Deep Memory Hierarchies

Research topic and goals

Deep Memory Hierarchies are an important part of future exascale systems and as they come opening new opportunities, they also bring significant challenges to the HPC world. In particular, it is not clear what is the best and more efficient way to use such devices, how to position the data related to performance metrics but also to reliability constrains is an open question. In this project we investigated all these issues, from memory access patterns to interfaces to easily handle multiple memory devices with different bandwidth, latency and reliability characteristics.

Results for 2018/2019

During the visit of Aleix to RIKEN, we studied the access pattern profiling phase prior to the actual memory relocation. We study the feasibility of using Intel’s Processor Event-Based Sampling (PEBS) feature to record memory accesses by sampling at runtime and study the overhead at scale. We have implemented a custom PEBS driver in the IHK/- McKernel lightweight multi-kernel operating system, one of whose advantages is minimal system interference due to the lightweight kernel’s simple design compared to other OS kernels such as Linux. We evaluated the PEBS overhead of a set of scientific applications and show the access patterns identified in noise sensitive HPC applica- tions. Our results show that clear access patterns can be captured with a 10% overhead in the worst-case and 1% in the best case when running on up to 128k CPU cores (2,048 Intel Xeon Phi Knights Landing nodes). We conclude that online memory access profiling using PEBS at large scale is promising for memory management in heterogeneous memory environments. All these results were published at the International Workshop on Memory Centric High Performance Computing Co-located with SC18 at Dallas (Nonell et al. 2018).

Visits and meetings

Internship of Aleix Roca at RIKEN during June 2018 to August 2018, under the supervision of Balazs Gerofi.

Impact and publications

    References

    1. Nonell, Aleix Roca, Balazs Gerofi, Leonardo Bautista-Gomez, Dominique Martinet, Vicenç Beltran Querol, and Yutaka Ishikawa. 2018. “On the Applicability of PEBS Based Online Memory Access Tracking for Heterogeneous Memory Management at Scale.” In Proceedings of the Workshop on Memory Centric High Performance Computing, 50–57. ACM.
      @inproceedings{RocaEtAl2018,
        title = {On the Applicability of PEBS based Online Memory Access Tracking for Heterogeneous Memory Management at Scale},
        author = {Nonell, Aleix Roca and Gerofi, Balazs and Bautista-Gomez, Leonardo and Martinet, Dominique and Querol, Vicen{\c{c}} Beltran and Ishikawa, Yutaka},
        booktitle = {Proceedings of the Workshop on Memory Centric High Performance Computing},
        pages = {50--57},
        year = {2018},
        organization = {ACM}
      }