The last CPU

Since the end of Dennard scaling and Moore's Law have been foreseen, specialized hardware has become the focus for continued scaling of application performance. Programmable accelerators such as smart memory, smart disks, and smart NICs are now being integrated into our systems. Many accelerators can be programmed to process their data autonomously and require little or no intervention during normal operation. In this way, entire applications are offloaded, leaving the CPU with the minimal responsibilities of initialization, coordination and error handling. We claim that these responsibilities can also be handled in simple hardware other than the CPU and that it is wasteful to use a CPU for these purposes. We explore the role and the structure of the OS in a system that has no CPU and demonstrate that all necessary functionality can be moved to other hardware. We show that almost all of the pieces for such a system design are already available today. The responsibilities of the operating system must be split between self-managing devices and a system bus that handles privileged operations.