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 = 32;
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;
298 _lwkt_thread_dtor(void *obj, void *privdata)
300 struct thread *td = (struct thread *)obj;
302 KASSERT(td->td_flags & TDF_ALLOCATED_THREAD,
303 ("_lwkt_thread_dtor: not allocated from objcache"));
304 KASSERT((td->td_flags & TDF_ALLOCATED_STACK) && td->td_kstack &&
305 td->td_kstack_size > 0,
306 ("_lwkt_thread_dtor: corrupted stack"));
307 kmem_free(&kernel_map, (vm_offset_t)td->td_kstack, td->td_kstack_size);
311 * Initialize the lwkt s/system.
313 * Nominally cache up to 32 thread + kstack structures.
318 TUNABLE_INT("lwkt.cache_threads", &lwkt_cache_threads);
319 thread_cache = objcache_create_mbacked(
320 M_THREAD, sizeof(struct thread),
321 NULL, lwkt_cache_threads,
322 _lwkt_thread_ctor, _lwkt_thread_dtor, NULL);
326 * Schedule a thread to run. As the current thread we can always safely
327 * schedule ourselves, and a shortcut procedure is provided for that
330 * (non-blocking, self contained on a per cpu basis)
333 lwkt_schedule_self(thread_t td)
335 KKASSERT((td->td_flags & TDF_MIGRATING) == 0);
336 crit_enter_quick(td);
337 KASSERT(td != &td->td_gd->gd_idlethread,
338 ("lwkt_schedule_self(): scheduling gd_idlethread is illegal!"));
339 KKASSERT(td->td_lwp == NULL || (td->td_lwp->lwp_flag & LWP_ONRUNQ) == 0);
345 * Deschedule a thread.
347 * (non-blocking, self contained on a per cpu basis)
350 lwkt_deschedule_self(thread_t td)
352 crit_enter_quick(td);
358 * LWKTs operate on a per-cpu basis
360 * WARNING! Called from early boot, 'mycpu' may not work yet.
363 lwkt_gdinit(struct globaldata *gd)
365 TAILQ_INIT(&gd->gd_tdrunq);
366 TAILQ_INIT(&gd->gd_tdallq);
370 * Create a new thread. The thread must be associated with a process context
371 * or LWKT start address before it can be scheduled. If the target cpu is
372 * -1 the thread will be created on the current cpu.
374 * If you intend to create a thread without a process context this function
375 * does everything except load the startup and switcher function.
378 lwkt_alloc_thread(struct thread *td, int stksize, int cpu, int flags)
380 static int cpu_rotator;
381 globaldata_t gd = mycpu;
385 * If static thread storage is not supplied allocate a thread. Reuse
386 * a cached free thread if possible. gd_freetd is used to keep an exiting
387 * thread intact through the exit.
391 if ((td = gd->gd_freetd) != NULL) {
392 KKASSERT((td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK|
394 gd->gd_freetd = NULL;
396 td = objcache_get(thread_cache, M_WAITOK);
397 KKASSERT((td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK|
401 KASSERT((td->td_flags &
402 (TDF_ALLOCATED_THREAD|TDF_RUNNING)) == TDF_ALLOCATED_THREAD,
403 ("lwkt_alloc_thread: corrupted td flags 0x%X", td->td_flags));
404 flags |= td->td_flags & (TDF_ALLOCATED_THREAD|TDF_ALLOCATED_STACK);
408 * Try to reuse cached stack.
410 if ((stack = td->td_kstack) != NULL && td->td_kstack_size != stksize) {
411 if (flags & TDF_ALLOCATED_STACK) {
412 kmem_free(&kernel_map, (vm_offset_t)stack, td->td_kstack_size);
417 stack = (void *)kmem_alloc_stack(&kernel_map, stksize);
418 flags |= TDF_ALLOCATED_STACK;
425 lwkt_init_thread(td, stack, stksize, flags, globaldata_find(cpu));
430 * Initialize a preexisting thread structure. This function is used by
431 * lwkt_alloc_thread() and also used to initialize the per-cpu idlethread.
433 * All threads start out in a critical section at a priority of
434 * TDPRI_KERN_DAEMON. Higher level code will modify the priority as
435 * appropriate. This function may send an IPI message when the
436 * requested cpu is not the current cpu and consequently gd_tdallq may
437 * not be initialized synchronously from the point of view of the originating
440 * NOTE! we have to be careful in regards to creating threads for other cpus
441 * if SMP has not yet been activated.
446 lwkt_init_thread_remote(void *arg)
451 * Protected by critical section held by IPI dispatch
453 TAILQ_INSERT_TAIL(&td->td_gd->gd_tdallq, td, td_allq);
459 * lwkt core thread structural initialization.
461 * NOTE: All threads are initialized as mpsafe threads.
