kernel/acpica: Change button type to int.
[dragonfly.git] / sys / kern / lwkt_thread.c
CommitLineData
8ad65e08 1/*
b12defdc 2 * Copyright (c) 2003-2011 The DragonFly Project. All rights reserved.
60f60350 3 *
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4 * This code is derived from software contributed to The DragonFly Project
5 * by Matthew Dillon <dillon@backplane.com>
60f60350 6 *
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7 * Redistribution and use in source and binary forms, with or without
8 * modification, are permitted provided that the following conditions
9 * are met:
60f60350 10 *
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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
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14 * notice, this list of conditions and the following disclaimer in
15 * the documentation and/or other materials provided with the
16 * distribution.
17 * 3. Neither the name of The DragonFly Project nor the names of its
18 * contributors may be used to endorse or promote products derived
19 * from this software without specific, prior written permission.
60f60350 20 *
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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
8ad65e08 32 * SUCH DAMAGE.
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33 */
34
35/*
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.
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40 */
41
42#include <sys/param.h>
43#include <sys/systm.h>
44#include <sys/kernel.h>
45#include <sys/proc.h>
46#include <sys/rtprio.h>
b37f18d6 47#include <sys/kinfo.h>
8ad65e08 48#include <sys/queue.h>
7d0bac62 49#include <sys/sysctl.h>
99df837e 50#include <sys/kthread.h>
f1d1c3fa 51#include <machine/cpu.h>
99df837e 52#include <sys/lock.h>
9d265729 53#include <sys/spinlock.h>
57aa743c 54#include <sys/ktr.h>
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55
56#include <sys/thread2.h>
57#include <sys/spinlock2.h>
684a93c4 58#include <sys/mplock2.h>
f1d1c3fa 59
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60#include <sys/dsched.h>
61
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62#include <vm/vm.h>
63#include <vm/vm_param.h>
64#include <vm/vm_kern.h>
65#include <vm/vm_object.h>
66#include <vm/vm_page.h>
67#include <vm/vm_map.h>
68#include <vm/vm_pager.h>
69#include <vm/vm_extern.h>
7d0bac62 70
99df837e 71#include <machine/stdarg.h>
96728c05 72#include <machine/smp.h>
99df837e 73
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74#ifdef _KERNEL_VIRTUAL
75#include <pthread.h>
76#endif
77
d850923c
AE
78#if !defined(KTR_CTXSW)
79#define KTR_CTXSW KTR_ALL
80#endif
81KTR_INFO_MASTER(ctxsw);
5bf48697
AE
82KTR_INFO(KTR_CTXSW, ctxsw, sw, 0, "#cpu[%d].td = %p", int cpu, struct thread *td);
83KTR_INFO(KTR_CTXSW, ctxsw, pre, 1, "#cpu[%d].td = %p", int cpu, struct thread *td);
84KTR_INFO(KTR_CTXSW, ctxsw, newtd, 2, "#threads[%p].name = %s", struct thread *td, char *comm);
85KTR_INFO(KTR_CTXSW, ctxsw, deadtd, 3, "#threads[%p].name = <dead>", struct thread *td);
1541028a 86
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87static MALLOC_DEFINE(M_THREAD, "thread", "lwkt threads");
88
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89#ifdef INVARIANTS
90static int panic_on_cscount = 0;
91#endif
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92static __int64_t switch_count = 0;
93static __int64_t preempt_hit = 0;
94static __int64_t preempt_miss = 0;
95static __int64_t preempt_weird = 0;
fb0f29c4 96static int lwkt_use_spin_port;
40aaf5fc 97static struct objcache *thread_cache;
a46b4a23 98int cpu_mwait_spin = 0;
05220613 99
e381e77c 100static void lwkt_schedule_remote(void *arg, int arg2, struct intrframe *frame);
cc9b6223 101static void lwkt_setcpu_remote(void *arg);
e381e77c 102
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103/*
104 * We can make all thread ports use the spin backend instead of the thread
105 * backend. This should only be set to debug the spin backend.
106 */
107TUNABLE_INT("lwkt.use_spin_port", &lwkt_use_spin_port);
108
0f7a3396 109#ifdef INVARIANTS
0c52fa62
SG
110SYSCTL_INT(_lwkt, OID_AUTO, panic_on_cscount, CTLFLAG_RW, &panic_on_cscount, 0,
111 "Panic if attempting to switch lwkt's while mastering cpusync");
0f7a3396 112#endif
0c52fa62
SG
113SYSCTL_QUAD(_lwkt, OID_AUTO, switch_count, CTLFLAG_RW, &switch_count, 0,
114 "Number of switched threads");
9733f757 115SYSCTL_QUAD(_lwkt, OID_AUTO, preempt_hit, CTLFLAG_RW, &preempt_hit, 0,
0c52fa62 116 "Successful preemption events");
9733f757 117SYSCTL_QUAD(_lwkt, OID_AUTO, preempt_miss, CTLFLAG_RW, &preempt_miss, 0,
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118 "Failed preemption events");
119SYSCTL_QUAD(_lwkt, OID_AUTO, preempt_weird, CTLFLAG_RW, &preempt_weird, 0,
120 "Number of preempted threads.");
b12defdc 121static int fairq_enable = 0;
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122SYSCTL_INT(_lwkt, OID_AUTO, fairq_enable, CTLFLAG_RW,
123 &fairq_enable, 0, "Turn on fairq priority accumulators");
85946b6c 124static int fairq_bypass = -1;
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125SYSCTL_INT(_lwkt, OID_AUTO, fairq_bypass, CTLFLAG_RW,
126 &fairq_bypass, 0, "Allow fairq to bypass td on token failure");
127extern int lwkt_sched_debug;
128int lwkt_sched_debug = 0;
129SYSCTL_INT(_lwkt, OID_AUTO, sched_debug, CTLFLAG_RW,
130 &lwkt_sched_debug, 0, "Scheduler debug");
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131static int lwkt_spin_loops = 10;
132SYSCTL_INT(_lwkt, OID_AUTO, spin_loops, CTLFLAG_RW,
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133 &lwkt_spin_loops, 0, "Scheduler spin loops until sorted decon");
134static int lwkt_spin_reseq = 0;
135SYSCTL_INT(_lwkt, OID_AUTO, spin_reseq, CTLFLAG_RW,
136 &lwkt_spin_reseq, 0, "Scheduler resequencer enable");
137static int lwkt_spin_monitor = 0;
138SYSCTL_INT(_lwkt, OID_AUTO, spin_monitor, CTLFLAG_RW,
139 &lwkt_spin_monitor, 0, "Scheduler uses monitor/mwait");
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140static int lwkt_spin_fatal = 0; /* disabled */
141SYSCTL_INT(_lwkt, OID_AUTO, spin_fatal, CTLFLAG_RW,
142 &lwkt_spin_fatal, 0, "LWKT scheduler spin loops till fatal panic");
fbc024e4 143static int preempt_enable = 1;
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144SYSCTL_INT(_lwkt, OID_AUTO, preempt_enable, CTLFLAG_RW,
145 &preempt_enable, 0, "Enable preemption");
7b234d8c 146static int lwkt_cache_threads = 0;
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147SYSCTL_INT(_lwkt, OID_AUTO, cache_threads, CTLFLAG_RD,
148 &lwkt_cache_threads, 0, "thread+kstack cache");
fbc024e4 149
8cee56f4 150#ifndef _KERNEL_VIRTUAL
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151static __cachealign int lwkt_cseq_rindex;
152static __cachealign int lwkt_cseq_windex;
8cee56f4 153#endif
05220613 154
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155/*
156 * These helper procedures handle the runq, they can only be called from
157 * within a critical section.
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158 *
159 * WARNING! Prior to SMP being brought up it is possible to enqueue and
160 * dequeue threads belonging to other cpus, so be sure to use td->td_gd
161 * instead of 'mycpu' when referencing the globaldata structure. Once
162 * SMP live enqueuing and dequeueing only occurs on the current cpu.
4b5f931b 163 */
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164static __inline
165void
166_lwkt_dequeue(thread_t td)
167{
168 if (td->td_flags & TDF_RUNQ) {
75cdbe6c 169 struct globaldata *gd = td->td_gd;
4b5f931b 170
f1d1c3fa 171 td->td_flags &= ~TDF_RUNQ;
f9235b6d 172 TAILQ_REMOVE(&gd->gd_tdrunq, td, td_threadq);
de4d4cb0 173 --gd->gd_tdrunqcount;
f9235b6d 174 if (TAILQ_FIRST(&gd->gd_tdrunq) == NULL)
2a418930 175 atomic_clear_int(&gd->gd_reqflags, RQF_RUNNING);
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176 }
177}
178
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179/*
180 * Priority enqueue.
181 *
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182 * There are a limited number of lwkt threads runnable since user
183 * processes only schedule one at a time per cpu. However, there can
184 * be many user processes in kernel mode exiting from a tsleep() which
e3e6be1f 185 * become runnable.
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186 *
187 * NOTE: lwkt_schedulerclock() will force a round-robin based on td_pri and
188 * will ignore user priority. This is to ensure that user threads in
189 * kernel mode get cpu at some point regardless of what the user
190 * scheduler thinks.
f9235b6d 191 */
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192static __inline
193void
194_lwkt_enqueue(thread_t td)
195{
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196 thread_t xtd;
197
7f5d7ed7 198 if ((td->td_flags & (TDF_RUNQ|TDF_MIGRATING|TDF_BLOCKQ)) == 0) {
75cdbe6c 199 struct globaldata *gd = td->td_gd;
4b5f931b 200
f1d1c3fa 201 td->td_flags |= TDF_RUNQ;
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202 xtd = TAILQ_FIRST(&gd->gd_tdrunq);
203 if (xtd == NULL) {
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204 TAILQ_INSERT_TAIL(&gd->gd_tdrunq, td, td_threadq);
205 atomic_set_int(&gd->gd_reqflags, RQF_RUNNING);
f9235b6d 206 } else {
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207 /*
208 * NOTE: td_upri - higher numbers more desireable, same sense
209 * as td_pri (typically reversed from lwp_upri).
