C is extremley performant. It is a compiled language with no runtime overhead. The compilers are very old and optimized. So there is a lot of optimization built into the compilers. Here is the performance of C ranked:
Not only that, but every part of the language of C is designed to reduce overhead and be optimized. To achieve this, C is very simple (as you can learn on the simplicity page).
Now, C is only fast if you write fast code, as stated in the previous paragraph, so you need to bring a lot to the table. However, this means that there is many things that C lets you do that other languages do not. Some of these are: