1 /* 2 * QEMU TCG Single Threaded vCPUs implementation 3 * 4 * Copyright (c) 2003-2008 Fabrice Bellard 5 * Copyright (c) 2014 Red Hat Inc. 6 * 7 * Permission is hereby granted, free of charge, to any person obtaining a copy 8 * of this software and associated documentation files (the "Software"), to deal 9 * in the Software without restriction, including without limitation the rights 10 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell 11 * copies of the Software, and to permit persons to whom the Software is 12 * furnished to do so, subject to the following conditions: 13 * 14 * The above copyright notice and this permission notice shall be included in 15 * all copies or substantial portions of the Software. 16 * 17 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR 18 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, 19 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL 20 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER 21 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, 22 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN 23 * THE SOFTWARE. 24 */ 25 26 #include "qemu/osdep.h" 27 #include "qemu/lockable.h" 28 #include "sysemu/tcg.h" 29 #include "sysemu/replay.h" 30 #include "sysemu/cpu-timers.h" 31 #include "qemu/main-loop.h" 32 #include "qemu/notify.h" 33 #include "qemu/guest-random.h" 34 #include "exec/exec-all.h" 35 #include "tcg/startup.h" 36 #include "tcg-accel-ops.h" 37 #include "tcg-accel-ops-rr.h" 38 #include "tcg-accel-ops-icount.h" 39 40 /* Kick all RR vCPUs */ 41 void rr_kick_vcpu_thread(CPUState *unused) 42 { 43 CPUState *cpu; 44 45 CPU_FOREACH(cpu) { 46 cpu_exit(cpu); 47 }; 48 } 49 50 /* 51 * TCG vCPU kick timer 52 * 53 * The kick timer is responsible for moving single threaded vCPU 54 * emulation on to the next vCPU. If more than one vCPU is running a 55 * timer event we force a cpu->exit so the next vCPU can get 56 * scheduled. 57 * 58 * The timer is removed if all vCPUs are idle and restarted again once 59 * idleness is complete. 60 */ 61 62 static QEMUTimer *rr_kick_vcpu_timer; 63 static CPUState *rr_current_cpu; 64 65 static inline int64_t rr_next_kick_time(void) 66 { 67 return qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL) + TCG_KICK_PERIOD; 68 } 69 70 /* Kick the currently round-robin scheduled vCPU to next */ 71 static void rr_kick_next_cpu(void) 72 { 73 CPUState *cpu; 74 do { 75 cpu = qatomic_read(&rr_current_cpu); 76 if (cpu) { 77 cpu_exit(cpu); 78 } 79 /* Finish kicking this cpu before reading again. */ 80 smp_mb(); 81 } while (cpu != qatomic_read(&rr_current_cpu)); 82 } 83 84 static void rr_kick_thread(void *opaque) 85 { 86 timer_mod(rr_kick_vcpu_timer, rr_next_kick_time()); 87 rr_kick_next_cpu(); 88 } 89 90 static void rr_start_kick_timer(void) 91 { 92 if (!rr_kick_vcpu_timer && CPU_NEXT(first_cpu)) { 93 rr_kick_vcpu_timer = timer_new_ns(QEMU_CLOCK_VIRTUAL, 94 rr_kick_thread, NULL); 95 } 96 if (rr_kick_vcpu_timer && !timer_pending(rr_kick_vcpu_timer)) { 97 timer_mod(rr_kick_vcpu_timer, rr_next_kick_time()); 98 } 99 } 100 101 static void rr_stop_kick_timer(void) 102 { 103 if (rr_kick_vcpu_timer && timer_pending(rr_kick_vcpu_timer)) { 104 timer_del(rr_kick_vcpu_timer); 105 } 106 } 107 108 static void rr_wait_io_event(void) 109 { 110 CPUState *cpu; 111 112 while (all_cpu_threads_idle() && replay_can_wait()) { 113 rr_stop_kick_timer(); 114 qemu_cond_wait_bql(first_cpu->halt_cond); 115 } 116 117 rr_start_kick_timer(); 118 119 CPU_FOREACH(cpu) { 120 qemu_wait_io_event_common(cpu); 121 } 122 } 123 124 /* 125 * Destroy any remaining vCPUs which have been unplugged and have 126 * finished running 127 */ 128 static void rr_deal_with_unplugged_cpus(void) 129 { 130 CPUState *cpu; 131 132 CPU_FOREACH(cpu) { 133 if (cpu->unplug && !cpu_can_run(cpu)) { 134 tcg_cpu_destroy(cpu); 135 break; 136 } 137 } 138 } 139 140 static void rr_force_rcu(Notifier *notify, void *data) 141 { 142 rr_kick_next_cpu(); 143 } 144 145 /* 146 * Calculate the number of CPUs that we will process in a single iteration of 147 * the main CPU thread loop so that we can fairly distribute the instruction 148 * count across CPUs. 149 * 150 * The CPU count is cached based on the CPU list generation ID to avoid 151 * iterating the list every time. 152 */ 153 static int rr_cpu_count(void) 154 { 155 static unsigned int last_gen_id = ~0; 156 static int cpu_count; 157 CPUState *cpu; 158 159 QEMU_LOCK_GUARD(&qemu_cpu_list_lock); 160 161 if (cpu_list_generation_id_get() != last_gen_id) { 162 cpu_count = 0; 163 CPU_FOREACH(cpu) { 164 ++cpu_count; 165 } 166 last_gen_id = cpu_list_generation_id_get(); 167 } 168 169 return cpu_count; 170 } 171 172 /* 173 * In the single-threaded case each vCPU is simulated in turn. If 174 * there is more than a single vCPU we create a simple timer to kick 175 * the vCPU and ensure we don't get stuck in a tight loop in one vCPU. 176 * This is done explicitly rather than relying on side-effects 177 * elsewhere. 