Tracking current time on multiprocessor hosts and virtual machines

• US 20080126820A1
• Filed: 07/17/2007
• Published: 05/29/2008
• Est. Priority Date: 07/17/2006
• Status: Active Grant

• Current Assignee: Citrix Systems, Inc. (Cloud Software Group)
• Original Assignee: XenSource, Inc. (Cloud Software Group)
• Inventors: Prat, Ian, Fraser, Keir
• Granted Patent: US 7,870,411 B2
• Time in Patent Office: Days
• US Class Current: 713/375
• CPC Class Codes: G06F 1/12 Synchronisation of different clock signals provided by a plurality of clock generators
• CPC Class Codes: G06F 1/14 Time supervision arrangements, e.g. real time clock

Abstract

An operating system in a virtual environment can obtain the current time of the processor that the OS is utilizing through a method for synchronizing timers on multiple processors with a standard reference time, such as the Coordinated Universal Time (UTC). A hypervisor controlling the processors obtains a number of synchronization values that, together with a local timer counter value, are utilized by the guest operating system to determine the physical processor time.

Claims

1. A computer readable set of instructions, comprising:

a first command for obtaining synchronization values,

a second command for calculating a synchronized time value,

a third command for placing the synchronized time value at an accessible location.

2. The computer readable set of instructions of claim 1, further comprising:

a command for synchronizing a guest operating system with the synchronized time value.

3. The computer readable set of instructions of claim 1, wherein the first command for obtaining synchronization values further comprises

instructions for obtaining a calibration constant,

instructions for storing a local timer counter value,

instructions for storing a previously calculated synchronized local time.

4. The computer readable set of instruction of claim 3, werein the instructions for obtaining a calibration constant further comprise:

instructions for calculating a calibration factor;

instructions for calculating an error correction factor.

5. The computer readable set of instructions of claim 1, further comprising:

a command for calculating initial synchronization values.

6. A method for synchronizing local timers, comprising:

obtaining synchronization values;

calculating a synchronized time value; and

placing the synchronized time value at an accessible location.

7. The method of claim 6, further comprising:

synchronizing an operating system with the synchronized time value.

8. The method of claim 6, wherein

one of the synchronization values is a calibration constant.

9. The method of claim 8, wherein the calibration constant is calculated by a hypervisor.

10. The method of claim 6, wherein the synchronized time value is calculated by a guest operating system.

11. The method of claim 6, further comprising:

assigning a guest operating system to a processor.

12. The method of claim 6, further comprising:

synchronizing a guest operating system after it is assigned to a processor by the hypervisor.

13. The method of claim 6, wherein the accessible location is chosen from the list consisting of a shared memory, a virtual memory, a shared hard drive, a virtual hard drive, a cd-rom, and a virtual cd-rom.

15. The computing system of claim 12, wherein the synchronizing program contains a computer readable set of instructions that

direct a hypervisor to calculate synchronization values and place the synchronization values in an accessible location;

direct an operating system to utilize the synchronization values to calculate a synchronized processor time; and

direct placement of the synchronized processor time in an accessible location.

16. The computing system of claim 12, wherein the operating system may be reassigned to different processors within the system.

14. A computing system, comprising:

a processor, including a local timer;

the processor communicatively connected with a guest operating system via a hypervisor; and

a platform timer communicatively coupled with the hypervisor;

wherein the system executes a synchronizing program for providing a synchronized time value.