464 lwkt_init_thread(thread_t td, void *stack, int stksize, int flags,
465 struct globaldata *gd)
467 globaldata_t mygd = mycpu;
469 bzero(td, sizeof(struct thread));
470 td->td_kstack = stack;
471 td->td_kstack_size = stksize;
472 td->td_flags = flags;
474 td->td_pri = TDPRI_KERN_DAEMON;
475 td->td_critcount = 1;
476 td->td_toks_have = NULL;
477 td->td_toks_stop = &td->td_toks_base;
478 if (lwkt_use_spin_port || (flags & TDF_FORCE_SPINPORT))
479 lwkt_initport_spin(&td->td_msgport);
481 lwkt_initport_thread(&td->td_msgport, td);
482 pmap_init_thread(td);
485 * Normally initializing a thread for a remote cpu requires sending an
486 * IPI. However, the idlethread is setup before the other cpus are
487 * activated so we have to treat it as a special case. XXX manipulation
488 * of gd_tdallq requires the BGL.
490 if (gd == mygd || td == &gd->gd_idlethread) {
492 TAILQ_INSERT_TAIL(&gd->gd_tdallq, td, td_allq);
495 lwkt_send_ipiq(gd, lwkt_init_thread_remote, td);
499 TAILQ_INSERT_TAIL(&gd->gd_tdallq, td, td_allq);
503 dsched_new_thread(td);
507 lwkt_set_comm(thread_t td, const char *ctl, ...)
512 kvsnprintf(td->td_comm, sizeof(td->td_comm), ctl, va);
514 KTR_LOG(ctxsw_newtd, td, &td->td_comm[0]);
518 lwkt_hold(thread_t td)
520 atomic_add_int(&td->td_refs, 1);
524 lwkt_rele(thread_t td)
526 KKASSERT(td->td_refs > 0);
527 atomic_add_int(&td->td_refs, -1);
531 lwkt_wait_free(thread_t td)
534 tsleep(td, 0, "tdreap", hz);
538 lwkt_free_thread(thread_t td)
540 KKASSERT(td->td_refs == 0);
541 KKASSERT((td->td_flags & (TDF_RUNNING | TDF_PREEMPT_LOCK |
542 TDF_RUNQ | TDF_TSLEEPQ)) == 0);
543 if (td->td_flags & TDF_ALLOCATED_THREAD) {
544 objcache_put(thread_cache, td);
545 } else if (td->td_flags & TDF_ALLOCATED_STACK) {
546 /* client-allocated struct with internally allocated stack */
547 KASSERT(td->td_kstack && td->td_kstack_size > 0,
548 ("lwkt_free_thread: corrupted stack"));
549 kmem_free(&kernel_map, (vm_offset_t)td->td_kstack, td->td_kstack_size);
550 td->td_kstack = NULL;
551 td->td_kstack_size = 0;
553 KTR_LOG(ctxsw_deadtd, td);
558 * Switch to the next runnable lwkt. If no LWKTs are runnable then
559 * switch to the idlethread. Switching must occur within a critical
560 * section to avoid races with the scheduling queue.
562 * We always have full control over our cpu's run queue. Other cpus
563 * that wish to manipulate our queue must use the cpu_*msg() calls to
564 * talk to our cpu, so a critical section is all that is needed and
565 * the result is very, very fast thread switching.
567 * The LWKT scheduler uses a fixed priority model and round-robins at
568 * each priority level. User process scheduling is a totally
569 * different beast and LWKT priorities should not be confused with
570 * user process priorities.
572 * PREEMPTION NOTE: Preemption occurs via lwkt_preempt(). lwkt_switch()
573 * is not called by the current thread in the preemption case, only when
574 * the preempting thread blocks (in order to return to the original thread).
576 * SPECIAL NOTE ON SWITCH ATOMICY: Certain operations such as thread
577 * migration and tsleep deschedule the current lwkt thread and call
578 * lwkt_switch(). In particular, the target cpu of the migration fully
579 * expects the thread to become non-runnable and can deadlock against
580 * cpusync operations if we run any IPIs prior to switching the thread out.
582 * WE MUST BE VERY CAREFUL NOT TO RUN SPLZ DIRECTLY OR INDIRECTLY IF
583 * THE CURRENT THREAD HAS BEEN DESCHEDULED!
588 globaldata_t gd = mycpu;
589 thread_t td = gd->gd_curthread;
594 KKASSERT(gd->gd_processing_ipiq == 0);
597 * Switching from within a 'fast' (non thread switched) interrupt or IPI
598 * is illegal. However, we may have to do it anyway if we hit a fatal
599 * kernel trap or we have paniced.
601 * If this case occurs save and restore the interrupt nesting level.
603 if (gd->gd_intr_nesting_level) {
607 if (gd->gd_trap_nesting_level == 0 && panic_cpu_gd != mycpu) {
608 panic("lwkt_switch: Attempt to switch from a "
609 "a fast interrupt, ipi, or hard code section, "
613 savegdnest = gd->gd_intr_nesting_level;
614 savegdtrap = gd->gd_trap_nesting_level;
615 gd->gd_intr_nesting_level = 0;
616 gd->gd_trap_nesting_level = 0;
617 if ((td->td_flags & TDF_PANICWARN) == 0) {
618 td->td_flags |= TDF_PANICWARN;
619 kprintf("Warning: thread switch from interrupt, IPI, "
620 "or hard code section.\n"
621 "thread %p (%s)\n", td, td->td_comm);
625 gd->gd_intr_nesting_level = savegdnest;
626 gd->gd_trap_nesting_level = savegdtrap;
632 * Release our current user process designation if we are blocking
633 * or if a user reschedule was requested.
