Re: [Qemu-devel] [PATCH] qobject: Replace property list with GHashTable

[David Gibson]

On Tue, Oct 06, 2015 at 03:41:56PM +0300, Pavel Fedin wrote:
> ARM GICv3 systems with large number of CPUs create lots of IRQ pins. Since
> every pin is represented as a property, number of these properties becomes
> very large. Every property add first makes sure there's no duplicates.
> Traversing the list becomes very slow, therefore qemu initialization takes
> significant time (several seconds for e. g. 16 CPUs).
> 
> This patch replaces list with GHashTable, making lookup very fast. The only
> drawback is that object_child_foreach() and object_child_foreach_recursive()
> cannot modify their objects during traversal, since GHashTableIter does not
> have modify-safe version. However, the code seems not to modify objects via
> these functions.

Hmm.. modifying a child object internally should be fine, shouldn't
it?  IIUC only trying to remove it, change the key or the pointer to
the value should be problematic.

> Signed-off-by: Pavel Fedin <address@hidden>
> ---
>  include/qom/object.h |  4 +--
>  qmp.c                |  8 +++--
>  qom/object.c         | 98 
> +++++++++++++++++++++++-----------------------------
>  vl.c                 |  4 ++-
>  4 files changed, 54 insertions(+), 60 deletions(-)
> 
> diff --git a/include/qom/object.h b/include/qom/object.h
> index be7280c..b100923 100644
> --- a/include/qom/object.h
> +++ b/include/qom/object.h
> @@ -345,7 +345,7 @@ typedef struct ObjectProperty
>      ObjectPropertyRelease *release;
>      void *opaque;
>  
> -    QTAILQ_ENTRY(ObjectProperty) node;
> +    Object *obj;

What is the new obj pointer here for?

>  } ObjectProperty;
>  
>  /**
> @@ -405,7 +405,7 @@ struct Object
>      /*< private >*/
>      ObjectClass *class;
>      ObjectFree *free;
> -    QTAILQ_HEAD(, ObjectProperty) properties;
> +    GHashTable *properties;

How much extra memory does each Object take with no (or few) properties by
using a hash table rather than a simple list here?

