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;
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);
312 * Initialize the lwkt s/system.
314 * Nominally cache up to 32 thread + kstack structures.
319 TUNABLE_INT("lwkt.cache_threads", &lwkt_cache_threads);
320 thread_cache = objcache_create_mbacked(
321 M_THREAD, sizeof(struct thread),
322 NULL, lwkt_cache_threads,
323 _lwkt_thread_ctor, _lwkt_thread_dtor, NULL);
327 * Schedule a thread to run. As the current thread we can always safely
328 * schedule ourselves, and a shortcut procedure is provided for that
331 * (non-blocking, self contained on a per cpu basis)
334 lwkt_schedule_self(thread_t td)
336 KKASSERT((td->td_flags & TDF_MIGRATING) == 0);
337 crit_enter_quick(td);
338 KASSERT(td != &td->td_gd->gd_idlethread,
339 ("lwkt_schedule_self(): scheduling gd_idlethread is illegal!"));
340 KKASSERT(td->td_lwp == NULL ||
341 (td->td_lwp->lwp_mpflags & LWP_MP_ONRUNQ) == 0);
347 * Deschedule a thread.
349 * (non-blocking, self contained on a per cpu basis)
352 lwkt_deschedule_self(thread_t td)
354 crit_enter_quick(td);
360 * LWKTs operate on a per-cpu basis
362 * WARNING! Called from early boot, 'mycpu' may not work yet.
365 lwkt_gdinit(struct globaldata *gd)
367 TAILQ_INIT(&gd->gd_tdrunq);
368 TAILQ_INIT(&gd->gd_tdallq);
372 * Create a new thread. The thread must be associated with a process context
373 * or LWKT start address before it can be scheduled. If the target cpu is
374 * -1 the thread will be created on the current cpu.
376 * If you intend to create a thread without a process context this function
377 * does everything except load the startup and switcher function.
380 lwkt_alloc_thread(struct thread *td, int stksize, int cpu, int flags)
382 static int cpu_rotator;
383 globaldata_t gd = mycpu;
387 * If static thread storage is not supplied allocate a thread. Reuse
388 * a cached free thread if possible. gd_freetd is used to keep an exiting
389 * thread intact through the exit.
393 if ((td = gd->gd_freetd) != NULL) {
394 KKASSERT((td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK|
396 gd->gd_freetd = NULL;
398 td = objcache_get(thread_cache, M_WAITOK);
399 KKASSERT((td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK|
403 KASSERT((td->td_flags &
404 (TDF_ALLOCATED_THREAD|TDF_RUNNING|TDF_PREEMPT_LOCK)) ==
405 TDF_ALLOCATED_THREAD,
406 ("lwkt_alloc_thread: corrupted td flags 0x%X", td->td_flags));
407 flags |= td->td_flags & (TDF_ALLOCATED_THREAD|TDF_ALLOCATED_STACK);
411 * Try to reuse cached stack.
413 if ((stack = td->td_kstack) != NULL && td->td_kstack_size != stksize) {
414 if (flags & TDF_ALLOCATED_STACK) {
415 kmem_free(&kernel_map, (vm_offset_t)stack, td->td_kstack_size);
420 stack = (void *)kmem_alloc_stack(&kernel_map, stksize);
421 flags |= TDF_ALLOCATED_STACK;
428 lwkt_init_thread(td, stack, stksize, flags, globaldata_find(cpu));
433 * Initialize a preexisting thread structure. This function is used by
434 * lwkt_alloc_thread() and also used to initialize the per-cpu idlethread.
436 * All threads start out in a critical section at a priority of
437 * TDPRI_KERN_DAEMON. Higher level code will modify the priority as
438 * appropriate. This function may send an IPI message when the
439 * requested cpu is not the current cpu and consequently gd_tdallq may
440 * not be initialized synchronously from the point of view of the originating
443 * NOTE! we have to be careful in regards to creating threads for other cpus
444 * if SMP has not yet been activated.
449 lwkt_init_thread_remote(void *arg)
454 * Protected by critical section held by IPI dispatch
456 TAILQ_INSERT_TAIL(&td->td_gd->gd_tdallq, td, td_allq);
462 * lwkt core thread structural initialization.
464 * NOTE: All threads are initialized as mpsafe threads.
467 lwkt_init_thread(thread_t td, void *stack, int stksize, int flags,
468 struct globaldata *gd)
470 globaldata_t mygd = mycpu;
472 bzero(td, sizeof(struct thread));
473 td->td_kstack = stack;
474 td->td_kstack_size = stksize;
475 td->td_flags = flags;
478 td->td_pri = TDPRI_KERN_DAEMON;
479 td->td_critcount = 1;
480 td->td_toks_have = NULL;
481 td->td_toks_stop = &td->td_toks_base;
482 if (lwkt_use_spin_port || (flags & TDF_FORCE_SPINPORT))
483 lwkt_initport_spin(&td->td_msgport);
485 lwkt_initport_thread(&td->td_msgport, td);
486 pmap_init_thread(td);
489 * Normally initializing a thread for a remote cpu requires sending an
490 * IPI. However, the idlethread is setup before the other cpus are
491 * activated so we have to treat it as a special case. XXX manipulation
492 * of gd_tdallq requires the BGL.
