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: releng/5.3/sys/kern/subr_smp.c 136588 2004-10-16 08:43:07Z cvs2svn $");
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/smp.h>
51
52 #include "opt_sched.h"
53
54 #ifdef SMP
55 volatile cpumask_t stopped_cpus;
56 volatile cpumask_t started_cpus;
57 cpumask_t idle_cpus_mask;
58 cpumask_t hlt_cpus_mask;
59 cpumask_t logical_cpus_mask;
60
61 void (*cpustop_restartfunc)(void);
62 #endif
63 /* This is used in modules that need to work in both SMP and UP. */
64 cpumask_t all_cpus;
65
66 int mp_ncpus;
67 /* export this for libkvm consumers. */
68 int mp_maxcpus = MAXCPU;
69
70 struct cpu_top *smp_topology;
71 volatile int smp_started;
72 u_int mp_maxid;
73
74 SYSCTL_NODE(_kern, OID_AUTO, smp, CTLFLAG_RD, NULL, "Kernel SMP");
75
76 SYSCTL_INT(_kern_smp, OID_AUTO, maxcpus, CTLFLAG_RD, &mp_maxcpus, 0,
77 "Max number of CPUs that the system was compiled for.");
78
79 int smp_active = 0; /* are the APs allowed to run? */
80 SYSCTL_INT(_kern_smp, OID_AUTO, active, CTLFLAG_RW, &smp_active, 0,
81 "Number of Auxillary Processors (APs) that were successfully started");
82
83 int smp_disabled = 0; /* has smp been disabled? */
84 SYSCTL_INT(_kern_smp, OID_AUTO, disabled, CTLFLAG_RDTUN, &smp_disabled, 0,
85 "SMP has been disabled from the loader");
86 TUNABLE_INT("kern.smp.disabled", &smp_disabled);
87
88 int smp_cpus = 1; /* how many cpu's running */
89 SYSCTL_INT(_kern_smp, OID_AUTO, cpus, CTLFLAG_RD, &smp_cpus, 0,
90 "Number of CPUs online");
91
92 #ifdef SMP
93 /* Enable forwarding of a signal to a process running on a different CPU */
94 static int forward_signal_enabled = 1;
95 SYSCTL_INT(_kern_smp, OID_AUTO, forward_signal_enabled, CTLFLAG_RW,
96 &forward_signal_enabled, 0,
97 "Forwarding of a signal to a process on a different CPU");
98
99 /* Enable forwarding of roundrobin to all other cpus */
100 static int forward_roundrobin_enabled = 1;
101 SYSCTL_INT(_kern_smp, OID_AUTO, forward_roundrobin_enabled, CTLFLAG_RW,
102 &forward_roundrobin_enabled, 0,
103 "Forwarding of roundrobin to all other CPUs");
104
105 /* Variables needed for SMP rendezvous. */
106 static void (*smp_rv_setup_func)(void *arg);
107 static void (*smp_rv_action_func)(void *arg);
108 static void (*smp_rv_teardown_func)(void *arg);
109 static void *smp_rv_func_arg;
110 static volatile int smp_rv_waiters[2];
111
112 /*
113 * Shared mutex to restrict busywaits between smp_rendezvous() and
114 * smp(_targeted)_tlb_shootdown(). A deadlock occurs if both of these
115 * functions trigger at once and cause multiple CPUs to busywait with
116 * interrupts disabled.
117 */
118 struct mtx smp_rv_mtx;
119
120 /*
121 * Let the MD SMP code initialize mp_maxid very early if it can.
122 */
123 static void
124 mp_setmaxid(void *dummy)
125 {
126 cpu_mp_setmaxid();
127 }
128 SYSINIT(cpu_mp_setmaxid, SI_SUB_TUNABLES, SI_ORDER_FIRST, mp_setmaxid, NULL)
129
130 /*
131 * Call the MD SMP initialization code.
