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[dragonfly.git] / sys / kern / lwkt_thread.c
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1 /*
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
9 * are met:
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
16 * distribution.
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
32 * SUCH DAMAGE.
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>
45 #include <sys/proc.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>
52 #include <sys/lock.h>
53 #include <sys/spinlock.h>
54 #include <sys/ktr.h>
55 #include <sys/indefinite.h>
57 #include <sys/thread2.h>
58 #include <sys/spinlock2.h>
59 #include <sys/indefinite2.h>
61 #include <sys/dsched.h>
63 #include <vm/vm.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>
74 #include <machine/clock.h>
76 #ifdef _KERNEL_VIRTUAL
77 #include <pthread.h>
78 #endif
80 #define LOOPMASK
82 #if !defined(KTR_CTXSW)
83 #define KTR_CTXSW KTR_ALL
84 #endif
85 KTR_INFO_MASTER(ctxsw);
86 KTR_INFO(KTR_CTXSW, ctxsw, sw, 0, "#cpu[%d].td = %p", int cpu, struct thread *td);
87 KTR_INFO(KTR_CTXSW, ctxsw, pre, 1, "#cpu[%d].td = %p", int cpu, struct thread *td);
88 KTR_INFO(KTR_CTXSW, ctxsw, newtd, 2, "#threads[%p].name = %s", struct thread *td, char *comm);
89 KTR_INFO(KTR_CTXSW, ctxsw, deadtd, 3, "#threads[%p].name = <dead>", struct thread *td);
91 static MALLOC_DEFINE(M_THREAD, "thread", "lwkt threads");
93 #ifdef INVARIANTS
94 static int panic_on_cscount = 0;
95 #endif
96 static int64_t switch_count = 0;
97 static int64_t preempt_hit = 0;
98 static int64_t preempt_miss = 0;
99 static int64_t preempt_weird = 0;
100 static int lwkt_use_spin_port;
101 static struct objcache *thread_cache;
102 int cpu_mwait_spin = 0;
104 static void lwkt_schedule_remote(void *arg, int arg2, struct intrframe *frame);
105 static void lwkt_setcpu_remote(void *arg);
108 * We can make all thread ports use the spin backend instead of the thread
109 * backend. This should only be set to debug the spin backend.
111 TUNABLE_INT("lwkt.use_spin_port", &lwkt_use_spin_port);
113 #ifdef INVARIANTS
114 SYSCTL_INT(_lwkt, OID_AUTO, panic_on_cscount, CTLFLAG_RW, &panic_on_cscount, 0,
115 "Panic if attempting to switch lwkt's while mastering cpusync");
116 #endif
117 SYSCTL_QUAD(_lwkt, OID_AUTO, switch_count, CTLFLAG_RW, &switch_count, 0,
118 "Number of switched threads");
119 SYSCTL_QUAD(_lwkt, OID_AUTO, preempt_hit, CTLFLAG_RW, &preempt_hit, 0,
120 "Successful preemption events");
121 SYSCTL_QUAD(_lwkt, OID_AUTO, preempt_miss, CTLFLAG_RW, &preempt_miss, 0,
122 "Failed preemption events");
123 SYSCTL_QUAD(_lwkt, OID_AUTO, preempt_weird, CTLFLAG_RW, &preempt_weird, 0,
124 "Number of preempted threads.");
125 static int fairq_enable = 0;
126 SYSCTL_INT(_lwkt, OID_AUTO, fairq_enable, CTLFLAG_RW,
127 &fairq_enable, 0, "Turn on fairq priority accumulators");
128 static int fairq_bypass = -1;
129 SYSCTL_INT(_lwkt, OID_AUTO, fairq_bypass, CTLFLAG_RW,
130 &fairq_bypass, 0, "Allow fairq to bypass td on token failure");
131 extern int lwkt_sched_debug;
132 int lwkt_sched_debug = 0;
133 SYSCTL_INT(_lwkt, OID_AUTO, sched_debug, CTLFLAG_RW,
134 &lwkt_sched_debug, 0, "Scheduler debug");
135 static u_int lwkt_spin_loops = 10;
136 SYSCTL_UINT(_lwkt, OID_AUTO, spin_loops, CTLFLAG_RW,
137 &lwkt_spin_loops, 0, "Scheduler spin loops until sorted decon");
138 static int preempt_enable = 1;
139 SYSCTL_INT(_lwkt, OID_AUTO, preempt_enable, CTLFLAG_RW,
140 &preempt_enable, 0, "Enable preemption");
141 static int lwkt_cache_threads = 0;
142 SYSCTL_INT(_lwkt, OID_AUTO, cache_threads, CTLFLAG_RD,
143 &lwkt_cache_threads, 0, "thread+kstack cache");
146 * These helper procedures handle the runq, they can only be called from
147 * within a critical section.
149 * WARNING! Prior to SMP being brought up it is possible to enqueue and
150 * dequeue threads belonging to other cpus, so be sure to use td->td_gd
151 * instead of 'mycpu' when referencing the globaldata structure. Once
152 * SMP live enqueuing and dequeueing only occurs on the current cpu.
154 static __inline
155 void
156 _lwkt_dequeue(thread_t td)
158 if (td->td_flags & TDF_RUNQ) {
159 struct globaldata *gd = td->td_gd;
161 td->td_flags &= ~TDF_RUNQ;
162 TAILQ_REMOVE(&gd->gd_tdrunq, td, td_threadq);
163 --gd->gd_tdrunqcount;
164 if (TAILQ_FIRST(&gd->gd_tdrunq) == NULL)
165 atomic_clear_int(&gd->gd_reqflags, RQF_RUNNING);
170 * Priority enqueue.
172 * There are a limited number of lwkt threads runnable since user
173 * processes only schedule one at a time per cpu. However, there can
174 * be many user processes in kernel mode exiting from a tsleep() which
175 * become runnable.
177 * We scan the queue in both directions to help deal with degenerate
178 * situations when hundreds or thousands (or more) threads are runnable.
180 * NOTE: lwkt_schedulerclock() will force a round-robin based on td_pri and
181 * will ignore user priority. This is to ensure that user threads in
182 * kernel mode get cpu at some point regardless of what the user
183 * scheduler thinks.
185 static __inline
186 void
187 _lwkt_enqueue(thread_t td)
189 thread_t xtd; /* forward scan */
190 thread_t rtd; /* reverse scan */
192 if ((td->td_flags & (TDF_RUNQ|TDF_MIGRATING|TDF_BLOCKQ)) == 0) {
193 struct globaldata *gd = td->td_gd;
195 td->td_flags |= TDF_RUNQ;
196 xtd = TAILQ_FIRST(&gd->gd_tdrunq);
197 if (xtd == NULL) {
198 TAILQ_INSERT_TAIL(&gd->gd_tdrunq, td, td_threadq);
199 atomic_set_int(&gd->gd_reqflags, RQF_RUNNING);
200 } else {
202 * NOTE: td_upri - higher numbers more desireable, same sense
203 * as td_pri (typically reversed from lwp_upri).
205 * In the equal priority case we want the best selection
206 * at the beginning so the less desireable selections know
207 * that they have to setrunqueue/go-to-another-cpu, even
208 * though it means switching back to the 'best' selection.
209 * This also avoids degenerate situations when many threads
210 * are runnable or waking up at the same time.
212 * If upri matches exactly place at end/round-robin.
