kernel - Optimize idle thread halt
[dragonfly.git] / sys / kern / lwkt_thread.c
CommitLineData
8ad65e08 1/*
3b998fa9 2 * Copyright (c) 2003-2010 The DragonFly Project. All rights reserved.
60f60350 3 *
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4 * This code is derived from software contributed to The DragonFly Project
5 * by Matthew Dillon <dillon@backplane.com>
60f60350 6 *
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7 * Redistribution and use in source and binary forms, with or without
8 * modification, are permitted provided that the following conditions
9 * are met:
60f60350 10 *
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11 * 1. Redistributions of source code must retain the above copyright
12 * notice, this list of conditions and the following disclaimer.
13 * 2. Redistributions in binary form must reproduce the above copyright
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14 * notice, this list of conditions and the following disclaimer in
15 * the documentation and/or other materials provided with the
16 * distribution.
17 * 3. Neither the name of The DragonFly Project nor the names of its
18 * contributors may be used to endorse or promote products derived
19 * from this software without specific, prior written permission.
60f60350 20 *
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21 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
22 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
23 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
24 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
25 * COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
26 * INCIDENTAL, SPECIAL, EXEMPLARY OR CONSEQUENTIAL DAMAGES (INCLUDING,
27 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
28 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
29 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
30 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
31 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
8ad65e08 32 * SUCH DAMAGE.
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33 */
34
35/*
36 * Each cpu in a system has its own self-contained light weight kernel
37 * thread scheduler, which means that generally speaking we only need
38 * to use a critical section to avoid problems. Foreign thread
39 * scheduling is queued via (async) IPIs.
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40 */
41
42#include <sys/param.h>
43#include <sys/systm.h>
44#include <sys/kernel.h>
45#include <sys/proc.h>
46#include <sys/rtprio.h>
b37f18d6 47#include <sys/kinfo.h>
8ad65e08 48#include <sys/queue.h>
7d0bac62 49#include <sys/sysctl.h>
99df837e 50#include <sys/kthread.h>
f1d1c3fa 51#include <machine/cpu.h>
99df837e 52#include <sys/lock.h>
f6bf3af1 53#include <sys/caps.h>
9d265729 54#include <sys/spinlock.h>
57aa743c 55#include <sys/ktr.h>
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56
57#include <sys/thread2.h>
58#include <sys/spinlock2.h>
684a93c4 59#include <sys/mplock2.h>
f1d1c3fa 60
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61#include <sys/dsched.h>
62
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63#include <vm/vm.h>
64#include <vm/vm_param.h>
65#include <vm/vm_kern.h>
66#include <vm/vm_object.h>
67#include <vm/vm_page.h>
68#include <vm/vm_map.h>
69#include <vm/vm_pager.h>
70#include <vm/vm_extern.h>
7d0bac62 71
99df837e 72#include <machine/stdarg.h>
96728c05 73#include <machine/smp.h>
99df837e 74
d850923c
AE
75#if !defined(KTR_CTXSW)
76#define KTR_CTXSW KTR_ALL
77#endif
78KTR_INFO_MASTER(ctxsw);
a1f0fb66
AE
79KTR_INFO(KTR_CTXSW, ctxsw, sw, 0, "#cpu[%d].td = %p",
80 sizeof(int) + sizeof(struct thread *));
81KTR_INFO(KTR_CTXSW, ctxsw, pre, 1, "#cpu[%d].td = %p",
82 sizeof(int) + sizeof(struct thread *));
83KTR_INFO(KTR_CTXSW, ctxsw, newtd, 2, "#threads[%p].name = %s",
84 sizeof (struct thread *) + sizeof(char *));
85KTR_INFO(KTR_CTXSW, ctxsw, deadtd, 3, "#threads[%p].name = <dead>", sizeof (struct thread *));
1541028a 86
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87static MALLOC_DEFINE(M_THREAD, "thread", "lwkt threads");
88
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89#ifdef INVARIANTS
90static int panic_on_cscount = 0;
91#endif
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92static __int64_t switch_count = 0;
93static __int64_t preempt_hit = 0;
94static __int64_t preempt_miss = 0;
95static __int64_t preempt_weird = 0;
f64b567c 96static __int64_t token_contention_count __debugvar = 0;
fb0f29c4 97static int lwkt_use_spin_port;
40aaf5fc 98static struct objcache *thread_cache;
05220613 99
88ebb169 100#ifdef SMP
e381e77c 101static void lwkt_schedule_remote(void *arg, int arg2, struct intrframe *frame);
88ebb169 102#endif
f9235b6d 103static void lwkt_fairq_accumulate(globaldata_t gd, thread_t td);
e381e77c 104
0855a2af
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105extern void cpu_heavy_restore(void);
106extern void cpu_lwkt_restore(void);
107extern void cpu_kthread_restore(void);
108extern void cpu_idle_restore(void);
109
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110/*
111 * We can make all thread ports use the spin backend instead of the thread
112 * backend. This should only be set to debug the spin backend.
113 */
114TUNABLE_INT("lwkt.use_spin_port", &lwkt_use_spin_port);
115
0f7a3396 116#ifdef INVARIANTS
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117SYSCTL_INT(_lwkt, OID_AUTO, panic_on_cscount, CTLFLAG_RW, &panic_on_cscount, 0,
118 "Panic if attempting to switch lwkt's while mastering cpusync");
0f7a3396 119#endif
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120SYSCTL_QUAD(_lwkt, OID_AUTO, switch_count, CTLFLAG_RW, &switch_count, 0,
121 "Number of switched threads");
9733f757 122SYSCTL_QUAD(_lwkt, OID_AUTO, preempt_hit, CTLFLAG_RW, &preempt_hit, 0,
0c52fa62 123 "Successful preemption events");
9733f757 124SYSCTL_QUAD(_lwkt, OID_AUTO, preempt_miss, CTLFLAG_RW, &preempt_miss, 0,
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125 "Failed preemption events");
126SYSCTL_QUAD(_lwkt, OID_AUTO, preempt_weird, CTLFLAG_RW, &preempt_weird, 0,
127 "Number of preempted threads.");
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128#ifdef INVARIANTS
129SYSCTL_QUAD(_lwkt, OID_AUTO, token_contention_count, CTLFLAG_RW,
130 &token_contention_count, 0, "spinning due to token contention");
38717797 131#endif
f9235b6d 132static int fairq_enable = 1;
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133SYSCTL_INT(_lwkt, OID_AUTO, fairq_enable, CTLFLAG_RW,
134 &fairq_enable, 0, "Turn on fairq priority accumulators");
135static int lwkt_spin_loops = 10;
136SYSCTL_INT(_lwkt, OID_AUTO, spin_loops, CTLFLAG_RW,
137 &lwkt_spin_loops, 0, "");
138static int lwkt_spin_delay = 1;
139SYSCTL_INT(_lwkt, OID_AUTO, spin_delay, CTLFLAG_RW,
140 &lwkt_spin_delay, 0, "Scheduler spin delay in microseconds 0=auto");
141static int lwkt_spin_method = 1;
142SYSCTL_INT(_lwkt, OID_AUTO, spin_method, CTLFLAG_RW,
143 &lwkt_spin_method, 0, "LWKT scheduler behavior when contended");
fbc024e4 144static int preempt_enable = 1;
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145SYSCTL_INT(_lwkt, OID_AUTO, preempt_enable, CTLFLAG_RW,
146 &preempt_enable, 0, "Enable preemption");
fbc024e4 147
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148static __cachealign int lwkt_cseq_rindex;
149static __cachealign int lwkt_cseq_windex;
05220613 150
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151/*
152 * These helper procedures handle the runq, they can only be called from
153 * within a critical section.
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154 *
155 * WARNING! Prior to SMP being brought up it is possible to enqueue and
156 * dequeue threads belonging to other cpus, so be sure to use td->td_gd
157 * instead of 'mycpu' when referencing the globaldata structure. Once
158 * SMP live enqueuing and dequeueing only occurs on the current cpu.
4b5f931b 159 */
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160static __inline
161void
162_lwkt_dequeue(thread_t td)
163{
164 if (td->td_flags & TDF_RUNQ) {
75cdbe6c 165 struct globaldata *gd = td->td_gd;
4b5f931b 166
f1d1c3fa 167 td->td_flags &= ~TDF_RUNQ;
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168 TAILQ_REMOVE(&gd->gd_tdrunq, td, td_threadq);
169 gd->gd_fairq_total_pri -= td->td_pri;
170 if (TAILQ_FIRST(&gd->gd_tdrunq) == NULL)
2a418930 171 atomic_clear_int(&gd->gd_reqflags, RQF_RUNNING);
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172 }
173}
174
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175/*
176 * Priority enqueue.
177 *
178 * NOTE: There are a limited number of lwkt threads runnable since user
179 * processes only schedule one at a time per cpu.
