How do software engineers generally go about finding how a particular module consumes more CPU or memory than expected?

Question

hartnn · Answer

Maybe : 
1. Finding out some of the recent changes in the data structures in that module. If the size of a very frequently used data structure has increased, it can lead to increase in memory consumption. If a variable of that data structure is passed between different modules, then more data is passed leading to increase in CPU consumption.

Any thoughts on this?
Any more reasons for the increase?

hartnn · Answer

There are tools which will give us the name of the function that caused the memory/CPU increase?