2 * Copyright (c) 2003-2011 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>
53 #include <sys/spinlock.h>
56 #include <sys/thread2.h>
57 #include <sys/spinlock2.h>
58 #include <sys/mplock2.h>
60 #include <sys/dsched.h>
63 #include <vm/vm_param.h>
64 #include <vm/vm_kern.h>
65 #include <vm/vm_object.h>
66 #include <vm/vm_page.h>
67 #include <vm/vm_map.h>
68 #include <vm/vm_pager.h>
69 #include <vm/vm_extern.h>
71 #include <machine/stdarg.h>
72 #include <machine/smp.h>
73 #include <machine/clock.h>
75 #ifdef _KERNEL_VIRTUAL
81 #if !defined(KTR_CTXSW)
82 #define KTR_CTXSW KTR_ALL
84 KTR_INFO_MASTER(ctxsw);
85 KTR_INFO(KTR_CTXSW, ctxsw, sw, 0, "#cpu[%d].td = %p", int cpu, struct thread *td);
86 KTR_INFO(KTR_CTXSW, ctxsw, pre, 1, "#cpu[%d].td = %p", int cpu, struct thread *td);
87 KTR_INFO(KTR_CTXSW, ctxsw, newtd, 2, "#threads[%p].name = %s", struct thread *td, char *comm);
88 KTR_INFO(KTR_CTXSW, ctxsw, deadtd, 3, "#threads[%p].name = <dead>", struct thread *td);
90 static MALLOC_DEFINE(M_THREAD, "thread", "lwkt threads");
93 static int panic_on_cscount = 0;
95 static int64_t switch_count = 0;
96 static int64_t preempt_hit = 0;
97 static int64_t preempt_miss = 0;
98 static int64_t preempt_weird = 0;
99 static int lwkt_use_spin_port;
100 static struct objcache *thread_cache;
101 int cpu_mwait_spin = 0;
103 static void lwkt_schedule_remote(void *arg, int arg2, struct intrframe *frame);
104 static void lwkt_setcpu_remote(void *arg);
107 * We can make all thread ports use the spin backend instead of the thread
108 * backend. This should only be set to debug the spin backend.
110 TUNABLE_INT("lwkt.use_spin_port", &lwkt_use_spin_port);
113 SYSCTL_INT(_lwkt, OID_AUTO, panic_on_cscount, CTLFLAG_RW, &panic_on_cscount, 0,
114 "Panic if attempting to switch lwkt's while mastering cpusync");
116 SYSCTL_QUAD(_lwkt, OID_AUTO, switch_count, CTLFLAG_RW, &switch_count, 0,
117 "Number of switched threads");
118 SYSCTL_QUAD(_lwkt, OID_AUTO, preempt_hit, CTLFLAG_RW, &preempt_hit, 0,
119 "Successful preemption events");
120 SYSCTL_QUAD(_lwkt, OID_AUTO, preempt_miss, CTLFLAG_RW, &preempt_miss, 0,
121 "Failed preemption events");
122 SYSCTL_QUAD(_lwkt, OID_AUTO, preempt_weird, CTLFLAG_RW, &preempt_weird, 0,
123 "Number of preempted threads.");
124 static int fairq_enable = 0;
125 SYSCTL_INT(_lwkt, OID_AUTO, fairq_enable, CTLFLAG_RW,
126 &fairq_enable, 0, "Turn on fairq priority accumulators");
127 static int fairq_bypass = -1;
128 SYSCTL_INT(_lwkt, OID_AUTO, fairq_bypass, CTLFLAG_RW,
129 &fairq_bypass, 0, "Allow fairq to bypass td on token failure");
130 extern int lwkt_sched_debug;
131 int lwkt_sched_debug = 0;
132 SYSCTL_INT(_lwkt, OID_AUTO, sched_debug, CTLFLAG_RW,
133 &lwkt_sched_debug, 0, "Scheduler debug");
134 static u_int lwkt_spin_loops = 10;
135 SYSCTL_UINT(_lwkt, OID_AUTO, spin_loops, CTLFLAG_RW,
136 &lwkt_spin_loops, 0, "Scheduler spin loops until sorted decon");
137 static int preempt_enable = 1;
138 SYSCTL_INT(_lwkt, OID_AUTO, preempt_enable, CTLFLAG_RW,
139 &preempt_enable, 0, "Enable preemption");
140 static int lwkt_cache_threads = 0;
141 SYSCTL_INT(_lwkt, OID_AUTO, cache_threads, CTLFLAG_RD,
142 &lwkt_cache_threads, 0, "thread+kstack cache");
145 * These helper procedures handle the runq, they can only be called from
146 * within a critical section.
148 * WARNING! Prior to SMP being brought up it is possible to enqueue and
149 * dequeue threads belonging to other cpus, so be sure to use td->td_gd
150 * instead of 'mycpu' when referencing the globaldata structure. Once
151 * SMP live enqueuing and dequeueing only occurs on the current cpu.
155 _lwkt_dequeue(thread_t td)
157 if (td->td_flags & TDF_RUNQ) {
158 struct globaldata *gd = td->td_gd;
160 td->td_flags &= ~TDF_RUNQ;
161 TAILQ_REMOVE(&gd->gd_tdrunq, td, td_threadq);
162 --gd->gd_tdrunqcount;
163 if (TAILQ_FIRST(&gd->gd_tdrunq) == NULL)
164 atomic_clear_int(&gd->gd_reqflags, RQF_RUNNING);
171 * There are a limited number of lwkt threads runnable since user
172 * processes only schedule one at a time per cpu. However, there can
173 * be many user processes in kernel mode exiting from a tsleep() which
176 * NOTE: lwkt_schedulerclock() will force a round-robin based on td_pri and
177 * will ignore user priority. This is to ensure that user threads in
178 * kernel mode get cpu at some point regardless of what the user
183 _lwkt_enqueue(thread_t td)
187 if ((td->td_flags & (TDF_RUNQ|TDF_MIGRATING|TDF_BLOCKQ)) == 0) {
188 struct globaldata *gd = td->td_gd;
190 td->td_flags |= TDF_RUNQ;
191 xtd = TAILQ_FIRST(&gd->gd_tdrunq);
193 TAILQ_INSERT_TAIL(&gd->gd_tdrunq, td, td_threadq);
194 atomic_set_int(&gd->gd_reqflags, RQF_RUNNING);
197 * NOTE: td_upri - higher numbers more desireable, same sense
198 * as td_pri (typically reversed from lwp_upri).