214 rtd = TAILQ_LAST(&gd->gd_tdrunq, lwkt_queue);
216 while (xtd &&
217 (xtd->td_pri > td->td_pri ||
218 (xtd->td_pri == td->td_pri &&
219 xtd->td_upri >= td->td_upri))) {
220 xtd = TAILQ_NEXT(xtd, td_threadq);
223 * Doing a reverse scan at the same time is an optimization
224 * for the insert-closer-to-tail case that avoids having to
225 * scan the entire list. This situation can occur when
226 * thousands of threads are woken up at the same time.
228 if (rtd->td_pri > td->td_pri ||
229 (rtd->td_pri == td->td_pri &&
230 rtd->td_upri >= td->td_upri)) {
231 TAILQ_INSERT_AFTER(&gd->gd_tdrunq, rtd, td, td_threadq);
232 goto skip;
234 rtd = TAILQ_PREV(rtd, lwkt_queue, td_threadq);
236 if (xtd)
237 TAILQ_INSERT_BEFORE(xtd, td, td_threadq);
238 else
239 TAILQ_INSERT_TAIL(&gd->gd_tdrunq, td, td_threadq);
241 skip:
242 ++gd->gd_tdrunqcount;
245 * Request a LWKT reschedule if we are now at the head of the queue.
247 if (TAILQ_FIRST(&gd->gd_tdrunq) == td)
248 need_lwkt_resched();
252 static boolean_t
253 _lwkt_thread_ctor(void *obj, void *privdata, int ocflags)
255 struct thread *td = (struct thread *)obj;
257 td->td_kstack = NULL;
258 td->td_kstack_size = 0;
259 td->td_flags = TDF_ALLOCATED_THREAD;
260 td->td_mpflags = 0;
261 return (1);
264 static void
265 _lwkt_thread_dtor(void *obj, void *privdata)
267 struct thread *td = (struct thread *)obj;
269 KASSERT(td->td_flags & TDF_ALLOCATED_THREAD,
270 ("_lwkt_thread_dtor: not allocated from objcache"));
271 KASSERT((td->td_flags & TDF_ALLOCATED_STACK) && td->td_kstack &&
272 td->td_kstack_size > 0,
273 ("_lwkt_thread_dtor: corrupted stack"));
274 kmem_free(&kernel_map, (vm_offset_t)td->td_kstack, td->td_kstack_size);
275 td->td_kstack = NULL;
276 td->td_flags = 0;
280 * Initialize the lwkt s/system.
282 * Nominally cache up to 32 thread + kstack structures. Cache more on
283 * systems with a lot of cpu cores.
285 static void
286 lwkt_init(void)
288 TUNABLE_INT("lwkt.cache_threads", &lwkt_cache_threads);
289 if (lwkt_cache_threads == 0) {
290 lwkt_cache_threads = ncpus * 4;
291 if (lwkt_cache_threads < 32)
292 lwkt_cache_threads = 32;
294 thread_cache = objcache_create_mbacked(
295 M_THREAD, sizeof(struct thread),
296 0, lwkt_cache_threads,
297 _lwkt_thread_ctor, _lwkt_thread_dtor, NULL);
299 SYSINIT(lwkt_init, SI_BOOT2_LWKT_INIT, SI_ORDER_FIRST, lwkt_init, NULL);
302 * Schedule a thread to run. As the current thread we can always safely
303 * schedule ourselves, and a shortcut procedure is provided for that
304 * function.
306 * (non-blocking, self contained on a per cpu basis)
308 void
309 lwkt_schedule_self(thread_t td)
311 KKASSERT((td->td_flags & TDF_MIGRATING) == 0);
312 crit_enter_quick(td);
313 KASSERT(td != &td->td_gd->gd_idlethread,
314 ("lwkt_schedule_self(): scheduling gd_idlethread is illegal!"));
315 KKASSERT(td->td_lwp == NULL ||
316 (td->td_lwp->lwp_mpflags & LWP_MP_ONRUNQ) == 0);
317 _lwkt_enqueue(td);
318 crit_exit_quick(td);
322 * Deschedule a thread.
324 * (non-blocking, self contained on a per cpu basis)
326 void
327 lwkt_deschedule_self(thread_t td)
329 crit_enter_quick(td);
330 _lwkt_dequeue(td);
331 crit_exit_quick(td);
335 * LWKTs operate on a per-cpu basis
337 * WARNING! Called from early boot, 'mycpu' may not work yet.
339 void
340 lwkt_gdinit(struct globaldata *gd)
342 TAILQ_INIT(&gd->gd_tdrunq);
343 TAILQ_INIT(&gd->gd_tdallq);
344 lockinit(&gd->gd_sysctllock, "sysctl", 0, LK_CANRECURSE);
348 * Create a new thread. The thread must be associated with a process context
349 * or LWKT start address before it can be scheduled. If the target cpu is
350 * -1 the thread will be created on the current cpu.
352 * If you intend to create a thread without a process context this function
353 * does everything except load the startup and switcher function.
355 thread_t
356 lwkt_alloc_thread(struct thread *td, int stksize, int cpu, int flags)
358 static int cpu_rotator;
359 globaldata_t gd = mycpu;
360 void *stack;
363 * If static thread storage is not supplied allocate a thread. Reuse
364 * a cached free thread if possible. gd_freetd is used to keep an exiting
365 * thread intact through the exit.
367 if (td == NULL) {
368 crit_enter_gd(gd);
369 if ((td = gd->gd_freetd) != NULL) {
370 KKASSERT((td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK|
371 TDF_RUNQ)) == 0);
372 gd->gd_freetd = NULL;
373 } else {
374 td = objcache_get(thread_cache, M_WAITOK);
375 KKASSERT((td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK|
376 TDF_RUNQ)) == 0);
378 crit_exit_gd(gd);
379 KASSERT((td->td_flags &
380 (TDF_ALLOCATED_THREAD|TDF_RUNNING|TDF_PREEMPT_LOCK)) ==
381 TDF_ALLOCATED_THREAD,
382 ("lwkt_alloc_thread: corrupted td flags 0x%X", td->td_flags));
383 flags |= td->td_flags & (TDF_ALLOCATED_THREAD|TDF_ALLOCATED_STACK);
387 * Try to reuse cached stack.
389 if ((stack = td->td_kstack) != NULL && td->td_kstack_size != stksize) {
390 if (flags & TDF_ALLOCATED_STACK) {
391 kmem_free(&kernel_map, (vm_offset_t)stack, td->td_kstack_size);
392 stack = NULL;
395 if (stack == NULL) {
396 if (cpu < 0)
397 stack = (void *)kmem_alloc_stack(&kernel_map, stksize, 0);
398 else
399 stack = (void *)kmem_alloc_stack(&kernel_map, stksize,
400 KM_CPU(cpu));
401 flags |= TDF_ALLOCATED_STACK;
403 if (cpu < 0) {
404 cpu = ++cpu_rotator;
405 cpu_ccfence();
406 cpu = (uint32_t)cpu % (uint32_t)ncpus;
408 lwkt_init_thread(td, stack, stksize, flags, globaldata_find(cpu));
409 return(td);
413 * Initialize a preexisting thread structure. This function is used by
414 * lwkt_alloc_thread() and also used to initialize the per-cpu idlethread.
416 * All threads start out in a critical section at a priority of
417 * TDPRI_KERN_DAEMON. Higher level code will modify the priority as
418 * appropriate. This function may send an IPI message when the
419 * requested cpu is not the current cpu and consequently gd_tdallq may
420 * not be initialized synchronously from the point of view of the originating
421 * cpu.