180 */
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181static __inline
182void
183_lwkt_enqueue(thread_t td)
184{
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185 thread_t xtd;
186
7f5d7ed7 187 if ((td->td_flags & (TDF_RUNQ|TDF_MIGRATING|TDF_BLOCKQ)) == 0) {
75cdbe6c 188 struct globaldata *gd = td->td_gd;
4b5f931b 189
f1d1c3fa 190 td->td_flags |= TDF_RUNQ;
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191 xtd = TAILQ_FIRST(&gd->gd_tdrunq);
192 if (xtd == NULL) {
193 TAILQ_INSERT_TAIL(&gd->gd_tdrunq, td, td_threadq);
2a418930 194 atomic_set_int(&gd->gd_reqflags, RQF_RUNNING);
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195 } else {
196 while (xtd && xtd->td_pri > td->td_pri)
197 xtd = TAILQ_NEXT(xtd, td_threadq);
198 if (xtd)
199 TAILQ_INSERT_BEFORE(xtd, td, td_threadq);
200 else
201 TAILQ_INSERT_TAIL(&gd->gd_tdrunq, td, td_threadq);
202 }
203 gd->gd_fairq_total_pri += td->td_pri;
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204 }
205}
8ad65e08 206
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207static __boolean_t
208_lwkt_thread_ctor(void *obj, void *privdata, int ocflags)
209{
210 struct thread *td = (struct thread *)obj;
211
212 td->td_kstack = NULL;
213 td->td_kstack_size = 0;
214 td->td_flags = TDF_ALLOCATED_THREAD;
215 return (1);
216}
217
218static void
219_lwkt_thread_dtor(void *obj, void *privdata)
220{
221 struct thread *td = (struct thread *)obj;
222
223 KASSERT(td->td_flags & TDF_ALLOCATED_THREAD,
224 ("_lwkt_thread_dtor: not allocated from objcache"));
225 KASSERT((td->td_flags & TDF_ALLOCATED_STACK) && td->td_kstack &&
226 td->td_kstack_size > 0,
227 ("_lwkt_thread_dtor: corrupted stack"));
228 kmem_free(&kernel_map, (vm_offset_t)td->td_kstack, td->td_kstack_size);
229}
230
231/*
232 * Initialize the lwkt s/system.
233 */
234void
235lwkt_init(void)
236{
237 /* An objcache has 2 magazines per CPU so divide cache size by 2. */
0aa16b5d
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238 thread_cache = objcache_create_mbacked(M_THREAD, sizeof(struct thread),
239 NULL, CACHE_NTHREADS/2,
240 _lwkt_thread_ctor, _lwkt_thread_dtor, NULL);
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241}
242
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243/*
244 * Schedule a thread to run. As the current thread we can always safely
245 * schedule ourselves, and a shortcut procedure is provided for that
246 * function.
247 *
248 * (non-blocking, self contained on a per cpu basis)
249 */
250void
251lwkt_schedule_self(thread_t td)
252{
253 crit_enter_quick(td);
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254 KASSERT(td != &td->td_gd->gd_idlethread,
255 ("lwkt_schedule_self(): scheduling gd_idlethread is illegal!"));
9388413d 256 KKASSERT(td->td_lwp == NULL || (td->td_lwp->lwp_flag & LWP_ONRUNQ) == 0);
37af14fe 257 _lwkt_enqueue(td);
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258 crit_exit_quick(td);
259}
260
261/*
262 * Deschedule a thread.
263 *
264 * (non-blocking, self contained on a per cpu basis)
265 */
266void
267lwkt_deschedule_self(thread_t td)
268{
269 crit_enter_quick(td);
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270 _lwkt_dequeue(td);
271 crit_exit_quick(td);
272}
273
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274/*
275 * LWKTs operate on a per-cpu basis
276 *
73e4f7b9 277 * WARNING! Called from early boot, 'mycpu' may not work yet.
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278 */
279void
280lwkt_gdinit(struct globaldata *gd)
281{
f9235b6d 282 TAILQ_INIT(&gd->gd_tdrunq);
73e4f7b9 283 TAILQ_INIT(&gd->gd_tdallq);
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284}
285
286/*
7d0bac62 287 * Create a new thread. The thread must be associated with a process context
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288 * or LWKT start address before it can be scheduled. If the target cpu is
289 * -1 the thread will be created on the current cpu.
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290 *
291 * If you intend to create a thread without a process context this function
292 * does everything except load the startup and switcher function.
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293 */
294thread_t
d3d32139 295lwkt_alloc_thread(struct thread *td, int stksize, int cpu, int flags)
7d0bac62 296{
c070746a 297 globaldata_t gd = mycpu;
99df837e 298 void *stack;
7d0bac62 299
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300 /*
301 * If static thread storage is not supplied allocate a thread. Reuse
302 * a cached free thread if possible. gd_freetd is used to keep an exiting
303 * thread intact through the exit.
304 */
ef0fdad1 305 if (td == NULL) {
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MD
306 crit_enter_gd(gd);
307 if ((td = gd->gd_freetd) != NULL) {
308 KKASSERT((td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK|
309 TDF_RUNQ)) == 0);
c070746a 310 gd->gd_freetd = NULL;
cf709dd2 311 } else {
c070746a 312 td = objcache_get(thread_cache, M_WAITOK);
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MD
313 KKASSERT((td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK|
314 TDF_RUNQ)) == 0);
315 }
316 crit_exit_gd(gd);
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317 KASSERT((td->td_flags &
318 (TDF_ALLOCATED_THREAD|TDF_RUNNING)) == TDF_ALLOCATED_THREAD,
319 ("lwkt_alloc_thread: corrupted td flags 0x%X", td->td_flags));
320 flags |= td->td_flags & (TDF_ALLOCATED_THREAD|TDF_ALLOCATED_STACK);
ef0fdad1 321 }
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322
323 /*
324 * Try to reuse cached stack.
325 */
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MD
326 if ((stack = td->td_kstack) != NULL && td->td_kstack_size != stksize) {
327 if (flags & TDF_ALLOCATED_STACK) {
e4846942 328 kmem_free(&kernel_map, (vm_offset_t)stack, td->td_kstack_size);
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MD
329 stack = NULL;
330 }
331 }
332 if (stack == NULL) {
e40cfbd7 333 stack = (void *)kmem_alloc_stack(&kernel_map, stksize);
ef0fdad1 334 flags |= TDF_ALLOCATED_STACK;
99df837e 335 }
75cdbe6c 336 if (cpu < 0)
c070746a 337 lwkt_init_thread(td, stack, stksize, flags, gd);
75cdbe6c 338 else
f470d0c8 339 lwkt_init_thread(td, stack, stksize, flags, globaldata_find(cpu));
99df837e 340 return(td);
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341}
342
343/*
344 * Initialize a preexisting thread structure. This function is used by
345 * lwkt_alloc_thread() and also used to initialize the per-cpu idlethread.
346 *
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347 * All threads start out in a critical section at a priority of
348 * TDPRI_KERN_DAEMON. Higher level code will modify the priority as
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349 * appropriate. This function may send an IPI message when the
350 * requested cpu is not the current cpu and consequently gd_tdallq may
351 * not be initialized synchronously from the point of view of the originating
352 * cpu.
353 *
354 * NOTE! we have to be careful in regards to creating threads for other cpus
355 * if SMP has not yet been activated.
7d0bac62 356 */
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357#ifdef SMP
358
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359static void
360lwkt_init_thread_remote(void *arg)
361{
362 thread_t td = arg;
363
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364 /*
365 * Protected by critical section held by IPI dispatch
366 */
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367 TAILQ_INSERT_TAIL(&td->td_gd->gd_tdallq, td, td_allq);
368}
369
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370#endif
371
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372/*
373 * lwkt core thread structural initialization.
374 *
375 * NOTE: All threads are initialized as mpsafe threads.
376 */
7d0bac62 377void
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378lwkt_init_thread(thread_t td, void *stack, int stksize, int flags,
379 struct globaldata *gd)
7d0bac62 380{
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MD
381 globaldata_t mygd = mycpu;
382
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383 bzero(td, sizeof(struct thread));
384 td->td_kstack = stack;
f470d0c8 385 td->td_kstack_size = stksize;
d3d32139 386 td->td_flags = flags;
26a0694b 387 td->td_gd = gd;
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MD
388 td->td_pri = TDPRI_KERN_DAEMON;
389 td->td_critcount = 1;
3b998fa9 390 td->td_toks_stop = &td->td_toks_base;
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391 if (lwkt_use_spin_port)
392 lwkt_initport_spin(&td->td_msgport);
393 else
394 lwkt_initport_thread(&td->td_msgport, td);
99df837e 395 pmap_init_thread(td);
0f7a3396 396#ifdef SMP
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397 /*
398 * Normally initializing a thread for a remote cpu requires sending an
399 * IPI. However, the idlethread is setup before the other cpus are
400 * activated so we have to treat it as a special case. XXX manipulation
401 * of gd_tdallq requires the BGL.
402 */
403 if (gd == mygd || td == &gd->gd_idlethread) {
37af14fe 404 crit_enter_gd(mygd);
75cdbe6c 405 TAILQ_INSERT_TAIL(&gd->gd_tdallq, td, td_allq);
37af14fe 406 crit_exit_gd(mygd);
75cdbe6c 407 } else {
2db3b277 408 lwkt_send_ipiq(gd, lwkt_init_thread_remote, td);
75cdbe6c 409 }
0f7a3396 410#else
37af14fe 411 crit_enter_gd(mygd);
0f7a3396 412 TAILQ_INSERT_TAIL(&gd->gd_tdallq, td, td_allq);
37af14fe 413 crit_exit_gd(mygd);
0f7a3396 414#endif
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415
416 dsched_new_thread(td);
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417}
418
419void
420lwkt_set_comm(thread_t td, const char *ctl, ...)
