accel/tcg/tcg-accel-ops-rr.c - qemu - Git at Google

 /*
  * QEMU TCG Single Threaded vCPUs implementation
  *
  * Copyright (c) 2003-2008 Fabrice Bellard
  * Copyright (c) 2014 Red Hat Inc.
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
  * in the Software without restriction, including without limitation the rights
  * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  * copies of the Software, and to permit persons to whom the Software is
  * furnished to do so, subject to the following conditions:
  *
  * The above copyright notice and this permission notice shall be included in
  * all copies or substantial portions of the Software.
  *
  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
  * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
  * THE SOFTWARE.
  */

 #include "qemu/osdep.h"
 #include "qemu/lockable.h"
 #include "system/tcg.h"
 #include "system/replay.h"
 #include "exec/icount.h"
 #include "qemu/main-loop.h"
 #include "qemu/notify.h"
 #include "qemu/guest-random.h"
 #include "exec/cpu-common.h"
 #include "tcg/startup.h"
 #include "tcg-accel-ops.h"
 #include "tcg-accel-ops-rr.h"
 #include "tcg-accel-ops-icount.h"

 /* Kick all RR vCPUs */
 void rr_kick_vcpu_thread(CPUState *unused)
 {
     CPUState *cpu;

     CPU_FOREACH(cpu) {
         tcg_kick_vcpu_thread(cpu);
     };
 }

 /*
  * TCG vCPU kick timer
  *
  * The kick timer is responsible for moving single threaded vCPU
  * emulation on to the next vCPU. If more than one vCPU is running a
  * timer event we force a cpu->exit so the next vCPU can get
  * scheduled.
  *
  * The timer is removed if all vCPUs are idle and restarted again once
  * idleness is complete.
  */

 static QEMUTimer *rr_kick_vcpu_timer;
 static CPUState *rr_current_cpu;

 static inline int64_t rr_next_kick_time(void)
 {
     return qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL) + TCG_KICK_PERIOD;
 }

 /* Kick the currently round-robin scheduled vCPU to next */
 static void rr_kick_next_cpu(void)
 {
     CPUState *cpu;
     do {
         cpu = qatomic_read(&rr_current_cpu);
         if (cpu) {
             cpu_exit(cpu);
         }
         /* Finish kicking this cpu before reading again.  */
         smp_mb();
     } while (cpu != qatomic_read(&rr_current_cpu));
 }

 static void rr_kick_thread(void *opaque)
 {
     timer_mod(rr_kick_vcpu_timer, rr_next_kick_time());
     rr_kick_next_cpu();
 }

 static void rr_start_kick_timer(void)
 {
     if (!rr_kick_vcpu_timer && CPU_NEXT(first_cpu)) {
         rr_kick_vcpu_timer = timer_new_ns(QEMU_CLOCK_VIRTUAL,
                                            rr_kick_thread, NULL);
     }
     if (rr_kick_vcpu_timer && !timer_pending(rr_kick_vcpu_timer)) {
         timer_mod(rr_kick_vcpu_timer, rr_next_kick_time());
     }
 }

 static void rr_stop_kick_timer(void)
 {
     if (rr_kick_vcpu_timer && timer_pending(rr_kick_vcpu_timer)) {
         timer_del(rr_kick_vcpu_timer);
     }
 }

 static void rr_wait_io_event(void)
 {
     CPUState *cpu;

     while (all_cpu_threads_idle()) {
         rr_stop_kick_timer();
         qemu_cond_wait_bql(first_cpu->halt_cond);
     }

     rr_start_kick_timer();

     CPU_FOREACH(cpu) {
         qemu_process_cpu_events_common(cpu);
     }
 }

 /*
  * Destroy any remaining vCPUs which have been unplugged and have
  * finished running
  */
 static void rr_deal_with_unplugged_cpus(void)
 {
     CPUState *cpu;

     CPU_FOREACH(cpu) {
         if (cpu->unplug && !cpu_can_run(cpu)) {
             tcg_cpu_destroy(cpu);
             break;
         }
     }
 }

 static void rr_force_rcu(Notifier *notify, void *data)
 {
     rr_kick_next_cpu();
 }

