This is up to you. Because foreigners also know that Chinese people generally don’t tip, and it’s okay if you don’t tip them. Just give a little and everyone will be happy. Tips in Madrid are not based on percentage. You usually leave 1 euro and 2 euro coins after finishing the meal (there are small plates at the checkout), just get up and leave. (Don't give it with your hands, that's not good, unless you are giving 5 or 10 euro notes, you can hand them to the waiter with your hands). I'm used to giving 1 euro, because when I go out to eat, I spend dozens of euros, so I don't miss that 1 euro. . Then there is the fact that the income of foreign waiters is a combination of salary and tips. It is not easy to work out and it is a meager effort.