There are cases that we want to extract a part of Fortran codes from a software application as a stand-alone executable. For example, when a programmer debugs a large software application such as CESM of NCAR, he/she needs to run whole CESM program up to the source line to debug. If we can take the part of codes that are only relevant to the debugging, it would remove time to run CESM and time to wait in queuing system. There are plenty of other potential use-cases such as collecting kernels from its own applications to setup a private benchmark test suite, or allowing multiple developer to work on each separate of code of a large application parallelly and so on.

However, extracting a kernel from an application has been a laborious manual work. To extract a kernel manually, a programmer looks through all relevant source codes to collect codes that provides required specification. Furthermore, it is trickier to generate data to drive generated kernel execution and to verify the output from the kernel execution. It is time-consuming work to figure out which variables are used in subroutines that are called by the kernel directly or indirectly. What's more, if a variable is a derived type having a pointer member that is another derive type, it is getting more difficult to trace correctly.

KGEN, Fortran Kernel Generator, extracts a Fortran subprogram as a stand-alone software out of a large software application such as CESM. In addition, it generates instrumented files that save input and output data for the generated kernel. For convenience, it also adds codes for correctness check and timing measurement in the generated kernel. Through using KGEN, it will save considerable amount of time that previously spent for manual kernel extraction and enables the potential use-cases mentioned in this abstract that was practically not feasible through manual kernel extraction.

KGEN is written in Python as an extension of F2PY package. During this talk, modest level of introduction to the tool and practical demo that extracts a kernel from CESM would be presented if time permits.