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);
111 * We can make all thread ports use the spin backend instead of the thread
112 * backend. This should only be set to debug the spin backend.
114 TUNABLE_INT("lwkt.use_spin_port", &lwkt_use_spin_port);
117 SYSCTL_INT(_lwkt, OID_AUTO, panic_on_cscount, CTLFLAG_RW, &panic_on_cscount, 0,
118 "Panic if attempting to switch lwkt's while mastering cpusync");
120 SYSCTL_QUAD(_lwkt, OID_AUTO, switch_count, CTLFLAG_RW, &switch_count, 0,
121 "Number of switched threads");
122 SYSCTL_QUAD(_lwkt, OID_AUTO, preempt_hit, CTLFLAG_RW, &preempt_hit, 0,
123 "Successful preemption events");
124 SYSCTL_QUAD(_lwkt, OID_AUTO, preempt_miss, CTLFLAG_RW, &preempt_miss, 0,
125 "Failed preemption events");
126 SYSCTL_QUAD(_lwkt, OID_AUTO, preempt_weird, CTLFLAG_RW, &preempt_weird, 0,
127 "Number of preempted threads.");
129 SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count, CTLFLAG_RW,
130 &token_contention_count, 0, "spinning due to token contention");
132 static int fairq_enable = 1;
133 SYSCTL_INT(_lwkt, OID_AUTO, fairq_enable, CTLFLAG_RW, &fairq_enable, 0,
134 "Turn on fairq priority accumulators");
135 static int user_pri_sched = 0;
136 SYSCTL_INT(_lwkt, OID_AUTO, user_pri_sched, CTLFLAG_RW, &user_pri_sched, 0,
138 static int preempt_enable = 1;
139 SYSCTL_INT(_lwkt, OID_AUTO, preempt_enable, CTLFLAG_RW, &preempt_enable, 0,
140 "Enable preemption");
144 * These helper procedures handle the runq, they can only be called from
145 * within a critical section.
147 * WARNING! Prior to SMP being brought up it is possible to enqueue and
148 * dequeue threads belonging to other cpus, so be sure to use td->td_gd
149 * instead of 'mycpu' when referencing the globaldata structure. Once
150 * SMP live enqueuing and dequeueing only occurs on the current cpu.
154 _lwkt_dequeue(thread_t td)
156 if (td->td_flags & TDF_RUNQ) {
157 struct globaldata *gd = td->td_gd;
159 td->td_flags &= ~TDF_RUNQ;
160 TAILQ_REMOVE(&gd->gd_tdrunq, td, td_threadq);
161 gd->gd_fairq_total_pri -= td->td_pri;
162 if (TAILQ_FIRST(&gd->gd_tdrunq) == NULL)
163 atomic_clear_int_nonlocked(&gd->gd_reqflags, RQF_RUNNING);
170 * NOTE: There are a limited number of lwkt threads runnable since user
171 * processes only schedule one at a time per cpu.
175 _lwkt_enqueue(thread_t td)
179 if ((td->td_flags & (TDF_RUNQ|TDF_MIGRATING|TDF_BLOCKQ)) == 0) {
180 struct globaldata *gd = td->td_gd;
182 td->td_flags |= TDF_RUNQ;
183 xtd = TAILQ_FIRST(&gd->gd_tdrunq);
185 TAILQ_INSERT_TAIL(&gd->gd_tdrunq, td, td_threadq);
186 atomic_set_int_nonlocked(&gd->gd_reqflags, RQF_RUNNING);
188 while (xtd && xtd->td_pri > td->td_pri)
189 xtd = TAILQ_NEXT(xtd, td_threadq);
191 TAILQ_INSERT_BEFORE(xtd, td, td_threadq);
193 TAILQ_INSERT_TAIL(&gd->gd_tdrunq, td, td_threadq);
195 gd->gd_fairq_total_pri += td->td_pri;
200 _lwkt_thread_ctor(void *obj, void *privdata, int ocflags)
202 struct thread *td = (struct thread *)obj;
204 td->td_kstack = NULL;
205 td->td_kstack_size = 0;
206 td->td_flags = TDF_ALLOCATED_THREAD;
211 _lwkt_thread_dtor(void *obj, void *privdata)
213 struct thread *td = (struct thread *)obj;
215 KASSERT(td->td_flags & TDF_ALLOCATED_THREAD,
216 ("_lwkt_thread_dtor: not allocated from objcache"));
217 KASSERT((td->td_flags & TDF_ALLOCATED_STACK) && td->td_kstack &&
218 td->td_kstack_size > 0,
219 ("_lwkt_thread_dtor: corrupted stack"));
220 kmem_free(&kernel_map, (vm_offset_t)td->td_kstack, td->td_kstack_size);
224 * Initialize the lwkt s/system.
229 /* An objcache has 2 magazines per CPU so divide cache size by 2. */
230 thread_cache = objcache_create_mbacked(M_THREAD, sizeof(struct thread),
231 NULL, CACHE_NTHREADS/2,
232 _lwkt_thread_ctor, _lwkt_thread_dtor, NULL);
236 * Schedule a thread to run. As the current thread we can always safely
237 * schedule ourselves, and a shortcut procedure is provided for that
240 * (non-blocking, self contained on a per cpu basis)
243 lwkt_schedule_self(thread_t td)
245 crit_enter_quick(td);
246 KASSERT(td != &td->td_gd->gd_idlethread,
247 ("lwkt_schedule_self(): scheduling gd_idlethread is illegal!"));
248 KKASSERT(td->td_lwp == NULL || (td->td_lwp->lwp_flag & LWP_ONRUNQ) == 0);
254 * Deschedule a thread.
