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 * $FreeBSD: releng/5.0/sys/kern/subr_smp.c 103216 2002-09-11 08:13:56Z julian $
30 */
31
32 /*
33 * This module holds the global variables and machine independent functions
34 * used for the kernel SMP support.
35 */
36
37 #include <sys/param.h>
38 #include <sys/systm.h>
39 #include <sys/kernel.h>
40 #include <sys/ktr.h>
41 #include <sys/proc.h>
42 #include <sys/lock.h>
43 #include <sys/mutex.h>
44 #include <sys/pcpu.h>
45 #include <sys/smp.h>
46 #include <sys/sysctl.h>
47
48 #include <machine/smp.h>
49
50 volatile u_int stopped_cpus;
51 volatile u_int started_cpus;
52
53 void (*cpustop_restartfunc)(void);
54 int mp_ncpus;
55
56 volatile int smp_started;
57 u_int all_cpus;
58 u_int mp_maxid;
59
60 SYSCTL_NODE(_kern, OID_AUTO, smp, CTLFLAG_RD, NULL, "Kernel SMP");
61
62 int smp_active = 0; /* are the APs allowed to run? */
63 SYSCTL_INT(_kern_smp, OID_AUTO, active, CTLFLAG_RW, &smp_active, 0, "");
64
65 int smp_cpus = 1; /* how many cpu's running */
66 SYSCTL_INT(_kern_smp, OID_AUTO, cpus, CTLFLAG_RD, &smp_cpus, 0, "");
67
68 /* Enable forwarding of a signal to a process running on a different CPU */
69 static int forward_signal_enabled = 1;
70 SYSCTL_INT(_kern_smp, OID_AUTO, forward_signal_enabled, CTLFLAG_RW,
71 &forward_signal_enabled, 0, "");
72
73 /* Enable forwarding of roundrobin to all other cpus */
74 static int forward_roundrobin_enabled = 1;
75 SYSCTL_INT(_kern_smp, OID_AUTO, forward_roundrobin_enabled, CTLFLAG_RW,
76 &forward_roundrobin_enabled, 0, "");
77
78 /* Variables needed for SMP rendezvous. */
79 static void (*smp_rv_setup_func)(void *arg);
80 static void (*smp_rv_action_func)(void *arg);
81 static void (*smp_rv_teardown_func)(void *arg);
82 static void *smp_rv_func_arg;
83 static volatile int smp_rv_waiters[2];
84 static struct mtx smp_rv_mtx;
85 static int mp_probe_status;
86
87 /*
88 * Initialize MI SMP variables.
89 */
90 static void
91 mp_probe(void *dummy)
92 {
93 mp_probe_status = cpu_mp_probe();
94 }
95 SYSINIT(cpu_mp_probe, SI_SUB_TUNABLES, SI_ORDER_FIRST, mp_probe, NULL)
96
97 /*
98 * Call the MD SMP initialization code.
99 */
100 static void
101 mp_start(void *dummy)
102 {
103
104 /* Probe for MP hardware. */
105 if (mp_probe_status == 0)
106 return;
107
108 mtx_init(&smp_rv_mtx, "smp rendezvous", NULL, MTX_SPIN);
109 cpu_mp_start();
110 printf("FreeBSD/SMP: Multiprocessor System Detected: %d CPUs\n",
111 mp_ncpus);
112 cpu_mp_announce();
113 }
114 SYSINIT(cpu_mp, SI_SUB_CPU, SI_ORDER_SECOND, mp_start, NULL)
115
116 void
117 forward_signal(struct thread *td)
118 {
119 int id;
120
121 /*
122 * signotify() has already set KEF_ASTPENDING and PS_NEEDSIGCHECK on
123 * this process, so all we need to do is poke it if it is currently
124 * executing so that it executes ast().
125 */
126 mtx_assert(&sched_lock, MA_OWNED);
127 KASSERT(TD_IS_RUNNING(td),
128 ("forward_signal: thread is not TDS_RUNNING"));
129
130 CTR1(KTR_SMP, "forward_signal(%p)", td->td_proc);
131
132 if (!smp_started || cold || panicstr)
133 return;
134 if (!forward_signal_enabled)
135 return;
136
137 /* No need to IPI ourself. */
138 if (td == curthread)
139 return;
140
141 id = td->td_kse->ke_oncpu;
142 if (id == NOCPU)
143 return;
144 ipi_selected(1 << id, IPI_AST);
145 }
146
147 void
148 forward_roundrobin(void)
149 {
150 struct pcpu *pc;
151 struct thread *td;
152 u_int id, map;
153
154 mtx_assert(&sched_lock, MA_OWNED);
155
156 CTR0(KTR_SMP, "forward_roundrobin()");
157
158 if (!smp_started || cold || panicstr)
159 return;
160 if (!forward_roundrobin_enabled)
161 return;
162 map = 0;
163 SLIST_FOREACH(pc, &cpuhead, pc_allcpu) {
164 td = pc->pc_curthread;
165 id = pc->pc_cpumask;
166 if (id != PCPU_GET(cpumask) && (id & stopped_cpus) == 0 &&
167 td != pc->pc_idlethread) {
168 td->td_kse->ke_flags |= KEF_NEEDRESCHED;
169 map |= id;
170 }
171 }
172 ipi_selected(map, IPI_AST);
173 }
174
175 /*
176 * When called the executing CPU will send an IPI to all other CPUs
177 * requesting that they halt execution.
