futhark profile JSONFILE


This tool produces human-readable profiling information based on information collected with futhark bench. Futhark has only rudimentary support for profiling. While the system can collect information about the run-time behaviour of the program, there is currently no automatic way to connect the information to the program source code. However, the collected information can still be useful for estimating the source of inefficiencies.


The first step is to run futhark bench on your program, while passing --profile and --json. This will produce a JSON file containing runtime measurements, as well as collected profiling information. If you neglect to pass --profile, the profiling information will be missing. The information in the JSON file is complete, but it is difficult for humans to read.

The next step is to run futhark profile on the JSON file. For a JSON file prog.json, this will create a top level directory prog.prof that contains files with human-readable profiling information. A set of files will be created for each benchmark dataset. If the original invocation of futhark bench included multiple programs, then futhark profile will create subdirectories for each program (although all inside the same top level directory).

Files produced

Supposing a dataset foo, futhark profile will produce the following files in the top level directory.

  • foo.log: the running log produced during execution. Contains many details on dynamic behaviour, depending on the exact backend.

  • foo.summary: a summary of memory usage and cost centres. For the GPU backends, the cost centres are kernel executions and memory copies.

  • foo.timeline: a list of all recorded profiling events, in the order in which they occurred, along with their runtime and other available information


The profiling information, including the log, is collected from a final run performed after all the measured runs. Profiling information is not collected during the runs that contribute to the runtime measurement reported by futhark bench. However, enabling profiling may still affect performance, as it changes the behaviour of the run time system.

Raw reports

Alternatively, the JSON can also contain a raw profiling report as produced by the C API function futhark_context_report(). A directory is still created, but it will only contain a single set of files, and it will not contain a log.


This shows the sequence of commands one might use to profile the program LocVolCalib.fut, which has three datasets associated with it, using the hip backend:

$ futhark bench --backend=hip --profile --json result.json LocVolCalib.fut
$ futhark profile result.json
$ tree result.prof/
├── LocVolCalib-data_large.in.log
├── LocVolCalib-data_large.in.summary
├── LocVolCalib-data_medium.in.log
├── LocVolCalib-data_medium.in.summary
├── LocVolCalib-data_small.in.log
└── LocVolCalib-data_small.in.summary


Only the C-based backends currently support profiling.

The c backend does not actually record useful profiling information.