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authorDavid Hildenbrand2022-10-14 15:47:16 +0200
committerDavid Hildenbrand2022-10-27 11:00:43 +0200
commite2de2c497e5744bc2c009aadd0af7633f2947948 (patch)
tree490d64fd81d6fab7e8ece6c521e632317aaa9933 /util
parentutil: Introduce qemu_thread_set_affinity() and qemu_thread_get_affinity() (diff)
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util: Introduce ThreadContext user-creatable object
Setting the CPU affinity of QEMU threads is a bit problematic, because QEMU doesn't always have permissions to set the CPU affinity itself, for example, with seccomp after initialized by QEMU: -sandbox enable=on,resourcecontrol=deny General information about CPU affinities can be found in the man page of taskset: CPU affinity is a scheduler property that "bonds" a process to a given set of CPUs on the system. The Linux scheduler will honor the given CPU affinity and the process will not run on any other CPUs. While upper layers are already aware of how to handle CPU affinities for long-lived threads like iothreads or vcpu threads, especially short-lived threads, as used for memory-backend preallocation, are more involved to handle. These threads are created on demand and upper layers are not even able to identify and configure them. Introduce the concept of a ThreadContext, that is essentially a thread used for creating new threads. All threads created via that context thread inherit the configured CPU affinity. Consequently, it's sufficient to create a ThreadContext and configure it once, and have all threads created via that ThreadContext inherit the same CPU affinity. The CPU affinity of a ThreadContext can be configured two ways: (1) Obtaining the thread id via the "thread-id" property and setting the CPU affinity manually (e.g., via taskset). (2) Setting the "cpu-affinity" property and letting QEMU try set the CPU affinity itself. This will fail if QEMU doesn't have permissions to do so anymore after seccomp was initialized. A simple QEMU example to set the CPU affinity to host CPU 0,1,6,7 would be: qemu-system-x86_64 -S \ -object thread-context,id=tc1,cpu-affinity=0-1,cpu-affinity=6-7 And we can query it via HMP/QMP: (qemu) qom-get tc1 cpu-affinity [ 0, 1, 6, 7 ] But note that due to dynamic library loading this example will not work before we actually make use of thread_context_create_thread() in QEMU code, because the type will otherwise not get registered. We'll wire this up next to make it work. In general, the interface behaves like pthread_setaffinity_np(): host CPU numbers that are currently not available are ignored; only host CPU numbers that are impossible with the current kernel will fail. If the list of host CPU numbers does not include a single CPU that is available, setting the CPU affinity will fail. A ThreadContext can be reused, simply by reconfiguring the CPU affinity. Note that the CPU affinity of previously created threads will not get adjusted. Reviewed-by: Michal Privoznik <mprivozn@redhat.com> Acked-by: Markus Armbruster <armbru@redhat.com> Message-Id: <20221014134720.168738-4-david@redhat.com> Signed-off-by: David Hildenbrand <david@redhat.com>
Diffstat (limited to 'util')
-rw-r--r--util/meson.build1
-rw-r--r--util/oslib-posix.c1
-rw-r--r--util/thread-context.c278
3 files changed, 280 insertions, 0 deletions
diff --git a/util/meson.build b/util/meson.build
index 5e282130df..e97cd2d779 100644
--- a/util/meson.build
+++ b/util/meson.build
@@ -1,4 +1,5 @@
util_ss.add(files('osdep.c', 'cutils.c', 'unicode.c', 'qemu-timer-common.c'))
+util_ss.add(files('thread-context.c'))
if not config_host_data.get('CONFIG_ATOMIC64')
util_ss.add(files('atomic64.c'))
endif
diff --git a/util/oslib-posix.c b/util/oslib-posix.c
index 905cbc27cc..28305cdea3 100644
--- a/util/oslib-posix.c
+++ b/util/oslib-posix.c
@@ -42,6 +42,7 @@
#include "qemu/cutils.h"
#include "qemu/compiler.h"
#include "qemu/units.h"
+#include "qemu/thread-context.h"
#ifdef CONFIG_LINUX
#include <sys/syscall.h>
diff --git a/util/thread-context.c b/util/thread-context.c
new file mode 100644
index 0000000000..c921905396
--- /dev/null
+++ b/util/thread-context.c
@@ -0,0 +1,278 @@
+/*
+ * QEMU Thread Context
+ *
+ * Copyright Red Hat Inc., 2022
+ *
+ * Authors:
+ * David Hildenbrand <david@redhat.com>
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2 or later.
+ * See the COPYING file in the top-level directory.
