CODA: How to Mitigate ColumnDisturb for (Almost) Free?

2026-07-15

AI Summary

This work addresses the performance degradation and high refresh overhead caused by ColumnDisturb errors, which induce bit flips across DRAM subarrays. The paper proposes CODA, the first near-zero-overhead defense mechanism that dynamically skips or reduces redundant counting operations by synergistically integrating three novel strategies: Evade, Fraction, and Gangskip. Leveraging the DRAM subarray architecture, CODA introduces Adjacent Counter Increment (ACI) optimization, combining demand-aware activation with multi-subarray cooperative scheduling. This approach ensures robust security while reducing ACI operations by 12× to 1300×, achieving effective protection with zero performance loss and negligible power overhead.

Abstract

ColumnDisturb is a new data-disturbance error in which activations to an aggressor row cause bitflips in a victim row located hundreds of rows away (intra-subarray bitflips) and in victim rows in adjacent subarrays (inter-subarray bitflips). Intra-subarray ColumnDisturb can be tolerated by solutions (such as SALT and REGA) that operate at subarray granularity. However, to tolerate inter-subarray ColumnDisturb, such solutions must be extended with ColumnDisturb Protection (CDP), which performs additional {\em Adjacent-Counter Increment (ACI)} for the neighboring subarrays. The ACIs ensure that adjacent subarrays also undergo mitigation, even if they receive no demand activations. Unfortunately, because ACIs occur at a 200\% rate relative to demand activations, they effectively increase the activations perceived by the bank to 3x, which causes significant slowdowns (17\% at a TRHD of 500) and refresh overheads. The goal of our paper is to tolerate ColumnDisturb while incurring negligible overheads. We propose CODA, a ColumnDisturb mitigation that significantly reduces the rate of ACI required to securely tolerate ColumnDisturb. We present three variants of CODA. First, CODA-E (Evade), which leverages the insight that ACI can be skipped if the neighboring subarray receives a demand activation, and reduces ACI by 2x. Second, CODA-F (Fraction), which uses the timing duration of ColumnDisturb to do only a fractional increment for ACI, thereby reducing the rate of ACI by 2x-16x. Finally, CODA-G (Gangskip), which operates at multi-subarray granularity and skips ACI for neighboring subarrays within the same gang, further reduces overall ACI by 2x-8x. Overall, CODA reduces ACI by 12x-1300x, thereby making it possible to tolerate ColumnDisturb while incurring zero performance and power overhead.

Problem

• ColumnDisturb
• bitflips
• subarray
• Adjacent-Counter Increment
• DRAM

Innovation

• ColumnDisturb
• Adjacent-Counter Increment (ACI)
• CODA
• subarray-level mitigation
• DRAM reliability