How to find closest tag when using git-bisect?

Hi everyone,

I'm trying to git-bisect for debugging, but how can I find the tag I need?

for example, I'm find the file change at maybe commit
fc2bd799c7c79c84a59da6f9221370bc6f38c503, how to find the closest tag
for this commit?

and a anther question is, is every bisect need to recopmile all kernel
code by `make`? or just need to build the thing I need?


thanks.

Louie.