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>
54 #include <sys/spinlock.h>
57 #include <sys/thread2.h>
58 #include <sys/spinlock2.h>
59 #include <sys/mplock2.h>
61 #include <sys/dsched.h>
64 #include <vm/vm_param.h>
65 #include <vm/vm_kern.h>
66 #include <vm/vm_object.h>
67 #include <vm/vm_page.h>
68 #include <vm/vm_map.h>
69 #include <vm/vm_pager.h>
70 #include <vm/vm_extern.h>
72 #include <machine/stdarg.h>
73 #include <machine/smp.h>
75 #if !defined(KTR_CTXSW)
76 #define KTR_CTXSW KTR_ALL
78 KTR_INFO_MASTER(ctxsw);
79 KTR_INFO(KTR_CTXSW, ctxsw, sw, 0, "#cpu[%d].td = %p",
80 sizeof(int) + sizeof(struct thread *));
81 KTR_INFO(KTR_CTXSW, ctxsw, pre, 1, "#cpu[%d].td = %p",
82 sizeof(int) + sizeof(struct thread *));
83 KTR_INFO(KTR_CTXSW, ctxsw, newtd, 2, "#threads[%p].name = %s",
84 sizeof (struct thread *) + sizeof(char *));
85 KTR_INFO(KTR_CTXSW, ctxsw, deadtd, 3, "#threads[%p].name = <dead>", sizeof (struct thread *));
87 static MALLOC_DEFINE(M_THREAD, "thread", "lwkt threads");
90 static int panic_on_cscount = 0;
92 static __int64_t switch_count = 0;
93 static __int64_t preempt_hit = 0;
94 static __int64_t preempt_miss = 0;
95 static __int64_t preempt_weird = 0;
96 static __int64_t token_contention_count[TDPRI_MAX+1] __debugvar;
97 static int lwkt_use_spin_port;
98 static struct objcache *thread_cache;
101 static void lwkt_schedule_remote(void *arg, int arg2, struct intrframe *frame);
102 static void lwkt_setcpu_remote(void *arg);
105 extern void cpu_heavy_restore(void);
106 extern void cpu_lwkt_restore(void);
107 extern void cpu_kthread_restore(void);
108 extern void cpu_idle_restore(void);
111 * We can make all thread ports use the spin backend instead of the thread
112 * backend. This should only be set to debug the spin backend.
114 TUNABLE_INT("lwkt.use_spin_port", &lwkt_use_spin_port);
117 SYSCTL_INT(_lwkt, OID_AUTO, panic_on_cscount, CTLFLAG_RW, &panic_on_cscount, 0,
118 "Panic if attempting to switch lwkt's while mastering cpusync");
120 SYSCTL_QUAD(_lwkt, OID_AUTO, switch_count, CTLFLAG_RW, &switch_count, 0,
121 "Number of switched threads");
122 SYSCTL_QUAD(_lwkt, OID_AUTO, preempt_hit, CTLFLAG_RW, &preempt_hit, 0,
123 "Successful preemption events");
124 SYSCTL_QUAD(_lwkt, OID_AUTO, preempt_miss, CTLFLAG_RW, &preempt_miss, 0,
125 "Failed preemption events");
126 SYSCTL_QUAD(_lwkt, OID_AUTO, preempt_weird, CTLFLAG_RW, &preempt_weird, 0,
127 "Number of preempted threads.");
129 SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count_00, CTLFLAG_RW,
130 &token_contention_count[0], 0, "spinning due to token contention");
131 SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count_01, CTLFLAG_RW,
132 &token_contention_count[1], 0, "spinning due to token contention");
133 SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count_02, CTLFLAG_RW,
134 &token_contention_count[2], 0, "spinning due to token contention");
135 SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count_03, CTLFLAG_RW,
136 &token_contention_count[3], 0, "spinning due to token contention");
137 SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count_04, CTLFLAG_RW,
138 &token_contention_count[4], 0, "spinning due to token contention");
139 SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count_05, CTLFLAG_RW,
140 &token_contention_count[5], 0, "spinning due to token contention");
141 SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count_06, CTLFLAG_RW,
142 &token_contention_count[6], 0, "spinning due to token contention");
143 SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count_07, CTLFLAG_RW,
144 &token_contention_count[7], 0, "spinning due to token contention");
145 SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count_08, CTLFLAG_RW,
146 &token_contention_count[8], 0, "spinning due to token contention");
147 SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count_09, CTLFLAG_RW,
148 &token_contention_count[9], 0, "spinning due to token contention");
149 SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count_10, CTLFLAG_RW,
150 &token_contention_count[10], 0, "spinning due to token contention");
151 SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count_11, CTLFLAG_RW,
152 &token_contention_count[11], 0, "spinning due to token contention");
153 SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count_12, CTLFLAG_RW,
154 &token_contention_count[12], 0, "spinning due to token contention");
155 SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count_13, CTLFLAG_RW,
156 &token_contention_count[13], 0, "spinning due to token contention");
157 SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count_14, CTLFLAG_RW,
158 &token_contention_count[14], 0, "spinning due to token contention");
159 SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count_15, CTLFLAG_RW,
160 &token_contention_count[15], 0, "spinning due to token contention");
161 SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count_16, CTLFLAG_RW,
162 &token_contention_count[16], 0, "spinning due to token contention");
163 SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count_17, CTLFLAG_RW,
164 &token_contention_count[17], 0, "spinning due to token contention");
165 SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count_18, CTLFLAG_RW,
166 &token_contention_count[18], 0, "spinning due to token contention");
167 SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count_19, CTLFLAG_RW,
168 &token_contention_count[19], 0, "spinning due to token contention");
169 SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count_20, CTLFLAG_RW,
170 &token_contention_count[20], 0, "spinning due to token contention");
171 SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count_21, CTLFLAG_RW,
172 &token_contention_count[21], 0, "spinning due to token contention");
173 SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count_22, CTLFLAG_RW,
174 &token_contention_count[22], 0, "spinning due to token contention");
