Cisco IOS Software does not guarantee 100 percent response to Internet Control Message Protocol (ICMP). Cisco IOS Software is programmed to allocate the main portion of the router's resources to forwarding traffic. This does not affect the router's performance.
If this is the only performance problem that you see (that is, there are no input errors or input queue drops on the interface on which ping requests are received), then no action is needed. For troubleshooting purposes, it is best to ping through the router, rather than to the router.