210 *
211 * In the equal priority case we want the best selection
212 * at the beginning so the less desireable selections know
213 * that they have to setrunqueue/go-to-another-cpu, even
214 * though it means switching back to the 'best' selection.
215 * This also avoids degenerate situations when many threads
216 * are runnable or waking up at the same time.
217 *
218 * If upri matches exactly place at end/round-robin.
219 */
d992c377 220 while (xtd &&
e3e6be1f 221 (xtd->td_pri >= td->td_pri ||
d992c377 222 (xtd->td_pri == td->td_pri &&
e3e6be1f 223 xtd->td_upri >= td->td_upri))) {
85946b6c 224 xtd = TAILQ_NEXT(xtd, td_threadq);
d992c377 225 }
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226 if (xtd)
227 TAILQ_INSERT_BEFORE(xtd, td, td_threadq);
228 else
229 TAILQ_INSERT_TAIL(&gd->gd_tdrunq, td, td_threadq);
f9235b6d 230 }
de4d4cb0 231 ++gd->gd_tdrunqcount;
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232
233 /*
85946b6c 234 * Request a LWKT reschedule if we are now at the head of the queue.
b12defdc 235 */
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236 if (TAILQ_FIRST(&gd->gd_tdrunq) == td)
237 need_lwkt_resched();
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MD
238 }
239}
8ad65e08 240
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241static __boolean_t
242_lwkt_thread_ctor(void *obj, void *privdata, int ocflags)
243{
244 struct thread *td = (struct thread *)obj;
245
246 td->td_kstack = NULL;
247 td->td_kstack_size = 0;
248 td->td_flags = TDF_ALLOCATED_THREAD;
4643740a 249 td->td_mpflags = 0;
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250 return (1);
251}
252
253static void
254_lwkt_thread_dtor(void *obj, void *privdata)
255{
256 struct thread *td = (struct thread *)obj;
257
258 KASSERT(td->td_flags & TDF_ALLOCATED_THREAD,
259 ("_lwkt_thread_dtor: not allocated from objcache"));
260 KASSERT((td->td_flags & TDF_ALLOCATED_STACK) && td->td_kstack &&
261 td->td_kstack_size > 0,
262 ("_lwkt_thread_dtor: corrupted stack"));
263 kmem_free(&kernel_map, (vm_offset_t)td->td_kstack, td->td_kstack_size);
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264 td->td_kstack = NULL;
265 td->td_flags = 0;
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266}
267
268/*
269 * Initialize the lwkt s/system.
765b1ae0 270 *
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271 * Nominally cache up to 32 thread + kstack structures. Cache more on
272 * systems with a lot of cpu cores.
40aaf5fc 273 */
ced589cb 274static void
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275lwkt_init(void)
276{
765b1ae0 277 TUNABLE_INT("lwkt.cache_threads", &lwkt_cache_threads);
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278 if (lwkt_cache_threads == 0) {
279 lwkt_cache_threads = ncpus * 4;
280 if (lwkt_cache_threads < 32)
281 lwkt_cache_threads = 32;
282 }
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MD
283 thread_cache = objcache_create_mbacked(
284 M_THREAD, sizeof(struct thread),
2fce2579 285 0, lwkt_cache_threads,
765b1ae0 286 _lwkt_thread_ctor, _lwkt_thread_dtor, NULL);
40aaf5fc 287}
ced589cb 288SYSINIT(lwkt_init, SI_BOOT2_LWKT_INIT, SI_ORDER_FIRST, lwkt_init, NULL);
40aaf5fc 289
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MD
290/*
291 * Schedule a thread to run. As the current thread we can always safely
292 * schedule ourselves, and a shortcut procedure is provided for that
293 * function.
294 *
295 * (non-blocking, self contained on a per cpu basis)
296 */
297void
298lwkt_schedule_self(thread_t td)
299{
cfaeae2a 300 KKASSERT((td->td_flags & TDF_MIGRATING) == 0);
37af14fe 301 crit_enter_quick(td);
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302 KASSERT(td != &td->td_gd->gd_idlethread,
303 ("lwkt_schedule_self(): scheduling gd_idlethread is illegal!"));
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MD
304 KKASSERT(td->td_lwp == NULL ||
305 (td->td_lwp->lwp_mpflags & LWP_MP_ONRUNQ) == 0);
37af14fe 306 _lwkt_enqueue(td);
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MD
307 crit_exit_quick(td);
308}
309
310/*
311 * Deschedule a thread.
312 *
313 * (non-blocking, self contained on a per cpu basis)
314 */
315void
316lwkt_deschedule_self(thread_t td)
317{
318 crit_enter_quick(td);
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319 _lwkt_dequeue(td);
320 crit_exit_quick(td);
321}
322
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323/*
324 * LWKTs operate on a per-cpu basis
325 *
73e4f7b9 326 * WARNING! Called from early boot, 'mycpu' may not work yet.
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327 */
328void
329lwkt_gdinit(struct globaldata *gd)
330{
f9235b6d 331 TAILQ_INIT(&gd->gd_tdrunq);
73e4f7b9 332 TAILQ_INIT(&gd->gd_tdallq);
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333}
334
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335/*
336 * Create a new thread. The thread must be associated with a process context
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337 * or LWKT start address before it can be scheduled. If the target cpu is
338 * -1 the thread will be created on the current cpu.
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339 *
340 * If you intend to create a thread without a process context this function
341 * does everything except load the startup and switcher function.
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342 */
343thread_t
d3d32139 344lwkt_alloc_thread(struct thread *td, int stksize, int cpu, int flags)
7d0bac62 345{
d2d8515b 346 static int cpu_rotator;
c070746a 347 globaldata_t gd = mycpu;
99df837e 348 void *stack;
7d0bac62 349
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350 /*
351 * If static thread storage is not supplied allocate a thread. Reuse
352 * a cached free thread if possible. gd_freetd is used to keep an exiting
353 * thread intact through the exit.
354 */
ef0fdad1 355 if (td == NULL) {
cf709dd2
MD
356 crit_enter_gd(gd);
357 if ((td = gd->gd_freetd) != NULL) {
358 KKASSERT((td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK|
359 TDF_RUNQ)) == 0);
c070746a 360 gd->gd_freetd = NULL;
cf709dd2 361 } else {
c070746a 362 td = objcache_get(thread_cache, M_WAITOK);
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363 KKASSERT((td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK|
364 TDF_RUNQ)) == 0);
365 }
366 crit_exit_gd(gd);
40aaf5fc 367 KASSERT((td->td_flags &
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368 (TDF_ALLOCATED_THREAD|TDF_RUNNING|TDF_PREEMPT_LOCK)) ==
369 TDF_ALLOCATED_THREAD,
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370 ("lwkt_alloc_thread: corrupted td flags 0x%X", td->td_flags));
371 flags |= td->td_flags & (TDF_ALLOCATED_THREAD|TDF_ALLOCATED_STACK);
ef0fdad1 372 }
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373
374 /*
375 * Try to reuse cached stack.
376 */
f470d0c8
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377 if ((stack = td->td_kstack) != NULL && td->td_kstack_size != stksize) {
378 if (flags & TDF_ALLOCATED_STACK) {
e4846942 379 kmem_free(&kernel_map, (vm_offset_t)stack, td->td_kstack_size);
f470d0c8
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380 stack = NULL;
381 }
382 }
383 if (stack == NULL) {
e40cfbd7 384 stack = (void *)kmem_alloc_stack(&kernel_map, stksize);
ef0fdad1 385 flags |= TDF_ALLOCATED_STACK;
99df837e 386 }
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387 if (cpu < 0) {
388 cpu = ++cpu_rotator;
389 cpu_ccfence();
390 cpu %= ncpus;
391 }
392 lwkt_init_thread(td, stack, stksize, flags, globaldata_find(cpu));
99df837e 393 return(td);
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MD
394}
395
396/*
397 * Initialize a preexisting thread structure. This function is used by
398 * lwkt_alloc_thread() and also used to initialize the per-cpu idlethread.
399 *
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400 * All threads start out in a critical section at a priority of
401 * TDPRI_KERN_DAEMON. Higher level code will modify the priority as
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402 * appropriate. This function may send an IPI message when the
403 * requested cpu is not the current cpu and consequently gd_tdallq may
404 * not be initialized synchronously from the point of view of the originating
405 * cpu.
406 *
407 * NOTE! we have to be careful in regards to creating threads for other cpus
408 * if SMP has not yet been activated.
7d0bac62 409 */
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410static void
411lwkt_init_thread_remote(void *arg)
412{
413 thread_t td = arg;
414
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415 /*
416 * Protected by critical section held by IPI dispatch
417 */
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418 TAILQ_INSERT_TAIL(&td->td_gd->gd_tdallq, td, td_allq);
419}
420
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421/*
422 * lwkt core thread structural initialization.
423 *
424 * NOTE: All threads are initialized as mpsafe threads.
