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How to get access to Mahti large partition

Projects with well scaling codes can get access to the large partition (20-200 nodes) on Mahti in three steps. First a 30 day test period for the large partition is requested. Second, during the test period the scalability and parallel performance of the code is demonstrated with appropriate test runs. Finally, the results are submitted for evaluation by the project manager.

The process is described in detail below.

Test access to the large partition on Mahti

To request the 30 day test period, proceed as follows:

  1. Login to MyCSC and select the project you want to modify.
  2. In the Services list, click open the settings for Mahti service. This opens a page where the project manager can modify the settings for disk quotas (Quota settings) and request access to the large partition (Large partition settings). Click open Large partition settings.
  3. Click the Apply for access button. After the access has been granted you should be able to submit jobs to the large partition.

Scalability testing

In the second phase, test runs demonstrating the scalability are to be performed. Here are some general guidelines for scalability testing.

  • Testing should be done at minimum three different node counts up to target in production (for example with 20, 40, 60, and 80 nodes).
  • Tests are run through the batch job system.
  • The test runs should reflect real production runs, i.e. the number of atoms, number of grid points, disk IO load etc. should be similar.
  • The input data set must be the same for each run.
  • The running time in tests should be reduced as much possible, for example by running only few times steps, iterations etc.
  • The running time should still be long enough that initialization does not affect results, typically few minutes for the shortest run time (largest node count) is fine.
  • Parameters affecting the scalability can, and are encouraged to be, changed. Note, also the performance checklist
  • Minimum requirement is 75 % parallel efficiency (i.e. speedup of 1.5 when doubling the number of nodes).

Reporting

The scalability report should contain a short description of the software and the test case, as well as wall times with each node count. If software is not installed by CSC describe briefly also the parallelization strategy used in the software including details about the IO implementation and load.

Attach to the report a representative batch job script, and if the application was run with hybrid MPI/OpenMP parallelization, attach also the stderr of a single run where the following settings are applied:

export OMP_AFFINITY_FORMAT="Process %P level %L thread %0.3n affinity %A"
export OMP_DISPLAY_AFFINITY=true

Reporting the results of the test runs or applicable previous scalability data is done through MyCSC portal as follows:

  1. Login to MyCSC and select the project you want to modify.
  2. In the Services list, click open the settings for Mahti service. This opens a page where the project manager can modify the settings for disk quotas (Quota settings) and request access to the large partition (Large partition settings). Click open Large partition settings.
  3. For the results and justification there is a text box and possibility to attach documents (please remember to upload the documents after you have selected them). Multiple documents can be attached. Finally, submit the justification.
  4. CSC experts will evaluate the results and grant production access to the large partition. If there is a problem with the code performance the project manager will be contacted.

Assistance

CSC's experts can help users in performing scalability tests if needed and also provide hints for improving the performance of their software. Contact CSC Service Desk if you need assistance with your software.

Last update: September 7, 2020