1 /* $NetBSD: subr_xcall.c,v 1.13 2011/05/13 22:16:44 rmind Exp $ */ 2 3 /*- 4 * Copyright (c) 2007-2010 The NetBSD Foundation, Inc. 5 * All rights reserved. 6 * 7 * This code is derived from software contributed to The NetBSD Foundation 8 * by Andrew Doran and Mindaugas Rasiukevicius. 9 * 10 * Redistribution and use in source and binary forms, with or without 11 * modification, are permitted provided that the following conditions 12 * are met: 13 * 1. Redistributions of source code must retain the above copyright 14 * notice, this list of conditions and the following disclaimer. 15 * 2. Redistributions in binary form must reproduce the above copyright 16 * notice, this list of conditions and the following disclaimer in the 17 * documentation and/or other materials provided with the distribution. 18 * 19 * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS 20 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED 21 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 22 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS 23 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 24 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF 25 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 26 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN 27 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 28 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 29 * POSSIBILITY OF SUCH DAMAGE. 30 */ 31 32 /* 33 * Cross call support 34 * 35 * Background 36 * 37 * Sometimes it is necessary to modify hardware state that is tied 38 * directly to individual CPUs (such as a CPU's local timer), and 39 * these updates can not be done remotely by another CPU. The LWP 40 * requesting the update may be unable to guarantee that it will be 41 * running on the CPU where the update must occur, when the update 42 * occurs. 43 * 44 * Additionally, it's sometimes necessary to modify per-CPU software 45 * state from a remote CPU. Where these update operations are so 46 * rare or the access to the per-CPU data so frequent that the cost 47 * of using locking or atomic operations to provide coherency is 48 * prohibitive, another way must be found. 49 * 50 * Cross calls help to solve these types of problem by allowing 51 * any CPU in the system to request that an arbitrary function be 52 * executed on any other CPU. 53 * 54 * Implementation 55 * 56 * A slow mechanism for making 'low priority' cross calls is 57 * provided. The function to be executed runs on the remote CPU 58 * within a bound kthread. No queueing is provided, and the 59 * implementation uses global state. The function being called may 60 * block briefly on locks, but in doing so must be careful to not 61 * interfere with other cross calls in the system. The function is 62 * called with thread context and not from a soft interrupt, so it 63 * can ensure that it is not interrupting other code running on the 64 * CPU, and so has exclusive access to the CPU. Since this facility 65 * is heavyweight, it's expected that it will not be used often. 66 * 67 * Cross calls must not allocate memory, as the pagedaemon uses 68 * them (and memory allocation may need to wait on the pagedaemon). 69 * 70 * A low-overhead mechanism for high priority calls (XC_HIGHPRI) is 71 * also provided. The function to be executed runs on a software 72 * interrupt context, at SOFTINT_CLOCK level, and is expected to be 73 * very lightweight, e.g. avoid blocking. 