kernel - refactor CPUMASK_ADDR()
[dragonfly.git] / sys / kern / lwkt_thread.c
CommitLineData
8ad65e08 1/*
b12defdc 2 * Copyright (c) 2003-2011 The DragonFly Project. All rights reserved.
60f60350 3 *
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4 * This code is derived from software contributed to The DragonFly Project
5 * by Matthew Dillon <dillon@backplane.com>
60f60350 6 *
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7 * Redistribution and use in source and binary forms, with or without
8 * modification, are permitted provided that the following conditions
9 * are met:
60f60350 10 *
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11 * 1. Redistributions of source code must retain the above copyright
12 * notice, this list of conditions and the following disclaimer.
13 * 2. Redistributions in binary form must reproduce the above copyright
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14 * notice, this list of conditions and the following disclaimer in
15 * the documentation and/or other materials provided with the
16 * distribution.
17 * 3. Neither the name of The DragonFly Project nor the names of its
18 * contributors may be used to endorse or promote products derived
19 * from this software without specific, prior written permission.
60f60350 20 *
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21 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
22 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
23 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
24 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
25 * COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
26 * INCIDENTAL, SPECIAL, EXEMPLARY OR CONSEQUENTIAL DAMAGES (INCLUDING,
27 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
28 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
29 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
30 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
31 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
8ad65e08 32 * SUCH DAMAGE.
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33 */
34
35/*
36 * Each cpu in a system has its own self-contained light weight kernel
37 * thread scheduler, which means that generally speaking we only need
38 * to use a critical section to avoid problems. Foreign thread
39 * scheduling is queued via (async) IPIs.
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40 */
41
42#include <sys/param.h>
43#include <sys/systm.h>
44#include <sys/kernel.h>
45#include <sys/proc.h>
46#include <sys/rtprio.h>
b37f18d6 47#include <sys/kinfo.h>
8ad65e08 48#include <sys/queue.h>
7d0bac62 49#include <sys/sysctl.h>
99df837e 50#include <sys/kthread.h>
f1d1c3fa 51#include <machine/cpu.h>
99df837e 52#include <sys/lock.h>
9d265729 53#include <sys/spinlock.h>
57aa743c 54#include <sys/ktr.h>
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55
56#include <sys/thread2.h>
57#include <sys/spinlock2.h>
684a93c4 58#include <sys/mplock2.h>
f1d1c3fa 59
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60#include <sys/dsched.h>
61
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62#include <vm/vm.h>
63#include <vm/vm_param.h>
64#include <vm/vm_kern.h>
65#include <vm/vm_object.h>
66#include <vm/vm_page.h>
67#include <vm/vm_map.h>
68#include <vm/vm_pager.h>
69#include <vm/vm_extern.h>
7d0bac62 70
99df837e 71#include <machine/stdarg.h>
96728c05 72#include <machine/smp.h>
3a06728e 73#include <machine/clock.h>
99df837e 74
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75#ifdef _KERNEL_VIRTUAL
76#include <pthread.h>
77#endif
78
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79#define LOOPMASK
80
d850923c
AE
81#if !defined(KTR_CTXSW)
82#define KTR_CTXSW KTR_ALL
83#endif
84KTR_INFO_MASTER(ctxsw);
5bf48697
AE
85KTR_INFO(KTR_CTXSW, ctxsw, sw, 0, "#cpu[%d].td = %p", int cpu, struct thread *td);
86KTR_INFO(KTR_CTXSW, ctxsw, pre, 1, "#cpu[%d].td = %p", int cpu, struct thread *td);
87KTR_INFO(KTR_CTXSW, ctxsw, newtd, 2, "#threads[%p].name = %s", struct thread *td, char *comm);
88KTR_INFO(KTR_CTXSW, ctxsw, deadtd, 3, "#threads[%p].name = <dead>", struct thread *td);
1541028a 89
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90static MALLOC_DEFINE(M_THREAD, "thread", "lwkt threads");
91
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92#ifdef INVARIANTS
93static int panic_on_cscount = 0;
94#endif
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95static int64_t switch_count = 0;
96static int64_t preempt_hit = 0;
97static int64_t preempt_miss = 0;
98static int64_t preempt_weird = 0;
fb0f29c4 99static int lwkt_use_spin_port;
40aaf5fc 100static struct objcache *thread_cache;
a46b4a23 101int cpu_mwait_spin = 0;
05220613 102
e381e77c 103static void lwkt_schedule_remote(void *arg, int arg2, struct intrframe *frame);
cc9b6223 104static void lwkt_setcpu_remote(void *arg);
e381e77c 105
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106/*
107 * We can make all thread ports use the spin backend instead of the thread
108 * backend. This should only be set to debug the spin backend.
109 */
110TUNABLE_INT("lwkt.use_spin_port", &lwkt_use_spin_port);
111
0f7a3396 112#ifdef INVARIANTS
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113SYSCTL_INT(_lwkt, OID_AUTO, panic_on_cscount, CTLFLAG_RW, &panic_on_cscount, 0,
114 "Panic if attempting to switch lwkt's while mastering cpusync");
0f7a3396 115#endif
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SG
116SYSCTL_QUAD(_lwkt, OID_AUTO, switch_count, CTLFLAG_RW, &switch_count, 0,
117 "Number of switched threads");
9733f757 118SYSCTL_QUAD(_lwkt, OID_AUTO, preempt_hit, CTLFLAG_RW, &preempt_hit, 0,
0c52fa62 119 "Successful preemption events");
9733f757 120SYSCTL_QUAD(_lwkt, OID_AUTO, preempt_miss, CTLFLAG_RW, &preempt_miss, 0,
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121 "Failed preemption events");
122SYSCTL_QUAD(_lwkt, OID_AUTO, preempt_weird, CTLFLAG_RW, &preempt_weird, 0,
123 "Number of preempted threads.");
b12defdc 124static int fairq_enable = 0;
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125SYSCTL_INT(_lwkt, OID_AUTO, fairq_enable, CTLFLAG_RW,
126 &fairq_enable, 0, "Turn on fairq priority accumulators");
85946b6c 127static int fairq_bypass = -1;
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128SYSCTL_INT(_lwkt, OID_AUTO, fairq_bypass, CTLFLAG_RW,
129 &fairq_bypass, 0, "Allow fairq to bypass td on token failure");
130extern int lwkt_sched_debug;
131int lwkt_sched_debug = 0;
132SYSCTL_INT(_lwkt, OID_AUTO, sched_debug, CTLFLAG_RW,
133 &lwkt_sched_debug, 0, "Scheduler debug");
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134static u_int lwkt_spin_loops = 10;
135SYSCTL_UINT(_lwkt, OID_AUTO, spin_loops, CTLFLAG_RW,
b12defdc 136 &lwkt_spin_loops, 0, "Scheduler spin loops until sorted decon");
fbc024e4 137static int preempt_enable = 1;
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138SYSCTL_INT(_lwkt, OID_AUTO, preempt_enable, CTLFLAG_RW,
139 &preempt_enable, 0, "Enable preemption");
7b234d8c 140static int lwkt_cache_threads = 0;
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141SYSCTL_INT(_lwkt, OID_AUTO, cache_threads, CTLFLAG_RD,
142 &lwkt_cache_threads, 0, "thread+kstack cache");
fbc024e4 143
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144/*
145 * These helper procedures handle the runq, they can only be called from
146 * within a critical section.
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147 *
148 * WARNING! Prior to SMP being brought up it is possible to enqueue and
149 * dequeue threads belonging to other cpus, so be sure to use td->td_gd
150 * instead of 'mycpu' when referencing the globaldata structure. Once
151 * SMP live enqueuing and dequeueing only occurs on the current cpu.
4b5f931b 152 */
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153static __inline
154void
155_lwkt_dequeue(thread_t td)
156{
157 if (td->td_flags & TDF_RUNQ) {
75cdbe6c 158 struct globaldata *gd = td->td_gd;
4b5f931b 159
f1d1c3fa 160 td->td_flags &= ~TDF_RUNQ;
f9235b6d 161 TAILQ_REMOVE(&gd->gd_tdrunq, td, td_threadq);
de4d4cb0 162 --gd->gd_tdrunqcount;
f9235b6d 163 if (TAILQ_FIRST(&gd->gd_tdrunq) == NULL)
2a418930 164 atomic_clear_int(&gd->gd_reqflags, RQF_RUNNING);
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165 }
166}
167
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168/*
169 * Priority enqueue.
170 *
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171 * There are a limited number of lwkt threads runnable since user
172 * processes only schedule one at a time per cpu. However, there can
173 * be many user processes in kernel mode exiting from a tsleep() which
e3e6be1f 174 * become runnable.
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175 *
176 * NOTE: lwkt_schedulerclock() will force a round-robin based on td_pri and
177 * will ignore user priority. This is to ensure that user threads in
178 * kernel mode get cpu at some point regardless of what the user
179 * scheduler thinks.
f9235b6d 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) {
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193 TAILQ_INSERT_TAIL(&gd->gd_tdrunq, td, td_threadq);
194 atomic_set_int(&gd->gd_reqflags, RQF_RUNNING);
f9235b6d 195 } else {
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196 /*
197 * NOTE: td_upri - higher numbers more desireable, same sense
198 * as td_pri (typically reversed from lwp_upri).