635 * NOTE: This function is NOT called if we are switching into or
636 * returning from a preemption.
638 * NOTE: Releasing our current user process designation may cause
639 * it to be assigned to another thread, which in turn will
640 * cause us to block in the usched acquire code when we attempt
641 * to return to userland.
643 * NOTE: On SMP systems this can be very nasty when heavy token
644 * contention is present so we want to be careful not to
645 * release the designation gratuitously.
647 if (td->td_release &&
648 (user_resched_wanted() || (td->td_flags & TDF_RUNQ) == 0)) {
656 if (TD_TOKS_HELD(td))
657 lwkt_relalltokens(td);
660 * We had better not be holding any spin locks, but don't get into an
661 * endless panic loop.
663 KASSERT(gd->gd_spinlocks_wr == 0 || panicstr != NULL,
664 ("lwkt_switch: still holding %d exclusive spinlocks!",
665 gd->gd_spinlocks_wr));
670 if (td->td_cscount) {
671 kprintf("Diagnostic: attempt to switch while mastering cpusync: %p\n",
673 if (panic_on_cscount)
674 panic("switching while mastering cpusync");
680 * If we had preempted another thread on this cpu, resume the preempted
681 * thread. This occurs transparently, whether the preempted thread
682 * was scheduled or not (it may have been preempted after descheduling
685 * We have to setup the MP lock for the original thread after backing
686 * out the adjustment that was made to curthread when the original
689 if ((ntd = td->td_preempted) != NULL) {
690 KKASSERT(ntd->td_flags & TDF_PREEMPT_LOCK);
691 ntd->td_flags |= TDF_PREEMPT_DONE;
694 * The interrupt may have woken a thread up, we need to properly
695 * set the reschedule flag if the originally interrupted thread is
696 * at a lower priority.
698 * The interrupt may not have descheduled.
700 if (TAILQ_FIRST(&gd->gd_tdrunq) != ntd)
702 goto havethread_preempted;
706 * If we cannot obtain ownership of the tokens we cannot immediately
707 * schedule the target thread.
709 * Reminder: Again, we cannot afford to run any IPIs in this path if
710 * the current thread has been descheduled.
713 clear_lwkt_resched();
716 * Hotpath - pull the head of the run queue and attempt to schedule
720 ntd = TAILQ_FIRST(&gd->gd_tdrunq);
724 * Runq is empty, switch to idle to allow it to halt.
726 ntd = &gd->gd_idlethread;
728 if (gd->gd_trap_nesting_level == 0 && panicstr == NULL)
729 ASSERT_NO_TOKENS_HELD(ntd);
731 cpu_time.cp_msg[0] = 0;
732 cpu_time.cp_stallpc = 0;
739 * Hotpath - schedule ntd.
741 * NOTE: For UP there is no mplock and lwkt_getalltokens()
744 if (TD_TOKS_NOT_HELD(ntd) ||
745 lwkt_getalltokens(ntd, (spinning >= lwkt_spin_loops)))
751 * Coldpath (SMP only since tokens always succeed on UP)
753 * We had some contention on the thread we wanted to schedule.
754 * What we do now is try to find a thread that we can schedule
757 * The coldpath scan does NOT rearrange threads in the run list.
758 * The lwkt_schedulerclock() will assert need_lwkt_resched() on
759 * the next tick whenever the current head is not the current thread.
762 ++token_contention_count[ntd->td_pri];
766 if (fairq_bypass > 0)
770 while ((ntd = TAILQ_NEXT(ntd, td_threadq)) != NULL) {
772 * Never schedule threads returning to userland or the
773 * user thread scheduler helper thread when higher priority
774 * threads are present.
776 if (ntd->td_pri < TDPRI_KERN_LPSCHED) {
784 if (TD_TOKS_NOT_HELD(ntd) ||
785 lwkt_getalltokens(ntd, (spinning >= lwkt_spin_loops))) {
789 ++token_contention_count[ntd->td_pri];
796 * We exhausted the run list, meaning that all runnable threads
800 ntd = &gd->gd_idlethread;
802 if (gd->gd_trap_nesting_level == 0 && panicstr == NULL)
803 ASSERT_NO_TOKENS_HELD(ntd);
804 /* contention case, do not clear contention mask */
808 * We are going to have to retry but if the current thread is not
809 * on the runq we instead switch through the idle thread to get away
810 * from the current thread. We have to flag for lwkt reschedule
811 * to prevent the idle thread from halting.
