Summary
Explore the mechanisms behind CPU virtualization through limited direct execution. Learn how the OS sets hardware restrictions to efficiently run processes and manage privileged operations. Understand the role of context switches, system calls, and timer interrupts, and their impact on operating system performance and scheduling.
We'll cover the following...
We have described some key low-level mechanisms to implement CPU virtualization, a set of techniques that we collectively refer to as limited direct execution. The basic idea is straightforward: just run the program you want to run on the CPU, but first, make sure to set up the hardware so as to limit what the process can do without OS assistance.
ASIDE: HOW LONG CONTEXT SWITCHES TAKE
A natural question you might have is: how long does something like a context switch take? Or even a system call? For those of you that are curious, there is a tool called
that measures exactly those things, as well as a few other performance ... lmbench “lmbench: Portable tools for performance analysis” by Larry McVoy and Carl Staelin. USENIX Annual Technical Conference, January 1996. A fun paper about how to measure a number of different things about your OS and its performance. Download lmbench and give it a try.