I'm sure there's a simple explanation: The CPU time graph I generate has useful information, but I see some method with odd hex names, such as 0000000200639fef. Unfortunately, some of these look to be slow, but I'm not sure where to look. Are these Proc identifiers?
I had the same issue when calling pprof.rb on the file written by rubyprof.
I solved it by running pprof.rb from within the same process like so:
# expensive code here
`pprof.rb --text /tmp/bench.tmp > bench.txt`
`pprof.rb --pdf /tmp/bench.tmp > bench.pdf`