cause reschedok to
1095 * be 0, prevented undesired reschedules.
1099 _lwkt_schedule_post(globaldata_t gd
, thread_t ntd
, int cpri
, int reschedok
)
1103 if (ntd
->td_flags
& TDF_RUNQ
) {
1104 if (ntd
->td_preemptable
&& reschedok
) {
1105 ntd
->td_preemptable(ntd
, cpri
); /* YYY +token */
1106 } else if (reschedok
) {
1108 if ((ntd
->td_pri
& TDPRI_MASK
) > (otd
->td_pri
& TDPRI_MASK
))
1109 need_lwkt_resched();
1116 _lwkt_schedule(thread_t td
, int reschedok
)
1118 globaldata_t mygd
= mycpu
;
1120 KASSERT(td
!= &td
->td_gd
->gd_idlethread
, ("lwkt_schedule(): scheduling gd_idlethread is illegal!"));
1121 crit_enter_gd(mygd
);
1122 KKASSERT(td
->td_lwp
== NULL
|| (td
->td_lwp
->lwp_flag
& LWP_ONRUNQ
) == 0);
1123 if (td
== mygd
->gd_curthread
) {
1127 * If we own the thread, there is no race (since we are in a
1128 * critical section). If we do not own the thread there might
1129 * be a race but the target cpu will deal with it.
1132 if (td
->td_gd
== mygd
) {
1134 _lwkt_schedule_post(mygd
, td
, TDPRI_CRIT
, reschedok
);
1136 lwkt_send_ipiq3(td
->td_gd
, lwkt_schedule_remote
, td
, 0);
1140 _lwkt_schedule_post(mygd
, td
, TDPRI_CRIT
, reschedok
);
1147 lwkt_schedule(thread_t td
)
1149 _lwkt_schedule(td
, 1);
1153 lwkt_schedule_noresched(thread_t td
)
1155 _lwkt_schedule(td
, 0);
1161 * When scheduled remotely if frame != NULL the IPIQ is being
1162 * run via doreti or an interrupt then preemption can be allowed.
1164 * To allow preemption we have to drop the critical section so only
1165 * one is present in _lwkt_schedule_post.
1168 lwkt_schedule_remote(void *arg
, int arg2
, struct intrframe
*frame
)
1170 thread_t td
= curthread
;
1173 if (frame
&& ntd
->td_preemptable
) {
1174 crit_exit_noyield(td
);
1175 _lwkt_schedule(ntd
, 1);
1176 crit_enter_quick(td
);
1178 _lwkt_schedule(ntd
, 1);
1183 * Thread migration using a 'Pull' method. The thread may or may not be
1184 * the current thread. It MUST be descheduled and in a stable state.
1185 * lwkt_giveaway() must be called on the cpu owning the thread.
1187 * At any point after lwkt_giveaway() is called, the target cpu may
1188 * 'pull' the thread by calling lwkt_acquire().
1190 * We have to make sure the thread is not sitting on a per-cpu tsleep
1191 * queue or it will blow up when it moves to another cpu.
1193 * MPSAFE - must be called under very specific conditions.
1196 lwkt_giveaway(thread_t td
)
1198 globaldata_t gd
= mycpu
;
1201 if (td
->td_flags
& TDF_TSLEEPQ
)
1203 KKASSERT(td
->td_gd
== gd
);
1204 TAILQ_REMOVE(&gd
->gd_tdallq
, td
, td_allq
);
1205 td
->td_flags
|= TDF_MIGRATING
;
1210 lwkt_acquire(thread_t td
)
1215 KKASSERT(td
->td_flags
& TDF_MIGRATING
);
1220 KKASSERT((td
->td_flags
& TDF_RUNQ
) == 0);
1221 crit_enter_gd(mygd
);
1222 while (td
->td_flags
& (TDF_RUNNING
|TDF_PREEMPT_LOCK
)) {
1224 lwkt_process_ipiq();
1229 TAILQ_INSERT_TAIL(&mygd
->gd_tdallq
, td
, td_allq
);
1230 td
->td_flags
&= ~TDF_MIGRATING
;
1233 crit_enter_gd(mygd
);
1234 TAILQ_INSERT_TAIL(&mygd
->gd_tdallq
, td
, td_allq
);
1235 td
->td_flags
&= ~TDF_MIGRATING
;
1243 * Generic deschedule. Descheduling threads other then your own should be
1244 * done only in carefully controlled circumstances. Descheduling is
1247 * This function may block if the cpu has run out of messages.
1250 lwkt_deschedule(thread_t td
)
1254 if (td
== curthread
) {
1257 if (td
->td_gd
== mycpu
) {
1260 lwkt_send_ipiq(td
->td_gd
, (ipifunc1_t
)lwkt_deschedule
, td
);
1270 * Set the target thread's priority. This routine does not automatically
1271 * switch to a higher priority thread, LWKT threads are not designed for
1272 * continuous priority changes. Yield if you want to switch.
