GCC and OpenACC

Mikel Mendizabal mikel.mendizabal.morentin@desy.de
Tue Jan 11 12:50:05 GMT 2022

Dear GCC developers,

In the past year we started the offload of our software to GPUs. We decided to go with OpenACC. The program we are trying to offload is Millepede2 (MP2),  a tracker alignment software used to align the CMS experiment tracker at the large hadron collider. 

We are using gcc as our main compiler. However, we found a major inconvenience with OpenACC 2.6, the REDUCTION clause does not accept arrays. Thus, it not possible for us to parallelise our largest loops due to array dependencies. We managed to offload MP2 for small datasets, we worked around the reduction issue. Nonetheless, if our alignment campaign is large the workarounds are not useful anymore. 

I went thought the new versions of OpenACC and I found that v2.7 accepts arrays for the REDUCTION clause. I was wondering if it is in your plans to include a newer version of OpenACC for the next releases. 

Mikel Mendizabal

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