494 if (gd == mygd || td == &gd->gd_idlethread) {
496 TAILQ_INSERT_TAIL(&gd->gd_tdallq, td, td_allq);
499 lwkt_send_ipiq(gd, lwkt_init_thread_remote, td);
503 TAILQ_INSERT_TAIL(&gd->gd_tdallq, td, td_allq);
507 dsched_new_thread(td);
511 lwkt_set_comm(thread_t td, const char *ctl, ...)
516 kvsnprintf(td->td_comm, sizeof(td->td_comm), ctl, va);
518 KTR_LOG(ctxsw_newtd, td, &td->td_comm[0]);
522 * Prevent the thread from getting destroyed. Note that unlike PHOLD/PRELE
523 * this does not prevent the thread from migrating to another cpu so the
524 * gd_tdallq state is not protected by this.
527 lwkt_hold(thread_t td)
529 atomic_add_int(&td->td_refs, 1);
533 lwkt_rele(thread_t td)
535 KKASSERT(td->td_refs > 0);
536 atomic_add_int(&td->td_refs, -1);
540 lwkt_free_thread(thread_t td)
542 KKASSERT(td->td_refs == 0);
543 KKASSERT((td->td_flags & (TDF_RUNNING | TDF_PREEMPT_LOCK |
544 TDF_RUNQ | TDF_TSLEEPQ)) == 0);
545 if (td->td_flags & TDF_ALLOCATED_THREAD) {
546 objcache_put(thread_cache, td);
547 } else if (td->td_flags & TDF_ALLOCATED_STACK) {
548 /* client-allocated struct with internally allocated stack */
549 KASSERT(td->td_kstack && td->td_kstack_size > 0,
550 ("lwkt_free_thread: corrupted stack"));
551 kmem_free(&kernel_map, (vm_offset_t)td->td_kstack, td->td_kstack_size);
552 td->td_kstack = NULL;
553 td->td_kstack_size = 0;
555 KTR_LOG(ctxsw_deadtd, td);
560 * Switch to the next runnable lwkt. If no LWKTs are runnable then
561 * switch to the idlethread. Switching must occur within a critical
562 * section to avoid races with the scheduling queue.
564 * We always have full control over our cpu's run queue. Other cpus
565 * that wish to manipulate our queue must use the cpu_*msg() calls to
566 * talk to our cpu, so a critical section is all that is needed and
567 * the result is very, very fast thread switching.
569 * The LWKT scheduler uses a fixed priority model and round-robins at
570 * each priority level. User process scheduling is a totally
571 * different beast and LWKT priorities should not be confused with
572 * user process priorities.
574 * PREEMPTION NOTE: Preemption occurs via lwkt_preempt(). lwkt_switch()
575 * is not called by the current thread in the preemption case, only when
576 * the preempting thread blocks (in order to return to the original thread).
578 * SPECIAL NOTE ON SWITCH ATOMICY: Certain operations such as thread
579 * migration and tsleep deschedule the current lwkt thread and call
580 * lwkt_switch(). In particular, the target cpu of the migration fully
581 * expects the thread to become non-runnable and can deadlock against
582 * cpusync operations if we run any IPIs prior to switching the thread out.
584 * WE MUST BE VERY CAREFUL NOT TO RUN SPLZ DIRECTLY OR INDIRECTLY IF
585 * THE CURRENT THREAD HAS BEEN DESCHEDULED!
590 globaldata_t gd = mycpu;
591 thread_t td = gd->gd_curthread;
596 KKASSERT(gd->gd_processing_ipiq == 0);
599 * Switching from within a 'fast' (non thread switched) interrupt or IPI
600 * is illegal. However, we may have to do it anyway if we hit a fatal
601 * kernel trap or we have paniced.
603 * If this case occurs save and restore the interrupt nesting level.
605 if (gd->gd_intr_nesting_level) {
609 if (gd->gd_trap_nesting_level == 0 && panic_cpu_gd != mycpu) {
610 panic("lwkt_switch: Attempt to switch from a "
611 "a fast interrupt, ipi, or hard code section, "
615 savegdnest = gd->gd_intr_nesting_level;
616 savegdtrap = gd->gd_trap_nesting_level;
617 gd->gd_intr_nesting_level = 0;
618 gd->gd_trap_nesting_level = 0;
619 if ((td->td_flags & TDF_PANICWARN) == 0) {
620 td->td_flags |= TDF_PANICWARN;
621 kprintf("Warning: thread switch from interrupt, IPI, "
622 "or hard code section.\n"
623 "thread %p (%s)\n", td, td->td_comm);
627 gd->gd_intr_nesting_level = savegdnest;
628 gd->gd_trap_nesting_level = savegdtrap;
634 * Release our current user process designation if we are blocking
635 * or if a user reschedule was requested.
637 * NOTE: This function is NOT called if we are switching into or
638 * returning from a preemption.