423 * NOTE! we have to be careful in regards to creating threads for other cpus
424 * if SMP has not yet been activated.
426 static void
427 lwkt_init_thread_remote(void *arg)
429 thread_t td = arg;
432 * Protected by critical section held by IPI dispatch
434 TAILQ_INSERT_TAIL(&td->td_gd->gd_tdallq, td, td_allq);
438 * lwkt core thread structural initialization.
440 * NOTE: All threads are initialized as mpsafe threads.
442 void
443 lwkt_init_thread(thread_t td, void *stack, int stksize, int flags,
444 struct globaldata *gd)
446 globaldata_t mygd = mycpu;
448 bzero(td, sizeof(struct thread));
449 td->td_kstack = stack;
450 td->td_kstack_size = stksize;
451 td->td_flags = flags;
452 td->td_mpflags = 0;
453 td->td_type = TD_TYPE_GENERIC;
454 td->td_gd = gd;
455 td->td_pri = TDPRI_KERN_DAEMON;
456 td->td_critcount = 1;
457 td->td_toks_have = NULL;
458 td->td_toks_stop = &td->td_toks_base;
459 if (lwkt_use_spin_port || (flags & TDF_FORCE_SPINPORT)) {
460 lwkt_initport_spin(&td->td_msgport, td,
461 (flags & TDF_FIXEDCPU) ? TRUE : FALSE);
462 } else {
463 lwkt_initport_thread(&td->td_msgport, td);
465 pmap_init_thread(td);
467 * Normally initializing a thread for a remote cpu requires sending an
468 * IPI. However, the idlethread is setup before the other cpus are
469 * activated so we have to treat it as a special case. XXX manipulation
470 * of gd_tdallq requires the BGL.
472 if (gd == mygd || td == &gd->gd_idlethread) {
473 crit_enter_gd(mygd);
474 TAILQ_INSERT_TAIL(&gd->gd_tdallq, td, td_allq);
475 crit_exit_gd(mygd);
476 } else {
477 lwkt_send_ipiq(gd, lwkt_init_thread_remote, td);
479 dsched_enter_thread(td);
482 void
483 lwkt_set_comm(thread_t td, const char *ctl, ...)
485 __va_list va;
487 __va_start(va, ctl);
488 kvsnprintf(td->td_comm, sizeof(td->td_comm), ctl, va);
489 __va_end(va);
490 KTR_LOG(ctxsw_newtd, td, td->td_comm);
494 * Prevent the thread from getting destroyed. Note that unlike PHOLD/PRELE
495 * this does not prevent the thread from migrating to another cpu so the
496 * gd_tdallq state is not protected by this.
498 void
499 lwkt_hold(thread_t td)
501 atomic_add_int(&td->td_refs, 1);
504 void
505 lwkt_rele(thread_t td)
507 KKASSERT(td->td_refs > 0);
508 atomic_add_int(&td->td_refs, -1);
511 void
512 lwkt_free_thread(thread_t td)
514 KKASSERT(td->td_refs == 0);
515 KKASSERT((td->td_flags & (TDF_RUNNING | TDF_PREEMPT_LOCK |
516 TDF_RUNQ | TDF_TSLEEPQ)) == 0);
517 if (td->td_flags & TDF_ALLOCATED_THREAD) {
518 objcache_put(thread_cache, td);
519 } else if (td->td_flags & TDF_ALLOCATED_STACK) {
520 /* client-allocated struct with internally allocated stack */
521 KASSERT(td->td_kstack && td->td_kstack_size > 0,
522 ("lwkt_free_thread: corrupted stack"));
523 kmem_free(&kernel_map, (vm_offset_t)td->td_kstack, td->td_kstack_size);
524 td->td_kstack = NULL;
525 td->td_kstack_size = 0;
528 KTR_LOG(ctxsw_deadtd, td);
533 * Switch to the next runnable lwkt. If no LWKTs are runnable then
534 * switch to the idlethread. Switching must occur within a critical
535 * section to avoid races with the scheduling queue.
537 * We always have full control over our cpu's run queue. Other cpus
538 * that wish to manipulate our queue must use the cpu_*msg() calls to
539 * talk to our cpu, so a critical section is all that is needed and
540 * the result is very, very fast thread switching.
542 * The LWKT scheduler uses a fixed priority model and round-robins at
543 * each priority level. User process scheduling is a totally
544 * different beast and LWKT priorities should not be confused with
545 * user process priorities.
547 * PREEMPTION NOTE: Preemption occurs via lwkt_preempt(). lwkt_switch()
548 * is not called by the current thread in the preemption case, only when
549 * the preempting thread blocks (in order to return to the original thread).
551 * SPECIAL NOTE ON SWITCH ATOMICY: Certain operations such as thread
552 * migration and tsleep deschedule the current lwkt thread and call
553 * lwkt_switch(). In particular, the target cpu of the migration fully
554 * expects the thread to become non-runnable and can deadlock against
555 * cpusync operations if we run any IPIs prior to switching the thread out.
557 * WE MUST BE VERY CAREFUL NOT TO RUN SPLZ DIRECTLY OR INDIRECTLY IF
558 * THE CURRENT THREAD HAS BEEN DESCHEDULED!
560 void
561 lwkt_switch(void)
563 globaldata_t gd = mycpu;
564 thread_t td = gd->gd_curthread;
565 thread_t ntd;
566 thread_t xtd;
567 int upri;
568 #ifdef LOOPMASK
569 uint64_t tsc_base = rdtsc();
570 #endif
572 KKASSERT(gd->gd_processing_ipiq == 0);
573 KKASSERT(td->td_flags & TDF_RUNNING);
576 * Switching from within a 'fast' (non thread switched) interrupt or IPI
577 * is illegal. However, we may have to do it anyway if we hit a fatal
578 * kernel trap or we have paniced.
580 * If this case occurs save and restore the interrupt nesting level.
582 if (gd->gd_intr_nesting_level) {
583 int savegdnest;
584 int savegdtrap;
586 if (gd->gd_trap_nesting_level == 0 && panic_cpu_gd != mycpu) {
587 panic("lwkt_switch: Attempt to switch from a "
588 "fast interrupt, ipi, or hard code section, "
589 "td %p\n",
590 td);
591 } else {
592 savegdnest = gd->gd_intr_nesting_level;
593 savegdtrap = gd->gd_trap_nesting_level;
594 gd->gd_intr_nesting_level = 0;
595 gd->gd_trap_nesting_level = 0;
596 if ((td->td_flags & TDF_PANICWARN) == 0) {
597 td->td_flags |= TDF_PANICWARN;
598 kprintf("Warning: thread switch from interrupt, IPI, "
599 "or hard code section.\n"
600 "thread %p (%s)\n", td, td->td_comm);
601 print_backtrace(-1);
603 lwkt_switch();
604 gd->gd_intr_nesting_level = savegdnest;
605 gd->gd_trap_nesting_level = savegdtrap;
606 return;
611 * Release our current user process designation if we are blocking
612 * or if a user reschedule was requested.
614 * NOTE: This function is NOT called if we are switching into or
615 * returning from a preemption.
617 * NOTE: Releasing our current user process designation may cause
618 * it to be assigned to another thread, which in turn will
619 * cause us to block in the usched acquire code when we attempt
620 * to return to userland.
622 * NOTE: On SMP systems this can be very nasty when heavy token
623 * contention is present so we want to be careful not to
624 * release the designation gratuitously.