200 * In the equal priority case we want the best selection
201 * at the beginning so the less desireable selections know
202 * that they have to setrunqueue/go-to-another-cpu, even
203 * though it means switching back to the 'best' selection.
204 * This also avoids degenerate situations when many threads
205 * are runnable or waking up at the same time.
207 * If upri matches exactly place at end/round-robin.
210 (xtd->td_pri >= td->td_pri ||
211 (xtd->td_pri == td->td_pri &&
212 xtd->td_upri >= td->td_upri))) {
213 xtd = TAILQ_NEXT(xtd, td_threadq);
216 TAILQ_INSERT_BEFORE(xtd, td, td_threadq);
218 TAILQ_INSERT_TAIL(&gd->gd_tdrunq, td, td_threadq);
220 ++gd->gd_tdrunqcount;
223 * Request a LWKT reschedule if we are now at the head of the queue.
225 if (TAILQ_FIRST(&gd->gd_tdrunq) == td)
231 _lwkt_thread_ctor(void *obj, void *privdata, int ocflags)
233 struct thread *td = (struct thread *)obj;
235 td->td_kstack = NULL;
236 td->td_kstack_size = 0;
237 td->td_flags = TDF_ALLOCATED_THREAD;
243 _lwkt_thread_dtor(void *obj, void *privdata)
245 struct thread *td = (struct thread *)obj;
247 KASSERT(td->td_flags & TDF_ALLOCATED_THREAD,
248 ("_lwkt_thread_dtor: not allocated from objcache"));
249 KASSERT((td->td_flags & TDF_ALLOCATED_STACK) && td->td_kstack &&
250 td->td_kstack_size > 0,
251 ("_lwkt_thread_dtor: corrupted stack"));
252 kmem_free(&kernel_map, (vm_offset_t)td->td_kstack, td->td_kstack_size);
253 td->td_kstack = NULL;
258 * Initialize the lwkt s/system.
260 * Nominally cache up to 32 thread + kstack structures. Cache more on
261 * systems with a lot of cpu cores.
266 TUNABLE_INT("lwkt.cache_threads", &lwkt_cache_threads);
267 if (lwkt_cache_threads == 0) {
268 lwkt_cache_threads = ncpus * 4;
269 if (lwkt_cache_threads < 32)
270 lwkt_cache_threads = 32;
272 thread_cache = objcache_create_mbacked(
273 M_THREAD, sizeof(struct thread),
274 0, lwkt_cache_threads,
275 _lwkt_thread_ctor, _lwkt_thread_dtor, NULL);
277 SYSINIT(lwkt_init, SI_BOOT2_LWKT_INIT, SI_ORDER_FIRST, lwkt_init, NULL);
280 * Schedule a thread to run. As the current thread we can always safely
281 * schedule ourselves, and a shortcut procedure is provided for that
284 * (non-blocking, self contained on a per cpu basis)
287 lwkt_schedule_self(thread_t td)
289 KKASSERT((td->td_flags & TDF_MIGRATING) == 0);
290 crit_enter_quick(td);
291 KASSERT(td != &td->td_gd->gd_idlethread,
292 ("lwkt_schedule_self(): scheduling gd_idlethread is illegal!"));
293 KKASSERT(td->td_lwp == NULL ||
294 (td->td_lwp->lwp_mpflags & LWP_MP_ONRUNQ) == 0);
300 * Deschedule a thread.
302 * (non-blocking, self contained on a per cpu basis)
305 lwkt_deschedule_self(thread_t td)
307 crit_enter_quick(td);
313 * LWKTs operate on a per-cpu basis
315 * WARNING! Called from early boot, 'mycpu' may not work yet.
318 lwkt_gdinit(struct globaldata *gd)
320 TAILQ_INIT(&gd->gd_tdrunq);
321 TAILQ_INIT(&gd->gd_tdallq);
325 * Create a new thread. The thread must be associated with a process context
326 * or LWKT start address before it can be scheduled. If the target cpu is
327 * -1 the thread will be created on the current cpu.
329 * If you intend to create a thread without a process context this function
330 * does everything except load the startup and switcher function.
333 lwkt_alloc_thread(struct thread *td, int stksize, int cpu, int flags)
335 static int cpu_rotator;
336 globaldata_t gd = mycpu;
340 * If static thread storage is not supplied allocate a thread. Reuse
341 * a cached free thread if possible. gd_freetd is used to keep an exiting
342 * thread intact through the exit.
346 if ((td = gd->gd_freetd) != NULL) {
347 KKASSERT((td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK|
349 gd->gd_freetd = NULL;
351 td = objcache_get(thread_cache, M_WAITOK);
352 KKASSERT((td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK|
356 KASSERT((td->td_flags &
357 (TDF_ALLOCATED_THREAD|TDF_RUNNING|TDF_PREEMPT_LOCK)) ==
358 TDF_ALLOCATED_THREAD,
359 ("lwkt_alloc_thread: corrupted td flags 0x%X", td->td_flags));
360 flags |= td->td_flags & (TDF_ALLOCATED_THREAD|TDF_ALLOCATED_STACK);
364 * Try to reuse cached stack.
366 if ((stack = td->td_kstack) != NULL && td->td_kstack_size != stksize) {
367 if (flags & TDF_ALLOCATED_STACK) {
368 kmem_free(&kernel_map, (vm_offset_t)stack, td->td_kstack_size);
373 stack = (void *)kmem_alloc_stack(&kernel_map, stksize);
374 flags |= TDF_ALLOCATED_STACK;
381 lwkt_init_thread(td, stack, stksize, flags, globaldata_find(cpu));
386 * Initialize a preexisting thread structure. This function is used by
387 * lwkt_alloc_thread() and also used to initialize the per-cpu idlethread.