 /*
  * Calculate the number of CPUs that we will process in a single iteration of
  * the main CPU thread loop so that we can fairly distribute the instruction
  * count across CPUs.
  *
  * The CPU count is cached based on the CPU list generation ID to avoid
  * iterating the list every time.
  */
 static int rr_cpu_count(void)
 {
     static unsigned int last_gen_id = ~0;
     static int cpu_count;
     CPUState *cpu;

     QEMU_LOCK_GUARD(&qemu_cpu_list_lock);

     if (cpu_list_generation_id_get() != last_gen_id) {
         cpu_count = 0;
         CPU_FOREACH(cpu) {
             ++cpu_count;
         }
         last_gen_id = cpu_list_generation_id_get();
     }

     return cpu_count;
 }

 /*
  * In the single-threaded case each vCPU is simulated in turn. If
  * there is more than a single vCPU we create a simple timer to kick
  * the vCPU and ensure we don't get stuck in a tight loop in one vCPU.
  * This is done explicitly rather than relying on side-effects
  * elsewhere.
  */

 static void *rr_cpu_thread_fn(void *arg)
 {
     Notifier force_rcu;
     CPUState *cpu = arg;

     assert(tcg_enabled());
     rcu_register_thread();
     force_rcu.notify = rr_force_rcu;
     rcu_add_force_rcu_notifier(&force_rcu);
     tcg_register_thread();

     bql_lock();
     qemu_thread_get_self(cpu->thread);

     cpu->thread_id = qemu_get_thread_id();
     cpu->neg.can_do_io = true;
     cpu_thread_signal_created(cpu);
     qemu_guest_random_seed_thread_part2(cpu->random_seed);

     /* wait for initial kick-off after machine start */
     while (first_cpu->stopped) {
         qemu_cond_wait_bql(first_cpu->halt_cond);

         /* process any pending work */
         CPU_FOREACH(cpu) {
             current_cpu = cpu;
             qemu_process_cpu_events_common(cpu);
         }
     }

     rr_start_kick_timer();

     cpu = first_cpu;

     /* process any pending work */
     qatomic_set(&cpu->exit_request, true);

     while (1) {
         /* Only used for icount_enabled() */
         int64_t cpu_budget = 0;

         bql_unlock();
         replay_mutex_lock();
         bql_lock();

         if (icount_enabled()) {
             int cpu_count = rr_cpu_count();

             /* Account partial waits to QEMU_CLOCK_VIRTUAL.  */
             icount_account_warp_timer();
             /*
              * Run the timers here.  This is much more efficient than
              * waking up the I/O thread and waiting for completion.
              */
             icount_handle_deadline();

             cpu_budget = icount_percpu_budget(cpu_count);
         }

         replay_mutex_unlock();

         if (!cpu) {
             cpu = first_cpu;
         }

         while (cpu && cpu_work_list_empty(cpu)) {
             /*
              * Store rr_current_cpu before evaluating cpu->exit_request.
              * Pairs with rr_kick_next_cpu().
              */
             qatomic_set_mb(&rr_current_cpu, cpu);

             /* Pairs with store-release in cpu_exit.  */
             if (qatomic_load_acquire(&cpu->exit_request)) {
                 break;
             }
             current_cpu = cpu;

             qemu_clock_enable(QEMU_CLOCK_VIRTUAL,
                               (cpu->singlestep_enabled & SSTEP_NOTIMER) == 0);

             if (cpu_can_run(cpu)) {
                 int r;

                 bql_unlock();
                 if (icount_enabled()) {
                     icount_prepare_for_run(cpu, cpu_budget);
                 }
                 r = tcg_cpu_exec(cpu);
                 if (icount_enabled()) {
                     icount_process_data(cpu);
                 }
                 bql_lock();

                 if (r == EXCP_DEBUG) {
                     cpu_handle_guest_debug(cpu);
                     break;
                 } else if (r == EXCP_ATOMIC) {
                     bql_unlock();
                     cpu_exec_step_atomic(cpu);
                     bql_lock();
                     break;
                 }
             } else if (cpu->stop) {
                 if (cpu->unplug) {
                     cpu = CPU_NEXT(cpu);
                 }
                 break;
             }