>      uint32_t ref;
>      Object *parent;
>  };
> diff --git a/qmp.c b/qmp.c
> index 057a7cb..683f427 100644
> --- a/qmp.c
> +++ b/qmp.c
> @@ -207,6 +207,7 @@ ObjectPropertyInfoList *qmp_qom_list(const char *path, 
> Error **errp)
>      Object *obj;
>      bool ambiguous = false;
>      ObjectPropertyInfoList *props = NULL;
> +    GHashTableIter iter;
>      ObjectProperty *prop;
>  
>      obj = object_resolve_path(path, &ambiguous);
> @@ -220,7 +221,8 @@ ObjectPropertyInfoList *qmp_qom_list(const char *path, 
> Error **errp)
>          return NULL;
>      }
>  
> -    QTAILQ_FOREACH(prop, &obj->properties, node) {
> +    g_hash_table_iter_init(&iter, obj->properties);
> +    while (g_hash_table_iter_next(&iter, NULL, (gpointer *)&prop)) {
>          ObjectPropertyInfoList *entry = g_malloc0(sizeof(*entry));
>  
>          entry->value = g_malloc0(sizeof(ObjectPropertyInfo));
> @@ -499,6 +501,7 @@ DevicePropertyInfoList *qmp_device_list_properties(const 
> char *typename,
>  {
>      ObjectClass *klass;
>      Object *obj;
> +    GHashTableIter iter;
>      ObjectProperty *prop;
>      DevicePropertyInfoList *prop_list = NULL;
>  
> @@ -517,7 +520,8 @@ DevicePropertyInfoList *qmp_device_list_properties(const 
> char *typename,
>  
>      obj = object_new(typename);
>  
> -    QTAILQ_FOREACH(prop, &obj->properties, node) {
> +    g_hash_table_iter_init(&iter, obj->properties);
> +    while (g_hash_table_iter_next(&iter, NULL, (gpointer *)&prop)) {
>          DevicePropertyInfo *info;
>          DevicePropertyInfoList *entry;
>  
> diff --git a/qom/object.c b/qom/object.c
> index 4805328..9649243 100644
> --- a/qom/object.c
> +++ b/qom/object.c
> @@ -326,6 +326,20 @@ static void object_post_init_with_type(Object *obj, 
> TypeImpl *ti)
>      }
>  }
>  
> +static void property_destroy(gpointer data)
> +{
> +    ObjectProperty *prop = data;
> +
> +    if (prop->release) {
> +        prop->release(prop->obj, prop->name, prop->opaque);
> +    }
> +
> +    g_free(prop->name);
> +    g_free(prop->type);
> +    g_free(prop->description);
> +    g_free(prop);
> +}
> +
>  void object_initialize_with_type(void *data, size_t size, TypeImpl *type)
>  {
>      Object *obj = data;
> @@ -340,7 +354,8 @@ void object_initialize_with_type(void *data, size_t size, 
> TypeImpl *type)
>      memset(obj, 0, type->instance_size);
>      obj->class = type->class;
>      object_ref(obj);
> -    QTAILQ_INIT(&obj->properties);
> +    obj->properties = g_hash_table_new_full(g_str_hash, g_str_equal,
> +                                            NULL, property_destroy);
>      object_init_with_type(obj, type);
>      object_post_init_with_type(obj, type);
>  }
> @@ -357,40 +372,19 @@ static inline bool 
> object_property_is_child(ObjectProperty *prop)
>      return strstart(prop->type, "child<", NULL);
>  }
>  
> -static void object_property_del_all(Object *obj)
> +static gboolean object_property_del_child(gpointer key, gpointer value,
> +                                          gpointer child)
>  {
> -    while (!QTAILQ_EMPTY(&obj->properties)) {
> -        ObjectProperty *prop = QTAILQ_FIRST(&obj->properties);
> -
> -        QTAILQ_REMOVE(&obj->properties, prop, node);
> +    ObjectProperty *prop = value;
>  
> -        if (prop->release) {
> -            prop->release(obj, prop->name, prop->opaque);
> -        }
> -
> -        g_free(prop->name);
> -        g_free(prop->type);
> -        g_free(prop->description);
> -        g_free(prop);
> -    }
> -}
> -
> -static void object_property_del_child(Object *obj, Object *child, Error 
> **errp)
> -{
> -    ObjectProperty *prop;
> -
> -    QTAILQ_FOREACH(prop, &obj->properties, node) {
> -        if (object_property_is_child(prop) && prop->opaque == child) {
> -            object_property_del(obj, prop->name, errp);
> -            break;
> -        }
> -    }
> +    return object_property_is_child(prop) && prop->opaque == child;
>  }
>  
>  void object_unparent(Object *obj)
>  {
>      if (obj->parent) {
> -        object_property_del_child(obj->parent, obj, NULL);
> +        g_hash_table_foreach_remove(obj->properties,
> +                                    object_property_del_child, obj);

Ugh.  Iterating through the whole hash table to delete a member is
pretty nasty, buy I guess you have to because you're essentially
deleting by value rather than by key.  I suppose it's no worse than
the current path.

