FreeBSD/Linux Kernel Cross Reference
sys/kern/subr_smp.c
1 /*-
2 * Copyright (c) 2001
3 * John Baldwin <jhb@FreeBSD.org>. All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
7 * are met:
8 * 1. Redistributions of source code must retain the above copyright
9 * notice, this list of conditions and the following disclaimer.
10 * 2. Redistributions in binary form must reproduce the above copyright
11 * notice, this list of conditions and the following disclaimer in the
12 * documentation and/or other materials provided with the distribution.
13 * 4. Neither the name of the author nor the names of any co-contributors
14 * may be used to endorse or promote products derived from this software
15 * without specific prior written permission.
16 *
17 * THIS SOFTWARE IS PROVIDED BY JOHN BALDWIN AND CONTRIBUTORS ``AS IS'' AND
18 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
19 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
20 * ARE DISCLAIMED. IN NO EVENT SHALL JOHN BALDWIN OR THE VOICES IN HIS HEAD
21 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
22 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
23 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
24 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
25 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
26 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
27 * THE POSSIBILITY OF SUCH DAMAGE.
28 */
29
30 /*
31 * This module holds the global variables and machine independent functions
32 * used for the kernel SMP support.
33 */
34
35 #include <sys/cdefs.h>
36 __FBSDID("$FreeBSD$");
37
38 #include <sys/param.h>
39 #include <sys/systm.h>
40 #include <sys/kernel.h>
41 #include <sys/ktr.h>
42 #include <sys/proc.h>
43 #include <sys/bus.h>
44 #include <sys/lock.h>
45 #include <sys/mutex.h>
46 #include <sys/pcpu.h>
47 #include <sys/smp.h>
48 #include <sys/sysctl.h>
49
50 #include <machine/cpu.h>
51 #include <machine/smp.h>
52
53 #include "opt_sched.h"
54
55 #ifdef SMP
56 volatile cpumask_t stopped_cpus;
57 volatile cpumask_t started_cpus;
58 cpumask_t idle_cpus_mask;
59 cpumask_t hlt_cpus_mask;
60 cpumask_t logical_cpus_mask;
61
62 void (*cpustop_restartfunc)(void);
63 #endif
64 /* This is used in modules that need to work in both SMP and UP. */
65 cpumask_t all_cpus;
66
67 int mp_ncpus;
68 /* export this for libkvm consumers. */
69 int mp_maxcpus = MAXCPU;
70
71 struct cpu_top *smp_topology;
72 volatile int smp_started;
73 u_int mp_maxid;
74
75 SYSCTL_NODE(_kern, OID_AUTO, smp, CTLFLAG_RD, NULL, "Kernel SMP");
76
77 SYSCTL_INT(_kern_smp, OID_AUTO, maxcpus, CTLFLAG_RD, &mp_maxcpus, 0,
78 "Max number of CPUs that the system was compiled for.");
79
80 int smp_active = 0; /* are the APs allowed to run? */
81 SYSCTL_INT(_kern_smp, OID_AUTO, active, CTLFLAG_RW, &smp_active, 0,
82 "Number of Auxillary Processors (APs) that were successfully started");
83
84 int smp_disabled = 0; /* has smp been disabled? */
85 SYSCTL_INT(_kern_smp, OID_AUTO, disabled, CTLFLAG_RDTUN, &smp_disabled, 0,
86 "SMP has been disabled from the loader");
87 TUNABLE_INT("kern.smp.disabled", &smp_disabled);
88
89 int smp_cpus = 1; /* how many cpu's running */
90 SYSCTL_INT(_kern_smp, OID_AUTO, cpus, CTLFLAG_RD, &smp_cpus, 0,
91 "Number of CPUs online");
92
93 #ifdef SMP
94 /* Enable forwarding of a signal to a process running on a different CPU */
95 static int forward_signal_enabled = 1;
96 SYSCTL_INT(_kern_smp, OID_AUTO, forward_signal_enabled, CTLFLAG_RW,
97 &forward_signal_enabled, 0,
98 "Forwarding of a signal to a process on a different CPU");
99
100 /* Enable forwarding of roundrobin to all other cpus */
101 static int forward_roundrobin_enabled = 1;
102 SYSCTL_INT(_kern_smp, OID_AUTO, forward_roundrobin_enabled, CTLFLAG_RW,
103 &forward_roundrobin_enabled, 0,
104 "Forwarding of roundrobin to all other CPUs");
105
106 /* Variables needed for SMP rendezvous. */
107 static void (*smp_rv_setup_func)(void *arg);
108 static void (*smp_rv_action_func)(void *arg);
109 static void (*smp_rv_teardown_func)(void *arg);
110 static void *smp_rv_func_arg;
111 static volatile int smp_rv_waiters[3];
112
113 /*
114 * Shared mutex to restrict busywaits between smp_rendezvous() and
115 * smp(_targeted)_tlb_shootdown(). A deadlock occurs if both of these
116 * functions trigger at once and cause multiple CPUs to busywait with
117 * interrupts disabled.
