1 /* $NetBSD: subr_pcu.c,v 1.1 2011/02/17 18:32:29 rmind 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 1.1 2011/02/17 18:32:29 rmind 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 #define PCU_SAVE 0x01 /* Save PCU state to the LWP. */ 69 #define PCU_RELEASE 0x02 /* Release PCU state on the CPU. */ 70 71 #if 0 72 /* 73 * pcu_init_lwp: initialize PCU structures for LWP. 74 */ 75 void 76 pcu_init_lwp(lwp_t *l) 77 { 78 79 memset(l->l_pcu_cpu, 0, sizeof(uint32_t) * PCU_UNIT_COUNT); 80 l->l_pcu_used = 0; 81 } 82 #endif 83 84 /* 85 * pcu_cpu_op: save/release PCU state on the current CPU. 86 * 87 * => Must be called at IPL_SOFTCLOCK or from the soft-interrupt. 88 */ 89 static void 90 pcu_cpu_op(const pcu_ops_t *pcu, const int flags) 91 { 92 const u_int id = pcu->pcu_id; 93 struct cpu_info *ci = curcpu(); 94 lwp_t *l = ci->ci_pcu_curlwp[id]; 95 96 /* If no state - nothing to do. */ 97 if (l == NULL) { 98 return; 99 } 100 if (flags & PCU_SAVE) { 101 pcu->pcu_state_save(l); 102 } 103 if (flags & PCU_RELEASE) { 104 ci->ci_pcu_curlwp[id] = NULL; 105 l->l_pcu_cpu[id] = NULL; 106 } 107 } 108 109 /* 110 * pcu_lwp_op: perform PCU state save, release or both operations on LWP. 111 */ 112 static void 113 pcu_lwp_op(const pcu_ops_t *pcu, lwp_t *l, int flags) 114 { 115 const u_int id = pcu->pcu_id; 116 struct cpu_info *ci; 117 uint64_t where; 118 int s; 119 120 /* 121 * Caller should have re-checked if there is any state to manage. 122 * Block the interrupts and inspect again, since cross-call sent 123 * by remote CPU could have changed the state. 124 */ 125 s = splsoftclock(); 126 ci = l->l_pcu_cpu[id]; 127 if (ci == curcpu()) { 128 /* 129 * State is on the current CPU - just perform the operations. 130 */ 131 KASSERT(ci->ci_pcu_curlwp[id] == l); 132 133 if (flags & PCU_SAVE) { 134 pcu->pcu_state_save(l); 135 } 136 if (flags & PCU_RELEASE) { 137 ci->ci_pcu_curlwp[id] = NULL; 138 l->l_pcu_cpu[id] = NULL; 139 } 140 splx(s); 141 return; 142 } 143 splx(s); 144 145 if (__predict_false(ci == NULL)) { 146 /* Cross-call has won the race - no state to manage. */ 147 return; 148 } 149 150 /* 151 * State is on the remote CPU - perform the operations there. 152 * Note: there is a race condition; see description in the top. 153 */ 154 where = xc_unicast(XC_HIGHPRI, (xcfunc_t)pcu_cpu_op, 155 __UNCONST(pcu), (void *)(uintptr_t)flags, ci); 156 xc_wait(where); 157 158 KASSERT((flags & PCU_RELEASE) == 0 || l->l_pcu_cpu[id] == NULL); 159 } 160 161 /* 162 * pcu_load: load/initialize the PCU state of current LWP on current CPU. 163 */ 164 void 165 pcu_load(const pcu_ops_t *pcu) 166 { 167 const u_int id = pcu->pcu_id; 168 struct cpu_info *ci, *curci; 169 lwp_t *l = curlwp; 170 uint64_t where; 171 int s; 172 173 KASSERT(!cpu_intr_p() && !cpu_softintr_p()); 174 175 s = splsoftclock(); 176 curci = curcpu(); 177 ci = l->l_pcu_cpu[id]; 178 179 /* Does this CPU already have our PCU state loaded? */ 180 if (ci == curci) { 181 KASSERT(curci->ci_pcu_curlwp[id] == l); 182 splx(s); 183 return; 184 } 185 186 /* If PCU state of this LWP is on the remote CPU - save it there. */ 187 if (ci) { 188 splx(s); 189 /* Note: there is a race; see description in the top. */ 190 where = xc_unicast(XC_HIGHPRI, (xcfunc_t)pcu_cpu_op, 191 __UNCONST(pcu), (void *)(PCU_SAVE | PCU_RELEASE), ci); 192 xc_wait(where); 193 194 /* Enter IPL_SOFTCLOCK and re-fetch the current CPU. */ 195 s = splsoftclock(); 196 curci = curcpu(); 197 } 198 KASSERT(l->l_pcu_cpu[id] == NULL); 199 200 /* Save the PCU state on the current CPU, if there is any. */ 201 pcu_cpu_op(pcu, PCU_SAVE | PCU_RELEASE); 202 KASSERT(curci->ci_pcu_curlwp[id] == NULL); 203 204 /* 205 * Finally, load the state for this LWP on this CPU. Indicate to 206 * load function whether PCU was used before. Note the usage. 207 */ 208 pcu->pcu_state_load(l, ((1 << id) & l->l_pcu_used) != 0); 209 curci->ci_pcu_curlwp[id] = l; 210 l->l_pcu_cpu[id] = curci; 211 l->l_pcu_used |= (1 << id); 212 splx(s); 213 } 214 215 /* 216 * pcu_discard: discard the PCU state of current LWP. 217 */ 218 void 219 pcu_discard(const pcu_ops_t *pcu) 220 { 221 const u_int id = pcu->pcu_id; 222 lwp_t *l = curlwp; 223 224 KASSERT(!cpu_intr_p() && !cpu_softintr_p()); 225 226 if (__predict_true(l->l_pcu_cpu[id] == NULL)) { 227 return; 228 } 229 pcu_lwp_op(pcu, l, PCU_RELEASE); 230 l->l_pcu_used &= ~(1 << id); 231 } 232 233 /* 234 * pcu_save_lwp: save PCU state to the given LWP. 235 */ 236 void 237 pcu_save_lwp(const pcu_ops_t *pcu, lwp_t *l) 238 { 239 const u_int id = pcu->pcu_id; 240 241 KASSERT(!cpu_intr_p() && !cpu_softintr_p()); 242 243 if (__predict_true(l->l_pcu_cpu[id] == NULL)) { 244 return; 245 } 246 pcu_lwp_op(pcu, l, PCU_SAVE | PCU_RELEASE); 247 } 248 249 /* 250 * pcu_used: return true if PCU was used (pcu_load() case) by the LWP. 251 */ 252 bool 253 pcu_used(const pcu_ops_t *pcu, lwp_t *l) 254 { 255 const u_int id = pcu->pcu_id; 256 257 return l->l_pcu_used & (1 << id); 258 } 259