In recent years, logically dividing one physical computer into plural computers using a virtual technology, these computers respectively run a separate Operating Systems (OS), for example, a guest OS. These logical computers may be referred to as a virtual machine (VM).
In addition, according to the virtual technology, consolidating or integrating the OS running on plural servers into one server, it may be possible to realize power saving by efficient use of resources. Further, a migration technology for dynamically shifting the running virtual machine to other server has been also known. Depending on this technology, a power-saving operating method for cutting power of redundant servers by efficiently consolidating the virtual machines in accordance with workload has been also known.
On the other hand, the virtual technology originally for a large computer such as a server started to be applied to client's devices such as a notebook PC and a cellular phone because of downsizing and significant increase in performance of the computer. Due to application of the virtual technology to these client's devices, it is possible to expect improvement of a convenience obtained by using plural guest OSs with different user interfaces and achievement of security depending on abstraction of hardware and management the OS from a lower layer. Further, the notebook PC and the cellular phone are directly used by a user, so that power-saving operation used by a server for consolidating or migrating one device to other is hardly applied to these devices.
An information processor such as a notebook PC and a cellular phone to be mainly driven by a battery highly requires reduction of power consumption, and conventionally, a state of a power source of a device has been carefully managed by the OS and applications. For example, such an information processor realizes a function such as shifting the device into a lower power consumption mode, for example, clock-down and power supply stop. However, it is not possible to apply these methods of managing a power source state to a virtual machine system because there is a possibility that plural guest OSs are carried out at the same time and the same device is shared by other guest OS, so that this makes one guest OS impossible to freely stop the operation state.
Therefore, conventionally, a method of arranging a state transition command notified by a guest OS (for example, Advanced Configuration and Power Interface (ACPI) command) by means of a management OS and managing device resources shared by this management OS has been known, for example. Thereby, controlling shift to a real power saving mode of the device, it is possible to reduce power consumption in the virtual machine system in which plural guest OSs run.
[Patent Document 1] Japanese Patent Application Publication No. 2005-115653
[Patent Document 2] Japanese Patent Application Publication No. 2006-113767
However, as described above, according to the method of arranging a state transition command from each guest OS running in the virtual machine by means of the management OS, in order to appropriately realize power saving by the entire system, it is required that all guest OSs appropriately issue the state transition commands at anytime to positively carry out power saving. In other words, this involves a problem that, if only one guest OS does not issue the state transition command, shift to the power saving mode cannot be realized.
On operation of the system, a legacy OS unequipped with a function to command a state transition command may be run as a guest OS in order to maintain a compatibility. In such a case, for example, it is difficult to modify the legacy guest OS so as to be able to issue an appropriate state transition command. In addition, not only for the legacy guest OS but also for all guest OSs, it may be difficult to have equal power saving mechanisms due to a development resource problem.
On the other hand, under the condition that the guest OS does not run actively, the device maybe shifted to the power saving mode not depending on the transition command from the guest OS but in the judgment of the management OS and the virtual machine monitor. This may have a problem that it takes time since the device should be recovered from the power saving mode when the guest OS tries to use the device.