Soft Tiles: Capturing Physical Implementation Flexibility for Tightly-Coupled Parallel Processing Clusters

Spatz

“…Assume a shared-L1 cluster implementation with C = 2 PEs, each controlling F = 4 FPUs. The eight FPUs per cluster are similar to equivalent Snitch-based clusters [8]. Based on [21], we estimate that it costs εPE = 3.1 pJ for Snitch to fetch, decode, and dispatch an instruction of the matrix multiplication kernel and εFPU = 13.3 pJ for an FPU to execute a double-precision FMA instruction.…”

“…Furthermore, another long path starting at the L0 I$ and through Snitch (without leaving the core) is about the same length. Therefore, Spatz' inclusion does not limit the cluster operating frequency, which is the same as that of the scalar Snitch-based cluster [8].…”

“…For example, each core must read two L1 SPM words per cycle to sustain the execution of a matrix multiplication kernel without incurring systematic structural hazards. This traffic is particularly taxing on the cluster's physical implementation, as the L1 SPM interconnect is the critical factor for its scalability [8]. Furthermore, the breakdown of SRAM and interconnect scaling makes achieving the L1 bandwidth required by SSRs challenging.…”

“…Based on [21], we estimate that it costs εPE = 3.1 pJ for Snitch to fetch, decode, and dispatch an instruction of the matrix multiplication kernel and εFPU = 13.3 pJ for an FPU to execute a double-precision FMA instruction. We can use Equations ( 4) to (8) to estimate the energy consumption of the shared-L1 cluster as a function of the vector length VLEN, as seen in Figure 5. The energy breakdown highlights the benefit of a lightweight PE.…”

“…Particularly, we tackle the interconnect and memory scaling issue on the shared-L1 cluster of Figure 1, a generic template for programmable computing architectures. Each shared-L1 cluster contains a set of PEs sharing tightly-coupled L1 memory through a lowlatency interconnect [8]. The cluster's L1 memory is typically implemented as a multi-banked SRAM data cache or SPM.…”