Why does my Intel® FPGA P-Tile Avalon® Memory Mapped (Avalon-MM) IP for PCI Express* show lower read performance in Intel® Quartus® Prime Pro version 19.3?

The Intel® FPGA P-Tile Avalon® Memory Mapped (Avalon-MM) IP for PCI Express* currently supports up to 64 outstanding requests with a Max Read request size of 512 Bytes. If the round trip latency (Time from Memory Read to Completion) is greater than 1.5 us, the number of outstanding requests may not be enough to saturate the Read throughput.