Commit 03587328 authored by Anthony Liguori's avatar Anthony Liguori
Browse files

qom: aggressively optimize qom casting 



This patch adds a small typename cache to ObjectClass.  This allows
caching positive casts within each ObjectClass.  Benchmarking a
PPC workload provided by Aurelien, this patch eliminates every
single g_hash_table_lookup() happening during the benchmark (which
was about 2 million per-second).

With this patch applied, I get exactly the same performance (within
the margin of error) as with --disable-qom-cast-debug.

N.B. it's safe to cache typenames only from the _assert() macros
because they are always called with string literals.

Signed-off-by: default avatarAnthony Liguori <aliguori@us.ibm.com>
parent b087143b

include/qom/object.h

+4 −0
Original line number Diff line number Diff line
@@ -344,6 +344,8 @@ typedef void (ObjectUnparent)(Object *obj); 
 */

typedef void (ObjectFree)(void *obj);



#define OBJECT_CLASS_CAST_CACHE 4



/**

 * ObjectClass:

 *
@@ -356,6 +358,8 @@ struct ObjectClass 
    Type type;

    GSList *interfaces;



    const char *cast_cache[OBJECT_CLASS_CAST_CACHE];



    ObjectUnparent *unparent;

};

qom/object.c

+38 −2
Original line number Diff line number Diff line
@@ -439,7 +439,16 @@ Object *object_dynamic_cast_assert(Object *obj, const char *typename, 
                                     typename, file, line, func);



#ifdef CONFIG_QOM_CAST_DEBUG

    Object *inst = object_dynamic_cast(obj, typename);

    int i;

    Object *inst;



    for (i = 0; i < OBJECT_CLASS_CAST_CACHE; i++) {

        if (obj->class->cast_cache[i] == typename) {

            goto out;

        }

    }



    inst = object_dynamic_cast(obj, typename);



    if (!inst && obj) {

        fprintf(stderr, "%s:%d:%s: Object %p is not an instance of type %s\n",
@@ -448,6 +457,15 @@ Object *object_dynamic_cast_assert(Object *obj, const char *typename, 
    }



    assert(obj == inst);



    if (obj == inst) {

        for (i = 1; i < OBJECT_CLASS_CAST_CACHE; i++) {

            obj->class->cast_cache[i - 1] = obj->class->cast_cache[i];

        }

        obj->class->cast_cache[i - 1] = typename;

    }



out:

#endif

    return obj;

}
@@ -510,7 +528,16 @@ ObjectClass *object_class_dynamic_cast_assert(ObjectClass *class, 
    trace_object_class_dynamic_cast_assert(class ? class->type->name : "(null)",

                                           typename, file, line, func);



#ifndef CONFIG_QOM_CAST_DEBUG

#ifdef CONFIG_QOM_CAST_DEBUG

    int i;



    for (i = 0; i < OBJECT_CLASS_CAST_CACHE; i++) {

        if (class->cast_cache[i] == typename) {

            ret = class;

            goto out;

        }

    }

#else

    if (!class->interfaces) {

        return class;

    }
@@ -523,6 +550,15 @@ ObjectClass *object_class_dynamic_cast_assert(ObjectClass *class, 
        abort();

    }



#ifdef CONFIG_QOM_CAST_DEBUG

    if (ret == class) {

        for (i = 1; i < OBJECT_CLASS_CAST_CACHE; i++) {

            class->cast_cache[i - 1] = class->cast_cache[i];

        }

        class->cast_cache[i - 1] = typename;

    }

out:

#endif

    return ret;

}