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separate thread for IO handling V2

PATCH In review Marcelo Tosatti 2 participants 4 messages Mar 28, 2008 – Mar 30, 2008 KVM

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Marcelo Tosatti

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#0 lore raw

cover separate thread for IO handling V2

- Fix reset, powerdown and shutdown.
- Fix kvmctl.

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#1 lore raw

PATCH 1/2 QEMU/KVM: separate thread for IO handling

Move IO processing from vcpu0 to a dedicated thread.

This removes load on vcpu0 by allowing better cache locality and also improves latency.

We can now block signal handling for IO events, so sigtimedwait won't race with handlers:

- Currently the SIGALRM handler fails to set CPU_INTERRUPT_EXIT because the "next_cpu" variable is not initialized in the KVM path, meaning that processing of timer expiration might be delayed until the next vcpu0 exit.

qemu/qemu-kvm.c +91 -57
Index: kvm-userspace.io/qemu/qemu-kvm.c
===================================================================
@@ -28,6 +28,8 @@ kvm_context_t kvm_context;
 
 extern int smp_cpus;
 
+static int qemu_kvm_reset_requested;
+
 pthread_mutex_t qemu_mutex = PTHREAD_MUTEX_INITIALIZER;
 pthread_cond_t qemu_aio_cond = PTHREAD_COND_INITIALIZER;
 __thread struct vcpu_info *vcpu;

@@ -38,6 +40,7 @@ struct qemu_kvm_signal_table {
 };
 
 static struct qemu_kvm_signal_table io_signal_table;
+static struct qemu_kvm_signal_table vcpu_signal_table;
 
 #define SIG_IPI (SIGRTMIN+4)
 

@@ -51,6 +54,8 @@ struct vcpu_info {
     int stopped;
 } vcpu_info[256];
 
+pthread_t io_thread;
+
 static inline unsigned long kvm_get_thread_id(void)
 {
     return syscall(SYS_gettid);

@@ -67,12 +72,19 @@ static void sig_ipi_handler(int n)
 
 void kvm_update_interrupt_request(CPUState *env)
 {
-    if (env && vcpu && env != vcpu->env) {
-	if (vcpu_info[env->cpu_index].signalled)
-	    return;
-	vcpu_info[env->cpu_index].signalled = 1;
-	if (vcpu_info[env->cpu_index].thread)
-	    pthread_kill(vcpu_info[env->cpu_index].thread, SIG_IPI);
+    int signal = 0;
+
+    if (env) {
+        if (!vcpu)
+            signal = 1;
+        if (vcpu && env != vcpu->env && !vcpu_info[env->cpu_index].signalled)
+            signal = 1;
+
+        if (signal) {
+            vcpu_info[env->cpu_index].signalled = 1;
+                if (vcpu_info[env->cpu_index].thread)
+                    pthread_kill(vcpu_info[env->cpu_index].thread, SIG_IPI);
+        }
     }
 }
 

@@ -105,7 +117,7 @@ static void post_kvm_run(void *opaque, i
 
 static int pre_kvm_run(void *opaque, int vcpu)
 {
-    CPUState *env = cpu_single_env;
+    CPUState *env = qemu_kvm_cpu_env(vcpu);
 
     kvm_arch_pre_kvm_run(opaque, vcpu);
 

@@ -151,7 +163,8 @@ static int has_work(CPUState *env)
     return kvm_arch_has_work(env);
 }
 
-static int kvm_eat_signal(CPUState *env, int timeout)
+static int kvm_eat_signal(struct qemu_kvm_signal_table *waitset, CPUState *env,
+                          int timeout)
 {
     struct timespec ts;
     int r, e, ret = 0;

@@ -160,12 +173,12 @@ static int kvm_eat_signal(CPUState *env,
 
     ts.tv_sec = timeout / 1000;
     ts.tv_nsec = (timeout % 1000) * 1000000;
-    r = sigtimedwait(&io_signal_table.sigset, &siginfo, &ts);
+    r = sigtimedwait(&waitset->sigset, &siginfo, &ts);
     if (r == -1 && (errno == EAGAIN || errno == EINTR) && !timeout)
 	return 0;
     e = errno;
     pthread_mutex_lock(&qemu_mutex);
-    if (vcpu)
+    if (env && vcpu)
         cpu_single_env = vcpu->env;
     if (r == -1 && !(errno == EAGAIN || errno == EINTR)) {
 	printf("sigtimedwait: %s\n", strerror(e));