175 SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count_23, CTLFLAG_RW,
176 &token_contention_count[23], 0, "spinning due to token contention");
177 SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count_24, CTLFLAG_RW,
178 &token_contention_count[24], 0, "spinning due to token contention");
179 SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count_25, CTLFLAG_RW,
180 &token_contention_count[25], 0, "spinning due to token contention");
181 SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count_26, CTLFLAG_RW,
182 &token_contention_count[26], 0, "spinning due to token contention");
183 SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count_27, CTLFLAG_RW,
184 &token_contention_count[27], 0, "spinning due to token contention");
185 SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count_28, CTLFLAG_RW,
186 &token_contention_count[28], 0, "spinning due to token contention");
187 SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count_29, CTLFLAG_RW,
188 &token_contention_count[29], 0, "spinning due to token contention");
189 SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count_30, CTLFLAG_RW,
190 &token_contention_count[30], 0, "spinning due to token contention");
191 SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count_31, CTLFLAG_RW,
192 &token_contention_count[31], 0, "spinning due to token contention");
194 static int fairq_enable = 0;
195 SYSCTL_INT(_lwkt, OID_AUTO, fairq_enable, CTLFLAG_RW,
196 &fairq_enable, 0, "Turn on fairq priority accumulators");
197 static int fairq_bypass = -1;
198 SYSCTL_INT(_lwkt, OID_AUTO, fairq_bypass, CTLFLAG_RW,
199 &fairq_bypass, 0, "Allow fairq to bypass td on token failure");
200 extern int lwkt_sched_debug;
201 int lwkt_sched_debug = 0;
202 SYSCTL_INT(_lwkt, OID_AUTO, sched_debug, CTLFLAG_RW,
203 &lwkt_sched_debug, 0, "Scheduler debug");
204 static int lwkt_spin_loops = 10;
205 SYSCTL_INT(_lwkt, OID_AUTO, spin_loops, CTLFLAG_RW,
206 &lwkt_spin_loops, 0, "Scheduler spin loops until sorted decon");
207 static int lwkt_spin_reseq = 0;
208 SYSCTL_INT(_lwkt, OID_AUTO, spin_reseq, CTLFLAG_RW,
209 &lwkt_spin_reseq, 0, "Scheduler resequencer enable");
210 static int lwkt_spin_monitor = 0;
211 SYSCTL_INT(_lwkt, OID_AUTO, spin_monitor, CTLFLAG_RW,
212 &lwkt_spin_monitor, 0, "Scheduler uses monitor/mwait");
213 static int lwkt_spin_fatal = 0; /* disabled */
214 SYSCTL_INT(_lwkt, OID_AUTO, spin_fatal, CTLFLAG_RW,
215 &lwkt_spin_fatal, 0, "LWKT scheduler spin loops till fatal panic");
216 static int preempt_enable = 1;
217 SYSCTL_INT(_lwkt, OID_AUTO, preempt_enable, CTLFLAG_RW,
218 &preempt_enable, 0, "Enable preemption");
219 static int lwkt_cache_threads = 0;
220 SYSCTL_INT(_lwkt, OID_AUTO, cache_threads, CTLFLAG_RD,
221 &lwkt_cache_threads, 0, "thread+kstack cache");
223 static __cachealign int lwkt_cseq_rindex;
224 static __cachealign int lwkt_cseq_windex;
227 * These helper procedures handle the runq, they can only be called from
228 * within a critical section.
230 * WARNING! Prior to SMP being brought up it is possible to enqueue and
231 * dequeue threads belonging to other cpus, so be sure to use td->td_gd
232 * instead of 'mycpu' when referencing the globaldata structure. Once
233 * SMP live enqueuing and dequeueing only occurs on the current cpu.
237 _lwkt_dequeue(thread_t td)
239 if (td->td_flags & TDF_RUNQ) {
240 struct globaldata *gd = td->td_gd;
242 td->td_flags &= ~TDF_RUNQ;
243 TAILQ_REMOVE(&gd->gd_tdrunq, td, td_threadq);
244 if (TAILQ_FIRST(&gd->gd_tdrunq) == NULL)
245 atomic_clear_int(&gd->gd_reqflags, RQF_RUNNING);
252 * NOTE: There are a limited number of lwkt threads runnable since user
253 * processes only schedule one at a time per cpu.
257 _lwkt_enqueue(thread_t td)
261 if ((td->td_flags & (TDF_RUNQ|TDF_MIGRATING|TDF_BLOCKQ)) == 0) {
262 struct globaldata *gd = td->td_gd;
264 td->td_flags |= TDF_RUNQ;
265 xtd = TAILQ_FIRST(&gd->gd_tdrunq);
267 TAILQ_INSERT_TAIL(&gd->gd_tdrunq, td, td_threadq);
268 atomic_set_int(&gd->gd_reqflags, RQF_RUNNING);
270 while (xtd && xtd->td_pri >= td->td_pri)
271 xtd = TAILQ_NEXT(xtd, td_threadq);
273 TAILQ_INSERT_BEFORE(xtd, td, td_threadq);
275 TAILQ_INSERT_TAIL(&gd->gd_tdrunq, td, td_threadq);
279 * Request a LWKT reschedule if we are now at the head of the queue.
281 if (TAILQ_FIRST(&gd->gd_tdrunq) == td)
287 _lwkt_thread_ctor(void *obj, void *privdata, int ocflags)
289 struct thread *td = (struct thread *)obj;
291 td->td_kstack = NULL;
292 td->td_kstack_size = 0;
293 td->td_flags = TDF_ALLOCATED_THREAD;
299 _lwkt_thread_dtor(void *obj, void *privdata)
301 struct thread *td = (struct thread *)obj;
303 KASSERT(td->td_flags & TDF_ALLOCATED_THREAD,
304 ("_lwkt_thread_dtor: not allocated from objcache"));
305 KASSERT((td->td_flags & TDF_ALLOCATED_STACK) && td->td_kstack &&
306 td->td_kstack_size > 0,
307 ("_lwkt_thread_dtor: corrupted stack"));
308 kmem_free(&kernel_map, (vm_offset_t)td->td_kstack, td->td_kstack_size);
309 td->td_kstack = NULL;
314 * Initialize the lwkt s/system.
316 * Nominally cache up to 32 thread + kstack structures. Cache more on
317 * systems with a lot of cpu cores.
322 TUNABLE_INT("lwkt.cache_threads", &lwkt_cache_threads);
323 if (lwkt_cache_threads == 0) {
324 lwkt_cache_threads = ncpus * 4;
325 if (lwkt_cache_threads < 32)
326 lwkt_cache_threads = 32;
328 thread_cache = objcache_create_mbacked(
329 M_THREAD, sizeof(struct thread),
330 NULL, lwkt_cache_threads,
331 _lwkt_thread_ctor, _lwkt_thread_dtor, NULL);
335 * Schedule a thread to run. As the current thread we can always safely
336 * schedule ourselves, and a shortcut procedure is provided for that
339 * (non-blocking, self contained on a per cpu basis)
342 lwkt_schedule_self(thread_t td)
344 KKASSERT((td->td_flags & TDF_MIGRATING) == 0);
345 crit_enter_quick(td);
346 KASSERT(td != &td->td_gd->gd_idlethread,
347 ("lwkt_schedule_self(): scheduling gd_idlethread is illegal!"));
348 KKASSERT(td->td_lwp == NULL ||
349 (td->td_lwp->lwp_mpflags & LWP_MP_ONRUNQ) == 0);
355 * Deschedule a thread.