1274 * We have to retain the critical section count which uses the high bits
1275 * of the td_pri field. The specified priority may also indicate zero or
1276 * more critical sections by adding TDPRI_CRIT*N.
1278 * Note that we requeue the thread whether it winds up on a different runq
1279 * or not. uio_yield() depends on this and the routine is not normally
1280 * called with the same priority otherwise.
1283 lwkt_setpri(thread_t td
, int pri
)
1286 KKASSERT(td
->td_gd
== mycpu
);
1288 if (td
->td_flags
& TDF_RUNQ
) {
1290 td
->td_pri
= (td
->td_pri
& ~TDPRI_MASK
) + pri
;
1293 td
->td_pri
= (td
->td_pri
& ~TDPRI_MASK
) + pri
;
1299 * Set the initial priority for a thread prior to it being scheduled for
1300 * the first time. The thread MUST NOT be scheduled before or during
1301 * this call. The thread may be assigned to a cpu other then the current
1304 * Typically used after a thread has been created with TDF_STOPPREQ,
1305 * and before the thread is initially scheduled.
1308 lwkt_setpri_initial(thread_t td
, int pri
)
1311 KKASSERT((td
->td_flags
& TDF_RUNQ
) == 0);
1312 td
->td_pri
= (td
->td_pri
& ~TDPRI_MASK
) + pri
;
1316 lwkt_setpri_self(int pri
)
1318 thread_t td
= curthread
;
1320 KKASSERT(pri
>= 0 && pri
<= TDPRI_MAX
);
1322 if (td
->td_flags
& TDF_RUNQ
) {
1324 td
->td_pri
= (td
->td_pri
& ~TDPRI_MASK
) + pri
;
1327 td
->td_pri
= (td
->td_pri
& ~TDPRI_MASK
) + pri
;
1333 * Migrate the current thread to the specified cpu.
1335 * This is accomplished by descheduling ourselves from the current cpu,
1336 * moving our thread to the tdallq of the target cpu, IPI messaging the
1337 * target cpu, and switching out. TDF_MIGRATING prevents scheduling
1338 * races while the thread is being migrated.
1340 * We must be sure to remove ourselves from the current cpu's tsleepq
1341 * before potentially moving to another queue. The thread can be on
1342 * a tsleepq due to a left-over tsleep_interlock().
1345 static void lwkt_setcpu_remote(void *arg
);
1349 lwkt_setcpu_self(globaldata_t rgd
)
1352 thread_t td
= curthread
;
1354 if (td
->td_gd
!= rgd
) {
1355 crit_enter_quick(td
);
1356 if (td
->td_flags
& TDF_TSLEEPQ
)
1358 td
->td_flags
|= TDF_MIGRATING
;
1359 lwkt_deschedule_self(td
);
1360 TAILQ_REMOVE(&td
->td_gd
->gd_tdallq
, td
, td_allq
);
1361 lwkt_send_ipiq(rgd
, (ipifunc1_t
)lwkt_setcpu_remote
, td
);
1363 /* we are now on the target cpu */
1364 TAILQ_INSERT_TAIL(&rgd
->gd_tdallq
, td
, td_allq
);
1365 crit_exit_quick(td
);
1371 lwkt_migratecpu(int cpuid
)
1376 rgd
= globaldata_find(cpuid
);
1377 lwkt_setcpu_self(rgd
);
1382 * Remote IPI for cpu migration (called while in a critical section so we
1383 * do not have to enter another one). The thread has already been moved to
1384 * our cpu's allq, but we must wait for the thread to be completely switched
1385 * out on the originating cpu before we schedule it on ours or the stack
1386 * state may be corrupt. We clear TDF_MIGRATING after flushing the GD
1387 * change to main memory.
1389 * XXX The use of TDF_MIGRATING might not be sufficient to avoid races
1390 * against wakeups. It is best if this interface is used only when there
1391 * are no pending events that might try to schedule the thread.
1395 lwkt_setcpu_remote(void *arg
)
1398 globaldata_t gd
= mycpu
;
1400 while (td
->td_flags
& (TDF_RUNNING
|TDF_PREEMPT_LOCK
)) {
1402 lwkt_process_ipiq();
1408 td
->td_flags
&= ~TDF_MIGRATING
;
1409 KKASSERT(td
->td_lwp
== NULL
|| (td
->td_lwp
->lwp_flag
& LWP_ONRUNQ
) == 0);
1415 lwkt_preempted_proc(void)
1417 thread_t td
= curthread
;
1418 while (td
->td_preempted
)
1419 td
= td
->td_preempted
;
1424 * Create a kernel process/thread/whatever. It shares it's address space
1425 * with proc0 - ie: kernel only.