+ */
+
+#include "qemu/osdep.h"
+#include "qemu/thread-context.h"
+#include "qapi/error.h"
+#include "qapi/qapi-builtin-visit.h"
+#include "qapi/visitor.h"
+#include "qemu/config-file.h"
+#include "qapi/qapi-builtin-visit.h"
+#include "qom/object_interfaces.h"
+#include "qemu/module.h"
+#include "qemu/bitmap.h"
+
+enum {
+ TC_CMD_NONE = 0,
+ TC_CMD_STOP,
+ TC_CMD_NEW,
+};
+
+typedef struct ThreadContextCmdNew {
+ QemuThread *thread;
+ const char *name;
+ void *(*start_routine)(void *);
+ void *arg;
+ int mode;
+} ThreadContextCmdNew;
+
+static void *thread_context_run(void *opaque)
+{
+ ThreadContext *tc = opaque;
+
+ tc->thread_id = qemu_get_thread_id();
+ qemu_sem_post(&tc->sem);
+
+ while (true) {
+ /*
+ * Threads inherit the CPU affinity of the creating thread. For this
+ * reason, we create new (especially short-lived) threads from our
+ * persistent context thread.
+ *
+ * Especially when QEMU is not allowed to set the affinity itself,
+ * management tools can simply set the affinity of the context thread
+ * after creating the context, to have new threads created via
+ * the context inherit the CPU affinity automatically.
+ */
+ switch (tc->thread_cmd) {
+ case TC_CMD_NONE:
+ break;
+ case TC_CMD_STOP:
+ tc->thread_cmd = TC_CMD_NONE;
+ qemu_sem_post(&tc->sem);
+ return NULL;
+ case TC_CMD_NEW: {
+ ThreadContextCmdNew *cmd_new = tc->thread_cmd_data;
+
+ qemu_thread_create(cmd_new->thread, cmd_new->name,
+ cmd_new->start_routine, cmd_new->arg,
+ cmd_new->mode);
+ tc->thread_cmd = TC_CMD_NONE;
+ tc->thread_cmd_data = NULL;
+ qemu_sem_post(&tc->sem);
+ break;
+ }
+ default:
+ g_assert_not_reached();
+ }
+ qemu_sem_wait(&tc->sem_thread);
+ }
+}
+
+static void thread_context_set_cpu_affinity(Object *obj, Visitor *v,
+ const char *name, void *opaque,
+ Error **errp)
+{
+ ThreadContext *tc = THREAD_CONTEXT(obj);
+ uint16List *l, *host_cpus = NULL;
+ unsigned long *bitmap = NULL;
+ int nbits = 0, ret;
+ Error *err = NULL;
+
+ visit_type_uint16List(v, name, &host_cpus, &err);
+ if (err) {
+ error_propagate(errp, err);
+ return;
+ }
+
+ if (!host_cpus) {
+ error_setg(errp, "CPU list is empty");
+ goto out;
+ }
+
+ for (l = host_cpus; l; l = l->next) {
+ nbits = MAX(nbits, l->value + 1);
+ }
+ bitmap = bitmap_new(nbits);
+ for (l = host_cpus; l; l = l->next) {
+ set_bit(l->value, bitmap);
+ }
+
+ if (tc->thread_id != -1) {
+ /*
+ * Note: we won't be adjusting the affinity of any thread that is still
+ * around, but only the affinity of the context thread.