626 if (td->td_release &&
627 (user_resched_wanted() || (td->td_flags & TDF_RUNQ) == 0)) {
628 td->td_release(td);
632 * Release all tokens. Once we do this we must remain in the critical
633 * section and cannot run IPIs or other interrupts until we switch away
634 * because they may implode if they try to get a token using our thread
635 * context.
637 crit_enter_gd(gd);
638 if (TD_TOKS_HELD(td))
639 lwkt_relalltokens(td);
642 * We had better not be holding any spin locks, but don't get into an
643 * endless panic loop.
645 KASSERT(gd->gd_spinlocks == 0 || panicstr != NULL,
646 ("lwkt_switch: still holding %d exclusive spinlocks!",
647 gd->gd_spinlocks));
649 #ifdef INVARIANTS
650 if (td->td_cscount) {
651 kprintf("Diagnostic: attempt to switch while mastering cpusync: %p\n",
652 td);
653 if (panic_on_cscount)
654 panic("switching while mastering cpusync");
656 #endif
659 * If we had preempted another thread on this cpu, resume the preempted
660 * thread. This occurs transparently, whether the preempted thread
661 * was scheduled or not (it may have been preempted after descheduling
662 * itself).
664 * We have to setup the MP lock for the original thread after backing
665 * out the adjustment that was made to curthread when the original
666 * was preempted.
668 if ((ntd = td->td_preempted) != NULL) {
669 KKASSERT(ntd->td_flags & TDF_PREEMPT_LOCK);
670 ntd->td_flags |= TDF_PREEMPT_DONE;
671 ntd->td_contended = 0; /* reset contended */
674 * The interrupt may have woken a thread up, we need to properly
675 * set the reschedule flag if the originally interrupted thread is
676 * at a lower priority.
678 * NOTE: The interrupt may not have descheduled ntd.
680 * NOTE: We do not reschedule if there are no threads on the runq.
681 * (ntd could be the idlethread).
683 xtd = TAILQ_FIRST(&gd->gd_tdrunq);
684 if (xtd && xtd != ntd)
685 need_lwkt_resched();
686 goto havethread_preempted;
690 * Figure out switch target. If we cannot switch to our desired target
691 * look for a thread that we can switch to.
693 * NOTE! The limited spin loop and related parameters are extremely
694 * important for system performance, particularly for pipes and
695 * concurrent conflicting VM faults.
697 clear_lwkt_resched();
698 ntd = TAILQ_FIRST(&gd->gd_tdrunq);
700 if (ntd) {
701 do {
702 if (TD_TOKS_NOT_HELD(ntd) ||
703 lwkt_getalltokens(ntd, (ntd->td_contended > lwkt_spin_loops)))
705 goto havethread;
707 ++ntd->td_contended; /* overflow ok */
708 if (gd->gd_indefinite.type == 0)
709 indefinite_init(&gd->gd_indefinite, NULL, 0, 't');
710 #ifdef LOOPMASK
711 if (tsc_frequency && rdtsc() - tsc_base > tsc_frequency) {
712 kprintf("lwkt_switch: excessive contended %d "
713 "thread %p\n", ntd->td_contended, ntd);
714 tsc_base = rdtsc();
716 #endif
717 } while (ntd->td_contended < (lwkt_spin_loops >> 1));
718 upri = ntd->td_upri;
721 * Bleh, the thread we wanted to switch to has a contended token.
722 * See if we can switch to another thread.
724 * We generally don't want to do this because it represents a
725 * priority inversion, but contending tokens on the same cpu can
726 * cause real problems if we don't now that we have an exclusive
727 * priority mechanism over shared for tokens.
729 * The solution is to allow threads with pending tokens to compete
730 * for them (a lower priority thread will get less cpu once it
731 * returns from the kernel anyway). If a thread does not have
732 * any contending tokens, we go by td_pri and upri.
734 while ((ntd = TAILQ_NEXT(ntd, td_threadq)) != NULL) {
735 if (TD_TOKS_NOT_HELD(ntd) &&
736 ntd->td_pri < TDPRI_KERN_LPSCHED && upri > ntd->td_upri) {
737 continue;
739 if (upri < ntd->td_upri)
740 upri = ntd->td_upri;
743 * Try this one.
745 if (TD_TOKS_NOT_HELD(ntd) ||
746 lwkt_getalltokens(ntd, (ntd->td_contended > lwkt_spin_loops))) {
747 goto havethread;
749 ++ntd->td_contended; /* overflow ok */
753 * Fall through, switch to idle thread to get us out of the current
754 * context. Since we were contended, prevent HLT by flagging a
755 * LWKT reschedule.
757 need_lwkt_resched();
761 * We either contended on ntd or the runq is empty. We must switch
762 * through the idle thread to get out of the current context.
764 ntd = &gd->gd_idlethread;
765 if (gd->gd_trap_nesting_level == 0 && panicstr == NULL)
766 ASSERT_NO_TOKENS_HELD(ntd);
767 cpu_time.cp_msg[0] = 0;
768 goto haveidle;
770 havethread:
772 * Clear gd_idle_repeat when doing a normal switch to a non-idle
773 * thread.
775 ntd->td_wmesg = NULL;
776 ntd->td_contended = 0; /* reset once scheduled */
777 ++gd->gd_cnt.v_swtch;
778 gd->gd_idle_repeat = 0;
781 * If we were busy waiting record final disposition
783 if (gd->gd_indefinite.type)
784 indefinite_done(&gd->gd_indefinite);
786 havethread_preempted:
788 * If the new target does not need the MP lock and we are holding it,
789 * release the MP lock. If the new target requires the MP lock we have
790 * already acquired it for the target.
793 haveidle:
794 KASSERT(ntd->td_critcount,
795 ("priority problem in lwkt_switch %d %d",
796 td->td_critcount, ntd->td_critcount));
798 if (td != ntd) {
800 * Execute the actual thread switch operation. This function
801 * returns to the current thread and returns the previous thread
802 * (which may be different from the thread we switched to).
804 * We are responsible for marking ntd as TDF_RUNNING.
806 KKASSERT((ntd->td_flags & TDF_RUNNING) == 0);
807 ++switch_count;
808 KTR_LOG(ctxsw_sw, gd->gd_cpuid, ntd);
809 ntd->td_flags |= TDF_RUNNING;
810 lwkt_switch_return(td->td_switch(ntd));
811 /* ntd invalid, td_switch() can return a different thread_t */
815 * catch-all. XXX is this strictly needed?
817 splz_check();
819 /* NOTE: current cpu may have changed after switch */
820 crit_exit_quick(td);
824 * Called by assembly in the td_switch (thread restore path) for thread
825 * bootstrap cases which do not 'return' to lwkt_switch().
827 void
828 lwkt_switch_return(thread_t otd)
830 globaldata_t rgd;
831 #ifdef LOOPMASK
832 uint64_t tsc_base = rdtsc();
833 #endif
834 int exiting;
836 exiting = otd->td_flags & TDF_EXITING;
837 cpu_ccfence();
840 * Check if otd was migrating. Now that we are on ntd we can finish
841 * up the migration. This is a bit messy but it is the only place
842 * where td is known to be fully descheduled.
844 * We can only activate the migration if otd was migrating but not
845 * held on the cpu due to a preemption chain. We still have to
846 * clear TDF_RUNNING on the old thread either way.
