Uniprocessor operating system design facilitating fast context switching

• US 7,313,797 B2
• Filed: 09/18/2002
• Issued: 12/25/2007
• Est. Priority Date: 09/18/2002
• Status: Active Grant

• Current Assignee: Wind River Systems Incorporated (Aptiv PLC)
• Original Assignee: Wind River Systems Incorporated (Aptiv PLC)
• Inventors: Sundaram, Anand, Koning, Maarten
• Primary Examiner(s): BULLOCK JR, LEWIS ALEXANDER
• Application Number:
  US10/246,830
• Publication Number:
  US 20040055003A1
• Time in Patent Office: 1,924 Days
• Field of Search: 718100-108, 712/228
• US Class Current: 718/108
• CPC Class Codes: G06F 9/461 Saving or restoring of program or task context
• CPC Class Codes: G06F 9/463 Program control block organisation

Abstract

A task stack and a context pointer in a task control block (TCB) are implemented to provide more efficient context switching. Additionally, multiple routines each of which saves or restores a certain combination of volatile registers is implemented. A task can store in its task control block a routine identifier to select from the multiple routines a set of routines for saving and restoring volatile registers during context switching. On the occurrence of an event that may lead to a context switch a scheduler selects based on the routine identifier a routine that only saves registers used by the task, thereby, reducing execution overhead. The registers are saved on the task stack and a context pointer to the registers is saved in the TCB. In the event a context switch is necessary, it is not necessary to copy the registers to the TCB because the context pointer is in the TCB. A non-volatile register indicator that indicates whether non-volatile registers are used is stored in the task control block. The non-volatile registers are only saved if used, also reducing execution overhead. Furthermore, a storage area is implemented for saving task context for the task when it is interrupted during context switch in. Upon the occurrence of an interrupt the task context is saved in the storage area. If the interrupt leads to a second task which has a higher priority being made ready, the second task is switched in without first returning to switch-in the task.

Claims

1. A method being stored as a set of instructions on a computer-readable medium, the set of instructions being executable by a processor to perform the method, the method comprising:

receiving an event leading to a context switch;

determining whether a user task uses first task context information by examining a first task context information indicator in a task data structure associated with the user task;

storing the first task context information in a temporary memory for use following the context switch only if the user task uses the first tank context information;

setting a context pointer so that the first task context information can be retrieved from the temporary memory; and

storing, in the task data structure, a context storage indicator indicative of the organization of information including the first task context information on the temporary memory.

2. The method of claim 1, wherein the temporary memory is a stack.

3. The method of claim 2, wherein the context pointer is stored in the task data structure.

4. The method of claim 3, wherein the task data structure is a task control block.

5. The method of claim 1, wherein the first task context information is at least one non-volatile register.

6. The method of claim 1, further comprising storing second task context information used by a second task in the temporary memory.

7. The method of claim 6, wherein the setting of the context pointer permits the retrieval of both the second task context information and the first task context information from the temporary memory.

8. The method of claim 6, wherein the second task context information is at least one volatile register.

9. The method of claim 6, wherein the second task context information is at least one callee volatile register.

10. The method of claim 6, further comprising storing non-compiler registers in the temporary memory.

11. The method of claim 6, further comprising storing non-compiler registers in the temporary memory.

12. The method of claim 6, further comprising making ready a second user task which has a higher priority than the user task.

13. The method of claim 12, further comprising storing a context storage indicator indicative of the event leading to the context switch.

14. The method of claim 13, wherein making the second user task ready cause the higher priority task to preempt the user task and the context storage indicator indicates that the event leading to the context switch was the user task being preempted.

15. The method of claim 6, wherein the storing includes selecting from a set of routines that stores the second context information.

16. A method being stored as a set of instructions on a computer-readable medium, the set instructions being executable by a processor to perform the method, the method comprising:

receiving an event leading to a context switch;

determining whether a user task uses first task context information by examining a first task context information indicator in a task data structure associated with the user task;

storing the first task context information in a temporary memory for use following the context switch only if the user task uses the first task context information;

setting a context pointer so that the first task context information can be retrieved from the temporary memory; and

storing in the task data structure a context storage indicator indicative of the event leading to the context switch.

17. The method of claim 16, wherein the event leading to the context switch is the task relinquishing processing.

18. The method of claim 16, wherein the event leading to the context switch is the task relinquishing processing due to an unavailable system resource.

19. The method being stored as a set of instructions on a computer-readable medium, the set of instructions being executable by a processor to perform the method, the method comprising:

executing first code for a first user task, the first code requiring first task context information to be saved in the event of a context switch;

receiving an indication to make a transition to execute second code for a second task, the second code requiring second context information to be saved in the event of the context switch the second context information being at least partially different than the first task context information;

saving in a temporary memory an identifier for a first routine that saves the first task context information, storing in a task data structure associated with the first user task a default identifier for a second routine that saves the second context information; and

saving the first task context information in the temporary memory.

20. The method of claim 19, wherein the temporary memory is a task stack and the task data structure is a task control block.

21. The method of claim 19, further comprising executing the second code.

22. The method of claim 21, further comprising:

returning to execute the first code after finishing execution of the second code;

retrieving the identifier from the temporary memory; and

storing the identifier in the task data structure.

23. A method being stored as a set of instructions on a computer-readable medium, the set of instructions being executable by a processor to perform the method, the method comprising:

receiving an event;

determining whether the event leads to a context switch;

wherein if the event leads to the context switch, determining, by examining a first task context information indicator in a task data structure associated with a user task, whether the user task uses first task context information; and

initiating an execution of function comprising a second set of instructions storing the first tank context information in a temporary memory for use following the context switch, setting a context pointer so that the first task context information can be retrieved from the temporary memory and storing, in the task data structure, a context storage indicator indicative of the organization of information including the first task context information on the temporary memory, only if the user task uses the first task context information.