421{
e2565a42 422 __va_list va;
73e4f7b9 423
e2565a42 424 __va_start(va, ctl);
379210cb 425 kvsnprintf(td->td_comm, sizeof(td->td_comm), ctl, va);
e2565a42 426 __va_end(va);
e7c0dbba 427 KTR_LOG(ctxsw_newtd, td, &td->td_comm[0]);
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428}
429
99df837e 430void
73e4f7b9 431lwkt_hold(thread_t td)
99df837e 432{
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433 ++td->td_refs;
434}
435
436void
437lwkt_rele(thread_t td)
438{
439 KKASSERT(td->td_refs > 0);
440 --td->td_refs;
441}
442
443void
444lwkt_wait_free(thread_t td)
445{
446 while (td->td_refs)
377d4740 447 tsleep(td, 0, "tdreap", hz);
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MD
448}
449
450void
451lwkt_free_thread(thread_t td)
452{
cf709dd2 453 KKASSERT((td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK|TDF_RUNQ)) == 0);
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NT
454 if (td->td_flags & TDF_ALLOCATED_THREAD) {
455 objcache_put(thread_cache, td);
456 } else if (td->td_flags & TDF_ALLOCATED_STACK) {
457 /* client-allocated struct with internally allocated stack */
458 KASSERT(td->td_kstack && td->td_kstack_size > 0,
459 ("lwkt_free_thread: corrupted stack"));
460 kmem_free(&kernel_map, (vm_offset_t)td->td_kstack, td->td_kstack_size);
461 td->td_kstack = NULL;
462 td->td_kstack_size = 0;
99df837e 463 }
e7c0dbba 464 KTR_LOG(ctxsw_deadtd, td);
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465}
466
467
7d0bac62 468/*
8ad65e08 469 * Switch to the next runnable lwkt. If no LWKTs are runnable then
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470 * switch to the idlethread. Switching must occur within a critical
471 * section to avoid races with the scheduling queue.
472 *
473 * We always have full control over our cpu's run queue. Other cpus
474 * that wish to manipulate our queue must use the cpu_*msg() calls to
475 * talk to our cpu, so a critical section is all that is needed and
476 * the result is very, very fast thread switching.
477 *
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478 * The LWKT scheduler uses a fixed priority model and round-robins at
479 * each priority level. User process scheduling is a totally
480 * different beast and LWKT priorities should not be confused with
481 * user process priorities.
f1d1c3fa 482 *
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483 * Note that the td_switch() function cannot do anything that requires
484 * the MP lock since the MP lock will have already been setup for
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485 * the target thread (not the current thread). It's nice to have a scheduler
486 * that does not need the MP lock to work because it allows us to do some
487 * really cool high-performance MP lock optimizations.
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488 *
489 * PREEMPTION NOTE: Preemption occurs via lwkt_preempt(). lwkt_switch()
490 * is not called by the current thread in the preemption case, only when
491 * the preempting thread blocks (in order to return to the original thread).
8ad65e08
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492 */
493void
494lwkt_switch(void)
495{
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496 globaldata_t gd = mycpu;
497 thread_t td = gd->gd_curthread;
8ad65e08 498 thread_t ntd;
f9235b6d 499 thread_t xtd;
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500 int spinning = lwkt_spin_loops; /* loops before HLTing */
501 int reqflags;
502 int cseq;
0f0466c0 503 int oseq;
8ad65e08 504
46a3f46d 505 /*
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506 * Switching from within a 'fast' (non thread switched) interrupt or IPI
507 * is illegal. However, we may have to do it anyway if we hit a fatal
508 * kernel trap or we have paniced.
509 *
510 * If this case occurs save and restore the interrupt nesting level.
46a3f46d 511 */
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512 if (gd->gd_intr_nesting_level) {
513 int savegdnest;
514 int savegdtrap;
515
5fddbda2 516 if (gd->gd_trap_nesting_level == 0 && panic_cpu_gd != mycpu) {
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517 panic("lwkt_switch: Attempt to switch from a "
518 "a fast interrupt, ipi, or hard code section, "
519 "td %p\n",
520 td);
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MD
521 } else {
522 savegdnest = gd->gd_intr_nesting_level;
523 savegdtrap = gd->gd_trap_nesting_level;
524 gd->gd_intr_nesting_level = 0;
525 gd->gd_trap_nesting_level = 0;
a7422615
MD
526 if ((td->td_flags & TDF_PANICWARN) == 0) {
527 td->td_flags |= TDF_PANICWARN;
4a28fe22
MD
528 kprintf("Warning: thread switch from interrupt, IPI, "
529 "or hard code section.\n"
a7422615 530 "thread %p (%s)\n", td, td->td_comm);
7ce2998e 531 print_backtrace(-1);
a7422615 532 }
27e88a6e
MD
533 lwkt_switch();
534 gd->gd_intr_nesting_level = savegdnest;
535 gd->gd_trap_nesting_level = savegdtrap;
536 return;
537 }
96728c05 538 }
ef0fdad1 539
cb973d15
MD
540 /*
541 * Passive release (used to transition from user to kernel mode
542 * when we block or switch rather then when we enter the kernel).
543 * This function is NOT called if we are switching into a preemption
544 * or returning from a preemption. Typically this causes us to lose
0a3f9b47
MD
545 * our current process designation (if we have one) and become a true
546 * LWKT thread, and may also hand the current process designation to
547 * another process and schedule thread.
cb973d15
MD
548 */
549 if (td->td_release)
550 td->td_release(td);
551
37af14fe 552 crit_enter_gd(gd);
3b998fa9 553 if (TD_TOKS_HELD(td))
9d265729
MD
554 lwkt_relalltokens(td);
555
556 /*
b02926de
MD
557 * We had better not be holding any spin locks, but don't get into an
558 * endless panic loop.
9d265729 559 */
d666840a
MD
560 KASSERT(gd->gd_spinlocks_wr == 0 || panicstr != NULL,
561 ("lwkt_switch: still holding %d exclusive spinlocks!",
562 gd->gd_spinlocks_wr));
9d265729 563
8a8d5d85
MD
564
565#ifdef SMP
0f7a3396
MD
566#ifdef INVARIANTS
567 if (td->td_cscount) {
6ea70f76 568 kprintf("Diagnostic: attempt to switch while mastering cpusync: %p\n",
0f7a3396
MD
569 td);
570 if (panic_on_cscount)
571 panic("switching while mastering cpusync");
572 }
573#endif
8a8d5d85 574#endif
f9235b6d
MD
575
576 /*
577 * If we had preempted another thread on this cpu, resume the preempted
578 * thread. This occurs transparently, whether the preempted thread
579 * was scheduled or not (it may have been preempted after descheduling
580 * itself).
581 *
582 * We have to setup the MP lock for the original thread after backing
583 * out the adjustment that was made to curthread when the original
584 * was preempted.
585 */
99df837e 586 if ((ntd = td->td_preempted) != NULL) {
26a0694b
MD
587 KKASSERT(ntd->td_flags & TDF_PREEMPT_LOCK);
588 ntd->td_flags |= TDF_PREEMPT_DONE;
8ec60c3f
MD
589
590 /*
b9eb1c19
MD
591 * The interrupt may have woken a thread up, we need to properly
592 * set the reschedule flag if the originally interrupted thread is
593 * at a lower priority.
8ec60c3f 594 */
f9235b6d
MD
595 if (TAILQ_FIRST(&gd->gd_tdrunq) &&
596 TAILQ_FIRST(&gd->gd_tdrunq)->td_pri > ntd->td_pri) {
8ec60c3f 597 need_lwkt_resched();
f9235b6d 598 }
8a8d5d85 599 /* YYY release mp lock on switchback if original doesn't need it */
f9235b6d
MD
600 goto havethread_preempted;
601 }
602
603 /*
604 * Implement round-robin fairq with priority insertion. The priority
605 * insertion is handled by _lwkt_enqueue()
606 *
607 * We have to adjust the MP lock for the target thread. If we
608 * need the MP lock and cannot obtain it we try to locate a
609 * thread that does not need the MP lock. If we cannot, we spin
610 * instead of HLT.
611 *
612 * A similar issue exists for the tokens held by the target thread.
613 * If we cannot obtain ownership of the tokens we cannot immediately
614 * schedule the thread.
615 */
616 for (;;) {
2a418930
MD
617 /*
618 * Clear RQF_AST_LWKT_RESCHED (we handle the reschedule request)
619 * and set RQF_WAKEUP (prevent unnecessary IPIs from being
620 * received).
621 */
622 for (;;) {
623 reqflags = gd->gd_reqflags;
624 if (atomic_cmpset_int(&gd->gd_reqflags, reqflags,
625 (reqflags & ~RQF_AST_LWKT_RESCHED) |
626 RQF_WAKEUP)) {
627 break;
628 }
629 }
f9235b6d 630
4b5f931b 631 /*
2a418930
MD
632 * Hotpath - pull the head of the run queue and attempt to schedule
633 * it. Fairq exhaustion moves the task to the end of the list. If
634 * no threads are runnable we switch to the idle thread.
41a01a4d 635 */
2a418930
MD
636 for (;;) {
637 ntd = TAILQ_FIRST(&gd->gd_tdrunq);
638
639 if (ntd == NULL) {
640 /*
641 * Runq is empty, switch to idle and clear RQF_WAKEUP
642 * to allow it to halt.