389 * All threads start out in a critical section at a priority of
390 * TDPRI_KERN_DAEMON. Higher level code will modify the priority as
391 * appropriate. This function may send an IPI message when the
392 * requested cpu is not the current cpu and consequently gd_tdallq may
393 * not be initialized synchronously from the point of view of the originating
396 * NOTE! we have to be careful in regards to creating threads for other cpus
397 * if SMP has not yet been activated.
400 lwkt_init_thread_remote(void *arg)
405 * Protected by critical section held by IPI dispatch
407 TAILQ_INSERT_TAIL(&td->td_gd->gd_tdallq, td, td_allq);
411 * lwkt core thread structural initialization.
413 * NOTE: All threads are initialized as mpsafe threads.
416 lwkt_init_thread(thread_t td, void *stack, int stksize, int flags,
417 struct globaldata *gd)
419 globaldata_t mygd = mycpu;
421 bzero(td, sizeof(struct thread));
422 td->td_kstack = stack;
423 td->td_kstack_size = stksize;
424 td->td_flags = flags;
426 td->td_type = TD_TYPE_GENERIC;
428 td->td_pri = TDPRI_KERN_DAEMON;
429 td->td_critcount = 1;
430 td->td_toks_have = NULL;
431 td->td_toks_stop = &td->td_toks_base;
432 if (lwkt_use_spin_port || (flags & TDF_FORCE_SPINPORT)) {
433 lwkt_initport_spin(&td->td_msgport, td,
434 (flags & TDF_FIXEDCPU) ? TRUE : FALSE);
436 lwkt_initport_thread(&td->td_msgport, td);
438 pmap_init_thread(td);
440 * Normally initializing a thread for a remote cpu requires sending an
441 * IPI. However, the idlethread is setup before the other cpus are
442 * activated so we have to treat it as a special case. XXX manipulation
443 * of gd_tdallq requires the BGL.
445 if (gd == mygd || td == &gd->gd_idlethread) {
447 TAILQ_INSERT_TAIL(&gd->gd_tdallq, td, td_allq);
450 lwkt_send_ipiq(gd, lwkt_init_thread_remote, td);
452 dsched_enter_thread(td);
456 lwkt_set_comm(thread_t td, const char *ctl, ...)
461 kvsnprintf(td->td_comm, sizeof(td->td_comm), ctl, va);
463 KTR_LOG(ctxsw_newtd, td, td->td_comm);
467 * Prevent the thread from getting destroyed. Note that unlike PHOLD/PRELE
468 * this does not prevent the thread from migrating to another cpu so the
469 * gd_tdallq state is not protected by this.
472 lwkt_hold(thread_t td)
474 atomic_add_int(&td->td_refs, 1);
478 lwkt_rele(thread_t td)
480 KKASSERT(td->td_refs > 0);
481 atomic_add_int(&td->td_refs, -1);
485 lwkt_free_thread(thread_t td)
487 KKASSERT(td->td_refs == 0);
488 KKASSERT((td->td_flags & (TDF_RUNNING | TDF_PREEMPT_LOCK |
489 TDF_RUNQ | TDF_TSLEEPQ)) == 0);
490 if (td->td_flags & TDF_ALLOCATED_THREAD) {
491 objcache_put(thread_cache, td);
492 } else if (td->td_flags & TDF_ALLOCATED_STACK) {
493 /* client-allocated struct with internally allocated stack */
494 KASSERT(td->td_kstack && td->td_kstack_size > 0,
495 ("lwkt_free_thread: corrupted stack"));
496 kmem_free(&kernel_map, (vm_offset_t)td->td_kstack, td->td_kstack_size);
497 td->td_kstack = NULL;
498 td->td_kstack_size = 0;
501 KTR_LOG(ctxsw_deadtd, td);
506 * Switch to the next runnable lwkt. If no LWKTs are runnable then
507 * switch to the idlethread. Switching must occur within a critical
508 * section to avoid races with the scheduling queue.
510 * We always have full control over our cpu's run queue. Other cpus
511 * that wish to manipulate our queue must use the cpu_*msg() calls to
512 * talk to our cpu, so a critical section is all that is needed and
513 * the result is very, very fast thread switching.
515 * The LWKT scheduler uses a fixed priority model and round-robins at
516 * each priority level. User process scheduling is a totally
517 * different beast and LWKT priorities should not be confused with
518 * user process priorities.
520 * PREEMPTION NOTE: Preemption occurs via lwkt_preempt(). lwkt_switch()
521 * is not called by the current thread in the preemption case, only when
522 * the preempting thread blocks (in order to return to the original thread).
524 * SPECIAL NOTE ON SWITCH ATOMICY: Certain operations such as thread
525 * migration and tsleep deschedule the current lwkt thread and call
526 * lwkt_switch(). In particular, the target cpu of the migration fully
527 * expects the thread to become non-runnable and can deadlock against
528 * cpusync operations if we run any IPIs prior to switching the thread out.
530 * WE MUST BE VERY CAREFUL NOT TO RUN SPLZ DIRECTLY OR INDIRECTLY IF
531 * THE CURRENT THREAD HAS BEEN DESCHEDULED!
536 globaldata_t gd = mycpu;
537 thread_t td = gd->gd_curthread;
541 uint64_t tsc_base = rdtsc();
544 KKASSERT(gd->gd_processing_ipiq == 0);
545 KKASSERT(td->td_flags & TDF_RUNNING);
548 * Switching from within a 'fast' (non thread switched) interrupt or IPI
549 * is illegal. However, we may have to do it anyway if we hit a fatal
550 * kernel trap or we have paniced.
552 * If this case occurs save and restore the interrupt nesting level.
554 if (gd->gd_intr_nesting_level) {
558 if (gd->gd_trap_nesting_level == 0 && panic_cpu_gd != mycpu) {
559 panic("lwkt_switch: Attempt to switch from a "
560 "fast interrupt, ipi, or hard code section, "
564 savegdnest = gd->gd_intr_nesting_level;
565 savegdtrap = gd->gd_trap_nesting_level;
566 gd->gd_intr_nesting_level = 0;
567 gd->gd_trap_nesting_level = 0;
568 if ((td->td_flags & TDF_PANICWARN) == 0) {
569 td->td_flags |= TDF_PANICWARN;
570 kprintf("Warning: thread switch from interrupt, IPI, "
571 "or hard code section.\n"
572 "thread %p (%s)\n", td, td->td_comm);
576 gd->gd_intr_nesting_level = savegdnest;
577 gd->gd_trap_nesting_level = savegdtrap;
583 * Release our current user process designation if we are blocking
584 * or if a user reschedule was requested.