             cpu = CPU_NEXT(cpu);
         } /* while (cpu && !cpu->exit_request).. */

         /* Does not need a memory barrier because a spurious wakeup is okay.  */
         qatomic_set(&rr_current_cpu, NULL);

         if (cpu && qatomic_read(&cpu->exit_request)) {
             qatomic_set_mb(&cpu->exit_request, 0);
         }

         if (icount_enabled() && all_cpu_threads_idle()) {
             /*
              * When all cpus are sleeping (e.g in WFI), to avoid a deadlock
              * in the main_loop, wake it up in order to start the warp timer.
              */
             qemu_notify_event();
         }

         rr_wait_io_event();
         rr_deal_with_unplugged_cpus();
     }

     g_assert_not_reached();
 }

 void rr_start_vcpu_thread(CPUState *cpu)
 {
     char thread_name[VCPU_THREAD_NAME_SIZE];
     static QemuCond *single_tcg_halt_cond;
     static QemuThread *single_tcg_cpu_thread;

     g_assert(tcg_enabled());
     tcg_cpu_init_cflags(cpu, false);

     if (!single_tcg_cpu_thread) {
         single_tcg_halt_cond = cpu->halt_cond;
         single_tcg_cpu_thread = cpu->thread;

         /* share a single thread for all cpus with TCG */
         snprintf(thread_name, VCPU_THREAD_NAME_SIZE, "ALL CPUs/TCG");
         qemu_thread_create(cpu->thread, thread_name,
                            rr_cpu_thread_fn,
                            cpu, QEMU_THREAD_JOINABLE);
     } else {
         /* we share the thread, dump spare data */
         g_free(cpu->thread);
         qemu_cond_destroy(cpu->halt_cond);
         g_free(cpu->halt_cond);
         cpu->thread = single_tcg_cpu_thread;
         cpu->halt_cond = single_tcg_halt_cond;

         /* copy the stuff done at start of rr_cpu_thread_fn */
         cpu->thread_id = first_cpu->thread_id;
         cpu->neg.can_do_io = 1;
         cpu->created = true;
     }
 }
	/*
	* QEMU TCG Single Threaded vCPUs implementation
	*
	* Copyright (c) 2003-2008 Fabrice Bellard
	* Copyright (c) 2014 Red Hat Inc.
	*
	* Permission is hereby granted, free of charge, to any person obtaining a copy
	* of this software and associated documentation files (the "Software"), to deal
	* in the Software without restriction, including without limitation the rights
	* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
	* copies of the Software, and to permit persons to whom the Software is
	* furnished to do so, subject to the following conditions:
	*
	* The above copyright notice and this permission notice shall be included in
	* all copies or substantial portions of the Software.
	*
	* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
	* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
	* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
	* THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
	* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
	* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
	* THE SOFTWARE.
	*/

	#include "qemu/osdep.h"
	#include "qemu/lockable.h"
	#include "system/tcg.h"
	#include "system/replay.h"
	#include "exec/icount.h"
	#include "qemu/main-loop.h"
	#include "qemu/notify.h"
	#include "qemu/guest-random.h"
	#include "exec/cpu-common.h"
	#include "tcg/startup.h"
	#include "tcg-accel-ops.h"
	#include "tcg-accel-ops-rr.h"
	#include "tcg-accel-ops-icount.h"

	/* Kick all RR vCPUs */
	void rr_kick_vcpu_thread(CPUState *unused)
	{
	CPUState *cpu;

	CPU_FOREACH(cpu) {
	tcg_kick_vcpu_thread(cpu);
	};
	}

	/*
	* TCG vCPU kick timer
	*
	* The kick timer is responsible for moving single threaded vCPU
	* emulation on to the next vCPU. If more than one vCPU is running a
	* timer event we force a cpu->exit so the next vCPU can get
	* scheduled.
	*
	* The timer is removed if all vCPUs are idle and restarted again once
	* idleness is complete.
	*/

	static QEMUTimer *rr_kick_vcpu_timer;
	static CPUState *rr_current_cpu;

	static inline int64_t rr_next_kick_time(void)
	{
	return qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL) + TCG_KICK_PERIOD;
	}

