kernel - KVABIO allocbuf() optimization
[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
8c10bfcf
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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.
8ad65e08
MD
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>
f1d1c3fa 58
8c72e3d5
AH
59#include <sys/dsched.h>
60
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61#include <vm/vm.h>
62#include <vm/vm_param.h>
63#include <vm/vm_kern.h>
64#include <vm/vm_object.h>
65#include <vm/vm_page.h>
66#include <vm/vm_map.h>
67#include <vm/vm_pager.h>
68#include <vm/vm_extern.h>
7d0bac62 69
99df837e 70#include <machine/stdarg.h>
96728c05 71#include <machine/smp.h>
3a06728e 72#include <machine/clock.h>
99df837e 73
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74#ifdef _KERNEL_VIRTUAL
75#include <pthread.h>
76#endif
77
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78#define LOOPMASK
79
d850923c
AE
80#if !defined(KTR_CTXSW)
81#define KTR_CTXSW KTR_ALL
82#endif
83KTR_INFO_MASTER(ctxsw);
5bf48697
AE
84KTR_INFO(KTR_CTXSW, ctxsw, sw, 0, "#cpu[%d].td = %p", int cpu, struct thread *td);
85KTR_INFO(KTR_CTXSW, ctxsw, pre, 1, "#cpu[%d].td = %p", int cpu, struct thread *td);
86KTR_INFO(KTR_CTXSW, ctxsw, newtd, 2, "#threads[%p].name = %s", struct thread *td, char *comm);
87KTR_INFO(KTR_CTXSW, ctxsw, deadtd, 3, "#threads[%p].name = <dead>", struct thread *td);
1541028a 88
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89static MALLOC_DEFINE(M_THREAD, "thread", "lwkt threads");
90
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91#ifdef INVARIANTS
92static int panic_on_cscount = 0;
93#endif
e28c8ef4
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94static int64_t switch_count = 0;
95static int64_t preempt_hit = 0;
96static int64_t preempt_miss = 0;
97static int64_t preempt_weird = 0;
fb0f29c4 98static int lwkt_use_spin_port;
40aaf5fc 99static struct objcache *thread_cache;
a46b4a23 100int cpu_mwait_spin = 0;
05220613 101
e381e77c 102static void lwkt_schedule_remote(void *arg, int arg2, struct intrframe *frame);
cc9b6223 103static void lwkt_setcpu_remote(void *arg);
e381e77c 104
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105/*
106 * We can make all thread ports use the spin backend instead of the thread
107 * backend. This should only be set to debug the spin backend.
108 */
109TUNABLE_INT("lwkt.use_spin_port", &lwkt_use_spin_port);
110
0f7a3396 111#ifdef INVARIANTS
0c52fa62
SG
112SYSCTL_INT(_lwkt, OID_AUTO, panic_on_cscount, CTLFLAG_RW, &panic_on_cscount, 0,
113 "Panic if attempting to switch lwkt's while mastering cpusync");
0f7a3396 114#endif
0c52fa62
SG
115SYSCTL_QUAD(_lwkt, OID_AUTO, switch_count, CTLFLAG_RW, &switch_count, 0,
116 "Number of switched threads");
9733f757 117SYSCTL_QUAD(_lwkt, OID_AUTO, preempt_hit, CTLFLAG_RW, &preempt_hit, 0,
0c52fa62 118 "Successful preemption events");
9733f757 119SYSCTL_QUAD(_lwkt, OID_AUTO, preempt_miss, CTLFLAG_RW, &preempt_miss, 0,
0c52fa62
SG
120 "Failed preemption events");
121SYSCTL_QUAD(_lwkt, OID_AUTO, preempt_weird, CTLFLAG_RW, &preempt_weird, 0,
122 "Number of preempted threads.");
b12defdc 123static int fairq_enable = 0;
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124SYSCTL_INT(_lwkt, OID_AUTO, fairq_enable, CTLFLAG_RW,
125 &fairq_enable, 0, "Turn on fairq priority accumulators");
85946b6c 126static int fairq_bypass = -1;
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127SYSCTL_INT(_lwkt, OID_AUTO, fairq_bypass, CTLFLAG_RW,
128 &fairq_bypass, 0, "Allow fairq to bypass td on token failure");
129extern int lwkt_sched_debug;
130int lwkt_sched_debug = 0;
131SYSCTL_INT(_lwkt, OID_AUTO, sched_debug, CTLFLAG_RW,
132 &lwkt_sched_debug, 0, "Scheduler debug");
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133static u_int lwkt_spin_loops = 10;
134SYSCTL_UINT(_lwkt, OID_AUTO, spin_loops, CTLFLAG_RW,
b12defdc 135 &lwkt_spin_loops, 0, "Scheduler spin loops until sorted decon");
fbc024e4 136static int preempt_enable = 1;
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137SYSCTL_INT(_lwkt, OID_AUTO, preempt_enable, CTLFLAG_RW,
138 &preempt_enable, 0, "Enable preemption");
7b234d8c 139static int lwkt_cache_threads = 0;
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140SYSCTL_INT(_lwkt, OID_AUTO, cache_threads, CTLFLAG_RD,
141 &lwkt_cache_threads, 0, "thread+kstack cache");
fbc024e4 142
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143/*
144 * These helper procedures handle the runq, they can only be called from
145 * within a critical section.
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146 *
147 * WARNING! Prior to SMP being brought up it is possible to enqueue and
148 * dequeue threads belonging to other cpus, so be sure to use td->td_gd
149 * instead of 'mycpu' when referencing the globaldata structure. Once
150 * SMP live enqueuing and dequeueing only occurs on the current cpu.
4b5f931b 151 */
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152static __inline
153void
154_lwkt_dequeue(thread_t td)
155{
156 if (td->td_flags & TDF_RUNQ) {
75cdbe6c 157 struct globaldata *gd = td->td_gd;
4b5f931b 158
f1d1c3fa 159 td->td_flags &= ~TDF_RUNQ;
f9235b6d 160 TAILQ_REMOVE(&gd->gd_tdrunq, td, td_threadq);
de4d4cb0 161 --gd->gd_tdrunqcount;
f9235b6d 162 if (TAILQ_FIRST(&gd->gd_tdrunq) == NULL)
2a418930 163 atomic_clear_int(&gd->gd_reqflags, RQF_RUNNING);
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164 }
165}
166
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167/*
168 * Priority enqueue.
169 *
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170 * There are a limited number of lwkt threads runnable since user
171 * processes only schedule one at a time per cpu. However, there can
172 * be many user processes in kernel mode exiting from a tsleep() which
e3e6be1f 173 * become runnable.
d992c377 174 *
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175 * We scan the queue in both directions to help deal with degenerate
176 * situations when hundreds or thousands (or more) threads are runnable.
177 *
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178 * NOTE: lwkt_schedulerclock() will force a round-robin based on td_pri and
179 * will ignore user priority. This is to ensure that user threads in
180 * kernel mode get cpu at some point regardless of what the user
181 * scheduler thinks.
f9235b6d 182 */
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183static __inline
184void
185_lwkt_enqueue(thread_t td)
186{
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187 thread_t xtd; /* forward scan */
188 thread_t rtd; /* reverse scan */
f9235b6d 189
7f5d7ed7 190 if ((td->td_flags & (TDF_RUNQ|TDF_MIGRATING|TDF_BLOCKQ)) == 0) {
75cdbe6c 191 struct globaldata *gd = td->td_gd;
4b5f931b 192
f1d1c3fa 193 td->td_flags |= TDF_RUNQ;
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194 xtd = TAILQ_FIRST(&gd->gd_tdrunq);
195 if (xtd == NULL) {
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196 TAILQ_INSERT_TAIL(&gd->gd_tdrunq, td, td_threadq);
197 atomic_set_int(&gd->gd_reqflags, RQF_RUNNING);
f9235b6d 198 } else {
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199 /*
200 * NOTE: td_upri - higher numbers more desireable, same sense
201 * as td_pri (typically reversed from lwp_upri).
202 *
203 * In the equal priority case we want the best selection
204 * at the beginning so the less desireable selections know
205 * that they have to setrunqueue/go-to-another-cpu, even
206 * though it means switching back to the 'best' selection.
207 * This also avoids degenerate situations when many threads
208 * are runnable or waking up at the same time.
209 *
210 * If upri matches exactly place at end/round-robin.
211 */
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212 rtd = TAILQ_LAST(&gd->gd_tdrunq, lwkt_queue);
213
d992c377 214 while (xtd &&
e6b81333 215 (xtd->td_pri > td->td_pri ||
d992c377 216 (xtd->td_pri == td->td_pri &&
e3e6be1f 217 xtd->td_upri >= td->td_upri))) {
85946b6c 218 xtd = TAILQ_NEXT(xtd, td_threadq);
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219
220 /*
221 * Doing a reverse scan at the same time is an optimization
222 * for the insert-closer-to-tail case that avoids having to
223 * scan the entire list. This situation can occur when
224 * thousands of threads are woken up at the same time.
