US 7493435 B2
A method and apparatus for efficient memory allocation and system management interrupt (SMI) handling is herein described. Upon waking a second processor in a multiple processor system, one may use a single SMI to initialize each processor, may use the location of a single default SMI handler as a wake-up vector to the second processor, and may patch an instruction pointer to a non-aligned address during the handling of the SMI with the second processor to forgo the traditional extra aligned memory allocation. In addition, one may use unified handler code to handle software generated SMIs on both the first and second processors and may use exit SMM directly after handling a hardware SMI to save execution time.
1. A method comprising:
receiving a first system management interrupt (SMI) with a first and a second processor;
handling the first SMI with the first processor;
generating a wake-up signal with the first processor after receiving the first SMI, wherein the wake-up signal references a first memory address of a default SMI handler;
receiving the wake-up signal with the second processor;
awakening the second processor, based on the wake-up signal from the first processor; and
handling the first SMI with the second processor.
2. The method of
3. The method of
4. The method of
5. The method of
6. The method of
7. The method of
8. The method of
9. The method of
10. The method of
11. The method of
12. A method comprising:
receiving a first system management interrupt (SMI);
executing code at a first memory location with a first processor in response to the first SMI;
generating a wake-up signal with the first processor;
awakening a second processor, based on a wake-up signal from the first processor; and
executing the code from the first memory location with the second processor, in response to the first SMI after awakening the second processor.
13. The method of
14. The method of
15. The method of
16. The method of
17. The method of
18. The method of
19. The method of
20. The method of
21. The method of
executing code at the second memory location after patching the instruction pointer to the second memory location.
22. The method of
23. The method of
24. The method of
25. The method of
26. A method comprising:
executing system management interrupt (SMI) code with a first processor to handle a SMI for the first processor;
checking if the SMI is a software generated SMI; and
executing the SMI code to handle the SMI for a second processor, if the SMI is software generated.
27. The method of
28. The method of
29. The method of
30. The method of
31. The method of
32. The method of
changing a target SMBase from the first SMBase to the second SMBase; and
executing the SMI code using the second SMBase as the target SMBase.
33. The method of
34. An apparatus comprising:
a controller to generate a first system management interrupt (SMI);
a first logical processor, coupled to the controller, to receive the first SMI, to handle the first SMI and to generate a wake-up signal after receiving the first SMI, wherein the wake-up signal references a first memory address of a default SMI handler; and
a second logical processor, coupled to the controller, to handle the first SMI after the wake-up signal is received from the first logical processor.
35. The apparatus of
36. The apparatus of
37. The apparatus of
38. The apparatus of
39. A system comprising:
a controller hub to generate a first system management interrupt (SMI);
a memory to hold code beginning at a first memory address;
a first processor coupled to the controller hub to receive the first SMI and to handle the first SMI, wherein the first processor is to execute the code beginning at the first memory address to handle the first SMI and is to generate a wake-up signal after receiving the first SMI; and
a second processor coupled to the controller hub to receive the first SMI, to be woken up in response to receiving the wake-up signal, and to handle the first SMI after receiving the wake-up signal, wherein the second processor is to execute the code beginning at the first memory address to handle the first SMI.
40. The system of
41. The system of
42. The system of
43. The system of
44. The system of
45. The system of
46. The system of
47. The system of
48. A system comprising:
a memory to hold system management interrupt (SMI) code beginning at a first memory address;
a first logical processor coupled to the memory to execute the SMI code beginning at the first memory address to handle an SMI for the first logical processor in response to receiving the SMI; and
a second logical processor coupled to the memory to execute the SMI code beginning at the first memory address to handle the SMI for the second logical processor in response to the SMI being software generated.
49. The system of
50. The system of
51. The system of
52. The system of
53. The system of
This invention relates to the field of computer systems and, in particular, to system management mode optimizations.
Computer systems are becoming increasingly pervasive in our society including everything from small handheld electronic devices, such as personal digital data assistants and cellular phones, to application-specific electronic components, such as set-top boxes and other consumer electronics, to full mobile, desktop, and server systems. However, as systems become smaller in size and in price, the need for efficient memory allocation and system management becomes more important.
Server systems have been traditionally characterized by a significant amount of conventional memory and multiple physical processors in the same system (a multiprocessor system), wherein a physical processor refers to a single processor die or single package. The significant amount of memory available to a server system has lead to extremely inefficient allocation of memory space and wasted execution time.
Typically, in a multi-processor system, upon boot every processor arbitrates for wake-up, which may include allocating memory and relocating the processor's base address (SMBase). In the process of initializing each processor, a system management interrupt (SMI) is generated, which is handled with a default SMI handler for each processor. Usually, the processors arbitrate with a race to the flag scheme, wherein the first processor to begin handling the SMI is able to begin initialization. Initialization typically includes allocation of a separate and distinct 4 kB aligned memory space for each processor, which forces one to allocate more memory than needed for system management.