199 *
200 * In the equal priority case we want the best selection
201 * at the beginning so the less desireable selections know
202 * that they have to setrunqueue/go-to-another-cpu, even
203 * though it means switching back to the 'best' selection.
204 * This also avoids degenerate situations when many threads
205 * are runnable or waking up at the same time.
206 *
207 * If upri matches exactly place at end/round-robin.
208 */
d992c377 209 while (xtd &&
e3e6be1f 210 (xtd->td_pri >= td->td_pri ||
d992c377 211 (xtd->td_pri == td->td_pri &&
e3e6be1f 212 xtd->td_upri >= td->td_upri))) {
85946b6c 213 xtd = TAILQ_NEXT(xtd, td_threadq);
d992c377 214 }
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215 if (xtd)
216 TAILQ_INSERT_BEFORE(xtd, td, td_threadq);
217 else
218 TAILQ_INSERT_TAIL(&gd->gd_tdrunq, td, td_threadq);
f9235b6d 219 }
de4d4cb0 220 ++gd->gd_tdrunqcount;
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221
222 /*
85946b6c 223 * Request a LWKT reschedule if we are now at the head of the queue.
b12defdc 224 */
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225 if (TAILQ_FIRST(&gd->gd_tdrunq) == td)
226 need_lwkt_resched();
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227 }
228}
8ad65e08 229
e28c8ef4 230static boolean_t
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231_lwkt_thread_ctor(void *obj, void *privdata, int ocflags)
232{
233 struct thread *td = (struct thread *)obj;
234
235 td->td_kstack = NULL;
236 td->td_kstack_size = 0;
237 td->td_flags = TDF_ALLOCATED_THREAD;
4643740a 238 td->td_mpflags = 0;
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239 return (1);
240}
241
242static void
243_lwkt_thread_dtor(void *obj, void *privdata)
244{
245 struct thread *td = (struct thread *)obj;
246
247 KASSERT(td->td_flags & TDF_ALLOCATED_THREAD,
248 ("_lwkt_thread_dtor: not allocated from objcache"));
249 KASSERT((td->td_flags & TDF_ALLOCATED_STACK) && td->td_kstack &&
250 td->td_kstack_size > 0,
251 ("_lwkt_thread_dtor: corrupted stack"));
252 kmem_free(&kernel_map, (vm_offset_t)td->td_kstack, td->td_kstack_size);
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253 td->td_kstack = NULL;
254 td->td_flags = 0;
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255}
256
257/*
258 * Initialize the lwkt s/system.
765b1ae0 259 *
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260 * Nominally cache up to 32 thread + kstack structures. Cache more on
261 * systems with a lot of cpu cores.
40aaf5fc 262 */
ced589cb 263static void
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264lwkt_init(void)
265{
765b1ae0 266 TUNABLE_INT("lwkt.cache_threads", &lwkt_cache_threads);
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267 if (lwkt_cache_threads == 0) {
268 lwkt_cache_threads = ncpus * 4;
269 if (lwkt_cache_threads < 32)
270 lwkt_cache_threads = 32;
271 }
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272 thread_cache = objcache_create_mbacked(
273 M_THREAD, sizeof(struct thread),
2fce2579 274 0, lwkt_cache_threads,
765b1ae0 275 _lwkt_thread_ctor, _lwkt_thread_dtor, NULL);
40aaf5fc 276}
ced589cb 277SYSINIT(lwkt_init, SI_BOOT2_LWKT_INIT, SI_ORDER_FIRST, lwkt_init, NULL);
40aaf5fc 278
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279/*
280 * Schedule a thread to run. As the current thread we can always safely
281 * schedule ourselves, and a shortcut procedure is provided for that
282 * function.
283 *
284 * (non-blocking, self contained on a per cpu basis)
285 */
286void
287lwkt_schedule_self(thread_t td)
288{
cfaeae2a 289 KKASSERT((td->td_flags & TDF_MIGRATING) == 0);
37af14fe 290 crit_enter_quick(td);
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291 KASSERT(td != &td->td_gd->gd_idlethread,
292 ("lwkt_schedule_self(): scheduling gd_idlethread is illegal!"));
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293 KKASSERT(td->td_lwp == NULL ||
294 (td->td_lwp->lwp_mpflags & LWP_MP_ONRUNQ) == 0);
37af14fe 295 _lwkt_enqueue(td);
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MD
296 crit_exit_quick(td);
297}
298
299/*
300 * Deschedule a thread.
301 *
302 * (non-blocking, self contained on a per cpu basis)
303 */
304void
305lwkt_deschedule_self(thread_t td)
306{
307 crit_enter_quick(td);
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308 _lwkt_dequeue(td);
309 crit_exit_quick(td);
310}
311
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312/*
313 * LWKTs operate on a per-cpu basis
314 *
73e4f7b9 315 * WARNING! Called from early boot, 'mycpu' may not work yet.
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316 */
317void
318lwkt_gdinit(struct globaldata *gd)
319{
f9235b6d 320 TAILQ_INIT(&gd->gd_tdrunq);
73e4f7b9 321 TAILQ_INIT(&gd->gd_tdallq);
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322}
323
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324/*
325 * Create a new thread. The thread must be associated with a process context
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326 * or LWKT start address before it can be scheduled. If the target cpu is
327 * -1 the thread will be created on the current cpu.
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328 *
329 * If you intend to create a thread without a process context this function
330 * does everything except load the startup and switcher function.
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331 */
332thread_t
d3d32139 333lwkt_alloc_thread(struct thread *td, int stksize, int cpu, int flags)
7d0bac62 334{
d2d8515b 335 static int cpu_rotator;
c070746a 336 globaldata_t gd = mycpu;
99df837e 337 void *stack;
7d0bac62 338
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339 /*
340 * If static thread storage is not supplied allocate a thread. Reuse
341 * a cached free thread if possible. gd_freetd is used to keep an exiting
342 * thread intact through the exit.
343 */
ef0fdad1 344 if (td == NULL) {
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MD
345 crit_enter_gd(gd);
346 if ((td = gd->gd_freetd) != NULL) {
347 KKASSERT((td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK|
348 TDF_RUNQ)) == 0);
c070746a 349 gd->gd_freetd = NULL;
cf709dd2 350 } else {
c070746a 351 td = objcache_get(thread_cache, M_WAITOK);
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MD
352 KKASSERT((td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK|
353 TDF_RUNQ)) == 0);
354 }
355 crit_exit_gd(gd);
40aaf5fc 356 KASSERT((td->td_flags &
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MD
357 (TDF_ALLOCATED_THREAD|TDF_RUNNING|TDF_PREEMPT_LOCK)) ==
358 TDF_ALLOCATED_THREAD,
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359 ("lwkt_alloc_thread: corrupted td flags 0x%X", td->td_flags));
360 flags |= td->td_flags & (TDF_ALLOCATED_THREAD|TDF_ALLOCATED_STACK);
ef0fdad1 361 }
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362
363 /*
364 * Try to reuse cached stack.
365 */
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MD
366 if ((stack = td->td_kstack) != NULL && td->td_kstack_size != stksize) {
367 if (flags & TDF_ALLOCATED_STACK) {
e4846942 368 kmem_free(&kernel_map, (vm_offset_t)stack, td->td_kstack_size);
f470d0c8
MD
369 stack = NULL;
370 }
371 }
372 if (stack == NULL) {
e40cfbd7 373 stack = (void *)kmem_alloc_stack(&kernel_map, stksize);
ef0fdad1 374 flags |= TDF_ALLOCATED_STACK;
99df837e 375 }
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MD
376 if (cpu < 0) {
377 cpu = ++cpu_rotator;
378 cpu_ccfence();
379 cpu %= ncpus;
380 }
381 lwkt_init_thread(td, stack, stksize, flags, globaldata_find(cpu));
99df837e 382 return(td);
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MD
383}
384
385/*
386 * Initialize a preexisting thread structure. This function is used by
387 * lwkt_alloc_thread() and also used to initialize the per-cpu idlethread.
388 *
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389 * All threads start out in a critical section at a priority of
390 * TDPRI_KERN_DAEMON. Higher level code will modify the priority as
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391 * appropriate. This function may send an IPI message when the
392 * requested cpu is not the current cpu and consequently gd_tdallq may
393 * not be initialized synchronously from the point of view of the originating
394 * cpu.
395 *
396 * NOTE! we have to be careful in regards to creating threads for other cpus
397 * if SMP has not yet been activated.
7d0bac62 398 */
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399static void
400lwkt_init_thread_remote(void *arg)
401{
402 thread_t td = arg;
403
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404 /*
405 * Protected by critical section held by IPI dispatch
406 */
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407 TAILQ_INSERT_TAIL(&td->td_gd->gd_tdallq, td, td_allq);
408}
409
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410/*
411 * lwkt core thread structural initialization.
412 *
413 * NOTE: All threads are initialized as mpsafe threads.