225 */
226 if (rtd->td_pri > td->td_pri ||
227 (rtd->td_pri == td->td_pri &&
228 rtd->td_upri >= td->td_upri)) {
229 TAILQ_INSERT_AFTER(&gd->gd_tdrunq, rtd, td, td_threadq);
230 goto skip;
231 }
232 rtd = TAILQ_PREV(rtd, lwkt_queue, td_threadq);
d992c377 233 }
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MD
234 if (xtd)
235 TAILQ_INSERT_BEFORE(xtd, td, td_threadq);
236 else
237 TAILQ_INSERT_TAIL(&gd->gd_tdrunq, td, td_threadq);
f9235b6d 238 }
e6b81333 239skip:
de4d4cb0 240 ++gd->gd_tdrunqcount;
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241
242 /*
85946b6c 243 * Request a LWKT reschedule if we are now at the head of the queue.
b12defdc 244 */
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245 if (TAILQ_FIRST(&gd->gd_tdrunq) == td)
246 need_lwkt_resched();
f1d1c3fa
MD
247 }
248}
8ad65e08 249
e28c8ef4 250static boolean_t
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NT
251_lwkt_thread_ctor(void *obj, void *privdata, int ocflags)
252{
253 struct thread *td = (struct thread *)obj;
254
255 td->td_kstack = NULL;
256 td->td_kstack_size = 0;
257 td->td_flags = TDF_ALLOCATED_THREAD;
4643740a 258 td->td_mpflags = 0;
40aaf5fc
NT
259 return (1);
260}
261
262static void
263_lwkt_thread_dtor(void *obj, void *privdata)
264{
265 struct thread *td = (struct thread *)obj;
266
267 KASSERT(td->td_flags & TDF_ALLOCATED_THREAD,
268 ("_lwkt_thread_dtor: not allocated from objcache"));
269 KASSERT((td->td_flags & TDF_ALLOCATED_STACK) && td->td_kstack &&
270 td->td_kstack_size > 0,
271 ("_lwkt_thread_dtor: corrupted stack"));
272 kmem_free(&kernel_map, (vm_offset_t)td->td_kstack, td->td_kstack_size);
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MD
273 td->td_kstack = NULL;
274 td->td_flags = 0;
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NT
275}
276
277/*
278 * Initialize the lwkt s/system.
765b1ae0 279 *
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280 * Nominally cache up to 32 thread + kstack structures. Cache more on
281 * systems with a lot of cpu cores.
40aaf5fc 282 */
ced589cb 283static void
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NT
284lwkt_init(void)
285{
765b1ae0 286 TUNABLE_INT("lwkt.cache_threads", &lwkt_cache_threads);
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MD
287 if (lwkt_cache_threads == 0) {
288 lwkt_cache_threads = ncpus * 4;
289 if (lwkt_cache_threads < 32)
290 lwkt_cache_threads = 32;
291 }
765b1ae0
MD
292 thread_cache = objcache_create_mbacked(
293 M_THREAD, sizeof(struct thread),
2fce2579 294 0, lwkt_cache_threads,
765b1ae0 295 _lwkt_thread_ctor, _lwkt_thread_dtor, NULL);
40aaf5fc 296}
ced589cb 297SYSINIT(lwkt_init, SI_BOOT2_LWKT_INIT, SI_ORDER_FIRST, lwkt_init, NULL);
40aaf5fc 298
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MD
299/*
300 * Schedule a thread to run. As the current thread we can always safely
301 * schedule ourselves, and a shortcut procedure is provided for that
302 * function.
303 *
304 * (non-blocking, self contained on a per cpu basis)
305 */
306void
307lwkt_schedule_self(thread_t td)
308{
cfaeae2a 309 KKASSERT((td->td_flags & TDF_MIGRATING) == 0);
37af14fe 310 crit_enter_quick(td);
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MD
311 KASSERT(td != &td->td_gd->gd_idlethread,
312 ("lwkt_schedule_self(): scheduling gd_idlethread is illegal!"));
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MD
313 KKASSERT(td->td_lwp == NULL ||
314 (td->td_lwp->lwp_mpflags & LWP_MP_ONRUNQ) == 0);
37af14fe 315 _lwkt_enqueue(td);
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MD
316 crit_exit_quick(td);
317}
318
319/*
320 * Deschedule a thread.
321 *
322 * (non-blocking, self contained on a per cpu basis)
323 */
324void
325lwkt_deschedule_self(thread_t td)
326{
327 crit_enter_quick(td);
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328 _lwkt_dequeue(td);
329 crit_exit_quick(td);
330}
331
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332/*
333 * LWKTs operate on a per-cpu basis
334 *
73e4f7b9 335 * WARNING! Called from early boot, 'mycpu' may not work yet.
8ad65e08
MD
336 */
337void
338lwkt_gdinit(struct globaldata *gd)
339{
f9235b6d 340 TAILQ_INIT(&gd->gd_tdrunq);
73e4f7b9 341 TAILQ_INIT(&gd->gd_tdallq);
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MD
342}
343
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344/*
345 * Create a new thread. The thread must be associated with a process context
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346 * or LWKT start address before it can be scheduled. If the target cpu is
347 * -1 the thread will be created on the current cpu.
0cfcada1
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348 *
349 * If you intend to create a thread without a process context this function
350 * does everything except load the startup and switcher function.
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351 */
352thread_t
d3d32139 353lwkt_alloc_thread(struct thread *td, int stksize, int cpu, int flags)
7d0bac62 354{
d2d8515b 355 static int cpu_rotator;
c070746a 356 globaldata_t gd = mycpu;
99df837e 357 void *stack;
7d0bac62 358
c070746a
MD
359 /*
360 * If static thread storage is not supplied allocate a thread. Reuse
361 * a cached free thread if possible. gd_freetd is used to keep an exiting
362 * thread intact through the exit.
363 */
ef0fdad1 364 if (td == NULL) {
cf709dd2
MD
365 crit_enter_gd(gd);
366 if ((td = gd->gd_freetd) != NULL) {
367 KKASSERT((td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK|
368 TDF_RUNQ)) == 0);
c070746a 369 gd->gd_freetd = NULL;
cf709dd2 370 } else {
c070746a 371 td = objcache_get(thread_cache, M_WAITOK);
cf709dd2
MD
372 KKASSERT((td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK|
373 TDF_RUNQ)) == 0);
374 }
375 crit_exit_gd(gd);
40aaf5fc 376 KASSERT((td->td_flags &
2af9d75d
MD
377 (TDF_ALLOCATED_THREAD|TDF_RUNNING|TDF_PREEMPT_LOCK)) ==
378 TDF_ALLOCATED_THREAD,
40aaf5fc
NT
379 ("lwkt_alloc_thread: corrupted td flags 0x%X", td->td_flags));
380 flags |= td->td_flags & (TDF_ALLOCATED_THREAD|TDF_ALLOCATED_STACK);
ef0fdad1 381 }
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MD
382
383 /*
384 * Try to reuse cached stack.
385 */
f470d0c8
MD
386 if ((stack = td->td_kstack) != NULL && td->td_kstack_size != stksize) {
387 if (flags & TDF_ALLOCATED_STACK) {
e4846942 388 kmem_free(&kernel_map, (vm_offset_t)stack, td->td_kstack_size);
f470d0c8
MD
389 stack = NULL;
390 }
391 }
392 if (stack == NULL) {
070a58b3
MD
393 if (cpu < 0)
394 stack = (void *)kmem_alloc_stack(&kernel_map, stksize, 0);
395 else
396 stack = (void *)kmem_alloc_stack(&kernel_map, stksize,
397 KM_CPU(cpu));
ef0fdad1 398 flags |= TDF_ALLOCATED_STACK;
99df837e 399 }
d2d8515b
MD
400 if (cpu < 0) {
401 cpu = ++cpu_rotator;
402 cpu_ccfence();
5dd85b08 403 cpu = (uint32_t)cpu % (uint32_t)ncpus;
d2d8515b
MD
404 }
405 lwkt_init_thread(td, stack, stksize, flags, globaldata_find(cpu));
99df837e 406 return(td);
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MD
407}
408
409/*
410 * Initialize a preexisting thread structure. This function is used by
411 * lwkt_alloc_thread() and also used to initialize the per-cpu idlethread.
412 *
f8c3996b
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413 * All threads start out in a critical section at a priority of
414 * TDPRI_KERN_DAEMON. Higher level code will modify the priority as
75cdbe6c
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415 * appropriate. This function may send an IPI message when the
416 * requested cpu is not the current cpu and consequently gd_tdallq may
417 * not be initialized synchronously from the point of view of the originating
418 * cpu.
419 *
420 * NOTE! we have to be careful in regards to creating threads for other cpus
421 * if SMP has not yet been activated.
7d0bac62 422 */
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423static void
424lwkt_init_thread_remote(void *arg)
425{
426 thread_t td = arg;
427
52eedfb5
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428 /*
429 * Protected by critical section held by IPI dispatch
430 */
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431 TAILQ_INSERT_TAIL(&td->td_gd->gd_tdallq, td, td_allq);
432}
433
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434/*
435 * lwkt core thread structural initialization.
436 *
437 * NOTE: All threads are initialized as mpsafe threads.