118 */
119 struct mtx smp_ipi_mtx;
120
121 /*
122 * Let the MD SMP code initialize mp_maxid very early if it can.
123 */
124 static void
125 mp_setmaxid(void *dummy)
126 {
127 cpu_mp_setmaxid();
128 }
129 SYSINIT(cpu_mp_setmaxid, SI_SUB_TUNABLES, SI_ORDER_FIRST, mp_setmaxid, NULL)
130
131 /*
132 * Call the MD SMP initialization code.
133 */
134 static void
135 mp_start(void *dummy)
136 {
137
138 /* Probe for MP hardware. */
139 if (smp_disabled != 0 || cpu_mp_probe() == 0) {
140 mp_ncpus = 1;
141 all_cpus = PCPU_GET(cpumask);
142 return;
143 }
144
145 mtx_init(&smp_ipi_mtx, "smp rendezvous", NULL, MTX_SPIN);
146 cpu_mp_start();
147 printf("FreeBSD/SMP: Multiprocessor System Detected: %d CPUs\n",
148 mp_ncpus);
149 cpu_mp_announce();
150 }
151 SYSINIT(cpu_mp, SI_SUB_CPU, SI_ORDER_THIRD, mp_start, NULL)
152
153 void
154 forward_signal(struct thread *td)
155 {
156 int id;
157
158 /*
159 * signotify() has already set TDF_ASTPENDING and TDF_NEEDSIGCHECK on
160 * this thread, so all we need to do is poke it if it is currently
161 * executing so that it executes ast().
162 */
163 THREAD_LOCK_ASSERT(td, MA_OWNED);
164 KASSERT(TD_IS_RUNNING(td),
165 ("forward_signal: thread is not TDS_RUNNING"));
166
167 CTR1(KTR_SMP, "forward_signal(%p)", td->td_proc);
168
169 if (!smp_started || cold || panicstr)
170 return;
171 if (!forward_signal_enabled)
172 return;
173
174 /* No need to IPI ourself. */
175 if (td == curthread)
176 return;
177
178 id = td->td_oncpu;
179 if (id == NOCPU)
180 return;
181 ipi_selected(1 << id, IPI_AST);
182 }
183
184 void
185 forward_roundrobin(void)
186 {
187 struct pcpu *pc;
188 struct thread *td;
189 cpumask_t id, map, me;
190
191 CTR0(KTR_SMP, "forward_roundrobin()");
192
193 if (!smp_started || cold || panicstr)
194 return;
195 if (!forward_roundrobin_enabled)
196 return;
197 map = 0;
198 me = PCPU_GET(cpumask);
199 SLIST_FOREACH(pc, &cpuhead, pc_allcpu) {
200 td = pc->pc_curthread;
201 id = pc->pc_cpumask;
202 if (id != me && (id & stopped_cpus) == 0 &&
203 !TD_IS_IDLETHREAD(td)) {
204 td->td_flags |= TDF_NEEDRESCHED;
205 map |= id;
206 }
207 }
208 ipi_selected(map, IPI_AST);
209 }
210
211 /*
212 * When called the executing CPU will send an IPI to all other CPUs
213 * requesting that they halt execution.
214 *
215 * Usually (but not necessarily) called with 'other_cpus' as its arg.
216 *
217 * - Signals all CPUs in map to stop.
218 * - Waits for each to stop.
219 *
220 * Returns:
221 * -1: error
222 * 0: NA
223 * 1: ok
224 *
225 * XXX FIXME: this is not MP-safe, needs a lock to prevent multiple CPUs
226 * from executing at same time.
227 */
228 int
229 stop_cpus(cpumask_t map)
230 {
231 int i;
232
233 if (!smp_started)
234 return 0;
235
236 CTR1(KTR_SMP, "stop_cpus(%x)", map);
237
238 /* send the stop IPI to all CPUs in map */
239 ipi_selected(map, IPI_STOP);
240
241 i = 0;
242 while ((stopped_cpus & map) != map) {
243 /* spin */
244 cpu_spinwait();
245 i++;
246 #ifdef DIAGNOSTIC
247 if (i == 100000) {
248 printf("timeout stopping cpus\n");
249 break;
250 }
251 #endif
252 }
253
254 return 1;
255 }
256
257 /*
258 * Called by a CPU to restart stopped CPUs.
