Merge branch 'master' of git://git.dragonflybsd.org/dragonfly
[dragonfly.git] / sys / kern / lwkt_thread.c
CommitLineData
8ad65e08 1/*
3b998fa9 2 * Copyright (c) 2003-2010 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>
f6bf3af1 53#include <sys/caps.h>
9d265729 54#include <sys/spinlock.h>
57aa743c 55#include <sys/ktr.h>
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56
57#include <sys/thread2.h>
58#include <sys/spinlock2.h>
684a93c4 59#include <sys/mplock2.h>
f1d1c3fa 60
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61#include <sys/dsched.h>
62
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63#include <vm/vm.h>
64#include <vm/vm_param.h>
65#include <vm/vm_kern.h>
66#include <vm/vm_object.h>
67#include <vm/vm_page.h>
68#include <vm/vm_map.h>
69#include <vm/vm_pager.h>
70#include <vm/vm_extern.h>
7d0bac62 71
99df837e 72#include <machine/stdarg.h>
96728c05 73#include <machine/smp.h>
99df837e 74
d850923c
AE
75#if !defined(KTR_CTXSW)
76#define KTR_CTXSW KTR_ALL
77#endif
78KTR_INFO_MASTER(ctxsw);
a1f0fb66
AE
79KTR_INFO(KTR_CTXSW, ctxsw, sw, 0, "#cpu[%d].td = %p",
80 sizeof(int) + sizeof(struct thread *));
81KTR_INFO(KTR_CTXSW, ctxsw, pre, 1, "#cpu[%d].td = %p",
82 sizeof(int) + sizeof(struct thread *));
83KTR_INFO(KTR_CTXSW, ctxsw, newtd, 2, "#threads[%p].name = %s",
84 sizeof (struct thread *) + sizeof(char *));
85KTR_INFO(KTR_CTXSW, ctxsw, deadtd, 3, "#threads[%p].name = <dead>", sizeof (struct thread *));
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;
f64b567c 96static __int64_t token_contention_count __debugvar = 0;
fb0f29c4 97static int lwkt_use_spin_port;
40aaf5fc 98static struct objcache *thread_cache;
05220613 99
88ebb169 100#ifdef SMP
e381e77c 101static void lwkt_schedule_remote(void *arg, int arg2, struct intrframe *frame);
88ebb169 102#endif
f9235b6d 103static void lwkt_fairq_accumulate(globaldata_t gd, thread_t td);
e381e77c 104
0855a2af
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105extern void cpu_heavy_restore(void);
106extern void cpu_lwkt_restore(void);
107extern void cpu_kthread_restore(void);
108extern void cpu_idle_restore(void);
109
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110/*
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.
113 */
114TUNABLE_INT("lwkt.use_spin_port", &lwkt_use_spin_port);
115
0f7a3396 116#ifdef INVARIANTS
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117SYSCTL_INT(_lwkt, OID_AUTO, panic_on_cscount, CTLFLAG_RW, &panic_on_cscount, 0,
118 "Panic if attempting to switch lwkt's while mastering cpusync");
0f7a3396 119#endif
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120SYSCTL_QUAD(_lwkt, OID_AUTO, switch_count, CTLFLAG_RW, &switch_count, 0,
121 "Number of switched threads");
9733f757 122SYSCTL_QUAD(_lwkt, OID_AUTO, preempt_hit, CTLFLAG_RW, &preempt_hit, 0,
0c52fa62 123 "Successful preemption events");
9733f757 124SYSCTL_QUAD(_lwkt, OID_AUTO, preempt_miss, CTLFLAG_RW, &preempt_miss, 0,
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125 "Failed preemption events");
126SYSCTL_QUAD(_lwkt, OID_AUTO, preempt_weird, CTLFLAG_RW, &preempt_weird, 0,
127 "Number of preempted threads.");
38717797
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128#ifdef INVARIANTS
129SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count, CTLFLAG_RW,
130 &token_contention_count, 0, "spinning due to token contention");
38717797 131#endif
f9235b6d 132static int fairq_enable = 1;
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133SYSCTL_INT(_lwkt, OID_AUTO, fairq_enable, CTLFLAG_RW,
134 &fairq_enable, 0, "Turn on fairq priority accumulators");
135static int lwkt_spin_loops = 10;
136SYSCTL_INT(_lwkt, OID_AUTO, spin_loops, CTLFLAG_RW,
137 &lwkt_spin_loops, 0, "");
138static int lwkt_spin_delay = 1;
139SYSCTL_INT(_lwkt, OID_AUTO, spin_delay, CTLFLAG_RW,
140 &lwkt_spin_delay, 0, "Scheduler spin delay in microseconds 0=auto");
141static int lwkt_spin_method = 1;
142SYSCTL_INT(_lwkt, OID_AUTO, spin_method, CTLFLAG_RW,
143 &lwkt_spin_method, 0, "LWKT scheduler behavior when contended");
fbc024e4 144static int preempt_enable = 1;
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145SYSCTL_INT(_lwkt, OID_AUTO, preempt_enable, CTLFLAG_RW,
146 &preempt_enable, 0, "Enable preemption");
fbc024e4 147
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148static __cachealign int lwkt_cseq_rindex;
149static __cachealign int lwkt_cseq_windex;
05220613 150
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151/*
152 * These helper procedures handle the runq, they can only be called from
153 * within a critical section.
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154 *
155 * WARNING! Prior to SMP being brought up it is possible to enqueue and
156 * dequeue threads belonging to other cpus, so be sure to use td->td_gd
157 * instead of 'mycpu' when referencing the globaldata structure. Once
158 * SMP live enqueuing and dequeueing only occurs on the current cpu.
4b5f931b 159 */
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160static __inline
161void
162_lwkt_dequeue(thread_t td)
163{
164 if (td->td_flags & TDF_RUNQ) {
75cdbe6c 165 struct globaldata *gd = td->td_gd;
4b5f931b 166
f1d1c3fa 167 td->td_flags &= ~TDF_RUNQ;
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168 TAILQ_REMOVE(&gd->gd_tdrunq, td, td_threadq);
169 gd->gd_fairq_total_pri -= td->td_pri;
170 if (TAILQ_FIRST(&gd->gd_tdrunq) == NULL)
2a418930 171 atomic_clear_int(&gd->gd_reqflags, RQF_RUNNING);
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172 }
173}
174
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175/*
176 * Priority enqueue.
177 *
178 * NOTE: There are a limited number of lwkt threads runnable since user
179 * processes only schedule one at a time per cpu.
180 */
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181static __inline
182void
183_lwkt_enqueue(thread_t td)
184{
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185 thread_t xtd;
186
7f5d7ed7 187 if ((td->td_flags & (TDF_RUNQ|TDF_MIGRATING|TDF_BLOCKQ)) == 0) {
75cdbe6c 188 struct globaldata *gd = td->td_gd;
4b5f931b 189
f1d1c3fa 190 td->td_flags |= TDF_RUNQ;
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191 xtd = TAILQ_FIRST(&gd->gd_tdrunq);
192 if (xtd == NULL) {
193 TAILQ_INSERT_TAIL(&gd->gd_tdrunq, td, td_threadq);
2a418930 194 atomic_set_int(&gd->gd_reqflags, RQF_RUNNING);
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195 } else {
196 while (xtd && xtd->td_pri > td->td_pri)
197 xtd = TAILQ_NEXT(xtd, td_threadq);
198 if (xtd)
199 TAILQ_INSERT_BEFORE(xtd, td, td_threadq);
200 else
201 TAILQ_INSERT_TAIL(&gd->gd_tdrunq, td, td_threadq);
202 }
203 gd->gd_fairq_total_pri += td->td_pri;
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204 }
205}
8ad65e08 206
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207static __boolean_t
208_lwkt_thread_ctor(void *obj, void *privdata, int ocflags)
209{
210 struct thread *td = (struct thread *)obj;
211
212 td->td_kstack = NULL;
213 td->td_kstack_size = 0;
214 td->td_flags = TDF_ALLOCATED_THREAD;
215 return (1);
216}
217
218static void
219_lwkt_thread_dtor(void *obj, void *privdata)
220{
221 struct thread *td = (struct thread *)obj;
222
223 KASSERT(td->td_flags & TDF_ALLOCATED_THREAD,
224 ("_lwkt_thread_dtor: not allocated from objcache"));
225 KASSERT((td->td_flags & TDF_ALLOCATED_STACK) && td->td_kstack &&
226 td->td_kstack_size > 0,
227 ("_lwkt_thread_dtor: corrupted stack"));
228 kmem_free(&kernel_map, (vm_offset_t)td->td_kstack, td->td_kstack_size);
229}
230
231/*
232 * Initialize the lwkt s/system.
