CNAMEs are just one type of DNS resource record, so they aren't something different than a DNS record.
I've seen several other posts recently about slow DNS resolution on Linux. I forget what the exact solution was, but I seem to recall it involved tweaking one of the kernel variables.
Try searching this forum (use the search button up near the top, on the right) and look for "dns slow resolve" or something similar. You should find the previous answer.