Exploiting expendable process-margins in DRAMs for run-time performance optimization

Chandrasekar, Karthik; Goossens, Sven; Weis, Christian; Koedam, Martijn; Åkesson, Benny; Wehn, Norbert; Goossens, Kees

doi:10.7873/date.2014.186

Cited by 43 publications

(81 citation statements)

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“…Several works investigated the possibility of reducing DRAM latency by either exploiting DRAM latency variation [7,65] or changing the DRAM architecture [34,36,45,61,62,66]. We discuss these below.…”

Section: Related Workmentioning

confidence: 99%

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Adaptive-latency DRAM: Optimizing DRAM timing for the common-case

Lee

Kim

Pekhimenko

et al. 2015

2015 IEEE 21st International Symposium on High Performance Computer Architecture (HPCA)

187

328

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In current systems, memory accesses to a DRAM chip must obey a set of minimum latency restrictions specified in the DRAM standard. Such timing parameters exist to guarantee reliable operation. When deciding the timing parameters, DRAM manufacturers incorporate a very large margin as a provision against two worst-case scenarios. First, due to process variation, some outlier chips are much slower than others and cannot be operated as fast. Second, chips become slower at higher temperatures, and all chips need to operate reliably at the highest supported (i.e., worst-case) DRAM temperature (85• C). In this paper, we show that typical DRAM chips operating at typical temperatures (e.g., 55• C) are capable of providing a much smaller access latency, but are nevertheless forced to operate at the largest latency of the worst-case.Our goal in this paper is to exploit the extra margin that is built into the DRAM timing parameters to improve performance. Using an FPGA-based testing platform, we first characterize the extra margin for 115 DRAM modules from three major manufacturers. Our results demonstrate that it is possible to reduce four of the most critical timing parameters by a minimum/maximum of 17.3%/54.8% at 55• C without sacrificing correctness. Based on this characterization, we propose Adaptive-Latency DRAM (AL-DRAM), a mechanism that adaptively reduces the timing parameters for DRAM modules based on the current operating condition. AL-DRAM does not require any changes to the DRAM chip or its interface.We evaluate AL-DRAM on a real system that allows us to reconfigure the timing parameters at runtime. We show that AL-DRAM improves the performance of memory-intensive workloads by an average of 14% without introducing any errors. We discuss and show why AL-DRAM does not compromise reliability. We conclude that dynamically optimizing the DRAM timing parameters can reliably improve system performance.

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Section: Related Workmentioning

confidence: 99%

“…DRAM Latency Variation: Recently, Chandrasekar et al [7] evaluate the potential of relaxing some DRAM timing parameters to reduce DRAM latency. This work observes latency variations across DIMMs as well as for a DIMM at different operating temperatures.…”

Section: Related Workmentioning

confidence: 99%

Adaptive-latency DRAM: Optimizing DRAM timing for the common-case

Lee

Kim

Pekhimenko

et al. 2015

2015 IEEE 21st International Symposium on High Performance Computer Architecture (HPCA)

187

328

View full text Add to dashboard Cite

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“…Hence, refreshing all DRAM chip rows per 64ms is sufficient to prevent data loss. (ii) The retention timing for cells in current commodity DRAM chips is conservative, which inspired designs to tighten timing for performance improvement [9,34]. The opportunity is diminishing in future chips as more cells become leaky.…”

Section: Retention Time and Refreshmentioning

confidence: 99%

“…Most DRAM chips can perform with smaller timing constraint values. Chandrasekar et al [9] proposed to identify the excess in process-margins for DRAM devices at runtime. AL-DRAM [34] analyzes the timing reduction opportunities and exploits the large margin of DRAM timing parameters to improve performance.…”

Section: Related Workmentioning

confidence: 99%

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Restore truncation for performance improvement in future DRAM systems

Zhang

Childers

et al. 2016

2016 IEEE International Symposium on High Performance Computer Architecture (HPCA)

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Scaling DRAM below 20nm has become a major challenge due to intrinsic limitations in the structure of a bit cell. Future DRAM chips are likely to suffer from significant variations and degraded timings, such as taking much more time to restore cell data after read and write access.In this paper, we propose restore truncation (RT), a lowcost restore strategy to improve performance of DRAM modules that adopt relaxed restore timing. After an access, RT restores a bit cell's voltage only to the level required to persist data to the next scheduled refresh rather than to the default full voltage. Because restore time is shortened, the performance of the cell is improved under process variations. We devise two schemes to balance performance, energy consumption, and hardware overhead. We simulate our proposed RT schemes and compare them with the state of the art. Experimental results show that, on average, RT improves performance by 19.5% and reduces energy consumption by 17%.

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RowHammer and Beyond

Mutlu

2019

Constructive Side-Channel Analysis and Secure Design

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We will discuss the RowHammer problem in DRAM, which is a prime (and likely the first) example of how a circuit-level failure mechanism in Dynamic Random Access Memory (DRAM) can cause a practical and widespread system security vulnerability. RowHammer is the phenomenon that repeatedly accessing a row in a modern DRAM chip predictably causes errors in physically-adjacent rows. It is caused by a hardware failure mechanism called read disturb errors. Building on our initial fundamental work that appeared at ISCA 2014, Google Project Zero demonstrated that this hardware phenomenon can be exploited by user-level programs to gain kernel privileges. Many other recent works demonstrated other attacks exploiting RowHammer, including remote takeover of a server vulnerable to RowHammer. We will analyze the root causes of the problem and examine solution directions. We will also discuss what other problems may be lurking in DRAM and other types of memories, e.g., NAND flash and Phase Change Memory, which can potentially threaten the foundations of reliable and secure systems, as the memory technologies scale to higher densities.

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Exploiting expendable process-margins in DRAMs for run-time performance optimization

Cited by 43 publications

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Adaptive-latency DRAM: Optimizing DRAM timing for the common-case

Adaptive-latency DRAM: Optimizing DRAM timing for the common-case

Restore truncation for performance improvement in future DRAM systems

RowHammer and Beyond

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