WinDRAM: Weak rows as in‐DRAM cache

Abstract

SummaryThe primary factor responsible for increasing the refresh rate is the presence of weak rows in a DRAM. They have a shorter retention time and lose charge faster than regular rows. Recently, a technique known as in‐DRAM cache was introduced in which some DRAM rows act as a separate module. The in‐DRAM cache can be used for a variety of purposes in DRAM. We present WinDRAM, an in‐DRAM cache comprised of all the DRAM's weak rows. The most recently accessed rows are copied into the in‐DRAM cache so that when the row is accessed again, both rows (original and copy) can be activated at the same time. Such simultaneous activation reduces activation time and, as a result, DRAM access latency. Dual‐row activation is the term for this concept. Because weak rows are part of the in‐DRAM cache and are frequently accessed, WinDRAM does not perform a periodic refresh on them. Existing techniques based on in‐DRAM cache do not design the in‐DRAM cache using weak rows. WinDRAM proposes a novel idea by designing the in‐DRAM cache using weak rows. Because the weak rows do not need to be refreshed, the refresh interval of the remaining rows can be increased, resulting in a refresh rate reduction of 80% to 90%. The speedup is 15% to 25% faster than standard DRAM and 12.77% faster than previous work for high memory‐intensive workloads. Overall energy consumption is also reduced by 10% to 15%.