256 * (non-blocking, self contained on a per cpu basis)
259 lwkt_deschedule_self(thread_t td)
261 crit_enter_quick(td);
267 * LWKTs operate on a per-cpu basis
269 * WARNING! Called from early boot, 'mycpu' may not work yet.
272 lwkt_gdinit(struct globaldata *gd)
274 TAILQ_INIT(&gd->gd_tdrunq);
275 TAILQ_INIT(&gd->gd_tdallq);
279 * Create a new thread. The thread must be associated with a process context
280 * or LWKT start address before it can be scheduled. If the target cpu is
281 * -1 the thread will be created on the current cpu.
283 * If you intend to create a thread without a process context this function
284 * does everything except load the startup and switcher function.
287 lwkt_alloc_thread(struct thread *td, int stksize, int cpu, int flags)
289 globaldata_t gd = mycpu;
293 * If static thread storage is not supplied allocate a thread. Reuse
294 * a cached free thread if possible. gd_freetd is used to keep an exiting
295 * thread intact through the exit.
299 if ((td = gd->gd_freetd) != NULL) {
300 KKASSERT((td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK|
302 gd->gd_freetd = NULL;
304 td = objcache_get(thread_cache, M_WAITOK);
305 KKASSERT((td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK|
309 KASSERT((td->td_flags &
310 (TDF_ALLOCATED_THREAD|TDF_RUNNING)) == TDF_ALLOCATED_THREAD,
311 ("lwkt_alloc_thread: corrupted td flags 0x%X", td->td_flags));
312 flags |= td->td_flags & (TDF_ALLOCATED_THREAD|TDF_ALLOCATED_STACK);
316 * Try to reuse cached stack.
318 if ((stack = td->td_kstack) != NULL && td->td_kstack_size != stksize) {
319 if (flags & TDF_ALLOCATED_STACK) {
320 kmem_free(&kernel_map, (vm_offset_t)stack, td->td_kstack_size);
325 stack = (void *)kmem_alloc_stack(&kernel_map, stksize);
326 flags |= TDF_ALLOCATED_STACK;
329 lwkt_init_thread(td, stack, stksize, flags, gd);
331 lwkt_init_thread(td, stack, stksize, flags, globaldata_find(cpu));
336 * Initialize a preexisting thread structure. This function is used by
337 * lwkt_alloc_thread() and also used to initialize the per-cpu idlethread.
339 * All threads start out in a critical section at a priority of
340 * TDPRI_KERN_DAEMON. Higher level code will modify the priority as
341 * appropriate. This function may send an IPI message when the
342 * requested cpu is not the current cpu and consequently gd_tdallq may
343 * not be initialized synchronously from the point of view of the originating
346 * NOTE! we have to be careful in regards to creating threads for other cpus
347 * if SMP has not yet been activated.
352 lwkt_init_thread_remote(void *arg)
357 * Protected by critical section held by IPI dispatch
359 TAILQ_INSERT_TAIL(&td->td_gd->gd_tdallq, td, td_allq);
365 * lwkt core thread structural initialization.
367 * NOTE: All threads are initialized as mpsafe threads.
370 lwkt_init_thread(thread_t td, void *stack, int stksize, int flags,
371 struct globaldata *gd)
373 globaldata_t mygd = mycpu;
375 bzero(td, sizeof(struct thread));
376 td->td_kstack = stack;
377 td->td_kstack_size = stksize;
378 td->td_flags = flags;
380 td->td_pri = TDPRI_KERN_DAEMON;
381 td->td_critcount = 1;
382 td->td_toks_stop = &td->td_toks_base;
383 if (lwkt_use_spin_port)
384 lwkt_initport_spin(&td->td_msgport);
386 lwkt_initport_thread(&td->td_msgport, td);
387 pmap_init_thread(td);
390 * Normally initializing a thread for a remote cpu requires sending an
391 * IPI. However, the idlethread is setup before the other cpus are
392 * activated so we have to treat it as a special case. XXX manipulation
393 * of gd_tdallq requires the BGL.
395 if (gd == mygd || td == &gd->gd_idlethread) {
397 TAILQ_INSERT_TAIL(&gd->gd_tdallq, td, td_allq);
400 lwkt_send_ipiq(gd, lwkt_init_thread_remote, td);
404 TAILQ_INSERT_TAIL(&gd->gd_tdallq, td, td_allq);
408 dsched_new_thread(td);
412 lwkt_set_comm(thread_t td, const char *ctl, ...)
417 kvsnprintf(td->td_comm, sizeof(td->td_comm), ctl, va);
419 KTR_LOG(ctxsw_newtd, td, &td->td_comm[0]);
423 lwkt_hold(thread_t td)
429 lwkt_rele(thread_t td)
431 KKASSERT(td->td_refs > 0);
436 lwkt_wait_free(thread_t td)
439 tsleep(td, 0, "tdreap", hz);
443 lwkt_free_thread(thread_t td)
445 KKASSERT((td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK|TDF_RUNQ)) == 0);
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;
456 KTR_LOG(ctxsw_deadtd, td);
461 * Switch to the next runnable lwkt. If no LWKTs are runnable then
462 * switch to the idlethread. Switching must occur within a critical
463 * section to avoid races with the scheduling queue.
465 * We always have full control over our cpu's run queue. Other cpus
466 * that wish to manipulate our queue must use the cpu_*msg() calls to
467 * talk to our cpu, so a critical section is all that is needed and
468 * the result is very, very fast thread switching.
470 * The LWKT scheduler uses a fixed priority model and round-robins at
471 * each priority level. User process scheduling is a totally
472 * different beast and LWKT priorities should not be confused with
473 * user process priorities.
