Both the normal conformance and regression tests and the supplemental performance tests work.
To run the conformance and regression tests with the parallel mode active,
  make check-parallel
  
    The log and summary files for conformance testing are in the
    testsuite/parallel directory.
  
To run the performance tests with the parallel mode active,
  check-performance-parallel
  
    The result file for performance testing are in the
    testsuite directory, in the file
    libstdc++_performance.sum. In addition, the
    policy-based containers have their own visualizations, which have
    additional software dependencies than the usual bare-boned text
    file, and can be generated by using the make
    doc-performance rule in the testsuite's Makefile.