438 */
7d0bac62 439void
f470d0c8
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440lwkt_init_thread(thread_t td, void *stack, int stksize, int flags,
441 struct globaldata *gd)
7d0bac62 442{
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MD
443 globaldata_t mygd = mycpu;
444
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MD
445 bzero(td, sizeof(struct thread));
446 td->td_kstack = stack;
f470d0c8 447 td->td_kstack_size = stksize;
d3d32139 448 td->td_flags = flags;
4643740a 449 td->td_mpflags = 0;
f256b6c0 450 td->td_type = TD_TYPE_GENERIC;
26a0694b 451 td->td_gd = gd;
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MD
452 td->td_pri = TDPRI_KERN_DAEMON;
453 td->td_critcount = 1;
54341a3b 454 td->td_toks_have = NULL;
3b998fa9 455 td->td_toks_stop = &td->td_toks_base;
c068fb59
SZ
456 if (lwkt_use_spin_port || (flags & TDF_FORCE_SPINPORT)) {
457 lwkt_initport_spin(&td->td_msgport, td,
458 (flags & TDF_FIXEDCPU) ? TRUE : FALSE);
459 } else {
fb0f29c4 460 lwkt_initport_thread(&td->td_msgport, td);
c068fb59 461 }
99df837e 462 pmap_init_thread(td);
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463 /*
464 * Normally initializing a thread for a remote cpu requires sending an
465 * IPI. However, the idlethread is setup before the other cpus are
466 * activated so we have to treat it as a special case. XXX manipulation
467 * of gd_tdallq requires the BGL.
468 */
469 if (gd == mygd || td == &gd->gd_idlethread) {
37af14fe 470 crit_enter_gd(mygd);
75cdbe6c 471 TAILQ_INSERT_TAIL(&gd->gd_tdallq, td, td_allq);
37af14fe 472 crit_exit_gd(mygd);
75cdbe6c 473 } else {
2db3b277 474 lwkt_send_ipiq(gd, lwkt_init_thread_remote, td);
75cdbe6c 475 }
3573cf7b 476 dsched_enter_thread(td);
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MD
477}
478
479void
480lwkt_set_comm(thread_t td, const char *ctl, ...)
481{
e2565a42 482 __va_list va;
73e4f7b9 483
e2565a42 484 __va_start(va, ctl);
379210cb 485 kvsnprintf(td->td_comm, sizeof(td->td_comm), ctl, va);
e2565a42 486 __va_end(va);
5bf48697 487 KTR_LOG(ctxsw_newtd, td, td->td_comm);
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MD
488}
489
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490/*
491 * Prevent the thread from getting destroyed. Note that unlike PHOLD/PRELE
492 * this does not prevent the thread from migrating to another cpu so the
493 * gd_tdallq state is not protected by this.
494 */
99df837e 495void
73e4f7b9 496lwkt_hold(thread_t td)
99df837e 497{
74c9628e 498 atomic_add_int(&td->td_refs, 1);
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MD
499}
500
501void
502lwkt_rele(thread_t td)
503{
504 KKASSERT(td->td_refs > 0);
74c9628e 505 atomic_add_int(&td->td_refs, -1);
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506}
507
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MD
508void
509lwkt_free_thread(thread_t td)
510{
74c9628e 511 KKASSERT(td->td_refs == 0);
c17a6852
MD
512 KKASSERT((td->td_flags & (TDF_RUNNING | TDF_PREEMPT_LOCK |
513 TDF_RUNQ | TDF_TSLEEPQ)) == 0);
40aaf5fc
NT
514 if (td->td_flags & TDF_ALLOCATED_THREAD) {
515 objcache_put(thread_cache, td);
516 } else if (td->td_flags & TDF_ALLOCATED_STACK) {
517 /* client-allocated struct with internally allocated stack */
518 KASSERT(td->td_kstack && td->td_kstack_size > 0,
519 ("lwkt_free_thread: corrupted stack"));
520 kmem_free(&kernel_map, (vm_offset_t)td->td_kstack, td->td_kstack_size);
521 td->td_kstack = NULL;
522 td->td_kstack_size = 0;
99df837e 523 }
a86ce0cd 524
e7c0dbba 525 KTR_LOG(ctxsw_deadtd, td);
99df837e
MD
526}
527
528
8ad65e08
MD
529/*
530 * Switch to the next runnable lwkt. If no LWKTs are runnable then
f1d1c3fa
MD
531 * switch to the idlethread. Switching must occur within a critical
532 * section to avoid races with the scheduling queue.
533 *
534 * We always have full control over our cpu's run queue. Other cpus
535 * that wish to manipulate our queue must use the cpu_*msg() calls to
536 * talk to our cpu, so a critical section is all that is needed and
537 * the result is very, very fast thread switching.
538 *
96728c05
MD
539 * The LWKT scheduler uses a fixed priority model and round-robins at
540 * each priority level. User process scheduling is a totally
541 * different beast and LWKT priorities should not be confused with
542 * user process priorities.
f1d1c3fa 543 *
69d78e99
MD
544 * PREEMPTION NOTE: Preemption occurs via lwkt_preempt(). lwkt_switch()
545 * is not called by the current thread in the preemption case, only when
546 * the preempting thread blocks (in order to return to the original thread).
cfaeae2a
MD
547 *
548 * SPECIAL NOTE ON SWITCH ATOMICY: Certain operations such as thread
549 * migration and tsleep deschedule the current lwkt thread and call
550 * lwkt_switch(). In particular, the target cpu of the migration fully
551 * expects the thread to become non-runnable and can deadlock against
552 * cpusync operations if we run any IPIs prior to switching the thread out.
553 *
554 * WE MUST BE VERY CAREFUL NOT TO RUN SPLZ DIRECTLY OR INDIRECTLY IF
95858b91 555 * THE CURRENT THREAD HAS BEEN DESCHEDULED!
8ad65e08
MD
556 */
557void
558lwkt_switch(void)
559{
37af14fe
MD
560 globaldata_t gd = mycpu;
561 thread_t td = gd->gd_curthread;
8ad65e08 562 thread_t ntd;
c6a766f4 563 thread_t xtd;
5411d8f1 564 int upri;
3a06728e
MD
565#ifdef LOOPMASK
566 uint64_t tsc_base = rdtsc();
567#endif
8ad65e08 568
da0b0e8b 569 KKASSERT(gd->gd_processing_ipiq == 0);
121f93bc 570 KKASSERT(td->td_flags & TDF_RUNNING);
da0b0e8b 571
46a3f46d 572 /*
27e88a6e
MD
573 * Switching from within a 'fast' (non thread switched) interrupt or IPI
574 * is illegal. However, we may have to do it anyway if we hit a fatal
575 * kernel trap or we have paniced.
576 *
577 * If this case occurs save and restore the interrupt nesting level.
46a3f46d 578 */
27e88a6e
MD
579 if (gd->gd_intr_nesting_level) {
580 int savegdnest;
581 int savegdtrap;
582
5fddbda2 583 if (gd->gd_trap_nesting_level == 0 && panic_cpu_gd != mycpu) {
4a28fe22 584 panic("lwkt_switch: Attempt to switch from a "
5a8df152 585 "fast interrupt, ipi, or hard code section, "
4a28fe22
MD
586 "td %p\n",
587 td);
27e88a6e
MD
588 } else {
589 savegdnest = gd->gd_intr_nesting_level;
590 savegdtrap = gd->gd_trap_nesting_level;
591 gd->gd_intr_nesting_level = 0;
592 gd->gd_trap_nesting_level = 0;
a7422615
MD
593 if ((td->td_flags & TDF_PANICWARN) == 0) {
594 td->td_flags |= TDF_PANICWARN;
4a28fe22
MD
595 kprintf("Warning: thread switch from interrupt, IPI, "
596 "or hard code section.\n"
a7422615 597 "thread %p (%s)\n", td, td->td_comm);
7ce2998e 598 print_backtrace(-1);
a7422615 599 }
27e88a6e
MD
600 lwkt_switch();
601 gd->gd_intr_nesting_level = savegdnest;
602 gd->gd_trap_nesting_level = savegdtrap;
603 return;
604 }
96728c05 605 }
ef0fdad1 606
cb973d15 607 /*
85946b6c
MD
608 * Release our current user process designation if we are blocking
609 * or if a user reschedule was requested.
610 *
611 * NOTE: This function is NOT called if we are switching into or
612 * returning from a preemption.
613 *
614 * NOTE: Releasing our current user process designation may cause
615 * it to be assigned to another thread, which in turn will
616 * cause us to block in the usched acquire code when we attempt
617 * to return to userland.
618 *
619 * NOTE: On SMP systems this can be very nasty when heavy token
620 * contention is present so we want to be careful not to
621 * release the designation gratuitously.
cb973d15 622 */
85946b6c
MD
623 if (td->td_release &&
624 (user_resched_wanted() || (td->td_flags & TDF_RUNQ) == 0)) {
cb973d15 625 td->td_release(td);
85946b6c 626 }
cb973d15 627
85946b6c 628 /*
5411d8f1
MD
629 * Release all tokens. Once we do this we must remain in the critical
630 * section and cannot run IPIs or other interrupts until we switch away
631 * because they may implode if they try to get a token using our thread
632 * context.
85946b6c 633 */
37af14fe 634 crit_enter_gd(gd);
3b998fa9 635 if (TD_TOKS_HELD(td))
9d265729
MD
636 lwkt_relalltokens(td);
637
638 /*
b02926de
MD
639 * We had better not be holding any spin locks, but don't get into an
640 * endless panic loop.
9d265729 641 */
0846e4ce 642 KASSERT(gd->gd_spinlocks == 0 || panicstr != NULL,
d666840a 643 ("lwkt_switch: still holding %d exclusive spinlocks!",
0846e4ce 644 gd->gd_spinlocks));
9d265729 645
0f7a3396
MD
646#ifdef INVARIANTS
647 if (td->td_cscount) {
6ea70f76 648 kprintf("Diagnostic: attempt to switch while mastering cpusync: %p\n",
0f7a3396
MD
649 td);
650 if (panic_on_cscount)
651 panic("switching while mastering cpusync");
652 }
8a8d5d85 653#endif
f9235b6d
MD
654
655 /*
656 * If we had preempted another thread on this cpu, resume the preempted
657 * thread. This occurs transparently, whether the preempted thread
658 * was scheduled or not (it may have been preempted after descheduling
659 * itself).
