accel/tcg/tcg-accel-ops-rr.c

   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 "sysemu/tcg.h"
  28 #include "sysemu/replay.h"
  29 #include "sysemu/cpu-timers.h"
  30 #include "qemu/main-loop.h"
  31 #include "qemu/notify.h"
  32 #include "qemu/guest-random.h"
  33 #include "exec/exec-all.h"
  34
  35 #include "tcg-accel-ops.h"
  36 #include "tcg-accel-ops-rr.h"
  37 #include "tcg-accel-ops-icount.h"
  38
  39 /* Kick all RR vCPUs */
  40 void rr_kick_vcpu_thread(CPUState *unused)
  41 {
  42     CPUState *cpu;
  43
  44     CPU_FOREACH(cpu) {
  45         cpu_exit(cpu);
  46     };
  47 }
  48
  49 /*
  50  * TCG vCPU kick timer
  51  *
  52  * The kick timer is responsible for moving single threaded vCPU
  53  * emulation on to the next vCPU. If more than one vCPU is running a
  54  * timer event with force a cpu->exit so the next vCPU can get
  55  * scheduled.
  56  *
  57  * The timer is removed if all vCPUs are idle and restarted again once
  58  * idleness is complete.
  59  */
  60
  61 static QEMUTimer *rr_kick_vcpu_timer;
  62 static CPUState *rr_current_cpu;
  63
  64 static inline int64_t rr_next_kick_time(void)
  65 {
  66     return qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL) + TCG_KICK_PERIOD;
  67 }
  68
  69 /* Kick the currently round-robin scheduled vCPU to next */
  70 static void rr_kick_next_cpu(void)
  71 {
  72     CPUState *cpu;
  73     do {
  74         cpu = qatomic_mb_read(&rr_current_cpu);
  75         if (cpu) {
  76             cpu_exit(cpu);
  77         }
  78     } while (cpu != qatomic_mb_read(&rr_current_cpu));
  79 }
  80
  81 static void rr_kick_thread(void *opaque)
  82 {
  83     timer_mod(rr_kick_vcpu_timer, rr_next_kick_time());
  84     rr_kick_next_cpu();
  85 }
  86
  87 static void rr_start_kick_timer(void)
  88 {
  89     if (!rr_kick_vcpu_timer && CPU_NEXT(first_cpu)) {
  90         rr_kick_vcpu_timer = timer_new_ns(QEMU_CLOCK_VIRTUAL,
  91                                            rr_kick_thread, NULL);
  92     }
  93     if (rr_kick_vcpu_timer && !timer_pending(rr_kick_vcpu_timer)) {
  94         timer_mod(rr_kick_vcpu_timer, rr_next_kick_time());
  95     }
  96 }
  97
  98 static void rr_stop_kick_timer(void)
  99 {
 100     if (rr_kick_vcpu_timer && timer_pending(rr_kick_vcpu_timer)) {
 101         timer_del(rr_kick_vcpu_timer);
 102     }
 103 }
 104
 105 static void rr_wait_io_event(void)
 106 {
 107     CPUState *cpu;
 108
 109     while (all_cpu_threads_idle()) {
 110         rr_stop_kick_timer();
 111         qemu_cond_wait_iothread(first_cpu->halt_cond);
 112     }
 113
 114     rr_start_kick_timer();
 115
 116     CPU_FOREACH(cpu) {
 117         qemu_wait_io_event_common(cpu);
 118     }
 119 }
 120
 121 /*
 122  * Destroy any remaining vCPUs which have been unplugged and have
 123  * finished running
 124  */
 125 static void rr_deal_with_unplugged_cpus(void)
 126 {
 127     CPUState *cpu;
 128
 129     CPU_FOREACH(cpu) {
 130         if (cpu->unplug && !cpu_can_run(cpu)) {
 131             tcg_cpus_destroy(cpu);
 132             break;
 133         }
 134     }
 135 }
 136
 137 static void rr_force_rcu(Notifier *notify, void *data)
 138 {
 139     rr_kick_next_cpu();
 140 }
 141
 142 /*
 143  * In the single-threaded case each vCPU is simulated in turn. If
 144  * there is more than a single vCPU we create a simple timer to kick
 145  * the vCPU and ensure we don't get stuck in a tight loop in one vCPU.
 146  * This is done explicitly rather than relying on side-effects
 147  * elsewhere.