74 */ 75 76 #include <sys/cdefs.h> 77 __KERNEL_RCSID(0, "$NetBSD: subr_xcall.c,v 1.13 2011/05/13 22:16:44 rmind Exp $"); 78 79 #include <sys/types.h> 80 #include <sys/param.h> 81 #include <sys/xcall.h> 82 #include <sys/mutex.h> 83 #include <sys/condvar.h> 84 #include <sys/evcnt.h> 85 #include <sys/kthread.h> 86 #include <sys/cpu.h> 87 88 /* Cross-call state box. */ 89 typedef struct { 90 kmutex_t xc_lock; 91 kcondvar_t xc_busy; 92 xcfunc_t xc_func; 93 void * xc_arg1; 94 void * xc_arg2; 95 uint64_t xc_headp; 96 uint64_t xc_donep; 97 } xc_state_t; 98 99 /* Bit indicating high (1) or low (0) priority. */ 100 #define XC_PRI_BIT (1ULL << 63) 101 102 /* Low priority xcall structures. */ 103 static xc_state_t xc_low_pri __cacheline_aligned; 104 static uint64_t xc_tailp __cacheline_aligned; 105 106 /* High priority xcall structures. */ 107 static xc_state_t xc_high_pri __cacheline_aligned; 108 static void * xc_sih __cacheline_aligned; 109 110 /* Event counters. */ 111 static struct evcnt xc_unicast_ev __cacheline_aligned; 112 static struct evcnt xc_broadcast_ev __cacheline_aligned; 113 114 static void xc_init(void); 115 static void xc_thread(void *); 116 static void xc_highpri_intr(void *); 117 118 static inline uint64_t xc_highpri(xcfunc_t, void *, void *, struct cpu_info *); 119 static inline uint64_t xc_lowpri(xcfunc_t, void *, void *, struct cpu_info *); 120 121 /* 122 * xc_init: 123 * 124 * Initialize low and high priority cross-call structures. 125 */ 126 static void 127 xc_init(void) 128 { 129 xc_state_t *xclo = &xc_low_pri, *xchi = &xc_high_pri; 130 131 memset(xclo, 0, sizeof(xc_state_t)); 132 mutex_init(&xclo->xc_lock, MUTEX_DEFAULT, IPL_NONE); 133 cv_init(&xclo->xc_busy, "xclocv"); 134 xc_tailp = 0; 135 136 memset(xchi, 0, sizeof(xc_state_t)); 137 mutex_init(&xchi->xc_lock, MUTEX_DEFAULT, IPL_SOFTCLOCK); 138 cv_init(&xchi->xc_busy, "xchicv"); 139 xc_sih = softint_establish(SOFTINT_CLOCK | SOFTINT_MPSAFE, 140 xc_highpri_intr, NULL); 141 KASSERT(xc_sih != NULL); 142 143 evcnt_attach_dynamic(&xc_unicast_ev, EVCNT_TYPE_MISC, NULL, 144 "crosscall", "unicast"); 145 evcnt_attach_dynamic(&xc_broadcast_ev, EVCNT_TYPE_MISC, NULL, 146 "crosscall", "broadcast"); 147 } 148 149 /* 150 * xc_init_cpu: 151 * 152 * Initialize the cross-call subsystem. Called once for each CPU 153 * in the system as they are attached. 154 */ 155 void 156 xc_init_cpu(struct cpu_info *ci) 157 { 158 static bool again = false; 159 int error; 160 161 if (!again) { 162 /* Autoconfiguration will prevent re-entry. */ 163 xc_init(); 164 again = true; 165 } 166 cv_init(&ci->ci_data.cpu_xcall, "xcall"); 167 error = kthread_create(PRI_XCALL, KTHREAD_MPSAFE, ci, xc_thread, 168 NULL, NULL, "xcall/%u", ci->ci_index); 169 KASSERT(error == 0); 170 } 171 172 /* 173 * xc_broadcast: 174 * 175 * Trigger a call on all CPUs in the system. 176 */ 177 uint64_t 178 xc_broadcast(u_int flags, xcfunc_t func, void *arg1, void *arg2) 179 { 180 181 KASSERT(!cpu_intr_p() && !cpu_softintr_p()); 182 183 if ((flags & XC_HIGHPRI) != 0) { 184 return xc_highpri(func, arg1, arg2, NULL); 185 } else { 186 return xc_lowpri(func, arg1, arg2, NULL); 187 } 188 } 189 190 /* 191 * xc_unicast: 192 * 193 * Trigger a call on one CPU. 194 */ 195 uint64_t 196 xc_unicast(u_int flags, xcfunc_t func, void *arg1, void *arg2, 197 struct cpu_info *ci) 198 { 199 200 KASSERT(ci != NULL); 201 KASSERT(!cpu_intr_p() && !cpu_softintr_p()); 202 203 if ((flags & XC_HIGHPRI) != 0) { 204 return xc_highpri(func, arg1, arg2, ci); 205 } else { 206 return xc_lowpri(func, arg1, arg2, ci); 207 } 208 } 209 210 /* 211 * xc_wait: 212 * 213 * Wait for a cross call to complete. 214 */ 215 void 216 xc_wait(uint64_t where) 217 { 218 xc_state_t *xc; 219 220 KASSERT(!cpu_intr_p() && !cpu_softintr_p()); 221 222 /* Determine whether it is high or low priority cross-call. */ 223 if ((where & XC_PRI_BIT) != 0) { 224 xc = &xc_high_pri; 225 where &= ~XC_PRI_BIT; 226 } else { 227 xc = &xc_low_pri; 228 } 229 230 /* Fast path, if already done. */ 231 if (xc->xc_donep >= where) { 232 return; 233 } 234 235 /* Slow path: block until awoken. */ 236 mutex_enter(&xc->xc_lock); 237 while (xc->xc_donep < where) { 238 cv_wait(&xc->xc_busy, &xc->xc_lock); 239 } 240 mutex_exit(&xc->xc_lock); 241 } 242 243 /* 244 * xc_lowpri: 245 * 246 * Trigger a low priority call on one or more CPUs. 247 */ 248 static inline uint64_t 249 xc_lowpri(xcfunc_t func, void *arg1, void *arg2, struct cpu_info *ci) 250 { 251 