INTELLIGENT CONTEXT MIGRATION FOR USER MODE SCHEDULING

• US 20100083261A1
• Filed: 09/30/2008
• Published: 04/01/2010
• Est. Priority Date: 09/30/2008
• Status: Active Grant

• Current Assignee: Microsoft Technology Licensing LLC (Microsoft Corporation)
• Original Assignee: Microsoft Corporation
• Inventors: Teixeira, Pedro, Probert, Dave, Jayamohan, Ajith, Kishan, Arun U.
• Granted Patent: US 8,321,874 B2
• Time in Patent Office: Days
• US Class Current: 718/102
• CPC Class Codes: G06F 9/461 Saving or restoring of program or task context
• CPC Class Codes: G06F 9/545 where tasks reside in different layers, e.g. user- and kernel-space

Abstract

Embodiments for performing directed switches between user mode schedulable (UMS) thread and primary threads are disclosed. In accordance with one embodiment, a primary thread user portion is switched to a UMS thread user portion so that the UMS thread user portion is executed in user mode via the primary thread user portion. The primary thread is then transferred into kernel mode via an implicit switch. A kernel portion of the UMS thread is then executed in kernel mode using the context information of a primary thread kernel portion.

Claims

1. A method, comprising:

switching a primary user portion of a primary thread to a user mode schedulable (UMS) user portion of a first UMS thread;

executing the UMS user portion via the primary user portion in user mode;

transferring the primary thread into kernel mode via an implicit switch; and

executing a UMS kernel portion of the first UMS thread in kernel mode using current context information of a primary kernel portion of the primary thread.

2. The method for of claim 1, further comprising creating the first UMS thread from a NT thread.

3. The method of claim 1, further comprising:

creating the first UMS thread portion from a NT thread;

moving the UMS user portion of the first UMS thread into a UMS completion list; and

parking the UMS kernel portion of the first UMS thread into a waiting state.

4. The method of claim 1, further comprising creating the primary thread from a second UMS thread.

5. The method of claim 1, wherein the switching includes switching the user thread descriptor of the primary user portion to the user thread descriptor of the UMS user portion via one of a pointer or a segment selector.

6. The method of claim 1, wherein the executing includes pulling the current context information of the primary kernel portion into the UMS kernel portion via a pointer, and replacing old context information of the UMS kernel portion with the current context information of the primary kernel portion.

7. The method of claim 1, wherein the executing includes swapping a first stack of the primary kernel portion with a second stack of a UMS kernel portion, each of the stacks including the context information of each respective thread.

8. The method of claim 1, wherein the executing includes executing the UMS kernel portion on a CPU while the CPU retains the current context information of the primary user portion in its cache if a first affinity of the primary thread and a second affinity of the first UMS thread share a non-zero intersection.

9. The method of claim 1, further comprising:

moving the UMS user portion of the first UMS thread into a UMS completion list; and

parking the UMS kernel portion of the first UMS thread into a waiting state;

clearing the states of the primary kernel portion of the primary thread;

transferring the primary thread from kernel mode to user mode via another implicit switch; and

executing one of the first UMS thread and a third UMS in user mode.

10. A computer readable medium storing computer-executable instructions that, when executed, cause one or more processors to perform acts comprising:

switching a first user portion of a primary thread to a second user portion of a first user mode schedulable (UMS) thread;

executing the first user portion in place of the second user portion in user mode;

transferring a primary thread into kernel mode by moving execution from the first user portion to a first kernel portion of the primary thread;

replacing first context information of a second kernel portion of the first UMS thread with second context information of the first kernel portion; and

executing the first kernel portion in kernel mode using the second context information.

11. The computer readable medium of claim 10, the computer-executable instructions causing the one or more processors to perform acts further comprising:

suspending the first kernel portion following the replacement of the first context information with the second context information; and

waking the first kernel portion from suspension when a second kernel portion of the first UMS thread becomes blocked in a waiting state.

12. The computer readable medium of claim 10, the computer-executable instructions causing the one or more processors to perform acts further comprising:

permitting the primary thread to exit kernel mode via an implicit switch from the first kernel portion to the first user portion; and

performing an implicit switch from the second kernel portion to the second user portion to execute the first UMS thread in user mode when the primary thread has not exited kernel mode.

13. The computer readable medium of claim 10, the computer-executable instructions causing the one or more processors to perform acts further comprising blocking the UMS thread in kernel mode when the UMS thread is executing in one of kernel mode and user mode.

14. The computer readable medium of claim 10, the computer-executable instructions causing the one or more processors to perform acts further comprising:

determining a second UMS thread to receive a yield from a first UMS thread when the first UMS thread exits to user mode from kernel mode;

moving the second user portion of the first UMS thread into a UMS completion list;

parking the first kernel portion of the first UMS thread in a waiting state; and

transferring the primary thread from kernel mode to user mode; and

executing the third user portion of the second UMS thread in user mode, the third user portion being retrieved from the UMS completion list.

15. The computer readable medium of claim 10, the computer-executable instructions causing the one or more processors to perform acts further comprising:

creating the first UMS thread from a NT thread; and

creating the primary thread from a third thread.

16. The computer readable medium of claim 10, wherein the executing includes pulling the current context information of the first kernel portion into the second kernel portion via a pointer, and replacing old context information of the second kernel portion with the current context information of the first kernel portion.

17. The computer readable medium of claim 10, wherein the executing includes swapping a first kernel portion stack with a second kernel portion stack, each of the stacks including the context information of each respective thread.

18. A system, comprising:

a user mode scheduler to switch a primary user portion of a primary thread to a user mode schedulable (UMS) user portion of a first UMS thread to execute the UMS user portion via the primary user portion in user mode;

an implicit switch component to transfer the primary thread into kernel mode; and

a central processing unit (CPU) to execute a UMS kernel portion of the first UMS thread in kernel mode using current context information of a primary kernel portion of the primary thread.

19. The system of claim 18, further comprising a pointer the enables the UMS kernel portion to pull the current context information of the primary kernel portion into the UMS kernel portion to replace old context information of the UMS kernel portion with the current context information of the primary kernel portion.

20. The system of claim 18, further comprising a CPU scheduler to schedule the execution of the UMS kernel portion on a CPU while the CPU retains the current context information of the primary user portion in its cache.