643 */
644 ntd = &gd->gd_idlethread;
6f207a2c 645#ifdef SMP
2a418930 646 if (gd->gd_trap_nesting_level == 0 && panicstr == NULL)
b5d16701 647 ASSERT_NO_TOKENS_HELD(ntd);
6f207a2c 648#endif
2a418930
MD
649 cpu_time.cp_msg[0] = 0;
650 cpu_time.cp_stallpc = 0;
651 atomic_clear_int(&gd->gd_reqflags, RQF_WAKEUP);
652 goto haveidle;
653 }
654
655 if (ntd->td_fairq_accum >= 0)
656 break;
657
658 splz_check();
659 lwkt_fairq_accumulate(gd, ntd);
660 TAILQ_REMOVE(&gd->gd_tdrunq, ntd, td_threadq);
661 TAILQ_INSERT_TAIL(&gd->gd_tdrunq, ntd, td_threadq);
f9235b6d 662 }
41a01a4d
MD
663
664 /*
2a418930
MD
665 * Hotpath - schedule ntd. Leaves RQF_WAKEUP set to prevent
666 * unwanted decontention IPIs.
6f207a2c
MD
667 *
668 * NOTE: For UP there is no mplock and lwkt_getalltokens()
669 * always succeeds.
8ec60c3f 670 */
2a418930 671 if (TD_TOKS_NOT_HELD(ntd) || lwkt_getalltokens(ntd))
f9235b6d 672 goto havethread;
f9235b6d 673
f9235b6d 674 /*
2a418930
MD
675 * Coldpath (SMP only since tokens always succeed on UP)
676 *
677 * We had some contention on the thread we wanted to schedule.
678 * What we do now is try to find a thread that we can schedule
679 * in its stead until decontention reschedules on our cpu.
680 *
681 * The coldpath scan does NOT rearrange threads in the run list
682 * and it also ignores the accumulator.
683 *
684 * We do not immediately schedule a user priority thread, instead
685 * we record it in xtd and continue looking for kernel threads.
686 * A cpu can only have one user priority thread (normally) so just
687 * record the first one.
688 *
689 * NOTE: This scan will also include threads whos fairq's were
690 * accumulated in the first loop.
f9235b6d 691 */
2a418930
MD
692 ++token_contention_count;
693 xtd = NULL;
694 while ((ntd = TAILQ_NEXT(ntd, td_threadq)) != NULL) {
41a01a4d 695 /*
2a418930
MD
696 * Try to switch to this thread. If the thread is running at
697 * user priority we clear WAKEUP to allow decontention IPIs
698 * (since this thread is simply running until the one we wanted
699 * decontends), and we make sure that LWKT_RESCHED is not set.
df6b8ba0 700 *
2a418930
MD
701 * Otherwise for kernel threads we leave WAKEUP set to avoid
702 * unnecessary decontention IPIs.
41a01a4d 703 */
2a418930
MD
704 if (ntd->td_pri < TDPRI_KERN_LPSCHED) {
705 if (xtd == NULL)
706 xtd = ntd;
707 continue;
f9235b6d 708 }
a453459d 709
f9235b6d 710 /*
2a418930
MD
711 * Do not let the fairq get too negative. Even though we are
712 * ignoring it atm once the scheduler decontends a very negative
713 * thread will get moved to the end of the queue.
f9235b6d 714 */
2a418930
MD
715 if (TD_TOKS_NOT_HELD(ntd) || lwkt_getalltokens(ntd)) {
716 if (ntd->td_fairq_accum < -TDFAIRQ_MAX(gd))
717 ntd->td_fairq_accum = -TDFAIRQ_MAX(gd);
718 goto havethread;
8a8d5d85 719 }
f9235b6d 720
df6b8ba0 721 /*
2a418930 722 * Well fubar, this thread is contended as well, loop
df6b8ba0 723 */
2a418930
MD
724 /* */
725 }
726
727 /*
728 * We exhausted the run list but we may have recorded a user
729 * thread to try. We have three choices based on
730 * lwkt.decontention_method.
731 *
732 * (0) Atomically clear RQF_WAKEUP in order to receive decontention
733 * IPIs (to interrupt the user process) and test
734 * RQF_AST_LWKT_RESCHED at the same time.
735 *
736 * This results in significant decontention IPI traffic but may
737 * be more responsive.
738 *
739 * (1) Leave RQF_WAKEUP set so we do not receive a decontention IPI.
740 * An automatic LWKT reschedule will occur on the next hardclock
741 * (typically 100hz).
742 *
743 * This results in no decontention IPI traffic but may be less
744 * responsive. This is the default.
745 *
746 * (2) Refuse to schedule the user process at this time.
747 *
748 * This is highly experimental and should not be used under
749 * normal circumstances. This can cause a user process to
750 * get starved out in situations where kernel threads are
751 * fighting each other for tokens.
752 */
753 if (xtd) {
754 ntd = xtd;
755
756 switch(lwkt_spin_method) {
757 case 0:
758 for (;;) {
759 reqflags = gd->gd_reqflags;
760 if (atomic_cmpset_int(&gd->gd_reqflags,
761 reqflags,
762 reqflags & ~RQF_WAKEUP)) {
763 break;
764 }
765 }
766 break;
767 case 1:
768 reqflags = gd->gd_reqflags;
769 break;
770 default:
771 goto skip;
772 break;
773 }
774 if ((reqflags & RQF_AST_LWKT_RESCHED) == 0 &&
b5d16701 775 (TD_TOKS_NOT_HELD(ntd) || lwkt_getalltokens(ntd))
f9235b6d 776 ) {
2a418930
MD
777 if (ntd->td_fairq_accum < -TDFAIRQ_MAX(gd))
778 ntd->td_fairq_accum = -TDFAIRQ_MAX(gd);
779 goto havethread;
df6b8ba0 780 }
9ac1ee6e 781
2a418930 782skip:
9ac1ee6e 783 /*
2a418930
MD
784 * Make sure RQF_WAKEUP is set if we failed to schedule the
785 * user thread to prevent the idle thread from halting.
9ac1ee6e 786 */
2a418930
MD
787 atomic_set_int(&gd->gd_reqflags, RQF_WAKEUP);
788 }
789
790 /*
791 * We exhausted the run list, meaning that all runnable threads
792 * are contended.
793 */
794 cpu_pause();
795 ntd = &gd->gd_idlethread;
796#ifdef SMP
797 if (gd->gd_trap_nesting_level == 0 && panicstr == NULL)
798 ASSERT_NO_TOKENS_HELD(ntd);
799 /* contention case, do not clear contention mask */
800#endif
801
802 /*
803 * Ok, we might want to spin a few times as some tokens are held for
804 * very short periods of time and IPI overhead is 1uS or worse
805 * (meaning it is usually better to spin). Regardless we have to
806 * call splz_check() to be sure to service any interrupts blocked
807 * by our critical section, otherwise we could livelock e.g. IPIs.
808 *
809 * The IPI mechanic is really a last resort. In nearly all other
810 * cases RQF_WAKEUP is left set to prevent decontention IPIs.
811 *
812 * When we decide not to spin we clear RQF_WAKEUP and switch to
813 * the idle thread. Clearing RQF_WEAKEUP allows the idle thread
814 * to halt and decontended tokens will issue an IPI to us. The
815 * idle thread will check for pending reschedules already set
816 * (RQF_AST_LWKT_RESCHED) before actually halting so we don't have
817 * to here.
818 */
819 if (spinning <= 0) {
820 atomic_clear_int(&gd->gd_reqflags, RQF_WAKEUP);
821 goto haveidle;
4b5f931b 822 }
2a418930 823 --spinning;
c5724852
MD
824
825 /*
2a418930
MD
826 * When spinning a delay is required both to avoid livelocks from
827 * token order reversals (a thread may be trying to acquire multiple
828 * tokens), and also to reduce cpu cache management traffic.
829 *
830 * In order to scale to a large number of CPUs we use a time slot
831 * resequencer to force contending cpus into non-contending
832 * time-slots. The scheduler may still contend with the lock holder
833 * but will not (generally) contend with all the other cpus trying
834 * trying to get the same token.
835 *
836 * The resequencer uses a FIFO counter mechanic. The owner of the
837 * rindex at the head of the FIFO is allowed to pull itself off
838 * the FIFO and fetchadd is used to enter into the FIFO. This bit
839 * of code is VERY cache friendly and forces all spinning schedulers
840 * into their own time slots.
c5724852 841 *
2a418930
MD
842 * This code has been tested to 48-cpus and caps the cache
843 * contention load at ~1uS intervals regardless of the number of
844 * cpus. Scaling beyond 64 cpus might require additional smarts
845 * (such as separate FIFOs for specific token cases).