640 * NOTE: Releasing our current user process designation may cause
641 * it to be assigned to another thread, which in turn will
642 * cause us to block in the usched acquire code when we attempt
643 * to return to userland.
645 * NOTE: On SMP systems this can be very nasty when heavy token
646 * contention is present so we want to be careful not to
647 * release the designation gratuitously.
649 if (td->td_release &&
650 (user_resched_wanted() || (td->td_flags & TDF_RUNQ) == 0)) {
658 if (TD_TOKS_HELD(td))
659 lwkt_relalltokens(td);
662 * We had better not be holding any spin locks, but don't get into an
663 * endless panic loop.
665 KASSERT(gd->gd_spinlocks_wr == 0 || panicstr != NULL,
666 ("lwkt_switch: still holding %d exclusive spinlocks!",
667 gd->gd_spinlocks_wr));
672 if (td->td_cscount) {
673 kprintf("Diagnostic: attempt to switch while mastering cpusync: %p\n",
675 if (panic_on_cscount)
676 panic("switching while mastering cpusync");
682 * If we had preempted another thread on this cpu, resume the preempted
683 * thread. This occurs transparently, whether the preempted thread
684 * was scheduled or not (it may have been preempted after descheduling
687 * We have to setup the MP lock for the original thread after backing
688 * out the adjustment that was made to curthread when the original
691 if ((ntd = td->td_preempted) != NULL) {
692 KKASSERT(ntd->td_flags & TDF_PREEMPT_LOCK);
693 ntd->td_flags |= TDF_PREEMPT_DONE;
696 * The interrupt may have woken a thread up, we need to properly
697 * set the reschedule flag if the originally interrupted thread is
698 * at a lower priority.
700 * The interrupt may not have descheduled.
702 if (TAILQ_FIRST(&gd->gd_tdrunq) != ntd)
704 goto havethread_preempted;
708 * If we cannot obtain ownership of the tokens we cannot immediately
709 * schedule the target thread.
711 * Reminder: Again, we cannot afford to run any IPIs in this path if
712 * the current thread has been descheduled.
715 clear_lwkt_resched();
718 * Hotpath - pull the head of the run queue and attempt to schedule
722 ntd = TAILQ_FIRST(&gd->gd_tdrunq);
726 * Runq is empty, switch to idle to allow it to halt.
728 ntd = &gd->gd_idlethread;
730 if (gd->gd_trap_nesting_level == 0 && panicstr == NULL)
731 ASSERT_NO_TOKENS_HELD(ntd);
733 cpu_time.cp_msg[0] = 0;
734 cpu_time.cp_stallpc = 0;
741 * Hotpath - schedule ntd.
743 * NOTE: For UP there is no mplock and lwkt_getalltokens()
746 if (TD_TOKS_NOT_HELD(ntd) ||
747 lwkt_getalltokens(ntd, (spinning >= lwkt_spin_loops)))
753 * Coldpath (SMP only since tokens always succeed on UP)
755 * We had some contention on the thread we wanted to schedule.
756 * What we do now is try to find a thread that we can schedule
759 * The coldpath scan does NOT rearrange threads in the run list.
760 * The lwkt_schedulerclock() will assert need_lwkt_resched() on
761 * the next tick whenever the current head is not the current thread.
764 ++token_contention_count[ntd->td_pri];
768 if (fairq_bypass > 0)
772 while ((ntd = TAILQ_NEXT(ntd, td_threadq)) != NULL) {
774 * Never schedule threads returning to userland or the
775 * user thread scheduler helper thread when higher priority
776 * threads are present.
778 if (ntd->td_pri < TDPRI_KERN_LPSCHED) {
786 if (TD_TOKS_NOT_HELD(ntd) ||
787 lwkt_getalltokens(ntd, (spinning >= lwkt_spin_loops))) {
791 ++token_contention_count[ntd->td_pri];
798 * We exhausted the run list, meaning that all runnable threads
802 ntd = &gd->gd_idlethread;
804 if (gd->gd_trap_nesting_level == 0 && panicstr == NULL)
805 ASSERT_NO_TOKENS_HELD(ntd);
806 /* contention case, do not clear contention mask */
810 * We are going to have to retry but if the current thread is not
811 * on the runq we instead switch through the idle thread to get away
812 * from the current thread. We have to flag for lwkt reschedule
813 * to prevent the idle thread from halting.
815 * NOTE: A non-zero spinning is passed to lwkt_getalltokens() to
816 * instruct it to deal with the potential for deadlocks by
817 * ordering the tokens by address.
819 if ((td->td_flags & TDF_RUNQ) == 0) {
820 need_lwkt_resched(); /* prevent hlt */
823 #if defined(INVARIANTS) && defined(__amd64__)
824 if ((read_rflags() & PSL_I) == 0) {
826 panic("lwkt_switch() called with interrupts disabled");
831 * Number iterations so far. After a certain point we switch to
832 * a sorted-address/monitor/mwait version of lwkt_getalltokens()
834 if (spinning < 0x7FFFFFFF)
839 * lwkt_getalltokens() failed in sorted token mode, we can use
840 * monitor/mwait in this case.