414 */
7d0bac62 415void
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416lwkt_init_thread(thread_t td, void *stack, int stksize, int flags,
417 struct globaldata *gd)
7d0bac62 418{
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419 globaldata_t mygd = mycpu;
420
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421 bzero(td, sizeof(struct thread));
422 td->td_kstack = stack;
f470d0c8 423 td->td_kstack_size = stksize;
d3d32139 424 td->td_flags = flags;
4643740a 425 td->td_mpflags = 0;
f256b6c0 426 td->td_type = TD_TYPE_GENERIC;
26a0694b 427 td->td_gd = gd;
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428 td->td_pri = TDPRI_KERN_DAEMON;
429 td->td_critcount = 1;
54341a3b 430 td->td_toks_have = NULL;
3b998fa9 431 td->td_toks_stop = &td->td_toks_base;
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432 if (lwkt_use_spin_port || (flags & TDF_FORCE_SPINPORT)) {
433 lwkt_initport_spin(&td->td_msgport, td,
434 (flags & TDF_FIXEDCPU) ? TRUE : FALSE);
435 } else {
fb0f29c4 436 lwkt_initport_thread(&td->td_msgport, td);
c068fb59 437 }
99df837e 438 pmap_init_thread(td);
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439 /*
440 * Normally initializing a thread for a remote cpu requires sending an
441 * IPI. However, the idlethread is setup before the other cpus are
442 * activated so we have to treat it as a special case. XXX manipulation
443 * of gd_tdallq requires the BGL.
444 */
445 if (gd == mygd || td == &gd->gd_idlethread) {
37af14fe 446 crit_enter_gd(mygd);
75cdbe6c 447 TAILQ_INSERT_TAIL(&gd->gd_tdallq, td, td_allq);
37af14fe 448 crit_exit_gd(mygd);
75cdbe6c 449 } else {
2db3b277 450 lwkt_send_ipiq(gd, lwkt_init_thread_remote, td);
75cdbe6c 451 }
3573cf7b 452 dsched_enter_thread(td);
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453}
454
455void
456lwkt_set_comm(thread_t td, const char *ctl, ...)
457{
e2565a42 458 __va_list va;
73e4f7b9 459
e2565a42 460 __va_start(va, ctl);
379210cb 461 kvsnprintf(td->td_comm, sizeof(td->td_comm), ctl, va);
e2565a42 462 __va_end(va);
5bf48697 463 KTR_LOG(ctxsw_newtd, td, td->td_comm);
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464}
465
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466/*
467 * Prevent the thread from getting destroyed. Note that unlike PHOLD/PRELE
468 * this does not prevent the thread from migrating to another cpu so the
469 * gd_tdallq state is not protected by this.
470 */
99df837e 471void
73e4f7b9 472lwkt_hold(thread_t td)
99df837e 473{
74c9628e 474 atomic_add_int(&td->td_refs, 1);
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475}
476
477void
478lwkt_rele(thread_t td)
479{
480 KKASSERT(td->td_refs > 0);
74c9628e 481 atomic_add_int(&td->td_refs, -1);
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482}
483
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484void
485lwkt_free_thread(thread_t td)
486{
74c9628e 487 KKASSERT(td->td_refs == 0);
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488 KKASSERT((td->td_flags & (TDF_RUNNING | TDF_PREEMPT_LOCK |
489 TDF_RUNQ | TDF_TSLEEPQ)) == 0);
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490 if (td->td_flags & TDF_ALLOCATED_THREAD) {
491 objcache_put(thread_cache, td);
492 } else if (td->td_flags & TDF_ALLOCATED_STACK) {
493 /* client-allocated struct with internally allocated stack */
494 KASSERT(td->td_kstack && td->td_kstack_size > 0,
495 ("lwkt_free_thread: corrupted stack"));
496 kmem_free(&kernel_map, (vm_offset_t)td->td_kstack, td->td_kstack_size);
497 td->td_kstack = NULL;
498 td->td_kstack_size = 0;
99df837e 499 }
a86ce0cd 500
e7c0dbba 501 KTR_LOG(ctxsw_deadtd, td);
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502}
503
504
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505/*
506 * Switch to the next runnable lwkt. If no LWKTs are runnable then
f1d1c3fa
MD
507 * switch to the idlethread. Switching must occur within a critical
508 * section to avoid races with the scheduling queue.
509 *
510 * We always have full control over our cpu's run queue. Other cpus
511 * that wish to manipulate our queue must use the cpu_*msg() calls to
512 * talk to our cpu, so a critical section is all that is needed and
513 * the result is very, very fast thread switching.
514 *
96728c05
MD
515 * The LWKT scheduler uses a fixed priority model and round-robins at
516 * each priority level. User process scheduling is a totally
517 * different beast and LWKT priorities should not be confused with
518 * user process priorities.
f1d1c3fa 519 *
69d78e99
MD
520 * PREEMPTION NOTE: Preemption occurs via lwkt_preempt(). lwkt_switch()
521 * is not called by the current thread in the preemption case, only when
522 * the preempting thread blocks (in order to return to the original thread).
cfaeae2a
MD
523 *
524 * SPECIAL NOTE ON SWITCH ATOMICY: Certain operations such as thread
525 * migration and tsleep deschedule the current lwkt thread and call
526 * lwkt_switch(). In particular, the target cpu of the migration fully
527 * expects the thread to become non-runnable and can deadlock against
528 * cpusync operations if we run any IPIs prior to switching the thread out.
529 *
530 * WE MUST BE VERY CAREFUL NOT TO RUN SPLZ DIRECTLY OR INDIRECTLY IF
95858b91 531 * THE CURRENT THREAD HAS BEEN DESCHEDULED!
8ad65e08
MD
532 */
533void
534lwkt_switch(void)
535{
37af14fe
MD
536 globaldata_t gd = mycpu;
537 thread_t td = gd->gd_curthread;
8ad65e08 538 thread_t ntd;
5411d8f1 539 int upri;
3a06728e
MD
540#ifdef LOOPMASK
541 uint64_t tsc_base = rdtsc();
542#endif
8ad65e08 543
da0b0e8b 544 KKASSERT(gd->gd_processing_ipiq == 0);
121f93bc 545 KKASSERT(td->td_flags & TDF_RUNNING);
da0b0e8b 546
46a3f46d 547 /*
27e88a6e
MD
548 * Switching from within a 'fast' (non thread switched) interrupt or IPI
549 * is illegal. However, we may have to do it anyway if we hit a fatal
550 * kernel trap or we have paniced.
551 *
552 * If this case occurs save and restore the interrupt nesting level.
46a3f46d 553 */
27e88a6e
MD
554 if (gd->gd_intr_nesting_level) {
555 int savegdnest;
556 int savegdtrap;
557
5fddbda2 558 if (gd->gd_trap_nesting_level == 0 && panic_cpu_gd != mycpu) {
4a28fe22 559 panic("lwkt_switch: Attempt to switch from a "
5a8df152 560 "fast interrupt, ipi, or hard code section, "
4a28fe22
MD
561 "td %p\n",
562 td);
27e88a6e
MD
563 } else {
564 savegdnest = gd->gd_intr_nesting_level;
565 savegdtrap = gd->gd_trap_nesting_level;
566 gd->gd_intr_nesting_level = 0;
567 gd->gd_trap_nesting_level = 0;
a7422615
MD
568 if ((td->td_flags & TDF_PANICWARN) == 0) {
569 td->td_flags |= TDF_PANICWARN;
4a28fe22
MD
570 kprintf("Warning: thread switch from interrupt, IPI, "
571 "or hard code section.\n"
a7422615 572 "thread %p (%s)\n", td, td->td_comm);
7ce2998e 573 print_backtrace(-1);
a7422615 574 }
27e88a6e
MD
575 lwkt_switch();
576 gd->gd_intr_nesting_level = savegdnest;
577 gd->gd_trap_nesting_level = savegdtrap;
578 return;
579 }
96728c05 580 }
ef0fdad1 581
cb973d15 582 /*
85946b6c
MD
583 * Release our current user process designation if we are blocking
584 * or if a user reschedule was requested.
585 *
586 * NOTE: This function is NOT called if we are switching into or
587 * returning from a preemption.
588 *
589 * NOTE: Releasing our current user process designation may cause
590 * it to be assigned to another thread, which in turn will
591 * cause us to block in the usched acquire code when we attempt
592 * to return to userland.
593 *
594 * NOTE: On SMP systems this can be very nasty when heavy token
595 * contention is present so we want to be careful not to
596 * release the designation gratuitously.
cb973d15 597 */
85946b6c
MD
598 if (td->td_release &&
599 (user_resched_wanted() || (td->td_flags & TDF_RUNQ) == 0)) {
cb973d15 600 td->td_release(td);
85946b6c 601 }
cb973d15 602
85946b6c 603 /*
5411d8f1
MD
604 * Release all tokens. Once we do this we must remain in the critical
605 * section and cannot run IPIs or other interrupts until we switch away
606 * because they may implode if they try to get a token using our thread
607 * context.
85946b6c 608 */
37af14fe 609 crit_enter_gd(gd);
3b998fa9 610 if (TD_TOKS_HELD(td))
9d265729
MD
611 lwkt_relalltokens(td);
612
613 /*
b02926de
MD
614 * We had better not be holding any spin locks, but don't get into an
615 * endless panic loop.