848 * We are responsible for clearing the previously running thread's
849 * TDF_RUNNING.
851 if ((rgd = otd->td_migrate_gd) != NULL &&
852 (otd->td_flags & TDF_PREEMPT_LOCK) == 0) {
853 KKASSERT((otd->td_flags & (TDF_MIGRATING | TDF_RUNNING)) ==
854 (TDF_MIGRATING | TDF_RUNNING));
855 otd->td_migrate_gd = NULL;
856 otd->td_flags &= ~TDF_RUNNING;
857 lwkt_send_ipiq(rgd, lwkt_setcpu_remote, otd);
858 } else {
859 otd->td_flags &= ~TDF_RUNNING;
863 * Final exit validations (see lwp_wait()). Note that otd becomes
864 * invalid the *instant* we set TDF_MP_EXITSIG.
866 * Use the EXITING status loaded from before we clear TDF_RUNNING,
867 * because if it is not set otd becomes invalid the instant we clear
868 * TDF_RUNNING on it (otherwise, if the system is fast enough, we
869 * might 'steal' TDF_EXITING from another switch-return!).
871 while (exiting) {
872 u_int mpflags;
874 mpflags = otd->td_mpflags;
875 cpu_ccfence();
877 if (mpflags & TDF_MP_EXITWAIT) {
878 if (atomic_cmpset_int(&otd->td_mpflags, mpflags,
879 mpflags | TDF_MP_EXITSIG)) {
880 wakeup(otd);
881 break;
883 } else {
884 if (atomic_cmpset_int(&otd->td_mpflags, mpflags,
885 mpflags | TDF_MP_EXITSIG)) {
886 wakeup(otd);
887 break;
891 #ifdef LOOPMASK
892 if (tsc_frequency && rdtsc() - tsc_base > tsc_frequency) {
893 kprintf("lwkt_switch_return: excessive TDF_EXITING "
894 "thread %p\n", otd);
895 tsc_base = rdtsc();
897 #endif
902 * Request that the target thread preempt the current thread. Preemption
903 * can only occur only:
905 * - If our critical section is the one that we were called with
906 * - The relative priority of the target thread is higher
907 * - The target is not excessively interrupt-nested via td_nest_count
908 * - The target thread holds no tokens.
909 * - The target thread is not already scheduled and belongs to the
910 * current cpu.
911 * - The current thread is not holding any spin-locks.
913 * THE CALLER OF LWKT_PREEMPT() MUST BE IN A CRITICAL SECTION. Typically
914 * this is called via lwkt_schedule() through the td_preemptable callback.
915 * critcount is the managed critical priority that we should ignore in order
916 * to determine whether preemption is possible (aka usually just the crit
917 * priority of lwkt_schedule() itself).
919 * Preemption is typically limited to interrupt threads.
921 * Operation works in a fairly straight-forward manner. The normal
922 * scheduling code is bypassed and we switch directly to the target
923 * thread. When the target thread attempts to block or switch away
924 * code at the base of lwkt_switch() will switch directly back to our
925 * thread. Our thread is able to retain whatever tokens it holds and
926 * if the target needs one of them the target will switch back to us
927 * and reschedule itself normally.
929 void
930 lwkt_preempt(thread_t ntd, int critcount)
932 struct globaldata *gd = mycpu;
933 thread_t xtd;
934 thread_t td;
935 int save_gd_intr_nesting_level;
938 * The caller has put us in a critical section. We can only preempt
939 * if the caller of the caller was not in a critical section (basically
940 * a local interrupt), as determined by the 'critcount' parameter. We
941 * also can't preempt if the caller is holding any spinlocks (even if
942 * he isn't in a critical section). This also handles the tokens test.
944 * YYY The target thread must be in a critical section (else it must
945 * inherit our critical section? I dunno yet).
947 KASSERT(ntd->td_critcount, ("BADCRIT0 %d", ntd->td_pri));
949 td = gd->gd_curthread;
950 if (preempt_enable == 0) {
951 ++preempt_miss;
952 return;
954 if (ntd->td_pri <= td->td_pri) {
955 ++preempt_miss;
956 return;
958 if (td->td_critcount > critcount) {
959 ++preempt_miss;
960 return;
962 if (td->td_nest_count >= 2) {
963 ++preempt_miss;
964 return;
966 if (td->td_cscount) {
967 ++preempt_miss;
968 return;
970 if (ntd->td_gd != gd) {
971 ++preempt_miss;
972 return;
976 * We don't have to check spinlocks here as they will also bump
977 * td_critcount.
979 * Do not try to preempt if the target thread is holding any tokens.
980 * We could try to acquire the tokens but this case is so rare there
981 * is no need to support it.
983 KKASSERT(gd->gd_spinlocks == 0);
985 if (TD_TOKS_HELD(ntd)) {
986 ++preempt_miss;
987 return;
989 if (td == ntd || ((td->td_flags | ntd->td_flags) & TDF_PREEMPT_LOCK)) {
990 ++preempt_weird;
991 return;
993 if (ntd->td_preempted) {
994 ++preempt_hit;
995 return;
997 KKASSERT(gd->gd_processing_ipiq == 0);
1000 * Since we are able to preempt the current thread, there is no need to
1001 * call need_lwkt_resched().
1003 * We must temporarily clear gd_intr_nesting_level around the switch
1004 * since switchouts from the target thread are allowed (they will just
1005 * return to our thread), and since the target thread has its own stack.
1007 * A preemption must switch back to the original thread, assert the
1008 * case.
1010 ++preempt_hit;
1011 ntd->td_preempted = td;
1012 td->td_flags |= TDF_PREEMPT_LOCK;
1013 KTR_LOG(ctxsw_pre, gd->gd_cpuid, ntd);
1014 save_gd_intr_nesting_level = gd->gd_intr_nesting_level;
1015 gd->gd_intr_nesting_level = 0;
1017 KKASSERT((ntd->td_flags & TDF_RUNNING) == 0);
1018 ntd->td_flags |= TDF_RUNNING;
1019 xtd = td->td_switch(ntd);
1020 KKASSERT(xtd == ntd);
1021 lwkt_switch_return(xtd);
1022 gd->gd_intr_nesting_level = save_gd_intr_nesting_level;
1024 KKASSERT(ntd->td_preempted && (td->td_flags & TDF_PREEMPT_DONE));
1025 ntd->td_preempted = NULL;
1026 td->td_flags &= ~(TDF_PREEMPT_LOCK|TDF_PREEMPT_DONE);
1030 * Conditionally call splz() if gd_reqflags indicates work is pending.
1031 * This will work inside a critical section but not inside a hard code
1032 * section.
1034 * (self contained on a per cpu basis)
1036 void
1037 splz_check(void)
1039 globaldata_t gd = mycpu;
1040 thread_t td = gd->gd_curthread;
1042 if ((gd->gd_reqflags & RQF_IDLECHECK_MASK) &&
1043 gd->gd_intr_nesting_level == 0 &&
1044 td->td_nest_count < 2)
1046 splz();
1051 * This version is integrated into crit_exit, reqflags has already
1052 * been tested but td_critcount has not.
1054 * We only want to execute the splz() on the 1->0 transition of
1055 * critcount and not in a hard code section or if too deeply nested.
1057 * NOTE: gd->gd_spinlocks is implied to be 0 when td_critcount is 0.