425 */
7d0bac62 426void
f470d0c8
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427lwkt_init_thread(thread_t td, void *stack, int stksize, int flags,
428 struct globaldata *gd)
7d0bac62 429{
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430 globaldata_t mygd = mycpu;
431
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432 bzero(td, sizeof(struct thread));
433 td->td_kstack = stack;
f470d0c8 434 td->td_kstack_size = stksize;
d3d32139 435 td->td_flags = flags;
4643740a 436 td->td_mpflags = 0;
f256b6c0 437 td->td_type = TD_TYPE_GENERIC;
26a0694b 438 td->td_gd = gd;
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439 td->td_pri = TDPRI_KERN_DAEMON;
440 td->td_critcount = 1;
54341a3b 441 td->td_toks_have = NULL;
3b998fa9 442 td->td_toks_stop = &td->td_toks_base;
c068fb59
SZ
443 if (lwkt_use_spin_port || (flags & TDF_FORCE_SPINPORT)) {
444 lwkt_initport_spin(&td->td_msgport, td,
445 (flags & TDF_FIXEDCPU) ? TRUE : FALSE);
446 } else {
fb0f29c4 447 lwkt_initport_thread(&td->td_msgport, td);
c068fb59 448 }
99df837e 449 pmap_init_thread(td);
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450 /*
451 * Normally initializing a thread for a remote cpu requires sending an
452 * IPI. However, the idlethread is setup before the other cpus are
453 * activated so we have to treat it as a special case. XXX manipulation
454 * of gd_tdallq requires the BGL.
455 */
456 if (gd == mygd || td == &gd->gd_idlethread) {
37af14fe 457 crit_enter_gd(mygd);
75cdbe6c 458 TAILQ_INSERT_TAIL(&gd->gd_tdallq, td, td_allq);
37af14fe 459 crit_exit_gd(mygd);
75cdbe6c 460 } else {
2db3b277 461 lwkt_send_ipiq(gd, lwkt_init_thread_remote, td);
75cdbe6c 462 }
8c72e3d5 463 dsched_new_thread(td);
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MD
464}
465
466void
467lwkt_set_comm(thread_t td, const char *ctl, ...)
468{
e2565a42 469 __va_list va;
73e4f7b9 470
e2565a42 471 __va_start(va, ctl);
379210cb 472 kvsnprintf(td->td_comm, sizeof(td->td_comm), ctl, va);
e2565a42 473 __va_end(va);
5bf48697 474 KTR_LOG(ctxsw_newtd, td, td->td_comm);
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475}
476
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477/*
478 * Prevent the thread from getting destroyed. Note that unlike PHOLD/PRELE
479 * this does not prevent the thread from migrating to another cpu so the
480 * gd_tdallq state is not protected by this.
481 */
99df837e 482void
73e4f7b9 483lwkt_hold(thread_t td)
99df837e 484{
74c9628e 485 atomic_add_int(&td->td_refs, 1);
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486}
487
488void
489lwkt_rele(thread_t td)
490{
491 KKASSERT(td->td_refs > 0);
74c9628e 492 atomic_add_int(&td->td_refs, -1);
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493}
494
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495void
496lwkt_free_thread(thread_t td)
497{
74c9628e 498 KKASSERT(td->td_refs == 0);
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499 KKASSERT((td->td_flags & (TDF_RUNNING | TDF_PREEMPT_LOCK |
500 TDF_RUNQ | TDF_TSLEEPQ)) == 0);
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NT
501 if (td->td_flags & TDF_ALLOCATED_THREAD) {
502 objcache_put(thread_cache, td);
503 } else if (td->td_flags & TDF_ALLOCATED_STACK) {
504 /* client-allocated struct with internally allocated stack */
505 KASSERT(td->td_kstack && td->td_kstack_size > 0,
506 ("lwkt_free_thread: corrupted stack"));
507 kmem_free(&kernel_map, (vm_offset_t)td->td_kstack, td->td_kstack_size);
508 td->td_kstack = NULL;
509 td->td_kstack_size = 0;
99df837e 510 }
a86ce0cd 511
e7c0dbba 512 KTR_LOG(ctxsw_deadtd, td);
99df837e
MD
513}
514
515
8ad65e08
MD
516/*
517 * Switch to the next runnable lwkt. If no LWKTs are runnable then
f1d1c3fa
MD
518 * switch to the idlethread. Switching must occur within a critical
519 * section to avoid races with the scheduling queue.
520 *
521 * We always have full control over our cpu's run queue. Other cpus
522 * that wish to manipulate our queue must use the cpu_*msg() calls to
523 * talk to our cpu, so a critical section is all that is needed and
524 * the result is very, very fast thread switching.
525 *
96728c05
MD
526 * The LWKT scheduler uses a fixed priority model and round-robins at
527 * each priority level. User process scheduling is a totally
528 * different beast and LWKT priorities should not be confused with
529 * user process priorities.
f1d1c3fa 530 *
69d78e99
MD
531 * PREEMPTION NOTE: Preemption occurs via lwkt_preempt(). lwkt_switch()
532 * is not called by the current thread in the preemption case, only when
533 * the preempting thread blocks (in order to return to the original thread).
cfaeae2a
MD
534 *
535 * SPECIAL NOTE ON SWITCH ATOMICY: Certain operations such as thread
536 * migration and tsleep deschedule the current lwkt thread and call
537 * lwkt_switch(). In particular, the target cpu of the migration fully
538 * expects the thread to become non-runnable and can deadlock against
539 * cpusync operations if we run any IPIs prior to switching the thread out.
540 *
541 * WE MUST BE VERY CAREFUL NOT TO RUN SPLZ DIRECTLY OR INDIRECTLY IF
95858b91 542 * THE CURRENT THREAD HAS BEEN DESCHEDULED!
8ad65e08
MD
543 */
544void
545lwkt_switch(void)
546{
37af14fe
MD
547 globaldata_t gd = mycpu;
548 thread_t td = gd->gd_curthread;
8ad65e08 549 thread_t ntd;
b12defdc 550 int spinning = 0;
8ad65e08 551
da0b0e8b 552 KKASSERT(gd->gd_processing_ipiq == 0);
121f93bc 553 KKASSERT(td->td_flags & TDF_RUNNING);
da0b0e8b 554
46a3f46d 555 /*
27e88a6e
MD
556 * Switching from within a 'fast' (non thread switched) interrupt or IPI
557 * is illegal. However, we may have to do it anyway if we hit a fatal
558 * kernel trap or we have paniced.
559 *
560 * If this case occurs save and restore the interrupt nesting level.
46a3f46d 561 */
27e88a6e
MD
562 if (gd->gd_intr_nesting_level) {
563 int savegdnest;
564 int savegdtrap;
565
5fddbda2 566 if (gd->gd_trap_nesting_level == 0 && panic_cpu_gd != mycpu) {
4a28fe22 567 panic("lwkt_switch: Attempt to switch from a "
5a8df152 568 "fast interrupt, ipi, or hard code section, "
4a28fe22
MD
569 "td %p\n",
570 td);
27e88a6e
MD
571 } else {
572 savegdnest = gd->gd_intr_nesting_level;
573 savegdtrap = gd->gd_trap_nesting_level;
574 gd->gd_intr_nesting_level = 0;
575 gd->gd_trap_nesting_level = 0;
a7422615
MD
576 if ((td->td_flags & TDF_PANICWARN) == 0) {
577 td->td_flags |= TDF_PANICWARN;
4a28fe22
MD
578 kprintf("Warning: thread switch from interrupt, IPI, "
579 "or hard code section.\n"
a7422615 580 "thread %p (%s)\n", td, td->td_comm);
7ce2998e 581 print_backtrace(-1);
a7422615 582 }
27e88a6e
MD
583 lwkt_switch();
584 gd->gd_intr_nesting_level = savegdnest;
585 gd->gd_trap_nesting_level = savegdtrap;
586 return;
587 }
96728c05 588 }
ef0fdad1 589
cb973d15 590 /*
85946b6c
MD
591 * Release our current user process designation if we are blocking
592 * or if a user reschedule was requested.
593 *
594 * NOTE: This function is NOT called if we are switching into or
595 * returning from a preemption.
596 *
597 * NOTE: Releasing our current user process designation may cause
598 * it to be assigned to another thread, which in turn will
599 * cause us to block in the usched acquire code when we attempt
600 * to return to userland.
601 *
602 * NOTE: On SMP systems this can be very nasty when heavy token
603 * contention is present so we want to be careful not to
604 * release the designation gratuitously.
cb973d15 605 */
85946b6c
MD
606 if (td->td_release &&
607 (user_resched_wanted() || (td->td_flags & TDF_RUNQ) == 0)) {
cb973d15 608 td->td_release(td);
85946b6c 609 }
cb973d15 610
85946b6c
MD
611 /*
612 * Release all tokens
613 */
37af14fe 614 crit_enter_gd(gd);
3b998fa9 615 if (TD_TOKS_HELD(td))
9d265729
MD
616 lwkt_relalltokens(td);
617
618 /*
b02926de
MD
619 * We had better not be holding any spin locks, but don't get into an
620 * endless panic loop.
9d265729 621 */
0846e4ce 622 KASSERT(gd->gd_spinlocks == 0 || panicstr != NULL,
d666840a 623 ("lwkt_switch: still holding %d exclusive spinlocks!",
0846e4ce 624 gd->gd_spinlocks));
9d265729 625
8a8d5d85 626
0f7a3396
MD
627#ifdef INVARIANTS
628 if (td->td_cscount) {
6ea70f76 629 kprintf("Diagnostic: attempt to switch while mastering cpusync: %p\n",
0f7a3396
MD
630 td);
631 if (panic_on_cscount)
632 panic("switching while mastering cpusync");
633 }
8a8d5d85 634#endif
f9235b6d
MD
635
636 /*
637 * If we had preempted another thread on this cpu, resume the preempted
638 * thread. This occurs transparently, whether the preempted thread
639 * was scheduled or not (it may have been preempted after descheduling
640 * itself).
641 *
642 * We have to setup the MP lock for the original thread after backing
643 * out the adjustment that was made to curthread when the original
644 * was preempted.