660 *
661 * We have to setup the MP lock for the original thread after backing
662 * out the adjustment that was made to curthread when the original
663 * was preempted.
664 */
99df837e 665 if ((ntd = td->td_preempted) != NULL) {
26a0694b
MD
666 KKASSERT(ntd->td_flags & TDF_PREEMPT_LOCK);
667 ntd->td_flags |= TDF_PREEMPT_DONE;
7fb451cb 668 ntd->td_contended = 0; /* reset contended */
8ec60c3f
MD
669
670 /*
b9eb1c19
MD
671 * The interrupt may have woken a thread up, we need to properly
672 * set the reschedule flag if the originally interrupted thread is
673 * at a lower priority.
85946b6c 674 *
c6a766f4
MD
675 * NOTE: The interrupt may not have descheduled ntd.
676 *
677 * NOTE: We do not reschedule if there are no threads on the runq.
678 * (ntd could be the idlethread).
8ec60c3f 679 */
c6a766f4
MD
680 xtd = TAILQ_FIRST(&gd->gd_tdrunq);
681 if (xtd && xtd != ntd)
8ec60c3f 682 need_lwkt_resched();
f9235b6d
MD
683 goto havethread_preempted;
684 }
685
b12defdc 686 /*
5411d8f1
MD
687 * Figure out switch target. If we cannot switch to our desired target
688 * look for a thread that we can switch to.
cfaeae2a 689 *
5411d8f1
MD
690 * NOTE! The limited spin loop and related parameters are extremely
691 * important for system performance, particularly for pipes and
692 * concurrent conflicting VM faults.
f9235b6d 693 */
5411d8f1
MD
694 clear_lwkt_resched();
695 ntd = TAILQ_FIRST(&gd->gd_tdrunq);
696
697 if (ntd) {
698 do {
699 if (TD_TOKS_NOT_HELD(ntd) ||
700 lwkt_getalltokens(ntd, (ntd->td_contended > lwkt_spin_loops)))
701 {
702 goto havethread;
703 }
704 ++gd->gd_cnt.v_lock_colls;
7fb451cb 705 ++ntd->td_contended; /* overflow ok */
3a06728e
MD
706#ifdef LOOPMASK
707 if (tsc_frequency && rdtsc() - tsc_base > tsc_frequency) {
708 kprintf("lwkt_switch: excessive contended %d "
709 "thread %p\n", ntd->td_contended, ntd);
710 tsc_base = rdtsc();
711 }
712#endif
5411d8f1
MD
713 } while (ntd->td_contended < (lwkt_spin_loops >> 1));
714 upri = ntd->td_upri;
f9235b6d 715
f9235b6d 716 /*
5411d8f1
MD
717 * Bleh, the thread we wanted to switch to has a contended token.
718 * See if we can switch to another thread.
2a418930 719 *
5411d8f1
MD
720 * We generally don't want to do this because it represents a
721 * priority inversion. Do not allow the case if the thread
722 * is returning to userland (not a kernel thread) AND the thread
723 * has a lower upri.
f9235b6d 724 */
b12defdc 725 while ((ntd = TAILQ_NEXT(ntd, td_threadq)) != NULL) {
5411d8f1
MD
726 if (ntd->td_pri < TDPRI_KERN_LPSCHED && upri > ntd->td_upri)
727 break;
728 upri = ntd->td_upri;
b12defdc 729
5411d8f1
MD
730 /*
731 * Try this one.
732 */
733 if (TD_TOKS_NOT_HELD(ntd) ||
734 lwkt_getalltokens(ntd, (ntd->td_contended > lwkt_spin_loops))) {
735 goto havethread;
736 }
7fb451cb 737 ++ntd->td_contended; /* overflow ok */
5411d8f1 738 ++gd->gd_cnt.v_lock_colls;
b12defdc 739 }
b12defdc
MD
740
741 /*
5411d8f1
MD
742 * Fall through, switch to idle thread to get us out of the current
743 * context. Since we were contended, prevent HLT by flagging a
744 * LWKT reschedule.
b12defdc 745 */
5411d8f1 746 need_lwkt_resched();
f1d1c3fa 747 }
8a8d5d85 748
5411d8f1
MD
749 /*
750 * We either contended on ntd or the runq is empty. We must switch
751 * through the idle thread to get out of the current context.
752 */
753 ntd = &gd->gd_idlethread;
754 if (gd->gd_trap_nesting_level == 0 && panicstr == NULL)
755 ASSERT_NO_TOKENS_HELD(ntd);
756 cpu_time.cp_msg[0] = 0;
5411d8f1
MD
757 goto haveidle;
758
2a418930 759havethread:
b12defdc 760 /*
be71787b
MD
761 * Clear gd_idle_repeat when doing a normal switch to a non-idle
762 * thread.
f9235b6d 763 */
9ac1ee6e 764 ntd->td_wmesg = NULL;
7fb451cb 765 ntd->td_contended = 0; /* reset once scheduled */
b12defdc 766 ++gd->gd_cnt.v_swtch;
be71787b 767 gd->gd_idle_repeat = 0;
2a418930 768
f9235b6d 769havethread_preempted:
f9235b6d
MD
770 /*
771 * If the new target does not need the MP lock and we are holding it,
772 * release the MP lock. If the new target requires the MP lock we have
773 * already acquired it for the target.
8a8d5d85 774 */
2a418930 775 ;
f9235b6d
MD
776haveidle:
777 KASSERT(ntd->td_critcount,
b5d16701
MD
778 ("priority problem in lwkt_switch %d %d",
779 td->td_critcount, ntd->td_critcount));
780
94f6d86e 781 if (td != ntd) {
cc9b6223
MD
782 /*
783 * Execute the actual thread switch operation. This function
784 * returns to the current thread and returns the previous thread
785 * (which may be different from the thread we switched to).
786 *
787 * We are responsible for marking ntd as TDF_RUNNING.
788 */
121f93bc 789 KKASSERT((ntd->td_flags & TDF_RUNNING) == 0);
94f6d86e 790 ++switch_count;
a1f0fb66 791 KTR_LOG(ctxsw_sw, gd->gd_cpuid, ntd);
cc9b6223
MD
792 ntd->td_flags |= TDF_RUNNING;
793 lwkt_switch_return(td->td_switch(ntd));
794 /* ntd invalid, td_switch() can return a different thread_t */
94f6d86e 795 }
b12defdc 796
b12defdc 797 /*
54341a3b 798 * catch-all. XXX is this strictly needed?
b12defdc
MD
799 */
800 splz_check();
54341a3b 801
37af14fe
MD
802 /* NOTE: current cpu may have changed after switch */
803 crit_exit_quick(td);
8ad65e08
MD
804}
805
cc9b6223
MD
806/*
807 * Called by assembly in the td_switch (thread restore path) for thread
808 * bootstrap cases which do not 'return' to lwkt_switch().
809 */
810void
811lwkt_switch_return(thread_t otd)
812{
cc9b6223 813 globaldata_t rgd;
3a06728e
MD
814#ifdef LOOPMASK
815 uint64_t tsc_base = rdtsc();
816#endif
817 int exiting;
818
819 exiting = otd->td_flags & TDF_EXITING;
820 cpu_ccfence();
cc9b6223
MD
821
822 /*
823 * Check if otd was migrating. Now that we are on ntd we can finish
824 * up the migration. This is a bit messy but it is the only place
825 * where td is known to be fully descheduled.
826 *
827 * We can only activate the migration if otd was migrating but not
828 * held on the cpu due to a preemption chain. We still have to
829 * clear TDF_RUNNING on the old thread either way.
830 *
831 * We are responsible for clearing the previously running thread's
832 * TDF_RUNNING.
833 */
834 if ((rgd = otd->td_migrate_gd) != NULL &&
835 (otd->td_flags & TDF_PREEMPT_LOCK) == 0) {
836 KKASSERT((otd->td_flags & (TDF_MIGRATING | TDF_RUNNING)) ==
837 (TDF_MIGRATING | TDF_RUNNING));
838 otd->td_migrate_gd = NULL;
839 otd->td_flags &= ~TDF_RUNNING;
840 lwkt_send_ipiq(rgd, lwkt_setcpu_remote, otd);
841 } else {
842 otd->td_flags &= ~TDF_RUNNING;
843 }
2b07d9aa
MD
844
845 /*
846 * Final exit validations (see lwp_wait()). Note that otd becomes
847 * invalid the *instant* we set TDF_MP_EXITSIG.
3a06728e
MD
848 *
849 * Use the EXITING status loaded from before we clear TDF_RUNNING,
850 * because if it is not set otd becomes invalid the instant we clear
851 * TDF_RUNNING on it (otherwise, if the system is fast enough, we
852 * might 'steal' TDF_EXITING from another switch-return!).