586 * NOTE: This function is NOT called if we are switching into or
587 * returning from a preemption.
589 * NOTE: Releasing our current user process designation may cause
590 * it to be assigned to another thread, which in turn will
591 * cause us to block in the usched acquire code when we attempt
592 * to return to userland.
594 * NOTE: On SMP systems this can be very nasty when heavy token
595 * contention is present so we want to be careful not to
596 * release the designation gratuitously.
598 if (td->td_release &&
599 (user_resched_wanted() || (td->td_flags & TDF_RUNQ) == 0)) {
604 * Release all tokens. Once we do this we must remain in the critical
605 * section and cannot run IPIs or other interrupts until we switch away
606 * because they may implode if they try to get a token using our thread
610 if (TD_TOKS_HELD(td))
611 lwkt_relalltokens(td);
614 * We had better not be holding any spin locks, but don't get into an
615 * endless panic loop.
617 KASSERT(gd->gd_spinlocks == 0 || panicstr != NULL,
618 ("lwkt_switch: still holding %d exclusive spinlocks!",
622 if (td->td_cscount) {
623 kprintf("Diagnostic: attempt to switch while mastering cpusync: %p\n",
625 if (panic_on_cscount)
626 panic("switching while mastering cpusync");
631 * If we had preempted another thread on this cpu, resume the preempted
632 * thread. This occurs transparently, whether the preempted thread
633 * was scheduled or not (it may have been preempted after descheduling
636 * We have to setup the MP lock for the original thread after backing
637 * out the adjustment that was made to curthread when the original
640 if ((ntd = td->td_preempted) != NULL) {
641 KKASSERT(ntd->td_flags & TDF_PREEMPT_LOCK);
642 ntd->td_flags |= TDF_PREEMPT_DONE;
643 ntd->td_contended = 0; /* reset contended */
646 * The interrupt may have woken a thread up, we need to properly
647 * set the reschedule flag if the originally interrupted thread is
648 * at a lower priority.
650 * The interrupt may not have descheduled.
652 if (TAILQ_FIRST(&gd->gd_tdrunq) != ntd)
654 goto havethread_preempted;
658 * Figure out switch target. If we cannot switch to our desired target
659 * look for a thread that we can switch to.
661 * NOTE! The limited spin loop and related parameters are extremely
662 * important for system performance, particularly for pipes and
663 * concurrent conflicting VM faults.
665 clear_lwkt_resched();
666 ntd = TAILQ_FIRST(&gd->gd_tdrunq);
670 if (TD_TOKS_NOT_HELD(ntd) ||
671 lwkt_getalltokens(ntd, (ntd->td_contended > lwkt_spin_loops)))
675 ++gd->gd_cnt.v_lock_colls;
676 ++ntd->td_contended; /* overflow ok */
678 if (tsc_frequency && rdtsc() - tsc_base > tsc_frequency) {
679 kprintf("lwkt_switch: excessive contended %d "
680 "thread %p\n", ntd->td_contended, ntd);
684 } while (ntd->td_contended < (lwkt_spin_loops >> 1));
688 * Bleh, the thread we wanted to switch to has a contended token.
689 * See if we can switch to another thread.
691 * We generally don't want to do this because it represents a
692 * priority inversion. Do not allow the case if the thread
693 * is returning to userland (not a kernel thread) AND the thread
696 while ((ntd = TAILQ_NEXT(ntd, td_threadq)) != NULL) {
697 if (ntd->td_pri < TDPRI_KERN_LPSCHED && upri > ntd->td_upri)
704 if (TD_TOKS_NOT_HELD(ntd) ||
705 lwkt_getalltokens(ntd, (ntd->td_contended > lwkt_spin_loops))) {
708 ++ntd->td_contended; /* overflow ok */
709 ++gd->gd_cnt.v_lock_colls;
713 * Fall through, switch to idle thread to get us out of the current
714 * context. Since we were contended, prevent HLT by flagging a
721 * We either contended on ntd or the runq is empty. We must switch
722 * through the idle thread to get out of the current context.
724 ntd = &gd->gd_idlethread;
725 if (gd->gd_trap_nesting_level == 0 && panicstr == NULL)
726 ASSERT_NO_TOKENS_HELD(ntd);
727 cpu_time.cp_msg[0] = 0;
732 * Clear gd_idle_repeat when doing a normal switch to a non-idle
735 ntd->td_wmesg = NULL;
736 ntd->td_contended = 0; /* reset once scheduled */
737 ++gd->gd_cnt.v_swtch;
738 gd->gd_idle_repeat = 0;
740 havethread_preempted:
742 * If the new target does not need the MP lock and we are holding it,
743 * release the MP lock. If the new target requires the MP lock we have
744 * already acquired it for the target.
748 KASSERT(ntd->td_critcount,
749 ("priority problem in lwkt_switch %d %d",
750 td->td_critcount, ntd->td_critcount));
754 * Execute the actual thread switch operation. This function
755 * returns to the current thread and returns the previous thread
756 * (which may be different from the thread we switched to).
758 * We are responsible for marking ntd as TDF_RUNNING.
760 KKASSERT((ntd->td_flags & TDF_RUNNING) == 0);
762 KTR_LOG(ctxsw_sw, gd->gd_cpuid, ntd);
763 ntd->td_flags |= TDF_RUNNING;
764 lwkt_switch_return(td->td_switch(ntd));
765 /* ntd invalid, td_switch() can return a different thread_t */
769 * catch-all. XXX is this strictly needed?
773 /* NOTE: current cpu may have changed after switch */
778 * Called by assembly in the td_switch (thread restore path) for thread
779 * bootstrap cases which do not 'return' to lwkt_switch().
782 lwkt_switch_return(thread_t otd)
786 uint64_t tsc_base = rdtsc();
790 exiting = otd->td_flags & TDF_EXITING;
794 * Check if otd was migrating. Now that we are on ntd we can finish
795 * up the migration. This is a bit messy but it is the only place
796 * where td is known to be fully descheduled.