9d265729 616 */
0846e4ce 617 KASSERT(gd->gd_spinlocks == 0 || panicstr != NULL,
d666840a 618 ("lwkt_switch: still holding %d exclusive spinlocks!",
0846e4ce 619 gd->gd_spinlocks));
9d265729 620
0f7a3396
MD
621#ifdef INVARIANTS
622 if (td->td_cscount) {
6ea70f76 623 kprintf("Diagnostic: attempt to switch while mastering cpusync: %p\n",
0f7a3396
MD
624 td);
625 if (panic_on_cscount)
626 panic("switching while mastering cpusync");
627 }
8a8d5d85 628#endif
f9235b6d
MD
629
630 /*
631 * If we had preempted another thread on this cpu, resume the preempted
632 * thread. This occurs transparently, whether the preempted thread
633 * was scheduled or not (it may have been preempted after descheduling
634 * itself).
635 *
636 * We have to setup the MP lock for the original thread after backing
637 * out the adjustment that was made to curthread when the original
638 * was preempted.
639 */
99df837e 640 if ((ntd = td->td_preempted) != NULL) {
26a0694b
MD
641 KKASSERT(ntd->td_flags & TDF_PREEMPT_LOCK);
642 ntd->td_flags |= TDF_PREEMPT_DONE;
7fb451cb 643 ntd->td_contended = 0; /* reset contended */
8ec60c3f
MD
644
645 /*
b9eb1c19
MD
646 * The interrupt may have woken a thread up, we need to properly
647 * set the reschedule flag if the originally interrupted thread is
648 * at a lower priority.
85946b6c
MD
649 *
650 * The interrupt may not have descheduled.
8ec60c3f 651 */
85946b6c 652 if (TAILQ_FIRST(&gd->gd_tdrunq) != ntd)
8ec60c3f 653 need_lwkt_resched();
f9235b6d
MD
654 goto havethread_preempted;
655 }
656
b12defdc 657 /*
5411d8f1
MD
658 * Figure out switch target. If we cannot switch to our desired target
659 * look for a thread that we can switch to.
cfaeae2a 660 *
5411d8f1
MD
661 * NOTE! The limited spin loop and related parameters are extremely
662 * important for system performance, particularly for pipes and
663 * concurrent conflicting VM faults.
f9235b6d 664 */
5411d8f1
MD
665 clear_lwkt_resched();
666 ntd = TAILQ_FIRST(&gd->gd_tdrunq);
667
668 if (ntd) {
669 do {
670 if (TD_TOKS_NOT_HELD(ntd) ||
671 lwkt_getalltokens(ntd, (ntd->td_contended > lwkt_spin_loops)))
672 {
673 goto havethread;
674 }
675 ++gd->gd_cnt.v_lock_colls;
7fb451cb 676 ++ntd->td_contended; /* overflow ok */
3a06728e
MD
677#ifdef LOOPMASK
678 if (tsc_frequency && rdtsc() - tsc_base > tsc_frequency) {
679 kprintf("lwkt_switch: excessive contended %d "
680 "thread %p\n", ntd->td_contended, ntd);
681 tsc_base = rdtsc();
682 }
683#endif
5411d8f1
MD
684 } while (ntd->td_contended < (lwkt_spin_loops >> 1));
685 upri = ntd->td_upri;
f9235b6d 686
f9235b6d 687 /*
5411d8f1
MD
688 * Bleh, the thread we wanted to switch to has a contended token.
689 * See if we can switch to another thread.
2a418930 690 *
5411d8f1
MD
691 * We generally don't want to do this because it represents a
692 * priority inversion. Do not allow the case if the thread
693 * is returning to userland (not a kernel thread) AND the thread
694 * has a lower upri.
f9235b6d 695 */
b12defdc 696 while ((ntd = TAILQ_NEXT(ntd, td_threadq)) != NULL) {
5411d8f1
MD
697 if (ntd->td_pri < TDPRI_KERN_LPSCHED && upri > ntd->td_upri)
698 break;
699 upri = ntd->td_upri;
b12defdc 700
5411d8f1
MD
701 /*
702 * Try this one.
703 */
704 if (TD_TOKS_NOT_HELD(ntd) ||
705 lwkt_getalltokens(ntd, (ntd->td_contended > lwkt_spin_loops))) {
706 goto havethread;
707 }
7fb451cb 708 ++ntd->td_contended; /* overflow ok */
5411d8f1 709 ++gd->gd_cnt.v_lock_colls;
b12defdc 710 }
b12defdc
MD
711
712 /*
5411d8f1
MD
713 * Fall through, switch to idle thread to get us out of the current
714 * context. Since we were contended, prevent HLT by flagging a
715 * LWKT reschedule.
b12defdc 716 */
5411d8f1 717 need_lwkt_resched();
f1d1c3fa 718 }
8a8d5d85 719
5411d8f1
MD
720 /*
721 * We either contended on ntd or the runq is empty. We must switch
722 * through the idle thread to get out of the current context.
723 */
724 ntd = &gd->gd_idlethread;
725 if (gd->gd_trap_nesting_level == 0 && panicstr == NULL)
726 ASSERT_NO_TOKENS_HELD(ntd);
727 cpu_time.cp_msg[0] = 0;
5411d8f1
MD
728 goto haveidle;
729
2a418930 730havethread:
b12defdc 731 /*
be71787b
MD
732 * Clear gd_idle_repeat when doing a normal switch to a non-idle
733 * thread.
f9235b6d 734 */
9ac1ee6e 735 ntd->td_wmesg = NULL;
7fb451cb 736 ntd->td_contended = 0; /* reset once scheduled */
b12defdc 737 ++gd->gd_cnt.v_swtch;
be71787b 738 gd->gd_idle_repeat = 0;
2a418930 739
f9235b6d 740havethread_preempted:
f9235b6d
MD
741 /*
742 * If the new target does not need the MP lock and we are holding it,
743 * release the MP lock. If the new target requires the MP lock we have
744 * already acquired it for the target.
8a8d5d85 745 */
2a418930 746 ;
f9235b6d
MD
747haveidle:
748 KASSERT(ntd->td_critcount,
b5d16701
MD
749 ("priority problem in lwkt_switch %d %d",
750 td->td_critcount, ntd->td_critcount));
751
94f6d86e 752 if (td != ntd) {
cc9b6223
MD
753 /*
754 * Execute the actual thread switch operation. This function
755 * returns to the current thread and returns the previous thread
756 * (which may be different from the thread we switched to).
757 *
758 * We are responsible for marking ntd as TDF_RUNNING.
759 */
121f93bc 760 KKASSERT((ntd->td_flags & TDF_RUNNING) == 0);
94f6d86e 761 ++switch_count;
a1f0fb66 762 KTR_LOG(ctxsw_sw, gd->gd_cpuid, ntd);
cc9b6223
MD
763 ntd->td_flags |= TDF_RUNNING;
764 lwkt_switch_return(td->td_switch(ntd));
765 /* ntd invalid, td_switch() can return a different thread_t */
94f6d86e 766 }
b12defdc 767
b12defdc 768 /*
54341a3b 769 * catch-all. XXX is this strictly needed?
b12defdc
MD
770 */
771 splz_check();
54341a3b 772
37af14fe
MD
773 /* NOTE: current cpu may have changed after switch */
774 crit_exit_quick(td);
8ad65e08
MD
775}
776
cc9b6223
MD
777/*
778 * Called by assembly in the td_switch (thread restore path) for thread
779 * bootstrap cases which do not 'return' to lwkt_switch().
780 */
781void
782lwkt_switch_return(thread_t otd)
783{
cc9b6223 784 globaldata_t rgd;
3a06728e
MD
785#ifdef LOOPMASK
786 uint64_t tsc_base = rdtsc();
787#endif
788 int exiting;
789
790 exiting = otd->td_flags & TDF_EXITING;
791 cpu_ccfence();
cc9b6223
MD
792
793 /*
794 * Check if otd was migrating. Now that we are on ntd we can finish
795 * up the migration. This is a bit messy but it is the only place
796 * where td is known to be fully descheduled.
797 *
798 * We can only activate the migration if otd was migrating but not
799 * held on the cpu due to a preemption chain. We still have to
800 * clear TDF_RUNNING on the old thread either way.
801 *
802 * We are responsible for clearing the previously running thread's
803 * TDF_RUNNING.
804 */
805 if ((rgd = otd->td_migrate_gd) != NULL &&
806 (otd->td_flags & TDF_PREEMPT_LOCK) == 0) {
807 KKASSERT((otd->td_flags & (TDF_MIGRATING | TDF_RUNNING)) ==
808 (TDF_MIGRATING | TDF_RUNNING));
809 otd->td_migrate_gd = NULL;
810 otd->td_flags &= ~TDF_RUNNING;
811 lwkt_send_ipiq(rgd, lwkt_setcpu_remote, otd);
812 } else {
813 otd->td_flags &= ~TDF_RUNNING;
814 }
2b07d9aa
MD
815
816 /*
817 * Final exit validations (see lwp_wait()). Note that otd becomes
818 * invalid the *instant* we set TDF_MP_EXITSIG.
3a06728e
MD
819 *
820 * Use the EXITING status loaded from before we clear TDF_RUNNING,
821 * because if it is not set otd becomes invalid the instant we clear
822 * TDF_RUNNING on it (otherwise, if the system is fast enough, we
823 * might 'steal' TDF_EXITING from another switch-return!).
