[LLVMdev] RFC - A tool to convert profiles from external profilers

[Bob Wilson]

> On Jul 16, 2014, at 11:20 AM, Diego Novillo <dnovillo at google.com> wrote:
> 
> 
> A few weeks ago, I announced the availability of a conversion tool that converts Linux Perf sample profiles to LLVM's sample profiler (https://github.com/google/autofdo).
> 
> I have now ported this tool to the LLVM tree, so it can be made available as part of LLVM. I've got a working version, but I still need to massage the code to use LLVM's own libraries (logging, flags, etc) and adapt it to LLVM's coding guidelines.
> 
> I expect to have an initial patch ready in a few days. In the meantime, I would like to open it up for some bike shedding on how this tool will integrate with LLVM. I cannot guarantee that I'll agree to address all feedback myself, but I do want to make sure that the major issues and direction are addressed.
> 
> The tool receives two inputs: a profile file and an ELF executable (built with -gmlt). It produces as output a profile in the format expected by -fprofile-sample-use.
> 
> The requirements on the input is that we must be able to map counts to specific source file locations. So, the profiling source must be some kind of sample-based instruction execution counter. Anything that keeps track of how frequently a specific instruction has been executed.
> 
> Using the executable's line table information, the tool maps instruction locations back to source locations.
> 
> Currently, the native profile reader for Linux Perf and the writer for LLVM's profile are part of the same tree. They both reside in llvm/tools/llvm-prof-converter.

What do you think about invoking this via the existing “llvm-profdata” tool?  It currently supports two commands: “show” and “merge”. We could add a new “convert” command.

> 
> I would like to support more than Linux Perf, eventually. So, I'm thinking that I want to move the LLVM profile writer to llvm/lib/ProfileData and only have the various readers under llvm/tools/llvm-prof-converter.
> 
> I don't think I will be working on supporting anything other than Linux Perf for now. But if anyone is interested in supporting profilers in other platforms, please let me know. I want to make sure the implementation doesn't tie itself too much to Linux Perf.
> 
> 
> Thanks. Diego.
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