Updates on usage of the Czech national HPC center

The distributed computing of the ATLAS experiment at LHC is using computing resources of the Czech national HPC center IT4Innovations for several years. The submission system is based on ARC-CEs installed at the Czech Tier2 site (praguelcg2). Recent improvements of this system will be discussed here. First, there was migration of the ARC-CE from version 5 to 6 which improves the reliability and scalability. The sshfs connection between praguelcg2 and IT4Innovations was a bottleneck of this system but this improved with new version and setting. Containerization using singularity allows for customization of environment and reduction in number of files needed to run jobs. System allowing sequential running of payloads in one job was adapted to HPC's environment, improving usage on worker nodes with very high number of cores. Overall, the system provides significant contribution to resources provided by praguelcg2.