2b07d9aa 824 */
3a06728e 825 while (exiting) {
2b07d9aa
MD
826 u_int mpflags;
827
828 mpflags = otd->td_mpflags;
829 cpu_ccfence();
830
831 if (mpflags & TDF_MP_EXITWAIT) {
832 if (atomic_cmpset_int(&otd->td_mpflags, mpflags,
833 mpflags | TDF_MP_EXITSIG)) {
834 wakeup(otd);
835 break;
836 }
837 } else {
838 if (atomic_cmpset_int(&otd->td_mpflags, mpflags,
839 mpflags | TDF_MP_EXITSIG)) {
840 wakeup(otd);
841 break;
842 }
843 }
3a06728e
MD
844
845#ifdef LOOPMASK
846 if (tsc_frequency && rdtsc() - tsc_base > tsc_frequency) {
847 kprintf("lwkt_switch_return: excessive TDF_EXITING "
848 "thread %p\n", otd);
849 tsc_base = rdtsc();
850 }
851#endif
2b07d9aa 852 }
cc9b6223
MD
853}
854
b68b7282 855/*
96728c05 856 * Request that the target thread preempt the current thread. Preemption
54341a3b
MD
857 * can only occur if our only critical section is the one that we were called
858 * with, the relative priority of the target thread is higher, and the target
859 * thread holds no tokens. This also only works if we are not holding any
860 * spinlocks (obviously).
96728c05
MD
861 *
862 * THE CALLER OF LWKT_PREEMPT() MUST BE IN A CRITICAL SECTION. Typically
863 * this is called via lwkt_schedule() through the td_preemptable callback.
f9235b6d 864 * critcount is the managed critical priority that we should ignore in order
96728c05
MD
865 * to determine whether preemption is possible (aka usually just the crit
866 * priority of lwkt_schedule() itself).
b68b7282 867 *
54341a3b
MD
868 * Preemption is typically limited to interrupt threads.
869 *
870 * Operation works in a fairly straight-forward manner. The normal
871 * scheduling code is bypassed and we switch directly to the target
872 * thread. When the target thread attempts to block or switch away
873 * code at the base of lwkt_switch() will switch directly back to our
874 * thread. Our thread is able to retain whatever tokens it holds and
875 * if the target needs one of them the target will switch back to us
876 * and reschedule itself normally.
b68b7282
MD
877 */
878void
f9235b6d 879lwkt_preempt(thread_t ntd, int critcount)
b68b7282 880{
46a3f46d 881 struct globaldata *gd = mycpu;
cc9b6223 882 thread_t xtd;
0a3f9b47 883 thread_t td;
2d910aaf 884 int save_gd_intr_nesting_level;
b68b7282 885
26a0694b 886 /*
96728c05
MD
887 * The caller has put us in a critical section. We can only preempt
888 * if the caller of the caller was not in a critical section (basically
f9235b6d 889 * a local interrupt), as determined by the 'critcount' parameter. We
47737962 890 * also can't preempt if the caller is holding any spinlocks (even if
d666840a 891 * he isn't in a critical section). This also handles the tokens test.
96728c05
MD
892 *
893 * YYY The target thread must be in a critical section (else it must
894 * inherit our critical section? I dunno yet).
26a0694b 895 */
f9235b6d 896 KASSERT(ntd->td_critcount, ("BADCRIT0 %d", ntd->td_pri));
26a0694b 897
b12defdc 898 td = gd->gd_curthread;
fbc024e4
MD
899 if (preempt_enable == 0) {
900 ++preempt_miss;
901 return;
902 }
f9235b6d 903 if (ntd->td_pri <= td->td_pri) {
57c254db
MD
904 ++preempt_miss;
905 return;
906 }
f9235b6d 907 if (td->td_critcount > critcount) {
96728c05
MD
908 ++preempt_miss;
909 return;
910 }
121f93bc
MD
911 if (td->td_cscount) {
912 ++preempt_miss;
913 return;
914 }
46a3f46d 915 if (ntd->td_gd != gd) {
96728c05
MD
916 ++preempt_miss;
917 return;
918 }
41a01a4d 919 /*
77912481
MD
920 * We don't have to check spinlocks here as they will also bump
921 * td_critcount.
d3d1cbc8
MD
922 *
923 * Do not try to preempt if the target thread is holding any tokens.
924 * We could try to acquire the tokens but this case is so rare there
925 * is no need to support it.
41a01a4d 926 */
0846e4ce 927 KKASSERT(gd->gd_spinlocks == 0);
77912481 928
3b998fa9 929 if (TD_TOKS_HELD(ntd)) {
d3d1cbc8 930 ++preempt_miss;
d3d1cbc8
MD
931 return;
932 }
26a0694b
MD
933 if (td == ntd || ((td->td_flags | ntd->td_flags) & TDF_PREEMPT_LOCK)) {
934 ++preempt_weird;
935 return;
936 }
937 if (ntd->td_preempted) {
4b5f931b 938 ++preempt_hit;
26a0694b 939 return;
b68b7282 940 }
da0b0e8b 941 KKASSERT(gd->gd_processing_ipiq == 0);
26a0694b 942
8ec60c3f
MD
943 /*
944 * Since we are able to preempt the current thread, there is no need to
945 * call need_lwkt_resched().
2d910aaf
MD
946 *
947 * We must temporarily clear gd_intr_nesting_level around the switch
948 * since switchouts from the target thread are allowed (they will just
949 * return to our thread), and since the target thread has its own stack.
cc9b6223
MD
950 *
951 * A preemption must switch back to the original thread, assert the
952 * case.
8ec60c3f 953 */
26a0694b
MD
954 ++preempt_hit;
955 ntd->td_preempted = td;
956 td->td_flags |= TDF_PREEMPT_LOCK;
a1f0fb66 957 KTR_LOG(ctxsw_pre, gd->gd_cpuid, ntd);
2d910aaf
MD
958 save_gd_intr_nesting_level = gd->gd_intr_nesting_level;
959 gd->gd_intr_nesting_level = 0;
121f93bc
MD
960
961 KKASSERT((ntd->td_flags & TDF_RUNNING) == 0);
cc9b6223
MD
962 ntd->td_flags |= TDF_RUNNING;
963 xtd = td->td_switch(ntd);
964 KKASSERT(xtd == ntd);
965 lwkt_switch_return(xtd);
2d910aaf 966 gd->gd_intr_nesting_level = save_gd_intr_nesting_level;
b9eb1c19 967
26a0694b
MD
968 KKASSERT(ntd->td_preempted && (td->td_flags & TDF_PREEMPT_DONE));
969 ntd->td_preempted = NULL;
970 td->td_flags &= ~(TDF_PREEMPT_LOCK|TDF_PREEMPT_DONE);
b68b7282
MD
971}
972
f1d1c3fa 973/*
faaeffac 974 * Conditionally call splz() if gd_reqflags indicates work is pending.
4a28fe22
MD
975 * This will work inside a critical section but not inside a hard code
976 * section.
ef0fdad1 977 *
f1d1c3fa
MD
978 * (self contained on a per cpu basis)
979 */
980void
faaeffac 981splz_check(void)
f1d1c3fa 982{
7966cb69
MD
983 globaldata_t gd = mycpu;
984 thread_t td = gd->gd_curthread;
ef0fdad1 985
4a28fe22
MD
986 if ((gd->gd_reqflags & RQF_IDLECHECK_MASK) &&
987 gd->gd_intr_nesting_level == 0 &&
988 td->td_nest_count < 2)
989 {
f1d1c3fa 990 splz();
4a28fe22
MD
991 }
992}
993
994/*
995 * This version is integrated into crit_exit, reqflags has already
996 * been tested but td_critcount has not.
997 *
998 * We only want to execute the splz() on the 1->0 transition of
999 * critcount and not in a hard code section or if too deeply nested.
925040f2 1000 *
0846e4ce 1001 * NOTE: gd->gd_spinlocks is implied to be 0 when td_critcount is 0.
4a28fe22
MD
1002 */
1003void
1004lwkt_maybe_splz(thread_t td)
1005{
1006 globaldata_t gd = td->td_gd;
1007
1008 if (td->td_critcount == 0 &&
1009 gd->gd_intr_nesting_level == 0 &&
1010 td->td_nest_count < 2)
1011 {
1012 splz();
1013 }
f1d1c3fa
MD
1014}
1015
e6546af9
MD
1016/*
1017 * Drivers which set up processing co-threads can call this function to
1018 * run the co-thread at a higher priority and to allow it to preempt
1019 * normal threads.
1020 */
1021void
1022lwkt_set_interrupt_support_thread(void)
1023{
1024 thread_t td = curthread;
1025
1026 lwkt_setpri_self(TDPRI_INT_SUPPORT);
1027 td->td_flags |= TDF_INTTHREAD;
1028 td->td_preemptable = lwkt_preempt;
1029}
1030
1031
8ad65e08 1032/*
f9235b6d
MD
1033 * This function is used to negotiate a passive release of the current
1034 * process/lwp designation with the user scheduler, allowing the user
1035 * scheduler to schedule another user thread. The related kernel thread
1036 * (curthread) continues running in the released state.