2b07d9aa 853 */
3a06728e 854 while (exiting) {
2b07d9aa
MD
855 u_int mpflags;
856
857 mpflags = otd->td_mpflags;
858 cpu_ccfence();
859
860 if (mpflags & TDF_MP_EXITWAIT) {
861 if (atomic_cmpset_int(&otd->td_mpflags, mpflags,
862 mpflags | TDF_MP_EXITSIG)) {
863 wakeup(otd);
864 break;
865 }
866 } else {
867 if (atomic_cmpset_int(&otd->td_mpflags, mpflags,
868 mpflags | TDF_MP_EXITSIG)) {
869 wakeup(otd);
870 break;
871 }
872 }
3a06728e
MD
873
874#ifdef LOOPMASK
875 if (tsc_frequency && rdtsc() - tsc_base > tsc_frequency) {
876 kprintf("lwkt_switch_return: excessive TDF_EXITING "
877 "thread %p\n", otd);
878 tsc_base = rdtsc();
879 }
880#endif
2b07d9aa 881 }
cc9b6223
MD
882}
883
b68b7282 884/*
96728c05 885 * Request that the target thread preempt the current thread. Preemption
203592a0
MD
886 * can only occur only:
887 *
888 * - If our critical section is the one that we were called with
889 * - The relative priority of the target thread is higher
890 * - The target is not excessively interrupt-nested via td_nest_count
891 * - The target thread holds no tokens.
892 * - The target thread is not already scheduled and belongs to the
893 * current cpu.
894 * - The current thread is not holding any spin-locks.
96728c05
MD
895 *
896 * THE CALLER OF LWKT_PREEMPT() MUST BE IN A CRITICAL SECTION. Typically
897 * this is called via lwkt_schedule() through the td_preemptable callback.
f9235b6d 898 * critcount is the managed critical priority that we should ignore in order
96728c05
MD
899 * to determine whether preemption is possible (aka usually just the crit
900 * priority of lwkt_schedule() itself).
b68b7282 901 *
54341a3b
MD
902 * Preemption is typically limited to interrupt threads.
903 *
904 * Operation works in a fairly straight-forward manner. The normal
905 * scheduling code is bypassed and we switch directly to the target
906 * thread. When the target thread attempts to block or switch away
907 * code at the base of lwkt_switch() will switch directly back to our
908 * thread. Our thread is able to retain whatever tokens it holds and
909 * if the target needs one of them the target will switch back to us
910 * and reschedule itself normally.
b68b7282
MD
911 */
912void
f9235b6d 913lwkt_preempt(thread_t ntd, int critcount)
b68b7282 914{
46a3f46d 915 struct globaldata *gd = mycpu;
cc9b6223 916 thread_t xtd;
0a3f9b47 917 thread_t td;
2d910aaf 918 int save_gd_intr_nesting_level;
b68b7282 919
26a0694b 920 /*
96728c05
MD
921 * The caller has put us in a critical section. We can only preempt
922 * if the caller of the caller was not in a critical section (basically
f9235b6d 923 * a local interrupt), as determined by the 'critcount' parameter. We
47737962 924 * also can't preempt if the caller is holding any spinlocks (even if
d666840a 925 * he isn't in a critical section). This also handles the tokens test.
96728c05
MD
926 *
927 * YYY The target thread must be in a critical section (else it must
928 * inherit our critical section? I dunno yet).
26a0694b 929 */
f9235b6d 930 KASSERT(ntd->td_critcount, ("BADCRIT0 %d", ntd->td_pri));
26a0694b 931
b12defdc 932 td = gd->gd_curthread;
fbc024e4
MD
933 if (preempt_enable == 0) {
934 ++preempt_miss;
935 return;
936 }
f9235b6d 937 if (ntd->td_pri <= td->td_pri) {
57c254db
MD
938 ++preempt_miss;
939 return;
940 }
f9235b6d 941 if (td->td_critcount > critcount) {
96728c05
MD
942 ++preempt_miss;
943 return;
944 }
203592a0
MD
945 if (td->td_nest_count >= 2) {
946 ++preempt_miss;
947 return;
948 }
121f93bc
MD
949 if (td->td_cscount) {
950 ++preempt_miss;
951 return;
952 }
46a3f46d 953 if (ntd->td_gd != gd) {
96728c05
MD
954 ++preempt_miss;
955 return;
956 }
ee89e80b 957
41a01a4d 958 /*
77912481
MD
959 * We don't have to check spinlocks here as they will also bump
960 * td_critcount.
d3d1cbc8
MD
961 *
962 * Do not try to preempt if the target thread is holding any tokens.
963 * We could try to acquire the tokens but this case is so rare there
964 * is no need to support it.
41a01a4d 965 */
0846e4ce 966 KKASSERT(gd->gd_spinlocks == 0);
77912481 967
3b998fa9 968 if (TD_TOKS_HELD(ntd)) {
d3d1cbc8 969 ++preempt_miss;
d3d1cbc8
MD
970 return;
971 }
26a0694b
MD
972 if (td == ntd || ((td->td_flags | ntd->td_flags) & TDF_PREEMPT_LOCK)) {
973 ++preempt_weird;
974 return;
975 }
976 if (ntd->td_preempted) {
4b5f931b 977 ++preempt_hit;
26a0694b 978 return;
b68b7282 979 }
da0b0e8b 980 KKASSERT(gd->gd_processing_ipiq == 0);
26a0694b 981
8ec60c3f
MD
982 /*
983 * Since we are able to preempt the current thread, there is no need to
984 * call need_lwkt_resched().
2d910aaf
MD
985 *
986 * We must temporarily clear gd_intr_nesting_level around the switch
987 * since switchouts from the target thread are allowed (they will just
988 * return to our thread), and since the target thread has its own stack.
cc9b6223
MD
989 *
990 * A preemption must switch back to the original thread, assert the
991 * case.
8ec60c3f 992 */
26a0694b
MD
993 ++preempt_hit;
994 ntd->td_preempted = td;
995 td->td_flags |= TDF_PREEMPT_LOCK;
a1f0fb66 996 KTR_LOG(ctxsw_pre, gd->gd_cpuid, ntd);
2d910aaf
MD
997 save_gd_intr_nesting_level = gd->gd_intr_nesting_level;
998 gd->gd_intr_nesting_level = 0;
121f93bc
MD
999
1000 KKASSERT((ntd->td_flags & TDF_RUNNING) == 0);
cc9b6223
MD
1001 ntd->td_flags |= TDF_RUNNING;
1002 xtd = td->td_switch(ntd);
1003 KKASSERT(xtd == ntd);
1004 lwkt_switch_return(xtd);
2d910aaf 1005 gd->gd_intr_nesting_level = save_gd_intr_nesting_level;
b9eb1c19 1006
26a0694b
MD
1007 KKASSERT(ntd->td_preempted && (td->td_flags & TDF_PREEMPT_DONE));
1008 ntd->td_preempted = NULL;
1009 td->td_flags &= ~(TDF_PREEMPT_LOCK|TDF_PREEMPT_DONE);
b68b7282
MD
1010}
1011
f1d1c3fa 1012/*
faaeffac 1013 * Conditionally call splz() if gd_reqflags indicates work is pending.
4a28fe22
MD
1014 * This will work inside a critical section but not inside a hard code
1015 * section.
ef0fdad1 1016 *
f1d1c3fa
MD
1017 * (self contained on a per cpu basis)
1018 */
1019void
faaeffac 1020splz_check(void)
f1d1c3fa 1021{
7966cb69
MD
1022 globaldata_t gd = mycpu;
1023 thread_t td = gd->gd_curthread;
ef0fdad1 1024
4a28fe22
MD
1025 if ((gd->gd_reqflags & RQF_IDLECHECK_MASK) &&
1026 gd->gd_intr_nesting_level == 0 &&
1027 td->td_nest_count < 2)
1028 {
f1d1c3fa 1029 splz();
4a28fe22
MD
1030 }
1031}
1032
1033/*
1034 * This version is integrated into crit_exit, reqflags has already
1035 * been tested but td_critcount has not.
1036 *
1037 * We only want to execute the splz() on the 1->0 transition of
1038 * critcount and not in a hard code section or if too deeply nested.
925040f2 1039 *
0846e4ce 1040 * NOTE: gd->gd_spinlocks is implied to be 0 when td_critcount is 0.
4a28fe22
MD
1041 */
1042void
1043lwkt_maybe_splz(thread_t td)
1044{
1045 globaldata_t gd = td->td_gd;
1046
1047 if (td->td_critcount == 0 &&
1048 gd->gd_intr_nesting_level == 0 &&
1049 td->td_nest_count < 2)
1050 {
1051 splz();
1052 }
f1d1c3fa
MD
1053}
1054
e6546af9
MD
1055/*
1056 * Drivers which set up processing co-threads can call this function to
1057 * run the co-thread at a higher priority and to allow it to preempt
1058 * normal threads.
1059 */
1060void
1061lwkt_set_interrupt_support_thread(void)
1062{
1063 thread_t td = curthread;
1064
1065 lwkt_setpri_self(TDPRI_INT_SUPPORT);
1066 td->td_flags |= TDF_INTTHREAD;
1067 td->td_preemptable = lwkt_preempt;
1068}
1069
1070
8ad65e08 1071/*
f9235b6d
MD
1072 * This function is used to negotiate a passive release of the current
1073 * process/lwp designation with the user scheduler, allowing the user
1074 * scheduler to schedule another user thread. The related kernel thread
1075 * (curthread) continues running in the released state.