132 */
133 static void
134 mp_start(void *dummy)
135 {
136
137 /* Probe for MP hardware. */
138 if (smp_disabled != 0 || cpu_mp_probe() == 0) {
139 mp_ncpus = 1;
140 all_cpus = PCPU_GET(cpumask);
141 return;
142 }
143
144 mtx_init(&smp_rv_mtx, "smp rendezvous", NULL, MTX_SPIN);
145 cpu_mp_start();
146 printf("FreeBSD/SMP: Multiprocessor System Detected: %d CPUs\n",
147 mp_ncpus);
148 cpu_mp_announce();
149 }
150 SYSINIT(cpu_mp, SI_SUB_CPU, SI_ORDER_SECOND, mp_start, NULL)
151
152 void
153 forward_signal(struct thread *td)
154 {
155 int id;
156
157 /*
158 * signotify() has already set TDF_ASTPENDING and TDF_NEEDSIGCHECK on
159 * this thread, so all we need to do is poke it if it is currently
160 * executing so that it executes ast().
161 */
162 mtx_assert(&sched_lock, MA_OWNED);
163 KASSERT(TD_IS_RUNNING(td),
164 ("forward_signal: thread is not TDS_RUNNING"));
165
166 CTR1(KTR_SMP, "forward_signal(%p)", td->td_proc);
167
168 if (!smp_started || cold || panicstr)
169 return;
170 if (!forward_signal_enabled)
171 return;
172
173 /* No need to IPI ourself. */
174 if (td == curthread)
175 return;
176
177 id = td->td_oncpu;
178 if (id == NOCPU)
179 return;
180 ipi_selected(1 << id, IPI_AST);
181 }
182
183 void
184 forward_roundrobin(void)
185 {
186 struct pcpu *pc;
187 struct thread *td;
188 cpumask_t id, map, me;
189
190 mtx_assert(&sched_lock, MA_OWNED);
191
192 CTR0(KTR_SMP, "forward_roundrobin()");
193
194 if (!smp_started || cold || panicstr)
195 return;
196 if (!forward_roundrobin_enabled)
197 return;
198 map = 0;
199 me = PCPU_GET(cpumask);
200 SLIST_FOREACH(pc, &cpuhead, pc_allcpu) {
201 td = pc->pc_curthread;
202 id = pc->pc_cpumask;
203 if (id != me && (id & stopped_cpus) == 0 &&
204 td != pc->pc_idlethread) {
205 td->td_flags |= TDF_NEEDRESCHED;
206 map |= id;
207 }
208 }
209 ipi_selected(map, IPI_AST);
210 }
211
212 /*
213 * When called the executing CPU will send an IPI to all other CPUs
214 * requesting that they halt execution.
215 *
216 * Usually (but not necessarily) called with 'other_cpus' as its arg.
217 *
218 * - Signals all CPUs in map to stop.
219 * - Waits for each to stop.
220 *
221 * Returns:
222 * -1: error
223 * 0: NA
224 * 1: ok
225 *
226 * XXX FIXME: this is not MP-safe, needs a lock to prevent multiple CPUs
227 * from executing at same time.
228 */
229 int
230 stop_cpus(cpumask_t map)
231 {
232 int i;
233
234 if (!smp_started)
235 return 0;
236
237 CTR1(KTR_SMP, "stop_cpus(%x)", map);
238
239 /* send the stop IPI to all CPUs in map */
240 ipi_selected(map, IPI_STOP);
241
242 i = 0;
243 while ((atomic_load_acq_int(&stopped_cpus) & map) != map) {
244 /* spin */
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 /*
259 * Called by a CPU to restart stopped CPUs.
260 *
261 * Usually (but not necessarily) called with 'stopped_cpus' as its arg.
262 *
263 * - Signals all CPUs in map to restart.
264 * - Waits for each to restart.