@@ -181,7 +194,7 @@ static int kvm_eat_signal(CPUState *env,
     if (env && vcpu_info[env->cpu_index].stop) {
 	vcpu_info[env->cpu_index].stop = 0;
 	vcpu_info[env->cpu_index].stopped = 1;
-	pthread_kill(vcpu_info[0].thread, SIG_IPI);
+	pthread_kill(io_thread, SIGUSR1);
     }
     pthread_mutex_unlock(&qemu_mutex);
 

@@ -192,24 +205,16 @@ static int kvm_eat_signal(CPUState *env,
 static void kvm_eat_signals(CPUState *env, int timeout)
 {
     int r = 0;
+    struct qemu_kvm_signal_table *waitset = &vcpu_signal_table;
 
-    while (kvm_eat_signal(env, 0))
+    while (kvm_eat_signal(waitset, env, 0))
 	r = 1;
     if (!r && timeout) {
-	r = kvm_eat_signal(env, timeout);
+	r = kvm_eat_signal(waitset, env, timeout);
 	if (r)
-	    while (kvm_eat_signal(env, 0))
+	    while (kvm_eat_signal(waitset, env, 0))
 		;
     }
-    /*
-     * we call select() even if no signal was received, to account for
-     * for which there is no signal handler installed.
-     */
-    pthread_mutex_lock(&qemu_mutex);
-    cpu_single_env = vcpu->env;
-    if (env->cpu_index == 0)
-	main_loop_wait(0);
-    pthread_mutex_unlock(&qemu_mutex);
 }
 
 static void kvm_main_loop_wait(CPUState *env, int timeout)

@@ -225,29 +230,29 @@ static int all_threads_paused(void)
 {
     int i;
 
-    for (i = 1; i < smp_cpus; ++i)
+    for (i = 0; i < smp_cpus; ++i)
 	if (vcpu_info[i].stopped)
 	    return 0;
     return 1;
 }
 
-static void pause_other_threads(void)
+static void pause_all_threads(void)
 {
     int i;
 
-    for (i = 1; i < smp_cpus; ++i) {
+    for (i = 0; i < smp_cpus; ++i) {
 	vcpu_info[i].stop = 1;
 	pthread_kill(vcpu_info[i].thread, SIG_IPI);
     }
     while (!all_threads_paused())
-	kvm_eat_signals(vcpu->env, 0);
+	kvm_eat_signal(&io_signal_table, NULL, 1000);
 }
 
-static void resume_other_threads(void)
+static void resume_all_threads(void)
 {
     int i;
 
-    for (i = 1; i < smp_cpus; ++i) {
+    for (i = 0; i < smp_cpus; ++i) {
 	vcpu_info[i].stop = 0;
 	vcpu_info[i].stopped = 0;
 	pthread_kill(vcpu_info[i].thread, SIG_IPI);

@@ -257,9 +262,9 @@ static void resume_other_threads(void)
 static void kvm_vm_state_change_handler(void *context, int running)
 {
     if (running)
-	resume_other_threads();
+	resume_all_threads();
     else
-	pause_other_threads();
+	pause_all_threads();
 }
 
 static void update_regs_for_sipi(CPUState *env)

@@ -281,8 +286,6 @@ static void setup_kernel_sigmask(CPUStat
 
     sigprocmask(SIG_BLOCK, NULL, &set);
     sigdelset(&set, SIG_IPI);
-    if (env->cpu_index == 0)
-	sigandset(&set, &set, &io_signal_table.negsigset);
     
     kvm_set_signal_mask(kvm_context, env->cpu_index, &set);
 }

@@ -314,11 +317,8 @@ static int kvm_main_loop_cpu(CPUState *e
 	    kvm_cpu_exec(env);
 	env->interrupt_request &= ~CPU_INTERRUPT_EXIT;
 	kvm_main_loop_wait(env, 0);
-	if (qemu_shutdown_requested())
-	    break;
-	else if (qemu_powerdown_requested())
-	    qemu_system_powerdown();
-	else if (qemu_reset_requested()) {
+        if (qemu_kvm_reset_requested && env->cpu_index == 0) {
+	    qemu_kvm_reset_requested = 0;
 	    env->interrupt_request = 0;
 	    qemu_system_reset();
 	    kvm_arch_load_regs(env);