798 * We can only activate the migration if otd was migrating but not
799 * held on the cpu due to a preemption chain. We still have to
800 * clear TDF_RUNNING on the old thread either way.
802 * We are responsible for clearing the previously running thread's
805 if ((rgd = otd->td_migrate_gd) != NULL &&
806 (otd->td_flags & TDF_PREEMPT_LOCK) == 0) {
807 KKASSERT((otd->td_flags & (TDF_MIGRATING | TDF_RUNNING)) ==
808 (TDF_MIGRATING | TDF_RUNNING));
809 otd->td_migrate_gd = NULL;
810 otd->td_flags &= ~TDF_RUNNING;
811 lwkt_send_ipiq(rgd, lwkt_setcpu_remote, otd);
813 otd->td_flags &= ~TDF_RUNNING;
817 * Final exit validations (see lwp_wait()). Note that otd becomes
818 * invalid the *instant* we set TDF_MP_EXITSIG.
820 * Use the EXITING status loaded from before we clear TDF_RUNNING,
821 * because if it is not set otd becomes invalid the instant we clear
822 * TDF_RUNNING on it (otherwise, if the system is fast enough, we
823 * might 'steal' TDF_EXITING from another switch-return!).
828 mpflags = otd->td_mpflags;
831 if (mpflags & TDF_MP_EXITWAIT) {
832 if (atomic_cmpset_int(&otd->td_mpflags, mpflags,
833 mpflags | TDF_MP_EXITSIG)) {
838 if (atomic_cmpset_int(&otd->td_mpflags, mpflags,
839 mpflags | TDF_MP_EXITSIG)) {
846 if (tsc_frequency && rdtsc() - tsc_base > tsc_frequency) {
847 kprintf("lwkt_switch_return: excessive TDF_EXITING "
856 * Request that the target thread preempt the current thread. Preemption
857 * can only occur if our only critical section is the one that we were called
858 * with, the relative priority of the target thread is higher, and the target
859 * thread holds no tokens. This also only works if we are not holding any
860 * spinlocks (obviously).
862 * THE CALLER OF LWKT_PREEMPT() MUST BE IN A CRITICAL SECTION. Typically
863 * this is called via lwkt_schedule() through the td_preemptable callback.
864 * critcount is the managed critical priority that we should ignore in order
865 * to determine whether preemption is possible (aka usually just the crit
866 * priority of lwkt_schedule() itself).
868 * Preemption is typically limited to interrupt threads.
870 * Operation works in a fairly straight-forward manner. The normal
871 * scheduling code is bypassed and we switch directly to the target
872 * thread. When the target thread attempts to block or switch away
873 * code at the base of lwkt_switch() will switch directly back to our
874 * thread. Our thread is able to retain whatever tokens it holds and
875 * if the target needs one of them the target will switch back to us
876 * and reschedule itself normally.
879 lwkt_preempt(thread_t ntd, int critcount)
881 struct globaldata *gd = mycpu;
884 int save_gd_intr_nesting_level;
887 * The caller has put us in a critical section. We can only preempt
888 * if the caller of the caller was not in a critical section (basically
889 * a local interrupt), as determined by the 'critcount' parameter. We
890 * also can't preempt if the caller is holding any spinlocks (even if
891 * he isn't in a critical section). This also handles the tokens test.
893 * YYY The target thread must be in a critical section (else it must
894 * inherit our critical section? I dunno yet).
896 KASSERT(ntd->td_critcount, ("BADCRIT0 %d", ntd->td_pri));
898 td = gd->gd_curthread;
899 if (preempt_enable == 0) {
903 if (ntd->td_pri <= td->td_pri) {
907 if (td->td_critcount > critcount) {
911 if (td->td_cscount) {
915 if (ntd->td_gd != gd) {
921 * We don't have to check spinlocks here as they will also bump
924 * Do not try to preempt if the target thread is holding any tokens.
925 * We could try to acquire the tokens but this case is so rare there
926 * is no need to support it.
928 KKASSERT(gd->gd_spinlocks == 0);
930 if (TD_TOKS_HELD(ntd)) {
934 if (td == ntd || ((td->td_flags | ntd->td_flags) & TDF_PREEMPT_LOCK)) {
938 if (ntd->td_preempted) {
942 KKASSERT(gd->gd_processing_ipiq == 0);
945 * Since we are able to preempt the current thread, there is no need to
946 * call need_lwkt_resched().
948 * We must temporarily clear gd_intr_nesting_level around the switch
949 * since switchouts from the target thread are allowed (they will just
950 * return to our thread), and since the target thread has its own stack.
952 * A preemption must switch back to the original thread, assert the
956 ntd->td_preempted = td;
957 td->td_flags |= TDF_PREEMPT_LOCK;
958 KTR_LOG(ctxsw_pre, gd->gd_cpuid, ntd);
959 save_gd_intr_nesting_level = gd->gd_intr_nesting_level;
960 gd->gd_intr_nesting_level = 0;
962 KKASSERT((ntd->td_flags & TDF_RUNNING) == 0);
963 ntd->td_flags |= TDF_RUNNING;
964 xtd = td->td_switch(ntd);
965 KKASSERT(xtd == ntd);
966 lwkt_switch_return(xtd);
967 gd->gd_intr_nesting_level = save_gd_intr_nesting_level;
969 KKASSERT(ntd->td_preempted && (td->td_flags & TDF_PREEMPT_DONE));
970 ntd->td_preempted = NULL;
971 td->td_flags &= ~(TDF_PREEMPT_LOCK|TDF_PREEMPT_DONE);
975 * Conditionally call splz() if gd_reqflags indicates work is pending.
976 * This will work inside a critical section but not inside a hard code
979 * (self contained on a per cpu basis)
984 globaldata_t gd = mycpu;
985 thread_t td = gd->gd_curthread;
987 if ((gd->gd_reqflags & RQF_IDLECHECK_MASK) &&
988 gd->gd_intr_nesting_level == 0 &&
989 td->td_nest_count < 2)
996 * This version is integrated into crit_exit, reqflags has already
997 * been tested but td_critcount has not.