813 * NOTE: A non-zero spinning is passed to lwkt_getalltokens() to
814 * instruct it to deal with the potential for deadlocks by
815 * ordering the tokens by address.
817 if ((td->td_flags & TDF_RUNQ) == 0) {
818 need_lwkt_resched(); /* prevent hlt */
821 #if defined(INVARIANTS) && defined(__amd64__)
822 if ((read_rflags() & PSL_I) == 0) {
824 panic("lwkt_switch() called with interrupts disabled");
829 * Number iterations so far. After a certain point we switch to
830 * a sorted-address/monitor/mwait version of lwkt_getalltokens()
832 if (spinning < 0x7FFFFFFF)
837 * lwkt_getalltokens() failed in sorted token mode, we can use
838 * monitor/mwait in this case.
840 if (spinning >= lwkt_spin_loops &&
841 (cpu_mi_feature & CPU_MI_MONITOR) &&
844 cpu_mmw_pause_int(&gd->gd_reqflags,
845 (gd->gd_reqflags | RQF_SPINNING) &
846 ~RQF_IDLECHECK_WK_MASK);
851 * We already checked that td is still scheduled so this should be
857 * This experimental resequencer is used as a fall-back to reduce
858 * hw cache line contention by placing each core's scheduler into a
859 * time-domain-multplexed slot.
861 * The resequencer is disabled by default. It's functionality has
862 * largely been superceeded by the token algorithm which limits races
863 * to a subset of cores.
865 * The resequencer algorithm tends to break down when more than
866 * 20 cores are contending. What appears to happen is that new
867 * tokens can be obtained out of address-sorted order by new cores
868 * while existing cores languish in long delays between retries and
869 * wind up being starved-out of the token acquisition.
871 if (lwkt_spin_reseq && spinning >= lwkt_spin_reseq) {
872 int cseq = atomic_fetchadd_int(&lwkt_cseq_windex, 1);
875 while ((oseq = lwkt_cseq_rindex) != cseq) {
878 if (cpu_mi_feature & CPU_MI_MONITOR) {
879 cpu_mmw_pause_int(&lwkt_cseq_rindex, oseq);
889 atomic_add_int(&lwkt_cseq_rindex, 1);
891 /* highest level for(;;) loop */
896 * Clear gd_idle_repeat when doing a normal switch to a non-idle
899 ntd->td_wmesg = NULL;
900 ++gd->gd_cnt.v_swtch;
901 gd->gd_idle_repeat = 0;
903 havethread_preempted:
905 * If the new target does not need the MP lock and we are holding it,
906 * release the MP lock. If the new target requires the MP lock we have
907 * already acquired it for the target.
911 KASSERT(ntd->td_critcount,
912 ("priority problem in lwkt_switch %d %d",
913 td->td_critcount, ntd->td_critcount));
917 * Execute the actual thread switch operation. This function
918 * returns to the current thread and returns the previous thread
919 * (which may be different from the thread we switched to).
921 * We are responsible for marking ntd as TDF_RUNNING.
924 KTR_LOG(ctxsw_sw, gd->gd_cpuid, ntd);
925 ntd->td_flags |= TDF_RUNNING;
926 lwkt_switch_return(td->td_switch(ntd));
927 /* ntd invalid, td_switch() can return a different thread_t */
931 * catch-all. XXX is this strictly needed?
935 /* NOTE: current cpu may have changed after switch */
940 * Called by assembly in the td_switch (thread restore path) for thread
941 * bootstrap cases which do not 'return' to lwkt_switch().
944 lwkt_switch_return(thread_t otd)
950 * Check if otd was migrating. Now that we are on ntd we can finish
951 * up the migration. This is a bit messy but it is the only place
952 * where td is known to be fully descheduled.
954 * We can only activate the migration if otd was migrating but not
955 * held on the cpu due to a preemption chain. We still have to
956 * clear TDF_RUNNING on the old thread either way.
958 * We are responsible for clearing the previously running thread's
961 if ((rgd = otd->td_migrate_gd) != NULL &&
962 (otd->td_flags & TDF_PREEMPT_LOCK) == 0) {
963 KKASSERT((otd->td_flags & (TDF_MIGRATING | TDF_RUNNING)) ==
964 (TDF_MIGRATING | TDF_RUNNING));
965 otd->td_migrate_gd = NULL;
966 otd->td_flags &= ~TDF_RUNNING;
967 lwkt_send_ipiq(rgd, lwkt_setcpu_remote, otd);
969 otd->td_flags &= ~TDF_RUNNING;
972 otd->td_flags &= ~TDF_RUNNING;
977 * Request that the target thread preempt the current thread. Preemption
978 * can only occur if our only critical section is the one that we were called
979 * with, the relative priority of the target thread is higher, and the target
980 * thread holds no tokens. This also only works if we are not holding any
981 * spinlocks (obviously).
983 * THE CALLER OF LWKT_PREEMPT() MUST BE IN A CRITICAL SECTION. Typically
984 * this is called via lwkt_schedule() through the td_preemptable callback.