846 *
847 * WARNING! We can't call splz_check() or anything else here as
848 * it could cause a deadlock.
c5724852 849 */
2a418930 850 cseq = atomic_fetchadd_int(&lwkt_cseq_windex, 1);
0f0466c0
MD
851 while ((oseq = lwkt_cseq_rindex) != cseq) {
852 cpu_ccfence();
853 if (cpu_mi_feature & CPU_MI_MONITOR) {
854 cpu_mmw_pause_int(&lwkt_cseq_rindex, oseq);
855 } else {
856 DELAY(1);
857 cpu_lfence();
858 }
2a418930
MD
859 }
860 cseq = lwkt_spin_delay; /* don't trust the system operator */
861 cpu_ccfence();
862 if (cseq < 1)
863 cseq = 1;
864 if (cseq > 1000)
865 cseq = 1000;
866 DELAY(cseq);
867 atomic_add_int(&lwkt_cseq_rindex, 1);
c5724852 868 splz_check();
2a418930 869 /* highest level for(;;) loop */
f1d1c3fa 870 }
8a8d5d85 871
2a418930 872havethread:
8a8d5d85 873 /*
f9235b6d
MD
874 * We must always decrement td_fairq_accum on non-idle threads just
875 * in case a thread never gets a tick due to being in a continuous
2a418930 876 * critical section. The page-zeroing code does this, for example.
f9235b6d
MD
877 *
878 * If the thread we came up with is a higher or equal priority verses
879 * the thread at the head of the queue we move our thread to the
880 * front. This way we can always check the front of the queue.
be71787b
MD
881 *
882 * Clear gd_idle_repeat when doing a normal switch to a non-idle
883 * thread.
f9235b6d 884 */
f9235b6d
MD
885 ++gd->gd_cnt.v_swtch;
886 --ntd->td_fairq_accum;
9ac1ee6e 887 ntd->td_wmesg = NULL;
f9235b6d
MD
888 xtd = TAILQ_FIRST(&gd->gd_tdrunq);
889 if (ntd != xtd && ntd->td_pri >= xtd->td_pri) {
890 TAILQ_REMOVE(&gd->gd_tdrunq, ntd, td_threadq);
891 TAILQ_INSERT_HEAD(&gd->gd_tdrunq, ntd, td_threadq);
892 }
be71787b 893 gd->gd_idle_repeat = 0;
2a418930 894
f9235b6d 895havethread_preempted:
f9235b6d
MD
896 /*
897 * If the new target does not need the MP lock and we are holding it,
898 * release the MP lock. If the new target requires the MP lock we have
899 * already acquired it for the target.
8a8d5d85 900 */
2a418930 901 ;
f9235b6d
MD
902haveidle:
903 KASSERT(ntd->td_critcount,
b5d16701
MD
904 ("priority problem in lwkt_switch %d %d",
905 td->td_critcount, ntd->td_critcount));
906
94f6d86e
MD
907 if (td != ntd) {
908 ++switch_count;
a1f0fb66 909 KTR_LOG(ctxsw_sw, gd->gd_cpuid, ntd);
f1d1c3fa 910 td->td_switch(ntd);
94f6d86e 911 }
37af14fe
MD
912 /* NOTE: current cpu may have changed after switch */
913 crit_exit_quick(td);
8ad65e08
MD
914}
915
f1d1c3fa 916/*
96728c05
MD
917 * Request that the target thread preempt the current thread. Preemption
918 * only works under a specific set of conditions:
b68b7282 919 *
96728c05
MD
920 * - We are not preempting ourselves
921 * - The target thread is owned by the current cpu
922 * - We are not currently being preempted
923 * - The target is not currently being preempted
d3d1cbc8
MD
924 * - We are not holding any spin locks
925 * - The target thread is not holding any tokens
96728c05
MD
926 * - We are able to satisfy the target's MP lock requirements (if any).
927 *
928 * THE CALLER OF LWKT_PREEMPT() MUST BE IN A CRITICAL SECTION. Typically
929 * this is called via lwkt_schedule() through the td_preemptable callback.
f9235b6d 930 * critcount is the managed critical priority that we should ignore in order
96728c05
MD
931 * to determine whether preemption is possible (aka usually just the crit
932 * priority of lwkt_schedule() itself).
b68b7282 933 *
26a0694b
MD
934 * XXX at the moment we run the target thread in a critical section during
935 * the preemption in order to prevent the target from taking interrupts
936 * that *WE* can't. Preemption is strictly limited to interrupt threads
937 * and interrupt-like threads, outside of a critical section, and the
938 * preempted source thread will be resumed the instant the target blocks
939 * whether or not the source is scheduled (i.e. preemption is supposed to
940 * be as transparent as possible).
b68b7282
MD
941 */
942void
f9235b6d 943lwkt_preempt(thread_t ntd, int critcount)
b68b7282 944{
46a3f46d 945 struct globaldata *gd = mycpu;
0a3f9b47 946 thread_t td;
2d910aaf 947 int save_gd_intr_nesting_level;
b68b7282 948
26a0694b 949 /*
96728c05
MD
950 * The caller has put us in a critical section. We can only preempt
951 * if the caller of the caller was not in a critical section (basically
f9235b6d 952 * a local interrupt), as determined by the 'critcount' parameter. We
47737962 953 * also can't preempt if the caller is holding any spinlocks (even if
d666840a 954 * he isn't in a critical section). This also handles the tokens test.
96728c05
MD
955 *
956 * YYY The target thread must be in a critical section (else it must
957 * inherit our critical section? I dunno yet).
41a01a4d 958 *
0a3f9b47 959 * Set need_lwkt_resched() unconditionally for now YYY.
26a0694b 960 */
f9235b6d 961 KASSERT(ntd->td_critcount, ("BADCRIT0 %d", ntd->td_pri));
26a0694b 962
fbc024e4
MD
963 if (preempt_enable == 0) {
964 ++preempt_miss;
965 return;
966 }
967
0a3f9b47 968 td = gd->gd_curthread;
f9235b6d 969 if (ntd->td_pri <= td->td_pri) {
57c254db
MD
970 ++preempt_miss;
971 return;
972 }
f9235b6d 973 if (td->td_critcount > critcount) {
96728c05 974 ++preempt_miss;
8ec60c3f 975 need_lwkt_resched();
96728c05
MD
976 return;
977 }
978#ifdef SMP
46a3f46d 979 if (ntd->td_gd != gd) {
96728c05 980 ++preempt_miss;
8ec60c3f 981 need_lwkt_resched();
96728c05
MD
982 return;
983 }
984#endif
41a01a4d 985 /*
77912481
MD
986 * We don't have to check spinlocks here as they will also bump
987 * td_critcount.
d3d1cbc8
MD
988 *
989 * Do not try to preempt if the target thread is holding any tokens.
990 * We could try to acquire the tokens but this case is so rare there
991 * is no need to support it.
41a01a4d 992 */
77912481
MD
993 KKASSERT(gd->gd_spinlocks_wr == 0);
994
3b998fa9 995 if (TD_TOKS_HELD(ntd)) {
d3d1cbc8
MD
996 ++preempt_miss;
997 need_lwkt_resched();
998 return;
999 }
26a0694b
MD
1000 if (td == ntd || ((td->td_flags | ntd->td_flags) & TDF_PREEMPT_LOCK)) {
1001 ++preempt_weird;
8ec60c3f 1002 need_lwkt_resched();
26a0694b
MD
1003 return;
1004 }
1005 if (ntd->td_preempted) {
4b5f931b 1006 ++preempt_hit;
8ec60c3f 1007 need_lwkt_resched();
26a0694b 1008 return;
b68b7282 1009 }
26a0694b 1010
8ec60c3f
MD
1011 /*
1012 * Since we are able to preempt the current thread, there is no need to
1013 * call need_lwkt_resched().
2d910aaf
MD
1014 *
1015 * We must temporarily clear gd_intr_nesting_level around the switch
1016 * since switchouts from the target thread are allowed (they will just
1017 * return to our thread), and since the target thread has its own stack.
8ec60c3f 1018 */
26a0694b
MD
1019 ++preempt_hit;
1020 ntd->td_preempted = td;
1021 td->td_flags |= TDF_PREEMPT_LOCK;
a1f0fb66 1022 KTR_LOG(ctxsw_pre, gd->gd_cpuid, ntd);
2d910aaf
MD
1023 save_gd_intr_nesting_level = gd->gd_intr_nesting_level;
1024 gd->gd_intr_nesting_level = 0;
26a0694b 1025 td->td_switch(ntd);
2d910aaf 1026 gd->gd_intr_nesting_level = save_gd_intr_nesting_level;
b9eb1c19 1027
26a0694b
MD
1028 KKASSERT(ntd->td_preempted && (td->td_flags & TDF_PREEMPT_DONE));
1029 ntd->td_preempted = NULL;
1030 td->td_flags &= ~(TDF_PREEMPT_LOCK|TDF_PREEMPT_DONE);
b68b7282
MD
1031}
1032
1033/*
faaeffac 1034 * Conditionally call splz() if gd_reqflags indicates work is pending.
4a28fe22
MD
1035 * This will work inside a critical section but not inside a hard code
1036 * section.
ef0fdad1 1037 *
f1d1c3fa
MD
1038 * (self contained on a per cpu basis)
1039 */
1040void
faaeffac 1041splz_check(void)
f1d1c3fa 1042{
7966cb69
MD
1043 globaldata_t gd = mycpu;
1044 thread_t td = gd->gd_curthread;
ef0fdad1 1045
4a28fe22
MD
1046 if ((gd->gd_reqflags & RQF_IDLECHECK_MASK) &&
1047 gd->gd_intr_nesting_level == 0 &&
1048 td->td_nest_count < 2)
1049 {
f1d1c3fa 1050 splz();
4a28fe22
MD
1051 }
1052}
1053
1054/*
1055 * This version is integrated into crit_exit, reqflags has already
1056 * been tested but td_critcount has not.
