grid: High performance primitives to power GPW & Co

This package hosts the performance critical grid operations of cp2k. The code is entirely written in C and can be built stand-alone in order to provide a good separation of concerns between computational chemists and performance engineers.

Currently, this package offers the following main features:

• Collocate a single task, see grid_collocate_pgf_product_cpu in grid_collocate_cpu.h for details.
• Collocate a list of tasks, see grid_collocate_task_list in grid_task_list.h for details.

In order to support diverse hardware architectures different backends are available. Currently, the following backends exist:

• ref: A reference implementations for documentation and validation purposes.
• cpu: A performance optimized implementation for x86 CPUs.

The .task files

For debugging all collocations by the reference backend can be written to .task files. To enable this feature edit the following line in grid_ref_collocate.c:

// Set this to true to write each task to a file.
const bool DUMP_TASKS = false;

The files are given sequential names like grid_collocate_00123.task. Beware that MPI ranks can overwrite each other's files.

The resulting .task files are human readable and diffable:

#Grid collocate task v9
orthorhombic 1
border_mask 0
func 100
...
grid 13 13 18 9.926167350636332098457e-24
#THE_END

For more information see grid_replay.c.

MiniApp

The grid_collocate_miniapp.x binary allows to run individual .task files. By default grid_collocate_pgf_product_cpu is called. When the --batch flag is set then grid_collocate_task_list is called instead.

$ cd cp2k/src/grid
$ make
$ ./grid_collocate_miniapp.x
Usage: grid_base_ref_miniapp.x [--batch <cycles-per-block>] <cycles> <task-file>

$ ./grid_collocate_miniapp.x --batch 10 100 sample_tasks/collocate_ortho_density_l2200.task
Task: sample_tasks/collocate_ortho_density_l2200.task                     Batched: yes   Cycles: 1.000000e+02   Max value: 1.579830e+02   Max diff: 1.705303e-13   Time: 1.884854e-03 sec

Unit Test

The grid_collocate_unittest.x binary runs the .task files from the sample_tasks directory - with and without batching. Beware that this is merely a smoke test. The cp2k regtest suite provides much more thorough testing.

$ cd cp2k/src/grid
$ make
$ ./grid_collocate_unittest.x
Usage: grid_base_ref_unittest.x <cp2k-root-dir>

$ ./grid_collocate_unittest.x ../../
Task: ../../src/grid/sample_tasks/collocate_ortho_density_l0000.task      Batched: no    Cycles: 1.000000e+00   Max value: 3.505772e+00   Max diff: 0.000000e+00   Time: 3.927400e-05 sec
Task: ../../src/grid/sample_tasks/collocate_ortho_density_l0000.task      Batched: yes   Cycles: 1.000000e+00   Max value: 3.505772e+00   Max diff: 0.000000e+00   Time: 1.112822e-03 sec
...
Task: ../../src/grid/sample_tasks/collocate_ortho_non_periodic.task       Batched: yes   Cycles: 1.000000e+00   Max value: 4.483815e-01   Max diff: 0.000000e+00   Time: 1.882868e-02 sec
All tests have passed :-)