 148  */
 149
 150 static void *rr_cpu_thread_fn(void *arg)
 151 {
 152     Notifier force_rcu;
 153     CPUState *cpu = arg;
 154
 155     g_assert(tcg_enabled());
 156     tcg_cpu_init_cflags(cpu, false);
 157
 158     rcu_register_thread();
 159     force_rcu.notify = rr_force_rcu;
 160     rcu_add_force_rcu_notifier(&force_rcu);
 161     tcg_register_thread();
 162
 163     qemu_mutex_lock_iothread();
 164     qemu_thread_get_self(cpu->thread);
 165
 166     cpu->thread_id = qemu_get_thread_id();
 167     cpu->can_do_io = 1;
 168     cpu_thread_signal_created(cpu);
 169     qemu_guest_random_seed_thread_part2(cpu->random_seed);
 170
 171     /* wait for initial kick-off after machine start */
 172     while (first_cpu->stopped) {
 173         qemu_cond_wait_iothread(first_cpu->halt_cond);
 174
 175         /* process any pending work */
 176         CPU_FOREACH(cpu) {
 177             current_cpu = cpu;
 178             qemu_wait_io_event_common(cpu);
 179         }
 180     }
 181
 182     rr_start_kick_timer();
 183
 184     cpu = first_cpu;
 185
 186     /* process any pending work */
 187     cpu->exit_request = 1;
 188
 189     while (1) {
 190         qemu_mutex_unlock_iothread();
 191         replay_mutex_lock();
 192         qemu_mutex_lock_iothread();
 193
 194         if (icount_enabled()) {
 195             /* Account partial waits to QEMU_CLOCK_VIRTUAL.  */
 196             icount_account_warp_timer();
 197             /*
 198              * Run the timers here.  This is much more efficient than
 199              * waking up the I/O thread and waiting for completion.
 200              */
 201             icount_handle_deadline();
 202         }
 203
 204         replay_mutex_unlock();
 205
 206         if (!cpu) {
 207             cpu = first_cpu;
 208         }
 209
 210         while (cpu && cpu_work_list_empty(cpu) && !cpu->exit_request) {
 211
 212             qatomic_mb_set(&rr_current_cpu, cpu);
 213             current_cpu = cpu;
 214
 215             qemu_clock_enable(QEMU_CLOCK_VIRTUAL,
 216                               (cpu->singlestep_enabled & SSTEP_NOTIMER) == 0);
 217
 218             if (cpu_can_run(cpu)) {
 219                 int r;
 220
 221                 qemu_mutex_unlock_iothread();
 222                 if (icount_enabled()) {
 223                     icount_prepare_for_run(cpu);
 224                 }
 225                 r = tcg_cpus_exec(cpu);
 226                 if (icount_enabled()) {
 227                     icount_process_data(cpu);
 228                 }
 229                 qemu_mutex_lock_iothread();
 230
 231                 if (r == EXCP_DEBUG) {
 232                     cpu_handle_guest_debug(cpu);
 233                     break;
 234                 } else if (r == EXCP_ATOMIC) {
 235                     qemu_mutex_unlock_iothread();
 236                     cpu_exec_step_atomic(cpu);
 237                     qemu_mutex_lock_iothread();
 238                     break;
 239                 }
 240             } else if (cpu->stop) {
 241                 if (cpu->unplug) {
 242                     cpu = CPU_NEXT(cpu);
 243                 }
 244                 break;
 245             }
 246
 247             cpu = CPU_NEXT(cpu);
 248         } /* while (cpu && !cpu->exit_request).. */
 249
 250         /* Does not need qatomic_mb_set because a spurious wakeup is okay.  */
 251         qatomic_set(&rr_current_cpu, NULL);
 252
 253         if (cpu && cpu->exit_request) {
 254             qatomic_mb_set(&cpu->exit_request, 0);
 255         }
 256
 257         if (icount_enabled() && all_cpu_threads_idle()) {
 258             /*
 259              * When all cpus are sleeping (e.g in WFI), to avoid a deadlock
 260              * in the main_loop, wake it up in order to start the warp timer.
 261              */
 262             qemu_notify_event();
 263         }
 264
 265         rr_wait_io_event();
 266         rr_deal_with_unplugged_cpus();
 267     }
 268
 269     rcu_remove_force_rcu_notifier(&force_rcu);
 270     rcu_unregister_thread();
 271     return NULL;
 272 }
 273
 274 void rr_start_vcpu_thread(CPUState *cpu)
 275 {
 276     char thread_name[VCPU_THREAD_NAME_SIZE];
 277     static QemuCond *single_tcg_halt_cond;
 278     static QemuThread *single_tcg_cpu_thread;
 279
 280     if (!single_tcg_cpu_thread) {
 281         cpu->thread = g_new0(QemuThread, 1);
 282         cpu->halt_cond = g_new0(QemuCond, 1);
 283         qemu_cond_init(cpu->halt_cond);
 284
 285         /* share a single thread for all cpus with TCG */
 286         snprintf(thread_name, VCPU_THREAD_NAME_SIZE, "ALL CPUs/TCG");
 287         qemu_thread_create(cpu->thread, thread_name,
 288                            rr_cpu_thread_fn,
 289                            cpu, QEMU_THREAD_JOINABLE);
 290
 291         single_tcg_halt_cond = cpu->halt_cond;
 292         single_tcg_cpu_thread = cpu->thread;
 293 #ifdef _WIN32
 294         cpu->hThread = qemu_thread_get_handle(cpu->thread);
 295 #endif
 296     } else {
 297         /* we share the thread */
 298         cpu->thread = single_tcg_cpu_thread;
 299         cpu->halt_cond = single_tcg_halt_cond;
 300         cpu->thread_id = first_cpu->thread_id;
 301         cpu->can_do_io = 1;
 302         cpu->created = true;
 303     }
 304 }