985 * critcount is the managed critical priority that we should ignore in order
986 * to determine whether preemption is possible (aka usually just the crit
987 * priority of lwkt_schedule() itself).
989 * Preemption is typically limited to interrupt threads.
991 * Operation works in a fairly straight-forward manner. The normal
992 * scheduling code is bypassed and we switch directly to the target
993 * thread. When the target thread attempts to block or switch away
994 * code at the base of lwkt_switch() will switch directly back to our
995 * thread. Our thread is able to retain whatever tokens it holds and
996 * if the target needs one of them the target will switch back to us
997 * and reschedule itself normally.
1000 lwkt_preempt(thread_t ntd, int critcount)
1002 struct globaldata *gd = mycpu;
1005 int save_gd_intr_nesting_level;
1008 * The caller has put us in a critical section. We can only preempt
1009 * if the caller of the caller was not in a critical section (basically
1010 * a local interrupt), as determined by the 'critcount' parameter. We
1011 * also can't preempt if the caller is holding any spinlocks (even if
1012 * he isn't in a critical section). This also handles the tokens test.
1014 * YYY The target thread must be in a critical section (else it must
1015 * inherit our critical section? I dunno yet).
1017 KASSERT(ntd->td_critcount, ("BADCRIT0 %d", ntd->td_pri));
1019 td = gd->gd_curthread;
1020 if (preempt_enable == 0) {
1024 if (ntd->td_pri <= td->td_pri) {
1028 if (td->td_critcount > critcount) {
1033 if (ntd->td_gd != gd) {
1039 * We don't have to check spinlocks here as they will also bump
1042 * Do not try to preempt if the target thread is holding any tokens.
1043 * We could try to acquire the tokens but this case is so rare there
1044 * is no need to support it.
1046 KKASSERT(gd->gd_spinlocks_wr == 0);
1048 if (TD_TOKS_HELD(ntd)) {
1052 if (td == ntd || ((td->td_flags | ntd->td_flags) & TDF_PREEMPT_LOCK)) {
1056 if (ntd->td_preempted) {
1060 KKASSERT(gd->gd_processing_ipiq == 0);
1063 * Since we are able to preempt the current thread, there is no need to
1064 * call need_lwkt_resched().
1066 * We must temporarily clear gd_intr_nesting_level around the switch
1067 * since switchouts from the target thread are allowed (they will just
1068 * return to our thread), and since the target thread has its own stack.
1070 * A preemption must switch back to the original thread, assert the
1074 ntd->td_preempted = td;
1075 td->td_flags |= TDF_PREEMPT_LOCK;
1076 KTR_LOG(ctxsw_pre, gd->gd_cpuid, ntd);
1077 save_gd_intr_nesting_level = gd->gd_intr_nesting_level;
1078 gd->gd_intr_nesting_level = 0;
1079 ntd->td_flags |= TDF_RUNNING;
1080 xtd = td->td_switch(ntd);
1081 KKASSERT(xtd == ntd);
1082 lwkt_switch_return(xtd);
1083 gd->gd_intr_nesting_level = save_gd_intr_nesting_level;
1085 KKASSERT(ntd->td_preempted && (td->td_flags & TDF_PREEMPT_DONE));
1086 ntd->td_preempted = NULL;
1087 td->td_flags &= ~(TDF_PREEMPT_LOCK|TDF_PREEMPT_DONE);
1091 * Conditionally call splz() if gd_reqflags indicates work is pending.
1092 * This will work inside a critical section but not inside a hard code
1095 * (self contained on a per cpu basis)
1100 globaldata_t gd = mycpu;
1101 thread_t td = gd->gd_curthread;
1103 if ((gd->gd_reqflags & RQF_IDLECHECK_MASK) &&
1104 gd->gd_intr_nesting_level == 0 &&
1105 td->td_nest_count < 2)
1112 * This version is integrated into crit_exit, reqflags has already
1113 * been tested but td_critcount has not.
1115 * We only want to execute the splz() on the 1->0 transition of
1116 * critcount and not in a hard code section or if too deeply nested.
1119 lwkt_maybe_splz(thread_t td)
1121 globaldata_t gd = td->td_gd;
1123 if (td->td_critcount == 0 &&
1124 gd->gd_intr_nesting_level == 0 &&
1125 td->td_nest_count < 2)
1132 * Drivers which set up processing co-threads can call this function to
1133 * run the co-thread at a higher priority and to allow it to preempt
1137 lwkt_set_interrupt_support_thread(void)
1139 thread_t td = curthread;
1141 lwkt_setpri_self(TDPRI_INT_SUPPORT);
1142 td->td_flags |= TDF_INTTHREAD;
1143 td->td_preemptable = lwkt_preempt;
1148 * This function is used to negotiate a passive release of the current
1149 * process/lwp designation with the user scheduler, allowing the user
1150 * scheduler to schedule another user thread. The related kernel thread
1151 * (curthread) continues running in the released state.