8ad65e08
MD
1076 */
1077void
f9235b6d 1078lwkt_passive_release(struct thread *td)
8ad65e08 1079{
f9235b6d
MD
1080 struct lwp *lp = td->td_lwp;
1081
1082 td->td_release = NULL;
1083 lwkt_setpri_self(TDPRI_KERN_USER);
d992c377 1084
f9235b6d 1085 lp->lwp_proc->p_usched->release_curproc(lp);
f1d1c3fa
MD
1086}
1087
f9235b6d 1088
3824f392 1089/*
d2d8515b
MD
1090 * This implements a LWKT yield, allowing a kernel thread to yield to other
1091 * kernel threads at the same or higher priority. This function can be
1092 * called in a tight loop and will typically only yield once per tick.
f9235b6d 1093 *
d2d8515b
MD
1094 * Most kernel threads run at the same priority in order to allow equal
1095 * sharing.
f9235b6d
MD
1096 *
1097 * (self contained on a per cpu basis)
3824f392
MD
1098 */
1099void
f9235b6d 1100lwkt_yield(void)
3824f392 1101{
f9235b6d
MD
1102 globaldata_t gd = mycpu;
1103 thread_t td = gd->gd_curthread;
3824f392 1104
fbe96076
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1105 /*
1106 * Should never be called with spinlocks held but there is a path
1107 * via ACPI where it might happen.
1108 */
1109 if (gd->gd_spinlocks)
1110 return;
1111
1112 /*
1113 * Safe to call splz if we are not too-heavily nested.
1114 */
f9235b6d
MD
1115 if ((gd->gd_reqflags & RQF_IDLECHECK_MASK) && td->td_nest_count < 2)
1116 splz();
fbe96076
MD
1117
1118 /*
1119 * Caller allows switching
1120 */
85946b6c 1121 if (lwkt_resched_wanted()) {
f9235b6d
MD
1122 lwkt_schedule_self(curthread);
1123 lwkt_switch();
f9235b6d 1124 }
3824f392
MD
1125}
1126
40504122
MD
1127/*
1128 * The quick version processes pending interrupts and higher-priority
1129 * LWKT threads but will not round-robin same-priority LWKT threads.
de4d4cb0
MD
1130 *
1131 * When called while attempting to return to userland the only same-pri
1132 * threads are the ones which have already tried to become the current
1133 * user process.
40504122
MD
1134 */
1135void
1136lwkt_yield_quick(void)
1137{
1138 globaldata_t gd = mycpu;
1139 thread_t td = gd->gd_curthread;
1140
1141 if ((gd->gd_reqflags & RQF_IDLECHECK_MASK) && td->td_nest_count < 2)
1142 splz();
1143 if (lwkt_resched_wanted()) {
9c99cb33 1144 crit_enter();
40504122
MD
1145 if (TAILQ_FIRST(&gd->gd_tdrunq) == td) {
1146 clear_lwkt_resched();
1147 } else {
1148 lwkt_schedule_self(curthread);
1149 lwkt_switch();
1150 }
9c99cb33 1151 crit_exit();
40504122
MD
1152 }
1153}
1154
3824f392 1155/*
f9235b6d
MD
1156 * This yield is designed for kernel threads with a user context.
1157 *
1158 * The kernel acting on behalf of the user is potentially cpu-bound,
1159 * this function will efficiently allow other threads to run and also
1160 * switch to other processes by releasing.
3824f392
MD
1161 *
1162 * The lwkt_user_yield() function is designed to have very low overhead
1163 * if no yield is determined to be needed.
1164 */
1165void
1166lwkt_user_yield(void)
1167{
f9235b6d
MD
1168 globaldata_t gd = mycpu;
1169 thread_t td = gd->gd_curthread;
1170
fbe96076
MD
1171 /*
1172 * Should never be called with spinlocks held but there is a path
1173 * via ACPI where it might happen.
1174 */
1175 if (gd->gd_spinlocks)
1176 return;
1177
f9235b6d
MD
1178 /*
1179 * Always run any pending interrupts in case we are in a critical
1180 * section.
1181 */
1182 if ((gd->gd_reqflags & RQF_IDLECHECK_MASK) && td->td_nest_count < 2)
1183 splz();
3824f392 1184
3824f392 1185 /*
f9235b6d
MD
1186 * Switch (which forces a release) if another kernel thread needs
1187 * the cpu, if userland wants us to resched, or if our kernel
1188 * quantum has run out.
3824f392 1189 */
f9235b6d 1190 if (lwkt_resched_wanted() ||
85946b6c 1191 user_resched_wanted())
f9235b6d 1192 {
3824f392 1193 lwkt_switch();
3824f392
MD
1194 }
1195
f9235b6d 1196#if 0
3824f392 1197 /*
f9235b6d
MD
1198 * Reacquire the current process if we are released.
1199 *
1200 * XXX not implemented atm. The kernel may be holding locks and such,
1201 * so we want the thread to continue to receive cpu.
3824f392 1202 */
f9235b6d
MD
1203 if (td->td_release == NULL && lp) {
1204 lp->lwp_proc->p_usched->acquire_curproc(lp);
1205 td->td_release = lwkt_passive_release;
1206 lwkt_setpri_self(TDPRI_USER_NORM);
3824f392 1207 }
f9235b6d 1208#endif
b9eb1c19
MD
1209}
1210
8ad65e08 1211/*
f1d1c3fa
MD
1212 * Generic schedule. Possibly schedule threads belonging to other cpus and
1213 * deal with threads that might be blocked on a wait queue.
1214 *
0a3f9b47
MD
1215 * We have a little helper inline function which does additional work after
1216 * the thread has been enqueued, including dealing with preemption and
1217 * setting need_lwkt_resched() (which prevents the kernel from returning
1218 * to userland until it has processed higher priority threads).
6330a558
MD
1219 *
1220 * It is possible for this routine to be called after a failed _enqueue
1221 * (due to the target thread migrating, sleeping, or otherwise blocked).
1222 * We have to check that the thread is actually on the run queue!
8ad65e08 1223 */
0a3f9b47
MD
1224static __inline
1225void
85946b6c 1226_lwkt_schedule_post(globaldata_t gd, thread_t ntd, int ccount)
0a3f9b47 1227{
6330a558 1228 if (ntd->td_flags & TDF_RUNQ) {
85946b6c 1229 if (ntd->td_preemptable) {
f9235b6d 1230 ntd->td_preemptable(ntd, ccount); /* YYY +token */
6330a558 1231 }
0a3f9b47
MD
1232 }
1233}
1234
361d01dd 1235static __inline
8ad65e08 1236void
85946b6c 1237_lwkt_schedule(thread_t td)
8ad65e08 1238{
37af14fe
MD
1239 globaldata_t mygd = mycpu;
1240
cf709dd2
MD
1241 KASSERT(td != &td->td_gd->gd_idlethread,
1242 ("lwkt_schedule(): scheduling gd_idlethread is illegal!"));
cfaeae2a 1243 KKASSERT((td->td_flags & TDF_MIGRATING) == 0);
37af14fe 1244 crit_enter_gd(mygd);
4643740a
MD
1245 KKASSERT(td->td_lwp == NULL ||
1246 (td->td_lwp->lwp_mpflags & LWP_MP_ONRUNQ) == 0);
1247
37af14fe 1248 if (td == mygd->gd_curthread) {
f1d1c3fa
MD
1249 _lwkt_enqueue(td);
1250 } else {
f1d1c3fa 1251 /*
7cd8d145
MD
1252 * If we own the thread, there is no race (since we are in a
1253 * critical section). If we do not own the thread there might
1254 * be a race but the target cpu will deal with it.
f1d1c3fa 1255 */
7cd8d145 1256 if (td->td_gd == mygd) {
9d265729 1257 _lwkt_enqueue(td);
85946b6c 1258 _lwkt_schedule_post(mygd, td, 1);
f1d1c3fa 1259 } else {
e381e77c 1260 lwkt_send_ipiq3(td->td_gd, lwkt_schedule_remote, td, 0);
7cd8d145 1261 }
8ad65e08 1262 }
37af14fe 1263 crit_exit_gd(mygd);
8ad65e08
MD
1264}
1265
361d01dd
MD
1266void
1267lwkt_schedule(thread_t td)
1268{
85946b6c 1269 _lwkt_schedule(td);
361d01dd
MD
1270}
1271
1272void
85946b6c 1273lwkt_schedule_noresched(thread_t td) /* XXX not impl */
361d01dd 1274{
85946b6c 1275 _lwkt_schedule(td);
361d01dd
MD
1276}
1277
e381e77c
MD
1278/*
1279 * When scheduled remotely if frame != NULL the IPIQ is being
1280 * run via doreti or an interrupt then preemption can be allowed.
1281 *
1282 * To allow preemption we have to drop the critical section so only
1283 * one is present in _lwkt_schedule_post.
1284 */
1285static void
1286lwkt_schedule_remote(void *arg, int arg2, struct intrframe *frame)
1287{
1288 thread_t td = curthread;
1289 thread_t ntd = arg;
1290
1291 if (frame && ntd->td_preemptable) {
1292 crit_exit_noyield(td);
85946b6c 1293 _lwkt_schedule(ntd);
e381e77c
MD
1294 crit_enter_quick(td);
1295 } else {
85946b6c 1296 _lwkt_schedule(ntd);
e381e77c
MD
1297 }
1298}
1299
d9eea1a5 1300/*
52eedfb5
MD
1301 * Thread migration using a 'Pull' method. The thread may or may not be
1302 * the current thread. It MUST be descheduled and in a stable state.
1303 * lwkt_giveaway() must be called on the cpu owning the thread.
1304 *
1305 * At any point after lwkt_giveaway() is called, the target cpu may
1306 * 'pull' the thread by calling lwkt_acquire().
