Shiftfly: Scaling the Accelerator Interconnect Past the Pod with a Shift-Routed Optical Tier

Eylon E. Krause

Google's TPU interconnect spent nine generations as a $k$-ary $n$-cube, whose diameter grows as $\hat{I}˜(N^{1/n})$, before TPU 8i replaced it with Boardfly: a three-tier hierarchy in wh…