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Method for a preemption timer for regaining control of a virtual machine

IP.com Disclosure Number: IPCOM000128942D
Publication Date: 2005-Sep-21
Document File: 2 page(s) / 38K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method for a preemption timer for regaining control of a virtual machine. Benefits include improved functionality and improved performance.

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Method for a preemption timer for regaining control of a virtual machine

Disclosed is a method for a preemption timer for regaining control of a virtual machine. Benefits include improved functionality and improved performance.

Background

              A preemption timer (host timer) is a device for regaining control of a virtual machine guest after a specific time has elapsed. In the conventional 32-bit virtualization technology architecture, a virtual machine (VM) exit occurs from a guest back to its parent monitor when the guest performs certain actions. No other timers within the system except are capable of delivering a logical-processor-specific event.

              The clocking of a preemption timer must have a very fine granularity. The timer must have low access latency and must be capable of delivering a logical processor specific event.

General description

              The disclosed method is a hardware-derived time source for a preemption timer. The method provides a flexible but stable architectural time source for on-timer elapse transitioning to the virtual machine monitor and to another guest.

Advantages

              The disclosed method provides advantages, including:
•             Improved functionality due to providing a preemption timer that includes an exit reason
•             Improved performance due to simplifying context switching

Detailed description

              The disclosed method is a preemption timer that passes an exit reason from the guest to the monitor when the timer expires. The method applies to the following usage models (see Figure 1):

•             Regaining control of an errant machine

•             Simple context switching between different guests to provide time-slicing on a single processor

•             Provide other multitasking switching

              The preemption timer is comprised of three parts: the counter, the control registers that program it, and the event logic.

              The disclosed method includes an N-bit decrementer. The counter is programmed by a write of some number, N, of bits from a control register. The count decreases when e...