1307 *
ae8e83e6
MD
1308 * We have to make sure the thread is not sitting on a per-cpu tsleep
1309 * queue or it will blow up when it moves to another cpu.
1310 *
52eedfb5 1311 * MPSAFE - must be called under very specific conditions.
d9eea1a5 1312 */
52eedfb5
MD
1313void
1314lwkt_giveaway(thread_t td)
1315{
3b4192fb 1316 globaldata_t gd = mycpu;
52eedfb5 1317
3b4192fb
MD
1318 crit_enter_gd(gd);
1319 if (td->td_flags & TDF_TSLEEPQ)
1320 tsleep_remove(td);
1321 KKASSERT(td->td_gd == gd);
1322 TAILQ_REMOVE(&gd->gd_tdallq, td, td_allq);
1323 td->td_flags |= TDF_MIGRATING;
1324 crit_exit_gd(gd);
52eedfb5
MD
1325}
1326
a2a5ad0d
MD
1327void
1328lwkt_acquire(thread_t td)
1329{
37af14fe
MD
1330 globaldata_t gd;
1331 globaldata_t mygd;
a2a5ad0d 1332
52eedfb5 1333 KKASSERT(td->td_flags & TDF_MIGRATING);
a2a5ad0d 1334 gd = td->td_gd;
37af14fe 1335 mygd = mycpu;
52eedfb5 1336 if (gd != mycpu) {
3a06728e
MD
1337#ifdef LOOPMASK
1338 uint64_t tsc_base = rdtsc();
1339#endif
35238fa5 1340 cpu_lfence();
52eedfb5 1341 KKASSERT((td->td_flags & TDF_RUNQ) == 0);
37af14fe 1342 crit_enter_gd(mygd);
cfaeae2a 1343 DEBUG_PUSH_INFO("lwkt_acquire");
df910c23 1344 while (td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK)) {
df910c23 1345 lwkt_process_ipiq();
52eedfb5 1346 cpu_lfence();
a86ce0cd
MD
1347#ifdef _KERNEL_VIRTUAL
1348 pthread_yield();
3a06728e
MD
1349#endif
1350#ifdef LOOPMASK
1351 if (tsc_frequency && rdtsc() - tsc_base > tsc_frequency) {
1352 kprintf("lwkt_acquire: stuck td %p td->td_flags %08x\n",
1353 td, td->td_flags);
1354 tsc_base = rdtsc();
1355 }
a86ce0cd 1356#endif
df910c23 1357 }
cfaeae2a 1358 DEBUG_POP_INFO();
562273ea 1359 cpu_mfence();
37af14fe 1360 td->td_gd = mygd;
52eedfb5
MD
1361 TAILQ_INSERT_TAIL(&mygd->gd_tdallq, td, td_allq);
1362 td->td_flags &= ~TDF_MIGRATING;
1363 crit_exit_gd(mygd);
1364 } else {
1365 crit_enter_gd(mygd);
1366 TAILQ_INSERT_TAIL(&mygd->gd_tdallq, td, td_allq);
1367 td->td_flags &= ~TDF_MIGRATING;
37af14fe 1368 crit_exit_gd(mygd);
a2a5ad0d
MD
1369 }
1370}
1371
f1d1c3fa
MD
1372/*
1373 * Generic deschedule. Descheduling threads other then your own should be
1374 * done only in carefully controlled circumstances. Descheduling is
1375 * asynchronous.
1376 *
1377 * This function may block if the cpu has run out of messages.
8ad65e08
MD
1378 */
1379void
1380lwkt_deschedule(thread_t td)
1381{
f1d1c3fa
MD
1382 crit_enter();
1383 if (td == curthread) {
1384 _lwkt_dequeue(td);
1385 } else {
a72187e9 1386 if (td->td_gd == mycpu) {
f1d1c3fa
MD
1387 _lwkt_dequeue(td);
1388 } else {
b8a98473 1389 lwkt_send_ipiq(td->td_gd, (ipifunc1_t)lwkt_deschedule, td);
f1d1c3fa
MD
1390 }
1391 }
1392 crit_exit();
1393}
1394
4b5f931b
MD
1395/*
1396 * Set the target thread's priority. This routine does not automatically
1397 * switch to a higher priority thread, LWKT threads are not designed for
1398 * continuous priority changes. Yield if you want to switch.
4b5f931b
MD
1399 */
1400void
1401lwkt_setpri(thread_t td, int pri)
1402{
f9235b6d
MD
1403 if (td->td_pri != pri) {
1404 KKASSERT(pri >= 0);
1405 crit_enter();
1406 if (td->td_flags & TDF_RUNQ) {
d2d8515b 1407 KKASSERT(td->td_gd == mycpu);
f9235b6d
MD
1408 _lwkt_dequeue(td);
1409 td->td_pri = pri;
1410 _lwkt_enqueue(td);
1411 } else {
1412 td->td_pri = pri;
1413 }
1414 crit_exit();
26a0694b 1415 }
26a0694b
MD
1416}
1417
03bd0a5e
MD
1418/*
1419 * Set the initial priority for a thread prior to it being scheduled for
1420 * the first time. The thread MUST NOT be scheduled before or during
1421 * this call. The thread may be assigned to a cpu other then the current
1422 * cpu.
1423 *
1424 * Typically used after a thread has been created with TDF_STOPPREQ,
1425 * and before the thread is initially scheduled.
1426 */
1427void
1428lwkt_setpri_initial(thread_t td, int pri)
1429{
1430 KKASSERT(pri >= 0);
1431 KKASSERT((td->td_flags & TDF_RUNQ) == 0);
f9235b6d 1432 td->td_pri = pri;
03bd0a5e
MD
1433}
1434
26a0694b
MD
1435void
1436lwkt_setpri_self(int pri)
1437{
1438 thread_t td = curthread;
1439
4b5f931b
MD
1440 KKASSERT(pri >= 0 && pri <= TDPRI_MAX);
1441 crit_enter();
1442 if (td->td_flags & TDF_RUNQ) {
1443 _lwkt_dequeue(td);
f9235b6d 1444 td->td_pri = pri;
4b5f931b
MD
1445 _lwkt_enqueue(td);
1446 } else {
f9235b6d 1447 td->td_pri = pri;
4b5f931b
MD
1448 }
1449 crit_exit();
1450}
1451
f9235b6d 1452/*
85946b6c 1453 * hz tick scheduler clock for LWKT threads
f9235b6d
MD
1454 */
1455void
85946b6c 1456lwkt_schedulerclock(thread_t td)
f9235b6d 1457{
85946b6c
MD
1458 globaldata_t gd = td->td_gd;
1459 thread_t xtd;
2a418930 1460
c6a766f4
MD
1461 xtd = TAILQ_FIRST(&gd->gd_tdrunq);
1462 if (xtd == td) {
85946b6c
MD
1463 /*
1464 * If the current thread is at the head of the runq shift it to the
1465 * end of any equal-priority threads and request a LWKT reschedule
1466 * if it moved.
d992c377
MD
1467 *
1468 * Ignore upri in this situation. There will only be one user thread
1469 * in user mode, all others will be user threads running in kernel
1470 * mode and we have to make sure they get some cpu.
85946b6c
MD
1471 */
1472 xtd = TAILQ_NEXT(td, td_threadq);
1473 if (xtd && xtd->td_pri == td->td_pri) {
1474 TAILQ_REMOVE(&gd->gd_tdrunq, td, td_threadq);
1475 while (xtd && xtd->td_pri == td->td_pri)
1476 xtd = TAILQ_NEXT(xtd, td_threadq);
1477 if (xtd)
1478 TAILQ_INSERT_BEFORE(xtd, td, td_threadq);
1479 else
1480 TAILQ_INSERT_TAIL(&gd->gd_tdrunq, td, td_threadq);
1481 need_lwkt_resched();
f9235b6d 1482 }
c6a766f4 1483 } else if (xtd) {
85946b6c
MD
1484 /*
1485 * If we scheduled a thread other than the one at the head of the
1486 * queue always request a reschedule every tick.
1487 */
1488 need_lwkt_resched();
f9235b6d 1489 }
c6a766f4 1490 /* else curthread probably the idle thread, no need to reschedule */
f9235b6d
MD
1491}
1492
5d21b981 1493/*
52eedfb5
MD
1494 * Migrate the current thread to the specified cpu.
1495 *
cc9b6223
MD
1496 * This is accomplished by descheduling ourselves from the current cpu
1497 * and setting td_migrate_gd. The lwkt_switch() code will detect that the
1498 * 'old' thread wants to migrate after it has been completely switched out
1499 * and will complete the migration.
1500 *
1501 * TDF_MIGRATING prevents scheduling races while the thread is being migrated.
1502 *
1503 * We must be sure to release our current process designation (if a user
1504 * process) before clearing out any tsleepq we are on because the release
1505 * code may re-add us.
ae8e83e6
MD
1506 *
1507 * We must be sure to remove ourselves from the current cpu's tsleepq
1508 * before potentially moving to another queue. The thread can be on
1509 * a tsleepq due to a left-over tsleep_interlock().