1059 void
1060 lwkt_maybe_splz(thread_t td)
1062 globaldata_t gd = td->td_gd;
1064 if (td->td_critcount == 0 &&
1065 gd->gd_intr_nesting_level == 0 &&
1066 td->td_nest_count < 2)
1068 splz();
1073 * Drivers which set up processing co-threads can call this function to
1074 * run the co-thread at a higher priority and to allow it to preempt
1075 * normal threads.
1077 void
1078 lwkt_set_interrupt_support_thread(void)
1080 thread_t td = curthread;
1082 lwkt_setpri_self(TDPRI_INT_SUPPORT);
1083 td->td_flags |= TDF_INTTHREAD;
1084 td->td_preemptable = lwkt_preempt;
1089 * This function is used to negotiate a passive release of the current
1090 * process/lwp designation with the user scheduler, allowing the user
1091 * scheduler to schedule another user thread. The related kernel thread
1092 * (curthread) continues running in the released state.
1094 void
1095 lwkt_passive_release(struct thread *td)
1097 struct lwp *lp = td->td_lwp;
1099 td->td_release = NULL;
1100 lwkt_setpri_self(TDPRI_KERN_USER);
1102 lp->lwp_proc->p_usched->release_curproc(lp);
1107 * This implements a LWKT yield, allowing a kernel thread to yield to other
1108 * kernel threads at the same or higher priority. This function can be
1109 * called in a tight loop and will typically only yield once per tick.
1111 * Most kernel threads run at the same priority in order to allow equal
1112 * sharing.
1114 * (self contained on a per cpu basis)
1116 void
1117 lwkt_yield(void)
1119 globaldata_t gd = mycpu;
1120 thread_t td = gd->gd_curthread;
1123 * Should never be called with spinlocks held but there is a path
1124 * via ACPI where it might happen.
1126 if (gd->gd_spinlocks)
1127 return;
1130 * Safe to call splz if we are not too-heavily nested.
1132 if ((gd->gd_reqflags & RQF_IDLECHECK_MASK) && td->td_nest_count < 2)
1133 splz();
1136 * Caller allows switching
1138 if (lwkt_resched_wanted()) {
1139 atomic_set_int(&td->td_mpflags, TDF_MP_DIDYIELD);
1140 lwkt_schedule_self(td);
1141 lwkt_switch();
1146 * The quick version processes pending interrupts and higher-priority
1147 * LWKT threads but will not round-robin same-priority LWKT threads.
1149 * When called while attempting to return to userland the only same-pri
1150 * threads are the ones which have already tried to become the current
1151 * user process.
1153 void
1154 lwkt_yield_quick(void)
1156 globaldata_t gd = mycpu;
1157 thread_t td = gd->gd_curthread;
1159 if ((gd->gd_reqflags & RQF_IDLECHECK_MASK) && td->td_nest_count < 2)
1160 splz();
1161 if (lwkt_resched_wanted()) {
1162 crit_enter();
1163 if (TAILQ_FIRST(&gd->gd_tdrunq) == td) {
1164 clear_lwkt_resched();
1165 } else {
1166 atomic_set_int(&td->td_mpflags, TDF_MP_DIDYIELD);
1167 lwkt_schedule_self(curthread);
1168 lwkt_switch();
1170 crit_exit();
1175 * This yield is designed for kernel threads with a user context.
1177 * The kernel acting on behalf of the user is potentially cpu-bound,
1178 * this function will efficiently allow other threads to run and also
1179 * switch to other processes by releasing.
1181 * The lwkt_user_yield() function is designed to have very low overhead
1182 * if no yield is determined to be needed.
1184 void
1185 lwkt_user_yield(void)
1187 globaldata_t gd = mycpu;
1188 thread_t td = gd->gd_curthread;
1191 * Should never be called with spinlocks held but there is a path
1192 * via ACPI where it might happen.
1194 if (gd->gd_spinlocks)
1195 return;
1198 * Always run any pending interrupts in case we are in a critical
1199 * section.
1201 if ((gd->gd_reqflags & RQF_IDLECHECK_MASK) && td->td_nest_count < 2)
1202 splz();
1205 * Switch (which forces a release) if another kernel thread needs
1206 * the cpu, if userland wants us to resched, or if our kernel
1207 * quantum has run out.
1209 if (lwkt_resched_wanted() ||
1210 user_resched_wanted())
1212 lwkt_switch();
1215 #if 0
1217 * Reacquire the current process if we are released.
1219 * XXX not implemented atm. The kernel may be holding locks and such,
1220 * so we want the thread to continue to receive cpu.
1222 if (td->td_release == NULL && lp) {
1223 lp->lwp_proc->p_usched->acquire_curproc(lp);
1224 td->td_release = lwkt_passive_release;
1225 lwkt_setpri_self(TDPRI_USER_NORM);
1227 #endif
1231 * Generic schedule. Possibly schedule threads belonging to other cpus and
1232 * deal with threads that might be blocked on a wait queue.
1234 * We have a little helper inline function which does additional work after
1235 * the thread has been enqueued, including dealing with preemption and
1236 * setting need_lwkt_resched() (which prevents the kernel from returning
1237 * to userland until it has processed higher priority threads).
1239 * It is possible for this routine to be called after a failed _enqueue
1240 * (due to the target thread migrating, sleeping, or otherwise blocked).
1241 * We have to check that the thread is actually on the run queue!
1243 static __inline
1244 void
1245 _lwkt_schedule_post(globaldata_t gd, thread_t ntd, int ccount)
1247 if (ntd->td_flags & TDF_RUNQ) {
1248 if (ntd->td_preemptable) {
1249 ntd->td_preemptable(ntd, ccount); /* YYY +token */
1254 static __inline
1255 void
1256 _lwkt_schedule(thread_t td)
1258 globaldata_t mygd = mycpu;
1260 KASSERT(td != &td->td_gd->gd_idlethread,
1261 ("lwkt_schedule(): scheduling gd_idlethread is illegal!"));
1262 KKASSERT((td->td_flags & TDF_MIGRATING) == 0);
1263 crit_enter_gd(mygd);
1264 KKASSERT(td->td_lwp == NULL ||
1265 (td->td_lwp->lwp_mpflags & LWP_MP_ONRUNQ) == 0);
1267 if (td == mygd->gd_curthread) {
1268 _lwkt_enqueue(td);
1269 } else {
1271 * If we own the thread, there is no race (since we are in a
1272 * critical section). If we do not own the thread there might
1273 * be a race but the target cpu will deal with it.
1275 if (td->td_gd == mygd) {
1276 _lwkt_enqueue(td);
1277 _lwkt_schedule_post(mygd, td, 1);
1278 } else {
1279 lwkt_send_ipiq3(td->td_gd, lwkt_schedule_remote, td, 0);
1282 crit_exit_gd(mygd);
1285 void
1286 lwkt_schedule(thread_t td)
1288 _lwkt_schedule(td);
1291 void
1292 lwkt_schedule_noresched(thread_t td) /* XXX not impl */
1294 _lwkt_schedule(td);
1298 * When scheduled remotely if frame != NULL the IPIQ is being
1299 * run via doreti or an interrupt then preemption can be allowed.
1301 * To allow preemption we have to drop the critical section so only
1302 * one is present in _lwkt_schedule_post.
1304 static void
1305 lwkt_schedule_remote(void *arg, int arg2, struct intrframe *frame)
1307 thread_t td = curthread;
1308 thread_t ntd = arg;
1310 if (frame && ntd->td_preemptable) {
1311 crit_exit_noyield(td);
1312 _lwkt_schedule(ntd);
1313 crit_enter_quick(td);
1314 } else {
1315 _lwkt_schedule(ntd);
1320 * Thread migration using a 'Pull' method. The thread may or may not be
1321 * the current thread. It MUST be descheduled and in a stable state.
