Version 5 (modified by hadcv, 21 months ago) (diff)

Name and subject of the action

Last edition: 11/30/20 20:05:57 by epico

The PI is responsible to closely follow the progress of the action, and especially to contact NEMO project manager if the delay on preview (or review) are longer than the 2 weeks expected.

  1. Summary
  2. Preview
  3. Tests
  4. Review


Action Implement 2D tiling (with the LFRA version of NEMO)
PI(S) Daley Calvert, Andrew Coward
Digest Implement 2D tiling to reduce traffic between main memory and L3 cache
Dependencies DO loop macros (2020WP/KERNEL-02_Coward_Do Loop Macros_part1), extended haloes (Italo Epicoco, Seb Masson and Francesca Mele), extension of XIOS to accept 2D tiles of data (Yann Meurdesoif & Seb Masson)
Branch source:/NEMO/branches/{YEAR}/dev_r{REV}_{ACTION_NAME}
Previewer(s) Gurvan Madec
Reviewer(s) Gurvan Madec
Ticket #2365


Implement loop tiling over horizontal dimensions (i and j).


A trial implementation of tra_ldf_iso is described in this document. It will be revised as described here.

The main code changes in the preferred approach (using public variables) are described below.

Summary of method

The full processor domain (1:jpi, 1:jpj) is split into one or more subdomains (tiles).

To work on a tile, the DO loop macros in do_loop_substitute are modified to use a new set of domain indices. A new subroutine DOM/domain/dom_tile sets the values of these indices and is also used to initialise the tile to the full domain in DOM/domain/dom_init.

A loop over tiles is implemented at the timestepping level in OCE/step/stp. The domain indices for the tile subdomain are set within this loop by dom_tile, then 'unset' (set back to the full domain) after exiting the loop. All DO loops within the tiling loop therefore work on the current tile, instead of the full processor domain.

The number of tiles is determined by the tile lengths, nn_tile_i and nn_tile_j defined in a new namelist namtile, with respect to the full domain.



New subroutines

  • dom_tile - Set domain indices

Modified modules

NOTE: the number of affected modules is expected to be much larger in the final implementation

  • cfgs/SHARED/namelist_ref - Add namelist namtile
  • OCE/DOM/dom_oce - Declare namelist variables
  • OCE/DOM/domain - Read namtile namelist and calculate tiling decomposition, add dom_tile, initialise domain indices
  • OCE/TRA/traldf - Changes to account for domain indices
  • OCE/TRA/traldf_iso - Changes to account for domain indices
  • OCE/do_loop_substitute - Implement domain indices
  • OCE/par_oce - Declare domain indices and tiling decomposition parameters
  • OCE/step - Add tiling loop and set domain indices using dom_tile
  • OCE/step_oce - Import dom_tile


  • Global variables
    • ntsi, ntsj- start index of tile
    • ntei, ntej- end index of tile
    • ntsim1, ntsjm1- start index of tile, minus 1
    • nteip1, ntejp1- end index of tile, plus 1
    • ntile- tile number
  • Parameters
    • jpnitile, jpnjtile, jpnijtile- number of tiles
  • Loop indices
    • jtile- loop over tiles
  • Namelist
    • ln_tile- Logical control on use of tiling
    • nn_tile_i, nn_tile_j- tile length
  • Pre-processor macros
    • IND_2D- substitution for ALLOCATE or DIMENSION arguments
  • Working variables
    • iitile, ijtile- tile number
  • Dummy arguments
    • kntile (ntile)


   &namtile        !   parameters of the tiling
      ln_tile = .false.     !  Use tiling (T) or not (F)
      nn_tile_i = 10        !  Length of tiles in i
      nn_tile_j = 10        !  Length of tiles in j

Documentation updates

Using previous parts, define the main changes to be done in the NEMO literature (manuals, guide, web pages, …).


Since the preview step must be completed before the PI starts the coding, the previewer(s) answers are expected to be completed within the two weeks after the PI has sent the request to the previewer(s).
Then an iterative process should take place between PI and previewer(s) in order to find a consensus

Possible bottlenecks:

  • the methodology
  • the flowchart and list of routines to be changed
  • the new list of variables wrt coding rules
  • the summary of updates in literature

Once an agreement has been reached, preview is ended and the PI can start the development into his branch.


Once the development is done, the PI should complete the tests section below and after ask the reviewers to start their review.

This part should contain the detailed results of SETTE tests (restartability and reproducibility for each of the reference configuration) and detailed results of restartability and reproducibility when the option is activated on specified configurations used for this test

Regular checks:

  • Can this change be shown to produce expected impact (option activated)?
  • Can this change be shown to have a null impact (option not activated)?
  • Results of the required bit comparability tests been run: are there no differences when activating the development?
  • If some differences appear, is reason for the change valid/understood?
  • If some differences appear, is the impact as expected on model configurations?
  • Is this change expected to preserve all diagnostics?
  • If no, is reason for the change valid/understood?
  • Are there significant changes in run time/memory?


A successful review is needed to schedule the merge of this development into the future NEMO release during next Merge Party (usually in November).


  • Is the proposed methodology now implemented?
  • Are the code changes in agreement with the flowchart defined at preview step?
  • Are the code changes in agreement with list of routines and variables as proposed at preview step?
    If, not, are the discrepancies acceptable?
  • Is the in-line documentation accurate and sufficient?
  • Do the code changes comply with NEMO coding standards?
  • Is the development documented with sufficient details for others to understand the impact of the change?
  • Is the project literature (manual, guide, web, …) now updated or completed following the proposed summary in preview section?


Is the review fully successful? If not, please indicate what is still missing

Once review is successful, the development must be scheduled for merge during next Merge Party Meeting.

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