High instruction cache hit rates are key to high performance. One known technique to improve the hit rate of caches is to use an optimizing compiler to minimize cache interference via an improved layout of the code. This technique, however, has been applied to application code only, even though there is evidence that the operating system often uses the cache heavily and with less uniform patterns than applications. Therefore, it is unknown how well existing optimizations perform for systems code and whether better optimizations can be found. We address this problem in this paper. This paper characterizes in detail the locality patterns of the operating system code and shows that there is substantial locality. Unfortunately, caches are not able to extract much of it: rarely-executed special-case code disrupts spatial locality, loops with few iterations that call routines make loop locality hard to exploit, and plenty of loop-less code hampers temporal locality. As a result, interference...

d this mentorship into a joyful and valuable life experience. Working very closely together, under his guidance, we persisted through numerous difficult times together as well as shared many happy rewards of success. I believe that, as I move into my career, I will carry with my continuous benefits from all I have learned from him. I also thank the members of my thesis committee, Professor David Padua and Professor Sharad Mehrotra, for their comments and suggestions in this dissertation. I would like to thank my friends and graduate students in CSRD: Zheng Zhang, Liuxi Yang, Russell Daigle, and Sharad Mehrotra. Zheng Zhang introduced me to Professor Torrellas and brought me into the world of computer architecture research. He consistently helped me with his insights on many important research issues. We also shared and enjoyed our common interests beyond research. My friendship with Liuxi Yang began in our undergraduate years. Beyond his remarkable role in my personal life, he always d