>      }
>  }
>  
> @@ -410,7 +404,7 @@ static void object_finalize(void *data)
>      Object *obj = data;
>      TypeImpl *ti = obj->class->type;
>  
> -    object_property_del_all(obj);
> +    g_hash_table_unref(obj->properties);
>      object_deinit(obj, ti);
>  
>      g_assert(obj->ref == 0);
> @@ -779,10 +773,12 @@ static int do_object_child_foreach(Object *obj,
>                                     int (*fn)(Object *child, void *opaque),
>                                     void *opaque, bool recurse)
>  {
> -    ObjectProperty *prop, *next;
> +    GHashTableIter iter;
> +    ObjectProperty *prop;
>      int ret = 0;
>  
> -    QTAILQ_FOREACH_SAFE(prop, &obj->properties, node, next) {
> +    g_hash_table_iter_init(&iter, obj->properties);
> +    while (g_hash_table_iter_next(&iter, NULL, (gpointer *)&prop)) {
>          if (object_property_is_child(prop)) {
>              Object *child = prop->opaque;
>  
> @@ -879,13 +875,11 @@ object_property_add(Object *obj, const char *name, 
> const char *type,
>          return ret;
>      }
>  
> -    QTAILQ_FOREACH(prop, &obj->properties, node) {
> -        if (strcmp(prop->name, name) == 0) {
> -            error_setg(errp, "attempt to add duplicate property '%s'"
> +    if (g_hash_table_contains(obj->properties, name)) {
> +        error_setg(errp, "attempt to add duplicate property '%s'"
>                         " to object (type '%s')", name,
>                         object_get_typename(obj));
> -            return NULL;
> -        }
> +        return NULL;
>      }
>  
>      prop = g_malloc0(sizeof(*prop));
> @@ -897,8 +891,9 @@ object_property_add(Object *obj, const char *name, const 
> char *type,
>      prop->set = set;
>      prop->release = release;
>      prop->opaque = opaque;
> +    prop->obj = obj;
>  
> -    QTAILQ_INSERT_TAIL(&obj->properties, prop, node);
> +    g_hash_table_insert(obj->properties, prop->name, prop);
>      return prop;
>  }
>  
> @@ -907,10 +902,9 @@ ObjectProperty *object_property_find(Object *obj, const 
> char *name,
>  {
>      ObjectProperty *prop;
>  
> -    QTAILQ_FOREACH(prop, &obj->properties, node) {
> -        if (strcmp(prop->name, name) == 0) {
> -            return prop;
> -        }
> +    prop = g_hash_table_lookup(obj->properties, name);
> +    if (prop) {
> +        return prop;
>      }
>  
>      error_setg(errp, "Property '.%s' not found", name);
> @@ -919,21 +913,11 @@ ObjectProperty *object_property_find(Object *obj, const 
> char *name,
>  
>  void object_property_del(Object *obj, const char *name, Error **errp)
>  {
> -    ObjectProperty *prop = object_property_find(obj, name, errp);
> -    if (prop == NULL) {
> +    if (g_hash_table_remove(obj->properties, name)) {
>          return;
>      }
>  
> -    if (prop->release) {
> -        prop->release(obj, name, prop->opaque);
> -    }
> -
> -    QTAILQ_REMOVE(&obj->properties, prop, node);
> -
> -    g_free(prop->name);
> -    g_free(prop->type);
> -    g_free(prop->description);
> -    g_free(prop);
> +    error_setg(errp, "Property '.%s' not found", name);
>  }
>  
>  void object_property_get(Object *obj, Visitor *v, const char *name,
> @@ -1453,11 +1437,13 @@ void object_property_add_const_link(Object *obj, 
> const char *name,
>  gchar *object_get_canonical_path_component(Object *obj)
>  {
>      ObjectProperty *prop = NULL;
> +    GHashTableIter iter;
>  
>      g_assert(obj);
>      g_assert(obj->parent != NULL);
>  
> -    QTAILQ_FOREACH(prop, &obj->parent->properties, node) {
> +    g_hash_table_iter_init(&iter, obj->parent->properties);
> +    while (g_hash_table_iter_next(&iter, NULL, (gpointer *)&prop)) {
>          if (!object_property_is_child(prop)) {
>              continue;
>          }
> @@ -1541,11 +1527,13 @@ static Object *object_resolve_partial_path(Object 
> *parent,
>                                                bool *ambiguous)
>  {
>      Object *obj;
> +    GHashTableIter iter;
>      ObjectProperty *prop;
>  
>      obj = object_resolve_abs_path(parent, parts, typename, 0);
>  
> -    QTAILQ_FOREACH(prop, &parent->properties, node) {
> +    g_hash_table_iter_init(&iter, parent->properties);
> +    while (g_hash_table_iter_next(&iter, NULL, (gpointer *)&prop)) {
>          Object *found;
>  
>          if (!object_property_is_child(prop)) {
> diff --git a/vl.c b/vl.c
> index e211f6a..7065d5f 100644
> --- a/vl.c
> +++ b/vl.c
> @@ -1506,13 +1506,15 @@ MachineInfoList *qmp_query_machines(Error **errp)
>  
>  static int machine_help_func(QemuOpts *opts, MachineState *machine)
>  {
> +    GHashTableIter iter;
>      ObjectProperty *prop;
>  
>      if (!qemu_opt_has_help_opt(opts)) {
>          return 0;
>      }
>  
> -    QTAILQ_FOREACH(prop, &OBJECT(machine)->properties, node) {
> +    g_hash_table_iter_init(&iter, OBJECT(machine)->properties);
> +    while (g_hash_table_iter_next(&iter, NULL, (gpointer *)&prop)) {
>          if (!prop->set) {
>              continue;
>          }

-- 
David Gibson                    | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au  | minimalist, thank you.  NOT _the_ _other_
                                | _way_ _around_!
http://www.ozlabs.org/~dgibson

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