CrossWalk: A Tool for Performance Profiling Across the User-Kernel Boundary

fy the ultimate cause of Squid's performance problems and remove them by modifying the application's source code. 1. Introduction Many applications make heavy use of functions provided by the operating system. Naturally, the performance of such applications depends on how they make use of these functions and how e#ciently these functions are implemented by the operating system. For example, I/O is key to the e#ciency of many high-performance applications. Network performance is often the constraining factor for such tools as Web and proxy servers, and e#cient use of synchronization primitives is crucial for multithreaded applications. Finding performance problems in OS-bound applications has always been a challenging task. A user-level profiler might locate a region of application's code where most of the system time is spent, but it might be unable to explain why this is happening or how to fix the problem. For example, if an application spent 90% of its time in the open system ca