I'm not sure what's de facto, but I most commonly see other Rust/Linux users reaching for valgrind (callgrind, cachegrind, etc). I've recently used massif (part of valgrind) for doing profiling of heap allocations, as well. In the past I also used oprofile because it gave me a nicely annotated source dump of sample rates in different statements.

I am growing to like perf a lot, though. It seems (haven't measured though) to impose less runtime overhead, and the reporting and source annotation tools are top notch.