qemu/util/thread-context.c

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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>
2022-10-14 16:47:16 +03:00
/*
* 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"
util: Add write-only "node-affinity" property for ThreadContext Let's make it easier to pin threads created via a ThreadContext to all host CPUs currently belonging to a given set of host NUMA nodes -- which is the common case. "node-affinity" is simply a shortcut for setting "cpu-affinity" manually to the list of host CPUs belonging to the set of host nodes. This property can only be written. A simple QEMU example to set the CPU affinity to host node 1 on a system with two nodes, 24 CPUs each, whereby odd-numbered host CPUs belong to host node 1: qemu-system-x86_64 -S \ -object thread-context,id=tc1,node-affinity=1 And we can query the cpu-affinity via HMP/QMP: (qemu) qom-get tc1 cpu-affinity [ 1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, 23, 25, 27, 29, 31, 33, 35, 37, 39, 41, 43, 45, 47 ] We cannot query the node-affinity: (qemu) qom-get tc1 node-affinity Error: Insufficient permission to perform this operation 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. Note that if the host CPUs for a host node change due do CPU hot(un)plug CPU onlining/offlining (i.e., lscpu output changes) after the ThreadContext was started, the CPU affinity will not get updated. Reviewed-by: Michal Privoznik <mprivozn@redhat.com> Acked-by: Markus Armbruster <armbru@redhat.com> Message-Id: <20221014134720.168738-5-david@redhat.com> Signed-off-by: David Hildenbrand <david@redhat.com>
2022-10-14 16:47:17 +03:00
#ifdef CONFIG_NUMA
#include <numa.h>
#endif
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>
2022-10-14 16:47:16 +03:00
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;
util: Add write-only "node-affinity" property for ThreadContext Let's make it easier to pin threads created via a ThreadContext to all host CPUs currently belonging to a given set of host NUMA nodes -- which is the common case. "node-affinity" is simply a shortcut for setting "cpu-affinity" manually to the list of host CPUs belonging to the set of host nodes. This property can only be written. A simple QEMU example to set the CPU affinity to host node 1 on a system with two nodes, 24 CPUs each, whereby odd-numbered host CPUs belong to host node 1: qemu-system-x86_64 -S \ -object thread-context,id=tc1,node-affinity=1 And we can query the cpu-affinity via HMP/QMP: (qemu) qom-get tc1 cpu-affinity [ 1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, 23, 25, 27, 29, 31, 33, 35, 37, 39, 41, 43, 45, 47 ] We cannot query the node-affinity: (qemu) qom-get tc1 node-affinity Error: Insufficient permission to perform this operation 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. Note that if the host CPUs for a host node change due do CPU hot(un)plug CPU onlining/offlining (i.e., lscpu output changes) after the ThreadContext was started, the CPU affinity will not get updated. Reviewed-by: Michal Privoznik <mprivozn@redhat.com> Acked-by: Markus Armbruster <armbru@redhat.com> Message-Id: <20221014134720.168738-5-david@redhat.com> Signed-off-by: David Hildenbrand <david@redhat.com>
2022-10-14 16:47:17 +03:00
if (tc->init_cpu_bitmap) {
error_setg(errp, "Mixing CPU and node affinity not supported");
return;
}
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>
2022-10-14 16:47:16 +03:00
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);
}
