difference between mysq 5.1 and 5.4

what are performance differences between mysql 5.1 and 5.4, how feasible it is to upgrade existing 5,1 to 5.4?

5.1 -> 5.4 performance is roughly comparable to 5.1 -> Percona-5.1. If you want better performance than that, you need to look at 5.5. Most of the time, performance is more a problem of the application and the architecture, not the database.