1 /* $NetBSD: subr_pcu.c,v 1.9 2011/06/13 21:32:42 matt Exp $ */ 2 3 /*- 4 * Copyright (c) 2011 The NetBSD Foundation, Inc. 5 * All rights reserved. 6 * 7 * This code is derived from software contributed to The NetBSD Foundation 8 * by 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 * Per CPU Unit (PCU) - is an interface to manage synchronization of any 34 * per CPU context (unit) tied with LWP context. Typical use: FPU state. 35 * 36 * Concurrency notes: 37 * 38 * PCU state may be loaded only by the current LWP, that is, curlwp. 39 * Therefore, only LWP itself can set a CPU for lwp_t::l_pcu_cpu[id]. 40 * 41 * Request for a PCU release can be from owner LWP (whether PCU state 42 * is on current CPU or remote CPU) or any other LWP running on that 43 * CPU (in such case, owner LWP is on a remote CPU or sleeping). 44 * 45 * In any case, PCU state can only be changed from the running CPU. 46 * If said PCU state is on the remote CPU, a cross-call will be sent 47 * by the owner LWP. Therefore struct cpu_info::ci_pcu_curlwp[id] 48 * may only be changed by current CPU, and lwp_t::l_pcu_cpu[id] may 49 * only be unset by the CPU which has PCU state loaded. 50 * 51 * There is a race condition: LWP may have a PCU state on a remote CPU, 52 * which it requests to be released via cross-call. At the same time, 53 * other LWP on remote CPU might release existing PCU state and load 54 * its own one. Cross-call may arrive after this and release different 55 * PCU state than intended. In such case, such LWP would re-load its 56 * PCU state again. 57 */ 58 59 #include <sys/cdefs.h> 60 __KERNEL_RCSID(0, "$NetBSD: subr_pcu.c,v 1.9 2011/06/13 21:32:42 matt Exp $"); 61 62 #include <sys/param.h> 63 #include <sys/cpu.h> 64 #include <sys/lwp.h> 65 #include <sys/pcu.h> 66 #include <sys/xcall.h> 67 68 #if PCU_UNIT_COUNT > 0 69 70 static void pcu_lwp_op(const pcu_ops_t *, lwp_t *, int); 71 72 #define PCU_SAVE 0x01 /* Save PCU state to the LWP. */ 73 #define PCU_RELEASE 0x02 /* Release PCU state on the CPU. */ 74 75 /* XXX */ 76 extern const pcu_ops_t * const pcu_ops_md_defs[]; 77 78 void 79 pcu_switchpoint(lwp_t *l) 80 { 81 const uint32_t pcu_inuse = l->l_pcu_used; 82 u_int id; 83 /* int s; */ 84 85 KASSERT(l == curlwp); 86 87 if (__predict_true(pcu_inuse == 0)) { 88 /* PCUs are not in use. */ 89 return; 90 } 91 /* s = splsoftclock(); */ 92 for (id = 0; id < PCU_UNIT_COUNT; id++) { 93 if ((pcu_inuse & (1 << id)) == 0) { 94 continue; 95 } 96 struct cpu_info * const pcu_ci = l->l_pcu_cpu[id]; 97 if (pcu_ci == NULL || pcu_ci == l->l_cpu) { 98 continue; 99 } 100 const pcu_ops_t * const pcu = pcu_ops_md_defs[id]; 101 pcu->pcu_state_release(l); 102 } 103 /* splx(s); */ 104 } 105 106 void 107 pcu_discard_all(lwp_t *l) 108 { 109 const uint32_t pcu_inuse = l->l_pcu_used; 110 111 KASSERT(l == curlwp || ((l->l_flag & LW_SYSTEM) && pcu_inuse == 0)); 112 113 if (__predict_true(pcu_inuse == 0)) { 114 /* PCUs are not in use. */ 115 return; 116 } 117 const int s = splsoftclock(); 118 for (u_int id = 0; id < PCU_UNIT_COUNT; id++) { 119 if ((pcu_inuse & (1 << id)) == 0) { 120 continue; 121 } 122 if (__predict_true(l->l_pcu_cpu[id] == NULL)) { 123 continue; 124 } 125 const pcu_ops_t * const pcu = pcu_ops_md_defs[id]; 126 /* 127 * We aren't releasing since this LWP isn't giving up PCU, 128 * just saving it. 129 */ 130 pcu_lwp_op(pcu, l, PCU_RELEASE); 131 } 132 l->l_pcu_used = 0; 133 splx(s); 134 } 135 136 void 137 pcu_save_all(lwp_t *l) 138 { 139 const uint32_t pcu_inuse = l->l_pcu_used; 140 const int flags = PCU_SAVE | (l->l_flag & LW_WCORE ? PCU_RELEASE : 0); 141 142 /* 143 * Normally we save for the current LWP, but sometimes we get called 144 * with a different LWP (forking a system LWP or doing a coredump of 145 * a process with multiple threads) and we need to deal with that. 146 */ 147 KASSERT(l == curlwp 148 || (((l->l_flag & LW_SYSTEM) 149 || (curlwp->l_proc == l->l_proc && l->l_stat == LSSUSPENDED)) 150 && pcu_inuse == 0)); 151 152 if (__predict_true(pcu_inuse == 0)) { 153 /* PCUs are not in use. */ 154 return; 155 } 156 const int s = splsoftclock(); 157 for (u_int id = 0; id < PCU_UNIT_COUNT; id++) { 158 if ((pcu_inuse & (1 << id)) == 0) { 159 continue; 160 } 161 if (__predict_true(l->l_pcu_cpu[id] == NULL)) { 162 continue; 163 } 164 const pcu_ops_t * const pcu = pcu_ops_md_defs[id]; 165 /* 166 * We aren't releasing since this LWP isn't giving up PCU, 167 * just saving it. 168 */ 169 pcu_lwp_op(pcu, l, flags); 170 } 171 splx(s); 172 } 173 174 /* 175 * pcu_do_op: save/release PCU state on the current CPU. 176 * 177 * => Must be called at IPL_SOFTCLOCK or from the soft-interrupt. 178 */ 179 static inline void 180 pcu_do_op(const pcu_ops_t *pcu, lwp_t * const l, const int flags) 181 { 182 struct cpu_info * const ci = curcpu(); 183 const u_int id = pcu->pcu_id; 184 185 KASSERT(l->l_pcu_cpu[id] == ci); 186 187 if (flags & PCU_SAVE) { 188 pcu->pcu_state_save(l); 189 } 190 if (flags & PCU_RELEASE) { 191 pcu->pcu_state_release(l); 192 ci->ci_pcu_curlwp[id] = NULL; 193 l->l_pcu_cpu[id] = NULL; 194 } 195 } 196 197 /* 198 * pcu_cpu_op: helper routine to call pcu_do_op() via xcall(9) or 199 * by pcu_load. 200 */ 201 static void 202 pcu_cpu_op(const pcu_ops_t *pcu, const int flags) 203 { 204 const u_int id = pcu->pcu_id; 205 lwp_t * const l = curcpu()->ci_pcu_curlwp[id]; 206 207 //KASSERT(cpu_softintr_p()); 208 209 /* If no state - nothing to do. */ 210 if (l == NULL) { 211 return; 212 } 213 pcu_do_op(pcu, l, flags); 214 } 215 216 /* 217 * pcu_lwp_op: perform PCU state save, release or both operations on LWP. 218 */ 219 static void 220 pcu_lwp_op(const pcu_ops_t *pcu, lwp_t *l, int flags) 221 { 222 const u_int id = pcu->pcu_id; 223 struct cpu_info *ci; 224 uint64_t where; 225 int s; 226 227 /* 228 * Caller should have re-checked if there is any state to manage. 229 * Block the interrupts and inspect again, since cross-call sent 230 * by remote CPU could have changed the state. 231 */ 232 s = splsoftclock(); 233 ci = l->l_pcu_cpu[id]; 234 if (ci == curcpu()) { 235 /* 236 * State is on the current CPU - just perform the operations. 