8ad65e08
MD
1037 */
1038void
f9235b6d 1039lwkt_passive_release(struct thread *td)
8ad65e08 1040{
f9235b6d
MD
1041 struct lwp *lp = td->td_lwp;
1042
1043 td->td_release = NULL;
1044 lwkt_setpri_self(TDPRI_KERN_USER);
d992c377 1045
f9235b6d 1046 lp->lwp_proc->p_usched->release_curproc(lp);
f1d1c3fa
MD
1047}
1048
f9235b6d 1049
3824f392 1050/*
d2d8515b
MD
1051 * This implements a LWKT yield, allowing a kernel thread to yield to other
1052 * kernel threads at the same or higher priority. This function can be
1053 * called in a tight loop and will typically only yield once per tick.
f9235b6d 1054 *
d2d8515b
MD
1055 * Most kernel threads run at the same priority in order to allow equal
1056 * sharing.
f9235b6d
MD
1057 *
1058 * (self contained on a per cpu basis)
3824f392
MD
1059 */
1060void
f9235b6d 1061lwkt_yield(void)
3824f392 1062{
f9235b6d
MD
1063 globaldata_t gd = mycpu;
1064 thread_t td = gd->gd_curthread;
3824f392 1065
f9235b6d
MD
1066 if ((gd->gd_reqflags & RQF_IDLECHECK_MASK) && td->td_nest_count < 2)
1067 splz();
85946b6c 1068 if (lwkt_resched_wanted()) {
f9235b6d
MD
1069 lwkt_schedule_self(curthread);
1070 lwkt_switch();
f9235b6d 1071 }
3824f392
MD
1072}
1073
40504122
MD
1074/*
1075 * The quick version processes pending interrupts and higher-priority
1076 * LWKT threads but will not round-robin same-priority LWKT threads.
de4d4cb0
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1077 *
1078 * When called while attempting to return to userland the only same-pri
1079 * threads are the ones which have already tried to become the current
1080 * user process.
40504122
MD
1081 */
1082void
1083lwkt_yield_quick(void)
1084{
1085 globaldata_t gd = mycpu;
1086 thread_t td = gd->gd_curthread;
1087
1088 if ((gd->gd_reqflags & RQF_IDLECHECK_MASK) && td->td_nest_count < 2)
1089 splz();
1090 if (lwkt_resched_wanted()) {
9c99cb33 1091 crit_enter();
40504122
MD
1092 if (TAILQ_FIRST(&gd->gd_tdrunq) == td) {
1093 clear_lwkt_resched();
1094 } else {
1095 lwkt_schedule_self(curthread);
1096 lwkt_switch();
1097 }
9c99cb33 1098 crit_exit();
40504122
MD
1099 }
1100}
1101
3824f392 1102/*
f9235b6d
MD
1103 * This yield is designed for kernel threads with a user context.
1104 *
1105 * The kernel acting on behalf of the user is potentially cpu-bound,
1106 * this function will efficiently allow other threads to run and also
1107 * switch to other processes by releasing.
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1108 *
1109 * The lwkt_user_yield() function is designed to have very low overhead
1110 * if no yield is determined to be needed.
1111 */
1112void
1113lwkt_user_yield(void)
1114{
f9235b6d
MD
1115 globaldata_t gd = mycpu;
1116 thread_t td = gd->gd_curthread;
1117
1118 /*
1119 * Always run any pending interrupts in case we are in a critical
1120 * section.
1121 */
1122 if ((gd->gd_reqflags & RQF_IDLECHECK_MASK) && td->td_nest_count < 2)
1123 splz();
3824f392 1124
3824f392 1125 /*
f9235b6d
MD
1126 * Switch (which forces a release) if another kernel thread needs
1127 * the cpu, if userland wants us to resched, or if our kernel
1128 * quantum has run out.
3824f392 1129 */
f9235b6d 1130 if (lwkt_resched_wanted() ||
85946b6c 1131 user_resched_wanted())
f9235b6d 1132 {
3824f392 1133 lwkt_switch();
3824f392
MD
1134 }
1135
f9235b6d 1136#if 0
3824f392 1137 /*
f9235b6d
MD
1138 * Reacquire the current process if we are released.
1139 *
1140 * XXX not implemented atm. The kernel may be holding locks and such,
1141 * so we want the thread to continue to receive cpu.
3824f392 1142 */
f9235b6d
MD
1143 if (td->td_release == NULL && lp) {
1144 lp->lwp_proc->p_usched->acquire_curproc(lp);
1145 td->td_release = lwkt_passive_release;
1146 lwkt_setpri_self(TDPRI_USER_NORM);
3824f392 1147 }
f9235b6d 1148#endif
b9eb1c19
MD
1149}
1150
8ad65e08 1151/*
f1d1c3fa
MD
1152 * Generic schedule. Possibly schedule threads belonging to other cpus and
1153 * deal with threads that might be blocked on a wait queue.
1154 *
0a3f9b47
MD
1155 * We have a little helper inline function which does additional work after
1156 * the thread has been enqueued, including dealing with preemption and
1157 * setting need_lwkt_resched() (which prevents the kernel from returning
1158 * to userland until it has processed higher priority threads).
6330a558
MD
1159 *
1160 * It is possible for this routine to be called after a failed _enqueue
1161 * (due to the target thread migrating, sleeping, or otherwise blocked).
1162 * We have to check that the thread is actually on the run queue!
8ad65e08 1163 */
0a3f9b47
MD
1164static __inline
1165void
85946b6c 1166_lwkt_schedule_post(globaldata_t gd, thread_t ntd, int ccount)
0a3f9b47 1167{
6330a558 1168 if (ntd->td_flags & TDF_RUNQ) {
85946b6c 1169 if (ntd->td_preemptable) {
f9235b6d 1170 ntd->td_preemptable(ntd, ccount); /* YYY +token */
6330a558 1171 }
0a3f9b47
MD
1172 }
1173}
1174
361d01dd 1175static __inline
8ad65e08 1176void
85946b6c 1177_lwkt_schedule(thread_t td)
8ad65e08 1178{
37af14fe
MD
1179 globaldata_t mygd = mycpu;
1180
cf709dd2
MD
1181 KASSERT(td != &td->td_gd->gd_idlethread,
1182 ("lwkt_schedule(): scheduling gd_idlethread is illegal!"));
cfaeae2a 1183 KKASSERT((td->td_flags & TDF_MIGRATING) == 0);
37af14fe 1184 crit_enter_gd(mygd);
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MD
1185 KKASSERT(td->td_lwp == NULL ||
1186 (td->td_lwp->lwp_mpflags & LWP_MP_ONRUNQ) == 0);
1187
37af14fe 1188 if (td == mygd->gd_curthread) {
f1d1c3fa
MD
1189 _lwkt_enqueue(td);
1190 } else {
f1d1c3fa 1191 /*
7cd8d145
MD
1192 * If we own the thread, there is no race (since we are in a
1193 * critical section). If we do not own the thread there might
1194 * be a race but the target cpu will deal with it.
f1d1c3fa 1195 */
7cd8d145 1196 if (td->td_gd == mygd) {
9d265729 1197 _lwkt_enqueue(td);
85946b6c 1198 _lwkt_schedule_post(mygd, td, 1);
f1d1c3fa 1199 } else {
e381e77c 1200 lwkt_send_ipiq3(td->td_gd, lwkt_schedule_remote, td, 0);
7cd8d145 1201 }
8ad65e08 1202 }
37af14fe 1203 crit_exit_gd(mygd);
8ad65e08
MD
1204}
1205
361d01dd
MD
1206void
1207lwkt_schedule(thread_t td)
1208{
85946b6c 1209 _lwkt_schedule(td);
361d01dd
MD
1210}
1211
1212void
85946b6c 1213lwkt_schedule_noresched(thread_t td) /* XXX not impl */
361d01dd 1214{
85946b6c 1215 _lwkt_schedule(td);
361d01dd
MD
1216}
1217
e381e77c
MD
1218/*
1219 * When scheduled remotely if frame != NULL the IPIQ is being
1220 * run via doreti or an interrupt then preemption can be allowed.
1221 *
1222 * To allow preemption we have to drop the critical section so only
1223 * one is present in _lwkt_schedule_post.
1224 */
1225static void
1226lwkt_schedule_remote(void *arg, int arg2, struct intrframe *frame)
1227{
1228 thread_t td = curthread;
1229 thread_t ntd = arg;
1230
1231 if (frame && ntd->td_preemptable) {
1232 crit_exit_noyield(td);
85946b6c 1233 _lwkt_schedule(ntd);
e381e77c
MD
1234 crit_enter_quick(td);
1235 } else {
85946b6c 1236 _lwkt_schedule(ntd);
e381e77c
MD
1237 }
1238}
1239
d9eea1a5 1240/*
52eedfb5
MD
1241 * Thread migration using a 'Pull' method. The thread may or may not be
1242 * the current thread. It MUST be descheduled and in a stable state.
1243 * lwkt_giveaway() must be called on the cpu owning the thread.
1244 *
1245 * At any point after lwkt_giveaway() is called, the target cpu may
1246 * 'pull' the thread by calling lwkt_acquire().
1247 *
ae8e83e6
MD
1248 * We have to make sure the thread is not sitting on a per-cpu tsleep
1249 * queue or it will blow up when it moves to another cpu.
