I have a 1841 running on c1841-spservicesk9-mz.124-7d.
I see more than 80% of CPU utilization soon after saving the configuration(write mem), which lasts for several seconds. Could this lead to a router crash at a particular stage?
Is it due to a bug in IOS?
the cpu on a router like yours can have these spikes.
About why saving the config can cause a so high cpu usage I think that modern routers that are SDM ready can actually have to create an XML file for the running config, then they have to translate it to a simple text file and to write it on the NVRAM.
So the duty can be now heavier then in the past.
I usually look at the cpu average 1min as the parameter to decide if a router is working fine or it is overloaded.
Hope to help