Furthermore, when a system management interrupt (SMI) occurs, whether during boot or regular operation, each processor in a multiprocessor system runs a separate and distinct SMI handler to service/handle the SMI. There are two types of SMIs. The first type is an asynchronous interrupt that may be generated by the system hardware, such as when a battery is low. An asynchronous interrupt may be handled separately by any processor, since knowledge of another processor's save state area is not needed to service the request. The second type of interrupt, a synchronous SMI, that is software generated, should be handled by every processor. Typically, a software generated SMI occurs when the operating system (OS) wants a processor to enter system management mode (SMM). SMM is an environment for executing software routines/handlers that does not interfere with the OS or application programs.
In current multiprocessor systems, each processor enters SMM and then one-by-one executes a distinct SMI handler to check their registers to find out which processor generated the SMI. This requires a separate SMI handler be executed for each processor, which introduces resource contention issues, thus making updates to the SMI handler code difficult.
However, these inefficient methods of initialization and handling are not limited to multiprocessor server systems, but exist in other systems, such as mobile multiprocessor systems. Hyper-Threading Technology (HT) is a technology from Intel.RTM. Corporation of Santa Clara, Calif. that enables execution of threads in parallel using a single physical processor. HT incorporates two logical processors on one physical processor (the same die). A logical processor is an independent processor visible to the operating system (OS), capable of executing code and maintaining a unique architectural state from other processor in a system. HT is achieved by having multiple architectural states that share one set of execution resources.
Therefore, HT enables one to implement a multi(logical)processor system in a mobile platform. As shown above, inefficient memory allocation, processor initialization, and SMI handling exist in traditional multiprocessor systems, such as server systems. Furthermore, as multiprocessor systems begin to infiltrate the mobile realm, where resources such as memory are limited, the need for optimizations of the aforementioned inefficiencies becomes even more important.
A method and apparatus for efficient memory allocation and system management interrupt handling is herein described. In one embodiment, a single SMI is used to initialize each processor in a multi-processor environment. In addition, a location of a default SMI handler may be used as a wake-up vector to inactive processors to efficiently utilize memory. In another embodiment, unified handler code is executed on multiple processors to handle software generated SMIs.
The present invention is illustrated by way of example and not intended to be limited by the figures of the accompanying drawings.
In the following description, numerous specific details are set forth such as examples of specific memory addresses, memory sizes, and component configurations in order to provide a thorough understanding of the present invention. It will be apparent, however, to one skilled in the art that these specific details need not be employed to practice the present invention. In other instances, well known components or methods, such as routine boot-up blocks (e.g. power on self-test (POST)), specific system management mode (SMM) implementation, and specific system management interrupt handler code have not been described in detail in order to avoid unnecessarily obscuring the present invention.
The method and apparatus described herein are for optimization of memory allocation when waking a processor and optimization of system management interrupt (SMI) handling in multiprocessor systems. The method of waking a processor may occur as a result of any number of normal operations. For example, when the computer is powered on or reset, one may wake an inactive/sleeping processor. Furthermore, when a system is returning from a low power state, such as sleep, standby, suspend, hibernation, wait-for-SIPI, sleep, deep sleep, reset, or any other mode where the second processor does not respond to interrupts one may wake an inactive processor.
It is readily apparent to one skilled in the art, that the method disclosed for waking a second processor may be applicable to any level computer system (personal digital assistants, mobile platforms, desktop platforms, and server platforms), as well as any number of processors. For example, a multiprocessor system with four or more processor may use this method to wake an inactive processor with an active processor.
Device 105 may include a first processor 120 and a second processor 125. Device 105 may be a physical processor. Device 105 may also be an embedded system or other device having at least two processors. Processors 120 and 125 may be logical processors. For example, processor 105 may include architecture state registers 130 and 135 that each holds a unique architecture state. It is readily apparent that device 105 may include more than two logical processors that each have an architecture state register associated with it to hold a separate architecture state. The two processors 120 and 125 share the same execution resources 140, caches 145, busses 115/150, and memory 155.
Device 105 may also include controller 110. Controller 110 may be an Advanced Programmable Interrupt Controller (APIC) controller. Controller 110 may be used to generate a system management interrupt (SMI). Controller 110 may also be used to communicate on an APIC bus, which is not depicted, coupling the first processor 120 and the second processor 125 together.
Device 105 may also include memory 155. Memory may be any style of storage, wherein data may be stored. For example, memory 155 may be registers to store information. Memory 155 may also be another level of cache 145. Memory 155 may also be a form of system memory placed on device 105.