178 *
179 * Usually (but not necessarily) called with 'other_cpus' as its arg.
180 *
181 * - Signals all CPUs in map to stop.
182 * - Waits for each to stop.
183 *
184 * Returns:
185 * -1: error
186 * 0: NA
187 * 1: ok
188 *
189 * XXX FIXME: this is not MP-safe, needs a lock to prevent multiple CPUs
190 * from executing at same time.
191 */
192 int
193 stop_cpus(u_int map)
194 {
195 int i;
196
197 if (!smp_started)
198 return 0;
199
200 CTR1(KTR_SMP, "stop_cpus(%x)", map);
201
202 /* send the stop IPI to all CPUs in map */
203 ipi_selected(map, IPI_STOP);
204
205 i = 0;
206 while ((atomic_load_acq_int(&stopped_cpus) & map) != map) {
207 /* spin */
208 i++;
209 #ifdef DIAGNOSTIC
210 if (i == 100000) {
211 printf("timeout stopping cpus\n");
212 break;
213 }
214 #endif
215 }
216
217 return 1;
218 }
219
220
221 /*
222 * Called by a CPU to restart stopped CPUs.
223 *
224 * Usually (but not necessarily) called with 'stopped_cpus' as its arg.
225 *
226 * - Signals all CPUs in map to restart.
227 * - Waits for each to restart.
228 *
229 * Returns:
230 * -1: error
231 * 0: NA
232 * 1: ok
233 */
234 int
235 restart_cpus(u_int map)
236 {
237
238 if (!smp_started)
239 return 0;
240
241 CTR1(KTR_SMP, "restart_cpus(%x)", map);
242
243 /* signal other cpus to restart */
244 atomic_store_rel_int(&started_cpus, map);
245
246 /* wait for each to clear its bit */
247 while ((atomic_load_acq_int(&stopped_cpus) & map) != 0)
248 ; /* nothing */
249
250 return 1;
251 }
252
253 /*
254 * All-CPU rendezvous. CPUs are signalled, all execute the setup function
255 * (if specified), rendezvous, execute the action function (if specified),
256 * rendezvous again, execute the teardown function (if specified), and then
257 * resume.
258 *
259 * Note that the supplied external functions _must_ be reentrant and aware
260 * that they are running in parallel and in an unknown lock context.
261 */
262 void
263 smp_rendezvous_action(void)
264 {
265
266 /* setup function */
267 if (smp_rv_setup_func != NULL)
268 smp_rv_setup_func(smp_rv_func_arg);
269 /* spin on entry rendezvous */
270 atomic_add_int(&smp_rv_waiters[0], 1);
271 while (atomic_load_acq_int(&smp_rv_waiters[0]) < mp_ncpus)
272 ; /* nothing */
273 /* action function */
274 if (smp_rv_action_func != NULL)
275 smp_rv_action_func(smp_rv_func_arg);
276 /* spin on exit rendezvous */
277 atomic_add_int(&smp_rv_waiters[1], 1);
278 while (atomic_load_acq_int(&smp_rv_waiters[1]) < mp_ncpus)
279 ; /* nothing */
280 /* teardown function */
281 if (smp_rv_teardown_func != NULL)
282 smp_rv_teardown_func(smp_rv_func_arg);
283 }
284
285 void
286 smp_rendezvous(void (* setup_func)(void *),
287 void (* action_func)(void *),
288 void (* teardown_func)(void *),
289 void *arg)
290 {
291
292 if (!smp_started) {
293 if (setup_func != NULL)
294 setup_func(arg);
295 if (action_func != NULL)
296 action_func(arg);
297 if (teardown_func != NULL)
298 teardown_func(arg);
299 return;
300 }
301
302 /* obtain rendezvous lock */
303 mtx_lock_spin(&smp_rv_mtx);
304
305 /* set static function pointers */
306 smp_rv_setup_func = setup_func;
307 smp_rv_action_func = action_func;
308 smp_rv_teardown_func = teardown_func;
309 smp_rv_func_arg = arg;
310 smp_rv_waiters[0] = 0;
311 smp_rv_waiters[1] = 0;
312
313 /* signal other processors, which will enter the IPI with interrupts off */
314 ipi_all_but_self(IPI_RENDEZVOUS);
315
316 /* call executor function */
317 smp_rendezvous_action();
318
319 /* release lock */
320 mtx_unlock_spin(&smp_rv_mtx);
321 }
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