645 */
99df837e 646 if ((ntd = td->td_preempted) != NULL) {
26a0694b
MD
647 KKASSERT(ntd->td_flags & TDF_PREEMPT_LOCK);
648 ntd->td_flags |= TDF_PREEMPT_DONE;
8ec60c3f
MD
649
650 /*
b9eb1c19
MD
651 * The interrupt may have woken a thread up, we need to properly
652 * set the reschedule flag if the originally interrupted thread is
653 * at a lower priority.
85946b6c
MD
654 *
655 * The interrupt may not have descheduled.
8ec60c3f 656 */
85946b6c 657 if (TAILQ_FIRST(&gd->gd_tdrunq) != ntd)
8ec60c3f 658 need_lwkt_resched();
f9235b6d
MD
659 goto havethread_preempted;
660 }
661
b12defdc 662 /*
f9235b6d 663 * If we cannot obtain ownership of the tokens we cannot immediately
cfaeae2a
MD
664 * schedule the target thread.
665 *
666 * Reminder: Again, we cannot afford to run any IPIs in this path if
667 * the current thread has been descheduled.
f9235b6d
MD
668 */
669 for (;;) {
b12defdc 670 clear_lwkt_resched();
f9235b6d 671
4b5f931b 672 /*
2a418930 673 * Hotpath - pull the head of the run queue and attempt to schedule
85946b6c 674 * it.
41a01a4d 675 */
7c3dd309
NA
676 ntd = TAILQ_FIRST(&gd->gd_tdrunq);
677
678 if (ntd == NULL) {
679 /*
680 * Runq is empty, switch to idle to allow it to halt.
681 */
682 ntd = &gd->gd_idlethread;
7c3dd309
NA
683 if (gd->gd_trap_nesting_level == 0 && panicstr == NULL)
684 ASSERT_NO_TOKENS_HELD(ntd);
7c3dd309
NA
685 cpu_time.cp_msg[0] = 0;
686 cpu_time.cp_stallpc = 0;
687 goto haveidle;
f9235b6d 688 }
41a01a4d 689
8ec60c3f 690 /*
b12defdc 691 * Hotpath - schedule ntd.
6f207a2c
MD
692 *
693 * NOTE: For UP there is no mplock and lwkt_getalltokens()
694 * always succeeds.
8ec60c3f 695 */
b12defdc
MD
696 if (TD_TOKS_NOT_HELD(ntd) ||
697 lwkt_getalltokens(ntd, (spinning >= lwkt_spin_loops)))
698 {
f9235b6d 699 goto havethread;
b12defdc 700 }
f9235b6d 701
f9235b6d 702 /*
2a418930
MD
703 * Coldpath (SMP only since tokens always succeed on UP)
704 *
705 * We had some contention on the thread we wanted to schedule.
706 * What we do now is try to find a thread that we can schedule
b12defdc 707 * in its stead.
2a418930 708 *
85946b6c
MD
709 * The coldpath scan does NOT rearrange threads in the run list.
710 * The lwkt_schedulerclock() will assert need_lwkt_resched() on
711 * the next tick whenever the current head is not the current thread.
f9235b6d 712 */
b12defdc 713#ifdef INVARIANTS
85946b6c 714 ++ntd->td_contended;
b12defdc 715#endif
050032ec 716 ++gd->gd_cnt.v_lock_colls;
b12defdc 717
85946b6c 718 if (fairq_bypass > 0)
b12defdc
MD
719 goto skip;
720
b12defdc 721 while ((ntd = TAILQ_NEXT(ntd, td_threadq)) != NULL) {
e3e6be1f 722#ifndef NO_LWKT_SPLIT_USERPRI
85946b6c
MD
723 /*
724 * Never schedule threads returning to userland or the
725 * user thread scheduler helper thread when higher priority
bb6860b5
NA
726 * threads are present. The runq is sorted by priority
727 * so we can give up traversing it when we find the first
728 * low priority thread.
85946b6c
MD
729 */
730 if (ntd->td_pri < TDPRI_KERN_LPSCHED) {
731 ntd = NULL;
732 break;
733 }
d992c377 734#endif
85946b6c
MD
735
736 /*
737 * Try this one.
738 */
b12defdc
MD
739 if (TD_TOKS_NOT_HELD(ntd) ||
740 lwkt_getalltokens(ntd, (spinning >= lwkt_spin_loops))) {
741 goto havethread;
742 }
85946b6c 743#ifdef INVARIANTS
85946b6c 744 ++ntd->td_contended;
b12defdc 745#endif
050032ec 746 ++gd->gd_cnt.v_lock_colls;
2a418930
MD
747 }
748
b12defdc 749skip:
2a418930
MD
750 /*
751 * We exhausted the run list, meaning that all runnable threads
b12defdc 752 * are contested.
2a418930
MD
753 */
754 cpu_pause();
8cee56f4
MD
755#ifdef _KERNEL_VIRTUAL
756 pthread_yield();
757#endif
2a418930 758 ntd = &gd->gd_idlethread;
2a418930
MD
759 if (gd->gd_trap_nesting_level == 0 && panicstr == NULL)
760 ASSERT_NO_TOKENS_HELD(ntd);
761 /* contention case, do not clear contention mask */
2a418930
MD
762
763 /*
b12defdc
MD
764 * We are going to have to retry but if the current thread is not
765 * on the runq we instead switch through the idle thread to get away
766 * from the current thread. We have to flag for lwkt reschedule
767 * to prevent the idle thread from halting.
2a418930 768 *
b12defdc
MD
769 * NOTE: A non-zero spinning is passed to lwkt_getalltokens() to
770 * instruct it to deal with the potential for deadlocks by
771 * ordering the tokens by address.
2a418930 772 */
b12defdc 773 if ((td->td_flags & TDF_RUNQ) == 0) {
85946b6c 774 need_lwkt_resched(); /* prevent hlt */
2a418930 775 goto haveidle;
4b5f931b 776 }
dbefba87 777#if defined(INVARIANTS) && defined(__x86_64__)
d5b2d319
MD
778 if ((read_rflags() & PSL_I) == 0) {
779 cpu_enable_intr();
780 panic("lwkt_switch() called with interrupts disabled");
781 }
782#endif
b12defdc
MD
783
784 /*
785 * Number iterations so far. After a certain point we switch to
786 * a sorted-address/monitor/mwait version of lwkt_getalltokens()
787 */
788 if (spinning < 0x7FFFFFFF)
789 ++spinning;
790
8cee56f4 791#ifndef _KERNEL_VIRTUAL
b12defdc
MD
792 /*
793 * lwkt_getalltokens() failed in sorted token mode, we can use
794 * monitor/mwait in this case.
795 */
796 if (spinning >= lwkt_spin_loops &&
797 (cpu_mi_feature & CPU_MI_MONITOR) &&
798 lwkt_spin_monitor)
799 {
800 cpu_mmw_pause_int(&gd->gd_reqflags,
801 (gd->gd_reqflags | RQF_SPINNING) &
a46b4a23 802 ~RQF_IDLECHECK_WK_MASK,
e5c52dd7 803 cpu_mwait_spin, 0);
b12defdc 804 }
8cee56f4 805#endif
b12defdc
MD
806
807 /*
808 * We already checked that td is still scheduled so this should be
809 * safe.
810 */
811 splz_check();
812
8cee56f4 813#ifndef _KERNEL_VIRTUAL
b12defdc
MD
814 /*
815 * This experimental resequencer is used as a fall-back to reduce
816 * hw cache line contention by placing each core's scheduler into a
817 * time-domain-multplexed slot.
818 *
819 * The resequencer is disabled by default. It's functionality has
820 * largely been superceeded by the token algorithm which limits races
821 * to a subset of cores.
822 *
823 * The resequencer algorithm tends to break down when more than
824 * 20 cores are contending. What appears to happen is that new
825 * tokens can be obtained out of address-sorted order by new cores
826 * while existing cores languish in long delays between retries and
827 * wind up being starved-out of the token acquisition.
828 */
829 if (lwkt_spin_reseq && spinning >= lwkt_spin_reseq) {
830 int cseq = atomic_fetchadd_int(&lwkt_cseq_windex, 1);
831 int oseq;
832
833 while ((oseq = lwkt_cseq_rindex) != cseq) {
834 cpu_ccfence();
835#if 1
836 if (cpu_mi_feature & CPU_MI_MONITOR) {
e5c52dd7
SZ
837 cpu_mmw_pause_int(&lwkt_cseq_rindex, oseq,
838 cpu_mwait_spin, 0);
b12defdc
MD
839 } else {
840#endif
841 cpu_pause();
842 cpu_lfence();
843#if 1
844 }
8b402283 845#endif
0f0466c0 846 }
b12defdc
MD
847 DELAY(1);
848 atomic_add_int(&lwkt_cseq_rindex, 1);
2a418930 849 }
8cee56f4 850#endif
2a418930 851 /* highest level for(;;) loop */
f1d1c3fa 852 }
8a8d5d85 853
2a418930 854havethread:
b12defdc 855 /*
be71787b
MD
856 * Clear gd_idle_repeat when doing a normal switch to a non-idle
857 * thread.
f9235b6d 858 */
9ac1ee6e 859 ntd->td_wmesg = NULL;
b12defdc 860 ++gd->gd_cnt.v_swtch;
be71787b 861 gd->gd_idle_repeat = 0;
2a418930 862
f9235b6d 863havethread_preempted:
f9235b6d
MD
864 /*
865 * If the new target does not need the MP lock and we are holding it,
866 * release the MP lock. If the new target requires the MP lock we have
867 * already acquired it for the target.
8a8d5d85 868 */
2a418930 869 ;
f9235b6d
MD
870haveidle:
871 KASSERT(ntd->td_critcount,
b5d16701
MD
872 ("priority problem in lwkt_switch %d %d",
873 td->td_critcount, ntd->td_critcount));
874
94f6d86e 875 if (td != ntd) {
cc9b6223
MD
876 /*
877 * Execute the actual thread switch operation. This function
878 * returns to the current thread and returns the previous thread
879 * (which may be different from the thread we switched to).