1057 *
1058 * We only want to execute the splz() on the 1->0 transition of
1059 * critcount and not in a hard code section or if too deeply nested.
1060 */
1061void
1062lwkt_maybe_splz(thread_t td)
1063{
1064 globaldata_t gd = td->td_gd;
1065
1066 if (td->td_critcount == 0 &&
1067 gd->gd_intr_nesting_level == 0 &&
1068 td->td_nest_count < 2)
1069 {
1070 splz();
1071 }
f1d1c3fa
MD
1072}
1073
8ad65e08 1074/*
f9235b6d
MD
1075 * This function is used to negotiate a passive release of the current
1076 * process/lwp designation with the user scheduler, allowing the user
1077 * scheduler to schedule another user thread. The related kernel thread
1078 * (curthread) continues running in the released state.
8ad65e08
MD
1079 */
1080void
f9235b6d 1081lwkt_passive_release(struct thread *td)
8ad65e08 1082{
f9235b6d
MD
1083 struct lwp *lp = td->td_lwp;
1084
1085 td->td_release = NULL;
1086 lwkt_setpri_self(TDPRI_KERN_USER);
1087 lp->lwp_proc->p_usched->release_curproc(lp);
f1d1c3fa
MD
1088}
1089
f9235b6d 1090
f1d1c3fa 1091/*
f9235b6d
MD
1092 * This implements a normal yield. This routine is virtually a nop if
1093 * there is nothing to yield to but it will always run any pending interrupts
1094 * if called from a critical section.
1095 *
1096 * This yield is designed for kernel threads without a user context.
1097 *
1098 * (self contained on a per cpu basis)
3824f392
MD
1099 */
1100void
f9235b6d 1101lwkt_yield(void)
3824f392 1102{
f9235b6d
MD
1103 globaldata_t gd = mycpu;
1104 thread_t td = gd->gd_curthread;
1105 thread_t xtd;
3824f392 1106
f9235b6d
MD
1107 if ((gd->gd_reqflags & RQF_IDLECHECK_MASK) && td->td_nest_count < 2)
1108 splz();
1109 if (td->td_fairq_accum < 0) {
1110 lwkt_schedule_self(curthread);
1111 lwkt_switch();
1112 } else {
1113 xtd = TAILQ_FIRST(&gd->gd_tdrunq);
1114 if (xtd && xtd->td_pri > td->td_pri) {
1115 lwkt_schedule_self(curthread);
1116 lwkt_switch();
1117 }
1118 }
3824f392
MD
1119}
1120
1121/*
f9235b6d
MD
1122 * This yield is designed for kernel threads with a user context.
1123 *
1124 * The kernel acting on behalf of the user is potentially cpu-bound,
1125 * this function will efficiently allow other threads to run and also
1126 * switch to other processes by releasing.
3824f392
MD
1127 *
1128 * The lwkt_user_yield() function is designed to have very low overhead
1129 * if no yield is determined to be needed.
1130 */
1131void
1132lwkt_user_yield(void)
1133{
f9235b6d
MD
1134 globaldata_t gd = mycpu;
1135 thread_t td = gd->gd_curthread;
1136
1137 /*
1138 * Always run any pending interrupts in case we are in a critical
1139 * section.
1140 */
1141 if ((gd->gd_reqflags & RQF_IDLECHECK_MASK) && td->td_nest_count < 2)
1142 splz();
3824f392 1143
3824f392 1144 /*
f9235b6d
MD
1145 * Switch (which forces a release) if another kernel thread needs
1146 * the cpu, if userland wants us to resched, or if our kernel
1147 * quantum has run out.
3824f392 1148 */
f9235b6d
MD
1149 if (lwkt_resched_wanted() ||
1150 user_resched_wanted() ||
1151 td->td_fairq_accum < 0)
1152 {
3824f392 1153 lwkt_switch();
3824f392
MD
1154 }
1155
f9235b6d 1156#if 0
3824f392 1157 /*
f9235b6d
MD
1158 * Reacquire the current process if we are released.
1159 *
1160 * XXX not implemented atm. The kernel may be holding locks and such,
1161 * so we want the thread to continue to receive cpu.
3824f392 1162 */
f9235b6d
MD
1163 if (td->td_release == NULL && lp) {
1164 lp->lwp_proc->p_usched->acquire_curproc(lp);
1165 td->td_release = lwkt_passive_release;
1166 lwkt_setpri_self(TDPRI_USER_NORM);
3824f392 1167 }
f9235b6d 1168#endif
b9eb1c19
MD
1169}
1170
1171/*
f1d1c3fa
MD
1172 * Generic schedule. Possibly schedule threads belonging to other cpus and
1173 * deal with threads that might be blocked on a wait queue.
1174 *
0a3f9b47
MD
1175 * We have a little helper inline function which does additional work after
1176 * the thread has been enqueued, including dealing with preemption and
1177 * setting need_lwkt_resched() (which prevents the kernel from returning
1178 * to userland until it has processed higher priority threads).
6330a558
MD
1179 *
1180 * It is possible for this routine to be called after a failed _enqueue
1181 * (due to the target thread migrating, sleeping, or otherwise blocked).
1182 * We have to check that the thread is actually on the run queue!
361d01dd
MD
1183 *
1184 * reschedok is an optimized constant propagated from lwkt_schedule() or
1185 * lwkt_schedule_noresched(). By default it is non-zero, causing a
1186 * reschedule to be requested if the target thread has a higher priority.
1187 * The port messaging code will set MSG_NORESCHED and cause reschedok to
1188 * be 0, prevented undesired reschedules.
8ad65e08 1189 */
0a3f9b47
MD
1190static __inline
1191void
f9235b6d 1192_lwkt_schedule_post(globaldata_t gd, thread_t ntd, int ccount, int reschedok)
0a3f9b47 1193{
b9eb1c19 1194 thread_t otd;
c730be20 1195
6330a558 1196 if (ntd->td_flags & TDF_RUNQ) {
361d01dd 1197 if (ntd->td_preemptable && reschedok) {
f9235b6d 1198 ntd->td_preemptable(ntd, ccount); /* YYY +token */
361d01dd 1199 } else if (reschedok) {
b9eb1c19 1200 otd = curthread;
f9235b6d 1201 if (ntd->td_pri > otd->td_pri)
c730be20 1202 need_lwkt_resched();
6330a558 1203 }
f9235b6d
MD
1204
1205 /*
1206 * Give the thread a little fair share scheduler bump if it
1207 * has been asleep for a while. This is primarily to avoid
1208 * a degenerate case for interrupt threads where accumulator
1209 * crosses into negative territory unnecessarily.
1210 */
1211 if (ntd->td_fairq_lticks != ticks) {
1212 ntd->td_fairq_lticks = ticks;
1213 ntd->td_fairq_accum += gd->gd_fairq_total_pri;
1214 if (ntd->td_fairq_accum > TDFAIRQ_MAX(gd))
1215 ntd->td_fairq_accum = TDFAIRQ_MAX(gd);
1216 }
0a3f9b47
MD
1217 }
1218}
1219
361d01dd 1220static __inline
8ad65e08 1221void
361d01dd 1222_lwkt_schedule(thread_t td, int reschedok)
8ad65e08 1223{
37af14fe
MD
1224 globaldata_t mygd = mycpu;
1225
cf709dd2
MD
1226 KASSERT(td != &td->td_gd->gd_idlethread,
1227 ("lwkt_schedule(): scheduling gd_idlethread is illegal!"));
37af14fe 1228 crit_enter_gd(mygd);
9388413d 1229 KKASSERT(td->td_lwp == NULL || (td->td_lwp->lwp_flag & LWP_ONRUNQ) == 0);
37af14fe 1230 if (td == mygd->gd_curthread) {
f1d1c3fa
MD
1231 _lwkt_enqueue(td);
1232 } else {
f1d1c3fa 1233 /*
7cd8d145
MD
1234 * If we own the thread, there is no race (since we are in a
1235 * critical section). If we do not own the thread there might
1236 * be a race but the target cpu will deal with it.
f1d1c3fa 1237 */
0f7a3396 1238#ifdef SMP
7cd8d145 1239 if (td->td_gd == mygd) {
9d265729 1240 _lwkt_enqueue(td);
f9235b6d 1241 _lwkt_schedule_post(mygd, td, 1, reschedok);
f1d1c3fa 1242 } else {
e381e77c 1243 lwkt_send_ipiq3(td->td_gd, lwkt_schedule_remote, td, 0);
7cd8d145 1244 }
0f7a3396 1245#else
7cd8d145 1246 _lwkt_enqueue(td);
f9235b6d 1247 _lwkt_schedule_post(mygd, td, 1, reschedok);
0f7a3396 1248#endif
8ad65e08 1249 }
37af14fe 1250 crit_exit_gd(mygd);
8ad65e08
MD
1251}
1252
361d01dd
MD
1253void
1254lwkt_schedule(thread_t td)
1255{
1256 _lwkt_schedule(td, 1);
1257}
1258
1259void
1260lwkt_schedule_noresched(thread_t td)
1261{
1262 _lwkt_schedule(td, 0);
1263}
1264
88ebb169
SW
1265#ifdef SMP
1266
e381e77c
MD
1267/*
1268 * When scheduled remotely if frame != NULL the IPIQ is being
1269 * run via doreti or an interrupt then preemption can be allowed.
