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One-stop performance analysis using atop [LWN.net]
https://lwn.net/Articles/387202/, posted 2012 by peter in free linux monitoring opensource software
Linux system administrators often receive complaints about the performance of their systems.
It can be rather difficult to track down these problems and to find why, when, and how often they happen. Being able to zoom in on the processes that are responsible, and to see what has happened in the past, is very valuable.
The atop utility was written with just these things in mind.