In http://reviews.llvm.org/D4850, I proposed porting a tool that converts Linux Perf profiles to LLVM. This tool would be invoked via llvm-profdata using a new 'convert' command. Unfortunately, there are some wrinkles in this port that are likely going to represent ongoing maintenance issues, as well as some licencing concerns due to some kernel headers used by the Perf parser. To make things simpler, I am changing my plans a bit. Since LLVM already has a canonical format that sample profilers must emit (http://clang.llvm.org/docs/UsersManual.html#sample-profile-format), any sample profiler (not just Linux Perf) that writes its profiles in that format can already be handled by LLVM. When using Linux Perf, a Perf->LLVM conversion tool is available at https://github.com/google/autofdo. Therefore, I'm dropping the patch http://reviews.llvm.org/D4850 to maintain the current status. The current format supported by LLVM is simple to generate from any sample profiler, so we can use it as an exchange format. The backend currently reads it directly, but in the near future I will introduce a more compact representation for which I will add a 'convert' operation to llvm-profdata. This way, we can easily add support for other sample profilers using the exchange format defined in http://clang.llvm.org/docs/UsersManual.html#sample-profile-format. We control that format, so we can make changes to it independently of what other sample profilers generate. Thanks. Diego.