357 * (non-blocking, self contained on a per cpu basis)
360 lwkt_deschedule_self(thread_t td)
362 crit_enter_quick(td);
368 * LWKTs operate on a per-cpu basis
370 * WARNING! Called from early boot, 'mycpu' may not work yet.
373 lwkt_gdinit(struct globaldata *gd)
375 TAILQ_INIT(&gd->gd_tdrunq);
376 TAILQ_INIT(&gd->gd_tdallq);
380 * Create a new thread. The thread must be associated with a process context
381 * or LWKT start address before it can be scheduled. If the target cpu is
382 * -1 the thread will be created on the current cpu.
384 * If you intend to create a thread without a process context this function
385 * does everything except load the startup and switcher function.
388 lwkt_alloc_thread(struct thread *td, int stksize, int cpu, int flags)
390 static int cpu_rotator;
391 globaldata_t gd = mycpu;
395 * If static thread storage is not supplied allocate a thread. Reuse
396 * a cached free thread if possible. gd_freetd is used to keep an exiting
397 * thread intact through the exit.
401 if ((td = gd->gd_freetd) != NULL) {
402 KKASSERT((td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK|
404 gd->gd_freetd = NULL;
406 td = objcache_get(thread_cache, M_WAITOK);
407 KKASSERT((td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK|
411 KASSERT((td->td_flags &
412 (TDF_ALLOCATED_THREAD|TDF_RUNNING|TDF_PREEMPT_LOCK)) ==
413 TDF_ALLOCATED_THREAD,
414 ("lwkt_alloc_thread: corrupted td flags 0x%X", td->td_flags));
415 flags |= td->td_flags & (TDF_ALLOCATED_THREAD|TDF_ALLOCATED_STACK);
419 * Try to reuse cached stack.
421 if ((stack = td->td_kstack) != NULL && td->td_kstack_size != stksize) {
422 if (flags & TDF_ALLOCATED_STACK) {
423 kmem_free(&kernel_map, (vm_offset_t)stack, td->td_kstack_size);
428 stack = (void *)kmem_alloc_stack(&kernel_map, stksize);
429 flags |= TDF_ALLOCATED_STACK;
436 lwkt_init_thread(td, stack, stksize, flags, globaldata_find(cpu));
441 * Initialize a preexisting thread structure. This function is used by
442 * lwkt_alloc_thread() and also used to initialize the per-cpu idlethread.
444 * All threads start out in a critical section at a priority of
445 * TDPRI_KERN_DAEMON. Higher level code will modify the priority as
446 * appropriate. This function may send an IPI message when the
447 * requested cpu is not the current cpu and consequently gd_tdallq may
448 * not be initialized synchronously from the point of view of the originating
451 * NOTE! we have to be careful in regards to creating threads for other cpus
452 * if SMP has not yet been activated.
457 lwkt_init_thread_remote(void *arg)
462 * Protected by critical section held by IPI dispatch
464 TAILQ_INSERT_TAIL(&td->td_gd->gd_tdallq, td, td_allq);
470 * lwkt core thread structural initialization.
472 * NOTE: All threads are initialized as mpsafe threads.
475 lwkt_init_thread(thread_t td, void *stack, int stksize, int flags,
476 struct globaldata *gd)
478 globaldata_t mygd = mycpu;
480 bzero(td, sizeof(struct thread));
481 td->td_kstack = stack;
482 td->td_kstack_size = stksize;
483 td->td_flags = flags;
486 td->td_pri = TDPRI_KERN_DAEMON;
487 td->td_critcount = 1;
488 td->td_toks_have = NULL;
489 td->td_toks_stop = &td->td_toks_base;
490 if (lwkt_use_spin_port || (flags & TDF_FORCE_SPINPORT))
491 lwkt_initport_spin(&td->td_msgport);
493 lwkt_initport_thread(&td->td_msgport, td);
494 pmap_init_thread(td);
497 * Normally initializing a thread for a remote cpu requires sending an
498 * IPI. However, the idlethread is setup before the other cpus are
499 * activated so we have to treat it as a special case. XXX manipulation
500 * of gd_tdallq requires the BGL.
502 if (gd == mygd || td == &gd->gd_idlethread) {
504 TAILQ_INSERT_TAIL(&gd->gd_tdallq, td, td_allq);
507 lwkt_send_ipiq(gd, lwkt_init_thread_remote, td);
511 TAILQ_INSERT_TAIL(&gd->gd_tdallq, td, td_allq);
515 dsched_new_thread(td);
519 lwkt_set_comm(thread_t td, const char *ctl, ...)
524 kvsnprintf(td->td_comm, sizeof(td->td_comm), ctl, va);
526 KTR_LOG(ctxsw_newtd, td, &td->td_comm[0]);
530 * Prevent the thread from getting destroyed. Note that unlike PHOLD/PRELE
531 * this does not prevent the thread from migrating to another cpu so the
532 * gd_tdallq state is not protected by this.
535 lwkt_hold(thread_t td)
537 atomic_add_int(&td->td_refs, 1);
541 lwkt_rele(thread_t td)
543 KKASSERT(td->td_refs > 0);
544 atomic_add_int(&td->td_refs, -1);
548 lwkt_free_thread(thread_t td)
550 KKASSERT(td->td_refs == 0);
551 KKASSERT((td->td_flags & (TDF_RUNNING | TDF_PREEMPT_LOCK |
552 TDF_RUNQ | TDF_TSLEEPQ)) == 0);
553 if (td->td_flags & TDF_ALLOCATED_THREAD) {
554 objcache_put(thread_cache, td);
555 } else if (td->td_flags & TDF_ALLOCATED_STACK) {
556 /* client-allocated struct with internally allocated stack */
557 KASSERT(td->td_kstack && td->td_kstack_size > 0,
558 ("lwkt_free_thread: corrupted stack"));
559 kmem_free(&kernel_map, (vm_offset_t)td->td_kstack, td->td_kstack_size);
560 td->td_kstack = NULL;
561 td->td_kstack_size = 0;
563 KTR_LOG(ctxsw_deadtd, td);
568 * Switch to the next runnable lwkt. If no LWKTs are runnable then
569 * switch to the idlethread. Switching must occur within a critical
570 * section to avoid races with the scheduling queue.
572 * We always have full control over our cpu's run queue. Other cpus
573 * that wish to manipulate our queue must use the cpu_*msg() calls to
574 * talk to our cpu, so a critical section is all that is needed and
575 * the result is very, very fast thread switching.