259 *
260 * Usually (but not necessarily) called with 'stopped_cpus' as its arg.
261 *
262 * - Signals all CPUs in map to restart.
263 * - Waits for each to restart.
264 *
265 * Returns:
266 * -1: error
267 * 0: NA
268 * 1: ok
269 */
270 int
271 restart_cpus(cpumask_t map)
272 {
273
274 if (!smp_started)
275 return 0;
276
277 CTR1(KTR_SMP, "restart_cpus(%x)", map);
278
279 /* signal other cpus to restart */
280 atomic_store_rel_int(&started_cpus, map);
281
282 /* wait for each to clear its bit */
283 while ((stopped_cpus & map) != 0)
284 cpu_spinwait();
285
286 return 1;
287 }
288
289 /*
290 * All-CPU rendezvous. CPUs are signalled, all execute the setup function
291 * (if specified), rendezvous, execute the action function (if specified),
292 * rendezvous again, execute the teardown function (if specified), and then
293 * resume.
294 *
295 * Note that the supplied external functions _must_ be reentrant and aware
296 * that they are running in parallel and in an unknown lock context.
297 */
298 void
299 smp_rendezvous_action(void)
300 {
301
302 /* Ensure we have up-to-date values. */
303 atomic_add_acq_int(&smp_rv_waiters[0], 1);
304 while (smp_rv_waiters[0] < mp_ncpus)
305 cpu_spinwait();
306
307 /* setup function */
308 if (smp_rv_setup_func != NULL)
309 smp_rv_setup_func(smp_rv_func_arg);
310
311 /* spin on entry rendezvous */
312 atomic_add_int(&smp_rv_waiters[1], 1);
313 while (smp_rv_waiters[1] < mp_ncpus)
314 cpu_spinwait();
315
316 /* action function */
317 if (smp_rv_action_func != NULL)
318 smp_rv_action_func(smp_rv_func_arg);
319
320 /* spin on exit rendezvous */
321 atomic_add_int(&smp_rv_waiters[2], 1);
322 while (smp_rv_waiters[2] < mp_ncpus)
323 cpu_spinwait();
324
325 /* teardown function */
326 if (smp_rv_teardown_func != NULL)
327 smp_rv_teardown_func(smp_rv_func_arg);
328 }
329
330 void
331 smp_rendezvous(void (* setup_func)(void *),
332 void (* action_func)(void *),
333 void (* teardown_func)(void *),
334 void *arg)
335 {
336
337 if (!smp_started) {
338 if (setup_func != NULL)
339 setup_func(arg);
340 if (action_func != NULL)
341 action_func(arg);
342 if (teardown_func != NULL)
343 teardown_func(arg);
344 return;
345 }
346
347 /* obtain rendezvous lock */
348 mtx_lock_spin(&smp_ipi_mtx);
349
350 /* set static function pointers */
351 smp_rv_setup_func = setup_func;
352 smp_rv_action_func = action_func;
353 smp_rv_teardown_func = teardown_func;
354 smp_rv_func_arg = arg;
355 smp_rv_waiters[1] = 0;
356 smp_rv_waiters[2] = 0;
357 atomic_store_rel_int(&smp_rv_waiters[0], 0);
358
359 /* signal other processors, which will enter the IPI with interrupts off */
360 ipi_all_but_self(IPI_RENDEZVOUS);
361
362 /* call executor function */
363 smp_rendezvous_action();
364
365 /* release lock */
366 mtx_unlock_spin(&smp_ipi_mtx);
367 }
368 #else /* !SMP */
369
370 /*
371 * Provide dummy SMP support for UP kernels. Modules that need to use SMP
372 * APIs will still work using this dummy support.
373 */
374 static void
375 mp_setvariables_for_up(void *dummy)
376 {
377 mp_ncpus = 1;
378 mp_maxid = PCPU_GET(cpuid);
379 all_cpus = PCPU_GET(cpumask);
380 KASSERT(PCPU_GET(cpuid) == 0, ("UP must have a CPU ID of zero"));
381 }
382 SYSINIT(cpu_mp_setvariables, SI_SUB_TUNABLES, SI_ORDER_FIRST,
383 mp_setvariables_for_up, NULL)
384
385 void
386 smp_rendezvous(void (* setup_func)(void *),
387 void (* action_func)(void *),
388 void (* teardown_func)(void *),
389 void *arg)
390 {
391
392 if (setup_func != NULL)
393 setup_func(arg);
394 if (action_func != NULL)
395 action_func(arg);
396 if (teardown_func != NULL)
397 teardown_func(arg);
398 }
399 #endif /* SMP */
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