880 *
881 * We are responsible for marking ntd as TDF_RUNNING.
882 */
121f93bc 883 KKASSERT((ntd->td_flags & TDF_RUNNING) == 0);
94f6d86e 884 ++switch_count;
a1f0fb66 885 KTR_LOG(ctxsw_sw, gd->gd_cpuid, ntd);
cc9b6223
MD
886 ntd->td_flags |= TDF_RUNNING;
887 lwkt_switch_return(td->td_switch(ntd));
888 /* ntd invalid, td_switch() can return a different thread_t */
94f6d86e 889 }
b12defdc 890
b12defdc 891 /*
54341a3b 892 * catch-all. XXX is this strictly needed?
b12defdc
MD
893 */
894 splz_check();
54341a3b 895
37af14fe
MD
896 /* NOTE: current cpu may have changed after switch */
897 crit_exit_quick(td);
8ad65e08
MD
898}
899
cc9b6223
MD
900/*
901 * Called by assembly in the td_switch (thread restore path) for thread
902 * bootstrap cases which do not 'return' to lwkt_switch().
903 */
904void
905lwkt_switch_return(thread_t otd)
906{
cc9b6223
MD
907 globaldata_t rgd;
908
909 /*
910 * Check if otd was migrating. Now that we are on ntd we can finish
911 * up the migration. This is a bit messy but it is the only place
912 * where td is known to be fully descheduled.
913 *
914 * We can only activate the migration if otd was migrating but not
915 * held on the cpu due to a preemption chain. We still have to
916 * clear TDF_RUNNING on the old thread either way.
917 *
918 * We are responsible for clearing the previously running thread's
919 * TDF_RUNNING.
920 */
921 if ((rgd = otd->td_migrate_gd) != NULL &&
922 (otd->td_flags & TDF_PREEMPT_LOCK) == 0) {
923 KKASSERT((otd->td_flags & (TDF_MIGRATING | TDF_RUNNING)) ==
924 (TDF_MIGRATING | TDF_RUNNING));
925 otd->td_migrate_gd = NULL;
926 otd->td_flags &= ~TDF_RUNNING;
927 lwkt_send_ipiq(rgd, lwkt_setcpu_remote, otd);
928 } else {
929 otd->td_flags &= ~TDF_RUNNING;
930 }
2b07d9aa
MD
931
932 /*
933 * Final exit validations (see lwp_wait()). Note that otd becomes
934 * invalid the *instant* we set TDF_MP_EXITSIG.
935 */
936 while (otd->td_flags & TDF_EXITING) {
937 u_int mpflags;
938
939 mpflags = otd->td_mpflags;
940 cpu_ccfence();
941
942 if (mpflags & TDF_MP_EXITWAIT) {
943 if (atomic_cmpset_int(&otd->td_mpflags, mpflags,
944 mpflags | TDF_MP_EXITSIG)) {
945 wakeup(otd);
946 break;
947 }
948 } else {
949 if (atomic_cmpset_int(&otd->td_mpflags, mpflags,
950 mpflags | TDF_MP_EXITSIG)) {
951 wakeup(otd);
952 break;
953 }
954 }
955 }
cc9b6223
MD
956}
957
b68b7282 958/*
96728c05 959 * Request that the target thread preempt the current thread. Preemption
54341a3b
MD
960 * can only occur if our only critical section is the one that we were called
961 * with, the relative priority of the target thread is higher, and the target
962 * thread holds no tokens. This also only works if we are not holding any
963 * spinlocks (obviously).
96728c05
MD
964 *
965 * THE CALLER OF LWKT_PREEMPT() MUST BE IN A CRITICAL SECTION. Typically
966 * this is called via lwkt_schedule() through the td_preemptable callback.
f9235b6d 967 * critcount is the managed critical priority that we should ignore in order
96728c05
MD
968 * to determine whether preemption is possible (aka usually just the crit
969 * priority of lwkt_schedule() itself).
b68b7282 970 *
54341a3b
MD
971 * Preemption is typically limited to interrupt threads.
972 *
973 * Operation works in a fairly straight-forward manner. The normal
974 * scheduling code is bypassed and we switch directly to the target
975 * thread. When the target thread attempts to block or switch away
976 * code at the base of lwkt_switch() will switch directly back to our
977 * thread. Our thread is able to retain whatever tokens it holds and
978 * if the target needs one of them the target will switch back to us
979 * and reschedule itself normally.
b68b7282
MD
980 */
981void
f9235b6d 982lwkt_preempt(thread_t ntd, int critcount)
b68b7282 983{
46a3f46d 984 struct globaldata *gd = mycpu;
cc9b6223 985 thread_t xtd;
0a3f9b47 986 thread_t td;
2d910aaf 987 int save_gd_intr_nesting_level;
b68b7282 988
26a0694b 989 /*
96728c05
MD
990 * The caller has put us in a critical section. We can only preempt
991 * if the caller of the caller was not in a critical section (basically
f9235b6d 992 * a local interrupt), as determined by the 'critcount' parameter. We
47737962 993 * also can't preempt if the caller is holding any spinlocks (even if
d666840a 994 * he isn't in a critical section). This also handles the tokens test.
96728c05
MD
995 *
996 * YYY The target thread must be in a critical section (else it must
997 * inherit our critical section? I dunno yet).
26a0694b 998 */
f9235b6d 999 KASSERT(ntd->td_critcount, ("BADCRIT0 %d", ntd->td_pri));
26a0694b 1000
b12defdc 1001 td = gd->gd_curthread;
fbc024e4
MD
1002 if (preempt_enable == 0) {
1003 ++preempt_miss;
1004 return;
1005 }
f9235b6d 1006 if (ntd->td_pri <= td->td_pri) {
57c254db
MD
1007 ++preempt_miss;
1008 return;
1009 }
f9235b6d 1010 if (td->td_critcount > critcount) {
96728c05
MD
1011 ++preempt_miss;
1012 return;
1013 }
121f93bc
MD
1014 if (td->td_cscount) {
1015 ++preempt_miss;
1016 return;
1017 }
46a3f46d 1018 if (ntd->td_gd != gd) {
96728c05
MD
1019 ++preempt_miss;
1020 return;
1021 }
41a01a4d 1022 /*
77912481
MD
1023 * We don't have to check spinlocks here as they will also bump
1024 * td_critcount.
d3d1cbc8
MD
1025 *
1026 * Do not try to preempt if the target thread is holding any tokens.
1027 * We could try to acquire the tokens but this case is so rare there
1028 * is no need to support it.
41a01a4d 1029 */
0846e4ce 1030 KKASSERT(gd->gd_spinlocks == 0);
77912481 1031
3b998fa9 1032 if (TD_TOKS_HELD(ntd)) {
d3d1cbc8 1033 ++preempt_miss;
d3d1cbc8
MD
1034 return;
1035 }
26a0694b
MD
1036 if (td == ntd || ((td->td_flags | ntd->td_flags) & TDF_PREEMPT_LOCK)) {
1037 ++preempt_weird;
1038 return;
1039 }
1040 if (ntd->td_preempted) {
4b5f931b 1041 ++preempt_hit;
26a0694b 1042 return;
b68b7282 1043 }
da0b0e8b 1044 KKASSERT(gd->gd_processing_ipiq == 0);
26a0694b 1045
8ec60c3f
MD
1046 /*
1047 * Since we are able to preempt the current thread, there is no need to
1048 * call need_lwkt_resched().
2d910aaf
MD
1049 *
1050 * We must temporarily clear gd_intr_nesting_level around the switch
1051 * since switchouts from the target thread are allowed (they will just
1052 * return to our thread), and since the target thread has its own stack.
cc9b6223
MD
1053 *
1054 * A preemption must switch back to the original thread, assert the
1055 * case.
8ec60c3f 1056 */
26a0694b
MD
1057 ++preempt_hit;
1058 ntd->td_preempted = td;
1059 td->td_flags |= TDF_PREEMPT_LOCK;
a1f0fb66 1060 KTR_LOG(ctxsw_pre, gd->gd_cpuid, ntd);
2d910aaf
MD
1061 save_gd_intr_nesting_level = gd->gd_intr_nesting_level;
1062 gd->gd_intr_nesting_level = 0;
121f93bc
MD
1063
1064 KKASSERT((ntd->td_flags & TDF_RUNNING) == 0);
cc9b6223
MD
1065 ntd->td_flags |= TDF_RUNNING;
1066 xtd = td->td_switch(ntd);
1067 KKASSERT(xtd == ntd);
1068 lwkt_switch_return(xtd);
2d910aaf 1069 gd->gd_intr_nesting_level = save_gd_intr_nesting_level;
b9eb1c19 1070
26a0694b
MD
1071 KKASSERT(ntd->td_preempted && (td->td_flags & TDF_PREEMPT_DONE));
1072 ntd->td_preempted = NULL;
1073 td->td_flags &= ~(TDF_PREEMPT_LOCK|TDF_PREEMPT_DONE);
b68b7282
MD
1074}
1075
f1d1c3fa 1076/*
faaeffac 1077 * Conditionally call splz() if gd_reqflags indicates work is pending.
4a28fe22
MD
1078 * This will work inside a critical section but not inside a hard code
1079 * section.
ef0fdad1 1080 *
f1d1c3fa
MD
1081 * (self contained on a per cpu basis)
1082 */
1083void
faaeffac 1084splz_check(void)
f1d1c3fa 1085{
7966cb69
MD
1086 globaldata_t gd = mycpu;
1087 thread_t td = gd->gd_curthread;
ef0fdad1 1088
4a28fe22
MD
1089 if ((gd->gd_reqflags & RQF_IDLECHECK_MASK) &&
1090 gd->gd_intr_nesting_level == 0 &&
1091 td->td_nest_count < 2)
1092 {
f1d1c3fa 1093 splz();
4a28fe22
MD
1094 }
1095}
1096
1097/*
1098 * This version is integrated into crit_exit, reqflags has already
1099 * been tested but td_critcount has not.