1270 *
1271 * To allow preemption we have to drop the critical section so only
1272 * one is present in _lwkt_schedule_post.
1273 */
1274static void
1275lwkt_schedule_remote(void *arg, int arg2, struct intrframe *frame)
1276{
1277 thread_t td = curthread;
1278 thread_t ntd = arg;
1279
1280 if (frame && ntd->td_preemptable) {
1281 crit_exit_noyield(td);
1282 _lwkt_schedule(ntd, 1);
1283 crit_enter_quick(td);
1284 } else {
1285 _lwkt_schedule(ntd, 1);
1286 }
1287}
1288
d9eea1a5 1289/*
52eedfb5
MD
1290 * Thread migration using a 'Pull' method. The thread may or may not be
1291 * the current thread. It MUST be descheduled and in a stable state.
1292 * lwkt_giveaway() must be called on the cpu owning the thread.
1293 *
1294 * At any point after lwkt_giveaway() is called, the target cpu may
1295 * 'pull' the thread by calling lwkt_acquire().
1296 *
ae8e83e6
MD
1297 * We have to make sure the thread is not sitting on a per-cpu tsleep
1298 * queue or it will blow up when it moves to another cpu.
1299 *
52eedfb5 1300 * MPSAFE - must be called under very specific conditions.
d9eea1a5 1301 */
a2a5ad0d 1302void
52eedfb5
MD
1303lwkt_giveaway(thread_t td)
1304{
3b4192fb 1305 globaldata_t gd = mycpu;
52eedfb5 1306
3b4192fb
MD
1307 crit_enter_gd(gd);
1308 if (td->td_flags & TDF_TSLEEPQ)
1309 tsleep_remove(td);
1310 KKASSERT(td->td_gd == gd);
1311 TAILQ_REMOVE(&gd->gd_tdallq, td, td_allq);
1312 td->td_flags |= TDF_MIGRATING;
1313 crit_exit_gd(gd);
52eedfb5
MD
1314}
1315
1316void
a2a5ad0d
MD
1317lwkt_acquire(thread_t td)
1318{
37af14fe
MD
1319 globaldata_t gd;
1320 globaldata_t mygd;
a2a5ad0d 1321
52eedfb5 1322 KKASSERT(td->td_flags & TDF_MIGRATING);
a2a5ad0d 1323 gd = td->td_gd;
37af14fe 1324 mygd = mycpu;
52eedfb5 1325 if (gd != mycpu) {
35238fa5 1326 cpu_lfence();
52eedfb5 1327 KKASSERT((td->td_flags & TDF_RUNQ) == 0);
37af14fe 1328 crit_enter_gd(mygd);
df910c23
MD
1329 while (td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK)) {
1330#ifdef SMP
1331 lwkt_process_ipiq();
1332#endif
52eedfb5 1333 cpu_lfence();
df910c23 1334 }
562273ea 1335 cpu_mfence();
37af14fe 1336 td->td_gd = mygd;
52eedfb5
MD
1337 TAILQ_INSERT_TAIL(&mygd->gd_tdallq, td, td_allq);
1338 td->td_flags &= ~TDF_MIGRATING;
1339 crit_exit_gd(mygd);
1340 } else {
1341 crit_enter_gd(mygd);
1342 TAILQ_INSERT_TAIL(&mygd->gd_tdallq, td, td_allq);
1343 td->td_flags &= ~TDF_MIGRATING;
37af14fe 1344 crit_exit_gd(mygd);
a2a5ad0d
MD
1345 }
1346}
1347
52eedfb5
MD
1348#endif
1349
8ad65e08 1350/*
f1d1c3fa
MD
1351 * Generic deschedule. Descheduling threads other then your own should be
1352 * done only in carefully controlled circumstances. Descheduling is
1353 * asynchronous.
1354 *
1355 * This function may block if the cpu has run out of messages.
8ad65e08
MD
1356 */
1357void
1358lwkt_deschedule(thread_t td)
1359{
f1d1c3fa 1360 crit_enter();
b8a98473 1361#ifdef SMP
f1d1c3fa
MD
1362 if (td == curthread) {
1363 _lwkt_dequeue(td);
1364 } else {
a72187e9 1365 if (td->td_gd == mycpu) {
f1d1c3fa
MD
1366 _lwkt_dequeue(td);
1367 } else {
b8a98473 1368 lwkt_send_ipiq(td->td_gd, (ipifunc1_t)lwkt_deschedule, td);
f1d1c3fa
MD
1369 }
1370 }
b8a98473
MD
1371#else
1372 _lwkt_dequeue(td);
1373#endif
f1d1c3fa
MD
1374 crit_exit();
1375}
1376
1377/*
4b5f931b
MD
1378 * Set the target thread's priority. This routine does not automatically
1379 * switch to a higher priority thread, LWKT threads are not designed for
1380 * continuous priority changes. Yield if you want to switch.
4b5f931b
MD
1381 */
1382void
1383lwkt_setpri(thread_t td, int pri)
1384{
a72187e9 1385 KKASSERT(td->td_gd == mycpu);
f9235b6d
MD
1386 if (td->td_pri != pri) {
1387 KKASSERT(pri >= 0);
1388 crit_enter();
1389 if (td->td_flags & TDF_RUNQ) {
1390 _lwkt_dequeue(td);
1391 td->td_pri = pri;
1392 _lwkt_enqueue(td);
1393 } else {
1394 td->td_pri = pri;
1395 }
1396 crit_exit();
26a0694b 1397 }
26a0694b
MD
1398}
1399
03bd0a5e
MD
1400/*
1401 * Set the initial priority for a thread prior to it being scheduled for
1402 * the first time. The thread MUST NOT be scheduled before or during
1403 * this call. The thread may be assigned to a cpu other then the current
1404 * cpu.
1405 *
1406 * Typically used after a thread has been created with TDF_STOPPREQ,
1407 * and before the thread is initially scheduled.
1408 */
1409void
1410lwkt_setpri_initial(thread_t td, int pri)
1411{
1412 KKASSERT(pri >= 0);
1413 KKASSERT((td->td_flags & TDF_RUNQ) == 0);
f9235b6d 1414 td->td_pri = pri;
03bd0a5e
MD
1415}
1416
26a0694b
MD
1417void
1418lwkt_setpri_self(int pri)
1419{
1420 thread_t td = curthread;
1421
4b5f931b
MD
1422 KKASSERT(pri >= 0 && pri <= TDPRI_MAX);
1423 crit_enter();
1424 if (td->td_flags & TDF_RUNQ) {
1425 _lwkt_dequeue(td);
f9235b6d 1426 td->td_pri = pri;
4b5f931b
MD
1427 _lwkt_enqueue(td);
1428 } else {
f9235b6d 1429 td->td_pri = pri;
4b5f931b
MD
1430 }
1431 crit_exit();
1432}
1433
5d21b981 1434/*
f9235b6d
MD
1435 * 1/hz tick (typically 10ms) x TDFAIRQ_SCALE (typ 8) = 80ms full cycle.
1436 *
1437 * Example: two competing threads, same priority N. decrement by (2*N)
1438 * increment by N*8, each thread will get 4 ticks.
1439 */
1440void
1441lwkt_fairq_schedulerclock(thread_t td)
1442{
2a418930
MD
1443 globaldata_t gd;
1444
f9235b6d
MD
1445 if (fairq_enable) {
1446 while (td) {
2a418930
MD
1447 gd = td->td_gd;
1448 if (td != &gd->gd_idlethread) {
1449 td->td_fairq_accum -= gd->gd_fairq_total_pri;
1450 if (td->td_fairq_accum < -TDFAIRQ_MAX(gd))
1451 td->td_fairq_accum = -TDFAIRQ_MAX(gd);
f9235b6d
MD
1452 if (td->td_fairq_accum < 0)
1453 need_lwkt_resched();
1454 td->td_fairq_lticks = ticks;
1455 }
1456 td = td->td_preempted;
1457 }
1458 }
1459}
1460
1461static void
1462lwkt_fairq_accumulate(globaldata_t gd, thread_t td)
1463{
1464 td->td_fairq_accum += td->td_pri * TDFAIRQ_SCALE;
1465 if (td->td_fairq_accum > TDFAIRQ_MAX(td->td_gd))
1466 td->td_fairq_accum = TDFAIRQ_MAX(td->td_gd);
1467}
1468
1469/*
52eedfb5
MD
1470 * Migrate the current thread to the specified cpu.
1471 *
1472 * This is accomplished by descheduling ourselves from the current cpu,
1473 * moving our thread to the tdallq of the target cpu, IPI messaging the
1474 * target cpu, and switching out. TDF_MIGRATING prevents scheduling
1475 * races while the thread is being migrated.
ae8e83e6
MD
1476 *
1477 * We must be sure to remove ourselves from the current cpu's tsleepq
1478 * before potentially moving to another queue. The thread can be on
1479 * a tsleepq due to a left-over tsleep_interlock().
