A Case for Transparent Reliability in DRAM Systems
share
Today's systems have diverse needs that are difficult to address using one-size-fits-all commodity DRAM. Unfortunately, although system designers can theoretically adapt commodity DRAM chips to meet their particular design goals (e.g., by reducing access timings to improve performance, implementing system-level RowHammer mitigations), we observe that designers today lack sufficient insight into commodity DRAM chips' reliability characteristics to implement these techniques in practice. In this work, we make a case for DRAM manufacturers to provide increased transparency into key aspects of DRAM reliability (e.g., basic chip design properties, testing strategies). Doing so enables system designers to make informed decisions to better adapt commodity DRAM to meet modern systems' needs while preserving its cost advantages. To support our argument, we study four ways that system designers can adapt commodity DRAM chips to system-specific design goals: (1) improving DRAM reliability; (2) reducing DRAM refresh overheads; (3) reducing DRAM access latency; and (4) mitigating RowHammer attacks. We observe that adopting solutions for any of the four goals requires system designers to make assumptions about a DRAM chip's reliability characteristics. These assumptions discourage system designers from using such solutions in practice due to the difficulty of both making and relying upon the assumption. We identify DRAM standards as the root of the problem: current standards rigidly enforce a fixed operating point with no specifications for how a system designer might explore alternative operating points. To overcome this problem, we introduce a two-step approach that reevaluates DRAM standards with a focus on transparency of DRAM reliability so that system designers are encouraged to make the most of commodity DRAM technology for both current and future DRAM chips.
READ FULL TEXT