475 * The MP lock may be out of sync with the thread's td_mpcount + td_xpcount.
476 * lwkt_switch() cleans it up.
478 * Note that the td_switch() function cannot do anything that requires
479 * the MP lock since the MP lock will have already been setup for
480 * the target thread (not the current thread). It's nice to have a scheduler
481 * that does not need the MP lock to work because it allows us to do some
482 * really cool high-performance MP lock optimizations.
484 * PREEMPTION NOTE: Preemption occurs via lwkt_preempt(). lwkt_switch()
485 * is not called by the current thread in the preemption case, only when
486 * the preempting thread blocks (in order to return to the original thread).
491 globaldata_t gd = mycpu;
492 thread_t td = gd->gd_curthread;
503 * Switching from within a 'fast' (non thread switched) interrupt or IPI
504 * is illegal. However, we may have to do it anyway if we hit a fatal
505 * kernel trap or we have paniced.
507 * If this case occurs save and restore the interrupt nesting level.
509 if (gd->gd_intr_nesting_level) {
513 if (gd->gd_trap_nesting_level == 0 && panic_cpu_gd != mycpu) {
514 panic("lwkt_switch: Attempt to switch from a "
515 "a fast interrupt, ipi, or hard code section, "
519 savegdnest = gd->gd_intr_nesting_level;
520 savegdtrap = gd->gd_trap_nesting_level;
521 gd->gd_intr_nesting_level = 0;
522 gd->gd_trap_nesting_level = 0;
523 if ((td->td_flags & TDF_PANICWARN) == 0) {
524 td->td_flags |= TDF_PANICWARN;
525 kprintf("Warning: thread switch from interrupt, IPI, "
526 "or hard code section.\n"
527 "thread %p (%s)\n", td, td->td_comm);
531 gd->gd_intr_nesting_level = savegdnest;
532 gd->gd_trap_nesting_level = savegdtrap;
538 * Passive release (used to transition from user to kernel mode
539 * when we block or switch rather then when we enter the kernel).
540 * This function is NOT called if we are switching into a preemption
541 * or returning from a preemption. Typically this causes us to lose
542 * our current process designation (if we have one) and become a true
543 * LWKT thread, and may also hand the current process designation to
544 * another process and schedule thread.
550 if (TD_TOKS_HELD(td))
551 lwkt_relalltokens(td);
554 * We had better not be holding any spin locks, but don't get into an
555 * endless panic loop.
557 KASSERT(gd->gd_spinlocks_wr == 0 || panicstr != NULL,
558 ("lwkt_switch: still holding %d exclusive spinlocks!",
559 gd->gd_spinlocks_wr));
564 * td_mpcount + td_xpcount cannot be used to determine if we currently
565 * hold the MP lock because get_mplock() will increment it prior to
566 * attempting to get the lock, and switch out if it can't. Our
567 * ownership of the actual lock will remain stable while we are
568 * in a critical section, and once we actually acquire the underlying
569 * lock as long as the count is greater than 0.
571 mpheld = MP_LOCK_HELD(gd);
573 if (td->td_cscount) {
574 kprintf("Diagnostic: attempt to switch while mastering cpusync: %p\n",
576 if (panic_on_cscount)
577 panic("switching while mastering cpusync");
583 * If we had preempted another thread on this cpu, resume the preempted
584 * thread. This occurs transparently, whether the preempted thread
585 * was scheduled or not (it may have been preempted after descheduling
588 * We have to setup the MP lock for the original thread after backing
589 * out the adjustment that was made to curthread when the original
592 if ((ntd = td->td_preempted) != NULL) {
593 KKASSERT(ntd->td_flags & TDF_PREEMPT_LOCK);
595 if (ntd->td_mpcount + ntd->td_xpcount && mpheld == 0) {
596 panic("MPLOCK NOT HELD ON RETURN: %p %p %d %d",
597 td, ntd, td->td_mpcount, ntd->td_mpcount + ntd->td_xpcount);
601 ntd->td_flags |= TDF_PREEMPT_DONE;
604 * The interrupt may have woken a thread up, we need to properly
605 * set the reschedule flag if the originally interrupted thread is
606 * at a lower priority.
608 if (TAILQ_FIRST(&gd->gd_tdrunq) &&
609 TAILQ_FIRST(&gd->gd_tdrunq)->td_pri > ntd->td_pri) {
612 /* YYY release mp lock on switchback if original doesn't need it */
613 goto havethread_preempted;
617 * Implement round-robin fairq with priority insertion. The priority
618 * insertion is handled by _lwkt_enqueue()
620 * We have to adjust the MP lock for the target thread. If we
621 * need the MP lock and cannot obtain it we try to locate a
622 * thread that does not need the MP lock. If we cannot, we spin
625 * A similar issue exists for the tokens held by the target thread.
626 * If we cannot obtain ownership of the tokens we cannot immediately
627 * schedule the thread.
630 clear_lwkt_resched();
632 ntd = TAILQ_FIRST(&gd->gd_tdrunq);
635 * Hotpath if we can get all necessary resources.