233 */
234void
235lwkt_init(void)
236{
237 /* An objcache has 2 magazines per CPU so divide cache size by 2. */
0aa16b5d
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238 thread_cache = objcache_create_mbacked(M_THREAD, sizeof(struct thread),
239 NULL, CACHE_NTHREADS/2,
240 _lwkt_thread_ctor, _lwkt_thread_dtor, NULL);
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NT
241}
242
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243/*
244 * Schedule a thread to run. As the current thread we can always safely
245 * schedule ourselves, and a shortcut procedure is provided for that
246 * function.
247 *
248 * (non-blocking, self contained on a per cpu basis)
249 */
250void
251lwkt_schedule_self(thread_t td)
252{
253 crit_enter_quick(td);
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254 KASSERT(td != &td->td_gd->gd_idlethread,
255 ("lwkt_schedule_self(): scheduling gd_idlethread is illegal!"));
9388413d 256 KKASSERT(td->td_lwp == NULL || (td->td_lwp->lwp_flag & LWP_ONRUNQ) == 0);
37af14fe 257 _lwkt_enqueue(td);
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258 crit_exit_quick(td);
259}
260
261/*
262 * Deschedule a thread.
263 *
264 * (non-blocking, self contained on a per cpu basis)
265 */
266void
267lwkt_deschedule_self(thread_t td)
268{
269 crit_enter_quick(td);
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270 _lwkt_dequeue(td);
271 crit_exit_quick(td);
272}
273
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274/*
275 * LWKTs operate on a per-cpu basis
276 *
73e4f7b9 277 * WARNING! Called from early boot, 'mycpu' may not work yet.
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278 */
279void
280lwkt_gdinit(struct globaldata *gd)
281{
f9235b6d 282 TAILQ_INIT(&gd->gd_tdrunq);
73e4f7b9 283 TAILQ_INIT(&gd->gd_tdallq);
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284}
285
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286/*
287 * Create a new thread. The thread must be associated with a process context
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288 * or LWKT start address before it can be scheduled. If the target cpu is
289 * -1 the thread will be created on the current cpu.
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290 *
291 * If you intend to create a thread without a process context this function
292 * does everything except load the startup and switcher function.
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293 */
294thread_t
d3d32139 295lwkt_alloc_thread(struct thread *td, int stksize, int cpu, int flags)
7d0bac62 296{
c070746a 297 globaldata_t gd = mycpu;
99df837e 298 void *stack;
7d0bac62 299
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300 /*
301 * If static thread storage is not supplied allocate a thread. Reuse
302 * a cached free thread if possible. gd_freetd is used to keep an exiting
303 * thread intact through the exit.
304 */
ef0fdad1 305 if (td == NULL) {
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MD
306 crit_enter_gd(gd);
307 if ((td = gd->gd_freetd) != NULL) {
308 KKASSERT((td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK|
309 TDF_RUNQ)) == 0);
c070746a 310 gd->gd_freetd = NULL;
cf709dd2 311 } else {
c070746a 312 td = objcache_get(thread_cache, M_WAITOK);
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313 KKASSERT((td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK|
314 TDF_RUNQ)) == 0);
315 }
316 crit_exit_gd(gd);
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317 KASSERT((td->td_flags &
318 (TDF_ALLOCATED_THREAD|TDF_RUNNING)) == TDF_ALLOCATED_THREAD,
319 ("lwkt_alloc_thread: corrupted td flags 0x%X", td->td_flags));
320 flags |= td->td_flags & (TDF_ALLOCATED_THREAD|TDF_ALLOCATED_STACK);
ef0fdad1 321 }
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322
323 /*
324 * Try to reuse cached stack.
325 */
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MD
326 if ((stack = td->td_kstack) != NULL && td->td_kstack_size != stksize) {
327 if (flags & TDF_ALLOCATED_STACK) {
e4846942 328 kmem_free(&kernel_map, (vm_offset_t)stack, td->td_kstack_size);
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MD
329 stack = NULL;
330 }
331 }
332 if (stack == NULL) {
e40cfbd7 333 stack = (void *)kmem_alloc_stack(&kernel_map, stksize);
ef0fdad1 334 flags |= TDF_ALLOCATED_STACK;
99df837e 335 }
75cdbe6c 336 if (cpu < 0)
c070746a 337 lwkt_init_thread(td, stack, stksize, flags, gd);
75cdbe6c 338 else
f470d0c8 339 lwkt_init_thread(td, stack, stksize, flags, globaldata_find(cpu));
99df837e 340 return(td);
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341}
342
343/*
344 * Initialize a preexisting thread structure. This function is used by
345 * lwkt_alloc_thread() and also used to initialize the per-cpu idlethread.
346 *
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347 * All threads start out in a critical section at a priority of
348 * TDPRI_KERN_DAEMON. Higher level code will modify the priority as
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349 * appropriate. This function may send an IPI message when the
350 * requested cpu is not the current cpu and consequently gd_tdallq may
351 * not be initialized synchronously from the point of view of the originating
352 * cpu.
353 *
354 * NOTE! we have to be careful in regards to creating threads for other cpus
355 * if SMP has not yet been activated.
7d0bac62 356 */
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357#ifdef SMP
358
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359static void
360lwkt_init_thread_remote(void *arg)
361{
362 thread_t td = arg;
363
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364 /*
365 * Protected by critical section held by IPI dispatch
366 */
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367 TAILQ_INSERT_TAIL(&td->td_gd->gd_tdallq, td, td_allq);
368}
369
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370#endif
371
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372/*
373 * lwkt core thread structural initialization.
374 *
375 * NOTE: All threads are initialized as mpsafe threads.
376 */
7d0bac62 377void
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378lwkt_init_thread(thread_t td, void *stack, int stksize, int flags,
379 struct globaldata *gd)
7d0bac62 380{
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MD
381 globaldata_t mygd = mycpu;
382
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383 bzero(td, sizeof(struct thread));
384 td->td_kstack = stack;
f470d0c8 385 td->td_kstack_size = stksize;
d3d32139 386 td->td_flags = flags;
26a0694b 387 td->td_gd = gd;
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388 td->td_pri = TDPRI_KERN_DAEMON;
389 td->td_critcount = 1;
3b998fa9 390 td->td_toks_stop = &td->td_toks_base;
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391 if (lwkt_use_spin_port)
392 lwkt_initport_spin(&td->td_msgport);
393 else
394 lwkt_initport_thread(&td->td_msgport, td);
99df837e 395 pmap_init_thread(td);
0f7a3396 396#ifdef SMP
5d21b981
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397 /*
398 * Normally initializing a thread for a remote cpu requires sending an
399 * IPI. However, the idlethread is setup before the other cpus are
400 * activated so we have to treat it as a special case. XXX manipulation
401 * of gd_tdallq requires the BGL.
402 */
403 if (gd == mygd || td == &gd->gd_idlethread) {
37af14fe 404 crit_enter_gd(mygd);
75cdbe6c 405 TAILQ_INSERT_TAIL(&gd->gd_tdallq, td, td_allq);
37af14fe 406 crit_exit_gd(mygd);
75cdbe6c 407 } else {
2db3b277 408 lwkt_send_ipiq(gd, lwkt_init_thread_remote, td);
75cdbe6c 409 }
0f7a3396 410#else
37af14fe 411 crit_enter_gd(mygd);
0f7a3396 412 TAILQ_INSERT_TAIL(&gd->gd_tdallq, td, td_allq);
37af14fe 413 crit_exit_gd(mygd);
0f7a3396 414#endif
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415
416 dsched_new_thread(td);
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417}
418
419void
420lwkt_set_comm(thread_t td, const char *ctl, ...)
421{
e2565a42 422 __va_list va;
73e4f7b9 423
e2565a42 424 __va_start(va, ctl);
379210cb 425 kvsnprintf(td->td_comm, sizeof(td->td_comm), ctl, va);
e2565a42 426 __va_end(va);
e7c0dbba 427 KTR_LOG(ctxsw_newtd, td, &td->td_comm[0]);
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428}
429
99df837e 430void
73e4f7b9 431lwkt_hold(thread_t td)
99df837e 432{
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433 ++td->td_refs;
434}
435
436void
437lwkt_rele(thread_t td)
438{
439 KKASSERT(td->td_refs > 0);
440 --td->td_refs;
441}
442
443void
444lwkt_wait_free(thread_t td)
445{
446 while (td->td_refs)
377d4740 447 tsleep(td, 0, "tdreap", hz);
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448}
449
450void
451lwkt_free_thread(thread_t td)
452{
cf709dd2 453 KKASSERT((td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK|TDF_RUNQ)) == 0);
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454 if (td->td_flags & TDF_ALLOCATED_THREAD) {
455 objcache_put(thread_cache, td);
456 } else if (td->td_flags & TDF_ALLOCATED_STACK) {
457 /* client-allocated struct with internally allocated stack */
458 KASSERT(td->td_kstack && td->td_kstack_size > 0,
459 ("lwkt_free_thread: corrupted stack"));
460 kmem_free(&kernel_map, (vm_offset_t)td->td_kstack, td->td_kstack_size);
461 td->td_kstack = NULL;
462 td->td_kstack_size = 0;
99df837e 463 }
e7c0dbba 464 KTR_LOG(ctxsw_deadtd, td);
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465}
466
467
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468/*
469 * Switch to the next runnable lwkt. If no LWKTs are runnable then
f1d1c3fa
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470 * switch to the idlethread. Switching must occur within a critical
471 * section to avoid races with the scheduling queue.