999 * We only want to execute the splz() on the 1->0 transition of
1000 * critcount and not in a hard code section or if too deeply nested.
1002 * NOTE: gd->gd_spinlocks is implied to be 0 when td_critcount is 0.
1005 lwkt_maybe_splz(thread_t td)
1007 globaldata_t gd = td->td_gd;
1009 if (td->td_critcount == 0 &&
1010 gd->gd_intr_nesting_level == 0 &&
1011 td->td_nest_count < 2)
1018 * Drivers which set up processing co-threads can call this function to
1019 * run the co-thread at a higher priority and to allow it to preempt
1023 lwkt_set_interrupt_support_thread(void)
1025 thread_t td = curthread;
1027 lwkt_setpri_self(TDPRI_INT_SUPPORT);
1028 td->td_flags |= TDF_INTTHREAD;
1029 td->td_preemptable = lwkt_preempt;
1034 * This function is used to negotiate a passive release of the current
1035 * process/lwp designation with the user scheduler, allowing the user
1036 * scheduler to schedule another user thread. The related kernel thread
1037 * (curthread) continues running in the released state.
1040 lwkt_passive_release(struct thread *td)
1042 struct lwp *lp = td->td_lwp;
1044 td->td_release = NULL;
1045 lwkt_setpri_self(TDPRI_KERN_USER);
1047 lp->lwp_proc->p_usched->release_curproc(lp);
1052 * This implements a LWKT yield, allowing a kernel thread to yield to other
1053 * kernel threads at the same or higher priority. This function can be
1054 * called in a tight loop and will typically only yield once per tick.
1056 * Most kernel threads run at the same priority in order to allow equal
1059 * (self contained on a per cpu basis)
1064 globaldata_t gd = mycpu;
1065 thread_t td = gd->gd_curthread;
1068 * Should never be called with spinlocks held but there is a path
1069 * via ACPI where it might happen.
1071 if (gd->gd_spinlocks)
1075 * Safe to call splz if we are not too-heavily nested.
1077 if ((gd->gd_reqflags & RQF_IDLECHECK_MASK) && td->td_nest_count < 2)
1081 * Caller allows switching
1083 if (lwkt_resched_wanted()) {
1084 lwkt_schedule_self(curthread);
1090 * The quick version processes pending interrupts and higher-priority
1091 * LWKT threads but will not round-robin same-priority LWKT threads.
1093 * When called while attempting to return to userland the only same-pri
1094 * threads are the ones which have already tried to become the current
1098 lwkt_yield_quick(void)
1100 globaldata_t gd = mycpu;
1101 thread_t td = gd->gd_curthread;
1103 if ((gd->gd_reqflags & RQF_IDLECHECK_MASK) && td->td_nest_count < 2)
1105 if (lwkt_resched_wanted()) {
1107 if (TAILQ_FIRST(&gd->gd_tdrunq) == td) {
1108 clear_lwkt_resched();
1110 lwkt_schedule_self(curthread);
1118 * This yield is designed for kernel threads with a user context.
1120 * The kernel acting on behalf of the user is potentially cpu-bound,
1121 * this function will efficiently allow other threads to run and also
1122 * switch to other processes by releasing.
1124 * The lwkt_user_yield() function is designed to have very low overhead
1125 * if no yield is determined to be needed.
1128 lwkt_user_yield(void)
1130 globaldata_t gd = mycpu;
1131 thread_t td = gd->gd_curthread;
1134 * Should never be called with spinlocks held but there is a path
1135 * via ACPI where it might happen.
1137 if (gd->gd_spinlocks)
1141 * Always run any pending interrupts in case we are in a critical
1144 if ((gd->gd_reqflags & RQF_IDLECHECK_MASK) && td->td_nest_count < 2)
1148 * Switch (which forces a release) if another kernel thread needs
1149 * the cpu, if userland wants us to resched, or if our kernel
1150 * quantum has run out.
1152 if (lwkt_resched_wanted() ||
1153 user_resched_wanted())
1160 * Reacquire the current process if we are released.
1162 * XXX not implemented atm. The kernel may be holding locks and such,
1163 * so we want the thread to continue to receive cpu.
1165 if (td->td_release == NULL && lp) {
1166 lp->lwp_proc->p_usched->acquire_curproc(lp);
1167 td->td_release = lwkt_passive_release;
1168 lwkt_setpri_self(TDPRI_USER_NORM);
1174 * Generic schedule. Possibly schedule threads belonging to other cpus and
1175 * deal with threads that might be blocked on a wait queue.
1177 * We have a little helper inline function which does additional work after
1178 * the thread has been enqueued, including dealing with preemption and
1179 * setting need_lwkt_resched() (which prevents the kernel from returning
1180 * to userland until it has processed higher priority threads).
1182 * It is possible for this routine to be called after a failed _enqueue
1183 * (due to the target thread migrating, sleeping, or otherwise blocked).
1184 * We have to check that the thread is actually on the run queue!
1188 _lwkt_schedule_post(globaldata_t gd, thread_t ntd, int ccount)
1190 if (ntd->td_flags & TDF_RUNQ) {
1191 if (ntd->td_preemptable) {
1192 ntd->td_preemptable(ntd, ccount); /* YYY +token */
1199 _lwkt_schedule(thread_t td)
1201 globaldata_t mygd = mycpu;
1203 KASSERT(td != &td->td_gd->gd_idlethread,
1204 ("lwkt_schedule(): scheduling gd_idlethread is illegal!"));
1205 KKASSERT((td->td_flags & TDF_MIGRATING) == 0);
1206 crit_enter_gd(mygd);
1207 KKASSERT(td->td_lwp == NULL ||
1208 (td->td_lwp->lwp_mpflags & LWP_MP_ONRUNQ) == 0);
1210 if (td == mygd->gd_curthread) {
1214 * If we own the thread, there is no race (since we are in a
1215 * critical section). If we do not own the thread there might
1216 * be a race but the target cpu will deal with it.
1218 if (td->td_gd == mygd) {
1220 _lwkt_schedule_post(mygd, td, 1);
1222 lwkt_send_ipiq3(td->td_gd, lwkt_schedule_remote, td, 0);
1229 lwkt_schedule(thread_t td)
1235 lwkt_schedule_noresched(thread_t td) /* XXX not impl */
1241 * When scheduled remotely if frame != NULL the IPIQ is being
1242 * run via doreti or an interrupt then preemption can be allowed.
