So, he's eating about 1 cup per day? That sounds like it'd be about right for a growing pup... especially if he's already 7.6lbs at only 3 1/2 months old.
Some like SD. I'm not a huge fan of it. I think there are better choices out there for a young, healthy pup.
I tend to avoid corn, wheat, soy, by-products, and most grains. Like to see a named meat as the first ingredient. But, also, be sure to look into where the food is being made or produced, as sometimes that's more important than an ingredient list.
Good luck,