@@ -337,7 +337,7 @@ static void *ap_main_loop(void *_env)
     vcpu->env = env;
     vcpu->env->thread_id = kvm_get_thread_id();
     sigfillset(&signals);
-    //sigdelset(&signals, SIG_IPI);
+    sigdelset(&signals, SIG_IPI);
     sigprocmask(SIG_BLOCK, &signals, NULL);
     kvm_create_vcpu(kvm_context, env->cpu_index);
     kvm_qemu_init_env(env);

@@ -364,38 +364,68 @@ void kvm_init_new_ap(int cpu, CPUState *
     pthread_create(&vcpu_info[cpu].thread, NULL, ap_main_loop, env);
 }
 
+static void qemu_kvm_init_signal_tables(void)
+{
+    qemu_kvm_init_signal_table(&io_signal_table);
+    qemu_kvm_init_signal_table(&vcpu_signal_table);
+
+    kvm_add_signal(&io_signal_table, SIGIO);
+    kvm_add_signal(&io_signal_table, SIGALRM);
+    kvm_add_signal(&io_signal_table, SIGUSR1);
+    kvm_add_signal(&io_signal_table, SIGUSR2);
+
+    kvm_add_signal(&vcpu_signal_table, SIG_IPI);
+
+    sigprocmask(SIG_BLOCK, &io_signal_table.sigset, NULL);
+}
+
 int kvm_init_ap(void)
 {
-    CPUState *env = first_cpu->next_cpu;
+    CPUState *env = first_cpu;
     int i;
 
 #ifdef TARGET_I386
     kvm_tpr_opt_setup();
 #endif
     qemu_add_vm_change_state_handler(kvm_vm_state_change_handler, NULL);
-    qemu_kvm_init_signal_table(&io_signal_table);
-    kvm_add_signal(&io_signal_table, SIGIO);
-    kvm_add_signal(&io_signal_table, SIGALRM);
-    kvm_add_signal(&io_signal_table, SIGUSR2);
-    kvm_add_signal(&io_signal_table, SIG_IPI);
-    sigprocmask(SIG_BLOCK, &io_signal_table.sigset, NULL);
+    qemu_kvm_init_signal_tables();
 
-    vcpu = &vcpu_info[0];
-    vcpu->env = first_cpu;
-    vcpu->env->thread_id = kvm_get_thread_id();
     signal(SIG_IPI, sig_ipi_handler);
-    for (i = 1; i < smp_cpus; ++i) {
+    for (i = 0; i < smp_cpus; ++i) {
         kvm_init_new_ap(i, env);
         env = env->next_cpu;
     }
     return 0;
 }
 
+/*
+ * The IO thread has all signals that inform machine events
+ * blocked (io_signal_table), so it won't get interrupted
+ * while processing in main_loop_wait().
+ */
+
 int kvm_main_loop(void)
 {
-    vcpu_info[0].thread = pthread_self();
+    io_thread = pthread_self();
     pthread_mutex_unlock(&qemu_mutex);
-    return kvm_main_loop_cpu(first_cpu);
+    while (1) {
+        kvm_eat_signal(&io_signal_table, NULL, 1000);
+        pthread_mutex_lock(&qemu_mutex);
+        cpu_single_env = NULL;
+        main_loop_wait(0);
+        if (qemu_shutdown_requested())
+            break;
+        else if (qemu_powerdown_requested())
+            qemu_system_powerdown();
+        else if (qemu_reset_requested()) {
+            pthread_kill(vcpu_info[0].thread, SIG_IPI);
+            qemu_kvm_reset_requested = 1;
+        }
+        pthread_mutex_unlock(&qemu_mutex);
+    }
+
+    pthread_mutex_unlock(&qemu_mutex);
+    return 0;
 }
 
 static int kvm_debug(void *opaque, int vcpu)