637 * If nothing is runnable switch to the idle thread
640 ntd = &gd->gd_idlethread;
641 if (gd->gd_reqflags & RQF_IDLECHECK_MASK)
642 ntd->td_flags |= TDF_IDLE_NOHLT;
644 KKASSERT(ntd->td_xpcount == 0);
645 if (ntd->td_mpcount) {
646 if (gd->gd_trap_nesting_level == 0 && panicstr == NULL)
647 panic("Idle thread %p was holding the BGL!", ntd);
649 set_cpu_contention_mask(gd);
650 handle_cpu_contention_mask();
652 mpheld = MP_LOCK_HELD(gd);
657 clr_cpu_contention_mask(gd);
659 cpu_time.cp_msg[0] = 0;
660 cpu_time.cp_stallpc = 0;
667 * NOTE: For UP there is no mplock and lwkt_getalltokens()
670 if (ntd->td_fairq_accum >= 0 &&
672 (ntd->td_mpcount + ntd->td_xpcount == 0 ||
673 mpheld || cpu_try_mplock_msg(&ntd->td_wmesg)) &&
675 (!TD_TOKS_HELD(ntd) ||
676 lwkt_getalltokens(ntd))
679 clr_cpu_contention_mask(gd);
685 if (ntd->td_fairq_accum >= 0)
686 set_cpu_contention_mask(gd);
687 /* Reload mpheld (it become stale after mplock/token ops) */
688 mpheld = MP_LOCK_HELD(gd);
692 * Coldpath - unable to schedule ntd, continue looking for threads
693 * to schedule. This is only allowed of the (presumably) kernel
694 * thread exhausted its fair share. A kernel thread stuck on
695 * resources does not currently allow a user thread to get in
699 nquserok = ((ntd->td_pri < TDPRI_KERN_LPSCHED) ||
700 (ntd->td_fairq_accum < 0));
708 * If the fair-share scheduler ran out ntd gets moved to the
709 * end and its accumulator will be bumped, if it didn't we
710 * maintain the same queue position.
712 * nlast keeps track of the last element prior to any moves.
714 if (ntd->td_fairq_accum < 0) {
715 lwkt_fairq_accumulate(gd, ntd);
721 xtd = TAILQ_NEXT(ntd, td_threadq);
722 TAILQ_REMOVE(&gd->gd_tdrunq, ntd, td_threadq);
723 TAILQ_INSERT_TAIL(&gd->gd_tdrunq, ntd, td_threadq);
726 * Set terminal element (nlast)
735 ntd = TAILQ_NEXT(ntd, td_threadq);
739 * If we exhausted the run list switch to the idle thread.
740 * Since one or more threads had resource acquisition issues
741 * we do not allow the idle thread to halt.
743 * NOTE: nlast can be NULL.
747 ntd = &gd->gd_idlethread;
748 ntd->td_flags |= TDF_IDLE_NOHLT;
750 KKASSERT(ntd->td_xpcount == 0);
751 if (ntd->td_mpcount) {
752 mpheld = MP_LOCK_HELD(gd);
753 if (gd->gd_trap_nesting_level == 0 && panicstr == NULL)
754 panic("Idle thread %p was holding the BGL!", ntd);
756 set_cpu_contention_mask(gd);
757 handle_cpu_contention_mask();
759 mpheld = MP_LOCK_HELD(gd);
761 break; /* try again from the top, almost */
767 * If fairq accumulations occured we do not schedule the
768 * idle thread. This will cause us to try again from
772 break; /* try again from the top, almost */
777 * Try to switch to this thread.
779 * NOTE: For UP there is no mplock and lwkt_getalltokens()
782 if ((ntd->td_pri >= TDPRI_KERN_LPSCHED || nquserok ||
783 user_pri_sched) && ntd->td_fairq_accum >= 0 &&
785 (ntd->td_mpcount + ntd->td_xpcount == 0 ||
786 mpheld || cpu_try_mplock_msg(&ntd->td_wmesg)) &&
788 (!TD_TOKS_HELD(ntd) || lwkt_getalltokens(ntd))
791 clr_cpu_contention_mask(gd);
797 * Thread was runnable but we were unable to get the required
798 * resources (tokens and/or mplock).
801 if (ntd->td_fairq_accum >= 0)
802 set_cpu_contention_mask(gd);
804 * Reload mpheld (it become stale after mplock/token ops).
806 mpheld = MP_LOCK_HELD(gd);
807 if (ntd->td_pri >= TDPRI_KERN_LPSCHED && ntd->td_fairq_accum >= 0)
813 * All threads exhausted but we can loop due to a negative
816 * While we are looping in the scheduler be sure to service
817 * any interrupts which were made pending due to our critical
818 * section, otherwise we could livelock (e.g.) IPIs.
820 * NOTE: splz can enter and exit the mplock so mpheld is
821 * stale after this call.
827 * Our mplock can be cached and cause other cpus to livelock
828 * if we loop due to e.g. not being able to acquire tokens.
830 if (MP_LOCK_HELD(gd))
831 cpu_rel_mplock(gd->gd_cpuid);
837 * Do the actual switch. WARNING: mpheld is stale here.
839 * We must always decrement td_fairq_accum on non-idle threads just
840 * in case a thread never gets a tick due to being in a continuous
841 * critical section. The page-zeroing code does that.
843 * If the thread we came up with is a higher or equal priority verses
844 * the thread at the head of the queue we move our thread to the
845 * front. This way we can always check the front of the queue.
848 ++gd->gd_cnt.v_swtch;
849 --ntd->td_fairq_accum;
850 ntd->td_wmesg = NULL;
851 xtd = TAILQ_FIRST(&gd->gd_tdrunq);
852 if (ntd != xtd && ntd->td_pri >= xtd->td_pri) {
853 TAILQ_REMOVE(&gd->gd_tdrunq, ntd, td_threadq);
854 TAILQ_INSERT_HEAD(&gd->gd_tdrunq, ntd, td_threadq);
856 havethread_preempted:
859 * If the new target does not need the MP lock and we are holding it,
860 * release the MP lock. If the new target requires the MP lock we have
861 * already acquired it for the target.
863 * WARNING: mpheld is stale here.
