Killing Blow with a Light or One-Handed Piercing Melee Weapon: When the swashbuckler reduces a creature to 0 or fewer hit points with a light or one-handed piercing melee weapon attack while in combat, she regains 1 panache point. Destroying an unattended object, reducing a helpless or unaware creature to 0 or fewer hit points, or reducing a creature that has fewer Hit Dice than half the swashbuckler’s character level to 0 or fewer hit points doesn’t restore any panache.
Does a level 3 Swashbuckler gain Panache from killing a 1-HD creature? Obviously 1 is less than half of 3, but also you should "round down" in Pathfinder.