265 *
266 * Returns:
267 * -1: error
268 * 0: NA
269 * 1: ok
270 */
271 int
272 restart_cpus(cpumask_t map)
273 {
274
275 if (!smp_started)
276 return 0;
277
278 CTR1(KTR_SMP, "restart_cpus(%x)", map);
279
280 /* signal other cpus to restart */
281 atomic_store_rel_int(&started_cpus, map);
282
283 /* wait for each to clear its bit */
284 while ((atomic_load_acq_int(&stopped_cpus) & map) != 0)
285 ; /* nothing */
286
287 return 1;
288 }
289
290 /*
291 * All-CPU rendezvous. CPUs are signalled, all execute the setup function
292 * (if specified), rendezvous, execute the action function (if specified),
293 * rendezvous again, execute the teardown function (if specified), and then
294 * resume.
295 *
296 * Note that the supplied external functions _must_ be reentrant and aware
297 * that they are running in parallel and in an unknown lock context.
298 */
299 void
300 smp_rendezvous_action(void)
301 {
302
303 /* setup function */
304 if (smp_rv_setup_func != NULL)
305 smp_rv_setup_func(smp_rv_func_arg);
306 /* spin on entry rendezvous */
307 atomic_add_int(&smp_rv_waiters[0], 1);
308 while (atomic_load_acq_int(&smp_rv_waiters[0]) < mp_ncpus)
309 ; /* nothing */
310 /* action function */
311 if (smp_rv_action_func != NULL)
312 smp_rv_action_func(smp_rv_func_arg);
313 /* spin on exit rendezvous */
314 atomic_add_int(&smp_rv_waiters[1], 1);
315 while (atomic_load_acq_int(&smp_rv_waiters[1]) < mp_ncpus)
316 ; /* nothing */
317 /* teardown function */
318 if (smp_rv_teardown_func != NULL)
319 smp_rv_teardown_func(smp_rv_func_arg);
320 }
321
322 void
323 smp_rendezvous(void (* setup_func)(void *),
324 void (* action_func)(void *),
325 void (* teardown_func)(void *),
326 void *arg)
327 {
328
329 if (!smp_started) {
330 if (setup_func != NULL)
331 setup_func(arg);
332 if (action_func != NULL)
333 action_func(arg);
334 if (teardown_func != NULL)
335 teardown_func(arg);
336 return;
337 }
338
339 /* obtain rendezvous lock */
340 mtx_lock_spin(&smp_rv_mtx);
341
342 /* set static function pointers */
343 smp_rv_setup_func = setup_func;
344 smp_rv_action_func = action_func;
345 smp_rv_teardown_func = teardown_func;
346 smp_rv_func_arg = arg;
347 smp_rv_waiters[0] = 0;
348 smp_rv_waiters[1] = 0;
349
350 /* signal other processors, which will enter the IPI with interrupts off */
351 ipi_all_but_self(IPI_RENDEZVOUS);
352
353 /* call executor function */
354 smp_rendezvous_action();
355
356 /* release lock */
357 mtx_unlock_spin(&smp_rv_mtx);
358 }
359 #else /* !SMP */
360
361 /*
362 * Provide dummy SMP support for UP kernels. Modules that need to use SMP
363 * APIs will still work using this dummy support.
364 */
365 static void
366 mp_setvariables_for_up(void *dummy)
367 {
368 mp_ncpus = 1;
369 mp_maxid = PCPU_GET(cpuid);
370 all_cpus = PCPU_GET(cpumask);
371 KASSERT(PCPU_GET(cpuid) == 0, ("UP must have a CPU ID of zero"));
372 }
373 SYSINIT(cpu_mp_setvariables, SI_SUB_TUNABLES, SI_ORDER_FIRST,
374 mp_setvariables_for_up, NULL)
375
376 void
377 smp_rendezvous(void (* setup_func)(void *),
378 void (* action_func)(void *),
379 void (* teardown_func)(void *),
380 void *arg)
381 {
382
383 if (setup_func != NULL)
384 setup_func(arg);
385 if (action_func != NULL)
386 action_func(arg);
387 if (teardown_func != NULL)
388 teardown_func(arg);
389 }
390 #endif /* SMP */
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