842 if (spinning >= lwkt_spin_loops &&
843 (cpu_mi_feature & CPU_MI_MONITOR) &&
846 cpu_mmw_pause_int(&gd->gd_reqflags,
847 (gd->gd_reqflags | RQF_SPINNING) &
848 ~RQF_IDLECHECK_WK_MASK);
853 * We already checked that td is still scheduled so this should be
859 * This experimental resequencer is used as a fall-back to reduce
860 * hw cache line contention by placing each core's scheduler into a
861 * time-domain-multplexed slot.
863 * The resequencer is disabled by default. It's functionality has
864 * largely been superceeded by the token algorithm which limits races
865 * to a subset of cores.
867 * The resequencer algorithm tends to break down when more than
868 * 20 cores are contending. What appears to happen is that new
869 * tokens can be obtained out of address-sorted order by new cores
870 * while existing cores languish in long delays between retries and
871 * wind up being starved-out of the token acquisition.
873 if (lwkt_spin_reseq && spinning >= lwkt_spin_reseq) {
874 int cseq = atomic_fetchadd_int(&lwkt_cseq_windex, 1);
877 while ((oseq = lwkt_cseq_rindex) != cseq) {
880 if (cpu_mi_feature & CPU_MI_MONITOR) {
881 cpu_mmw_pause_int(&lwkt_cseq_rindex, oseq);
891 atomic_add_int(&lwkt_cseq_rindex, 1);
893 /* highest level for(;;) loop */
898 * Clear gd_idle_repeat when doing a normal switch to a non-idle
901 ntd->td_wmesg = NULL;
902 ++gd->gd_cnt.v_swtch;
903 gd->gd_idle_repeat = 0;
905 havethread_preempted:
907 * If the new target does not need the MP lock and we are holding it,
908 * release the MP lock. If the new target requires the MP lock we have
909 * already acquired it for the target.
913 KASSERT(ntd->td_critcount,
914 ("priority problem in lwkt_switch %d %d",
915 td->td_critcount, ntd->td_critcount));
919 * Execute the actual thread switch operation. This function
920 * returns to the current thread and returns the previous thread
921 * (which may be different from the thread we switched to).
923 * We are responsible for marking ntd as TDF_RUNNING.
926 KTR_LOG(ctxsw_sw, gd->gd_cpuid, ntd);
927 ntd->td_flags |= TDF_RUNNING;
928 lwkt_switch_return(td->td_switch(ntd));
929 /* ntd invalid, td_switch() can return a different thread_t */
933 * catch-all. XXX is this strictly needed?
937 /* NOTE: current cpu may have changed after switch */
942 * Called by assembly in the td_switch (thread restore path) for thread
943 * bootstrap cases which do not 'return' to lwkt_switch().
946 lwkt_switch_return(thread_t otd)
952 * Check if otd was migrating. Now that we are on ntd we can finish
953 * up the migration. This is a bit messy but it is the only place
954 * where td is known to be fully descheduled.
956 * We can only activate the migration if otd was migrating but not
957 * held on the cpu due to a preemption chain. We still have to
958 * clear TDF_RUNNING on the old thread either way.
960 * We are responsible for clearing the previously running thread's
963 if ((rgd = otd->td_migrate_gd) != NULL &&
964 (otd->td_flags & TDF_PREEMPT_LOCK) == 0) {
965 KKASSERT((otd->td_flags & (TDF_MIGRATING | TDF_RUNNING)) ==
966 (TDF_MIGRATING | TDF_RUNNING));
967 otd->td_migrate_gd = NULL;
968 otd->td_flags &= ~TDF_RUNNING;
969 lwkt_send_ipiq(rgd, lwkt_setcpu_remote, otd);
971 otd->td_flags &= ~TDF_RUNNING;
974 otd->td_flags &= ~TDF_RUNNING;
979 * Request that the target thread preempt the current thread. Preemption
980 * can only occur if our only critical section is the one that we were called
981 * with, the relative priority of the target thread is higher, and the target
982 * thread holds no tokens. This also only works if we are not holding any
983 * spinlocks (obviously).
985 * THE CALLER OF LWKT_PREEMPT() MUST BE IN A CRITICAL SECTION. Typically
986 * this is called via lwkt_schedule() through the td_preemptable callback.
987 * critcount is the managed critical priority that we should ignore in order
988 * to determine whether preemption is possible (aka usually just the crit
989 * priority of lwkt_schedule() itself).
991 * Preemption is typically limited to interrupt threads.
993 * Operation works in a fairly straight-forward manner. The normal
994 * scheduling code is bypassed and we switch directly to the target
995 * thread. When the target thread attempts to block or switch away
996 * code at the base of lwkt_switch() will switch directly back to our
997 * thread. Our thread is able to retain whatever tokens it holds and
998 * if the target needs one of them the target will switch back to us
999 * and reschedule itself normally.