472 *
473 * We always have full control over our cpu's run queue. Other cpus
474 * that wish to manipulate our queue must use the cpu_*msg() calls to
475 * talk to our cpu, so a critical section is all that is needed and
476 * the result is very, very fast thread switching.
477 *
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478 * The LWKT scheduler uses a fixed priority model and round-robins at
479 * each priority level. User process scheduling is a totally
480 * different beast and LWKT priorities should not be confused with
481 * user process priorities.
f1d1c3fa 482 *
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483 * Note that the td_switch() function cannot do anything that requires
484 * the MP lock since the MP lock will have already been setup for
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485 * the target thread (not the current thread). It's nice to have a scheduler
486 * that does not need the MP lock to work because it allows us to do some
487 * really cool high-performance MP lock optimizations.
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488 *
489 * PREEMPTION NOTE: Preemption occurs via lwkt_preempt(). lwkt_switch()
490 * is not called by the current thread in the preemption case, only when
491 * the preempting thread blocks (in order to return to the original thread).
8ad65e08
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492 */
493void
494lwkt_switch(void)
495{
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496 globaldata_t gd = mycpu;
497 thread_t td = gd->gd_curthread;
8ad65e08 498 thread_t ntd;
f9235b6d 499 thread_t xtd;
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500 int spinning = lwkt_spin_loops; /* loops before HLTing */
501 int reqflags;
502 int cseq;
8ad65e08 503
46a3f46d 504 /*
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505 * Switching from within a 'fast' (non thread switched) interrupt or IPI
506 * is illegal. However, we may have to do it anyway if we hit a fatal
507 * kernel trap or we have paniced.
508 *
509 * If this case occurs save and restore the interrupt nesting level.
46a3f46d 510 */
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511 if (gd->gd_intr_nesting_level) {
512 int savegdnest;
513 int savegdtrap;
514
5fddbda2 515 if (gd->gd_trap_nesting_level == 0 && panic_cpu_gd != mycpu) {
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516 panic("lwkt_switch: Attempt to switch from a "
517 "a fast interrupt, ipi, or hard code section, "
518 "td %p\n",
519 td);
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MD
520 } else {
521 savegdnest = gd->gd_intr_nesting_level;
522 savegdtrap = gd->gd_trap_nesting_level;
523 gd->gd_intr_nesting_level = 0;
524 gd->gd_trap_nesting_level = 0;
a7422615
MD
525 if ((td->td_flags & TDF_PANICWARN) == 0) {
526 td->td_flags |= TDF_PANICWARN;
4a28fe22
MD
527 kprintf("Warning: thread switch from interrupt, IPI, "
528 "or hard code section.\n"
a7422615 529 "thread %p (%s)\n", td, td->td_comm);
7ce2998e 530 print_backtrace(-1);
a7422615 531 }
27e88a6e
MD
532 lwkt_switch();
533 gd->gd_intr_nesting_level = savegdnest;
534 gd->gd_trap_nesting_level = savegdtrap;
535 return;
536 }
96728c05 537 }
ef0fdad1 538
cb973d15
MD
539 /*
540 * Passive release (used to transition from user to kernel mode
541 * when we block or switch rather then when we enter the kernel).
542 * This function is NOT called if we are switching into a preemption
543 * or returning from a preemption. Typically this causes us to lose
0a3f9b47
MD
544 * our current process designation (if we have one) and become a true
545 * LWKT thread, and may also hand the current process designation to
546 * another process and schedule thread.
cb973d15
MD
547 */
548 if (td->td_release)
549 td->td_release(td);
550
37af14fe 551 crit_enter_gd(gd);
3b998fa9 552 if (TD_TOKS_HELD(td))
9d265729
MD
553 lwkt_relalltokens(td);
554
555 /*
b02926de
MD
556 * We had better not be holding any spin locks, but don't get into an
557 * endless panic loop.
9d265729 558 */
d666840a
MD
559 KASSERT(gd->gd_spinlocks_wr == 0 || panicstr != NULL,
560 ("lwkt_switch: still holding %d exclusive spinlocks!",
561 gd->gd_spinlocks_wr));
9d265729 562
8a8d5d85
MD
563
564#ifdef SMP
0f7a3396
MD
565#ifdef INVARIANTS
566 if (td->td_cscount) {
6ea70f76 567 kprintf("Diagnostic: attempt to switch while mastering cpusync: %p\n",
0f7a3396
MD
568 td);
569 if (panic_on_cscount)
570 panic("switching while mastering cpusync");
571 }
572#endif
8a8d5d85 573#endif
f9235b6d
MD
574
575 /*
576 * If we had preempted another thread on this cpu, resume the preempted
577 * thread. This occurs transparently, whether the preempted thread
578 * was scheduled or not (it may have been preempted after descheduling
579 * itself).
580 *
581 * We have to setup the MP lock for the original thread after backing
582 * out the adjustment that was made to curthread when the original
583 * was preempted.
584 */
99df837e 585 if ((ntd = td->td_preempted) != NULL) {
26a0694b
MD
586 KKASSERT(ntd->td_flags & TDF_PREEMPT_LOCK);
587 ntd->td_flags |= TDF_PREEMPT_DONE;
8ec60c3f
MD
588
589 /*
b9eb1c19
MD
590 * The interrupt may have woken a thread up, we need to properly
591 * set the reschedule flag if the originally interrupted thread is
592 * at a lower priority.
8ec60c3f 593 */
f9235b6d
MD
594 if (TAILQ_FIRST(&gd->gd_tdrunq) &&
595 TAILQ_FIRST(&gd->gd_tdrunq)->td_pri > ntd->td_pri) {
8ec60c3f 596 need_lwkt_resched();
f9235b6d 597 }
8a8d5d85 598 /* YYY release mp lock on switchback if original doesn't need it */
f9235b6d
MD
599 goto havethread_preempted;
600 }
601
602 /*
603 * Implement round-robin fairq with priority insertion. The priority
604 * insertion is handled by _lwkt_enqueue()
605 *
606 * We have to adjust the MP lock for the target thread. If we
607 * need the MP lock and cannot obtain it we try to locate a
608 * thread that does not need the MP lock. If we cannot, we spin
609 * instead of HLT.
610 *
611 * A similar issue exists for the tokens held by the target thread.
612 * If we cannot obtain ownership of the tokens we cannot immediately
613 * schedule the thread.
614 */
615 for (;;) {
2a418930
MD
616 /*
617 * Clear RQF_AST_LWKT_RESCHED (we handle the reschedule request)
618 * and set RQF_WAKEUP (prevent unnecessary IPIs from being
619 * received).
620 */
621 for (;;) {
622 reqflags = gd->gd_reqflags;
623 if (atomic_cmpset_int(&gd->gd_reqflags, reqflags,
624 (reqflags & ~RQF_AST_LWKT_RESCHED) |
625 RQF_WAKEUP)) {
626 break;
627 }
628 }
f9235b6d 629
4b5f931b 630 /*
2a418930
MD
631 * Hotpath - pull the head of the run queue and attempt to schedule
632 * it. Fairq exhaustion moves the task to the end of the list. If
633 * no threads are runnable we switch to the idle thread.
41a01a4d 634 */
2a418930
MD
635 for (;;) {
636 ntd = TAILQ_FIRST(&gd->gd_tdrunq);
637
638 if (ntd == NULL) {
639 /*
640 * Runq is empty, switch to idle and clear RQF_WAKEUP
641 * to allow it to halt.
642 */
643 ntd = &gd->gd_idlethread;
6f207a2c 644#ifdef SMP
2a418930 645 if (gd->gd_trap_nesting_level == 0 && panicstr == NULL)
b5d16701 646 ASSERT_NO_TOKENS_HELD(ntd);
6f207a2c 647#endif
2a418930
MD
648 cpu_time.cp_msg[0] = 0;
649 cpu_time.cp_stallpc = 0;
650 atomic_clear_int(&gd->gd_reqflags, RQF_WAKEUP);
651 goto haveidle;
652 }
653
654 if (ntd->td_fairq_accum >= 0)
655 break;
656
657 splz_check();
658 lwkt_fairq_accumulate(gd, ntd);
659 TAILQ_REMOVE(&gd->gd_tdrunq, ntd, td_threadq);
660 TAILQ_INSERT_TAIL(&gd->gd_tdrunq, ntd, td_threadq);
f9235b6d 661 }
41a01a4d 662
8ec60c3f 663 /*
2a418930
MD
664 * Hotpath - schedule ntd. Leaves RQF_WAKEUP set to prevent
665 * unwanted decontention IPIs.
6f207a2c
MD
666 *
667 * NOTE: For UP there is no mplock and lwkt_getalltokens()
668 * always succeeds.
