[lamontcg]

When I've needed to dump a stack trace, I've just included an interrupt handler which prints the call stack to a debug log.

That has been good enough for the problem of "wtf is this ruby process doing for _minutes_ at a time?" That doesn't get you flame graphs, but you can take a few snapshots and get an idea of what is happening.

For more involved perf debugging I've used ruby-prof.