DHE_DSS vs. DHE_RSA

I have been studying to learn about various cipher suites and their performance; I'm wondering about the difference between DHE_DSS_AES256_CBC ciphersuites and DHE_RSA_AES256_CBC ciphersuites. I gathered that DSS is efficient when compared with RSA. Is that correct, and can anyone explain in more detail what the differences are and how they perform?