8ec60c3f 669 */
2a418930 670 if (TD_TOKS_NOT_HELD(ntd) || lwkt_getalltokens(ntd))
f9235b6d 671 goto havethread;
f9235b6d 672
f9235b6d 673 /*
2a418930
MD
674 * Coldpath (SMP only since tokens always succeed on UP)
675 *
676 * We had some contention on the thread we wanted to schedule.
677 * What we do now is try to find a thread that we can schedule
678 * in its stead until decontention reschedules on our cpu.
679 *
680 * The coldpath scan does NOT rearrange threads in the run list
681 * and it also ignores the accumulator.
682 *
683 * We do not immediately schedule a user priority thread, instead
684 * we record it in xtd and continue looking for kernel threads.
685 * A cpu can only have one user priority thread (normally) so just
686 * record the first one.
687 *
688 * NOTE: This scan will also include threads whos fairq's were
689 * accumulated in the first loop.
f9235b6d 690 */
2a418930
MD
691 ++token_contention_count;
692 xtd = NULL;
693 while ((ntd = TAILQ_NEXT(ntd, td_threadq)) != NULL) {
41a01a4d 694 /*
2a418930
MD
695 * Try to switch to this thread. If the thread is running at
696 * user priority we clear WAKEUP to allow decontention IPIs
697 * (since this thread is simply running until the one we wanted
698 * decontends), and we make sure that LWKT_RESCHED is not set.
df6b8ba0 699 *
2a418930
MD
700 * Otherwise for kernel threads we leave WAKEUP set to avoid
701 * unnecessary decontention IPIs.
41a01a4d 702 */
2a418930
MD
703 if (ntd->td_pri < TDPRI_KERN_LPSCHED) {
704 if (xtd == NULL)
705 xtd = ntd;
706 continue;
f9235b6d 707 }
a453459d 708
f9235b6d 709 /*
2a418930
MD
710 * Do not let the fairq get too negative. Even though we are
711 * ignoring it atm once the scheduler decontends a very negative
712 * thread will get moved to the end of the queue.
f9235b6d 713 */
2a418930
MD
714 if (TD_TOKS_NOT_HELD(ntd) || lwkt_getalltokens(ntd)) {
715 if (ntd->td_fairq_accum < -TDFAIRQ_MAX(gd))
716 ntd->td_fairq_accum = -TDFAIRQ_MAX(gd);
717 goto havethread;
8a8d5d85 718 }
f9235b6d 719
df6b8ba0 720 /*
2a418930 721 * Well fubar, this thread is contended as well, loop
df6b8ba0 722 */
2a418930
MD
723 /* */
724 }
725
726 /*
727 * We exhausted the run list but we may have recorded a user
728 * thread to try. We have three choices based on
729 * lwkt.decontention_method.
730 *
731 * (0) Atomically clear RQF_WAKEUP in order to receive decontention
732 * IPIs (to interrupt the user process) and test
733 * RQF_AST_LWKT_RESCHED at the same time.
734 *
735 * This results in significant decontention IPI traffic but may
736 * be more responsive.
737 *
738 * (1) Leave RQF_WAKEUP set so we do not receive a decontention IPI.
739 * An automatic LWKT reschedule will occur on the next hardclock
740 * (typically 100hz).
741 *
742 * This results in no decontention IPI traffic but may be less
743 * responsive. This is the default.
744 *
745 * (2) Refuse to schedule the user process at this time.
746 *
747 * This is highly experimental and should not be used under
748 * normal circumstances. This can cause a user process to
749 * get starved out in situations where kernel threads are
750 * fighting each other for tokens.
751 */
752 if (xtd) {
753 ntd = xtd;
754
755 switch(lwkt_spin_method) {
756 case 0:
757 for (;;) {
758 reqflags = gd->gd_reqflags;
759 if (atomic_cmpset_int(&gd->gd_reqflags,
760 reqflags,
761 reqflags & ~RQF_WAKEUP)) {
762 break;
763 }
764 }
765 break;
766 case 1:
767 reqflags = gd->gd_reqflags;
768 break;
769 default:
770 goto skip;
771 break;
772 }
773 if ((reqflags & RQF_AST_LWKT_RESCHED) == 0 &&
b5d16701 774 (TD_TOKS_NOT_HELD(ntd) || lwkt_getalltokens(ntd))
f9235b6d 775 ) {
2a418930
MD
776 if (ntd->td_fairq_accum < -TDFAIRQ_MAX(gd))
777 ntd->td_fairq_accum = -TDFAIRQ_MAX(gd);
778 goto havethread;
df6b8ba0 779 }
9ac1ee6e 780
2a418930 781skip:
9ac1ee6e 782 /*
2a418930
MD
783 * Make sure RQF_WAKEUP is set if we failed to schedule the
784 * user thread to prevent the idle thread from halting.
9ac1ee6e 785 */
2a418930
MD
786 atomic_set_int(&gd->gd_reqflags, RQF_WAKEUP);
787 }
788
789 /*
790 * We exhausted the run list, meaning that all runnable threads
791 * are contended.
792 */
793 cpu_pause();
794 ntd = &gd->gd_idlethread;
795#ifdef SMP
796 if (gd->gd_trap_nesting_level == 0 && panicstr == NULL)
797 ASSERT_NO_TOKENS_HELD(ntd);
798 /* contention case, do not clear contention mask */
799#endif
800
801 /*
802 * Ok, we might want to spin a few times as some tokens are held for
803 * very short periods of time and IPI overhead is 1uS or worse
804 * (meaning it is usually better to spin). Regardless we have to
805 * call splz_check() to be sure to service any interrupts blocked
806 * by our critical section, otherwise we could livelock e.g. IPIs.
807 *
808 * The IPI mechanic is really a last resort. In nearly all other
809 * cases RQF_WAKEUP is left set to prevent decontention IPIs.
810 *
811 * When we decide not to spin we clear RQF_WAKEUP and switch to
812 * the idle thread. Clearing RQF_WEAKEUP allows the idle thread
813 * to halt and decontended tokens will issue an IPI to us. The
814 * idle thread will check for pending reschedules already set
815 * (RQF_AST_LWKT_RESCHED) before actually halting so we don't have
816 * to here.
817 */
818 if (spinning <= 0) {
819 atomic_clear_int(&gd->gd_reqflags, RQF_WAKEUP);
820 goto haveidle;
4b5f931b 821 }
2a418930 822 --spinning;
c5724852
MD
823
824 /*
2a418930
MD
825 * When spinning a delay is required both to avoid livelocks from
826 * token order reversals (a thread may be trying to acquire multiple
827 * tokens), and also to reduce cpu cache management traffic.
828 *
829 * In order to scale to a large number of CPUs we use a time slot
830 * resequencer to force contending cpus into non-contending
831 * time-slots. The scheduler may still contend with the lock holder
832 * but will not (generally) contend with all the other cpus trying
833 * trying to get the same token.
834 *
835 * The resequencer uses a FIFO counter mechanic. The owner of the
836 * rindex at the head of the FIFO is allowed to pull itself off
837 * the FIFO and fetchadd is used to enter into the FIFO. This bit
838 * of code is VERY cache friendly and forces all spinning schedulers
839 * into their own time slots.
c5724852 840 *
2a418930
MD
841 * This code has been tested to 48-cpus and caps the cache
842 * contention load at ~1uS intervals regardless of the number of
843 * cpus. Scaling beyond 64 cpus might require additional smarts
844 * (such as separate FIFOs for specific token cases).
845 *
846 * WARNING! We can't call splz_check() or anything else here as
847 * it could cause a deadlock.
c5724852 848 */
2a418930
MD
849 cseq = atomic_fetchadd_int(&lwkt_cseq_windex, 1);
850 while (lwkt_cseq_rindex != cseq) {
851 DELAY(1);
852 cpu_lfence();
853 }
854 cseq = lwkt_spin_delay; /* don't trust the system operator */
855 cpu_ccfence();
856 if (cseq < 1)
857 cseq = 1;
858 if (cseq > 1000)
859 cseq = 1000;
860 DELAY(cseq);
861 atomic_add_int(&lwkt_cseq_rindex, 1);
c5724852 862 splz_check();
2a418930 863 /* highest level for(;;) loop */
f1d1c3fa 864 }
8a8d5d85 865
2a418930 866havethread:
8a8d5d85 867 /*
f9235b6d
MD
868 * We must always decrement td_fairq_accum on non-idle threads just
869 * in case a thread never gets a tick due to being in a continuous
2a418930 870 * critical section. The page-zeroing code does this, for example.
f9235b6d
MD
871 *
872 * If the thread we came up with is a higher or equal priority verses
873 * the thread at the head of the queue we move our thread to the
874 * front. This way we can always check the front of the queue.