+ */
+ ret = qemu_thread_set_affinity(&tc->thread, bitmap, nbits);
+ if (ret) {
+ error_setg(errp, "Setting CPU affinity failed: %s", strerror(ret));
+ }
+ } else {
+ tc->init_cpu_bitmap = bitmap;
+ bitmap = NULL;
+ tc->init_cpu_nbits = nbits;
+ }
+out:
+ g_free(bitmap);
+ qapi_free_uint16List(host_cpus);
+}
+
+static void thread_context_get_cpu_affinity(Object *obj, Visitor *v,
+ const char *name, void *opaque,
+ Error **errp)
+{
+ unsigned long *bitmap, nbits, value;
+ ThreadContext *tc = THREAD_CONTEXT(obj);
+ uint16List *host_cpus = NULL;
+ uint16List **tail = &host_cpus;
+ int ret;
+
+ if (tc->thread_id == -1) {
+ error_setg(errp, "Object not initialized yet");
+ return;
+ }
+
+ ret = qemu_thread_get_affinity(&tc->thread, &bitmap, &nbits);
+ if (ret) {
+ error_setg(errp, "Getting CPU affinity failed: %s", strerror(ret));
+ return;
+ }
+
+ value = find_first_bit(bitmap, nbits);
+ while (value < nbits) {
+ QAPI_LIST_APPEND(tail, value);
+
+ value = find_next_bit(bitmap, nbits, value + 1);
+ }
+ g_free(bitmap);
+
+ visit_type_uint16List(v, name, &host_cpus, errp);
+ qapi_free_uint16List(host_cpus);
+}
+
+static void thread_context_get_thread_id(Object *obj, Visitor *v,
+ const char *name, void *opaque,
+ Error **errp)
+{
+ ThreadContext *tc = THREAD_CONTEXT(obj);
+ uint64_t value = tc->thread_id;
+
+ visit_type_uint64(v, name, &value, errp);
+}
+
+static void thread_context_instance_complete(UserCreatable *uc, Error **errp)
+{
+ ThreadContext *tc = THREAD_CONTEXT(uc);
+ char *thread_name;
+ int ret;
+
+ thread_name = g_strdup_printf("TC %s",
+ object_get_canonical_path_component(OBJECT(uc)));
+ qemu_thread_create(&tc->thread, thread_name, thread_context_run, tc,
+ QEMU_THREAD_JOINABLE);
+ g_free(thread_name);
+
+ /* Wait until initialization of the thread is done. */
+ while (tc->thread_id == -1) {
+ qemu_sem_wait(&tc->sem);
+ }
+
+ if (tc->init_cpu_bitmap) {
+ ret = qemu_thread_set_affinity(&tc->thread, tc->init_cpu_bitmap,
+ tc->init_cpu_nbits);
+ if (ret) {
+ error_setg(errp, "Setting CPU affinity failed: %s", strerror(ret));
+ }
+ g_free(tc->init_cpu_bitmap);
+ tc->init_cpu_bitmap = NULL;
+ }
+}
+
+static void thread_context_class_init(ObjectClass *oc, void *data)
+{
+ UserCreatableClass *ucc = USER_CREATABLE_CLASS(oc);
+
+ ucc->complete = thread_context_instance_complete;
+ object_class_property_add(oc, "thread-id", "int",
+ thread_context_get_thread_id, NULL, NULL,
+ NULL);
+ object_class_property_add(oc, "cpu-affinity", "int",
+ thread_context_get_cpu_affinity,
+ thread_context_set_cpu_affinity, NULL, NULL);
+}
+
+static void thread_context_instance_init(Object *obj)
+{
+ ThreadContext *tc = THREAD_CONTEXT(obj);
+
+ tc->thread_id = -1;
+ qemu_sem_init(&tc->sem, 0);
+ qemu_sem_init(&tc->sem_thread, 0);
+ qemu_mutex_init(&tc->mutex);
+}
+
+static void thread_context_instance_finalize(Object *obj)
+{
+ ThreadContext *tc = THREAD_CONTEXT(obj);
+
+ if (tc->thread_id != -1) {
+ tc->thread_cmd = TC_CMD_STOP;
+ qemu_sem_post(&tc->sem_thread);
+ qemu_thread_join(&tc->thread);
+ }
+ qemu_sem_destroy(&tc->sem);
+ qemu_sem_destroy(&tc->sem_thread);
+ qemu_mutex_destroy(&tc->mutex);
+}
+
+static const TypeInfo thread_context_info = {
+ .name = TYPE_THREAD_CONTEXT,
+ .parent = TYPE_OBJECT,
+ .class_init = thread_context_class_init,
+ .instance_size = sizeof(ThreadContext),
+ .instance_init = thread_context_instance_init,
+ .instance_finalize = thread_context_instance_finalize,
+ .interfaces = (InterfaceInfo[]) {
+ { TYPE_USER_CREATABLE },
+ { }
+ }
+};
+
+static void thread_context_register_types(void)
+{
+ type_register_static(&thread_context_info);
+}
+type_init(thread_context_register_types)
+
+void thread_context_create_thread(ThreadContext *tc, QemuThread *thread,
+ const char *name,
+ void *(*start_routine)(void *), void *arg,
+ int mode)
+{
+ ThreadContextCmdNew data = {
+ .thread = thread,
+ .name = name,
+ .start_routine = start_routine,
+ .arg = arg,
+ .mode = mode,
+ };
+
+ qemu_mutex_lock(&tc->mutex);
+ tc->thread_cmd = TC_CMD_NEW;
+ tc->thread_cmd_data = &data;
+ qemu_sem_post(&tc->sem_thread);
+
+ while (tc->thread_cmd != TC_CMD_NONE) {
+ qemu_sem_wait(&tc->sem);
+ }
+ qemu_mutex_unlock(&tc->mutex);
+}