Systems Performance: Enterprise and the Cloud" by Brendan Gregg.
In today's modern server and cloud based systems the multi-layered complexity can make it hard to pin point performance issues and bottlenecks. This book is packed full useful analysis techniques covering tracing, kernel internals, tools and benchmarking.
Critical to getting a well balanced and tuned system are all the different components, and the book has chapters covering CPU optimisation (cores, threading, caching and internconnects), memory optimisation (virtual memory, paging, swapping, allocators, busses), file system I/O, storage, networking (protcols, sockets, physical connections) and typical issues facing cloud computing.
The book is full of very useful examples and practical instructions on how to drill down and discover performance issues in a system and also includes some real-world case studies too.
It has helped me become even more focused on how to analyse performance issues and consider how to do deep system instrumentation to be able to understand where any why performance regressions occur.
All-in-all, a most systematic and well written book that I'd recommend to anyone running large complex servers and cloud computing environments.