1154 lwkt_passive_release(struct thread *td)
1156 struct lwp *lp = td->td_lwp;
1158 td->td_release = NULL;
1159 lwkt_setpri_self(TDPRI_KERN_USER);
1160 lp->lwp_proc->p_usched->release_curproc(lp);
1165 * This implements a LWKT yield, allowing a kernel thread to yield to other
1166 * kernel threads at the same or higher priority. This function can be
1167 * called in a tight loop and will typically only yield once per tick.
1169 * Most kernel threads run at the same priority in order to allow equal
1172 * (self contained on a per cpu basis)
1177 globaldata_t gd = mycpu;
1178 thread_t td = gd->gd_curthread;
1180 if ((gd->gd_reqflags & RQF_IDLECHECK_MASK) && td->td_nest_count < 2)
1182 if (lwkt_resched_wanted()) {
1183 lwkt_schedule_self(curthread);
1189 * This yield is designed for kernel threads with a user context.
1191 * The kernel acting on behalf of the user is potentially cpu-bound,
1192 * this function will efficiently allow other threads to run and also
1193 * switch to other processes by releasing.
1195 * The lwkt_user_yield() function is designed to have very low overhead
1196 * if no yield is determined to be needed.
1199 lwkt_user_yield(void)
1201 globaldata_t gd = mycpu;
1202 thread_t td = gd->gd_curthread;
1205 * Always run any pending interrupts in case we are in a critical
1208 if ((gd->gd_reqflags & RQF_IDLECHECK_MASK) && td->td_nest_count < 2)
1212 * Switch (which forces a release) if another kernel thread needs
1213 * the cpu, if userland wants us to resched, or if our kernel
1214 * quantum has run out.
1216 if (lwkt_resched_wanted() ||
1217 user_resched_wanted())
1224 * Reacquire the current process if we are released.
1226 * XXX not implemented atm. The kernel may be holding locks and such,
1227 * so we want the thread to continue to receive cpu.
1229 if (td->td_release == NULL && lp) {
1230 lp->lwp_proc->p_usched->acquire_curproc(lp);
1231 td->td_release = lwkt_passive_release;
1232 lwkt_setpri_self(TDPRI_USER_NORM);
1238 * Generic schedule. Possibly schedule threads belonging to other cpus and
1239 * deal with threads that might be blocked on a wait queue.
1241 * We have a little helper inline function which does additional work after
1242 * the thread has been enqueued, including dealing with preemption and
1243 * setting need_lwkt_resched() (which prevents the kernel from returning
1244 * to userland until it has processed higher priority threads).
1246 * It is possible for this routine to be called after a failed _enqueue
1247 * (due to the target thread migrating, sleeping, or otherwise blocked).
1248 * We have to check that the thread is actually on the run queue!
1252 _lwkt_schedule_post(globaldata_t gd, thread_t ntd, int ccount)
1254 if (ntd->td_flags & TDF_RUNQ) {
1255 if (ntd->td_preemptable) {
1256 ntd->td_preemptable(ntd, ccount); /* YYY +token */
1263 _lwkt_schedule(thread_t td)
1265 globaldata_t mygd = mycpu;
1267 KASSERT(td != &td->td_gd->gd_idlethread,
1268 ("lwkt_schedule(): scheduling gd_idlethread is illegal!"));
1269 KKASSERT((td->td_flags & TDF_MIGRATING) == 0);
1270 crit_enter_gd(mygd);
1271 KKASSERT(td->td_lwp == NULL || (td->td_lwp->lwp_flag & LWP_ONRUNQ) == 0);
1272 if (td == mygd->gd_curthread) {
1276 * If we own the thread, there is no race (since we are in a
1277 * critical section). If we do not own the thread there might
1278 * be a race but the target cpu will deal with it.
1281 if (td->td_gd == mygd) {
1283 _lwkt_schedule_post(mygd, td, 1);
1285 lwkt_send_ipiq3(td->td_gd, lwkt_schedule_remote, td, 0);
1289 _lwkt_schedule_post(mygd, td, 1);
1296 lwkt_schedule(thread_t td)
1302 lwkt_schedule_noresched(thread_t td) /* XXX not impl */
1310 * When scheduled remotely if frame != NULL the IPIQ is being
1311 * run via doreti or an interrupt then preemption can be allowed.
1313 * To allow preemption we have to drop the critical section so only
1314 * one is present in _lwkt_schedule_post.
1317 lwkt_schedule_remote(void *arg, int arg2, struct intrframe *frame)
1319 thread_t td = curthread;
1322 if (frame && ntd->td_preemptable) {
1323 crit_exit_noyield(td);
1324 _lwkt_schedule(ntd);
1325 crit_enter_quick(td);
1327 _lwkt_schedule(ntd);
1332 * Thread migration using a 'Pull' method. The thread may or may not be
1333 * the current thread. It MUST be descheduled and in a stable state.
1334 * lwkt_giveaway() must be called on the cpu owning the thread.
1336 * At any point after lwkt_giveaway() is called, the target cpu may
1337 * 'pull' the thread by calling lwkt_acquire().
