[LLVMdev] Announcement - A tool to convert Perf profiles to use with LLVM's sample profiler

[Diego Novillo]

I'm glad to announce the availability of the AutoFDO converter for LLVM.
This tool reads a profile generated with Linux Perf (
https://perf.wiki.kernel.org/) and converts it into a format readable with
LLVM's sample-based profiler. The converter shares a significant amount of
code with GCC's converter tool (authored by Dehao Chen), so we can support
both compilers with it.

At this time, I'm looking for volunteers to try out the tool and use it
with their own code. There will be missing documentation, sharp edges and
other issues typical of a tool that so far has had limited use.

To download and build the converter:

$ git clone https://github.com/google/autofdo.git autofdo
$ cd autofdo && ./configure && make

Note that you will need a compiler with C++11 support (either gcc 4.7+ or a
recent Clang/LLVM).

To use the converter, you need to use Perf with a kernel that supports LBR
(any kernel post 3.4 should suffice) and LLVM from trunk (there is some
support in the 3.4 release, but there were changes post 3.4 that are only
present in trunk).  The workflow is:

$ clang++ -O2 -gline-tables-only code.cc -o code
$ perf record -b ./code
$ create_llvm_prof --binary=./code --out=code.prof
$ clang++ -O2 -fprofile-sample-use=code.prof code.cc -o code

The second version of 'code' should run faster than the first one. In
theory.

For issues with the tool itself, please use the issue tracker in github (
https://github.com/google/autofdo/issues). There is also a mailing list
where you can ask questions about it (
https://groups.google.com/forum/#!forum/autofdo).


Thanks. Diego.
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