On 7/21/22 14:07, David Hildenbrand wrote:
> 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
>
> While upper layers are already aware how to handl;e 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.
>
> (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 ThreadContext can be reused, simply be reconfiguring the CPU affinity.
>
> Signed-off-by: David Hildenbrand <da...@redhat.com>
> ---
> include/qemu/thread-context.h | 58 +++++++
> qapi/qom.json | 16 ++
> util/meson.build | 1 +
> util/oslib-posix.c | 1 +
> util/thread-context.c | 279 ++++++++++++++++++++++++++++++++++
> 5 files changed, 355 insertions(+)
> create mode 100644 include/qemu/thread-context.h
> create mode 100644 util/thread-context.c
>
> diff --git a/include/qemu/thread-context.h b/include/qemu/thread-context.h
> new file mode 100644
> index 0000000000..c799cbe7a1
> --- /dev/null
> +++ b/include/qemu/thread-context.h
> @@ -0,0 +1,58 @@
> +/*
> + * QEMU Thread Context
> + *
> + * Copyright Red Hat Inc., 2022
> + *
> + * Authors:
> + * David Hildenbrand <da...@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.
> + *
> + */
> +
> +#ifndef SYSEMU_THREAD_CONTEXT_H
> +#define SYSEMU_THREAD_CONTEXT_H
> +
> +#include "qapi/qapi-types-machine.h"
> +#include "qemu/thread.h"
> +#include "qom/object.h"
> +
> +#define TYPE_THREAD_CONTEXT "thread-context"
> +OBJECT_DECLARE_TYPE(ThreadContext, ThreadContextClass,
> + THREAD_CONTEXT)
> +
> +struct ThreadContextClass {
> + ObjectClass parent_class;
> +};
> +
> +struct ThreadContext {
> + /* private */
> + Object parent;
> +
> + /* private */
> + unsigned int thread_id;
> + QemuThread thread;
> +
> + /* Semaphore to wait for context thread action. */
> + QemuSemaphore sem;
> + /* Semaphore to wait for action in context thread. */
> + QemuSemaphore sem_thread;
> + /* Mutex to synchronize requests. */
> + QemuMutex mutex;
> +
> + /* Commands for the thread to execute. */
> + int thread_cmd;
> + void *thread_cmd_data;
> +
> + /* CPU affinity bitmap used for initialization. */
> + unsigned long *init_cpu_bitmap;
> + int init_cpu_nbits;
> +};
> +
> +void thread_context_create_thread(ThreadContext *tc, QemuThread *thread,
> + const char *name,
> + void *(*start_routine)(void *), void *arg,
> + int mode);
> +
> +#endif /* SYSEMU_THREAD_CONTEXT_H */
> diff --git a/qapi/qom.json b/qapi/qom.json
> index 80dd419b39..4775a333ed 100644
> --- a/qapi/qom.json
> +++ b/qapi/qom.json
> @@ -830,6 +830,20 @@
> 'reduced-phys-bits': 'uint32',
> '*kernel-hashes': 'bool' } }
>
> +##
> +# @ThreadContextProperties:
> +#
> +# Properties for thread context objects.
> +#
> +# @cpu-affinity: the CPU affinity for all threads created in the thread
> +# context (default: QEMU main thread affinity)
> +#
> +# Since: 7.2
> +##
> +{ 'struct': 'ThreadContextProperties',
> + 'data': { '*cpu-affinity': ['uint16'] } }
> +
> +
> ##
> # @ObjectType:
> #
> @@ -882,6 +896,7 @@
> { 'name': 'secret_keyring',
> 'if': 'CONFIG_SECRET_KEYRING' },
> 'sev-guest',
> + 'thread-context',
> 's390-pv-guest',
> 'throttle-group',
> 'tls-creds-anon',
> @@ -948,6 +963,7 @@
> 'secret_keyring': { 'type': 'SecretKeyringProperties',
> 'if': 'CONFIG_SECRET_KEYRING' },
> 'sev-guest': 'SevGuestProperties',
> + 'thread-context': 'ThreadContextProperties',
> 'throttle-group': 'ThrottleGroupProperties',
> 'tls-creds-anon': 'TlsCredsAnonProperties',
> 'tls-creds-psk': 'TlsCredsPskProperties',
> 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 75e8cdcf3e..fa66f73bf8 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..dcd607c532
> --- /dev/null
> +++ b/util/thread-context.c
> @@ -0,0 +1,279 @@
> +/*
> + * QEMU Thread Context
> + *
> + * Copyright Red Hat Inc., 2022
> + *
> + * Authors:
> + * David Hildenbrand <da...@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);
This ^^^^ (see my comment to 7/7)
> + 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;
> + }
> +}
Michal