178 */ 179 180 static void *rr_cpu_thread_fn(void *arg) 181 { 182 Notifier force_rcu; 183 CPUState *cpu = arg; 184 185 assert(tcg_enabled()); 186 rcu_register_thread(); 187 force_rcu.notify = rr_force_rcu; 188 rcu_add_force_rcu_notifier(&force_rcu); 189 tcg_register_thread(); 190 191 bql_lock(); 192 qemu_thread_get_self(cpu->thread); 193 194 cpu->thread_id = qemu_get_thread_id(); 195 cpu->neg.can_do_io = true; 196 cpu_thread_signal_created(cpu); 197 qemu_guest_random_seed_thread_part2(cpu->random_seed); 198 199 /* wait for initial kick-off after machine start */ 200 while (first_cpu->stopped) { 201 qemu_cond_wait_bql(first_cpu->halt_cond); 202 203 /* process any pending work */ 204 CPU_FOREACH(cpu) { 205 current_cpu = cpu; 206 qemu_wait_io_event_common(cpu); 207 } 208 } 209 210 rr_start_kick_timer(); 211 212 cpu = first_cpu; 213 214 /* process any pending work */ 215 cpu->exit_request = 1; 216 217 while (1) { 218 /* Only used for icount_enabled() */ 219 int64_t cpu_budget = 0; 220 221 bql_unlock(); 222 replay_mutex_lock(); 223 bql_lock(); 224 225 if (icount_enabled()) { 226 int cpu_count = rr_cpu_count(); 227 228 /* Account partial waits to QEMU_CLOCK_VIRTUAL. */ 229 icount_account_warp_timer(); 230 /* 231 * Run the timers here. This is much more efficient than 232 * waking up the I/O thread and waiting for completion. 233 */ 234 icount_handle_deadline(); 235 236 cpu_budget = icount_percpu_budget(cpu_count); 237 } 238 239 replay_mutex_unlock(); 240 241 if (!cpu) { 242 cpu = first_cpu; 243 } 244 245 while (cpu && cpu_work_list_empty(cpu) && !cpu->exit_request) { 246 /* Store rr_current_cpu before evaluating cpu_can_run(). */ 247 qatomic_set_mb(&rr_current_cpu, cpu); 248 249 current_cpu = cpu; 250 251 qemu_clock_enable(QEMU_CLOCK_VIRTUAL, 252 (cpu->singlestep_enabled & SSTEP_NOTIMER) == 0); 253 254 if (cpu_can_run(cpu)) { 255 int r; 256 257 bql_unlock(); 258 if (icount_enabled()) { 259 icount_prepare_for_run(cpu, cpu_budget); 260 } 261 r = tcg_cpu_exec(cpu); 262 if (icount_enabled()) { 263 icount_process_data(cpu); 264 } 265 bql_lock(); 266 267 if (r == EXCP_DEBUG) { 268 cpu_handle_guest_debug(cpu); 269 break; 270 } else if (r == EXCP_ATOMIC) { 271 bql_unlock(); 272 cpu_exec_step_atomic(cpu); 273 bql_lock(); 274 break; 275 } 276 } else if (cpu->stop) { 277 if (cpu->unplug) { 278 cpu = CPU_NEXT(cpu); 279 } 280 break; 281 } 282 283 cpu = CPU_NEXT(cpu); 284 } /* while (cpu && !cpu->exit_request).. */ 285 286 /* Does not need a memory barrier because a spurious wakeup is okay. */ 287 qatomic_set(&rr_current_cpu, NULL); 288 289 if (cpu && cpu->exit_request) { 290 qatomic_set_mb(&cpu->exit_request, 0); 291 } 292 293 if (icount_enabled() && all_cpu_threads_idle()) { 294 /* 295 * When all cpus are sleeping (e.g in WFI), to avoid a deadlock 296 * in the main_loop, wake it up in order to start the warp timer. 297 */ 298 qemu_notify_event(); 299 } 300 301 rr_wait_io_event(); 302 rr_deal_with_unplugged_cpus(); 303 } 304 305 rcu_remove_force_rcu_notifier(&force_rcu); 306 rcu_unregister_thread(); 307 return NULL; 308 } 309 310 void rr_start_vcpu_thread(CPUState *cpu) 311 { 312 char thread_name[VCPU_THREAD_NAME_SIZE]; 313 static QemuCond *single_tcg_halt_cond; 314 static QemuThread *single_tcg_cpu_thread; 315 316 g_assert(tcg_enabled()); 317 tcg_cpu_init_cflags(cpu, false); 318 319 if (!single_tcg_cpu_thread) { 320 single_tcg_halt_cond = cpu->halt_cond; 321 single_tcg_cpu_thread = cpu->thread; 322 323 /* share a single thread for all cpus with TCG */ 324 snprintf(thread_name, VCPU_THREAD_NAME_SIZE, "ALL CPUs/TCG"); 325 qemu_thread_create(cpu->thread, thread_name, 326 rr_cpu_thread_fn, 327 cpu, QEMU_THREAD_JOINABLE); 328 } else { 329 /* we share the thread, dump spare data */ 330 g_free(cpu->thread); 331 qemu_cond_destroy(cpu->halt_cond); 332 cpu->thread = single_tcg_cpu_thread; 333 cpu->halt_cond = single_tcg_halt_cond; 334 335 /* copy the stuff done at start of rr_cpu_thread_fn */ 336 cpu->thread_id = first_cpu->thread_id; 337 cpu->neg.can_do_io = 1; 338 cpu->created = true; 339 } 340 } 341