1100 *
1101 * We only want to execute the splz() on the 1->0 transition of
1102 * critcount and not in a hard code section or if too deeply nested.
925040f2 1103 *
0846e4ce 1104 * NOTE: gd->gd_spinlocks is implied to be 0 when td_critcount is 0.
4a28fe22
MD
1105 */
1106void
1107lwkt_maybe_splz(thread_t td)
1108{
1109 globaldata_t gd = td->td_gd;
1110
1111 if (td->td_critcount == 0 &&
1112 gd->gd_intr_nesting_level == 0 &&
1113 td->td_nest_count < 2)
1114 {
1115 splz();
1116 }
f1d1c3fa
MD
1117}
1118
e6546af9
MD
1119/*
1120 * Drivers which set up processing co-threads can call this function to
1121 * run the co-thread at a higher priority and to allow it to preempt
1122 * normal threads.
1123 */
1124void
1125lwkt_set_interrupt_support_thread(void)
1126{
1127 thread_t td = curthread;
1128
1129 lwkt_setpri_self(TDPRI_INT_SUPPORT);
1130 td->td_flags |= TDF_INTTHREAD;
1131 td->td_preemptable = lwkt_preempt;
1132}
1133
1134
8ad65e08 1135/*
f9235b6d
MD
1136 * This function is used to negotiate a passive release of the current
1137 * process/lwp designation with the user scheduler, allowing the user
1138 * scheduler to schedule another user thread. The related kernel thread
1139 * (curthread) continues running in the released state.
8ad65e08
MD
1140 */
1141void
f9235b6d 1142lwkt_passive_release(struct thread *td)
8ad65e08 1143{
f9235b6d
MD
1144 struct lwp *lp = td->td_lwp;
1145
e3e6be1f 1146#ifndef NO_LWKT_SPLIT_USERPRI
f9235b6d
MD
1147 td->td_release = NULL;
1148 lwkt_setpri_self(TDPRI_KERN_USER);
d992c377
MD
1149#endif
1150
f9235b6d 1151 lp->lwp_proc->p_usched->release_curproc(lp);
f1d1c3fa
MD
1152}
1153
f9235b6d 1154
3824f392 1155/*
d2d8515b
MD
1156 * This implements a LWKT yield, allowing a kernel thread to yield to other
1157 * kernel threads at the same or higher priority. This function can be
1158 * called in a tight loop and will typically only yield once per tick.
f9235b6d 1159 *
d2d8515b
MD
1160 * Most kernel threads run at the same priority in order to allow equal
1161 * sharing.
f9235b6d
MD
1162 *
1163 * (self contained on a per cpu basis)
3824f392
MD
1164 */
1165void
f9235b6d 1166lwkt_yield(void)
3824f392 1167{
f9235b6d
MD
1168 globaldata_t gd = mycpu;
1169 thread_t td = gd->gd_curthread;
3824f392 1170
f9235b6d
MD
1171 if ((gd->gd_reqflags & RQF_IDLECHECK_MASK) && td->td_nest_count < 2)
1172 splz();
85946b6c 1173 if (lwkt_resched_wanted()) {
f9235b6d
MD
1174 lwkt_schedule_self(curthread);
1175 lwkt_switch();
f9235b6d 1176 }
3824f392
MD
1177}
1178
40504122
MD
1179/*
1180 * The quick version processes pending interrupts and higher-priority
1181 * LWKT threads but will not round-robin same-priority LWKT threads.
de4d4cb0
MD
1182 *
1183 * When called while attempting to return to userland the only same-pri
1184 * threads are the ones which have already tried to become the current
1185 * user process.
40504122
MD
1186 */
1187void
1188lwkt_yield_quick(void)
1189{
1190 globaldata_t gd = mycpu;
1191 thread_t td = gd->gd_curthread;
1192
1193 if ((gd->gd_reqflags & RQF_IDLECHECK_MASK) && td->td_nest_count < 2)
1194 splz();
1195 if (lwkt_resched_wanted()) {
9c99cb33 1196 crit_enter();
40504122
MD
1197 if (TAILQ_FIRST(&gd->gd_tdrunq) == td) {
1198 clear_lwkt_resched();
1199 } else {
1200 lwkt_schedule_self(curthread);
1201 lwkt_switch();
1202 }
9c99cb33 1203 crit_exit();
40504122
MD
1204 }
1205}
1206
3824f392 1207/*
f9235b6d
MD
1208 * This yield is designed for kernel threads with a user context.
1209 *
1210 * The kernel acting on behalf of the user is potentially cpu-bound,
1211 * this function will efficiently allow other threads to run and also
1212 * switch to other processes by releasing.
3824f392
MD
1213 *
1214 * The lwkt_user_yield() function is designed to have very low overhead
1215 * if no yield is determined to be needed.
1216 */
1217void
1218lwkt_user_yield(void)
1219{
f9235b6d
MD
1220 globaldata_t gd = mycpu;
1221 thread_t td = gd->gd_curthread;
1222
1223 /*
1224 * Always run any pending interrupts in case we are in a critical
1225 * section.
1226 */
1227 if ((gd->gd_reqflags & RQF_IDLECHECK_MASK) && td->td_nest_count < 2)
1228 splz();
3824f392 1229
3824f392 1230 /*
f9235b6d
MD
1231 * Switch (which forces a release) if another kernel thread needs
1232 * the cpu, if userland wants us to resched, or if our kernel
1233 * quantum has run out.
3824f392 1234 */
f9235b6d 1235 if (lwkt_resched_wanted() ||
85946b6c 1236 user_resched_wanted())
f9235b6d 1237 {
3824f392 1238 lwkt_switch();
3824f392
MD
1239 }
1240
f9235b6d 1241#if 0
3824f392 1242 /*
f9235b6d
MD
1243 * Reacquire the current process if we are released.
1244 *
1245 * XXX not implemented atm. The kernel may be holding locks and such,
1246 * so we want the thread to continue to receive cpu.
3824f392 1247 */
f9235b6d
MD
1248 if (td->td_release == NULL && lp) {
1249 lp->lwp_proc->p_usched->acquire_curproc(lp);
1250 td->td_release = lwkt_passive_release;
1251 lwkt_setpri_self(TDPRI_USER_NORM);
3824f392 1252 }
f9235b6d 1253#endif
b9eb1c19
MD
1254}
1255
8ad65e08 1256/*
f1d1c3fa
MD
1257 * Generic schedule. Possibly schedule threads belonging to other cpus and
1258 * deal with threads that might be blocked on a wait queue.
1259 *
0a3f9b47
MD
1260 * We have a little helper inline function which does additional work after
1261 * the thread has been enqueued, including dealing with preemption and
1262 * setting need_lwkt_resched() (which prevents the kernel from returning
1263 * to userland until it has processed higher priority threads).
6330a558
MD
1264 *
1265 * It is possible for this routine to be called after a failed _enqueue
1266 * (due to the target thread migrating, sleeping, or otherwise blocked).
1267 * We have to check that the thread is actually on the run queue!
8ad65e08 1268 */
0a3f9b47
MD
1269static __inline
1270void
85946b6c 1271_lwkt_schedule_post(globaldata_t gd, thread_t ntd, int ccount)
0a3f9b47 1272{
6330a558 1273 if (ntd->td_flags & TDF_RUNQ) {
85946b6c 1274 if (ntd->td_preemptable) {
f9235b6d 1275 ntd->td_preemptable(ntd, ccount); /* YYY +token */
6330a558 1276 }
0a3f9b47
MD
1277 }
1278}
1279
361d01dd 1280static __inline
8ad65e08 1281void
85946b6c 1282_lwkt_schedule(thread_t td)
8ad65e08 1283{
37af14fe
MD
1284 globaldata_t mygd = mycpu;
1285
cf709dd2
MD
1286 KASSERT(td != &td->td_gd->gd_idlethread,
1287 ("lwkt_schedule(): scheduling gd_idlethread is illegal!"));
cfaeae2a 1288 KKASSERT((td->td_flags & TDF_MIGRATING) == 0);
37af14fe 1289 crit_enter_gd(mygd);
4643740a
MD
1290 KKASSERT(td->td_lwp == NULL ||
1291 (td->td_lwp->lwp_mpflags & LWP_MP_ONRUNQ) == 0);
1292
37af14fe 1293 if (td == mygd->gd_curthread) {
f1d1c3fa
MD
1294 _lwkt_enqueue(td);
1295 } else {
f1d1c3fa 1296 /*
7cd8d145
MD
1297 * If we own the thread, there is no race (since we are in a
1298 * critical section). If we do not own the thread there might
1299 * be a race but the target cpu will deal with it.
f1d1c3fa 1300 */
7cd8d145 1301 if (td->td_gd == mygd) {
9d265729 1302 _lwkt_enqueue(td);
85946b6c 1303 _lwkt_schedule_post(mygd, td, 1);
f1d1c3fa 1304 } else {
e381e77c 1305 lwkt_send_ipiq3(td->td_gd, lwkt_schedule_remote, td, 0);
7cd8d145 1306 }
8ad65e08 1307 }
37af14fe 1308 crit_exit_gd(mygd);
8ad65e08
MD
1309}
1310
361d01dd
MD
1311void
1312lwkt_schedule(thread_t td)
1313{
85946b6c 1314 _lwkt_schedule(td);
361d01dd
MD
1315}
1316
1317void
85946b6c 1318lwkt_schedule_noresched(thread_t td) /* XXX not impl */
361d01dd 1319{
85946b6c 1320 _lwkt_schedule(td);
361d01dd
MD
1321}
1322
e381e77c
MD
1323/*
1324 * When scheduled remotely if frame != NULL the IPIQ is being
1325 * run via doreti or an interrupt then preemption can be allowed.