237 */ 238 KASSERTMSG(ci->ci_pcu_curlwp[id] == l, 239 ("%s: cpu%u: pcu_curlwp[%u] (%p) != l (%p)", 240 __func__, cpu_index(ci), id, ci->ci_pcu_curlwp[id], l)); 241 pcu_do_op(pcu, l, flags); 242 splx(s); 243 return; 244 } 245 splx(s); 246 247 if (__predict_false(ci == NULL)) { 248 /* Cross-call has won the race - no state to manage. */ 249 return; 250 } 251 252 /* 253 * State is on the remote CPU - perform the operations there. 254 * Note: there is a race condition; see description in the top. 255 */ 256 where = xc_unicast(XC_HIGHPRI, (xcfunc_t)pcu_cpu_op, 257 __UNCONST(pcu), (void *)(uintptr_t)flags, ci); 258 xc_wait(where); 259 260 KASSERT((flags & PCU_RELEASE) == 0 || l->l_pcu_cpu[id] == NULL); 261 } 262 263 /* 264 * pcu_load: load/initialize the PCU state of current LWP on current CPU. 265 */ 266 void 267 pcu_load(const pcu_ops_t *pcu) 268 { 269 const u_int id = pcu->pcu_id; 270 struct cpu_info *ci, *curci; 271 lwp_t * const l = curlwp; 272 uint64_t where; 273 int s; 274 275 KASSERT(!cpu_intr_p() && !cpu_softintr_p()); 276 277 s = splsoftclock(); 278 curci = curcpu(); 279 ci = l->l_pcu_cpu[id]; 280 281 /* Does this CPU already have our PCU state loaded? */ 282 if (ci == curci) { 283 KASSERT(curci->ci_pcu_curlwp[id] == l); 284 splx(s); 285 return; 286 } 287 288 /* If PCU state of this LWP is on the remote CPU - save it there. */ 289 if (ci) { 290 splx(s); 291 /* Note: there is a race; see description in the top. */ 292 where = xc_unicast(XC_HIGHPRI, (xcfunc_t)pcu_cpu_op, 293 __UNCONST(pcu), (void *)(PCU_SAVE | PCU_RELEASE), ci); 294 xc_wait(where); 295 296 /* Enter IPL_SOFTCLOCK and re-fetch the current CPU. */ 297 s = splsoftclock(); 298 curci = curcpu(); 299 } 300 KASSERT(l->l_pcu_cpu[id] == NULL); 301 302 /* Save the PCU state on the current CPU, if there is any. */ 303 pcu_cpu_op(pcu, PCU_SAVE | PCU_RELEASE); 304 KASSERT(curci->ci_pcu_curlwp[id] == NULL); 305 306 /* 307 * Finally, load the state for this LWP on this CPU. Indicate to 308 * load function whether PCU was used before. Note the usage. 309 */ 310 pcu->pcu_state_load(l, ((1 << id) & l->l_pcu_used) != 0); 311 curci->ci_pcu_curlwp[id] = l; 312 l->l_pcu_cpu[id] = curci; 313 l->l_pcu_used |= (1 << id); 314 splx(s); 315 } 316 317 /* 318 * pcu_discard: discard the PCU state of current LWP. 319 */ 320 void 321 pcu_discard(const pcu_ops_t *pcu) 322 { 323 const u_int id = pcu->pcu_id; 324 lwp_t * const l = curlwp; 325 326 KASSERT(!cpu_intr_p() && !cpu_softintr_p()); 327 328 if (__predict_true(l->l_pcu_cpu[id] == NULL)) { 329 return; 330 } 331 pcu_lwp_op(pcu, l, PCU_RELEASE); 332 l->l_pcu_used &= ~(1 << id); 333 } 334 335 /* 336 * pcu_save_lwp: save PCU state to the given LWP. 337 */ 338 void 339 pcu_save(const pcu_ops_t *pcu) 340 { 341 const u_int id = pcu->pcu_id; 342 lwp_t * const l = curlwp; 343 344 KASSERT(!cpu_intr_p() && !cpu_softintr_p()); 345 346 if (__predict_true(l->l_pcu_cpu[id] == NULL)) { 347 return; 348 } 349 pcu_lwp_op(pcu, l, PCU_SAVE | PCU_RELEASE); 350 } 351 352 /* 353 * pcu_used: return true if PCU was used (pcu_load() case) by the LWP. 354 */ 355 bool 356 pcu_used_p(const pcu_ops_t *pcu) 357 { 358 const u_int id = pcu->pcu_id; 359 lwp_t * const l = curlwp; 360 361 return l->l_pcu_used & (1 << id); 362 } 363 364 #endif /* PCU_UNIT_COUNT > 0 */ 365