How long do i cook a 8-9lb boneless pork loin?

i have a 8-9 lb pork loin boneless how long and at what temp should i cook this on the charcoal grill? my grill gets to 250F no prob so getting ENOUGH heat and holding it isn't a issue and i also have a smoker attachment its a little side compartment so coals arnt under it do i use that? i just need to know how long and what temp to cook it i have about 1-2lbs of my custom made secret rub to go on it as well