util: Add write-only "node-affinity" property for ThreadContext Let's make it easier to pin threads created via a ThreadContext to all host CPUs currently belonging to a given set of host NUMA nodes -- which is the common case. "node-affinity" is simply a shortcut for setting "cpu-affinity" manually to the list of host CPUs belonging to the set of host nodes. This property can only be written. A simple QEMU example to set the CPU affinity to host node 1 on a system with two nodes, 24 CPUs each, whereby odd-numbered host CPUs belong to host node 1: qemu-system-x86_64 -S \ -object thread-context,id=tc1,node-affinity=1 And we can query the cpu-affinity via HMP/QMP: (qemu) qom-get tc1 cpu-affinity [ 1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, 23, 25, 27, 29, 31, 33, 35, 37, 39, 41, 43, 45, 47 ] We cannot query the node-affinity: (qemu) qom-get tc1 node-affinity Error: Insufficient permission to perform this operation 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. Note that if the host CPUs for a host node change due do CPU hot(un)plug CPU onlining/offlining (i.e., lscpu output changes) after the ThreadContext was started, the CPU affinity will not get updated. Reviewed-by: Michal Privoznik <mprivozn@redhat.com> Acked-by: Markus Armbruster <armbru@redhat.com> Message-Id: <20221014134720.168738-5-david@redhat.com> Signed-off-by: David Hildenbrand <david@redhat.com>
2022-10-14 16:47:17 +03:00
static void thread_context_set_node_affinity(Object *obj, Visitor *v,
const char *name, void *opaque,
Error **errp)
{
#ifdef CONFIG_NUMA
const int nbits = numa_num_possible_cpus();
ThreadContext *tc = THREAD_CONTEXT(obj);
uint16List *l, *host_nodes = NULL;
unsigned long *bitmap = NULL;
struct bitmask *tmp_cpus;
Error *err = NULL;
int ret, i;
if (tc->init_cpu_bitmap) {
error_setg(errp, "Mixing CPU and node affinity not supported");
return;
}
visit_type_uint16List(v, name, &host_nodes, &err);
if (err) {
error_propagate(errp, err);
return;
}
if (!host_nodes) {
error_setg(errp, "Node list is empty");
goto out;
}
bitmap = bitmap_new(nbits);
tmp_cpus = numa_allocate_cpumask();
for (l = host_nodes; l; l = l->next) {
numa_bitmask_clearall(tmp_cpus);
ret = numa_node_to_cpus(l->value, tmp_cpus);
if (ret) {
/* We ignore any errors, such as impossible nodes. */
continue;
}
for (i = 0; i < nbits; i++) {
if (numa_bitmask_isbitset(tmp_cpus, i)) {
set_bit(i, bitmap);
}
}
}
numa_free_cpumask(tmp_cpus);
if (bitmap_empty(bitmap, nbits)) {
error_setg(errp, "The nodes select no CPUs");
goto out;
}
if (tc->thread_id != -1) {
/*
* Note: we won't be adjusting the affinity of any thread that is still
* around for now, 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_nodes);
#else
error_setg(errp, "NUMA node affinity is not supported by this QEMU");
#endif
}
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>
2022-10-14 16:47:16 +03:00
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);
util: Add write-only "node-affinity" property for ThreadContext Let's make it easier to pin threads created via a ThreadContext to all host CPUs currently belonging to a given set of host NUMA nodes -- which is the common case. "node-affinity" is simply a shortcut for setting "cpu-affinity" manually to the list of host CPUs belonging to the set of host nodes. This property can only be written. A simple QEMU example to set the CPU affinity to host node 1 on a system with two nodes, 24 CPUs each, whereby odd-numbered host CPUs belong to host node 1: qemu-system-x86_64 -S \ -object thread-context,id=tc1,node-affinity=1 And we can query the cpu-affinity via HMP/QMP: (qemu) qom-get tc1 cpu-affinity [ 1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, 23, 25, 27, 29, 31, 33, 35, 37, 39, 41, 43, 45, 47 ] We cannot query the node-affinity: (qemu) qom-get tc1 node-affinity Error: Insufficient permission to perform this operation 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. Note that if the host CPUs for a host node change due do CPU hot(un)plug CPU onlining/offlining (i.e., lscpu output changes) after the ThreadContext was started, the CPU affinity will not get updated. Reviewed-by: Michal Privoznik <mprivozn@redhat.com> Acked-by: Markus Armbruster <armbru@redhat.com> Message-Id: <20221014134720.168738-5-david@redhat.com> Signed-off-by: David Hildenbrand <david@redhat.com>
2022-10-14 16:47:17 +03:00
object_class_property_add(oc, "node-affinity", "int", NULL,
thread_context_set_node_affinity, NULL, NULL);
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>
2022-10-14 16:47:16 +03:00
}
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);
}