1326 *
1327 * To allow preemption we have to drop the critical section so only
1328 * one is present in _lwkt_schedule_post.
1329 */
1330static void
1331lwkt_schedule_remote(void *arg, int arg2, struct intrframe *frame)
1332{
1333 thread_t td = curthread;
1334 thread_t ntd = arg;
1335
1336 if (frame && ntd->td_preemptable) {
1337 crit_exit_noyield(td);
85946b6c 1338 _lwkt_schedule(ntd);
e381e77c
MD
1339 crit_enter_quick(td);
1340 } else {
85946b6c 1341 _lwkt_schedule(ntd);
e381e77c
MD
1342 }
1343}
1344
d9eea1a5 1345/*
52eedfb5
MD
1346 * Thread migration using a 'Pull' method. The thread may or may not be
1347 * the current thread. It MUST be descheduled and in a stable state.
1348 * lwkt_giveaway() must be called on the cpu owning the thread.
1349 *
1350 * At any point after lwkt_giveaway() is called, the target cpu may
1351 * 'pull' the thread by calling lwkt_acquire().
1352 *
ae8e83e6
MD
1353 * We have to make sure the thread is not sitting on a per-cpu tsleep
1354 * queue or it will blow up when it moves to another cpu.
1355 *
52eedfb5 1356 * MPSAFE - must be called under very specific conditions.
d9eea1a5 1357 */
52eedfb5
MD
1358void
1359lwkt_giveaway(thread_t td)
1360{
3b4192fb 1361 globaldata_t gd = mycpu;
52eedfb5 1362
3b4192fb
MD
1363 crit_enter_gd(gd);
1364 if (td->td_flags & TDF_TSLEEPQ)
1365 tsleep_remove(td);
1366 KKASSERT(td->td_gd == gd);
1367 TAILQ_REMOVE(&gd->gd_tdallq, td, td_allq);
1368 td->td_flags |= TDF_MIGRATING;
1369 crit_exit_gd(gd);
52eedfb5
MD
1370}
1371
a2a5ad0d
MD
1372void
1373lwkt_acquire(thread_t td)
1374{
37af14fe
MD
1375 globaldata_t gd;
1376 globaldata_t mygd;
cc9b6223 1377 int retry = 10000000;
a2a5ad0d 1378
52eedfb5 1379 KKASSERT(td->td_flags & TDF_MIGRATING);
a2a5ad0d 1380 gd = td->td_gd;
37af14fe 1381 mygd = mycpu;
52eedfb5 1382 if (gd != mycpu) {
35238fa5 1383 cpu_lfence();
52eedfb5 1384 KKASSERT((td->td_flags & TDF_RUNQ) == 0);
37af14fe 1385 crit_enter_gd(mygd);
cfaeae2a 1386 DEBUG_PUSH_INFO("lwkt_acquire");
df910c23 1387 while (td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK)) {
df910c23 1388 lwkt_process_ipiq();
52eedfb5 1389 cpu_lfence();
cc9b6223
MD
1390 if (--retry == 0) {
1391 kprintf("lwkt_acquire: stuck: td %p td->td_flags %08x\n",
1392 td, td->td_flags);
1393 retry = 10000000;
1394 }
a86ce0cd
MD
1395#ifdef _KERNEL_VIRTUAL
1396 pthread_yield();
1397#endif
df910c23 1398 }
cfaeae2a 1399 DEBUG_POP_INFO();
562273ea 1400 cpu_mfence();
37af14fe 1401 td->td_gd = mygd;
52eedfb5
MD
1402 TAILQ_INSERT_TAIL(&mygd->gd_tdallq, td, td_allq);
1403 td->td_flags &= ~TDF_MIGRATING;
1404 crit_exit_gd(mygd);
1405 } else {
1406 crit_enter_gd(mygd);
1407 TAILQ_INSERT_TAIL(&mygd->gd_tdallq, td, td_allq);
1408 td->td_flags &= ~TDF_MIGRATING;
37af14fe 1409 crit_exit_gd(mygd);
a2a5ad0d
MD
1410 }
1411}
1412
f1d1c3fa
MD
1413/*
1414 * Generic deschedule. Descheduling threads other then your own should be
1415 * done only in carefully controlled circumstances. Descheduling is
1416 * asynchronous.
1417 *
1418 * This function may block if the cpu has run out of messages.
8ad65e08
MD
1419 */
1420void
1421lwkt_deschedule(thread_t td)
1422{
f1d1c3fa
MD
1423 crit_enter();
1424 if (td == curthread) {
1425 _lwkt_dequeue(td);
1426 } else {
a72187e9 1427 if (td->td_gd == mycpu) {
f1d1c3fa
MD
1428 _lwkt_dequeue(td);
1429 } else {
b8a98473 1430 lwkt_send_ipiq(td->td_gd, (ipifunc1_t)lwkt_deschedule, td);
f1d1c3fa
MD
1431 }
1432 }
1433 crit_exit();
1434}
1435
4b5f931b
MD
1436/*
1437 * Set the target thread's priority. This routine does not automatically
1438 * switch to a higher priority thread, LWKT threads are not designed for
1439 * continuous priority changes. Yield if you want to switch.
4b5f931b
MD
1440 */
1441void
1442lwkt_setpri(thread_t td, int pri)
1443{
f9235b6d
MD
1444 if (td->td_pri != pri) {
1445 KKASSERT(pri >= 0);
1446 crit_enter();
1447 if (td->td_flags & TDF_RUNQ) {
d2d8515b 1448 KKASSERT(td->td_gd == mycpu);
f9235b6d
MD
1449 _lwkt_dequeue(td);
1450 td->td_pri = pri;
1451 _lwkt_enqueue(td);
1452 } else {
1453 td->td_pri = pri;
1454 }
1455 crit_exit();
26a0694b 1456 }
26a0694b
MD
1457}
1458
03bd0a5e
MD
1459/*
1460 * Set the initial priority for a thread prior to it being scheduled for
1461 * the first time. The thread MUST NOT be scheduled before or during
1462 * this call. The thread may be assigned to a cpu other then the current
1463 * cpu.
1464 *
1465 * Typically used after a thread has been created with TDF_STOPPREQ,
1466 * and before the thread is initially scheduled.
1467 */
1468void
1469lwkt_setpri_initial(thread_t td, int pri)
1470{
1471 KKASSERT(pri >= 0);
1472 KKASSERT((td->td_flags & TDF_RUNQ) == 0);
f9235b6d 1473 td->td_pri = pri;
03bd0a5e
MD
1474}
1475
26a0694b
MD
1476void
1477lwkt_setpri_self(int pri)
1478{
1479 thread_t td = curthread;
1480
4b5f931b
MD
1481 KKASSERT(pri >= 0 && pri <= TDPRI_MAX);
1482 crit_enter();
1483 if (td->td_flags & TDF_RUNQ) {
1484 _lwkt_dequeue(td);
f9235b6d 1485 td->td_pri = pri;
4b5f931b
MD
1486 _lwkt_enqueue(td);
1487 } else {
f9235b6d 1488 td->td_pri = pri;
4b5f931b
MD
1489 }
1490 crit_exit();
1491}
1492
f9235b6d 1493/*
85946b6c 1494 * hz tick scheduler clock for LWKT threads
f9235b6d
MD
1495 */
1496void
85946b6c 1497lwkt_schedulerclock(thread_t td)
f9235b6d 1498{
85946b6c
MD
1499 globaldata_t gd = td->td_gd;
1500 thread_t xtd;
2a418930 1501
85946b6c
MD
1502 if (TAILQ_FIRST(&gd->gd_tdrunq) == td) {
1503 /*
1504 * If the current thread is at the head of the runq shift it to the
1505 * end of any equal-priority threads and request a LWKT reschedule
1506 * if it moved.
d992c377
MD
1507 *
1508 * Ignore upri in this situation. There will only be one user thread
1509 * in user mode, all others will be user threads running in kernel
1510 * mode and we have to make sure they get some cpu.
85946b6c
MD
1511 */
1512 xtd = TAILQ_NEXT(td, td_threadq);
1513 if (xtd && xtd->td_pri == td->td_pri) {
1514 TAILQ_REMOVE(&gd->gd_tdrunq, td, td_threadq);
1515 while (xtd && xtd->td_pri == td->td_pri)
1516 xtd = TAILQ_NEXT(xtd, td_threadq);
1517 if (xtd)
1518 TAILQ_INSERT_BEFORE(xtd, td, td_threadq);
1519 else
1520 TAILQ_INSERT_TAIL(&gd->gd_tdrunq, td, td_threadq);
1521 need_lwkt_resched();
f9235b6d 1522 }
85946b6c
MD
1523 } else {
1524 /*
1525 * If we scheduled a thread other than the one at the head of the
1526 * queue always request a reschedule every tick.
1527 */
1528 need_lwkt_resched();
f9235b6d
MD
1529 }
1530}
1531
5d21b981 1532/*
52eedfb5
MD
1533 * Migrate the current thread to the specified cpu.
1534 *
cc9b6223
MD
1535 * This is accomplished by descheduling ourselves from the current cpu
1536 * and setting td_migrate_gd. The lwkt_switch() code will detect that the
1537 * 'old' thread wants to migrate after it has been completely switched out
1538 * and will complete the migration.
1539 *
1540 * TDF_MIGRATING prevents scheduling races while the thread is being migrated.
1541 *
1542 * We must be sure to release our current process designation (if a user
1543 * process) before clearing out any tsleepq we are on because the release
1544 * code may re-add us.
ae8e83e6
MD
1545 *
1546 * We must be sure to remove ourselves from the current cpu's tsleepq
1547 * before potentially moving to another queue. The thread can be on
1548 * a tsleepq due to a left-over tsleep_interlock().