577 * The LWKT scheduler uses a fixed priority model and round-robins at
578 * each priority level. User process scheduling is a totally
579 * different beast and LWKT priorities should not be confused with
580 * user process priorities.
582 * PREEMPTION NOTE: Preemption occurs via lwkt_preempt(). lwkt_switch()
583 * is not called by the current thread in the preemption case, only when
584 * the preempting thread blocks (in order to return to the original thread).
586 * SPECIAL NOTE ON SWITCH ATOMICY: Certain operations such as thread
587 * migration and tsleep deschedule the current lwkt thread and call
588 * lwkt_switch(). In particular, the target cpu of the migration fully
589 * expects the thread to become non-runnable and can deadlock against
590 * cpusync operations if we run any IPIs prior to switching the thread out.
592 * WE MUST BE VERY CAREFUL NOT TO RUN SPLZ DIRECTLY OR INDIRECTLY IF
593 * THE CURRENT THREAD HAS BEEN DESCHEDULED!
598 globaldata_t gd = mycpu;
599 thread_t td = gd->gd_curthread;
604 KKASSERT(gd->gd_processing_ipiq == 0);
605 KKASSERT(td->td_flags & TDF_RUNNING);
608 * Switching from within a 'fast' (non thread switched) interrupt or IPI
609 * is illegal. However, we may have to do it anyway if we hit a fatal
610 * kernel trap or we have paniced.
612 * If this case occurs save and restore the interrupt nesting level.
614 if (gd->gd_intr_nesting_level) {
618 if (gd->gd_trap_nesting_level == 0 && panic_cpu_gd != mycpu) {
619 panic("lwkt_switch: Attempt to switch from a "
620 "a fast interrupt, ipi, or hard code section, "
624 savegdnest = gd->gd_intr_nesting_level;
625 savegdtrap = gd->gd_trap_nesting_level;
626 gd->gd_intr_nesting_level = 0;
627 gd->gd_trap_nesting_level = 0;
628 if ((td->td_flags & TDF_PANICWARN) == 0) {
629 td->td_flags |= TDF_PANICWARN;
630 kprintf("Warning: thread switch from interrupt, IPI, "
631 "or hard code section.\n"
632 "thread %p (%s)\n", td, td->td_comm);
636 gd->gd_intr_nesting_level = savegdnest;
637 gd->gd_trap_nesting_level = savegdtrap;
643 * Release our current user process designation if we are blocking
644 * or if a user reschedule was requested.
646 * NOTE: This function is NOT called if we are switching into or
647 * returning from a preemption.
649 * NOTE: Releasing our current user process designation may cause
650 * it to be assigned to another thread, which in turn will
651 * cause us to block in the usched acquire code when we attempt
652 * to return to userland.
654 * NOTE: On SMP systems this can be very nasty when heavy token
655 * contention is present so we want to be careful not to
656 * release the designation gratuitously.
658 if (td->td_release &&
659 (user_resched_wanted() || (td->td_flags & TDF_RUNQ) == 0)) {
667 if (TD_TOKS_HELD(td))
668 lwkt_relalltokens(td);
671 * We had better not be holding any spin locks, but don't get into an
672 * endless panic loop.
674 KASSERT(gd->gd_spinlocks_wr == 0 || panicstr != NULL,
675 ("lwkt_switch: still holding %d exclusive spinlocks!",
676 gd->gd_spinlocks_wr));
681 if (td->td_cscount) {
682 kprintf("Diagnostic: attempt to switch while mastering cpusync: %p\n",
684 if (panic_on_cscount)
685 panic("switching while mastering cpusync");
691 * If we had preempted another thread on this cpu, resume the preempted
692 * thread. This occurs transparently, whether the preempted thread
693 * was scheduled or not (it may have been preempted after descheduling
696 * We have to setup the MP lock for the original thread after backing
697 * out the adjustment that was made to curthread when the original
700 if ((ntd = td->td_preempted) != NULL) {
701 KKASSERT(ntd->td_flags & TDF_PREEMPT_LOCK);
702 ntd->td_flags |= TDF_PREEMPT_DONE;
705 * The interrupt may have woken a thread up, we need to properly
706 * set the reschedule flag if the originally interrupted thread is
707 * at a lower priority.
709 * The interrupt may not have descheduled.
711 if (TAILQ_FIRST(&gd->gd_tdrunq) != ntd)
713 goto havethread_preempted;
717 * If we cannot obtain ownership of the tokens we cannot immediately
718 * schedule the target thread.
720 * Reminder: Again, we cannot afford to run any IPIs in this path if
721 * the current thread has been descheduled.
724 clear_lwkt_resched();
727 * Hotpath - pull the head of the run queue and attempt to schedule
731 ntd = TAILQ_FIRST(&gd->gd_tdrunq);
735 * Runq is empty, switch to idle to allow it to halt.
737 ntd = &gd->gd_idlethread;
739 if (gd->gd_trap_nesting_level == 0 && panicstr == NULL)
740 ASSERT_NO_TOKENS_HELD(ntd);
742 cpu_time.cp_msg[0] = 0;
743 cpu_time.cp_stallpc = 0;
750 * Hotpath - schedule ntd.
752 * NOTE: For UP there is no mplock and lwkt_getalltokens()
755 if (TD_TOKS_NOT_HELD(ntd) ||
756 lwkt_getalltokens(ntd, (spinning >= lwkt_spin_loops)))
762 * Coldpath (SMP only since tokens always succeed on UP)
764 * We had some contention on the thread we wanted to schedule.
765 * What we do now is try to find a thread that we can schedule
768 * The coldpath scan does NOT rearrange threads in the run list.
769 * The lwkt_schedulerclock() will assert need_lwkt_resched() on
770 * the next tick whenever the current head is not the current thread.
773 ++token_contention_count[ntd->td_pri];
777 if (fairq_bypass > 0)
781 while ((ntd = TAILQ_NEXT(ntd, td_threadq)) != NULL) {
783 * Never schedule threads returning to userland or the
784 * user thread scheduler helper thread when higher priority
785 * threads are present.
787 if (ntd->td_pri < TDPRI_KERN_LPSCHED) {
795 if (TD_TOKS_NOT_HELD(ntd) ||
796 lwkt_getalltokens(ntd, (spinning >= lwkt_spin_loops))) {
800 ++token_contention_count[ntd->td_pri];
807 * We exhausted the run list, meaning that all runnable threads
811 ntd = &gd->gd_idlethread;
813 if (gd->gd_trap_nesting_level == 0 && panicstr == NULL)
814 ASSERT_NO_TOKENS_HELD(ntd);
815 /* contention case, do not clear contention mask */
819 * We are going to have to retry but if the current thread is not
820 * on the runq we instead switch through the idle thread to get away
821 * from the current thread. We have to flag for lwkt reschedule
822 * to prevent the idle thread from halting.
