While the previous title is all hands on, this book steps back and looks at performance more holistically. It discusses in detail where bottlenecks are likely to occur and then explains what can be done about them. It eventually follows through to specific tips, but these are presented in the context of the larger discussion, rather than the previous volume, which simply shows them one right after the other.
Both books are short and useful and I would suggest to readers who are greatly concerned about performance that they buy both titles. I would start my reading with the Zakas book and then proceed to the Barker Title.