866 KASSERT(ntd->td_critcount,
867 ("priority problem in lwkt_switch %d %d", td->td_pri, ntd->td_pri));
869 if (ntd->td_mpcount + ntd->td_xpcount == 0 ) {
870 if (MP_LOCK_HELD(gd))
871 cpu_rel_mplock(gd->gd_cpuid);
873 ASSERT_MP_LOCK_HELD(ntd);
878 KTR_LOG(ctxsw_sw, gd->gd_cpuid, ntd);
881 /* NOTE: current cpu may have changed after switch */
886 * Request that the target thread preempt the current thread. Preemption
887 * only works under a specific set of conditions:
889 * - We are not preempting ourselves
890 * - The target thread is owned by the current cpu
891 * - We are not currently being preempted
892 * - The target is not currently being preempted
893 * - We are not holding any spin locks
894 * - The target thread is not holding any tokens
895 * - We are able to satisfy the target's MP lock requirements (if any).
897 * THE CALLER OF LWKT_PREEMPT() MUST BE IN A CRITICAL SECTION. Typically
898 * this is called via lwkt_schedule() through the td_preemptable callback.
899 * critcount is the managed critical priority that we should ignore in order
900 * to determine whether preemption is possible (aka usually just the crit
901 * priority of lwkt_schedule() itself).
903 * XXX at the moment we run the target thread in a critical section during
904 * the preemption in order to prevent the target from taking interrupts
905 * that *WE* can't. Preemption is strictly limited to interrupt threads
906 * and interrupt-like threads, outside of a critical section, and the
907 * preempted source thread will be resumed the instant the target blocks
908 * whether or not the source is scheduled (i.e. preemption is supposed to
909 * be as transparent as possible).
911 * The target thread inherits our MP count (added to its own) for the
912 * duration of the preemption in order to preserve the atomicy of the
913 * MP lock during the preemption. Therefore, any preempting targets must be
914 * careful in regards to MP assertions. Note that the MP count may be
915 * out of sync with the physical mp_lock, but we do not have to preserve
916 * the original ownership of the lock if it was out of synch (that is, we
917 * can leave it synchronized on return).
920 lwkt_preempt(thread_t ntd, int critcount)
922 struct globaldata *gd = mycpu;
928 int save_gd_intr_nesting_level;
931 * The caller has put us in a critical section. We can only preempt
932 * if the caller of the caller was not in a critical section (basically
933 * a local interrupt), as determined by the 'critcount' parameter. We
934 * also can't preempt if the caller is holding any spinlocks (even if
935 * he isn't in a critical section). This also handles the tokens test.
937 * YYY The target thread must be in a critical section (else it must
938 * inherit our critical section? I dunno yet).
940 * Set need_lwkt_resched() unconditionally for now YYY.
942 KASSERT(ntd->td_critcount, ("BADCRIT0 %d", ntd->td_pri));
944 if (preempt_enable == 0) {
949 td = gd->gd_curthread;
950 if (ntd->td_pri <= td->td_pri) {
954 if (td->td_critcount > critcount) {
960 if (ntd->td_gd != gd) {
967 * We don't have to check spinlocks here as they will also bump
970 * Do not try to preempt if the target thread is holding any tokens.
971 * We could try to acquire the tokens but this case is so rare there
972 * is no need to support it.
974 KKASSERT(gd->gd_spinlocks_wr == 0);
976 if (TD_TOKS_HELD(ntd)) {
981 if (td == ntd || ((td->td_flags | ntd->td_flags) & TDF_PREEMPT_LOCK)) {
986 if (ntd->td_preempted) {
993 * NOTE: An interrupt might have occured just as we were transitioning
994 * to or from the MP lock. In this case td_mpcount will be pre-disposed
995 * (non-zero) but not actually synchronized with the mp_lock itself.
996 * We can use it to imply an MP lock requirement for the preemption but
997 * we cannot use it to test whether we hold the MP lock or not.
999 savecnt = td->td_mpcount;
1000 mpheld = MP_LOCK_HELD(gd);
1001 ntd->td_xpcount = td->td_mpcount + td->td_xpcount;
1002 if (mpheld == 0 && ntd->td_mpcount + ntd->td_xpcount && !cpu_try_mplock()) {
1003 ntd->td_xpcount = 0;
1005 need_lwkt_resched();
1011 * Since we are able to preempt the current thread, there is no need to
1012 * call need_lwkt_resched().
1014 * We must temporarily clear gd_intr_nesting_level around the switch
1015 * since switchouts from the target thread are allowed (they will just
1016 * return to our thread), and since the target thread has its own stack.
1019 ntd->td_preempted = td;
1020 td->td_flags |= TDF_PREEMPT_LOCK;
1021 KTR_LOG(ctxsw_pre, gd->gd_cpuid, ntd);
1022 save_gd_intr_nesting_level = gd->gd_intr_nesting_level;
1023 gd->gd_intr_nesting_level = 0;
1025 gd->gd_intr_nesting_level = save_gd_intr_nesting_level;
1027 KKASSERT(ntd->td_preempted && (td->td_flags & TDF_PREEMPT_DONE));
1029 KKASSERT(savecnt == td->td_mpcount);
1030 mpheld = MP_LOCK_HELD(gd);
1031 if (mpheld && td->td_mpcount == 0)
1032 cpu_rel_mplock(gd->gd_cpuid);
1033 else if (mpheld == 0 && td->td_mpcount + td->td_xpcount)
1034 panic("lwkt_preempt(): MP lock was not held through");
1036 ntd->td_preempted = NULL;
1037 td->td_flags &= ~(TDF_PREEMPT_LOCK|TDF_PREEMPT_DONE);
1041 * Conditionally call splz() if gd_reqflags indicates work is pending.