824 * NOTE: A non-zero spinning is passed to lwkt_getalltokens() to
825 * instruct it to deal with the potential for deadlocks by
826 * ordering the tokens by address.
828 if ((td->td_flags & TDF_RUNQ) == 0) {
829 need_lwkt_resched(); /* prevent hlt */
832 #if defined(INVARIANTS) && defined(__amd64__)
833 if ((read_rflags() & PSL_I) == 0) {
835 panic("lwkt_switch() called with interrupts disabled");
840 * Number iterations so far. After a certain point we switch to
841 * a sorted-address/monitor/mwait version of lwkt_getalltokens()
843 if (spinning < 0x7FFFFFFF)
848 * lwkt_getalltokens() failed in sorted token mode, we can use
849 * monitor/mwait in this case.
851 if (spinning >= lwkt_spin_loops &&
852 (cpu_mi_feature & CPU_MI_MONITOR) &&
855 cpu_mmw_pause_int(&gd->gd_reqflags,
856 (gd->gd_reqflags | RQF_SPINNING) &
857 ~RQF_IDLECHECK_WK_MASK);
862 * We already checked that td is still scheduled so this should be
868 * This experimental resequencer is used as a fall-back to reduce
869 * hw cache line contention by placing each core's scheduler into a
870 * time-domain-multplexed slot.
872 * The resequencer is disabled by default. It's functionality has
873 * largely been superceeded by the token algorithm which limits races
874 * to a subset of cores.
876 * The resequencer algorithm tends to break down when more than
877 * 20 cores are contending. What appears to happen is that new
878 * tokens can be obtained out of address-sorted order by new cores
879 * while existing cores languish in long delays between retries and
880 * wind up being starved-out of the token acquisition.
882 if (lwkt_spin_reseq && spinning >= lwkt_spin_reseq) {
883 int cseq = atomic_fetchadd_int(&lwkt_cseq_windex, 1);
886 while ((oseq = lwkt_cseq_rindex) != cseq) {
889 if (cpu_mi_feature & CPU_MI_MONITOR) {
890 cpu_mmw_pause_int(&lwkt_cseq_rindex, oseq);
900 atomic_add_int(&lwkt_cseq_rindex, 1);
902 /* highest level for(;;) loop */
907 * Clear gd_idle_repeat when doing a normal switch to a non-idle
910 ntd->td_wmesg = NULL;
911 ++gd->gd_cnt.v_swtch;
912 gd->gd_idle_repeat = 0;
914 havethread_preempted:
916 * If the new target does not need the MP lock and we are holding it,
917 * release the MP lock. If the new target requires the MP lock we have
918 * already acquired it for the target.
922 KASSERT(ntd->td_critcount,
923 ("priority problem in lwkt_switch %d %d",
924 td->td_critcount, ntd->td_critcount));
928 * Execute the actual thread switch operation. This function
929 * returns to the current thread and returns the previous thread
930 * (which may be different from the thread we switched to).
932 * We are responsible for marking ntd as TDF_RUNNING.
934 KKASSERT((ntd->td_flags & TDF_RUNNING) == 0);
936 KTR_LOG(ctxsw_sw, gd->gd_cpuid, ntd);
937 ntd->td_flags |= TDF_RUNNING;
938 lwkt_switch_return(td->td_switch(ntd));
939 /* ntd invalid, td_switch() can return a different thread_t */
943 * catch-all. XXX is this strictly needed?
947 /* NOTE: current cpu may have changed after switch */
952 * Called by assembly in the td_switch (thread restore path) for thread
953 * bootstrap cases which do not 'return' to lwkt_switch().
956 lwkt_switch_return(thread_t otd)
962 * Check if otd was migrating. Now that we are on ntd we can finish
963 * up the migration. This is a bit messy but it is the only place
964 * where td is known to be fully descheduled.
966 * We can only activate the migration if otd was migrating but not
967 * held on the cpu due to a preemption chain. We still have to
968 * clear TDF_RUNNING on the old thread either way.
970 * We are responsible for clearing the previously running thread's
973 if ((rgd = otd->td_migrate_gd) != NULL &&
974 (otd->td_flags & TDF_PREEMPT_LOCK) == 0) {
975 KKASSERT((otd->td_flags & (TDF_MIGRATING | TDF_RUNNING)) ==
976 (TDF_MIGRATING | TDF_RUNNING));
977 otd->td_migrate_gd = NULL;
978 otd->td_flags &= ~TDF_RUNNING;
979 lwkt_send_ipiq(rgd, lwkt_setcpu_remote, otd);
981 otd->td_flags &= ~TDF_RUNNING;
984 otd->td_flags &= ~TDF_RUNNING;
989 * Request that the target thread preempt the current thread. Preemption
990 * can only occur if our only critical section is the one that we were called
991 * with, the relative priority of the target thread is higher, and the target
992 * thread holds no tokens. This also only works if we are not holding any
993 * spinlocks (obviously).
995 * THE CALLER OF LWKT_PREEMPT() MUST BE IN A CRITICAL SECTION. Typically
996 * this is called via lwkt_schedule() through the td_preemptable callback.
997 * critcount is the managed critical priority that we should ignore in order
998 * to determine whether preemption is possible (aka usually just the crit
999 * priority of lwkt_schedule() itself).
1001 * Preemption is typically limited to interrupt threads.
1003 * Operation works in a fairly straight-forward manner. The normal
1004 * scheduling code is bypassed and we switch directly to the target
1005 * thread. When the target thread attempts to block or switch away
1006 * code at the base of lwkt_switch() will switch directly back to our
1007 * thread. Our thread is able to retain whatever tokens it holds and
1008 * if the target needs one of them the target will switch back to us
1009 * and reschedule itself normally.
1012 lwkt_preempt(thread_t ntd, int critcount)
1014 struct globaldata *gd = mycpu;
1017 int save_gd_intr_nesting_level;
1020 * The caller has put us in a critical section. We can only preempt
1021 * if the caller of the caller was not in a critical section (basically
1022 * a local interrupt), as determined by the 'critcount' parameter. We
1023 * also can't preempt if the caller is holding any spinlocks (even if
1024 * he isn't in a critical section). This also handles the tokens test.
1026 * YYY The target thread must be in a critical section (else it must
1027 * inherit our critical section? I dunno yet).