875 */
f9235b6d
MD
876 ++gd->gd_cnt.v_swtch;
877 --ntd->td_fairq_accum;
9ac1ee6e 878 ntd->td_wmesg = NULL;
f9235b6d
MD
879 xtd = TAILQ_FIRST(&gd->gd_tdrunq);
880 if (ntd != xtd && ntd->td_pri >= xtd->td_pri) {
881 TAILQ_REMOVE(&gd->gd_tdrunq, ntd, td_threadq);
882 TAILQ_INSERT_HEAD(&gd->gd_tdrunq, ntd, td_threadq);
883 }
2a418930 884
f9235b6d 885havethread_preempted:
f9235b6d
MD
886 /*
887 * If the new target does not need the MP lock and we are holding it,
888 * release the MP lock. If the new target requires the MP lock we have
889 * already acquired it for the target.
8a8d5d85 890 */
2a418930 891 ;
f9235b6d
MD
892haveidle:
893 KASSERT(ntd->td_critcount,
b5d16701
MD
894 ("priority problem in lwkt_switch %d %d",
895 td->td_critcount, ntd->td_critcount));
896
94f6d86e
MD
897 if (td != ntd) {
898 ++switch_count;
a1f0fb66 899 KTR_LOG(ctxsw_sw, gd->gd_cpuid, ntd);
f1d1c3fa 900 td->td_switch(ntd);
94f6d86e 901 }
37af14fe
MD
902 /* NOTE: current cpu may have changed after switch */
903 crit_exit_quick(td);
8ad65e08
MD
904}
905
b68b7282 906/*
96728c05
MD
907 * Request that the target thread preempt the current thread. Preemption
908 * only works under a specific set of conditions:
b68b7282 909 *
96728c05
MD
910 * - We are not preempting ourselves
911 * - The target thread is owned by the current cpu
912 * - We are not currently being preempted
913 * - The target is not currently being preempted
d3d1cbc8
MD
914 * - We are not holding any spin locks
915 * - The target thread is not holding any tokens
96728c05
MD
916 * - We are able to satisfy the target's MP lock requirements (if any).
917 *
918 * THE CALLER OF LWKT_PREEMPT() MUST BE IN A CRITICAL SECTION. Typically
919 * this is called via lwkt_schedule() through the td_preemptable callback.
f9235b6d 920 * critcount is the managed critical priority that we should ignore in order
96728c05
MD
921 * to determine whether preemption is possible (aka usually just the crit
922 * priority of lwkt_schedule() itself).
b68b7282 923 *
26a0694b
MD
924 * XXX at the moment we run the target thread in a critical section during
925 * the preemption in order to prevent the target from taking interrupts
926 * that *WE* can't. Preemption is strictly limited to interrupt threads
927 * and interrupt-like threads, outside of a critical section, and the
928 * preempted source thread will be resumed the instant the target blocks
929 * whether or not the source is scheduled (i.e. preemption is supposed to
930 * be as transparent as possible).
b68b7282
MD
931 */
932void
f9235b6d 933lwkt_preempt(thread_t ntd, int critcount)
b68b7282 934{
46a3f46d 935 struct globaldata *gd = mycpu;
0a3f9b47 936 thread_t td;
2d910aaf 937 int save_gd_intr_nesting_level;
b68b7282 938
26a0694b 939 /*
96728c05
MD
940 * The caller has put us in a critical section. We can only preempt
941 * if the caller of the caller was not in a critical section (basically
f9235b6d 942 * a local interrupt), as determined by the 'critcount' parameter. We
47737962 943 * also can't preempt if the caller is holding any spinlocks (even if
d666840a 944 * he isn't in a critical section). This also handles the tokens test.
96728c05
MD
945 *
946 * YYY The target thread must be in a critical section (else it must
947 * inherit our critical section? I dunno yet).
41a01a4d 948 *
0a3f9b47 949 * Set need_lwkt_resched() unconditionally for now YYY.
26a0694b 950 */
f9235b6d 951 KASSERT(ntd->td_critcount, ("BADCRIT0 %d", ntd->td_pri));
26a0694b 952
fbc024e4
MD
953 if (preempt_enable == 0) {
954 ++preempt_miss;
955 return;
956 }
957
0a3f9b47 958 td = gd->gd_curthread;
f9235b6d 959 if (ntd->td_pri <= td->td_pri) {
57c254db
MD
960 ++preempt_miss;
961 return;
962 }
f9235b6d 963 if (td->td_critcount > critcount) {
96728c05 964 ++preempt_miss;
8ec60c3f 965 need_lwkt_resched();
96728c05
MD
966 return;
967 }
968#ifdef SMP
46a3f46d 969 if (ntd->td_gd != gd) {
96728c05 970 ++preempt_miss;
8ec60c3f 971 need_lwkt_resched();
96728c05
MD
972 return;
973 }
974#endif
41a01a4d 975 /*
77912481
MD
976 * We don't have to check spinlocks here as they will also bump
977 * td_critcount.
d3d1cbc8
MD
978 *
979 * Do not try to preempt if the target thread is holding any tokens.
980 * We could try to acquire the tokens but this case is so rare there
981 * is no need to support it.
41a01a4d 982 */
77912481
MD
983 KKASSERT(gd->gd_spinlocks_wr == 0);
984
3b998fa9 985 if (TD_TOKS_HELD(ntd)) {
d3d1cbc8
MD
986 ++preempt_miss;
987 need_lwkt_resched();
988 return;
989 }
26a0694b
MD
990 if (td == ntd || ((td->td_flags | ntd->td_flags) & TDF_PREEMPT_LOCK)) {
991 ++preempt_weird;
8ec60c3f 992 need_lwkt_resched();
26a0694b
MD
993 return;
994 }
995 if (ntd->td_preempted) {
4b5f931b 996 ++preempt_hit;
8ec60c3f 997 need_lwkt_resched();
26a0694b 998 return;
b68b7282 999 }
26a0694b 1000
8ec60c3f
MD
1001 /*
1002 * Since we are able to preempt the current thread, there is no need to
1003 * call need_lwkt_resched().
2d910aaf
MD
1004 *
1005 * We must temporarily clear gd_intr_nesting_level around the switch
1006 * since switchouts from the target thread are allowed (they will just
1007 * return to our thread), and since the target thread has its own stack.
8ec60c3f 1008 */
26a0694b
MD
1009 ++preempt_hit;
1010 ntd->td_preempted = td;
1011 td->td_flags |= TDF_PREEMPT_LOCK;
a1f0fb66 1012 KTR_LOG(ctxsw_pre, gd->gd_cpuid, ntd);
2d910aaf
MD
1013 save_gd_intr_nesting_level = gd->gd_intr_nesting_level;
1014 gd->gd_intr_nesting_level = 0;
26a0694b 1015 td->td_switch(ntd);
2d910aaf 1016 gd->gd_intr_nesting_level = save_gd_intr_nesting_level;
b9eb1c19 1017
26a0694b
MD
1018 KKASSERT(ntd->td_preempted && (td->td_flags & TDF_PREEMPT_DONE));
1019 ntd->td_preempted = NULL;
1020 td->td_flags &= ~(TDF_PREEMPT_LOCK|TDF_PREEMPT_DONE);
b68b7282
MD
1021}
1022
f1d1c3fa 1023/*
faaeffac 1024 * Conditionally call splz() if gd_reqflags indicates work is pending.
4a28fe22
MD
1025 * This will work inside a critical section but not inside a hard code
1026 * section.
ef0fdad1 1027 *
f1d1c3fa
MD
1028 * (self contained on a per cpu basis)
1029 */
1030void
faaeffac 1031splz_check(void)
f1d1c3fa 1032{
7966cb69
MD
1033 globaldata_t gd = mycpu;
1034 thread_t td = gd->gd_curthread;
ef0fdad1 1035
4a28fe22
MD
1036 if ((gd->gd_reqflags & RQF_IDLECHECK_MASK) &&
1037 gd->gd_intr_nesting_level == 0 &&
1038 td->td_nest_count < 2)
1039 {
f1d1c3fa 1040 splz();
4a28fe22
MD
1041 }
1042}
1043
1044/*
1045 * This version is integrated into crit_exit, reqflags has already
1046 * been tested but td_critcount has not.
1047 *
1048 * We only want to execute the splz() on the 1->0 transition of
1049 * critcount and not in a hard code section or if too deeply nested.
1050 */
1051void
1052lwkt_maybe_splz(thread_t td)
1053{
1054 globaldata_t gd = td->td_gd;
1055
1056 if (td->td_critcount == 0 &&
1057 gd->gd_intr_nesting_level == 0 &&
1058 td->td_nest_count < 2)
1059 {
1060 splz();
1061 }
f1d1c3fa
MD
1062}
1063
8ad65e08 1064/*
f9235b6d
MD
1065 * This function is used to negotiate a passive release of the current
1066 * process/lwp designation with the user scheduler, allowing the user
1067 * scheduler to schedule another user thread. The related kernel thread
1068 * (curthread) continues running in the released state.