1002 lwkt_preempt(thread_t ntd, int critcount)
1004 struct globaldata *gd = mycpu;
1007 int save_gd_intr_nesting_level;
1010 * The caller has put us in a critical section. We can only preempt
1011 * if the caller of the caller was not in a critical section (basically
1012 * a local interrupt), as determined by the 'critcount' parameter. We
1013 * also can't preempt if the caller is holding any spinlocks (even if
1014 * he isn't in a critical section). This also handles the tokens test.
1016 * YYY The target thread must be in a critical section (else it must
1017 * inherit our critical section? I dunno yet).
1019 KASSERT(ntd->td_critcount, ("BADCRIT0 %d", ntd->td_pri));
1021 td = gd->gd_curthread;
1022 if (preempt_enable == 0) {
1026 if (ntd->td_pri <= td->td_pri) {
1030 if (td->td_critcount > critcount) {
1035 if (ntd->td_gd != gd) {
1041 * We don't have to check spinlocks here as they will also bump
1044 * Do not try to preempt if the target thread is holding any tokens.
1045 * We could try to acquire the tokens but this case is so rare there
1046 * is no need to support it.
1048 KKASSERT(gd->gd_spinlocks_wr == 0);
1050 if (TD_TOKS_HELD(ntd)) {
1054 if (td == ntd || ((td->td_flags | ntd->td_flags) & TDF_PREEMPT_LOCK)) {
1058 if (ntd->td_preempted) {
1062 KKASSERT(gd->gd_processing_ipiq == 0);
1065 * Since we are able to preempt the current thread, there is no need to
1066 * call need_lwkt_resched().
1068 * We must temporarily clear gd_intr_nesting_level around the switch
1069 * since switchouts from the target thread are allowed (they will just
1070 * return to our thread), and since the target thread has its own stack.
1072 * A preemption must switch back to the original thread, assert the
1076 ntd->td_preempted = td;
1077 td->td_flags |= TDF_PREEMPT_LOCK;
1078 KTR_LOG(ctxsw_pre, gd->gd_cpuid, ntd);
1079 save_gd_intr_nesting_level = gd->gd_intr_nesting_level;
1080 gd->gd_intr_nesting_level = 0;
1081 ntd->td_flags |= TDF_RUNNING;
1082 xtd = td->td_switch(ntd);
1083 KKASSERT(xtd == ntd);
1084 lwkt_switch_return(xtd);
1085 gd->gd_intr_nesting_level = save_gd_intr_nesting_level;
1087 KKASSERT(ntd->td_preempted && (td->td_flags & TDF_PREEMPT_DONE));
1088 ntd->td_preempted = NULL;
1089 td->td_flags &= ~(TDF_PREEMPT_LOCK|TDF_PREEMPT_DONE);
1093 * Conditionally call splz() if gd_reqflags indicates work is pending.
1094 * This will work inside a critical section but not inside a hard code
1097 * (self contained on a per cpu basis)
1102 globaldata_t gd = mycpu;
1103 thread_t td = gd->gd_curthread;
1105 if ((gd->gd_reqflags & RQF_IDLECHECK_MASK) &&
1106 gd->gd_intr_nesting_level == 0 &&
1107 td->td_nest_count < 2)
1114 * This version is integrated into crit_exit, reqflags has already
1115 * been tested but td_critcount has not.
1117 * We only want to execute the splz() on the 1->0 transition of
1118 * critcount and not in a hard code section or if too deeply nested.
1121 lwkt_maybe_splz(thread_t td)
1123 globaldata_t gd = td->td_gd;
1125 if (td->td_critcount == 0 &&
1126 gd->gd_intr_nesting_level == 0 &&
1127 td->td_nest_count < 2)
1134 * Drivers which set up processing co-threads can call this function to
1135 * run the co-thread at a higher priority and to allow it to preempt
1139 lwkt_set_interrupt_support_thread(void)
1141 thread_t td = curthread;
1143 lwkt_setpri_self(TDPRI_INT_SUPPORT);
1144 td->td_flags |= TDF_INTTHREAD;
1145 td->td_preemptable = lwkt_preempt;
1150 * This function is used to negotiate a passive release of the current
1151 * process/lwp designation with the user scheduler, allowing the user
1152 * scheduler to schedule another user thread. The related kernel thread
1153 * (curthread) continues running in the released state.
1156 lwkt_passive_release(struct thread *td)
1158 struct lwp *lp = td->td_lwp;
1160 td->td_release = NULL;
1161 lwkt_setpri_self(TDPRI_KERN_USER);
1162 lp->lwp_proc->p_usched->release_curproc(lp);
1167 * This implements a LWKT yield, allowing a kernel thread to yield to other
1168 * kernel threads at the same or higher priority. This function can be
1169 * called in a tight loop and will typically only yield once per tick.
1171 * Most kernel threads run at the same priority in order to allow equal
1174 * (self contained on a per cpu basis)
1179 globaldata_t gd = mycpu;
1180 thread_t td = gd->gd_curthread;
1182 if ((gd->gd_reqflags & RQF_IDLECHECK_MASK) && td->td_nest_count < 2)
1184 if (lwkt_resched_wanted()) {
1185 lwkt_schedule_self(curthread);
1191 * This yield is designed for kernel threads with a user context.