1244 * To allow preemption we have to drop the critical section so only
1245 * one is present in _lwkt_schedule_post.
1248 lwkt_schedule_remote(void *arg, int arg2, struct intrframe *frame)
1250 thread_t td = curthread;
1253 if (frame && ntd->td_preemptable) {
1254 crit_exit_noyield(td);
1255 _lwkt_schedule(ntd);
1256 crit_enter_quick(td);
1258 _lwkt_schedule(ntd);
1263 * Thread migration using a 'Pull' method. The thread may or may not be
1264 * the current thread. It MUST be descheduled and in a stable state.
1265 * lwkt_giveaway() must be called on the cpu owning the thread.
1267 * At any point after lwkt_giveaway() is called, the target cpu may
1268 * 'pull' the thread by calling lwkt_acquire().
1270 * We have to make sure the thread is not sitting on a per-cpu tsleep
1271 * queue or it will blow up when it moves to another cpu.
1273 * MPSAFE - must be called under very specific conditions.
1276 lwkt_giveaway(thread_t td)
1278 globaldata_t gd = mycpu;
1281 if (td->td_flags & TDF_TSLEEPQ)
1283 KKASSERT(td->td_gd == gd);
1284 TAILQ_REMOVE(&gd->gd_tdallq, td, td_allq);
1285 td->td_flags |= TDF_MIGRATING;
1290 lwkt_acquire(thread_t td)
1295 KKASSERT(td->td_flags & TDF_MIGRATING);
1300 uint64_t tsc_base = rdtsc();
1303 KKASSERT((td->td_flags & TDF_RUNQ) == 0);
1304 crit_enter_gd(mygd);
1305 DEBUG_PUSH_INFO("lwkt_acquire");
1306 while (td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK)) {
1307 lwkt_process_ipiq();
1309 #ifdef _KERNEL_VIRTUAL
1313 if (tsc_frequency && rdtsc() - tsc_base > tsc_frequency) {
1314 kprintf("lwkt_acquire: stuck td %p td->td_flags %08x\n",
1323 TAILQ_INSERT_TAIL(&mygd->gd_tdallq, td, td_allq);
1324 td->td_flags &= ~TDF_MIGRATING;
1327 crit_enter_gd(mygd);
1328 TAILQ_INSERT_TAIL(&mygd->gd_tdallq, td, td_allq);
1329 td->td_flags &= ~TDF_MIGRATING;
1335 * Generic deschedule. Descheduling threads other then your own should be
1336 * done only in carefully controlled circumstances. Descheduling is
1339 * This function may block if the cpu has run out of messages.
1342 lwkt_deschedule(thread_t td)
1345 if (td == curthread) {
1348 if (td->td_gd == mycpu) {
1351 lwkt_send_ipiq(td->td_gd, (ipifunc1_t)lwkt_deschedule, td);
1358 * Set the target thread's priority. This routine does not automatically
1359 * switch to a higher priority thread, LWKT threads are not designed for
1360 * continuous priority changes. Yield if you want to switch.
1363 lwkt_setpri(thread_t td, int pri)
1365 if (td->td_pri != pri) {
1368 if (td->td_flags & TDF_RUNQ) {
1369 KKASSERT(td->td_gd == mycpu);
1381 * Set the initial priority for a thread prior to it being scheduled for
1382 * the first time. The thread MUST NOT be scheduled before or during
1383 * this call. The thread may be assigned to a cpu other then the current
1386 * Typically used after a thread has been created with TDF_STOPPREQ,
1387 * and before the thread is initially scheduled.
1390 lwkt_setpri_initial(thread_t td, int pri)
1393 KKASSERT((td->td_flags & TDF_RUNQ) == 0);
1398 lwkt_setpri_self(int pri)
1400 thread_t td = curthread;
1402 KKASSERT(pri >= 0 && pri <= TDPRI_MAX);
1404 if (td->td_flags & TDF_RUNQ) {
1415 * hz tick scheduler clock for LWKT threads
1418 lwkt_schedulerclock(thread_t td)
1420 globaldata_t gd = td->td_gd;
1423 if (TAILQ_FIRST(&gd->gd_tdrunq) == td) {
1425 * If the current thread is at the head of the runq shift it to the
1426 * end of any equal-priority threads and request a LWKT reschedule
1429 * Ignore upri in this situation. There will only be one user thread
1430 * in user mode, all others will be user threads running in kernel
1431 * mode and we have to make sure they get some cpu.
1433 xtd = TAILQ_NEXT(td, td_threadq);
1434 if (xtd && xtd->td_pri == td->td_pri) {
1435 TAILQ_REMOVE(&gd->gd_tdrunq, td, td_threadq);
1436 while (xtd && xtd->td_pri == td->td_pri)
1437 xtd = TAILQ_NEXT(xtd, td_threadq);
1439 TAILQ_INSERT_BEFORE(xtd, td, td_threadq);
1441 TAILQ_INSERT_TAIL(&gd->gd_tdrunq, td, td_threadq);
1442 need_lwkt_resched();
1446 * If we scheduled a thread other than the one at the head of the
1447 * queue always request a reschedule every tick.
1449 need_lwkt_resched();
1454 * Migrate the current thread to the specified cpu.
1456 * This is accomplished by descheduling ourselves from the current cpu
1457 * and setting td_migrate_gd. The lwkt_switch() code will detect that the
1458 * 'old' thread wants to migrate after it has been completely switched out
1459 * and will complete the migration.
1461 * TDF_MIGRATING prevents scheduling races while the thread is being migrated.
1463 * We must be sure to release our current process designation (if a user
1464 * process) before clearing out any tsleepq we are on because the release
1465 * code may re-add us.
1467 * We must be sure to remove ourselves from the current cpu's tsleepq
1468 * before potentially moving to another queue. The thread can be on
1469 * a tsleepq due to a left-over tsleep_interlock().