5d21b981 1549 */
5d21b981
MD
1550
1551void
1552lwkt_setcpu_self(globaldata_t rgd)
1553{
5d21b981
MD
1554 thread_t td = curthread;
1555
1556 if (td->td_gd != rgd) {
1557 crit_enter_quick(td);
cc9b6223 1558
95858b91
MD
1559 if (td->td_release)
1560 td->td_release(td);
ae8e83e6 1561 if (td->td_flags & TDF_TSLEEPQ)
3b4192fb 1562 tsleep_remove(td);
cc9b6223
MD
1563
1564 /*
1565 * Set TDF_MIGRATING to prevent a spurious reschedule while we are
1566 * trying to deschedule ourselves and switch away, then deschedule
1567 * ourself, remove us from tdallq, and set td_migrate_gd. Finally,
1568 * call lwkt_switch() to complete the operation.
1569 */
5d21b981
MD
1570 td->td_flags |= TDF_MIGRATING;
1571 lwkt_deschedule_self(td);
52eedfb5 1572 TAILQ_REMOVE(&td->td_gd->gd_tdallq, td, td_allq);
cc9b6223 1573 td->td_migrate_gd = rgd;
5d21b981 1574 lwkt_switch();
cc9b6223
MD
1575
1576 /*
1577 * We are now on the target cpu
1578 */
1579 KKASSERT(rgd == mycpu);
52eedfb5 1580 TAILQ_INSERT_TAIL(&rgd->gd_tdallq, td, td_allq);
5d21b981
MD
1581 crit_exit_quick(td);
1582 }
5d21b981
MD
1583}
1584
ecdefdda
MD
1585void
1586lwkt_migratecpu(int cpuid)
1587{
ecdefdda
MD
1588 globaldata_t rgd;
1589
1590 rgd = globaldata_find(cpuid);
1591 lwkt_setcpu_self(rgd);
ecdefdda
MD
1592}
1593
5d21b981
MD
1594/*
1595 * Remote IPI for cpu migration (called while in a critical section so we
cc9b6223
MD
1596 * do not have to enter another one).
1597 *
1598 * The thread (td) has already been completely descheduled from the
1599 * originating cpu and we can simply assert the case. The thread is
1600 * assigned to the new cpu and enqueued.
5d21b981 1601 *
cc9b6223 1602 * The thread will re-add itself to tdallq when it resumes execution.
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1603 */
1604static void
1605lwkt_setcpu_remote(void *arg)
1606{
1607 thread_t td = arg;
1608 globaldata_t gd = mycpu;
1609
cc9b6223 1610 KKASSERT((td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK)) == 0);
5d21b981 1611 td->td_gd = gd;
562273ea 1612 cpu_mfence();
5d21b981 1613 td->td_flags &= ~TDF_MIGRATING;
cc9b6223 1614 KKASSERT(td->td_migrate_gd == NULL);
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1615 KKASSERT(td->td_lwp == NULL ||
1616 (td->td_lwp->lwp_mpflags & LWP_MP_ONRUNQ) == 0);
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1617 _lwkt_enqueue(td);
1618}
1619
553ea3c8 1620struct lwp *
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1621lwkt_preempted_proc(void)
1622{
73e4f7b9 1623 thread_t td = curthread;
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1624 while (td->td_preempted)
1625 td = td->td_preempted;
553ea3c8 1626 return(td->td_lwp);
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1627}
1628
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1629/*
1630 * Create a kernel process/thread/whatever. It shares it's address space
1631 * with proc0 - ie: kernel only.
1632 *
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1633 * If the cpu is not specified one will be selected. In the future
1634 * specifying a cpu of -1 will enable kernel thread migration between
1635 * cpus.
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1636 */
1637int
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1638lwkt_create(void (*func)(void *), void *arg, struct thread **tdp,
1639 thread_t template, int tdflags, int cpu, const char *fmt, ...)
99df837e 1640{
73e4f7b9 1641 thread_t td;
e2565a42 1642 __va_list ap;
99df837e 1643
d3d32139 1644 td = lwkt_alloc_thread(template, LWKT_THREAD_STACK, cpu,
dbcd0c9b 1645 tdflags);
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1646 if (tdp)
1647 *tdp = td;
709799ea 1648 cpu_set_thread_handler(td, lwkt_exit, func, arg);
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1649
1650 /*
1651 * Set up arg0 for 'ps' etc
1652 */
e2565a42 1653 __va_start(ap, fmt);
379210cb 1654 kvsnprintf(td->td_comm, sizeof(td->td_comm), fmt, ap);
e2565a42 1655 __va_end(ap);
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1656
1657 /*
1658 * Schedule the thread to run
1659 */
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1660 if (td->td_flags & TDF_NOSTART)
1661 td->td_flags &= ~TDF_NOSTART;
ef0fdad1 1662 else
4643740a 1663 lwkt_schedule(td);
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1664 return 0;
1665}
1666
1667/*
1668 * Destroy an LWKT thread. Warning! This function is not called when
1669 * a process exits, cpu_proc_exit() directly calls cpu_thread_exit() and
1670 * uses a different reaping mechanism.
1671 */
1672void
1673lwkt_exit(void)
1674{
1675 thread_t td = curthread;
c070746a 1676 thread_t std;
8826f33a 1677 globaldata_t gd;
99df837e 1678
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1679 /*
1680 * Do any cleanup that might block here
1681 */
99df837e 1682 if (td->td_flags & TDF_VERBOSE)
6ea70f76 1683 kprintf("kthread %p %s has exited\n", td, td->td_comm);
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1684 biosched_done(td);
1685 dsched_exit_thread(td);
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1686
1687 /*
1688 * Get us into a critical section to interlock gd_freetd and loop
1689 * until we can get it freed.
1690 *
1691 * We have to cache the current td in gd_freetd because objcache_put()ing
1692 * it would rip it out from under us while our thread is still active.
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1693 *
1694 * We are the current thread so of course our own TDF_RUNNING bit will
1695 * be set, so unlike the lwp reap code we don't wait for it to clear.
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1696 */
1697 gd = mycpu;
37af14fe 1698 crit_enter_quick(td);
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1699 for (;;) {
1700 if (td->td_refs) {
1701 tsleep(td, 0, "tdreap", 1);
1702 continue;
1703 }
1704 if ((std = gd->gd_freetd) != NULL) {
1705 KKASSERT((std->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK)) == 0);
1706 gd->gd_freetd = NULL;
1707 objcache_put(thread_cache, std);
1708 continue;
1709 }
1710 break;
c070746a 1711 }
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1712
1713 /*
1714 * Remove thread resources from kernel lists and deschedule us for
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1715 * the last time. We cannot block after this point or we may end
1716 * up with a stale td on the tsleepq.
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1717 *
1718 * None of this may block, the critical section is the only thing
1719 * protecting tdallq and the only thing preventing new lwkt_hold()
1720 * thread refs now.
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1721 */
1722 if (td->td_flags & TDF_TSLEEPQ)
1723 tsleep_remove(td);
37af14fe 1724 lwkt_deschedule_self(td);
e56e4dea 1725 lwkt_remove_tdallq(td);
74c9628e 1726 KKASSERT(td->td_refs == 0);
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1727
1728 /*
1729 * Final cleanup
1730 */
1731 KKASSERT(gd->gd_freetd == NULL);
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1732 if (td->td_flags & TDF_ALLOCATED_THREAD)
1733 gd->gd_freetd = td;
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1734 cpu_thread_exit();
1735}
1736
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1737void
1738lwkt_remove_tdallq(thread_t td)
1739{
1740 KKASSERT(td->td_gd == mycpu);
1741 TAILQ_REMOVE(&td->td_gd->gd_tdallq, td, td_allq);
1742}
1743
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1744/*
1745 * Code reduction and branch prediction improvements. Call/return
1746 * overhead on modern cpus often degenerates into 0 cycles due to
1747 * the cpu's branch prediction hardware and return pc cache. We
1748 * can take advantage of this by not inlining medium-complexity
1749 * functions and we can also reduce the branch prediction impact
1750 * by collapsing perfectly predictable branches into a single
1751 * procedure instead of duplicating it.
1752 *
1753 * Is any of this noticeable? Probably not, so I'll take the
1754 * smaller code size.
1755 */
1756void
b6468f56 1757crit_exit_wrapper(__DEBUG_CRIT_ARG__)
9cf43f91 1758{
b6468f56 1759 _crit_exit(mycpu __DEBUG_CRIT_PASS_ARG__);
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1760}
1761
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1762void
1763crit_panic(void)
1764{
1765 thread_t td = curthread;
850634cc 1766 int lcrit = td->td_critcount;
2d93b37a 1767
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AH
1768 td->td_critcount = 0;
1769 panic("td_critcount is/would-go negative! %p %d", td, lcrit);
4a28fe22 1770 /* NOT REACHED */
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1771}
1772
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1773/*
1774 * Called from debugger/panic on cpus which have been stopped. We must still
b19f40a4 1775 * process the IPIQ while stopped.
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1776 *
1777 * If we are dumping also try to process any pending interrupts. This may
1778 * or may not work depending on the state of the cpu at the point it was
1779 * stopped.
1780 */
1781void
1782lwkt_smp_stopped(void)
1783{
1784 globaldata_t gd = mycpu;
1785
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1786 if (dumping) {
1787 lwkt_process_ipiq();
b19f40a4 1788 --gd->gd_intr_nesting_level;
bd8015ca 1789 splz();
b19f40a4 1790 ++gd->gd_intr_nesting_level;
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1791 } else {
1792 lwkt_process_ipiq();
1793 }
bd8015ca 1794}