1193 * The kernel acting on behalf of the user is potentially cpu-bound,
1194 * this function will efficiently allow other threads to run and also
1195 * switch to other processes by releasing.
1197 * The lwkt_user_yield() function is designed to have very low overhead
1198 * if no yield is determined to be needed.
1201 lwkt_user_yield(void)
1203 globaldata_t gd = mycpu;
1204 thread_t td = gd->gd_curthread;
1207 * Always run any pending interrupts in case we are in a critical
1210 if ((gd->gd_reqflags & RQF_IDLECHECK_MASK) && td->td_nest_count < 2)
1214 * Switch (which forces a release) if another kernel thread needs
1215 * the cpu, if userland wants us to resched, or if our kernel
1216 * quantum has run out.
1218 if (lwkt_resched_wanted() ||
1219 user_resched_wanted())
1226 * Reacquire the current process if we are released.
1228 * XXX not implemented atm. The kernel may be holding locks and such,
1229 * so we want the thread to continue to receive cpu.
1231 if (td->td_release == NULL && lp) {
1232 lp->lwp_proc->p_usched->acquire_curproc(lp);
1233 td->td_release = lwkt_passive_release;
1234 lwkt_setpri_self(TDPRI_USER_NORM);
1240 * Generic schedule. Possibly schedule threads belonging to other cpus and
1241 * deal with threads that might be blocked on a wait queue.
1243 * We have a little helper inline function which does additional work after
1244 * the thread has been enqueued, including dealing with preemption and
1245 * setting need_lwkt_resched() (which prevents the kernel from returning
1246 * to userland until it has processed higher priority threads).
1248 * It is possible for this routine to be called after a failed _enqueue
1249 * (due to the target thread migrating, sleeping, or otherwise blocked).
1250 * We have to check that the thread is actually on the run queue!
1254 _lwkt_schedule_post(globaldata_t gd, thread_t ntd, int ccount)
1256 if (ntd->td_flags & TDF_RUNQ) {
1257 if (ntd->td_preemptable) {
1258 ntd->td_preemptable(ntd, ccount); /* YYY +token */
1265 _lwkt_schedule(thread_t td)
1267 globaldata_t mygd = mycpu;
1269 KASSERT(td != &td->td_gd->gd_idlethread,
1270 ("lwkt_schedule(): scheduling gd_idlethread is illegal!"));
1271 KKASSERT((td->td_flags & TDF_MIGRATING) == 0);
1272 crit_enter_gd(mygd);
1273 KKASSERT(td->td_lwp == NULL ||
1274 (td->td_lwp->lwp_mpflags & LWP_MP_ONRUNQ) == 0);
1276 if (td == mygd->gd_curthread) {
1280 * If we own the thread, there is no race (since we are in a
1281 * critical section). If we do not own the thread there might
1282 * be a race but the target cpu will deal with it.
1285 if (td->td_gd == mygd) {
1287 _lwkt_schedule_post(mygd, td, 1);
1289 lwkt_send_ipiq3(td->td_gd, lwkt_schedule_remote, td, 0);
1293 _lwkt_schedule_post(mygd, td, 1);
1300 lwkt_schedule(thread_t td)
1306 lwkt_schedule_noresched(thread_t td) /* XXX not impl */
1314 * When scheduled remotely if frame != NULL the IPIQ is being
1315 * run via doreti or an interrupt then preemption can be allowed.
1317 * To allow preemption we have to drop the critical section so only
1318 * one is present in _lwkt_schedule_post.
1321 lwkt_schedule_remote(void *arg, int arg2, struct intrframe *frame)
1323 thread_t td = curthread;
1326 if (frame && ntd->td_preemptable) {
1327 crit_exit_noyield(td);
1328 _lwkt_schedule(ntd);
1329 crit_enter_quick(td);
1331 _lwkt_schedule(ntd);
1336 * Thread migration using a 'Pull' method. The thread may or may not be
1337 * the current thread. It MUST be descheduled and in a stable state.
1338 * lwkt_giveaway() must be called on the cpu owning the thread.
1340 * At any point after lwkt_giveaway() is called, the target cpu may
1341 * 'pull' the thread by calling lwkt_acquire().
1343 * We have to make sure the thread is not sitting on a per-cpu tsleep
1344 * queue or it will blow up when it moves to another cpu.
1346 * MPSAFE - must be called under very specific conditions.
1349 lwkt_giveaway(thread_t td)
1351 globaldata_t gd = mycpu;
1354 if (td->td_flags & TDF_TSLEEPQ)
1356 KKASSERT(td->td_gd == gd);
1357 TAILQ_REMOVE(&gd->gd_tdallq, td, td_allq);
1358 td->td_flags |= TDF_MIGRATING;
1363 lwkt_acquire(thread_t td)
1367 int retry = 10000000;
1369 KKASSERT(td->td_flags & TDF_MIGRATING);
1374 KKASSERT((td->td_flags & TDF_RUNQ) == 0);
1375 crit_enter_gd(mygd);
1376 DEBUG_PUSH_INFO("lwkt_acquire");
1377 while (td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK)) {
1379 lwkt_process_ipiq();
1383 kprintf("lwkt_acquire: stuck: td %p td->td_flags %08x\n",
1391 TAILQ_INSERT_TAIL(&mygd->gd_tdallq, td, td_allq);
1392 td->td_flags &= ~TDF_MIGRATING;
1395 crit_enter_gd(mygd);
1396 TAILQ_INSERT_TAIL(&mygd->gd_tdallq, td, td_allq);
1397 td->td_flags &= ~TDF_MIGRATING;
1405 * Generic deschedule. Descheduling threads other then your own should be
1406 * done only in carefully controlled circumstances. Descheduling is
1409 * This function may block if the cpu has run out of messages.
1412 lwkt_deschedule(thread_t td)
1416 if (td == curthread) {
1419 if (td->td_gd == mycpu) {
1422 lwkt_send_ipiq(td->td_gd, (ipifunc1_t)lwkt_deschedule, td);
1432 * Set the target thread's priority. This routine does not automatically
1433 * switch to a higher priority thread, LWKT threads are not designed for
1434 * continuous priority changes. Yield if you want to switch.
1437 lwkt_setpri(thread_t td, int pri)
1439 if (td->td_pri != pri) {
1442 if (td->td_flags & TDF_RUNQ) {
1443 KKASSERT(td->td_gd == mycpu);
1455 * Set the initial priority for a thread prior to it being scheduled for
1456 * the first time. The thread MUST NOT be scheduled before or during
1457 * this call. The thread may be assigned to a cpu other then the current
1460 * Typically used after a thread has been created with TDF_STOPPREQ,
1461 * and before the thread is initially scheduled.
1464 lwkt_setpri_initial(thread_t td, int pri)
1467 KKASSERT((td->td_flags & TDF_RUNQ) == 0);
1472 lwkt_setpri_self(int pri)
1474 thread_t td = curthread;
1476 KKASSERT(pri >= 0 && pri <= TDPRI_MAX);
1478 if (td->td_flags & TDF_RUNQ) {
1489 * hz tick scheduler clock for LWKT threads
1492 lwkt_schedulerclock(thread_t td)
1494 globaldata_t gd = td->td_gd;
1497 if (TAILQ_FIRST(&gd->gd_tdrunq) == td) {
1499 * If the current thread is at the head of the runq shift it to the
1500 * end of any equal-priority threads and request a LWKT reschedule
1503 xtd = TAILQ_NEXT(td, td_threadq);
1504 if (xtd && xtd->td_pri == td->td_pri) {
1505 TAILQ_REMOVE(&gd->gd_tdrunq, td, td_threadq);
1506 while (xtd && xtd->td_pri == td->td_pri)
1507 xtd = TAILQ_NEXT(xtd, td_threadq);
1509 TAILQ_INSERT_BEFORE(xtd, td, td_threadq);
1511 TAILQ_INSERT_TAIL(&gd->gd_tdrunq, td, td_threadq);
1512 need_lwkt_resched();
1516 * If we scheduled a thread other than the one at the head of the
1517 * queue always request a reschedule every tick.
1519 need_lwkt_resched();
1524 * Migrate the current thread to the specified cpu.
1526 * This is accomplished by descheduling ourselves from the current cpu
1527 * and setting td_migrate_gd. The lwkt_switch() code will detect that the
1528 * 'old' thread wants to migrate after it has been completely switched out
1529 * and will complete the migration.
1531 * TDF_MIGRATING prevents scheduling races while the thread is being migrated.
1533 * We must be sure to release our current process designation (if a user
1534 * process) before clearing out any tsleepq we are on because the release
1535 * code may re-add us.
1537 * We must be sure to remove ourselves from the current cpu's tsleepq
1538 * before potentially moving to another queue. The thread can be on
1539 * a tsleepq due to a left-over tsleep_interlock().
1543 lwkt_setcpu_self(globaldata_t rgd)
1546 thread_t td = curthread;
1548 if (td->td_gd != rgd) {
1549 crit_enter_quick(td);
1553 if (td->td_flags & TDF_TSLEEPQ)
1557 * Set TDF_MIGRATING to prevent a spurious reschedule while we are
1558 * trying to deschedule ourselves and switch away, then deschedule
1559 * ourself, remove us from tdallq, and set td_migrate_gd. Finally,
1560 * call lwkt_switch() to complete the operation.
1562 td->td_flags |= TDF_MIGRATING;
1563 lwkt_deschedule_self(td);
1564 TAILQ_REMOVE(&td->td_gd->gd_tdallq, td, td_allq);
1565 td->td_migrate_gd = rgd;
1569 * We are now on the target cpu
1571 KKASSERT(rgd == mycpu);
1572 TAILQ_INSERT_TAIL(&rgd->gd_tdallq, td, td_allq);
1573 crit_exit_quick(td);
1579 lwkt_migratecpu(int cpuid)
1584 rgd = globaldata_find(cpuid);
1585 lwkt_setcpu_self(rgd);
1591 * Remote IPI for cpu migration (called while in a critical section so we
1592 * do not have to enter another one).