5d21b981 1480 */
3d28ff59 1481#ifdef SMP
5d21b981 1482static void lwkt_setcpu_remote(void *arg);
3d28ff59 1483#endif
5d21b981
MD
1484
1485void
1486lwkt_setcpu_self(globaldata_t rgd)
1487{
1488#ifdef SMP
1489 thread_t td = curthread;
1490
1491 if (td->td_gd != rgd) {
1492 crit_enter_quick(td);
ae8e83e6 1493 if (td->td_flags & TDF_TSLEEPQ)
3b4192fb 1494 tsleep_remove(td);
5d21b981
MD
1495 td->td_flags |= TDF_MIGRATING;
1496 lwkt_deschedule_self(td);
52eedfb5 1497 TAILQ_REMOVE(&td->td_gd->gd_tdallq, td, td_allq);
b8a98473 1498 lwkt_send_ipiq(rgd, (ipifunc1_t)lwkt_setcpu_remote, td);
5d21b981
MD
1499 lwkt_switch();
1500 /* we are now on the target cpu */
52eedfb5 1501 TAILQ_INSERT_TAIL(&rgd->gd_tdallq, td, td_allq);
5d21b981
MD
1502 crit_exit_quick(td);
1503 }
1504#endif
1505}
1506
ecdefdda
MD
1507void
1508lwkt_migratecpu(int cpuid)
1509{
1510#ifdef SMP
1511 globaldata_t rgd;
1512
1513 rgd = globaldata_find(cpuid);
1514 lwkt_setcpu_self(rgd);
1515#endif
1516}
1517
5d21b981
MD
1518/*
1519 * Remote IPI for cpu migration (called while in a critical section so we
1520 * do not have to enter another one). The thread has already been moved to
1521 * our cpu's allq, but we must wait for the thread to be completely switched
1522 * out on the originating cpu before we schedule it on ours or the stack
1523 * state may be corrupt. We clear TDF_MIGRATING after flushing the GD
1524 * change to main memory.
1525 *
1526 * XXX The use of TDF_MIGRATING might not be sufficient to avoid races
1527 * against wakeups. It is best if this interface is used only when there
1528 * are no pending events that might try to schedule the thread.
1529 */
3d28ff59 1530#ifdef SMP
5d21b981
MD
1531static void
1532lwkt_setcpu_remote(void *arg)
1533{
1534 thread_t td = arg;
1535 globaldata_t gd = mycpu;
1536
df910c23
MD
1537 while (td->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK)) {
1538#ifdef SMP
1539 lwkt_process_ipiq();
1540#endif
35238fa5 1541 cpu_lfence();
562273ea 1542 cpu_pause();
df910c23 1543 }
5d21b981 1544 td->td_gd = gd;
562273ea 1545 cpu_mfence();
5d21b981 1546 td->td_flags &= ~TDF_MIGRATING;
9388413d 1547 KKASSERT(td->td_lwp == NULL || (td->td_lwp->lwp_flag & LWP_ONRUNQ) == 0);
5d21b981
MD
1548 _lwkt_enqueue(td);
1549}
3d28ff59 1550#endif
5d21b981 1551
553ea3c8 1552struct lwp *
4b5f931b
MD
1553lwkt_preempted_proc(void)
1554{
73e4f7b9 1555 thread_t td = curthread;
4b5f931b
MD
1556 while (td->td_preempted)
1557 td = td->td_preempted;
553ea3c8 1558 return(td->td_lwp);
4b5f931b
MD
1559}
1560
4b5f931b 1561/*
99df837e
MD
1562 * Create a kernel process/thread/whatever. It shares it's address space
1563 * with proc0 - ie: kernel only.
1564 *
365fa13f
MD
1565 * NOTE! By default new threads are created with the MP lock held. A
1566 * thread which does not require the MP lock should release it by calling
1567 * rel_mplock() at the start of the new thread.
99df837e
MD
1568 */
1569int
c9e9fb21
MD
1570lwkt_create(void (*func)(void *), void *arg, struct thread **tdp,
1571 thread_t template, int tdflags, int cpu, const char *fmt, ...)
99df837e 1572{
73e4f7b9 1573 thread_t td;
e2565a42 1574 __va_list ap;
99df837e 1575
d3d32139 1576 td = lwkt_alloc_thread(template, LWKT_THREAD_STACK, cpu,
dbcd0c9b 1577 tdflags);
a2a5ad0d
MD
1578 if (tdp)
1579 *tdp = td;
709799ea 1580 cpu_set_thread_handler(td, lwkt_exit, func, arg);
99df837e
MD
1581
1582 /*
1583 * Set up arg0 for 'ps' etc
1584 */
e2565a42 1585 __va_start(ap, fmt);
379210cb 1586 kvsnprintf(td->td_comm, sizeof(td->td_comm), fmt, ap);
e2565a42 1587 __va_end(ap);
99df837e
MD
1588
1589 /*
1590 * Schedule the thread to run
1591 */
ef0fdad1
MD
1592 if ((td->td_flags & TDF_STOPREQ) == 0)
1593 lwkt_schedule(td);
1594 else
1595 td->td_flags &= ~TDF_STOPREQ;
99df837e
MD
1596 return 0;
1597}
1598
1599/*
1600 * Destroy an LWKT thread. Warning! This function is not called when
1601 * a process exits, cpu_proc_exit() directly calls cpu_thread_exit() and
1602 * uses a different reaping mechanism.
1603 */
1604void
1605lwkt_exit(void)
1606{
1607 thread_t td = curthread;
c070746a 1608 thread_t std;
8826f33a 1609 globaldata_t gd;
99df837e 1610
2883d2d8
MD
1611 /*
1612 * Do any cleanup that might block here
1613 */
99df837e 1614 if (td->td_flags & TDF_VERBOSE)
6ea70f76 1615 kprintf("kthread %p %s has exited\n", td, td->td_comm);
f6bf3af1 1616 caps_exit(td);
2883d2d8
MD
1617 biosched_done(td);
1618 dsched_exit_thread(td);
c070746a
MD
1619
1620 /*
1621 * Get us into a critical section to interlock gd_freetd and loop
1622 * until we can get it freed.
1623 *
1624 * We have to cache the current td in gd_freetd because objcache_put()ing
1625 * it would rip it out from under us while our thread is still active.
1626 */
1627 gd = mycpu;
37af14fe 1628 crit_enter_quick(td);
c070746a 1629 while ((std = gd->gd_freetd) != NULL) {
cf709dd2 1630 KKASSERT((std->td_flags & (TDF_RUNNING|TDF_PREEMPT_LOCK)) == 0);
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1631 gd->gd_freetd = NULL;
1632 objcache_put(thread_cache, std);
1633 }
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1634
1635 /*
1636 * Remove thread resources from kernel lists and deschedule us for
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1637 * the last time. We cannot block after this point or we may end
1638 * up with a stale td on the tsleepq.
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1639 */
1640 if (td->td_flags & TDF_TSLEEPQ)
1641 tsleep_remove(td);
37af14fe 1642 lwkt_deschedule_self(td);
e56e4dea 1643 lwkt_remove_tdallq(td);
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1644
1645 /*
1646 * Final cleanup
1647 */
1648 KKASSERT(gd->gd_freetd == NULL);
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1649 if (td->td_flags & TDF_ALLOCATED_THREAD)
1650 gd->gd_freetd = td;
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1651 cpu_thread_exit();
1652}
1653
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1654void
1655lwkt_remove_tdallq(thread_t td)
1656{
1657 KKASSERT(td->td_gd == mycpu);
1658 TAILQ_REMOVE(&td->td_gd->gd_tdallq, td, td_allq);
1659}
1660
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1661/*
1662 * Code reduction and branch prediction improvements. Call/return
1663 * overhead on modern cpus often degenerates into 0 cycles due to
1664 * the cpu's branch prediction hardware and return pc cache. We
1665 * can take advantage of this by not inlining medium-complexity
1666 * functions and we can also reduce the branch prediction impact
1667 * by collapsing perfectly predictable branches into a single
1668 * procedure instead of duplicating it.
1669 *
1670 * Is any of this noticeable? Probably not, so I'll take the
1671 * smaller code size.
1672 */
1673void
b6468f56 1674crit_exit_wrapper(__DEBUG_CRIT_ARG__)
9cf43f91 1675{
b6468f56 1676 _crit_exit(mycpu __DEBUG_CRIT_PASS_ARG__);
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1677}
1678
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1679void
1680crit_panic(void)
1681{
1682 thread_t td = curthread;
850634cc 1683 int lcrit = td->td_critcount;
2d93b37a 1684
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1685 td->td_critcount = 0;
1686 panic("td_critcount is/would-go negative! %p %d", td, lcrit);
4a28fe22 1687 /* NOT REACHED */
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1688}
1689
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1690#ifdef SMP
1691
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1692/*
1693 * Called from debugger/panic on cpus which have been stopped. We must still
1694 * process the IPIQ while stopped, even if we were stopped while in a critical
1695 * section (XXX).
1696 *
1697 * If we are dumping also try to process any pending interrupts. This may
1698 * or may not work depending on the state of the cpu at the point it was
1699 * stopped.
1700 */
1701void
1702lwkt_smp_stopped(void)
1703{
1704 globaldata_t gd = mycpu;
1705
1706 crit_enter_gd(gd);
1707 if (dumping) {
1708 lwkt_process_ipiq();
1709 splz();
1710 } else {
1711 lwkt_process_ipiq();
1712 }
1713 crit_exit_gd(gd);
1714}
1715
d165e668 1716#endif