Rub pork loin with 1 teaspoon garlic powder, 1 teaspoon onion powder, 1 1/2 teaspoons thyme, then sprinkle with salt and pepper; place pork loin in a shallow roasting pan. Roast at 325° for 50 to 55 minutes.
Meanwhile, peel and quarter potatoes; cook in boiling water for about 10 minutes. Drain, let cool, and place potatoes in a large bowl; toss with olive oil, 1 teaspoon dried thyme, chives, 1/2 teaspoon garlic powder, and salt and pepper. Place potatoes around pork loin; roast an additional 45 to 60 minutes, or until pork registers at least 155° on a thermometer.
Cover roast pork loin with foil and let stand for about 15 minutes before slicing.