How to add asm code to a '.C' file

[nickle]

My developing environment is: OS(fedora2), compiler(arm-linux-gcc), target(arm9)
I am doing some work, it does not perform as what I expected. So I want to change some C code to asm code to improve the performance. But I have not found any useful article or books. Somebody told me to watch the examples, however, I don't think it is good way.
Any help will be appreciated!

[Krendoshazin]

It should just be a case of the following:

main() {
  asm("... assembly code ")
}