	/* Kick the currently round-robin scheduled vCPU to next */
	static void rr_kick_next_cpu(void)
	{
	CPUState *cpu;
	do {
	cpu = qatomic_read(&rr_current_cpu);
	if (cpu) {
	cpu_exit(cpu);
	}
	/* Finish kicking this cpu before reading again. */
	smp_mb();
	} while (cpu != qatomic_read(&rr_current_cpu));
	}

	static void rr_kick_thread(void *opaque)
	{
	timer_mod(rr_kick_vcpu_timer, rr_next_kick_time());
	rr_kick_next_cpu();
	}

	static void rr_start_kick_timer(void)
	{
	if (!rr_kick_vcpu_timer && CPU_NEXT(first_cpu)) {
	rr_kick_vcpu_timer = timer_new_ns(QEMU_CLOCK_VIRTUAL,
	rr_kick_thread, NULL);
	}
	if (rr_kick_vcpu_timer && !timer_pending(rr_kick_vcpu_timer)) {
	timer_mod(rr_kick_vcpu_timer, rr_next_kick_time());
	}
	}

	static void rr_stop_kick_timer(void)
	{
	if (rr_kick_vcpu_timer && timer_pending(rr_kick_vcpu_timer)) {
	timer_del(rr_kick_vcpu_timer);
	}
	}

	static void rr_wait_io_event(void)
	{
	CPUState *cpu;

	while (all_cpu_threads_idle()) {
	rr_stop_kick_timer();
	qemu_cond_wait_bql(first_cpu->halt_cond);
	}

	rr_start_kick_timer();

	CPU_FOREACH(cpu) {
	qemu_process_cpu_events_common(cpu);
	}
	}

	/*
	* Destroy any remaining vCPUs which have been unplugged and have
	* finished running
	*/
	static void rr_deal_with_unplugged_cpus(void)
	{
	CPUState *cpu;

	CPU_FOREACH(cpu) {
	if (cpu->unplug && !cpu_can_run(cpu)) {
	tcg_cpu_destroy(cpu);
	break;
	}
	}
	}

	static void rr_force_rcu(Notifier notify, void data)
	{
	rr_kick_next_cpu();
	}

	/*
	* Calculate the number of CPUs that we will process in a single iteration of
	* the main CPU thread loop so that we can fairly distribute the instruction
	* count across CPUs.
	*
	* The CPU count is cached based on the CPU list generation ID to avoid
	* iterating the list every time.
	*/
	static int rr_cpu_count(void)
	{
	static unsigned int last_gen_id = ~0;
	static int cpu_count;
	CPUState *cpu;

	QEMU_LOCK_GUARD(&qemu_cpu_list_lock);

	if (cpu_list_generation_id_get() != last_gen_id) {
	cpu_count = 0;
	CPU_FOREACH(cpu) {
	++cpu_count;
	}
	last_gen_id = cpu_list_generation_id_get();
	}

	return cpu_count;
	}

	/*
	* In the single-threaded case each vCPU is simulated in turn. If
	* there is more than a single vCPU we create a simple timer to kick
	* the vCPU and ensure we don't get stuck in a tight loop in one vCPU.
	* This is done explicitly rather than relying on side-effects
	* elsewhere.
	*/

	static void rr_cpu_thread_fn(void arg)
	{
	Notifier force_rcu;
	CPUState *cpu = arg;

	assert(tcg_enabled());
	rcu_register_thread();
	force_rcu.notify = rr_force_rcu;
	rcu_add_force_rcu_notifier(&force_rcu);
	tcg_register_thread();

	bql_lock();
	qemu_thread_get_self(cpu->thread);

	cpu->thread_id = qemu_get_thread_id();
	cpu->neg.can_do_io = true;
	cpu_thread_signal_created(cpu);
	qemu_guest_random_seed_thread_part2(cpu->random_seed);

	/* wait for initial kick-off after machine start */
	while (first_cpu->stopped) {
	qemu_cond_wait_bql(first_cpu->halt_cond);

	/* process any pending work */
	CPU_FOREACH(cpu) {
	current_cpu = cpu;
	qemu_process_cpu_events_common(cpu);
	}
	}

	rr_start_kick_timer();

	cpu = first_cpu;

