@article{elkhouly_alshboul_hayashi_solihin_kimura_2019, title={Compiler-support for Critical Data Persistence in NVM}, volume={16}, ISSN={["1544-3973"]}, DOI={10.1145/3371236}, abstractNote={Non-volatile Main Memories (NVMs) offer a promising way to preserve data persistence and enable computation recovery in case of failure. While the use of NVMs can significantly reduce the overhead of failure recovery, which is the case with High-Performance Computing (HPC) kernels, rewriting existing programs or writing new applications for NVMs is non-trivial. In this article, we present a compiler-support that automatically inserts complex instructions into kernels to achieve NVM data-persistence based on a simple programmer directive. Unlike checkpointing techniques that store the whole system state, our technique only persists user-designated objects as well as some parameters required for safe recovery such as loop induction variables. Also, our technique can reduce the number of data transfer operations, because our compiler coalesces consecutive memory-persisting operations into a single memory transaction per cache line when possible.
          Our compiler-support is implemented in the LLVM tool-chain and introduces the necessary modifications to loop-intensive computational kernels (e.g., TMM, LU, Gauss, and FFT) to force data persistence. The experiments show that our proposed compiler-support outperforms the most recent checkpointing techniques while its performance overheads are insignificant.}, number={4}, journal={ACM TRANSACTIONS ON ARCHITECTURE AND CODE OPTIMIZATION}, author={Elkhouly, Reem and Alshboul, Mohammad and Hayashi, Akihiro and Solihin, Yan and Kimura, Keiji}, year={2019}, month={Dec} }
 @article{alshboul_elnawawy_elkhouly_kimura_tuck_solihin_2019, title={Efficient Checkpointing with Recompute Scheme for Non-volatile Main Memory}, volume={16}, ISSN={["1544-3973"]}, DOI={10.1145/3323091}, abstractNote={Future main memory will likely include Non-Volatile Memory. Non-Volatile Main Memory (NVMM) provides an opportunity to rethink checkpointing strategies for providing failure safety to applications. While there are many checkpointing and logging schemes in the literature, their use must be revisited as they incur high execution time overheads as well as a large number of additional writes to NVMM, which may significantly impact write endurance.
          In this article, we propose a novel recompute-based failure safety approach and demonstrate its applicability to loop-based code. Rather than keeping a fully consistent logging state, we only log enough state to enable recomputation. Upon a failure, our approach recovers to a consistent state by determining which parts of the computation were not completed and recomputing them. Effectively, our approach removes the need to keep checkpoints or logs, thus reducing execution time overheads and improving NVMM write endurance at the expense of more complex recovery. We compare our new approach against logging and checkpointing on five scientific workloads, including tiled matrix multiplication, on a computer system model that was built on gem5 and supports Intel PMEM instruction extensions. For tiled matrix multiplication, our recompute approach incurs an execution time overhead of only 5%, in contrast to 8% overhead with logging and 207% overhead with checkpointing. Furthermore, recompute only adds 7% additional NVMM writes, compared to 111% with logging and 330% with checkpointing. We also conduct experiments on real hardware, allowing us to run our workloads to completion while varying the number of threads used for computation. These experiments substantiate our simulation-based observations and provide a sensitivity study and performance comparison between the Recompute Scheme and Naive Checkpointing.}, number={2}, journal={ACM TRANSACTIONS ON ARCHITECTURE AND CODE OPTIMIZATION}, author={Alshboul, Mohammad and Elnawawy, Hussein and Elkhouly, Reem and Kimura, Keiji and Tuck, James and Solihin, Yan}, year={2019}, month={May} }