5d21b981 1510 */
5d21b981
MD
1511
1512void
1513lwkt_setcpu_self(globaldata_t rgd)
1514{
5d21b981
MD
1515 thread_t td = curthread;
1516
1517 if (td->td_gd != rgd) {
1518 crit_enter_quick(td);
cc9b6223 1519
95858b91
MD
1520 if (td->td_release)
1521 td->td_release(td);
ae8e83e6 1522 if (td->td_flags & TDF_TSLEEPQ)
3b4192fb 1523 tsleep_remove(td);
cc9b6223
MD
1524
1525 /*
1526 * Set TDF_MIGRATING to prevent a spurious reschedule while we are
1527 * trying to deschedule ourselves and switch away, then deschedule
1528 * ourself, remove us from tdallq, and set td_migrate_gd. Finally,
1529 * call lwkt_switch() to complete the operation.
1530 */
5d21b981
MD
1531 td->td_flags |= TDF_MIGRATING;
1532 lwkt_deschedule_self(td);
52eedfb5 1533 TAILQ_REMOVE(&td->td_gd->gd_tdallq, td, td_allq);
cc9b6223 1534 td->td_migrate_gd = rgd;
5d21b981 1535 lwkt_switch();
cc9b6223
MD
1536
1537 /*
1538 * We are now on the target cpu
1539 */
1540 KKASSERT(rgd == mycpu);
52eedfb5 1541 TAILQ_INSERT_TAIL(&rgd->gd_tdallq, td, td_allq);
5d21b981
MD
1542 crit_exit_quick(td);
1543 }
5d21b981
MD
1544}
1545
ecdefdda
MD
1546void
1547lwkt_migratecpu(int cpuid)
1548{
ecdefdda
MD
1549 globaldata_t rgd;
1550
1551 rgd = globaldata_find(cpuid);
1552 lwkt_setcpu_self(rgd);
ecdefdda
MD
1553}
1554
5d21b981
MD
1555/*
1556 * Remote IPI for cpu migration (called while in a critical section so we
cc9b6223
MD
1557 * do not have to enter another one).
1558 *
1559 * The thread (td) has already been completely descheduled from the
1560 * originating cpu and we can simply assert the case. The thread is
1561 * assigned to the new cpu and enqueued.
5d21b981 1562 *
cc9b6223 1563 * The thread will re-add itself to tdallq when it resumes execution.
5d21b981
MD
1564 */
1565static void
1566lwkt_setcpu_remote(void *arg)
1567{
1568 thread_t td = arg;
1569 globaldata_t gd = mycpu;
1570
cc9b6223 1571 KKASSERT((td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK)) == 0);
5d21b981 1572 td->td_gd = gd;
562273ea 1573 cpu_mfence();
5d21b981 1574 td->td_flags &= ~TDF_MIGRATING;
cc9b6223 1575 KKASSERT(td->td_migrate_gd == NULL);
4643740a
MD
1576 KKASSERT(td->td_lwp == NULL ||
1577 (td->td_lwp->lwp_mpflags & LWP_MP_ONRUNQ) == 0);
5d21b981
MD
1578 _lwkt_enqueue(td);
1579}
1580
553ea3c8 1581struct lwp *
4b5f931b
MD
1582lwkt_preempted_proc(void)
1583{
73e4f7b9 1584 thread_t td = curthread;
4b5f931b
MD
1585 while (td->td_preempted)
1586 td = td->td_preempted;
553ea3c8 1587 return(td->td_lwp);
4b5f931b
MD
1588}
1589
99df837e
MD
1590/*
1591 * Create a kernel process/thread/whatever. It shares it's address space
1592 * with proc0 - ie: kernel only.
1593 *
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1594 * If the cpu is not specified one will be selected. In the future
1595 * specifying a cpu of -1 will enable kernel thread migration between
1596 * cpus.
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1597 */
1598int
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1599lwkt_create(void (*func)(void *), void *arg, struct thread **tdp,
1600 thread_t template, int tdflags, int cpu, const char *fmt, ...)
99df837e 1601{
73e4f7b9 1602 thread_t td;
e2565a42 1603 __va_list ap;
99df837e 1604
d3d32139 1605 td = lwkt_alloc_thread(template, LWKT_THREAD_STACK, cpu,
dbcd0c9b 1606 tdflags);
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1607 if (tdp)
1608 *tdp = td;
709799ea 1609 cpu_set_thread_handler(td, lwkt_exit, func, arg);
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1610
1611 /*
1612 * Set up arg0 for 'ps' etc
1613 */
e2565a42 1614 __va_start(ap, fmt);
379210cb 1615 kvsnprintf(td->td_comm, sizeof(td->td_comm), fmt, ap);
e2565a42 1616 __va_end(ap);
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1617
1618 /*
1619 * Schedule the thread to run
1620 */
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1621 if (td->td_flags & TDF_NOSTART)
1622 td->td_flags &= ~TDF_NOSTART;
ef0fdad1 1623 else
4643740a 1624 lwkt_schedule(td);
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1625 return 0;
1626}
1627
1628/*
1629 * Destroy an LWKT thread. Warning! This function is not called when
1630 * a process exits, cpu_proc_exit() directly calls cpu_thread_exit() and
1631 * uses a different reaping mechanism.
1632 */
1633void
1634lwkt_exit(void)
1635{
1636 thread_t td = curthread;
c070746a 1637 thread_t std;
8826f33a 1638 globaldata_t gd;
99df837e 1639
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1640 /*
1641 * Do any cleanup that might block here
1642 */
99df837e 1643 if (td->td_flags & TDF_VERBOSE)
6ea70f76 1644 kprintf("kthread %p %s has exited\n", td, td->td_comm);
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1645 biosched_done(td);
1646 dsched_exit_thread(td);
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1647
1648 /*
1649 * Get us into a critical section to interlock gd_freetd and loop
1650 * until we can get it freed.
1651 *
1652 * We have to cache the current td in gd_freetd because objcache_put()ing
1653 * it would rip it out from under us while our thread is still active.
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1654 *
1655 * We are the current thread so of course our own TDF_RUNNING bit will
1656 * be set, so unlike the lwp reap code we don't wait for it to clear.
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1657 */
1658 gd = mycpu;
37af14fe 1659 crit_enter_quick(td);
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1660 for (;;) {
1661 if (td->td_refs) {
1662 tsleep(td, 0, "tdreap", 1);
1663 continue;
1664 }
1665 if ((std = gd->gd_freetd) != NULL) {
1666 KKASSERT((std->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK)) == 0);
1667 gd->gd_freetd = NULL;
1668 objcache_put(thread_cache, std);
1669 continue;
1670 }
1671 break;
c070746a 1672 }
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1673
1674 /*
1675 * Remove thread resources from kernel lists and deschedule us for
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1676 * the last time. We cannot block after this point or we may end
1677 * up with a stale td on the tsleepq.
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1678 *
1679 * None of this may block, the critical section is the only thing
1680 * protecting tdallq and the only thing preventing new lwkt_hold()
1681 * thread refs now.
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1682 */
1683 if (td->td_flags & TDF_TSLEEPQ)
1684 tsleep_remove(td);
37af14fe 1685 lwkt_deschedule_self(td);
e56e4dea 1686 lwkt_remove_tdallq(td);
74c9628e 1687 KKASSERT(td->td_refs == 0);
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1688
1689 /*
1690 * Final cleanup
1691 */
1692 KKASSERT(gd->gd_freetd == NULL);
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1693 if (td->td_flags & TDF_ALLOCATED_THREAD)
1694 gd->gd_freetd = td;
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1695 cpu_thread_exit();
1696}
1697
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1698void
1699lwkt_remove_tdallq(thread_t td)
1700{
1701 KKASSERT(td->td_gd == mycpu);
1702 TAILQ_REMOVE(&td->td_gd->gd_tdallq, td, td_allq);
1703}
1704
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1705/*
1706 * Code reduction and branch prediction improvements. Call/return
1707 * overhead on modern cpus often degenerates into 0 cycles due to
1708 * the cpu's branch prediction hardware and return pc cache. We
1709 * can take advantage of this by not inlining medium-complexity
1710 * functions and we can also reduce the branch prediction impact
1711 * by collapsing perfectly predictable branches into a single
1712 * procedure instead of duplicating it.
1713 *
1714 * Is any of this noticeable? Probably not, so I'll take the
1715 * smaller code size.
1716 */
1717void
b6468f56 1718crit_exit_wrapper(__DEBUG_CRIT_ARG__)
9cf43f91 1719{
b6468f56 1720 _crit_exit(mycpu __DEBUG_CRIT_PASS_ARG__);
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1721}
1722
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1723void
1724crit_panic(void)
1725{
1726 thread_t td = curthread;
850634cc 1727 int lcrit = td->td_critcount;
2d93b37a 1728
850634cc 1729 td->td_critcount = 0;
a4d95680 1730 cpu_ccfence();
850634cc 1731 panic("td_critcount is/would-go negative! %p %d", td, lcrit);
4a28fe22 1732 /* NOT REACHED */
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1733}
1734
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1735/*
1736 * Called from debugger/panic on cpus which have been stopped. We must still
b19f40a4 1737 * process the IPIQ while stopped.
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1738 *
1739 * If we are dumping also try to process any pending interrupts. This may
1740 * or may not work depending on the state of the cpu at the point it was
1741 * stopped.
1742 */
1743void
1744lwkt_smp_stopped(void)
1745{
1746 globaldata_t gd = mycpu;
1747
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1748 if (dumping) {
1749 lwkt_process_ipiq();
b19f40a4 1750 --gd->gd_intr_nesting_level;
bd8015ca 1751 splz();
b19f40a4 1752 ++gd->gd_intr_nesting_level;
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1753 } else {
1754 lwkt_process_ipiq();
1755 }
63cff036 1756 cpu_smp_stopped();
bd8015ca 1757}