Leveraging 3D Technology for Improved Reliability

Aggressive technology scaling over the years has helped improve processor performance but has caused a reduction in processor reliability. Shrinking transistor sizes and lower supply voltages have increased the vulnerability of computer systems towards transient faults. An increase in within-die and die-to-die parameter variations has also led to a greater number of dynamic timing errors. A potential solution to mitigate the impact of such errors is redundancy via an in-order checker processor. Emerging 3D chip technology promises increased processor performance as well as reduced power consumption because of shorter on-chip wires. In this paper, we leverage the "snap-on" functionality provided by 3D integration and propose implementing the redundant checker processor on a second die. This allows manufacturers to easily create a family of "reliable processors" without significantly impacting the cost or performance for customers that care less about reliability. We comprehensively evaluate design choices for this second die, including the effects of L2 cache organization, deep pipelining, and frequency. An interesting feature made possible by 3D integration is the incorporation of heterogeneous process technologies within a single chip. We evaluate the possibility of providing redundancy with an older process technology, an unexplored and especially compelling application of die heterogeneity. We show that with the most pessimistic assumptions, the overhead of the second die can be as high as either a 7degC temperature increase or a 8% performance loss. However, with the use of an older process, this overhead can be reduced to a 3degC temperature increase or a 4% performance loss, while also providing higher error resilience.