The ICMP packets that fast ping sends to device will not be forwarded to CPU, and they are responded at the interface directly, so the delay is very little. It is often used by carriers that have requirements on the delay.
NE40/NE80 VRP3.10 starts to support it from the version 2307, and so does the version 2351(it is defaulted to shutdown). VRP5.3 starts to support it from 8011V3R2B02D025 (it is defaulted to shutdown).
Run icmp fast command in the system mode to enable the fast ping function.