1250 *
52eedfb5 1251 * MPSAFE - must be called under very specific conditions.
d9eea1a5 1252 */
52eedfb5
MD
1253void
1254lwkt_giveaway(thread_t td)
1255{
3b4192fb 1256 globaldata_t gd = mycpu;
52eedfb5 1257
3b4192fb
MD
1258 crit_enter_gd(gd);
1259 if (td->td_flags & TDF_TSLEEPQ)
1260 tsleep_remove(td);
1261 KKASSERT(td->td_gd == gd);
1262 TAILQ_REMOVE(&gd->gd_tdallq, td, td_allq);
1263 td->td_flags |= TDF_MIGRATING;
1264 crit_exit_gd(gd);
52eedfb5
MD
1265}
1266
a2a5ad0d
MD
1267void
1268lwkt_acquire(thread_t td)
1269{
37af14fe
MD
1270 globaldata_t gd;
1271 globaldata_t mygd;
a2a5ad0d 1272
52eedfb5 1273 KKASSERT(td->td_flags & TDF_MIGRATING);
a2a5ad0d 1274 gd = td->td_gd;
37af14fe 1275 mygd = mycpu;
52eedfb5 1276 if (gd != mycpu) {
3a06728e
MD
1277#ifdef LOOPMASK
1278 uint64_t tsc_base = rdtsc();
1279#endif
35238fa5 1280 cpu_lfence();
52eedfb5 1281 KKASSERT((td->td_flags & TDF_RUNQ) == 0);
37af14fe 1282 crit_enter_gd(mygd);
cfaeae2a 1283 DEBUG_PUSH_INFO("lwkt_acquire");
df910c23 1284 while (td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK)) {
df910c23 1285 lwkt_process_ipiq();
52eedfb5 1286 cpu_lfence();
a86ce0cd
MD
1287#ifdef _KERNEL_VIRTUAL
1288 pthread_yield();
3a06728e
MD
1289#endif
1290#ifdef LOOPMASK
1291 if (tsc_frequency && rdtsc() - tsc_base > tsc_frequency) {
1292 kprintf("lwkt_acquire: stuck td %p td->td_flags %08x\n",
1293 td, td->td_flags);
1294 tsc_base = rdtsc();
1295 }
a86ce0cd 1296#endif
df910c23 1297 }
cfaeae2a 1298 DEBUG_POP_INFO();
562273ea 1299 cpu_mfence();
37af14fe 1300 td->td_gd = mygd;
52eedfb5
MD
1301 TAILQ_INSERT_TAIL(&mygd->gd_tdallq, td, td_allq);
1302 td->td_flags &= ~TDF_MIGRATING;
1303 crit_exit_gd(mygd);
1304 } else {
1305 crit_enter_gd(mygd);
1306 TAILQ_INSERT_TAIL(&mygd->gd_tdallq, td, td_allq);
1307 td->td_flags &= ~TDF_MIGRATING;
37af14fe 1308 crit_exit_gd(mygd);
a2a5ad0d
MD
1309 }
1310}
1311
f1d1c3fa
MD
1312/*
1313 * Generic deschedule. Descheduling threads other then your own should be
1314 * done only in carefully controlled circumstances. Descheduling is
1315 * asynchronous.
1316 *
1317 * This function may block if the cpu has run out of messages.
8ad65e08
MD
1318 */
1319void
1320lwkt_deschedule(thread_t td)
1321{
f1d1c3fa
MD
1322 crit_enter();
1323 if (td == curthread) {
1324 _lwkt_dequeue(td);
1325 } else {
a72187e9 1326 if (td->td_gd == mycpu) {
f1d1c3fa
MD
1327 _lwkt_dequeue(td);
1328 } else {
b8a98473 1329 lwkt_send_ipiq(td->td_gd, (ipifunc1_t)lwkt_deschedule, td);
f1d1c3fa
MD
1330 }
1331 }
1332 crit_exit();
1333}
1334
4b5f931b
MD
1335/*
1336 * Set the target thread's priority. This routine does not automatically
1337 * switch to a higher priority thread, LWKT threads are not designed for
1338 * continuous priority changes. Yield if you want to switch.
4b5f931b
MD
1339 */
1340void
1341lwkt_setpri(thread_t td, int pri)
1342{
f9235b6d
MD
1343 if (td->td_pri != pri) {
1344 KKASSERT(pri >= 0);
1345 crit_enter();
1346 if (td->td_flags & TDF_RUNQ) {
d2d8515b 1347 KKASSERT(td->td_gd == mycpu);
f9235b6d
MD
1348 _lwkt_dequeue(td);
1349 td->td_pri = pri;
1350 _lwkt_enqueue(td);
1351 } else {
1352 td->td_pri = pri;
1353 }
1354 crit_exit();
26a0694b 1355 }
26a0694b
MD
1356}
1357
03bd0a5e
MD
1358/*
1359 * Set the initial priority for a thread prior to it being scheduled for
1360 * the first time. The thread MUST NOT be scheduled before or during
1361 * this call. The thread may be assigned to a cpu other then the current
1362 * cpu.
1363 *
1364 * Typically used after a thread has been created with TDF_STOPPREQ,
1365 * and before the thread is initially scheduled.
1366 */
1367void
1368lwkt_setpri_initial(thread_t td, int pri)
1369{
1370 KKASSERT(pri >= 0);
1371 KKASSERT((td->td_flags & TDF_RUNQ) == 0);
f9235b6d 1372 td->td_pri = pri;
03bd0a5e
MD
1373}
1374
26a0694b
MD
1375void
1376lwkt_setpri_self(int pri)
1377{
1378 thread_t td = curthread;
1379
4b5f931b
MD
1380 KKASSERT(pri >= 0 && pri <= TDPRI_MAX);
1381 crit_enter();
1382 if (td->td_flags & TDF_RUNQ) {
1383 _lwkt_dequeue(td);
f9235b6d 1384 td->td_pri = pri;
4b5f931b
MD
1385 _lwkt_enqueue(td);
1386 } else {
f9235b6d 1387 td->td_pri = pri;
4b5f931b
MD
1388 }
1389 crit_exit();
1390}
1391
f9235b6d 1392/*
85946b6c 1393 * hz tick scheduler clock for LWKT threads
f9235b6d
MD
1394 */
1395void
85946b6c 1396lwkt_schedulerclock(thread_t td)
f9235b6d 1397{
85946b6c
MD
1398 globaldata_t gd = td->td_gd;
1399 thread_t xtd;
2a418930 1400
85946b6c
MD
1401 if (TAILQ_FIRST(&gd->gd_tdrunq) == td) {
1402 /*
1403 * If the current thread is at the head of the runq shift it to the
1404 * end of any equal-priority threads and request a LWKT reschedule
1405 * if it moved.
d992c377
MD
1406 *
1407 * Ignore upri in this situation. There will only be one user thread
1408 * in user mode, all others will be user threads running in kernel
1409 * mode and we have to make sure they get some cpu.
85946b6c
MD
1410 */
1411 xtd = TAILQ_NEXT(td, td_threadq);
1412 if (xtd && xtd->td_pri == td->td_pri) {
1413 TAILQ_REMOVE(&gd->gd_tdrunq, td, td_threadq);
1414 while (xtd && xtd->td_pri == td->td_pri)
1415 xtd = TAILQ_NEXT(xtd, td_threadq);
1416 if (xtd)
1417 TAILQ_INSERT_BEFORE(xtd, td, td_threadq);
1418 else
1419 TAILQ_INSERT_TAIL(&gd->gd_tdrunq, td, td_threadq);
1420 need_lwkt_resched();
f9235b6d 1421 }
85946b6c
MD
1422 } else {
1423 /*
1424 * If we scheduled a thread other than the one at the head of the
1425 * queue always request a reschedule every tick.
1426 */
1427 need_lwkt_resched();
f9235b6d
MD
1428 }
1429}
1430
5d21b981 1431/*
52eedfb5
MD
1432 * Migrate the current thread to the specified cpu.
1433 *
cc9b6223
MD
1434 * This is accomplished by descheduling ourselves from the current cpu
1435 * and setting td_migrate_gd. The lwkt_switch() code will detect that the
1436 * 'old' thread wants to migrate after it has been completely switched out
1437 * and will complete the migration.
1438 *
1439 * TDF_MIGRATING prevents scheduling races while the thread is being migrated.
1440 *
1441 * We must be sure to release our current process designation (if a user
1442 * process) before clearing out any tsleepq we are on because the release
1443 * code may re-add us.
ae8e83e6
MD
1444 *
1445 * We must be sure to remove ourselves from the current cpu's tsleepq
1446 * before potentially moving to another queue. The thread can be on
1447 * a tsleepq due to a left-over tsleep_interlock().
5d21b981 1448 */
5d21b981
MD
1449
1450void
1451lwkt_setcpu_self(globaldata_t rgd)
1452{
5d21b981
MD
1453 thread_t td = curthread;
1454
1455 if (td->td_gd != rgd) {
1456 crit_enter_quick(td);
cc9b6223 1457
95858b91
MD
1458 if (td->td_release)
1459 td->td_release(td);
ae8e83e6 1460 if (td->td_flags & TDF_TSLEEPQ)
3b4192fb 1461 tsleep_remove(td);
cc9b6223
MD
1462
1463 /*
1464 * Set TDF_MIGRATING to prevent a spurious reschedule while we are
1465 * trying to deschedule ourselves and switch away, then deschedule
1466 * ourself, remove us from tdallq, and set td_migrate_gd. Finally,
1467 * call lwkt_switch() to complete the operation.
