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 "qemu-common.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
  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 with 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_mb_read(&rr_current_cpu);
  76         if (cpu) {
  77             cpu_exit(cpu);
  78         }
  79     } while (cpu != qatomic_mb_read(&rr_current_cpu));
  80 }
  81
  82 static void rr_kick_thread(void *opaque)
  83 {
  84     timer_mod(rr_kick_vcpu_timer, rr_next_kick_time());
  85     rr_kick_next_cpu();
  86 }
  87
  88 static void rr_start_kick_timer(void)
  89 {
  90     if (!rr_kick_vcpu_timer && CPU_NEXT(first_cpu)) {
  91         rr_kick_vcpu_timer = timer_new_ns(QEMU_CLOCK_VIRTUAL,
  92                                            rr_kick_thread, NULL);
  93     }
  94     if (rr_kick_vcpu_timer && !timer_pending(rr_kick_vcpu_timer)) {
  95         timer_mod(rr_kick_vcpu_timer, rr_next_kick_time());
  96     }
  97 }
  98
  99 static void rr_stop_kick_timer(void)
 100 {
 101     if (rr_kick_vcpu_timer && timer_pending(rr_kick_vcpu_timer)) {
 102         timer_del(rr_kick_vcpu_timer);
 103     }
 104 }
 105
 106 static void rr_wait_io_event(void)
 107 {
 108     CPUState *cpu;
 109
 110     while (all_cpu_threads_idle()) {
 111         rr_stop_kick_timer();
 112         qemu_cond_wait_iothread(first_cpu->halt_cond);
 113     }
 114
 115     rr_start_kick_timer();
 116
 117     CPU_FOREACH(cpu) {
 118         qemu_wait_io_event_common(cpu);
 119     }
 120 }
 121
 122 /*
 123  * Destroy any remaining vCPUs which have been unplugged and have
 124  * finished running
 125  */
 126 static void rr_deal_with_unplugged_cpus(void)
 127 {
 128     CPUState *cpu;
 129
 130     CPU_FOREACH(cpu) {
 131         if (cpu->unplug && !cpu_can_run(cpu)) {
 132             tcg_cpus_destroy(cpu);
 133             break;
 134         }
 135     }
 136 }
 137
 138 static void rr_force_rcu(Notifier *notify, void *data)
 139 {
 140     rr_kick_next_cpu();
 141 }
 142
 143 /*
 144  * In the single-threaded case each vCPU is simulated in turn. If
 145  * there is more than a single vCPU we create a simple timer to kick
 146  * the vCPU and ensure we don't get stuck in a tight loop in one vCPU.
 147  * This is done explicitly rather than relying on side-effects
 148  * elsewhere.
 149  */
 150
 151 static void *rr_cpu_thread_fn(void *arg)
 152 {
 153     Notifier force_rcu;
 154     CPUState *cpu = arg;
 155
 156     assert(tcg_enabled());
 157     rcu_register_thread();
 158     force_rcu.notify = rr_force_rcu;
 159     rcu_add_force_rcu_notifier(&force_rcu);
 160     tcg_register_thread();
 161
 162     qemu_mutex_lock_iothread();
 163     qemu_thread_get_self(cpu->thread);
 164
 165     cpu->thread_id = qemu_get_thread_id();
 166     cpu->can_do_io = 1;
 167     cpu_thread_signal_created(cpu);
 168     qemu_guest_random_seed_thread_part2(cpu->random_seed);
 169
 170     /* wait for initial kick-off after machine start */
 171     while (first_cpu->stopped) {
 172         qemu_cond_wait_iothread(first_cpu->halt_cond);
 173
 174         /* process any pending work */
 175         CPU_FOREACH(cpu) {
 176             current_cpu = cpu;
 177             qemu_wait_io_event_common(cpu);
 178         }
 179     }
 180
 181     rr_start_kick_timer();
 182
 183     cpu = first_cpu;
 184
 185     /* process any pending work */
 186     cpu->exit_request = 1;
 187
 188     while (1) {
 189         qemu_mutex_unlock_iothread();
 190         replay_mutex_lock();
 191         qemu_mutex_lock_iothread();
 192
 193         if (icount_enabled()) {
 194             /* Account partial waits to QEMU_CLOCK_VIRTUAL.  */
 195             icount_account_warp_timer();
 196             /*
 197              * Run the timers here.  This is much more efficient than
 198              * waking up the I/O thread and waiting for completion.
