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  1. The demand for memory is ever increasing. Many prior works have explored hardware memory compression to increase effective memory capacity. However, prior works compress and pack/migrate data at a small - memory blocklevel - granularity; this introduces an additional block-level translation after the page-level virtual address translation. In general, the smaller the granularity of address translation, the higher the translation overhead. As such, this additional block-level translation exacerbates the well-known address translation problem for large and/or irregular workloads. A promising solution is to only save memory from cold (i.e., less recently accessed) pages without saving memory from hot (i.e., more recently accessed) pages (e.g., keep the hot pages uncompressed); this avoids block-level translation overhead for hot pages. However, it still faces two challenges. First, after a compressed cold page becomes hot again, migrating the page to a full 4KB DRAM location still adds another level (albeit page-level, instead of block-level) of translation on top of existing virtual address translation. Second, only compressing cold data require compressing them very aggressively to achieve high overall memory savings; decompressing very aggressively compressed data is very slow (e.g., > 800ns assuming the latest Deflate ASIC in industry). This paper presents Translation-optimized Memory Compression formore »Capacity (TMCC) to tackle the two challenges above. To address the first challenge, we propose compressing page table blocks in hardware to opportunistically embed compression translations into them in a software-transparent manner to effectively prefetch compression translations during a page walk, instead of serially fetching them after the walk. To address the second challenge, we perform a large design space exploration across many hardware configurations and diverse workloads to derive and implement in HDL an ASIC Deflate that is specialized for memory; for memory pages, it is 4X as fast as the state-of-the art ASIC Deflate, with little to no sacrifice in compression ratio. Our evaluations show that for large and/or irregular workloads, TMCC can either improve performance by 14% without sacrificing effective capacity or provide 2.2x the effective capacity without sacrificing performance compared to a stateof-the-art hardware memory compression for capacity.« less
    Free, publicly-accessible full text available October 1, 2023
  2. DELAUNAYSPARSE contains both serial and parallel codes written in Fortran 2003 (with OpenMP) for performing medium- to high-dimensional interpolation via the Delaunay triangulation. To accommodate the exponential growth in the size of the Delaunay triangulation in high dimensions, DELAUNAYSPARSE computes only a sparse subset of the complete Delaunay triangulation, as necessary for performing interpolation at the user specified points. This article includes algorithm and implementation details, complexity and sensitivity analyses, usage information, and a brief performance study.
  3. Time-driven and access-driven attacks are two dominant types of the timing-based cache side-channel attacks. Despite access-driven attacks are popular in recent years, investigating the time-driven attacks is still worth the effort. It is because, in contrast to the access-driven attacks, time-driven attacks are independent of the attackers’ cache access privilege. Although cache configurations can impact the time-driven attacks’ performance, it is unclear how different cache parameters influence the attacks’ success rates. This question remains open because it is extremely difficult to conduct comparative measurements. The difficulty comes from the unavailability of the configurable caches in existing CPU products. In this paper, we utilize the GEM5 platform to measure the impacts of different cache parameters, including Private Cache Size and Associativity, Shared Cache Size and Associativity, Cache-line Size, Replacement Policy, and Clusivity. In order to make the time-driven attacks comparable, we define the equivalent key length (EKL) to describe the attacks’ success rates. Key findings from the measurement results include (i) private cache has a key effect on the attacks’ success rates; (ii) changing shared cache has a trivial effect on the success rates, but adding neighbor processes can make the effect significant; (iii) the Random replacement policy leads to themore »highest success rates while the LRU/LFU are the other way around; (iv) the exclusive policy makes the attacks harder to succeed compared to the inclusive policy. We finally leverage these findings to provide suggestions to the attackers and defenders as well as the future system designers.« less
  4. Heterogeneous computing systems, e.g., those with accelerators than the host CPUs, offer the accelerated performance for a variety of workloads. However, most parallel programming models require platform dependent, time-consuming hand-tuning efforts for collectively using all the resources in a system to achieve efficient results. In this work, we explore the use of OpenMP parallel language extensions to empower users with the ability to design applications that automatically and simultaneously leverage CPUs and accelerators to further optimize use of available resources. We believe such automation will be key to ensuring codes adapt to increases in the number and diversity of accelerator resources for future computing systems. The proposed system combines language extensions to OpenMP, load-balancing algorithms and heuristics, and a runtime system for loop distribution across heterogeneous processing elements. We demonstrate the effectiveness of our automated approach to program on systems with multiple CPUs, GPUs, and MICs.