1468 */
5d21b981
MD
1469 td->td_flags |= TDF_MIGRATING;
1470 lwkt_deschedule_self(td);
52eedfb5 1471 TAILQ_REMOVE(&td->td_gd->gd_tdallq, td, td_allq);
cc9b6223 1472 td->td_migrate_gd = rgd;
5d21b981 1473 lwkt_switch();
cc9b6223
MD
1474
1475 /*
1476 * We are now on the target cpu
1477 */
1478 KKASSERT(rgd == mycpu);
52eedfb5 1479 TAILQ_INSERT_TAIL(&rgd->gd_tdallq, td, td_allq);
5d21b981
MD
1480 crit_exit_quick(td);
1481 }
5d21b981
MD
1482}
1483
ecdefdda
MD
1484void
1485lwkt_migratecpu(int cpuid)
1486{
ecdefdda
MD
1487 globaldata_t rgd;
1488
1489 rgd = globaldata_find(cpuid);
1490 lwkt_setcpu_self(rgd);
ecdefdda
MD
1491}
1492
5d21b981
MD
1493/*
1494 * Remote IPI for cpu migration (called while in a critical section so we
cc9b6223
MD
1495 * do not have to enter another one).
1496 *
1497 * The thread (td) has already been completely descheduled from the
1498 * originating cpu and we can simply assert the case. The thread is
1499 * assigned to the new cpu and enqueued.
5d21b981 1500 *
cc9b6223 1501 * The thread will re-add itself to tdallq when it resumes execution.
5d21b981
MD
1502 */
1503static void
1504lwkt_setcpu_remote(void *arg)
1505{
1506 thread_t td = arg;
1507 globaldata_t gd = mycpu;
1508
cc9b6223 1509 KKASSERT((td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK)) == 0);
5d21b981 1510 td->td_gd = gd;
562273ea 1511 cpu_mfence();
5d21b981 1512 td->td_flags &= ~TDF_MIGRATING;
cc9b6223 1513 KKASSERT(td->td_migrate_gd == NULL);
4643740a
MD
1514 KKASSERT(td->td_lwp == NULL ||
1515 (td->td_lwp->lwp_mpflags & LWP_MP_ONRUNQ) == 0);
5d21b981
MD
1516 _lwkt_enqueue(td);
1517}
1518
553ea3c8 1519struct lwp *
4b5f931b
MD
1520lwkt_preempted_proc(void)
1521{
73e4f7b9 1522 thread_t td = curthread;
4b5f931b
MD
1523 while (td->td_preempted)
1524 td = td->td_preempted;
553ea3c8 1525 return(td->td_lwp);
4b5f931b
MD
1526}
1527
99df837e
MD
1528/*
1529 * Create a kernel process/thread/whatever. It shares it's address space
1530 * with proc0 - ie: kernel only.
1531 *
d2d8515b
MD
1532 * If the cpu is not specified one will be selected. In the future
1533 * specifying a cpu of -1 will enable kernel thread migration between
1534 * cpus.
99df837e
MD
1535 */
1536int
c9e9fb21
MD
1537lwkt_create(void (*func)(void *), void *arg, struct thread **tdp,
1538 thread_t template, int tdflags, int cpu, const char *fmt, ...)
99df837e 1539{
73e4f7b9 1540 thread_t td;
e2565a42 1541 __va_list ap;
99df837e 1542
d3d32139 1543 td = lwkt_alloc_thread(template, LWKT_THREAD_STACK, cpu,
dbcd0c9b 1544 tdflags);
a2a5ad0d
MD
1545 if (tdp)
1546 *tdp = td;
709799ea 1547 cpu_set_thread_handler(td, lwkt_exit, func, arg);
99df837e
MD
1548
1549 /*
1550 * Set up arg0 for 'ps' etc
1551 */
e2565a42 1552 __va_start(ap, fmt);
379210cb 1553 kvsnprintf(td->td_comm, sizeof(td->td_comm), fmt, ap);
e2565a42 1554 __va_end(ap);
99df837e
MD
1555
1556 /*
1557 * Schedule the thread to run
1558 */
4643740a
MD
1559 if (td->td_flags & TDF_NOSTART)
1560 td->td_flags &= ~TDF_NOSTART;
ef0fdad1 1561 else
4643740a 1562 lwkt_schedule(td);
99df837e
MD
1563 return 0;
1564}
1565
1566/*
1567 * Destroy an LWKT thread. Warning! This function is not called when
1568 * a process exits, cpu_proc_exit() directly calls cpu_thread_exit() and
1569 * uses a different reaping mechanism.
1570 */
1571void
1572lwkt_exit(void)
1573{
1574 thread_t td = curthread;
c070746a 1575 thread_t std;
8826f33a 1576 globaldata_t gd;
99df837e 1577
2883d2d8
MD
1578 /*
1579 * Do any cleanup that might block here
1580 */
99df837e 1581 if (td->td_flags & TDF_VERBOSE)
6ea70f76 1582 kprintf("kthread %p %s has exited\n", td, td->td_comm);
2883d2d8
MD
1583 biosched_done(td);
1584 dsched_exit_thread(td);
c070746a
MD
1585
1586 /*
1587 * Get us into a critical section to interlock gd_freetd and loop
1588 * until we can get it freed.
1589 *
1590 * We have to cache the current td in gd_freetd because objcache_put()ing
1591 * it would rip it out from under us while our thread is still active.
2af9d75d
MD
1592 *
1593 * We are the current thread so of course our own TDF_RUNNING bit will
1594 * be set, so unlike the lwp reap code we don't wait for it to clear.
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1595 */
1596 gd = mycpu;
37af14fe 1597 crit_enter_quick(td);
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1598 for (;;) {
1599 if (td->td_refs) {
1600 tsleep(td, 0, "tdreap", 1);
1601 continue;
1602 }
1603 if ((std = gd->gd_freetd) != NULL) {
1604 KKASSERT((std->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK)) == 0);
1605 gd->gd_freetd = NULL;
1606 objcache_put(thread_cache, std);
1607 continue;
1608 }
1609 break;
c070746a 1610 }
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1611
1612 /*
1613 * Remove thread resources from kernel lists and deschedule us for
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1614 * the last time. We cannot block after this point or we may end
1615 * up with a stale td on the tsleepq.
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1616 *
1617 * None of this may block, the critical section is the only thing
1618 * protecting tdallq and the only thing preventing new lwkt_hold()
1619 * thread refs now.
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1620 */
1621 if (td->td_flags & TDF_TSLEEPQ)
1622 tsleep_remove(td);
37af14fe 1623 lwkt_deschedule_self(td);
e56e4dea 1624 lwkt_remove_tdallq(td);
74c9628e 1625 KKASSERT(td->td_refs == 0);
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1626
1627 /*
1628 * Final cleanup
1629 */
1630 KKASSERT(gd->gd_freetd == NULL);
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1631 if (td->td_flags & TDF_ALLOCATED_THREAD)
1632 gd->gd_freetd = td;
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1633 cpu_thread_exit();
1634}
1635
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1636void
1637lwkt_remove_tdallq(thread_t td)
1638{
1639 KKASSERT(td->td_gd == mycpu);
1640 TAILQ_REMOVE(&td->td_gd->gd_tdallq, td, td_allq);
1641}
1642
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1643/*
1644 * Code reduction and branch prediction improvements. Call/return
1645 * overhead on modern cpus often degenerates into 0 cycles due to
1646 * the cpu's branch prediction hardware and return pc cache. We
1647 * can take advantage of this by not inlining medium-complexity
1648 * functions and we can also reduce the branch prediction impact
1649 * by collapsing perfectly predictable branches into a single
1650 * procedure instead of duplicating it.
1651 *
1652 * Is any of this noticeable? Probably not, so I'll take the
1653 * smaller code size.
1654 */
1655void
b6468f56 1656crit_exit_wrapper(__DEBUG_CRIT_ARG__)
9cf43f91 1657{
b6468f56 1658 _crit_exit(mycpu __DEBUG_CRIT_PASS_ARG__);
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1659}
1660
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1661void
1662crit_panic(void)
1663{
1664 thread_t td = curthread;
850634cc 1665 int lcrit = td->td_critcount;
2d93b37a 1666
850634cc
AH
1667 td->td_critcount = 0;
1668 panic("td_critcount is/would-go negative! %p %d", td, lcrit);
4a28fe22 1669 /* NOT REACHED */
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1670}
1671
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1672/*
1673 * Called from debugger/panic on cpus which have been stopped. We must still
b19f40a4 1674 * process the IPIQ while stopped.
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1675 *
1676 * If we are dumping also try to process any pending interrupts. This may
1677 * or may not work depending on the state of the cpu at the point it was
1678 * stopped.
1679 */
1680void
1681lwkt_smp_stopped(void)
1682{
1683 globaldata_t gd = mycpu;
1684
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1685 if (dumping) {
1686 lwkt_process_ipiq();
b19f40a4 1687 --gd->gd_intr_nesting_level;
bd8015ca 1688 splz();
b19f40a4 1689 ++gd->gd_intr_nesting_level;
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1690 } else {
1691 lwkt_process_ipiq();
1692 }
bd8015ca 1693}