1042 * This will work inside a critical section but not inside a hard code
1045 * (self contained on a per cpu basis)
1050 globaldata_t gd = mycpu;
1051 thread_t td = gd->gd_curthread;
1053 if ((gd->gd_reqflags & RQF_IDLECHECK_MASK) &&
1054 gd->gd_intr_nesting_level == 0 &&
1055 td->td_nest_count < 2)
1062 * This version is integrated into crit_exit, reqflags has already
1063 * been tested but td_critcount has not.
1065 * We only want to execute the splz() on the 1->0 transition of
1066 * critcount and not in a hard code section or if too deeply nested.
1069 lwkt_maybe_splz(thread_t td)
1071 globaldata_t gd = td->td_gd;
1073 if (td->td_critcount == 0 &&
1074 gd->gd_intr_nesting_level == 0 &&
1075 td->td_nest_count < 2)
1082 * This function is used to negotiate a passive release of the current
1083 * process/lwp designation with the user scheduler, allowing the user
1084 * scheduler to schedule another user thread. The related kernel thread
1085 * (curthread) continues running in the released state.
1088 lwkt_passive_release(struct thread *td)
1090 struct lwp *lp = td->td_lwp;
1092 td->td_release = NULL;
1093 lwkt_setpri_self(TDPRI_KERN_USER);
1094 lp->lwp_proc->p_usched->release_curproc(lp);
1099 * This implements a normal yield. This routine is virtually a nop if
1100 * there is nothing to yield to but it will always run any pending interrupts
1101 * if called from a critical section.
1103 * This yield is designed for kernel threads without a user context.
1105 * (self contained on a per cpu basis)
1110 globaldata_t gd = mycpu;
1111 thread_t td = gd->gd_curthread;
1114 if ((gd->gd_reqflags & RQF_IDLECHECK_MASK) && td->td_nest_count < 2)
1116 if (td->td_fairq_accum < 0) {
1117 lwkt_schedule_self(curthread);
1120 xtd = TAILQ_FIRST(&gd->gd_tdrunq);
1121 if (xtd && xtd->td_pri > td->td_pri) {
1122 lwkt_schedule_self(curthread);
1129 * This yield is designed for kernel threads with a user context.
1131 * The kernel acting on behalf of the user is potentially cpu-bound,
1132 * this function will efficiently allow other threads to run and also
1133 * switch to other processes by releasing.
1135 * The lwkt_user_yield() function is designed to have very low overhead
1136 * if no yield is determined to be needed.
1139 lwkt_user_yield(void)
1141 globaldata_t gd = mycpu;
1142 thread_t td = gd->gd_curthread;
1145 * Always run any pending interrupts in case we are in a critical
1148 if ((gd->gd_reqflags & RQF_IDLECHECK_MASK) && td->td_nest_count < 2)
1153 * XXX SEVERE TEMPORARY HACK. A cpu-bound operation running in the
1154 * kernel can prevent other cpus from servicing interrupt threads
1155 * which still require the MP lock (which is a lot of them). This
1156 * has a chaining effect since if the interrupt is blocked, so is
1157 * the event, so normal scheduling will not pick up on the problem.
1159 if (cpu_contention_mask && td->td_mpcount + td->td_xpcount) {
1165 * Switch (which forces a release) if another kernel thread needs
1166 * the cpu, if userland wants us to resched, or if our kernel
1167 * quantum has run out.
1169 if (lwkt_resched_wanted() ||
1170 user_resched_wanted() ||
1171 td->td_fairq_accum < 0)
1178 * Reacquire the current process if we are released.
1180 * XXX not implemented atm. The kernel may be holding locks and such,
1181 * so we want the thread to continue to receive cpu.
1183 if (td->td_release == NULL && lp) {
1184 lp->lwp_proc->p_usched->acquire_curproc(lp);
1185 td->td_release = lwkt_passive_release;
1186 lwkt_setpri_self(TDPRI_USER_NORM);
1192 * Generic schedule. Possibly schedule threads belonging to other cpus and
1193 * deal with threads that might be blocked on a wait queue.
1195 * We have a little helper inline function which does additional work after
1196 * the thread has been enqueued, including dealing with preemption and
1197 * setting need_lwkt_resched() (which prevents the kernel from returning
1198 * to userland until it has processed higher priority threads).
1200 * It is possible for this routine to be called after a failed _enqueue
1201 * (due to the target thread migrating, sleeping, or otherwise blocked).
1202 * We have to check that the thread is actually on the run queue!
1204 * reschedok is an optimized constant propagated from lwkt_schedule() or
1205 * lwkt_schedule_noresched(). By default it is non-zero, causing a
1206 * reschedule to be requested if the target thread has a higher priority.
1207 * The port messaging code will set MSG_NORESCHED and cause reschedok to
1208 * be 0, prevented undesired reschedules.
1212 _lwkt_schedule_post(globaldata_t gd, thread_t ntd, int ccount, int reschedok)
1216 if (ntd->td_flags & TDF_RUNQ) {
1217 if (ntd->td_preemptable && reschedok) {
1218 ntd->td_preemptable(ntd, ccount); /* YYY +token */
1219 } else if (reschedok) {
1221 if (ntd->td_pri > otd->td_pri)
1222 need_lwkt_resched();
1226 * Give the thread a little fair share scheduler bump if it
1227 * has been asleep for a while. This is primarily to avoid
1228 * a degenerate case for interrupt threads where accumulator
1229 * crosses into negative territory unnecessarily.