1029 KASSERT(ntd->td_critcount, ("BADCRIT0 %d", ntd->td_pri));
1031 td = gd->gd_curthread;
1032 if (preempt_enable == 0) {
1036 if (ntd->td_pri <= td->td_pri) {
1040 if (td->td_critcount > critcount) {
1045 if (td->td_cscount) {
1049 if (ntd->td_gd != gd) {
1055 * We don't have to check spinlocks here as they will also bump
1058 * Do not try to preempt if the target thread is holding any tokens.
1059 * We could try to acquire the tokens but this case is so rare there
1060 * is no need to support it.
1062 KKASSERT(gd->gd_spinlocks_wr == 0);
1064 if (TD_TOKS_HELD(ntd)) {
1068 if (td == ntd || ((td->td_flags | ntd->td_flags) & TDF_PREEMPT_LOCK)) {
1072 if (ntd->td_preempted) {
1076 KKASSERT(gd->gd_processing_ipiq == 0);
1079 * Since we are able to preempt the current thread, there is no need to
1080 * call need_lwkt_resched().
1082 * We must temporarily clear gd_intr_nesting_level around the switch
1083 * since switchouts from the target thread are allowed (they will just
1084 * return to our thread), and since the target thread has its own stack.
1086 * A preemption must switch back to the original thread, assert the
1090 ntd->td_preempted = td;
1091 td->td_flags |= TDF_PREEMPT_LOCK;
1092 KTR_LOG(ctxsw_pre, gd->gd_cpuid, ntd);
1093 save_gd_intr_nesting_level = gd->gd_intr_nesting_level;
1094 gd->gd_intr_nesting_level = 0;
1096 KKASSERT((ntd->td_flags & TDF_RUNNING) == 0);
1097 ntd->td_flags |= TDF_RUNNING;
1098 xtd = td->td_switch(ntd);
1099 KKASSERT(xtd == ntd);
1100 lwkt_switch_return(xtd);
1101 gd->gd_intr_nesting_level = save_gd_intr_nesting_level;
1103 KKASSERT(ntd->td_preempted && (td->td_flags & TDF_PREEMPT_DONE));
1104 ntd->td_preempted = NULL;
1105 td->td_flags &= ~(TDF_PREEMPT_LOCK|TDF_PREEMPT_DONE);
1109 * Conditionally call splz() if gd_reqflags indicates work is pending.
1110 * This will work inside a critical section but not inside a hard code
1113 * (self contained on a per cpu basis)
1118 globaldata_t gd = mycpu;
1119 thread_t td = gd->gd_curthread;
1121 if ((gd->gd_reqflags & RQF_IDLECHECK_MASK) &&
1122 gd->gd_intr_nesting_level == 0 &&
1123 td->td_nest_count < 2)
1130 * This version is integrated into crit_exit, reqflags has already
1131 * been tested but td_critcount has not.
1133 * We only want to execute the splz() on the 1->0 transition of
1134 * critcount and not in a hard code section or if too deeply nested.
1137 lwkt_maybe_splz(thread_t td)
1139 globaldata_t gd = td->td_gd;
1141 if (td->td_critcount == 0 &&
1142 gd->gd_intr_nesting_level == 0 &&
1143 td->td_nest_count < 2)
1150 * Drivers which set up processing co-threads can call this function to
1151 * run the co-thread at a higher priority and to allow it to preempt
1155 lwkt_set_interrupt_support_thread(void)
1157 thread_t td = curthread;
1159 lwkt_setpri_self(TDPRI_INT_SUPPORT);
1160 td->td_flags |= TDF_INTTHREAD;
1161 td->td_preemptable = lwkt_preempt;
1166 * This function is used to negotiate a passive release of the current
1167 * process/lwp designation with the user scheduler, allowing the user
1168 * scheduler to schedule another user thread. The related kernel thread
1169 * (curthread) continues running in the released state.
1172 lwkt_passive_release(struct thread *td)
1174 struct lwp *lp = td->td_lwp;
1176 td->td_release = NULL;
1177 lwkt_setpri_self(TDPRI_KERN_USER);
1178 lp->lwp_proc->p_usched->release_curproc(lp);
1183 * This implements a LWKT yield, allowing a kernel thread to yield to other
1184 * kernel threads at the same or higher priority. This function can be
1185 * called in a tight loop and will typically only yield once per tick.
1187 * Most kernel threads run at the same priority in order to allow equal
1190 * (self contained on a per cpu basis)
1195 globaldata_t gd = mycpu;
1196 thread_t td = gd->gd_curthread;
1198 if ((gd->gd_reqflags & RQF_IDLECHECK_MASK) && td->td_nest_count < 2)
1200 if (lwkt_resched_wanted()) {
1201 lwkt_schedule_self(curthread);
1207 * This yield is designed for kernel threads with a user context.
1209 * The kernel acting on behalf of the user is potentially cpu-bound,
1210 * this function will efficiently allow other threads to run and also
1211 * switch to other processes by releasing.
1213 * The lwkt_user_yield() function is designed to have very low overhead
1214 * if no yield is determined to be needed.
1217 lwkt_user_yield(void)
1219 globaldata_t gd = mycpu;
1220 thread_t td = gd->gd_curthread;
1223 * Always run any pending interrupts in case we are in a critical
1226 if ((gd->gd_reqflags & RQF_IDLECHECK_MASK) && td->td_nest_count < 2)
1230 * Switch (which forces a release) if another kernel thread needs
1231 * the cpu, if userland wants us to resched, or if our kernel
1232 * quantum has run out.
1234 if (lwkt_resched_wanted() ||
1235 user_resched_wanted())
1242 * Reacquire the current process if we are released.
1244 * XXX not implemented atm. The kernel may be holding locks and such,
1245 * so we want the thread to continue to receive cpu.
1247 if (td->td_release == NULL && lp) {
1248 lp->lwp_proc->p_usched->acquire_curproc(lp);
1249 td->td_release = lwkt_passive_release;
1250 lwkt_setpri_self(TDPRI_USER_NORM);
1256 * Generic schedule. Possibly schedule threads belonging to other cpus and
1257 * deal with threads that might be blocked on a wait queue.
1259 * We have a little helper inline function which does additional work after
1260 * the thread has been enqueued, including dealing with preemption and
1261 * setting need_lwkt_resched() (which prevents the kernel from returning
1262 * to userland until it has processed higher priority threads).
1264 * It is possible for this routine to be called after a failed _enqueue
1265 * (due to the target thread migrating, sleeping, or otherwise blocked).
1266 * We have to check that the thread is actually on the run queue!