1339 * We have to make sure the thread is not sitting on a per-cpu tsleep
1340 * queue or it will blow up when it moves to another cpu.
1342 * MPSAFE - must be called under very specific conditions.
1345 lwkt_giveaway(thread_t td)
1347 globaldata_t gd = mycpu;
1350 if (td->td_flags & TDF_TSLEEPQ)
1352 KKASSERT(td->td_gd == gd);
1353 TAILQ_REMOVE(&gd->gd_tdallq, td, td_allq);
1354 td->td_flags |= TDF_MIGRATING;
1359 lwkt_acquire(thread_t td)
1363 int retry = 10000000;
1365 KKASSERT(td->td_flags & TDF_MIGRATING);
1370 KKASSERT((td->td_flags & TDF_RUNQ) == 0);
1371 crit_enter_gd(mygd);
1372 DEBUG_PUSH_INFO("lwkt_acquire");
1373 while (td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK)) {
1375 lwkt_process_ipiq();
1379 kprintf("lwkt_acquire: stuck: td %p td->td_flags %08x\n",
1387 TAILQ_INSERT_TAIL(&mygd->gd_tdallq, td, td_allq);
1388 td->td_flags &= ~TDF_MIGRATING;
1391 crit_enter_gd(mygd);
1392 TAILQ_INSERT_TAIL(&mygd->gd_tdallq, td, td_allq);
1393 td->td_flags &= ~TDF_MIGRATING;
1401 * Generic deschedule. Descheduling threads other then your own should be
1402 * done only in carefully controlled circumstances. Descheduling is
1405 * This function may block if the cpu has run out of messages.
1408 lwkt_deschedule(thread_t td)
1412 if (td == curthread) {
1415 if (td->td_gd == mycpu) {
1418 lwkt_send_ipiq(td->td_gd, (ipifunc1_t)lwkt_deschedule, td);
1428 * Set the target thread's priority. This routine does not automatically
1429 * switch to a higher priority thread, LWKT threads are not designed for
1430 * continuous priority changes. Yield if you want to switch.
1433 lwkt_setpri(thread_t td, int pri)
1435 if (td->td_pri != pri) {
1438 if (td->td_flags & TDF_RUNQ) {
1439 KKASSERT(td->td_gd == mycpu);
1451 * Set the initial priority for a thread prior to it being scheduled for
1452 * the first time. The thread MUST NOT be scheduled before or during
1453 * this call. The thread may be assigned to a cpu other then the current
1456 * Typically used after a thread has been created with TDF_STOPPREQ,
1457 * and before the thread is initially scheduled.
1460 lwkt_setpri_initial(thread_t td, int pri)
1463 KKASSERT((td->td_flags & TDF_RUNQ) == 0);
1468 lwkt_setpri_self(int pri)
1470 thread_t td = curthread;
1472 KKASSERT(pri >= 0 && pri <= TDPRI_MAX);
1474 if (td->td_flags & TDF_RUNQ) {
1485 * hz tick scheduler clock for LWKT threads
1488 lwkt_schedulerclock(thread_t td)
1490 globaldata_t gd = td->td_gd;
1493 if (TAILQ_FIRST(&gd->gd_tdrunq) == td) {
1495 * If the current thread is at the head of the runq shift it to the
1496 * end of any equal-priority threads and request a LWKT reschedule
1499 xtd = TAILQ_NEXT(td, td_threadq);
1500 if (xtd && xtd->td_pri == td->td_pri) {
1501 TAILQ_REMOVE(&gd->gd_tdrunq, td, td_threadq);
1502 while (xtd && xtd->td_pri == td->td_pri)
1503 xtd = TAILQ_NEXT(xtd, td_threadq);
1505 TAILQ_INSERT_BEFORE(xtd, td, td_threadq);
1507 TAILQ_INSERT_TAIL(&gd->gd_tdrunq, td, td_threadq);
1508 need_lwkt_resched();
1512 * If we scheduled a thread other than the one at the head of the
1513 * queue always request a reschedule every tick.
1515 need_lwkt_resched();
1520 * Migrate the current thread to the specified cpu.
1522 * This is accomplished by descheduling ourselves from the current cpu
1523 * and setting td_migrate_gd. The lwkt_switch() code will detect that the
1524 * 'old' thread wants to migrate after it has been completely switched out
1525 * and will complete the migration.
1527 * TDF_MIGRATING prevents scheduling races while the thread is being migrated.
1529 * We must be sure to release our current process designation (if a user
1530 * process) before clearing out any tsleepq we are on because the release
1531 * code may re-add us.
1533 * We must be sure to remove ourselves from the current cpu's tsleepq
1534 * before potentially moving to another queue. The thread can be on
1535 * a tsleepq due to a left-over tsleep_interlock().
