Pub Date : 2023-07-19DOI: 10.1109/LCA.2023.3296251
Ahmed Nematallah;Chang Hyun Park;David Black-Schaffer
With DRAM latencies increasing relative to CPU speeds, the performance of caches has become more important. This has led to increasingly sophisticated replacement policies that require complex calculations to update their replacement metadata, which often require multiple cycles. To minimize the negative impact of these metadata updates, architects have focused on policies that incur as little update latency as possible through a combination of reducing the policies’ precision and using parallel hardware. In this work we investigate whether these tradeoffs to reduce cache metadata update latency are needed. Specifically, we look at the performance and energy impact of increasing the latency of cache replacement policy updates. We find that even dramatic increases in replacement policy update latency have very limited effect. This indicates that designers have far more freedom to increase policy complexity and latency than previously assumed.
{"title":"Exploring the Latency Sensitivity of Cache Replacement Policies","authors":"Ahmed Nematallah;Chang Hyun Park;David Black-Schaffer","doi":"10.1109/LCA.2023.3296251","DOIUrl":"10.1109/LCA.2023.3296251","url":null,"abstract":"With DRAM latencies increasing relative to CPU speeds, the performance of caches has become more important. This has led to increasingly sophisticated replacement policies that require complex calculations to update their replacement metadata, which often require multiple cycles. To minimize the negative impact of these metadata updates, architects have focused on policies that incur as little update latency as possible through a combination of reducing the policies’ precision and using parallel hardware. In this work we investigate whether these tradeoffs to reduce cache metadata update latency are needed. Specifically, we look at the performance and energy impact of increasing the latency of cache replacement policy updates. We find that even dramatic increases in replacement policy update latency have very limited effect. This indicates that designers have far more freedom to increase policy complexity and latency than previously assumed.","PeriodicalId":51248,"journal":{"name":"IEEE Computer Architecture Letters","volume":"22 2","pages":"93-96"},"PeriodicalIF":2.3,"publicationDate":"2023-07-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43674521","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"计算机科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The demand for accurate information about the internal structure and characteristics of DRAM has been on the rise. Recent studies have explored the structure and characteristics of DRAM to improve processing in memory, enhance reliability, and mitigate a vulnerability known as rowhammer. However, DRAM manufacturers only disclose limited information through official documents, making it difficult to find specific information about actual DRAM devices. This paper presents reliable findings on the internal structure and characteristics of DRAM using activate-induced bitflips (AIBs), retention time test, and row-copy operation. While previous studies have attempted to understand the internal behaviors of DRAM devices, they have only shown results without identifying the causes or have analyzed DRAM modules rather than individual chips. We first uncover the size, structure, and operation of DRAM subarrays and verify our findings on the characteristics of DRAM. Then, we correct misunderstood information related to AIBs and demonstrate experimental results supporting the cause of rowhammer.
{"title":"X-ray: Discovering DRAM Internal Structure and Error Characteristics by Issuing Memory Commands","authors":"Hwayong Nam;Seungmin Baek;Minbok Wi;Michael Jaemin Kim;Jaehyun Park;Chihun Song;Nam Sung Kim;Jung Ho Ahn","doi":"10.1109/LCA.2023.3296153","DOIUrl":"10.1109/LCA.2023.3296153","url":null,"abstract":"The demand for accurate information about the internal structure and characteristics of DRAM has been on the rise. Recent studies have explored the structure and characteristics of DRAM to improve processing in memory, enhance reliability, and mitigate a vulnerability known as rowhammer. However, DRAM manufacturers only disclose limited information through official documents, making it difficult to find specific information about actual DRAM devices. This paper presents reliable findings on the internal structure and characteristics of DRAM using activate-induced bitflips (AIBs), retention time test, and row-copy operation. While previous studies have attempted to understand the internal behaviors of DRAM devices, they have only shown results without identifying the causes or have analyzed DRAM modules rather than individual chips. We first uncover the size, structure, and operation of DRAM subarrays and verify our findings on the characteristics of DRAM. Then, we correct misunderstood information related to AIBs and demonstrate experimental results supporting the cause of rowhammer.","PeriodicalId":51248,"journal":{"name":"IEEE Computer Architecture Letters","volume":"22 2","pages":"89-92"},"PeriodicalIF":2.3,"publicationDate":"2023-07-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49364167","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"计算机科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-07-03DOI: 10.1109/LCA.2023.3290427
Ipoom Jeong;Jiaqi Lou;Yongseok Son;Yongjoo Park;Yifan Yuan;Nam Sung Kim
The advancement in I/O technology has posed an unprecedented demand for high-performance processing on I/O data, leading to the development of Data Direct I/O (DDIO) technology. DDIO improves I/O processing efficiency by directly injecting all inbound I/O data into the last-level cache (LLC) in cooperation with any type of I/O device. Nonetheless, in certain scenarios with more than one I/O applications, DDIO may have sub-optimal performance caused by interference inside the LLC, resulting in the degradation of system performance. Especially, in this paper, we demonstrate that storage I/O on modern high-performance NVMe SSDs hardly benefits from DDIO, sometimes causing inefficient use of the shared LLC due to the “leaky DMA problem”. To address this problem, we propose LADIO