Most of us set idlepc value in GNS3 but do not really know the actual reason of setting it or what it does with CPU to stop its continuous process…
Here is the brief explanation that why idlepc value is set in GNS3
When an IOS image is launched using Dynamips/GNS3 your PC will not be able to differentiate between the router’s real work and idle routines and so the router instance will use as much resource as possible, this becomes obvious when your CPU hits 100%. IdlePC is a value set locally that tells your computer when the router is idle or not and therefore when software needs to compute routines.
It is set on a per-IOS image level, not router or host machine level which means values that are known to be good are valid on all GNS3/dynamips servers.