xc_state_t *xc = &xc_low_pri; 252 CPU_INFO_ITERATOR cii; 253 uint64_t where; 254 255 mutex_enter(&xc->xc_lock); 256 while (xc->xc_headp != xc_tailp) { 257 cv_wait(&xc->xc_busy, &xc->xc_lock); 258 } 259 xc->xc_arg1 = arg1; 260 xc->xc_arg2 = arg2; 261 xc->xc_func = func; 262 if (ci == NULL) { 263 xc_broadcast_ev.ev_count++; 264 for (CPU_INFO_FOREACH(cii, ci)) { 265 if ((ci->ci_schedstate.spc_flags & SPCF_RUNNING) == 0) 266 continue; 267 xc->xc_headp += 1; 268 ci->ci_data.cpu_xcall_pending = true; 269 cv_signal(&ci->ci_data.cpu_xcall); 270 } 271 } else { 272 xc_unicast_ev.ev_count++; 273 xc->xc_headp += 1; 274 ci->ci_data.cpu_xcall_pending = true; 275 cv_signal(&ci->ci_data.cpu_xcall); 276 } 277 KASSERT(xc_tailp < xc->xc_headp); 278 where = xc->xc_headp; 279 mutex_exit(&xc->xc_lock); 280 281 /* Return a low priority ticket. */ 282 KASSERT((where & XC_PRI_BIT) == 0); 283 return where; 284 } 285 286 /* 287 * xc_thread: 288 * 289 * One thread per-CPU to dispatch low priority calls. 290 */ 291 static void 292 xc_thread(void *cookie) 293 { 294 struct cpu_info *ci = curcpu(); 295 xc_state_t *xc = &xc_low_pri; 296 void *arg1, *arg2; 297 xcfunc_t func; 298 299 mutex_enter(&xc->xc_lock); 300 for (;;) { 301 while (!ci->ci_data.cpu_xcall_pending) { 302 if (xc->xc_headp == xc_tailp) { 303 cv_broadcast(&xc->xc_busy); 304 } 305 cv_wait(&ci->ci_data.cpu_xcall, &xc->xc_lock); 306 KASSERT(ci == curcpu()); 307 } 308 ci->ci_data.cpu_xcall_pending = false; 309 func = xc->xc_func; 310 arg1 = xc->xc_arg1; 311 arg2 = xc->xc_arg2; 312 xc_tailp++; 313 mutex_exit(&xc->xc_lock); 314 315 KASSERT(func != NULL); 316 (*func)(arg1, arg2); 317 318 mutex_enter(&xc->xc_lock); 319 xc->xc_donep++; 320 } 321 /* NOTREACHED */ 322 } 323 324 /* 325 * xc_ipi_handler: 326 * 327 * Handler of cross-call IPI. 328 */ 329 void 330 xc_ipi_handler(void) 331 { 332 /* Executes xc_highpri_intr() via software interrupt. */ 333 softint_schedule(xc_sih); 334 } 335 336 /* 337 * xc_highpri_intr: 338 * 339 * A software interrupt handler for high priority calls. 340 */ 341 static void 342 xc_highpri_intr(void *dummy) 343 { 344 xc_state_t *xc = &xc_high_pri; 345 void *arg1, *arg2; 346 xcfunc_t func; 347 348 KASSERT(cpu_softintr_p()); 349 /* 350 * Lock-less fetch of function and its arguments. 351 * Safe since it cannot change at this point. 352 */ 353 KASSERT(xc->xc_donep < xc->xc_headp); 354 func = xc->xc_func; 355 arg1 = xc->xc_arg1; 356 arg2 = xc->xc_arg2; 357 358 KASSERT(func != NULL); 359 (*func)(arg1, arg2); 360 361 /* 362 * Note the request as done, and if we have reached the head, 363 * cross-call has been processed - notify waiters, if any. 364 */ 365 mutex_enter(&xc->xc_lock); 366 if (++xc->xc_donep == xc->xc_headp) { 367 cv_broadcast(&xc->xc_busy); 368 } 369 mutex_exit(&xc->xc_lock); 370 } 371 372 /* 373 * xc_highpri: 374 * 375 * Trigger a high priority call on one or more CPUs. 376 */ 377 static inline uint64_t 378 xc_highpri(xcfunc_t func, void *arg1, void *arg2, struct cpu_info *ci) 379 { 380 xc_state_t *xc = &xc_high_pri; 381 uint64_t where; 382 383 mutex_enter(&xc->xc_lock); 384 while (xc->xc_headp != xc->xc_donep) { 385 cv_wait(&xc->xc_busy, &xc->xc_lock); 386 } 387 xc->xc_func = func; 388 xc->xc_arg1 = arg1; 389 xc->xc_arg2 = arg2; 390 xc->xc_headp += (ci ? 1 : ncpu); 391 where = xc->xc_headp; 392 mutex_exit(&xc->xc_lock); 393 394 /* 395 * Send the IPI once lock is released. 396 * Note: it will handle the local CPU case. 397 */ 398 399 #ifdef MULTIPROCESSOR 400 kpreempt_disable(); 401 if (curcpu() == ci) { 402 /* Unicast: local CPU. */ 403 xc_ipi_handler(); 404 } else if (ci) { 405 /* Unicast: remote CPU. */ 406 xc_send_ipi(ci); 407 } else { 408 /* Broadcast: all, including local. */ 409 xc_send_ipi(NULL); 410 xc_ipi_handler(); 411 } 412 kpreempt_enable(); 413 #else 414 KASSERT(curcpu() == ci); 415 xc_ipi_handler(); 416 #endif 417 418 /* Indicate a high priority ticket. */ 419 return (where | XC_PRI_BIT); 420 } 421