 199              */
 200             icount_handle_deadline();
 201         }
 202
 203         replay_mutex_unlock();
 204
 205         if (!cpu) {
 206             cpu = first_cpu;
 207         }
 208
 209         while (cpu && cpu_work_list_empty(cpu) && !cpu->exit_request) {
 210
 211             qatomic_mb_set(&rr_current_cpu, cpu);
 212             current_cpu = cpu;
 213
 214             qemu_clock_enable(QEMU_CLOCK_VIRTUAL,
 215                               (cpu->singlestep_enabled & SSTEP_NOTIMER) == 0);
 216
 217             if (cpu_can_run(cpu)) {
 218                 int r;
 219
 220                 qemu_mutex_unlock_iothread();
 221                 if (icount_enabled()) {
 222                     icount_prepare_for_run(cpu);
 223                 }
 224                 r = tcg_cpus_exec(cpu);
 225                 if (icount_enabled()) {
 226                     icount_process_data(cpu);
 227                 }
 228                 qemu_mutex_lock_iothread();
 229
 230                 if (r == EXCP_DEBUG) {
 231                     cpu_handle_guest_debug(cpu);
 232                     break;
 233                 } else if (r == EXCP_ATOMIC) {
 234                     qemu_mutex_unlock_iothread();
 235                     cpu_exec_step_atomic(cpu);
 236                     qemu_mutex_lock_iothread();
 237                     break;
 238                 }
 239             } else if (cpu->stop) {
 240                 if (cpu->unplug) {
 241                     cpu = CPU_NEXT(cpu);
 242                 }
 243                 break;
 244             }
 245
 246             cpu = CPU_NEXT(cpu);
 247         } /* while (cpu && !cpu->exit_request).. */
 248
 249         /* Does not need qatomic_mb_set because a spurious wakeup is okay.  */
 250         qatomic_set(&rr_current_cpu, NULL);
 251
 252         if (cpu && cpu->exit_request) {
 253             qatomic_mb_set(&cpu->exit_request, 0);
 254         }
 255
 256         if (icount_enabled() && all_cpu_threads_idle()) {
 257             /*
 258              * When all cpus are sleeping (e.g in WFI), to avoid a deadlock
 259              * in the main_loop, wake it up in order to start the warp timer.
 260              */
 261             qemu_notify_event();
 262         }
 263
 264         rr_wait_io_event();
 265         rr_deal_with_unplugged_cpus();
 266     }
 267
 268     rcu_remove_force_rcu_notifier(&force_rcu);
 269     rcu_unregister_thread();
 270     return NULL;
 271 }
 272
 273 void rr_start_vcpu_thread(CPUState *cpu)
 274 {
 275     char thread_name[VCPU_THREAD_NAME_SIZE];
 276     static QemuCond *single_tcg_halt_cond;
 277     static QemuThread *single_tcg_cpu_thread;
 278
 279     g_assert(tcg_enabled());
 280     tcg_cpu_init_cflags(cpu, false);
 281
 282     if (!single_tcg_cpu_thread) {
 283         cpu->thread = g_new0(QemuThread, 1);
 284         cpu->halt_cond = g_new0(QemuCond, 1);
 285         qemu_cond_init(cpu->halt_cond);
 286
 287         /* share a single thread for all cpus with TCG */
 288         snprintf(thread_name, VCPU_THREAD_NAME_SIZE, "ALL CPUs/TCG");
 289         qemu_thread_create(cpu->thread, thread_name,
 290                            rr_cpu_thread_fn,
 291                            cpu, QEMU_THREAD_JOINABLE);
 292
 293         single_tcg_halt_cond = cpu->halt_cond;
 294         single_tcg_cpu_thread = cpu->thread;
 295 #ifdef _WIN32
 296         cpu->hThread = qemu_thread_get_handle(cpu->thread);
 297 #endif
 298     } else {
 299         /* we share the thread */
 300         cpu->thread = single_tcg_cpu_thread;
 301         cpu->halt_cond = single_tcg_halt_cond;
 302         cpu->thread_id = first_cpu->thread_id;
 303         cpu->can_do_io = 1;
 304         cpu->created = true;
 305     }
 306 }