Memory 155 has at least a first memory location 160 and a second memory location 165. First memory location 160 may contain default system management handler code. First memory location 160 may also be 1 k aligned. Second memory location 165 may be another non-1 k aligned address. First memory location 160 and second memory location 165 may also be base addresses for a first processor 120 and second processor 125 respectively. Second memory location 165 may also be used as temporary storage space, when relocating first processor 120's base address. The first and second memory locations will be discussed in more detail in reference to the methods described in
FIG. 3's illustrative system will be used to describe the methods depicted in FIG'S. 4-9. Although
In block 405, a first system management interrupt (SMI) is received. Often a SMI is generated to request a service from a processor. Once an SMI is received, a processor enters system management mode (SMM) to service the request by running SMI handler code and routines in conventional memory, unless the processor is inactive and not responding to interrupts.
As an illustrative example, the first SMI in block 405 may be generated by a controller hub, such as controller hub 345 depicted in
The first SMI in block 405 may be a service request to initialize SMM, to allocate address space for system management, and/or to relocate a processors base address (SMBase). The SMBase may be the address where the system management portion of memory begins. The SMBase may also be the address where the system management portion of memory is referenced from. For example, the SMBase may be a value of 0x30000. The SMI handler for that portion of memory might be referenced to the SMBase by an offset. For example, the SMI handler may be offset from the SMBase by 0x8000 (SMBase+0x8000), which would put the SMI handler at 0x38000 in the example.
When the SMI is generated in a multiprocessor system both a first processor and a second processor should receive/latch the SMI. However, the second processor may not enter SMM and handle the SMI at this time, since it may be in an inactive state (not responding to interrupts). In contrast, in block 410, the first processor may be active and may handle the first SMI received in block 405. When the first SMI is received by the first processor, the first processor may enter system management mode (SMM) to service/handle the SMI.
As shown in
As depicted in
Turning back to
In the next block, block 425, the first SMI received in block 405, is handled by the second processor. Although, the second processor may have been inactive when first SMI in block 405 was received, and therefore, unable to service the SMI at that time; the second processor may still have latched the SMI when it was in an inactive state. Once awake, the second processor may handle the first SMI that was previously latched.
In block 610, a first processor executes SMI code (an SMI handler) to handle the SMI for the first processor. Handling an SMI may include executing SMI code to determine if the current processor's save-state area being examined generated the SMI. Handling the SMI may also include servicing the SMI request.
As stated above in reference to
As an illustrative example, the target SMBase may be set by default to reference a first SMBase address, which is the starting address of a first processor's system management area. Therefore, when an SMI is received and the SMI handler code is executed, the SMI handler code is able to access the first processor system management area, which may include the first processor's save-state area, by referencing off the target SMBase.
After executing the SMI code in block 610 to handle the SMI for the first processor, the same SMI code/handler may be executed to handle the SMI for second processor, as shown in block 615. In
Continuing the illustrative example from above, after executing the SMI handler code with the target SMBase targeting the first SMBase, the target SMBase may be changed to target the second SMBase address. The second SMBase address may be the starting address of the second processor's system management area (memory space). Therefore, when the SMI handler is executed using the second processor's SMBase as the target SMBase, as in block 710, the same SMI code/handler is able to handle the SMI for the second processor by referencing off the second processor's SMBase address.
However, if the SMI was software generated then the second processor should handle the SMI as well. In block 820, the second processor may then execute the same SMI code that first processor executed in block 805.
An illustrative example of executing the same SMI code is depicted in
It is readily apparent that any combination of the first and second processor may execute the SMI code. For example, the first processor may execute the SMI code for the first processor. Then, after the target SMBase is changed to the second processor's SMBase, the first processor may execute the SMI code again to handle the SMI for the second processor. As another example, the second processor may execute the SMI code both times. As yet another example, the first processor may execute the SMI code the first time the SMI code is executed to handle the SMI for the first processor, and the second processor may execute the SMI code the second time to handle the SMI for the second processor.
Therefore, unlike current systems these optimizations may use only one SMI to be generated to wake and begin execution of a second processor. Furthermore, unlike traditional methods, which start each processor at a different default memory address, memory may be saved by sending a wake-up signal that starts the second processor at first memory address, which may be the location of a default SMI handler. Moreover, by patching the instruction pointer when the second processor handles the first SMI, the second processor may resume at a second memory address, which may be non-aligned. Allowing second processor to resume at second memory address saves the allocation of a separate aligned memory space for each processor.
In addition, handling an SMI may be done with a unified handler, by executing the same handler code with a first processor and then with a second processor. By checking to see if the SMI being handled was software generated and exiting SMM if the SMI was not software generated, one may save a significant amount of execution time. Furthermore, this implementation allows for easier platform development since all changes required for the software SMI handler may easily be contained in wrapper code without requiring modification to the software SMI handler routines.
In the foregoing specification, the invention has been described with reference to specific exemplary embodiments thereof. It will, however, be evident that various modifications and changes may be made thereto without departing from the broader spirit and scope of the invention as set forth in the appended claims. The specification and drawings are, accordingly, to be regarded in an illustrative sense rather than a restrictive sense.