8ad65e08
MD
1069 */
1070void
f9235b6d 1071lwkt_passive_release(struct thread *td)
8ad65e08 1072{
f9235b6d
MD
1073 struct lwp *lp = td->td_lwp;
1074
1075 td->td_release = NULL;
1076 lwkt_setpri_self(TDPRI_KERN_USER);
1077 lp->lwp_proc->p_usched->release_curproc(lp);
f1d1c3fa
MD
1078}
1079
f9235b6d 1080
3824f392 1081/*
f9235b6d
MD
1082 * This implements a normal yield. This routine is virtually a nop if
1083 * there is nothing to yield to but it will always run any pending interrupts
1084 * if called from a critical section.
1085 *
1086 * This yield is designed for kernel threads without a user context.
1087 *
1088 * (self contained on a per cpu basis)
3824f392
MD
1089 */
1090void
f9235b6d 1091lwkt_yield(void)
3824f392 1092{
f9235b6d
MD
1093 globaldata_t gd = mycpu;
1094 thread_t td = gd->gd_curthread;
1095 thread_t xtd;
3824f392 1096
f9235b6d
MD
1097 if ((gd->gd_reqflags & RQF_IDLECHECK_MASK) && td->td_nest_count < 2)
1098 splz();
1099 if (td->td_fairq_accum < 0) {
1100 lwkt_schedule_self(curthread);
1101 lwkt_switch();
1102 } else {
1103 xtd = TAILQ_FIRST(&gd->gd_tdrunq);
1104 if (xtd && xtd->td_pri > td->td_pri) {
1105 lwkt_schedule_self(curthread);
1106 lwkt_switch();
1107 }
1108 }
3824f392
MD
1109}
1110
1111/*
f9235b6d
MD
1112 * This yield is designed for kernel threads with a user context.
1113 *
1114 * The kernel acting on behalf of the user is potentially cpu-bound,
1115 * this function will efficiently allow other threads to run and also
1116 * switch to other processes by releasing.
3824f392
MD
1117 *
1118 * The lwkt_user_yield() function is designed to have very low overhead
1119 * if no yield is determined to be needed.
1120 */
1121void
1122lwkt_user_yield(void)
1123{
f9235b6d
MD
1124 globaldata_t gd = mycpu;
1125 thread_t td = gd->gd_curthread;
1126
1127 /*
1128 * Always run any pending interrupts in case we are in a critical
1129 * section.
1130 */
1131 if ((gd->gd_reqflags & RQF_IDLECHECK_MASK) && td->td_nest_count < 2)
1132 splz();
3824f392 1133
3824f392 1134 /*
f9235b6d
MD
1135 * Switch (which forces a release) if another kernel thread needs
1136 * the cpu, if userland wants us to resched, or if our kernel
1137 * quantum has run out.
3824f392 1138 */
f9235b6d
MD
1139 if (lwkt_resched_wanted() ||
1140 user_resched_wanted() ||
1141 td->td_fairq_accum < 0)
1142 {
3824f392 1143 lwkt_switch();
3824f392
MD
1144 }
1145
f9235b6d 1146#if 0
3824f392 1147 /*
f9235b6d
MD
1148 * Reacquire the current process if we are released.
1149 *
1150 * XXX not implemented atm. The kernel may be holding locks and such,
1151 * so we want the thread to continue to receive cpu.
3824f392 1152 */
f9235b6d
MD
1153 if (td->td_release == NULL && lp) {
1154 lp->lwp_proc->p_usched->acquire_curproc(lp);
1155 td->td_release = lwkt_passive_release;
1156 lwkt_setpri_self(TDPRI_USER_NORM);
3824f392 1157 }
f9235b6d 1158#endif
b9eb1c19
MD
1159}
1160
8ad65e08 1161/*
f1d1c3fa
MD
1162 * Generic schedule. Possibly schedule threads belonging to other cpus and
1163 * deal with threads that might be blocked on a wait queue.
1164 *
0a3f9b47
MD
1165 * We have a little helper inline function which does additional work after
1166 * the thread has been enqueued, including dealing with preemption and
1167 * setting need_lwkt_resched() (which prevents the kernel from returning
1168 * to userland until it has processed higher priority threads).
6330a558
MD
1169 *
1170 * It is possible for this routine to be called after a failed _enqueue
1171 * (due to the target thread migrating, sleeping, or otherwise blocked).
1172 * We have to check that the thread is actually on the run queue!
361d01dd
MD
1173 *
1174 * reschedok is an optimized constant propagated from lwkt_schedule() or
1175 * lwkt_schedule_noresched(). By default it is non-zero, causing a
1176 * reschedule to be requested if the target thread has a higher priority.
1177 * The port messaging code will set MSG_NORESCHED and cause reschedok to
1178 * be 0, prevented undesired reschedules.
8ad65e08 1179 */
0a3f9b47
MD
1180static __inline
1181void
f9235b6d 1182_lwkt_schedule_post(globaldata_t gd, thread_t ntd, int ccount, int reschedok)
0a3f9b47 1183{
b9eb1c19 1184 thread_t otd;
c730be20 1185
6330a558 1186 if (ntd->td_flags & TDF_RUNQ) {
361d01dd 1187 if (ntd->td_preemptable && reschedok) {
f9235b6d 1188 ntd->td_preemptable(ntd, ccount); /* YYY +token */
361d01dd 1189 } else if (reschedok) {
b9eb1c19 1190 otd = curthread;
f9235b6d 1191 if (ntd->td_pri > otd->td_pri)
c730be20 1192 need_lwkt_resched();
6330a558 1193 }
f9235b6d
MD
1194
1195 /*
1196 * Give the thread a little fair share scheduler bump if it
1197 * has been asleep for a while. This is primarily to avoid
1198 * a degenerate case for interrupt threads where accumulator
1199 * crosses into negative territory unnecessarily.
1200 */
1201 if (ntd->td_fairq_lticks != ticks) {
1202 ntd->td_fairq_lticks = ticks;
1203 ntd->td_fairq_accum += gd->gd_fairq_total_pri;
1204 if (ntd->td_fairq_accum > TDFAIRQ_MAX(gd))
1205 ntd->td_fairq_accum = TDFAIRQ_MAX(gd);
1206 }
0a3f9b47
MD
1207 }
1208}
1209
361d01dd 1210static __inline
8ad65e08 1211void
361d01dd 1212_lwkt_schedule(thread_t td, int reschedok)
8ad65e08 1213{
37af14fe
MD
1214 globaldata_t mygd = mycpu;
1215
cf709dd2
MD
1216 KASSERT(td != &td->td_gd->gd_idlethread,
1217 ("lwkt_schedule(): scheduling gd_idlethread is illegal!"));
37af14fe 1218 crit_enter_gd(mygd);
9388413d 1219 KKASSERT(td->td_lwp == NULL || (td->td_lwp->lwp_flag & LWP_ONRUNQ) == 0);
37af14fe 1220 if (td == mygd->gd_curthread) {
f1d1c3fa
MD
1221 _lwkt_enqueue(td);
1222 } else {
f1d1c3fa 1223 /*
7cd8d145
MD
1224 * If we own the thread, there is no race (since we are in a
1225 * critical section). If we do not own the thread there might
1226 * be a race but the target cpu will deal with it.
f1d1c3fa 1227 */
0f7a3396 1228#ifdef SMP
7cd8d145 1229 if (td->td_gd == mygd) {
9d265729 1230 _lwkt_enqueue(td);
f9235b6d 1231 _lwkt_schedule_post(mygd, td, 1, reschedok);
f1d1c3fa 1232 } else {
e381e77c 1233 lwkt_send_ipiq3(td->td_gd, lwkt_schedule_remote, td, 0);
7cd8d145 1234 }
0f7a3396 1235#else
7cd8d145 1236 _lwkt_enqueue(td);
f9235b6d 1237 _lwkt_schedule_post(mygd, td, 1, reschedok);
0f7a3396 1238#endif
8ad65e08 1239 }
37af14fe 1240 crit_exit_gd(mygd);
8ad65e08
MD
1241}
1242
361d01dd
MD
1243void
1244lwkt_schedule(thread_t td)
1245{
1246 _lwkt_schedule(td, 1);
1247}
1248
1249void
1250lwkt_schedule_noresched(thread_t td)
1251{
1252 _lwkt_schedule(td, 0);
1253}
1254
88ebb169
SW
1255#ifdef SMP
1256
e381e77c
MD
1257/*
1258 * When scheduled remotely if frame != NULL the IPIQ is being
1259 * run via doreti or an interrupt then preemption can be allowed.
1260 *
1261 * To allow preemption we have to drop the critical section so only
1262 * one is present in _lwkt_schedule_post.
1263 */
1264static void
1265lwkt_schedule_remote(void *arg, int arg2, struct intrframe *frame)
1266{
1267 thread_t td = curthread;
1268 thread_t ntd = arg;
1269
1270 if (frame && ntd->td_preemptable) {
1271 crit_exit_noyield(td);
1272 _lwkt_schedule(ntd, 1);
1273 crit_enter_quick(td);
1274 } else {
1275 _lwkt_schedule(ntd, 1);
1276 }
1277}
1278
d9eea1a5 1279/*
52eedfb5
MD
1280 * Thread migration using a 'Pull' method. The thread may or may not be
1281 * the current thread. It MUST be descheduled and in a stable state.