	/* process any pending work */
	qatomic_set(&cpu->exit_request, true);

	while (1) {
	/* Only used for icount_enabled() */
	int64_t cpu_budget = 0;

	bql_unlock();
	replay_mutex_lock();
	bql_lock();

	if (icount_enabled()) {
	int cpu_count = rr_cpu_count();

	/* Account partial waits to QEMU_CLOCK_VIRTUAL. */
	icount_account_warp_timer();
	/*
	* Run the timers here. This is much more efficient than
	* waking up the I/O thread and waiting for completion.
	*/
	icount_handle_deadline();

	cpu_budget = icount_percpu_budget(cpu_count);
	}

	replay_mutex_unlock();

	if (!cpu) {
	cpu = first_cpu;
	}

	while (cpu && cpu_work_list_empty(cpu)) {
	/*
	* Store rr_current_cpu before evaluating cpu->exit_request.
	* Pairs with rr_kick_next_cpu().
	*/
	qatomic_set_mb(&rr_current_cpu, cpu);

	/* Pairs with store-release in cpu_exit. */
	if (qatomic_load_acquire(&cpu->exit_request)) {
	break;
	}
	current_cpu = cpu;

	qemu_clock_enable(QEMU_CLOCK_VIRTUAL,
	(cpu->singlestep_enabled & SSTEP_NOTIMER) == 0);

	if (cpu_can_run(cpu)) {
	int r;

	bql_unlock();
	if (icount_enabled()) {
	icount_prepare_for_run(cpu, cpu_budget);
	}
	r = tcg_cpu_exec(cpu);
	if (icount_enabled()) {
	icount_process_data(cpu);
	}
	bql_lock();

	if (r == EXCP_DEBUG) {
	cpu_handle_guest_debug(cpu);
	break;
	} else if (r == EXCP_ATOMIC) {
	bql_unlock();
	cpu_exec_step_atomic(cpu);
	bql_lock();
	break;
	}
	} else if (cpu->stop) {
	if (cpu->unplug) {
	cpu = CPU_NEXT(cpu);
	}
	break;
	}

	cpu = CPU_NEXT(cpu);
	} /* while (cpu && !cpu->exit_request).. */

	/* Does not need a memory barrier because a spurious wakeup is okay. */
	qatomic_set(&rr_current_cpu, NULL);

	if (cpu && qatomic_read(&cpu->exit_request)) {
	qatomic_set_mb(&cpu->exit_request, 0);
	}

	if (icount_enabled() && all_cpu_threads_idle()) {
	/*
	* When all cpus are sleeping (e.g in WFI), to avoid a deadlock
	* in the main_loop, wake it up in order to start the warp timer.
	*/
	qemu_notify_event();
	}

	rr_wait_io_event();
	rr_deal_with_unplugged_cpus();
	}

	g_assert_not_reached();
	}

	void rr_start_vcpu_thread(CPUState *cpu)
	{
	char thread_name[VCPU_THREAD_NAME_SIZE];
	static QemuCond *single_tcg_halt_cond;
	static QemuThread *single_tcg_cpu_thread;

	g_assert(tcg_enabled());
	tcg_cpu_init_cflags(cpu, false);

	if (!single_tcg_cpu_thread) {
	single_tcg_halt_cond = cpu->halt_cond;
	single_tcg_cpu_thread = cpu->thread;

	/* share a single thread for all cpus with TCG */
	snprintf(thread_name, VCPU_THREAD_NAME_SIZE, "ALL CPUs/TCG");
	qemu_thread_create(cpu->thread, thread_name,
	rr_cpu_thread_fn,
	cpu, QEMU_THREAD_JOINABLE);
	} else {
	/* we share the thread, dump spare data */
	g_free(cpu->thread);
	qemu_cond_destroy(cpu->halt_cond);
	g_free(cpu->halt_cond);
	cpu->thread = single_tcg_cpu_thread;
	cpu->halt_cond = single_tcg_halt_cond;

	/* copy the stuff done at start of rr_cpu_thread_fn */
	cpu->thread_id = first_cpu->thread_id;
	cpu->neg.can_do_io = 1;
	cpu->created = true;
	}
	}