A computer system, comprising: a hardware platform including at least one physical processor; a virtualization layer which is installed on the hardware platform; a virtual machine supported by the virtualization layer; wherein the virtual machine includes a plurality of virtual processors (122 1-N), and wherein the virtual processors (122 1-N) have a guest operating system executing thereon, characterised in that: the guest operating system comprises a device driver configured to communicate with the virtualization layer to receive a target number of virtual processors (122 1-N) for the virtual machine based on processor demand by the virtual machine, and determine that the target number is less than a current number of virtual processors (122 1-N) activated for the virtual machine; the device driver is further configured to launch a prioritized process thread in the guest operating system, wherein the prioritized process thread is associated with a first virtual processor of the plurality of virtual processors (122 1-N) and includes a halt instruction; the guest operating system, by operation of a guest scheduler, is further configured to execute the prioritized process thread using the first virtual processor of the plurality of virtual processors (122 1-N); and the virtualization layer is configured to manage sharing of the processor between the plurality of virtual processors (122 1-N) for the virtual machine, wherein the virtualization layer is configured to, responsive to detecting that the first virtual processor is executing the halt instruction, deschedule execution of the first virtual processor on the physical processor of the computer system. a hardware platform including at least one physical processor; a virtualization layer which is installed on the hardware platform; a virtual machine supported by the virtualization layer; wherein the virtual machine includes a plurality of virtual processors (122 1-N), and wherein the virtual processors (122 1-N) have a guest operating system executing thereon, characterised in that: the guest operating system comprises a device driver configured to communicate with the virtualization layer to receive a target number of virtual processors (122 1-N) for the virtual machine based on processor demand by the virtual machine, and determine that the target number is less than a current number of virtual processors (122 1-N) activated for the virtual machine; the device driver is further configured to launch a prioritized process thread in the guest operating system, wherein the prioritized process thread is associated with a first virtual processor of the plurality of virtual processors (122 1-N) and includes a halt instruction; the guest operating system, by operation of a guest scheduler, is further configured to execute the prioritized process thread using the first virtual processor of the plurality of virtual processors (122 1-N); and the virtualization layer is configured to manage sharing of the processor between the plurality of virtual processors (122 1-N) for the virtual machine, wherein the virtualization layer is configured to, responsive to detecting that the first virtual processor is executing the halt instruction, deschedule execution of the first virtual processor on the physical processor of the computer system. the guest operating system comprises a device driver configured to communicate with the virtualization layer to receive a target number of virtual processors (122 1-N) for the virtual machine based on processor demand by the virtual machine, and determine that the target number is less than a current number of virtual processors (122 1-N) activated for the virtual machine; the device driver is further configured to launch a prioritized process thread in the guest operating system, wherein the prioritized process thread is associated with a first virtual processor of the plurality of virtual processors (122 1-N) and includes a halt instruction; the guest operating system, by operation of a guest scheduler, is further configured to execute the prioritized process thread using the first virtual processor of the plurality of virtual processors (122 1-N); and the virtualization layer is configured to manage sharing of the processor between the plurality of virtual processors (122 1-N) for the virtual machine, wherein the virtualization layer is configured to, responsive to detecting that the first virtual processor is executing the halt instruction, deschedule execution of the first virtual processor on the physical processor of the computer system.