1427 * NOTE! By default new threads are created with the MP lock held. A
1428 * thread which does not require the MP lock should release it by calling
1429 * rel_mplock() at the start of the new thread.
1432 lwkt_create(void (*func
)(void *), void *arg
,
1433 struct thread
**tdp
, thread_t
template, int tdflags
, int cpu
,
1434 const char *fmt
, ...)
1439 td
= lwkt_alloc_thread(template, LWKT_THREAD_STACK
, cpu
,
1443 cpu_set_thread_handler(td
, lwkt_exit
, func
, arg
);
1446 * Set up arg0 for 'ps' etc
1448 __va_start(ap
, fmt
);
1449 kvsnprintf(td
->td_comm
, sizeof(td
->td_comm
), fmt
, ap
);
1453 * Schedule the thread to run
1455 if ((td
->td_flags
& TDF_STOPREQ
) == 0)
1458 td
->td_flags
&= ~TDF_STOPREQ
;
1463 * Destroy an LWKT thread. Warning! This function is not called when
1464 * a process exits, cpu_proc_exit() directly calls cpu_thread_exit() and
1465 * uses a different reaping mechanism.
1470 thread_t td
= curthread
;
1474 if (td
->td_flags
& TDF_VERBOSE
)
1475 kprintf("kthread %p %s has exited\n", td
, td
->td_comm
);
1479 * Get us into a critical section to interlock gd_freetd and loop
1480 * until we can get it freed.
1482 * We have to cache the current td in gd_freetd because objcache_put()ing
1483 * it would rip it out from under us while our thread is still active.
1486 crit_enter_quick(td
);
1487 while ((std
= gd
->gd_freetd
) != NULL
) {
1488 gd
->gd_freetd
= NULL
;
1489 objcache_put(thread_cache
, std
);
1493 * Remove thread resources from kernel lists and deschedule us for
1496 if (td
->td_flags
& TDF_TSLEEPQ
)
1499 lwkt_deschedule_self(td
);
1500 lwkt_remove_tdallq(td
);
1501 if (td
->td_flags
& TDF_ALLOCATED_THREAD
)
1507 lwkt_remove_tdallq(thread_t td
)
1509 KKASSERT(td
->td_gd
== mycpu
);
1510 TAILQ_REMOVE(&td
->td_gd
->gd_tdallq
, td
, td_allq
);
1516 thread_t td
= curthread
;
1517 int lpri
= td
->td_pri
;
1520 panic("td_pri is/would-go negative! %p %d", td
, lpri
);
1526 * Called from debugger/panic on cpus which have been stopped. We must still
1527 * process the IPIQ while stopped, even if we were stopped while in a critical
1530 * If we are dumping also try to process any pending interrupts. This may
1531 * or may not work depending on the state of the cpu at the point it was
1535 lwkt_smp_stopped(void)
1537 globaldata_t gd
= mycpu
;
1541 lwkt_process_ipiq();
1544 lwkt_process_ipiq();
1550 * get_mplock() calls this routine if it is unable to obtain the MP lock.
1551 * get_mplock() has already incremented td_mpcount. We must block and
1552 * not return until giant is held.
1554 * All we have to do is lwkt_switch() away. The LWKT scheduler will not
1555 * reschedule the thread until it can obtain the giant lock for it.
1558 lwkt_mp_lock_contested(void)
1567 * The rel_mplock() code will call this function after releasing the
1568 * last reference on the MP lock if mp_lock_contention_mask is non-zero.
1570 * We then chain an IPI to a single other cpu potentially needing the
1571 * lock. This is a bit heuristical and we can wind up with IPIs flying
1572 * all over the place.
1574 static void lwkt_mp_lock_uncontested_remote(void *arg __unused
);
1577 lwkt_mp_lock_uncontested(void)
1587 atomic_clear_int(&mp_lock_contention_mask
, gd
->gd_cpumask
);
1588 mask
= mp_lock_contention_mask
;
1589 tmpmask
= ~((1 << gd
->gd_cpuid
) - 1);
1593 cpuid
= bsfl(mask
& tmpmask
);
1596 atomic_clear_int(&mp_lock_contention_mask
, 1 << cpuid
);
1597 dgd
= globaldata_find(cpuid
);
1598 lwkt_send_ipiq(dgd
, lwkt_mp_lock_uncontested_remote
, NULL
);
1604 * The idea is for this IPI to interrupt a potentially lower priority
1605 * thread, such as a user thread, to allow the scheduler to reschedule
1606 * a higher priority kernel thread that needs the MP lock.
1608 * For now we set the LWKT reschedule flag which generates an AST in
1609 * doreti, though theoretically it is also possible to possibly preempt
1610 * here if the underlying thread was operating in user mode. Nah.
1613 lwkt_mp_lock_uncontested_remote(void *arg __unused
)
1615 need_lwkt_resched();