1594 * The thread (td) has already been completely descheduled from the
1595 * originating cpu and we can simply assert the case. The thread is
1596 * assigned to the new cpu and enqueued.
1598 * The thread will re-add itself to tdallq when it resumes execution.
1601 lwkt_setcpu_remote(void *arg)
1604 globaldata_t gd = mycpu;
1606 KKASSERT((td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK)) == 0);
1609 td->td_flags &= ~TDF_MIGRATING;
1610 KKASSERT(td->td_migrate_gd == NULL);
1611 KKASSERT(td->td_lwp == NULL ||
1612 (td->td_lwp->lwp_mpflags & LWP_MP_ONRUNQ) == 0);
1618 lwkt_preempted_proc(void)
1620 thread_t td = curthread;
1621 while (td->td_preempted)
1622 td = td->td_preempted;
1627 * Create a kernel process/thread/whatever. It shares it's address space
1628 * with proc0 - ie: kernel only.
1630 * If the cpu is not specified one will be selected. In the future
1631 * specifying a cpu of -1 will enable kernel thread migration between
1635 lwkt_create(void (*func)(void *), void *arg, struct thread **tdp,
1636 thread_t template, int tdflags, int cpu, const char *fmt, ...)
1641 td = lwkt_alloc_thread(template, LWKT_THREAD_STACK, cpu,
1645 cpu_set_thread_handler(td, lwkt_exit, func, arg);
1648 * Set up arg0 for 'ps' etc
1650 __va_start(ap, fmt);
1651 kvsnprintf(td->td_comm, sizeof(td->td_comm), fmt, ap);
1655 * Schedule the thread to run
1657 if (td->td_flags & TDF_NOSTART)
1658 td->td_flags &= ~TDF_NOSTART;
1665 * Destroy an LWKT thread. Warning! This function is not called when
1666 * a process exits, cpu_proc_exit() directly calls cpu_thread_exit() and
1667 * uses a different reaping mechanism.
1672 thread_t td = curthread;
1677 * Do any cleanup that might block here
1679 if (td->td_flags & TDF_VERBOSE)
1680 kprintf("kthread %p %s has exited\n", td, td->td_comm);
1683 dsched_exit_thread(td);
1686 * Get us into a critical section to interlock gd_freetd and loop
1687 * until we can get it freed.
1689 * We have to cache the current td in gd_freetd because objcache_put()ing
1690 * it would rip it out from under us while our thread is still active.
1692 * We are the current thread so of course our own TDF_RUNNING bit will
1693 * be set, so unlike the lwp reap code we don't wait for it to clear.
1696 crit_enter_quick(td);
1699 tsleep(td, 0, "tdreap", 1);
1702 if ((std = gd->gd_freetd) != NULL) {
1703 KKASSERT((std->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK)) == 0);
1704 gd->gd_freetd = NULL;
1705 objcache_put(thread_cache, std);
1712 * Remove thread resources from kernel lists and deschedule us for
1713 * the last time. We cannot block after this point or we may end
1714 * up with a stale td on the tsleepq.
1716 * None of this may block, the critical section is the only thing
1717 * protecting tdallq and the only thing preventing new lwkt_hold()
1720 if (td->td_flags & TDF_TSLEEPQ)
1722 lwkt_deschedule_self(td);
1723 lwkt_remove_tdallq(td);
1724 KKASSERT(td->td_refs == 0);
1729 KKASSERT(gd->gd_freetd == NULL);
1730 if (td->td_flags & TDF_ALLOCATED_THREAD)
1736 lwkt_remove_tdallq(thread_t td)
1738 KKASSERT(td->td_gd == mycpu);
1739 TAILQ_REMOVE(&td->td_gd->gd_tdallq, td, td_allq);
1743 * Code reduction and branch prediction improvements. Call/return
1744 * overhead on modern cpus often degenerates into 0 cycles due to
1745 * the cpu's branch prediction hardware and return pc cache. We
1746 * can take advantage of this by not inlining medium-complexity
1747 * functions and we can also reduce the branch prediction impact
1748 * by collapsing perfectly predictable branches into a single
1749 * procedure instead of duplicating it.
1751 * Is any of this noticeable? Probably not, so I'll take the
1752 * smaller code size.
1755 crit_exit_wrapper(__DEBUG_CRIT_ARG__)
1757 _crit_exit(mycpu __DEBUG_CRIT_PASS_ARG__);
1763 thread_t td = curthread;
1764 int lcrit = td->td_critcount;
1766 td->td_critcount = 0;
1767 panic("td_critcount is/would-go negative! %p %d", td, lcrit);
1774 * Called from debugger/panic on cpus which have been stopped. We must still
1775 * process the IPIQ while stopped, even if we were stopped while in a critical
1778 * If we are dumping also try to process any pending interrupts. This may
1779 * or may not work depending on the state of the cpu at the point it was
1783 lwkt_smp_stopped(void)
1785 globaldata_t gd = mycpu;
1789 lwkt_process_ipiq();
1792 lwkt_process_ipiq();