1282 * lwkt_giveaway() must be called on the cpu owning the thread.
1283 *
1284 * At any point after lwkt_giveaway() is called, the target cpu may
1285 * 'pull' the thread by calling lwkt_acquire().
1286 *
ae8e83e6
MD
1287 * We have to make sure the thread is not sitting on a per-cpu tsleep
1288 * queue or it will blow up when it moves to another cpu.
1289 *
52eedfb5 1290 * MPSAFE - must be called under very specific conditions.
d9eea1a5 1291 */
52eedfb5
MD
1292void
1293lwkt_giveaway(thread_t td)
1294{
3b4192fb 1295 globaldata_t gd = mycpu;
52eedfb5 1296
3b4192fb
MD
1297 crit_enter_gd(gd);
1298 if (td->td_flags & TDF_TSLEEPQ)
1299 tsleep_remove(td);
1300 KKASSERT(td->td_gd == gd);
1301 TAILQ_REMOVE(&gd->gd_tdallq, td, td_allq);
1302 td->td_flags |= TDF_MIGRATING;
1303 crit_exit_gd(gd);
52eedfb5
MD
1304}
1305
a2a5ad0d
MD
1306void
1307lwkt_acquire(thread_t td)
1308{
37af14fe
MD
1309 globaldata_t gd;
1310 globaldata_t mygd;
a2a5ad0d 1311
52eedfb5 1312 KKASSERT(td->td_flags & TDF_MIGRATING);
a2a5ad0d 1313 gd = td->td_gd;
37af14fe 1314 mygd = mycpu;
52eedfb5 1315 if (gd != mycpu) {
35238fa5 1316 cpu_lfence();
52eedfb5 1317 KKASSERT((td->td_flags & TDF_RUNQ) == 0);
37af14fe 1318 crit_enter_gd(mygd);
df910c23
MD
1319 while (td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK)) {
1320#ifdef SMP
1321 lwkt_process_ipiq();
1322#endif
52eedfb5 1323 cpu_lfence();
df910c23 1324 }
562273ea 1325 cpu_mfence();
37af14fe 1326 td->td_gd = mygd;
52eedfb5
MD
1327 TAILQ_INSERT_TAIL(&mygd->gd_tdallq, td, td_allq);
1328 td->td_flags &= ~TDF_MIGRATING;
1329 crit_exit_gd(mygd);
1330 } else {
1331 crit_enter_gd(mygd);
1332 TAILQ_INSERT_TAIL(&mygd->gd_tdallq, td, td_allq);
1333 td->td_flags &= ~TDF_MIGRATING;
37af14fe 1334 crit_exit_gd(mygd);
a2a5ad0d
MD
1335 }
1336}
1337
52eedfb5
MD
1338#endif
1339
f1d1c3fa
MD
1340/*
1341 * Generic deschedule. Descheduling threads other then your own should be
1342 * done only in carefully controlled circumstances. Descheduling is
1343 * asynchronous.
1344 *
1345 * This function may block if the cpu has run out of messages.
8ad65e08
MD
1346 */
1347void
1348lwkt_deschedule(thread_t td)
1349{
f1d1c3fa 1350 crit_enter();
b8a98473 1351#ifdef SMP
f1d1c3fa
MD
1352 if (td == curthread) {
1353 _lwkt_dequeue(td);
1354 } else {
a72187e9 1355 if (td->td_gd == mycpu) {
f1d1c3fa
MD
1356 _lwkt_dequeue(td);
1357 } else {
b8a98473 1358 lwkt_send_ipiq(td->td_gd, (ipifunc1_t)lwkt_deschedule, td);
f1d1c3fa
MD
1359 }
1360 }
b8a98473
MD
1361#else
1362 _lwkt_dequeue(td);
1363#endif
f1d1c3fa
MD
1364 crit_exit();
1365}
1366
4b5f931b
MD
1367/*
1368 * Set the target thread's priority. This routine does not automatically
1369 * switch to a higher priority thread, LWKT threads are not designed for
1370 * continuous priority changes. Yield if you want to switch.
4b5f931b
MD
1371 */
1372void
1373lwkt_setpri(thread_t td, int pri)
1374{
a72187e9 1375 KKASSERT(td->td_gd == mycpu);
f9235b6d
MD
1376 if (td->td_pri != pri) {
1377 KKASSERT(pri >= 0);
1378 crit_enter();
1379 if (td->td_flags & TDF_RUNQ) {
1380 _lwkt_dequeue(td);
1381 td->td_pri = pri;
1382 _lwkt_enqueue(td);
1383 } else {
1384 td->td_pri = pri;
1385 }
1386 crit_exit();
26a0694b 1387 }
26a0694b
MD
1388}
1389
03bd0a5e
MD
1390/*
1391 * Set the initial priority for a thread prior to it being scheduled for
1392 * the first time. The thread MUST NOT be scheduled before or during
1393 * this call. The thread may be assigned to a cpu other then the current
1394 * cpu.
1395 *
1396 * Typically used after a thread has been created with TDF_STOPPREQ,
1397 * and before the thread is initially scheduled.
1398 */
1399void
1400lwkt_setpri_initial(thread_t td, int pri)
1401{
1402 KKASSERT(pri >= 0);
1403 KKASSERT((td->td_flags & TDF_RUNQ) == 0);
f9235b6d 1404 td->td_pri = pri;
03bd0a5e
MD
1405}
1406
26a0694b
MD
1407void
1408lwkt_setpri_self(int pri)
1409{
1410 thread_t td = curthread;
1411
4b5f931b
MD
1412 KKASSERT(pri >= 0 && pri <= TDPRI_MAX);
1413 crit_enter();
1414 if (td->td_flags & TDF_RUNQ) {
1415 _lwkt_dequeue(td);
f9235b6d 1416 td->td_pri = pri;
4b5f931b
MD
1417 _lwkt_enqueue(td);
1418 } else {
f9235b6d 1419 td->td_pri = pri;
4b5f931b
MD
1420 }
1421 crit_exit();
1422}
1423
f9235b6d
MD
1424/*
1425 * 1/hz tick (typically 10ms) x TDFAIRQ_SCALE (typ 8) = 80ms full cycle.
1426 *
1427 * Example: two competing threads, same priority N. decrement by (2*N)
1428 * increment by N*8, each thread will get 4 ticks.
1429 */
1430void
1431lwkt_fairq_schedulerclock(thread_t td)
1432{
2a418930
MD
1433 globaldata_t gd;
1434
f9235b6d
MD
1435 if (fairq_enable) {
1436 while (td) {
2a418930
MD
1437 gd = td->td_gd;
1438 if (td != &gd->gd_idlethread) {
1439 td->td_fairq_accum -= gd->gd_fairq_total_pri;
1440 if (td->td_fairq_accum < -TDFAIRQ_MAX(gd))
1441 td->td_fairq_accum = -TDFAIRQ_MAX(gd);
f9235b6d
MD
1442 if (td->td_fairq_accum < 0)
1443 need_lwkt_resched();
1444 td->td_fairq_lticks = ticks;
1445 }
1446 td = td->td_preempted;
1447 }
1448 }
1449}
1450
1451static void
1452lwkt_fairq_accumulate(globaldata_t gd, thread_t td)
1453{
1454 td->td_fairq_accum += td->td_pri * TDFAIRQ_SCALE;
1455 if (td->td_fairq_accum > TDFAIRQ_MAX(td->td_gd))
1456 td->td_fairq_accum = TDFAIRQ_MAX(td->td_gd);
1457}
1458
5d21b981 1459/*
52eedfb5
MD
1460 * Migrate the current thread to the specified cpu.
1461 *
1462 * This is accomplished by descheduling ourselves from the current cpu,
1463 * moving our thread to the tdallq of the target cpu, IPI messaging the
1464 * target cpu, and switching out. TDF_MIGRATING prevents scheduling
1465 * races while the thread is being migrated.
ae8e83e6
MD
1466 *
1467 * We must be sure to remove ourselves from the current cpu's tsleepq
1468 * before potentially moving to another queue. The thread can be on
1469 * a tsleepq due to a left-over tsleep_interlock().