1270 _lwkt_schedule_post(globaldata_t gd, thread_t ntd, int ccount)
1272 if (ntd->td_flags & TDF_RUNQ) {
1273 if (ntd->td_preemptable) {
1274 ntd->td_preemptable(ntd, ccount); /* YYY +token */
1281 _lwkt_schedule(thread_t td)
1283 globaldata_t mygd = mycpu;
1285 KASSERT(td != &td->td_gd->gd_idlethread,
1286 ("lwkt_schedule(): scheduling gd_idlethread is illegal!"));
1287 KKASSERT((td->td_flags & TDF_MIGRATING) == 0);
1288 crit_enter_gd(mygd);
1289 KKASSERT(td->td_lwp == NULL ||
1290 (td->td_lwp->lwp_mpflags & LWP_MP_ONRUNQ) == 0);
1292 if (td == mygd->gd_curthread) {
1296 * If we own the thread, there is no race (since we are in a
1297 * critical section). If we do not own the thread there might
1298 * be a race but the target cpu will deal with it.
1301 if (td->td_gd == mygd) {
1303 _lwkt_schedule_post(mygd, td, 1);
1305 lwkt_send_ipiq3(td->td_gd, lwkt_schedule_remote, td, 0);
1309 _lwkt_schedule_post(mygd, td, 1);
1316 lwkt_schedule(thread_t td)
1322 lwkt_schedule_noresched(thread_t td) /* XXX not impl */
1330 * When scheduled remotely if frame != NULL the IPIQ is being
1331 * run via doreti or an interrupt then preemption can be allowed.
1333 * To allow preemption we have to drop the critical section so only
1334 * one is present in _lwkt_schedule_post.
1337 lwkt_schedule_remote(void *arg, int arg2, struct intrframe *frame)
1339 thread_t td = curthread;
1342 if (frame && ntd->td_preemptable) {
1343 crit_exit_noyield(td);
1344 _lwkt_schedule(ntd);
1345 crit_enter_quick(td);
1347 _lwkt_schedule(ntd);
1352 * Thread migration using a 'Pull' method. The thread may or may not be
1353 * the current thread. It MUST be descheduled and in a stable state.
1354 * lwkt_giveaway() must be called on the cpu owning the thread.
1356 * At any point after lwkt_giveaway() is called, the target cpu may
1357 * 'pull' the thread by calling lwkt_acquire().
1359 * We have to make sure the thread is not sitting on a per-cpu tsleep
1360 * queue or it will blow up when it moves to another cpu.
1362 * MPSAFE - must be called under very specific conditions.
1365 lwkt_giveaway(thread_t td)
1367 globaldata_t gd = mycpu;
1370 if (td->td_flags & TDF_TSLEEPQ)
1372 KKASSERT(td->td_gd == gd);
1373 TAILQ_REMOVE(&gd->gd_tdallq, td, td_allq);
1374 td->td_flags |= TDF_MIGRATING;
1379 lwkt_acquire(thread_t td)
1383 int retry = 10000000;
1385 KKASSERT(td->td_flags & TDF_MIGRATING);
1390 KKASSERT((td->td_flags & TDF_RUNQ) == 0);
1391 crit_enter_gd(mygd);
1392 DEBUG_PUSH_INFO("lwkt_acquire");
1393 while (td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK)) {
1395 lwkt_process_ipiq();
1399 kprintf("lwkt_acquire: stuck: td %p td->td_flags %08x\n",
1407 TAILQ_INSERT_TAIL(&mygd->gd_tdallq, td, td_allq);
1408 td->td_flags &= ~TDF_MIGRATING;
1411 crit_enter_gd(mygd);
1412 TAILQ_INSERT_TAIL(&mygd->gd_tdallq, td, td_allq);
1413 td->td_flags &= ~TDF_MIGRATING;
1421 * Generic deschedule. Descheduling threads other then your own should be
1422 * done only in carefully controlled circumstances. Descheduling is
1425 * This function may block if the cpu has run out of messages.
1428 lwkt_deschedule(thread_t td)
1432 if (td == curthread) {
1435 if (td->td_gd == mycpu) {
1438 lwkt_send_ipiq(td->td_gd, (ipifunc1_t)lwkt_deschedule, td);
1448 * Set the target thread's priority. This routine does not automatically
1449 * switch to a higher priority thread, LWKT threads are not designed for
1450 * continuous priority changes. Yield if you want to switch.
1453 lwkt_setpri(thread_t td, int pri)
1455 if (td->td_pri != pri) {
1458 if (td->td_flags & TDF_RUNQ) {
1459 KKASSERT(td->td_gd == mycpu);
1471 * Set the initial priority for a thread prior to it being scheduled for
1472 * the first time. The thread MUST NOT be scheduled before or during
1473 * this call. The thread may be assigned to a cpu other then the current
1476 * Typically used after a thread has been created with TDF_STOPPREQ,
1477 * and before the thread is initially scheduled.
1480 lwkt_setpri_initial(thread_t td, int pri)
1483 KKASSERT((td->td_flags & TDF_RUNQ) == 0);
1488 lwkt_setpri_self(int pri)
1490 thread_t td = curthread;
1492 KKASSERT(pri >= 0 && pri <= TDPRI_MAX);
1494 if (td->td_flags & TDF_RUNQ) {
1505 * hz tick scheduler clock for LWKT threads
1508 lwkt_schedulerclock(thread_t td)
1510 globaldata_t gd = td->td_gd;
1513 if (TAILQ_FIRST(&gd->gd_tdrunq) == td) {
1515 * If the current thread is at the head of the runq shift it to the
1516 * end of any equal-priority threads and request a LWKT reschedule
1519 xtd = TAILQ_NEXT(td, td_threadq);
1520 if (xtd && xtd->td_pri == td->td_pri) {
1521 TAILQ_REMOVE(&gd->gd_tdrunq, td, td_threadq);
1522 while (xtd && xtd->td_pri == td->td_pri)
1523 xtd = TAILQ_NEXT(xtd, td_threadq);
1525 TAILQ_INSERT_BEFORE(xtd, td, td_threadq);
1527 TAILQ_INSERT_TAIL(&gd->gd_tdrunq, td, td_threadq);
1528 need_lwkt_resched();
1532 * If we scheduled a thread other than the one at the head of the
1533 * queue always request a reschedule every tick.
1535 need_lwkt_resched();
1540 * Migrate the current thread to the specified cpu.
1542 * This is accomplished by descheduling ourselves from the current cpu
1543 * and setting td_migrate_gd. The lwkt_switch() code will detect that the
1544 * 'old' thread wants to migrate after it has been completely switched out
1545 * and will complete the migration.
