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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: Anthony Liguori <aliguori@us.ibm.com>
This commit is contained in:
Anthony Liguori 2013-05-13 15:22:24 -05:00
parent b087143b4d
commit 035873283b
2 changed files with 42 additions and 2 deletions
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4
include/qom/object.h
View File

@ -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;
};

40
qom/object.c
View File

@ -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;
}