5d21b981 1470 */
3d28ff59 1471#ifdef SMP
5d21b981 1472static void lwkt_setcpu_remote(void *arg);
3d28ff59 1473#endif
5d21b981
MD
1474
1475void
1476lwkt_setcpu_self(globaldata_t rgd)
1477{
1478#ifdef SMP
1479 thread_t td = curthread;
1480
1481 if (td->td_gd != rgd) {
1482 crit_enter_quick(td);
ae8e83e6 1483 if (td->td_flags & TDF_TSLEEPQ)
3b4192fb 1484 tsleep_remove(td);
5d21b981
MD
1485 td->td_flags |= TDF_MIGRATING;
1486 lwkt_deschedule_self(td);
52eedfb5 1487 TAILQ_REMOVE(&td->td_gd->gd_tdallq, td, td_allq);
b8a98473 1488 lwkt_send_ipiq(rgd, (ipifunc1_t)lwkt_setcpu_remote, td);
5d21b981
MD
1489 lwkt_switch();
1490 /* we are now on the target cpu */
52eedfb5 1491 TAILQ_INSERT_TAIL(&rgd->gd_tdallq, td, td_allq);
5d21b981
MD
1492 crit_exit_quick(td);
1493 }
1494#endif
1495}
1496
ecdefdda
MD
1497void
1498lwkt_migratecpu(int cpuid)
1499{
1500#ifdef SMP
1501 globaldata_t rgd;
1502
1503 rgd = globaldata_find(cpuid);
1504 lwkt_setcpu_self(rgd);
1505#endif
1506}
1507
5d21b981
MD
1508/*
1509 * Remote IPI for cpu migration (called while in a critical section so we
1510 * do not have to enter another one). The thread has already been moved to
1511 * our cpu's allq, but we must wait for the thread to be completely switched
1512 * out on the originating cpu before we schedule it on ours or the stack
1513 * state may be corrupt. We clear TDF_MIGRATING after flushing the GD
1514 * change to main memory.
1515 *
1516 * XXX The use of TDF_MIGRATING might not be sufficient to avoid races
1517 * against wakeups. It is best if this interface is used only when there
1518 * are no pending events that might try to schedule the thread.
1519 */
3d28ff59 1520#ifdef SMP
5d21b981
MD
1521static void
1522lwkt_setcpu_remote(void *arg)
1523{
1524 thread_t td = arg;
1525 globaldata_t gd = mycpu;
1526
df910c23
MD
1527 while (td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK)) {
1528#ifdef SMP
1529 lwkt_process_ipiq();
1530#endif
35238fa5 1531 cpu_lfence();
562273ea 1532 cpu_pause();
df910c23 1533 }
5d21b981 1534 td->td_gd = gd;
562273ea 1535 cpu_mfence();
5d21b981 1536 td->td_flags &= ~TDF_MIGRATING;
9388413d 1537 KKASSERT(td->td_lwp == NULL || (td->td_lwp->lwp_flag & LWP_ONRUNQ) == 0);
5d21b981
MD
1538 _lwkt_enqueue(td);
1539}
3d28ff59 1540#endif
5d21b981 1541
553ea3c8 1542struct lwp *
4b5f931b
MD
1543lwkt_preempted_proc(void)
1544{
73e4f7b9 1545 thread_t td = curthread;
4b5f931b
MD
1546 while (td->td_preempted)
1547 td = td->td_preempted;
553ea3c8 1548 return(td->td_lwp);
4b5f931b
MD
1549}
1550
99df837e
MD
1551/*
1552 * Create a kernel process/thread/whatever. It shares it's address space
1553 * with proc0 - ie: kernel only.
1554 *
365fa13f
MD
1555 * NOTE! By default new threads are created with the MP lock held. A
1556 * thread which does not require the MP lock should release it by calling
1557 * rel_mplock() at the start of the new thread.
99df837e
MD
1558 */
1559int
c9e9fb21
MD
1560lwkt_create(void (*func)(void *), void *arg, struct thread **tdp,
1561 thread_t template, int tdflags, int cpu, const char *fmt, ...)
99df837e 1562{
73e4f7b9 1563 thread_t td;
e2565a42 1564 __va_list ap;
99df837e 1565
d3d32139 1566 td = lwkt_alloc_thread(template, LWKT_THREAD_STACK, cpu,
dbcd0c9b 1567 tdflags);
a2a5ad0d
MD
1568 if (tdp)
1569 *tdp = td;
709799ea 1570 cpu_set_thread_handler(td, lwkt_exit, func, arg);
99df837e
MD
1571
1572 /*
1573 * Set up arg0 for 'ps' etc
1574 */
e2565a42 1575 __va_start(ap, fmt);
379210cb 1576 kvsnprintf(td->td_comm, sizeof(td->td_comm), fmt, ap);
e2565a42 1577 __va_end(ap);
99df837e
MD
1578
1579 /*
1580 * Schedule the thread to run
1581 */
ef0fdad1
MD
1582 if ((td->td_flags & TDF_STOPREQ) == 0)
1583 lwkt_schedule(td);
1584 else
1585 td->td_flags &= ~TDF_STOPREQ;
99df837e
MD
1586 return 0;
1587}
1588
1589/*
1590 * Destroy an LWKT thread. Warning! This function is not called when
1591 * a process exits, cpu_proc_exit() directly calls cpu_thread_exit() and
1592 * uses a different reaping mechanism.
1593 */
1594void
1595lwkt_exit(void)
1596{
1597 thread_t td = curthread;
c070746a 1598 thread_t std;
8826f33a 1599 globaldata_t gd;
99df837e 1600
2883d2d8
MD
1601 /*
1602 * Do any cleanup that might block here
1603 */
99df837e 1604 if (td->td_flags & TDF_VERBOSE)
6ea70f76 1605 kprintf("kthread %p %s has exited\n", td, td->td_comm);
f6bf3af1 1606 caps_exit(td);
2883d2d8
MD
1607 biosched_done(td);
1608 dsched_exit_thread(td);
c070746a
MD
1609
1610 /*
1611 * Get us into a critical section to interlock gd_freetd and loop
1612 * until we can get it freed.
1613 *
1614 * We have to cache the current td in gd_freetd because objcache_put()ing
1615 * it would rip it out from under us while our thread is still active.
1616 */
1617 gd = mycpu;
37af14fe 1618 crit_enter_quick(td);
c070746a 1619 while ((std = gd->gd_freetd) != NULL) {
cf709dd2 1620 KKASSERT((std->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK)) == 0);
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1621 gd->gd_freetd = NULL;
1622 objcache_put(thread_cache, std);
1623 }
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1624
1625 /*
1626 * Remove thread resources from kernel lists and deschedule us for
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1627 * the last time. We cannot block after this point or we may end
1628 * up with a stale td on the tsleepq.
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1629 */
1630 if (td->td_flags & TDF_TSLEEPQ)
1631 tsleep_remove(td);
37af14fe 1632 lwkt_deschedule_self(td);
e56e4dea 1633 lwkt_remove_tdallq(td);
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1634
1635 /*
1636 * Final cleanup
1637 */
1638 KKASSERT(gd->gd_freetd == NULL);
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1639 if (td->td_flags & TDF_ALLOCATED_THREAD)
1640 gd->gd_freetd = td;
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1641 cpu_thread_exit();
1642}
1643
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1644void
1645lwkt_remove_tdallq(thread_t td)
1646{
1647 KKASSERT(td->td_gd == mycpu);
1648 TAILQ_REMOVE(&td->td_gd->gd_tdallq, td, td_allq);
1649}
1650
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1651/*
1652 * Code reduction and branch prediction improvements. Call/return
1653 * overhead on modern cpus often degenerates into 0 cycles due to
1654 * the cpu's branch prediction hardware and return pc cache. We
1655 * can take advantage of this by not inlining medium-complexity
1656 * functions and we can also reduce the branch prediction impact
1657 * by collapsing perfectly predictable branches into a single
1658 * procedure instead of duplicating it.
1659 *
1660 * Is any of this noticeable? Probably not, so I'll take the
1661 * smaller code size.
1662 */
1663void
b6468f56 1664crit_exit_wrapper(__DEBUG_CRIT_ARG__)
9cf43f91 1665{
b6468f56 1666 _crit_exit(mycpu __DEBUG_CRIT_PASS_ARG__);
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1667}
1668
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1669void
1670crit_panic(void)
1671{
1672 thread_t td = curthread;
850634cc 1673 int lcrit = td->td_critcount;
2d93b37a 1674
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AH
1675 td->td_critcount = 0;
1676 panic("td_critcount is/would-go negative! %p %d", td, lcrit);
4a28fe22 1677 /* NOT REACHED */
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1678}
1679
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1680#ifdef SMP
1681
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1682/*
1683 * Called from debugger/panic on cpus which have been stopped. We must still
1684 * process the IPIQ while stopped, even if we were stopped while in a critical
1685 * section (XXX).
1686 *
1687 * If we are dumping also try to process any pending interrupts. This may
1688 * or may not work depending on the state of the cpu at the point it was
1689 * stopped.
1690 */
1691void
1692lwkt_smp_stopped(void)
1693{
1694 globaldata_t gd = mycpu;
1695
1696 crit_enter_gd(gd);
1697 if (dumping) {
1698 lwkt_process_ipiq();
1699 splz();
1700 } else {
1701 lwkt_process_ipiq();
1702 }
1703 crit_exit_gd(gd);
1704}
1705
d165e668 1706#endif