@@ -749,12 +779,16 @@ void qemu_kvm_aio_wait_start(void)
 
 void qemu_kvm_aio_wait(void)
 {
-    if (!cpu_single_env || cpu_single_env->cpu_index == 0) {
-	pthread_mutex_unlock(&qemu_mutex);
-	kvm_eat_signal(cpu_single_env, 1000);
-	pthread_mutex_lock(&qemu_mutex);
+    CPUState *cpu_single = cpu_single_env;
+
+    if (!cpu_single_env) {
+        pthread_mutex_unlock(&qemu_mutex);
+        kvm_eat_signal(&io_signal_table, cpu_single_env, 1000);
+        pthread_mutex_lock(&qemu_mutex);
+        cpu_single_env = NULL;
     } else {
-	pthread_cond_wait(&qemu_aio_cond, &qemu_mutex);
+        pthread_cond_wait(&qemu_aio_cond, &qemu_mutex);
+        cpu_single_env = cpu_single;
     }
 }
libkvm/libkvm.c +0 -3
Index: kvm-userspace.io/libkvm/libkvm.c
===================================================================
@@ -388,9 +388,6 @@ int kvm_create(kvm_context_t kvm, unsign
 	if (r < 0)
 	        return r;
 	kvm_create_irqchip(kvm);
-	r = kvm_create_vcpu(kvm, 0);
-	if (r < 0)
-		return r;
 
 	return 0;
 }
user/main.c +1 -2
Index: kvm-userspace.io/user/main.c
===================================================================
@@ -560,8 +560,7 @@ int main(int argc, char **argv)
 	misc_init();
 
 	sem_init(&init_sem, 0, 0);
-	init_vcpu(0);
-	for (i = 1; i < ncpus; ++i)
+	for (i = 0; i < ncpus; ++i)
 		start_vcpu(i);
 	for (i = 0; i < ncpus; ++i)
 		sem_wait(&init_sem);
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author
#2 lore raw

PATCH 2/2 QEMU/KVM: add function to handle signals

In reply to Marcelo Tosatti

SIGUSR1 has no handler, and the SIGUSR2 one does nothing useful anymore (thats also true for SIGIO on tap fd, which runs host_alarm_handler unnecessarily).

qemu/qemu-kvm.c +21 -8
Index: kvm-userspace.io/qemu/qemu-kvm.c
===================================================================
@@ -163,13 +163,30 @@ static int has_work(CPUState *env)
     return kvm_arch_has_work(env);
 }
 
+static int kvm_process_signal(int si_signo)
+{
+    struct sigaction sa;
+
+    switch (si_signo) {
+    case SIGUSR2:
+        pthread_cond_signal(&qemu_aio_cond);
+        break;
+    case SIGALRM:
+    case SIGIO:
+        sigaction(si_signo, NULL, &sa);
+        sa.sa_handler(si_signo);
+        break;
+    }
+
+    return 1;
+}
+
 static int kvm_eat_signal(struct qemu_kvm_signal_table *waitset, CPUState *env,
                           int timeout)
 {
     struct timespec ts;
     int r, e, ret = 0;
     siginfo_t siginfo;
-    struct sigaction sa;
 
     ts.tv_sec = timeout / 1000;
     ts.tv_nsec = (timeout % 1000) * 1000000;

@@ -184,13 +201,9 @@ static int kvm_eat_signal(struct qemu_kv
 	printf("sigtimedwait: %s\n", strerror(e));
 	exit(1);
     }
-    if (r != -1) {
-	sigaction(siginfo.si_signo, NULL, &sa);
-	sa.sa_handler(siginfo.si_signo);
-	if (siginfo.si_signo == SIGUSR2)
-	    pthread_cond_signal(&qemu_aio_cond);
-	ret = 1;
-    }
+    if (r != -1)
+        ret = kvm_process_signal(siginfo.si_signo);
+
     if (env && vcpu_info[env->cpu_index].stop) {
 	vcpu_info[env->cpu_index].stop = 0;
 	vcpu_info[env->cpu_index].stopped = 1;
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#3 lore raw
In reply to Marcelo Tosatti
Quoted 4 lines · Marcelo Tosatti

- Fix reset, powerdown and shutdown.
- Fix kvmctl.

Unfortunately, this is still broken:
- typing into a linux guest console, qemu locked up waiting for a signal
- the regression tests still fail due to guest slowdown. I haven't isolated the cause yet (doesn't reproduce on my machines)

Signature · 8 lines
error compiling committee.c: too many arguments to function


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