1231 if (ntd->td_fairq_lticks != ticks) {
1232 ntd->td_fairq_lticks = ticks;
1233 ntd->td_fairq_accum += gd->gd_fairq_total_pri;
1234 if (ntd->td_fairq_accum > TDFAIRQ_MAX(gd))
1235 ntd->td_fairq_accum = TDFAIRQ_MAX(gd);
1242 _lwkt_schedule(thread_t td, int reschedok)
1244 globaldata_t mygd = mycpu;
1246 KASSERT(td != &td->td_gd->gd_idlethread,
1247 ("lwkt_schedule(): scheduling gd_idlethread is illegal!"));
1248 crit_enter_gd(mygd);
1249 KKASSERT(td->td_lwp == NULL || (td->td_lwp->lwp_flag & LWP_ONRUNQ) == 0);
1250 if (td == mygd->gd_curthread) {
1254 * If we own the thread, there is no race (since we are in a
1255 * critical section). If we do not own the thread there might
1256 * be a race but the target cpu will deal with it.
1259 if (td->td_gd == mygd) {
1261 _lwkt_schedule_post(mygd, td, 1, reschedok);
1263 lwkt_send_ipiq3(td->td_gd, lwkt_schedule_remote, td, 0);
1267 _lwkt_schedule_post(mygd, td, 1, reschedok);
1274 lwkt_schedule(thread_t td)
1276 _lwkt_schedule(td, 1);
1280 lwkt_schedule_noresched(thread_t td)
1282 _lwkt_schedule(td, 0);
1288 * When scheduled remotely if frame != NULL the IPIQ is being
1289 * run via doreti or an interrupt then preemption can be allowed.
1291 * To allow preemption we have to drop the critical section so only
1292 * one is present in _lwkt_schedule_post.
1295 lwkt_schedule_remote(void *arg, int arg2, struct intrframe *frame)
1297 thread_t td = curthread;
1300 if (frame && ntd->td_preemptable) {
1301 crit_exit_noyield(td);
1302 _lwkt_schedule(ntd, 1);
1303 crit_enter_quick(td);
1305 _lwkt_schedule(ntd, 1);
1310 * Thread migration using a 'Pull' method. The thread may or may not be
1311 * the current thread. It MUST be descheduled and in a stable state.
1312 * lwkt_giveaway() must be called on the cpu owning the thread.
1314 * At any point after lwkt_giveaway() is called, the target cpu may
1315 * 'pull' the thread by calling lwkt_acquire().
1317 * We have to make sure the thread is not sitting on a per-cpu tsleep
1318 * queue or it will blow up when it moves to another cpu.
1320 * MPSAFE - must be called under very specific conditions.
1323 lwkt_giveaway(thread_t td)
1325 globaldata_t gd = mycpu;
1328 if (td->td_flags & TDF_TSLEEPQ)
1330 KKASSERT(td->td_gd == gd);
1331 TAILQ_REMOVE(&gd->gd_tdallq, td, td_allq);
1332 td->td_flags |= TDF_MIGRATING;
1337 lwkt_acquire(thread_t td)
1342 KKASSERT(td->td_flags & TDF_MIGRATING);
1347 KKASSERT((td->td_flags & TDF_RUNQ) == 0);
1348 crit_enter_gd(mygd);
1349 while (td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK)) {
1351 lwkt_process_ipiq();
1357 TAILQ_INSERT_TAIL(&mygd->gd_tdallq, td, td_allq);
1358 td->td_flags &= ~TDF_MIGRATING;
1361 crit_enter_gd(mygd);
1362 TAILQ_INSERT_TAIL(&mygd->gd_tdallq, td, td_allq);
1363 td->td_flags &= ~TDF_MIGRATING;
1371 * Generic deschedule. Descheduling threads other then your own should be
1372 * done only in carefully controlled circumstances. Descheduling is
1375 * This function may block if the cpu has run out of messages.
1378 lwkt_deschedule(thread_t td)
1382 if (td == curthread) {
1385 if (td->td_gd == mycpu) {
1388 lwkt_send_ipiq(td->td_gd, (ipifunc1_t)lwkt_deschedule, td);
1398 * Set the target thread's priority. This routine does not automatically
1399 * switch to a higher priority thread, LWKT threads are not designed for
1400 * continuous priority changes. Yield if you want to switch.
1403 lwkt_setpri(thread_t td, int pri)
1405 KKASSERT(td->td_gd == mycpu);
1406 if (td->td_pri != pri) {
1409 if (td->td_flags & TDF_RUNQ) {
1421 * Set the initial priority for a thread prior to it being scheduled for
1422 * the first time. The thread MUST NOT be scheduled before or during
1423 * this call. The thread may be assigned to a cpu other then the current
1426 * Typically used after a thread has been created with TDF_STOPPREQ,
1427 * and before the thread is initially scheduled.
1430 lwkt_setpri_initial(thread_t td, int pri)
1433 KKASSERT((td->td_flags & TDF_RUNQ) == 0);
1438 lwkt_setpri_self(int pri)
1440 thread_t td = curthread;
1442 KKASSERT(pri >= 0 && pri <= TDPRI_MAX);
1444 if (td->td_flags & TDF_RUNQ) {
1455 * 1/hz tick (typically 10ms) x TDFAIRQ_SCALE (typ 8) = 80ms full cycle.
1457 * Example: two competing threads, same priority N. decrement by (2*N)
1458 * increment by N*8, each thread will get 4 ticks.