1322 * lwkt_giveaway() must be called on the cpu owning the thread.
1324 * At any point after lwkt_giveaway() is called, the target cpu may
1325 * 'pull' the thread by calling lwkt_acquire().
1327 * We have to make sure the thread is not sitting on a per-cpu tsleep
1328 * queue or it will blow up when it moves to another cpu.
1330 * MPSAFE - must be called under very specific conditions.
1332 void
1333 lwkt_giveaway(thread_t td)
1335 globaldata_t gd = mycpu;
1337 crit_enter_gd(gd);
1338 if (td->td_flags & TDF_TSLEEPQ)
1339 tsleep_remove(td);
1340 KKASSERT(td->td_gd == gd);
1341 TAILQ_REMOVE(&gd->gd_tdallq, td, td_allq);
1342 td->td_flags |= TDF_MIGRATING;
1343 crit_exit_gd(gd);
1346 void
1347 lwkt_acquire(thread_t td)
1349 globaldata_t gd;
1350 globaldata_t mygd;
1352 KKASSERT(td->td_flags & TDF_MIGRATING);
1353 gd = td->td_gd;
1354 mygd = mycpu;
1355 if (gd != mycpu) {
1356 #ifdef LOOPMASK
1357 uint64_t tsc_base = rdtsc();
1358 #endif
1359 cpu_lfence();
1360 KKASSERT((td->td_flags & TDF_RUNQ) == 0);
1361 crit_enter_gd(mygd);
1362 DEBUG_PUSH_INFO("lwkt_acquire");
1363 while (td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK)) {
1364 lwkt_process_ipiq();
1365 cpu_lfence();
1366 #ifdef _KERNEL_VIRTUAL
1367 pthread_yield();
1368 #endif
1369 #ifdef LOOPMASK
1370 if (tsc_frequency && rdtsc() - tsc_base > tsc_frequency) {
1371 kprintf("lwkt_acquire: stuck td %p td->td_flags %08x\n",
1372 td, td->td_flags);
1373 tsc_base = rdtsc();
1375 #endif
1377 DEBUG_POP_INFO();
1378 cpu_mfence();
1379 td->td_gd = mygd;
1380 TAILQ_INSERT_TAIL(&mygd->gd_tdallq, td, td_allq);
1381 td->td_flags &= ~TDF_MIGRATING;
1382 crit_exit_gd(mygd);
1383 } else {
1384 crit_enter_gd(mygd);
1385 TAILQ_INSERT_TAIL(&mygd->gd_tdallq, td, td_allq);
1386 td->td_flags &= ~TDF_MIGRATING;
1387 crit_exit_gd(mygd);
1392 * Generic deschedule. Descheduling threads other then your own should be
1393 * done only in carefully controlled circumstances. Descheduling is
1394 * asynchronous.
1396 * This function may block if the cpu has run out of messages.
1398 void
1399 lwkt_deschedule(thread_t td)
1401 crit_enter();
1402 if (td == curthread) {
1403 _lwkt_dequeue(td);
1404 } else {
1405 if (td->td_gd == mycpu) {
1406 _lwkt_dequeue(td);
1407 } else {
1408 lwkt_send_ipiq(td->td_gd, (ipifunc1_t)lwkt_deschedule, td);
1411 crit_exit();
1415 * Set the target thread's priority. This routine does not automatically
1416 * switch to a higher priority thread, LWKT threads are not designed for
1417 * continuous priority changes. Yield if you want to switch.
1419 void
1420 lwkt_setpri(thread_t td, int pri)
1422 if (td->td_pri != pri) {
1423 KKASSERT(pri >= 0);
1424 crit_enter();
1425 if (td->td_flags & TDF_RUNQ) {
1426 KKASSERT(td->td_gd == mycpu);
1427 _lwkt_dequeue(td);
1428 td->td_pri = pri;
1429 _lwkt_enqueue(td);
1430 } else {
1431 td->td_pri = pri;
1433 crit_exit();
1438 * Set the initial priority for a thread prior to it being scheduled for
1439 * the first time. The thread MUST NOT be scheduled before or during
1440 * this call. The thread may be assigned to a cpu other then the current
1441 * cpu.
1443 * Typically used after a thread has been created with TDF_STOPPREQ,
1444 * and before the thread is initially scheduled.
1446 void
1447 lwkt_setpri_initial(thread_t td, int pri)
1449 KKASSERT(pri >= 0);
1450 KKASSERT((td->td_flags & TDF_RUNQ) == 0);
1451 td->td_pri = pri;
1454 void
1455 lwkt_setpri_self(int pri)
1457 thread_t td = curthread;
1459 KKASSERT(pri >= 0 && pri <= TDPRI_MAX);
1460 crit_enter();
1461 if (td->td_flags & TDF_RUNQ) {
1462 _lwkt_dequeue(td);
1463 td->td_pri = pri;
1464 _lwkt_enqueue(td);
1465 } else {
1466 td->td_pri = pri;
1468 crit_exit();
1472 * hz tick scheduler clock for LWKT threads
1474 void
1475 lwkt_schedulerclock(thread_t td)
1477 globaldata_t gd = td->td_gd;
1478 thread_t xtd;
1480 xtd = TAILQ_FIRST(&gd->gd_tdrunq);
1481 if (xtd == td) {
1483 * If the current thread is at the head of the runq shift it to the
1484 * end of any equal-priority threads and request a LWKT reschedule
1485 * if it moved.
1487 * Ignore upri in this situation. There will only be one user thread
1488 * in user mode, all others will be user threads running in kernel
1489 * mode and we have to make sure they get some cpu.
1491 xtd = TAILQ_NEXT(td, td_threadq);
1492 if (xtd && xtd->td_pri == td->td_pri) {
1493 TAILQ_REMOVE(&gd->gd_tdrunq, td, td_threadq);
1494 while (xtd && xtd->td_pri == td->td_pri)
1495 xtd = TAILQ_NEXT(xtd, td_threadq);
1496 if (xtd)
1497 TAILQ_INSERT_BEFORE(xtd, td, td_threadq);
1498 else
1499 TAILQ_INSERT_TAIL(&gd->gd_tdrunq, td, td_threadq);
1500 need_lwkt_resched();
1502 } else if (xtd) {
1504 * If we scheduled a thread other than the one at the head of the
1505 * queue always request a reschedule every tick.
1507 need_lwkt_resched();
1509 /* else curthread probably the idle thread, no need to reschedule */
1513 * Migrate the current thread to the specified cpu.
1515 * This is accomplished by descheduling ourselves from the current cpu
1516 * and setting td_migrate_gd. The lwkt_switch() code will detect that the
1517 * 'old' thread wants to migrate after it has been completely switched out
1518 * and will complete the migration.
1520 * TDF_MIGRATING prevents scheduling races while the thread is being migrated.
1522 * We must be sure to release our current process designation (if a user
1523 * process) before clearing out any tsleepq we are on because the release
1524 * code may re-add us.
1526 * We must be sure to remove ourselves from the current cpu's tsleepq
1527 * before potentially moving to another queue. The thread can be on
1528 * a tsleepq due to a left-over tsleep_interlock().
