Why is this slow?

["Jakab, Steve" <sjakab@...>]

When doing benchmark tests between Lua and Python, Lua beat it on almost
every test. However, it was considerably slower on a test of passing data
between Lua and C. Here is the Lua code:

function TestDataPass(caller)
	local c = {}
	c.peer = caller

	value = getData(c.peer, "testdata")
	setData(c.peer, "testdata", value + 1)

	return c
end

Here is the C code:

int getData(lua_State *L) 
{
	// 1st argument = calling object pointer (userdata)
	// 2nd argument = data name (string)
	TestObject *object = (TestObject *)lua_touserdata(L, 1);
	const char *varname = lua_tostring(L, 2);

	int value = object->GetData(varname);

	// push the return value on the stack
	lua_pushnumber(L, value);

	return 1;
} // getData

int setData(lua_State *L) 
{
	// 1st argument = calling object pointer (userdata)
	// 2nd argument = data name (string)
	// 3rd argument = data value (number)
	TestObject *object = (TestObject *)lua_touserdata(L, 1);
	const char *varname = lua_tostring(L, 2);
	int value = (int)lua_tonumber(L, 3);

	object->SetData(varname, value);

	return 0;
} // setData

void runtest(TestObject *obj)
{
	int oldtop = lua_gettop(L);
	int result = lua_dofile(L, "TestDataPass.lua");
	if (result != 0)
		return;

	// call the constructor
	lua_getglobal(L, "TestDataPass");
	lua_pushuserdata(L, obj);
	result = lua_call(L, 1, 1);
	if (result != 0)
	{
		lua_settop(L, oldtop);
		return;
	}
	// get the reference to the returned class (locking it so it won't
be
	// garbage collected)
	int classRef = lua_ref(L, 1);
	// free the class reference
	lua_unref(L, classRef);
} // runtest

TestObject is just a structure that maps a string to an integer.

I was able to call the runtest function around 30,000 times in 10 seconds,
but similar test using Python ran 500,000 times in 10 seconds. Am I doing
something wrong in my calls? When I tried a test just calling a do-nothing
function in Lua, it beat Python easily, so I assume that it's the paramater
passing that's slowing Lua down.

-Steve Jakab
Verant