1547 * TDF_MIGRATING prevents scheduling races while the thread is being migrated.
1549 * We must be sure to release our current process designation (if a user
1550 * process) before clearing out any tsleepq we are on because the release
1551 * code may re-add us.
1553 * We must be sure to remove ourselves from the current cpu's tsleepq
1554 * before potentially moving to another queue. The thread can be on
1555 * a tsleepq due to a left-over tsleep_interlock().
1559 lwkt_setcpu_self(globaldata_t rgd)
1562 thread_t td = curthread;
1564 if (td->td_gd != rgd) {
1565 crit_enter_quick(td);
1569 if (td->td_flags & TDF_TSLEEPQ)
1573 * Set TDF_MIGRATING to prevent a spurious reschedule while we are
1574 * trying to deschedule ourselves and switch away, then deschedule
1575 * ourself, remove us from tdallq, and set td_migrate_gd. Finally,
1576 * call lwkt_switch() to complete the operation.
1578 td->td_flags |= TDF_MIGRATING;
1579 lwkt_deschedule_self(td);
1580 TAILQ_REMOVE(&td->td_gd->gd_tdallq, td, td_allq);
1581 td->td_migrate_gd = rgd;
1585 * We are now on the target cpu
1587 KKASSERT(rgd == mycpu);
1588 TAILQ_INSERT_TAIL(&rgd->gd_tdallq, td, td_allq);
1589 crit_exit_quick(td);
1595 lwkt_migratecpu(int cpuid)
1600 rgd = globaldata_find(cpuid);
1601 lwkt_setcpu_self(rgd);
1607 * Remote IPI for cpu migration (called while in a critical section so we
1608 * do not have to enter another one).
1610 * The thread (td) has already been completely descheduled from the
1611 * originating cpu and we can simply assert the case. The thread is
1612 * assigned to the new cpu and enqueued.
1614 * The thread will re-add itself to tdallq when it resumes execution.
1617 lwkt_setcpu_remote(void *arg)
1620 globaldata_t gd = mycpu;
1622 KKASSERT((td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK)) == 0);
1625 td->td_flags &= ~TDF_MIGRATING;
1626 KKASSERT(td->td_migrate_gd == NULL);
1627 KKASSERT(td->td_lwp == NULL ||
1628 (td->td_lwp->lwp_mpflags & LWP_MP_ONRUNQ) == 0);
1634 lwkt_preempted_proc(void)
1636 thread_t td = curthread;
1637 while (td->td_preempted)
1638 td = td->td_preempted;
1643 * Create a kernel process/thread/whatever. It shares it's address space
1644 * with proc0 - ie: kernel only.
1646 * If the cpu is not specified one will be selected. In the future
1647 * specifying a cpu of -1 will enable kernel thread migration between
1651 lwkt_create(void (*func)(void *), void *arg, struct thread **tdp,
1652 thread_t template, int tdflags, int cpu, const char *fmt, ...)
1657 td = lwkt_alloc_thread(template, LWKT_THREAD_STACK, cpu,
1661 cpu_set_thread_handler(td, lwkt_exit, func, arg);
1664 * Set up arg0 for 'ps' etc
1666 __va_start(ap, fmt);
1667 kvsnprintf(td->td_comm, sizeof(td->td_comm), fmt, ap);
1671 * Schedule the thread to run
1673 if (td->td_flags & TDF_NOSTART)
1674 td->td_flags &= ~TDF_NOSTART;
1681 * Destroy an LWKT thread. Warning! This function is not called when
1682 * a process exits, cpu_proc_exit() directly calls cpu_thread_exit() and
1683 * uses a different reaping mechanism.
1688 thread_t td = curthread;
1693 * Do any cleanup that might block here
1695 if (td->td_flags & TDF_VERBOSE)
1696 kprintf("kthread %p %s has exited\n", td, td->td_comm);
1699 dsched_exit_thread(td);
1702 * Get us into a critical section to interlock gd_freetd and loop
1703 * until we can get it freed.
1705 * We have to cache the current td in gd_freetd because objcache_put()ing
1706 * it would rip it out from under us while our thread is still active.
1708 * We are the current thread so of course our own TDF_RUNNING bit will
1709 * be set, so unlike the lwp reap code we don't wait for it to clear.
1712 crit_enter_quick(td);
1715 tsleep(td, 0, "tdreap", 1);
1718 if ((std = gd->gd_freetd) != NULL) {
1719 KKASSERT((std->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK)) == 0);
1720 gd->gd_freetd = NULL;
1721 objcache_put(thread_cache, std);
1728 * Remove thread resources from kernel lists and deschedule us for
1729 * the last time. We cannot block after this point or we may end
1730 * up with a stale td on the tsleepq.
1732 * None of this may block, the critical section is the only thing
1733 * protecting tdallq and the only thing preventing new lwkt_hold()
1736 if (td->td_flags & TDF_TSLEEPQ)
1738 lwkt_deschedule_self(td);
1739 lwkt_remove_tdallq(td);
1740 KKASSERT(td->td_refs == 0);
1745 KKASSERT(gd->gd_freetd == NULL);
1746 if (td->td_flags & TDF_ALLOCATED_THREAD)
1752 lwkt_remove_tdallq(thread_t td)
1754 KKASSERT(td->td_gd == mycpu);
1755 TAILQ_REMOVE(&td->td_gd->gd_tdallq, td, td_allq);
1759 * Code reduction and branch prediction improvements. Call/return
1760 * overhead on modern cpus often degenerates into 0 cycles due to
1761 * the cpu's branch prediction hardware and return pc cache. We
1762 * can take advantage of this by not inlining medium-complexity
1763 * functions and we can also reduce the branch prediction impact
1764 * by collapsing perfectly predictable branches into a single
1765 * procedure instead of duplicating it.
1767 * Is any of this noticeable? Probably not, so I'll take the
1768 * smaller code size.
1771 crit_exit_wrapper(__DEBUG_CRIT_ARG__)
1773 _crit_exit(mycpu __DEBUG_CRIT_PASS_ARG__);
1779 thread_t td = curthread;
1780 int lcrit = td->td_critcount;
1782 td->td_critcount = 0;
1783 panic("td_critcount is/would-go negative! %p %d", td, lcrit);
1790 * Called from debugger/panic on cpus which have been stopped. We must still
1791 * process the IPIQ while stopped, even if we were stopped while in a critical
1794 * If we are dumping also try to process any pending interrupts. This may
1795 * or may not work depending on the state of the cpu at the point it was
1799 lwkt_smp_stopped(void)
1801 globaldata_t gd = mycpu;
1805 lwkt_process_ipiq();
1808 lwkt_process_ipiq();