1531 void
1532 lwkt_setcpu_self(globaldata_t rgd)
1534 thread_t td = curthread;
1536 if (td->td_gd != rgd) {
1537 crit_enter_quick(td);
1539 if (td->td_release)
1540 td->td_release(td);
1541 if (td->td_flags & TDF_TSLEEPQ)
1542 tsleep_remove(td);
1545 * Set TDF_MIGRATING to prevent a spurious reschedule while we are
1546 * trying to deschedule ourselves and switch away, then deschedule
1547 * ourself, remove us from tdallq, and set td_migrate_gd. Finally,
1548 * call lwkt_switch() to complete the operation.
1550 td->td_flags |= TDF_MIGRATING;
1551 lwkt_deschedule_self(td);
1552 TAILQ_REMOVE(&td->td_gd->gd_tdallq, td, td_allq);
1553 td->td_migrate_gd = rgd;
1554 lwkt_switch();
1557 * We are now on the target cpu
1559 KKASSERT(rgd == mycpu);
1560 TAILQ_INSERT_TAIL(&rgd->gd_tdallq, td, td_allq);
1561 crit_exit_quick(td);
1565 void
1566 lwkt_migratecpu(int cpuid)
1568 globaldata_t rgd;
1570 rgd = globaldata_find(cpuid);
1571 lwkt_setcpu_self(rgd);
1575 * Remote IPI for cpu migration (called while in a critical section so we
1576 * do not have to enter another one).
1578 * The thread (td) has already been completely descheduled from the
1579 * originating cpu and we can simply assert the case. The thread is
1580 * assigned to the new cpu and enqueued.
1582 * The thread will re-add itself to tdallq when it resumes execution.
1584 static void
1585 lwkt_setcpu_remote(void *arg)
1587 thread_t td = arg;
1588 globaldata_t gd = mycpu;
1590 KKASSERT((td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK)) == 0);
1591 td->td_gd = gd;
1592 cpu_mfence();
1593 td->td_flags &= ~TDF_MIGRATING;
1594 KKASSERT(td->td_migrate_gd == NULL);
1595 KKASSERT(td->td_lwp == NULL ||
1596 (td->td_lwp->lwp_mpflags & LWP_MP_ONRUNQ) == 0);
1597 _lwkt_enqueue(td);
1600 struct lwp *
1601 lwkt_preempted_proc(void)
1603 thread_t td = curthread;
1604 while (td->td_preempted)
1605 td = td->td_preempted;
1606 return(td->td_lwp);
1610 * Create a kernel process/thread/whatever. It shares it's address space
1611 * with proc0 - ie: kernel only.
1613 * If the cpu is not specified one will be selected. In the future
1614 * specifying a cpu of -1 will enable kernel thread migration between
1615 * cpus.
1618 lwkt_create(void (*func)(void *), void *arg, struct thread **tdp,
1619 thread_t template, int tdflags, int cpu, const char *fmt, ...)
1621 thread_t td;
1622 __va_list ap;
1624 td = lwkt_alloc_thread(template, LWKT_THREAD_STACK, cpu,
1625 tdflags);
1626 if (tdp)
1627 *tdp = td;
1628 cpu_set_thread_handler(td, lwkt_exit, func, arg);
1631 * Set up arg0 for 'ps' etc
1633 __va_start(ap, fmt);
1634 kvsnprintf(td->td_comm, sizeof(td->td_comm), fmt, ap);
1635 __va_end(ap);
1638 * Schedule the thread to run
1640 if (td->td_flags & TDF_NOSTART)
1641 td->td_flags &= ~TDF_NOSTART;
1642 else
1643 lwkt_schedule(td);
1644 return 0;
1648 * Destroy an LWKT thread. Warning! This function is not called when
1649 * a process exits, cpu_proc_exit() directly calls cpu_thread_exit() and
1650 * uses a different reaping mechanism.
1652 void
1653 lwkt_exit(void)
1655 thread_t td = curthread;
1656 thread_t std;
1657 globaldata_t gd;
1660 * Do any cleanup that might block here
1662 biosched_done(td);
1663 dsched_exit_thread(td);
1666 * Get us into a critical section to interlock gd_freetd and loop
1667 * until we can get it freed.
1669 * We have to cache the current td in gd_freetd because objcache_put()ing
1670 * it would rip it out from under us while our thread is still active.
1672 * We are the current thread so of course our own TDF_RUNNING bit will
1673 * be set, so unlike the lwp reap code we don't wait for it to clear.
1675 gd = mycpu;
1676 crit_enter_quick(td);
1677 for (;;) {
1678 if (td->td_refs) {
1679 tsleep(td, 0, "tdreap", 1);
1680 continue;
1682 if ((std = gd->gd_freetd) != NULL) {
1683 KKASSERT((std->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK)) == 0);
1684 gd->gd_freetd = NULL;
1685 objcache_put(thread_cache, std);
1686 continue;
1688 break;
1692 * Remove thread resources from kernel lists and deschedule us for
1693 * the last time. We cannot block after this point or we may end
1694 * up with a stale td on the tsleepq.
1696 * None of this may block, the critical section is the only thing
1697 * protecting tdallq and the only thing preventing new lwkt_hold()
1698 * thread refs now.
1700 if (td->td_flags & TDF_TSLEEPQ)
1701 tsleep_remove(td);
1702 lwkt_deschedule_self(td);
1703 lwkt_remove_tdallq(td);
1704 KKASSERT(td->td_refs == 0);
1707 * Final cleanup
1709 KKASSERT(gd->gd_freetd == NULL);
1710 if (td->td_flags & TDF_ALLOCATED_THREAD)
1711 gd->gd_freetd = td;
1712 cpu_thread_exit();
1715 void
1716 lwkt_remove_tdallq(thread_t td)
1718 KKASSERT(td->td_gd == mycpu);
1719 TAILQ_REMOVE(&td->td_gd->gd_tdallq, td, td_allq);
1723 * Code reduction and branch prediction improvements. Call/return
1724 * overhead on modern cpus often degenerates into 0 cycles due to
1725 * the cpu's branch prediction hardware and return pc cache. We
1726 * can take advantage of this by not inlining medium-complexity
1727 * functions and we can also reduce the branch prediction impact
1728 * by collapsing perfectly predictable branches into a single
1729 * procedure instead of duplicating it.
1731 * Is any of this noticeable? Probably not, so I'll take the
1732 * smaller code size.
1734 void
1735 crit_exit_wrapper(__DEBUG_CRIT_ARG__)
1737 _crit_exit(mycpu __DEBUG_CRIT_PASS_ARG__);
1740 void
1741 crit_panic(void)
1743 thread_t td = curthread;
1744 int lcrit = td->td_critcount;
1746 td->td_critcount = 0;
1747 cpu_ccfence();
1748 panic("td_critcount is/would-go negative! %p %d", td, lcrit);
1749 /* NOT REACHED */
1753 * Called from debugger/panic on cpus which have been stopped. We must still
1754 * process the IPIQ while stopped.
1756 * If we are dumping also try to process any pending interrupts. This may
1757 * or may not work depending on the state of the cpu at the point it was
1758 * stopped.
1760 void
1761 lwkt_smp_stopped(void)
1763 globaldata_t gd = mycpu;
1765 if (dumping) {
1766 lwkt_process_ipiq();
1767 --gd->gd_intr_nesting_level;
1768 splz();
1769 ++gd->gd_intr_nesting_level;
1770 } else {
1771 lwkt_process_ipiq();
1773 cpu_smp_stopped();