1539 lwkt_setcpu_self(globaldata_t rgd)
1542 thread_t td = curthread;
1544 if (td->td_gd != rgd) {
1545 crit_enter_quick(td);
1549 if (td->td_flags & TDF_TSLEEPQ)
1553 * Set TDF_MIGRATING to prevent a spurious reschedule while we are
1554 * trying to deschedule ourselves and switch away, then deschedule
1555 * ourself, remove us from tdallq, and set td_migrate_gd. Finally,
1556 * call lwkt_switch() to complete the operation.
1558 td->td_flags |= TDF_MIGRATING;
1559 lwkt_deschedule_self(td);
1560 TAILQ_REMOVE(&td->td_gd->gd_tdallq, td, td_allq);
1561 td->td_migrate_gd = rgd;
1565 * We are now on the target cpu
1567 KKASSERT(rgd == mycpu);
1568 TAILQ_INSERT_TAIL(&rgd->gd_tdallq, td, td_allq);
1569 crit_exit_quick(td);
1575 lwkt_migratecpu(int cpuid)
1580 rgd = globaldata_find(cpuid);
1581 lwkt_setcpu_self(rgd);
1587 * Remote IPI for cpu migration (called while in a critical section so we
1588 * do not have to enter another one).
1590 * The thread (td) has already been completely descheduled from the
1591 * originating cpu and we can simply assert the case. The thread is
1592 * assigned to the new cpu and enqueued.
1594 * The thread will re-add itself to tdallq when it resumes execution.
1597 lwkt_setcpu_remote(void *arg)
1600 globaldata_t gd = mycpu;
1602 KKASSERT((td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK)) == 0);
1605 td->td_flags &= ~TDF_MIGRATING;
1606 KKASSERT(td->td_migrate_gd == NULL);
1607 KKASSERT(td->td_lwp == NULL || (td->td_lwp->lwp_flag & LWP_ONRUNQ) == 0);
1613 lwkt_preempted_proc(void)
1615 thread_t td = curthread;
1616 while (td->td_preempted)
1617 td = td->td_preempted;
1622 * Create a kernel process/thread/whatever. It shares it's address space
1623 * with proc0 - ie: kernel only.
1625 * If the cpu is not specified one will be selected. In the future
1626 * specifying a cpu of -1 will enable kernel thread migration between
1630 lwkt_create(void (*func)(void *), void *arg, struct thread **tdp,
1631 thread_t template, int tdflags, int cpu, const char *fmt, ...)
1636 td = lwkt_alloc_thread(template, LWKT_THREAD_STACK, cpu,
1640 cpu_set_thread_handler(td, lwkt_exit, func, arg);
1643 * Set up arg0 for 'ps' etc
1645 __va_start(ap, fmt);
1646 kvsnprintf(td->td_comm, sizeof(td->td_comm), fmt, ap);
1650 * Schedule the thread to run
1652 if ((td->td_flags & TDF_STOPREQ) == 0)
1655 td->td_flags &= ~TDF_STOPREQ;
1660 * Destroy an LWKT thread. Warning! This function is not called when
1661 * a process exits, cpu_proc_exit() directly calls cpu_thread_exit() and
1662 * uses a different reaping mechanism.
1667 thread_t td = curthread;
1672 * Do any cleanup that might block here
1674 if (td->td_flags & TDF_VERBOSE)
1675 kprintf("kthread %p %s has exited\n", td, td->td_comm);
1678 dsched_exit_thread(td);
1681 * Get us into a critical section to interlock gd_freetd and loop
1682 * until we can get it freed.
1684 * We have to cache the current td in gd_freetd because objcache_put()ing
1685 * it would rip it out from under us while our thread is still active.
1688 crit_enter_quick(td);
1689 while ((std = gd->gd_freetd) != NULL) {
1690 KKASSERT((std->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK)) == 0);
1691 gd->gd_freetd = NULL;
1692 objcache_put(thread_cache, std);
1696 * Remove thread resources from kernel lists and deschedule us for
1697 * the last time. We cannot block after this point or we may end
1698 * up with a stale td on the tsleepq.
1700 if (td->td_flags & TDF_TSLEEPQ)
1702 lwkt_deschedule_self(td);
1703 lwkt_remove_tdallq(td);
1704 KKASSERT(td->td_refs == 0);
1709 KKASSERT(gd->gd_freetd == NULL);
1710 if (td->td_flags & TDF_ALLOCATED_THREAD)
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.
1735 crit_exit_wrapper(__DEBUG_CRIT_ARG__)
1737 _crit_exit(mycpu __DEBUG_CRIT_PASS_ARG__);
1743 thread_t td = curthread;
1744 int lcrit = td->td_critcount;
1746 td->td_critcount = 0;
1747 panic("td_critcount is/would-go negative! %p %d", td, lcrit);
1754 * Called from debugger/panic on cpus which have been stopped. We must still
1755 * process the IPIQ while stopped, even if we were stopped while in a critical
1758 * If we are dumping also try to process any pending interrupts. This may
1759 * or may not work depending on the state of the cpu at the point it was
1763 lwkt_smp_stopped(void)
1765 globaldata_t gd = mycpu;
1769 lwkt_process_ipiq();
1772 lwkt_process_ipiq();