1473 lwkt_setcpu_self(globaldata_t rgd)
1475 thread_t td = curthread;
1477 if (td->td_gd != rgd) {
1478 crit_enter_quick(td);
1482 if (td->td_flags & TDF_TSLEEPQ)
1486 * Set TDF_MIGRATING to prevent a spurious reschedule while we are
1487 * trying to deschedule ourselves and switch away, then deschedule
1488 * ourself, remove us from tdallq, and set td_migrate_gd. Finally,
1489 * call lwkt_switch() to complete the operation.
1491 td->td_flags |= TDF_MIGRATING;
1492 lwkt_deschedule_self(td);
1493 TAILQ_REMOVE(&td->td_gd->gd_tdallq, td, td_allq);
1494 td->td_migrate_gd = rgd;
1498 * We are now on the target cpu
1500 KKASSERT(rgd == mycpu);
1501 TAILQ_INSERT_TAIL(&rgd->gd_tdallq, td, td_allq);
1502 crit_exit_quick(td);
1507 lwkt_migratecpu(int cpuid)
1511 rgd = globaldata_find(cpuid);
1512 lwkt_setcpu_self(rgd);
1516 * Remote IPI for cpu migration (called while in a critical section so we
1517 * do not have to enter another one).
1519 * The thread (td) has already been completely descheduled from the
1520 * originating cpu and we can simply assert the case. The thread is
1521 * assigned to the new cpu and enqueued.
1523 * The thread will re-add itself to tdallq when it resumes execution.
1526 lwkt_setcpu_remote(void *arg)
1529 globaldata_t gd = mycpu;
1531 KKASSERT((td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK)) == 0);
1534 td->td_flags &= ~TDF_MIGRATING;
1535 KKASSERT(td->td_migrate_gd == NULL);
1536 KKASSERT(td->td_lwp == NULL ||
1537 (td->td_lwp->lwp_mpflags & LWP_MP_ONRUNQ) == 0);
1542 lwkt_preempted_proc(void)
1544 thread_t td = curthread;
1545 while (td->td_preempted)
1546 td = td->td_preempted;
1551 * Create a kernel process/thread/whatever. It shares it's address space
1552 * with proc0 - ie: kernel only.
1554 * If the cpu is not specified one will be selected. In the future
1555 * specifying a cpu of -1 will enable kernel thread migration between
1559 lwkt_create(void (*func)(void *), void *arg, struct thread **tdp,
1560 thread_t template, int tdflags, int cpu, const char *fmt, ...)
1565 td = lwkt_alloc_thread(template, LWKT_THREAD_STACK, cpu,
1569 cpu_set_thread_handler(td, lwkt_exit, func, arg);
1572 * Set up arg0 for 'ps' etc
1574 __va_start(ap, fmt);
1575 kvsnprintf(td->td_comm, sizeof(td->td_comm), fmt, ap);
1579 * Schedule the thread to run
1581 if (td->td_flags & TDF_NOSTART)
1582 td->td_flags &= ~TDF_NOSTART;
1589 * Destroy an LWKT thread. Warning! This function is not called when
1590 * a process exits, cpu_proc_exit() directly calls cpu_thread_exit() and
1591 * uses a different reaping mechanism.
1596 thread_t td = curthread;
1601 * Do any cleanup that might block here
1603 if (td->td_flags & TDF_VERBOSE)
1604 kprintf("kthread %p %s has exited\n", td, td->td_comm);
1606 dsched_exit_thread(td);
1609 * Get us into a critical section to interlock gd_freetd and loop
1610 * until we can get it freed.
1612 * We have to cache the current td in gd_freetd because objcache_put()ing
1613 * it would rip it out from under us while our thread is still active.
1615 * We are the current thread so of course our own TDF_RUNNING bit will
1616 * be set, so unlike the lwp reap code we don't wait for it to clear.
1619 crit_enter_quick(td);
1622 tsleep(td, 0, "tdreap", 1);
1625 if ((std = gd->gd_freetd) != NULL) {
1626 KKASSERT((std->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK)) == 0);
1627 gd->gd_freetd = NULL;
1628 objcache_put(thread_cache, std);
1635 * Remove thread resources from kernel lists and deschedule us for
1636 * the last time. We cannot block after this point or we may end
1637 * up with a stale td on the tsleepq.
1639 * None of this may block, the critical section is the only thing
1640 * protecting tdallq and the only thing preventing new lwkt_hold()
1643 if (td->td_flags & TDF_TSLEEPQ)
1645 lwkt_deschedule_self(td);
1646 lwkt_remove_tdallq(td);
1647 KKASSERT(td->td_refs == 0);
1652 KKASSERT(gd->gd_freetd == NULL);
1653 if (td->td_flags & TDF_ALLOCATED_THREAD)
1659 lwkt_remove_tdallq(thread_t td)
1661 KKASSERT(td->td_gd == mycpu);
1662 TAILQ_REMOVE(&td->td_gd->gd_tdallq, td, td_allq);
1666 * Code reduction and branch prediction improvements. Call/return
1667 * overhead on modern cpus often degenerates into 0 cycles due to
1668 * the cpu's branch prediction hardware and return pc cache. We
1669 * can take advantage of this by not inlining medium-complexity
1670 * functions and we can also reduce the branch prediction impact
1671 * by collapsing perfectly predictable branches into a single
1672 * procedure instead of duplicating it.
1674 * Is any of this noticeable? Probably not, so I'll take the
1675 * smaller code size.
1678 crit_exit_wrapper(__DEBUG_CRIT_ARG__)
1680 _crit_exit(mycpu __DEBUG_CRIT_PASS_ARG__);
1686 thread_t td = curthread;
1687 int lcrit = td->td_critcount;
1689 td->td_critcount = 0;
1690 panic("td_critcount is/would-go negative! %p %d", td, lcrit);
1695 * Called from debugger/panic on cpus which have been stopped. We must still
1696 * process the IPIQ while stopped.
1698 * If we are dumping also try to process any pending interrupts. This may
1699 * or may not work depending on the state of the cpu at the point it was
1703 lwkt_smp_stopped(void)
1705 globaldata_t gd = mycpu;
1708 lwkt_process_ipiq();
1709 --gd->gd_intr_nesting_level;
1711 ++gd->gd_intr_nesting_level;
1713 lwkt_process_ipiq();