1461 lwkt_fairq_schedulerclock(thread_t td)
1465 if (td != &td->td_gd->gd_idlethread) {
1466 td->td_fairq_accum -= td->td_gd->gd_fairq_total_pri;
1467 if (td->td_fairq_accum < -TDFAIRQ_MAX(td->td_gd))
1468 td->td_fairq_accum = -TDFAIRQ_MAX(td->td_gd);
1469 if (td->td_fairq_accum < 0)
1470 need_lwkt_resched();
1471 td->td_fairq_lticks = ticks;
1473 td = td->td_preempted;
1479 lwkt_fairq_accumulate(globaldata_t gd, thread_t td)
1481 td->td_fairq_accum += td->td_pri * TDFAIRQ_SCALE;
1482 if (td->td_fairq_accum > TDFAIRQ_MAX(td->td_gd))
1483 td->td_fairq_accum = TDFAIRQ_MAX(td->td_gd);
1487 * Migrate the current thread to the specified cpu.
1489 * This is accomplished by descheduling ourselves from the current cpu,
1490 * moving our thread to the tdallq of the target cpu, IPI messaging the
1491 * target cpu, and switching out. TDF_MIGRATING prevents scheduling
1492 * races while the thread is being migrated.
1494 * We must be sure to remove ourselves from the current cpu's tsleepq
1495 * before potentially moving to another queue. The thread can be on
1496 * a tsleepq due to a left-over tsleep_interlock().
1499 static void lwkt_setcpu_remote(void *arg);
1503 lwkt_setcpu_self(globaldata_t rgd)
1506 thread_t td = curthread;
1508 if (td->td_gd != rgd) {
1509 crit_enter_quick(td);
1510 if (td->td_flags & TDF_TSLEEPQ)
1512 td->td_flags |= TDF_MIGRATING;
1513 lwkt_deschedule_self(td);
1514 TAILQ_REMOVE(&td->td_gd->gd_tdallq, td, td_allq);
1515 lwkt_send_ipiq(rgd, (ipifunc1_t)lwkt_setcpu_remote, td);
1517 /* we are now on the target cpu */
1518 TAILQ_INSERT_TAIL(&rgd->gd_tdallq, td, td_allq);
1519 crit_exit_quick(td);
1525 lwkt_migratecpu(int cpuid)
1530 rgd = globaldata_find(cpuid);
1531 lwkt_setcpu_self(rgd);
1536 * Remote IPI for cpu migration (called while in a critical section so we
1537 * do not have to enter another one). The thread has already been moved to
1538 * our cpu's allq, but we must wait for the thread to be completely switched
1539 * out on the originating cpu before we schedule it on ours or the stack
1540 * state may be corrupt. We clear TDF_MIGRATING after flushing the GD
1541 * change to main memory.
1543 * XXX The use of TDF_MIGRATING might not be sufficient to avoid races
1544 * against wakeups. It is best if this interface is used only when there
1545 * are no pending events that might try to schedule the thread.
1549 lwkt_setcpu_remote(void *arg)
1552 globaldata_t gd = mycpu;
1554 while (td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK)) {
1556 lwkt_process_ipiq();
1563 td->td_flags &= ~TDF_MIGRATING;
1564 KKASSERT(td->td_lwp == NULL || (td->td_lwp->lwp_flag & LWP_ONRUNQ) == 0);
1570 lwkt_preempted_proc(void)
1572 thread_t td = curthread;
1573 while (td->td_preempted)
1574 td = td->td_preempted;
1579 * Create a kernel process/thread/whatever. It shares it's address space
1580 * with proc0 - ie: kernel only.
1582 * NOTE! By default new threads are created with the MP lock held. A
1583 * thread which does not require the MP lock should release it by calling
1584 * rel_mplock() at the start of the new thread.
1587 lwkt_create(void (*func)(void *), void *arg, struct thread **tdp,
1588 thread_t template, int tdflags, int cpu, const char *fmt, ...)
1593 td = lwkt_alloc_thread(template, LWKT_THREAD_STACK, cpu,
1597 cpu_set_thread_handler(td, lwkt_exit, func, arg);
1600 * Set up arg0 for 'ps' etc
1602 __va_start(ap, fmt);
1603 kvsnprintf(td->td_comm, sizeof(td->td_comm), fmt, ap);
1607 * Schedule the thread to run
1609 if ((td->td_flags & TDF_STOPREQ) == 0)
1612 td->td_flags &= ~TDF_STOPREQ;
1617 * Destroy an LWKT thread. Warning! This function is not called when
1618 * a process exits, cpu_proc_exit() directly calls cpu_thread_exit() and
1619 * uses a different reaping mechanism.
1624 thread_t td = curthread;
1629 * Do any cleanup that might block here
1631 if (td->td_flags & TDF_VERBOSE)
1632 kprintf("kthread %p %s has exited\n", td, td->td_comm);
1635 dsched_exit_thread(td);
1638 * Get us into a critical section to interlock gd_freetd and loop
1639 * until we can get it freed.
1641 * We have to cache the current td in gd_freetd because objcache_put()ing
1642 * it would rip it out from under us while our thread is still active.
1645 crit_enter_quick(td);
1646 while ((std = gd->gd_freetd) != NULL) {
1647 KKASSERT((std->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK)) == 0);
1648 gd->gd_freetd = NULL;
1649 objcache_put(thread_cache, std);
1653 * Remove thread resources from kernel lists and deschedule us for
1654 * the last time. We cannot block after this point or we may end
1655 * up with a stale td on the tsleepq.
1657 if (td->td_flags & TDF_TSLEEPQ)
1659 lwkt_deschedule_self(td);
1660 lwkt_remove_tdallq(td);
1665 KKASSERT(gd->gd_freetd == NULL);
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(__DEBUG_CRIT_ARG__)
1693 _crit_exit(mycpu __DEBUG_CRIT_PASS_ARG__);
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();