Double-precision floating-point (FP64) performance of all GCN 5th generation GPUs, except for Vega 20, is 1/16 of FP32 performance. For Vega 20 with Radeon Instinct this is 1/2 of FP32 performance. For Vega 20 with Radeon VII this is 1/4 of FP32 performance. All GCN 5th generation GPUs support half-precision floating-point (FP16) calculations which is double of FP32 performance.
