Partition adjunct with non-native device driver for facilitating access to a physical input/output device

[0001] This application claims priority from U.S. Patent Provisional Application No. 60/953,512, filed Aug. 2, 2007, entitled “Partition Adjunct Environment”, the entirety of which is hereby incorporated herein by reference.

[0002] The present invention relates generally to data processing systems, and more particularly, to creation and utilization of a partition adjunct, comprising a new execution environment for the data processing system. The partition adjunct is utilized, in one aspect, as a dedicated adjunct providing a logical partition with access to a physical input/output (I/O) device.

[0003] Logical partitions (LPARs) running atop a hypervisor of a data processing system are often used to provide higher-level function than provided by the hypervisor itself. For example, one LPAR may be designated a virtual input/output server (VIOS), which provides input/output services to one or more other LPARs of the data processing system. This offloading of higher-level function avoids complex code in the hypervisor, and thus, assists in maintaining the hypervisor small and secure within the data processing system. Using logical partitions to provide such services to other logical partitions, however, requires relatively high overhead to instantiate and run the logical partition, and thus, a full operating system, in order to provide such services.

[0004] Disclosed herein is a solution which allows services to be provided to a logical partition without requiring another full logical partition to provide the services, and without requiring embedding of the services in the initiating logical partition or in the hypervisor. A partition adjunct, such as described and claimed herein, is a new execution environment which provides this middle ground.

[0005] Provided herein, in one aspect, is a method of establishing access to a physical input/output (I/O) device of a data processing system. The method includes: initiating, by an initiating logical partition of the data processing system, creation of a partition adjunct; invoking a hypervisor of the data processing system to instantiate the partition adjunct with resources donated from the initiating logical partition, the donated resources comprising a donated virtual address space of the initiating logical partition and the physical I/O device; creating, by the hypervisor, the partition adjunct and assigning the donated virtual address space and donated physical I/O device to the created partition adjunct; and interfacing, by the hypervisor, the initiating logical partition and the created partition adjunct, the interfacing including providing the initiating logical partition with a virtual I/O device which replaces the donated physical I/O device, wherein the donated physical I/O device is non-configurable by the initiating logical partition, and the virtual I/O device is configurable by the initiating logical partition.

[0006] In another aspect, a method is provided of establishing access by a logical partition to a physical input/output (I/O) device owned by the logical partition. The method includes: creating a partition adjunct within the data processing system, the partition adjunct being created employing the physical I/O device and virtual address space donated from the logical partition to the partition adjunct, the logical partition including a native operating system, and the partition adjunct including a non-native operating system's device driver for the physical I/O device, the physical I/O device being non-configurable by the logical partition; and providing the logical partition with a virtual I/O device interfaced through the partition adjunct's non-native operating system's device driver to the donated physical I/O device.

[0007] In yet another aspect, a data processing system is provided which includes a processor. The processor includes a logical partition and a partition adjunct to process an input/output request of the logical partition. The partition adjunct and the logical partition share a virtual address space range, and the partition adjunct processes the input/output request utilizing virtual address space donated to the partition adjunct from the logical partition. The partition adjunct further includes a physical input/output (I/O) device donated from the logical partition to the partition adjunct, and the logical partition has a native operating system, and the partition adjunct includes a non-native operating system's device driver for the physical I/O device. The physical I/O device is non-configurable by the logical partition, and the logical partition includes a virtual I/O device interfaced through the partition adjunct's non-native operating system's device driver to the donated physical I/O device.

[0008] In a further aspect, the invention comprises an article of manufacture which includes at least one computer-readable medium having computer-readable program code logic to define a method of establishing access to a physical input/output (I/O) device of a data processing system. The computer-readable program code logic, when executing on the processor performing: initiating, by an initiating logical partition of the data processing system, creation of a partition adjunct; invoking a hypervisor of the data processing system to instantiate the partition adjunct with resources donated from the initiating logical partition, the donated resources comprising a donated virtual address space of the initiating logical partition and the physical I/O device; creating, by the hypervisor, the partition adjunct and assigning the donated virtual address space and donated physical I/O device to the created partition adjunct; and interfacing, by the hypervisor, the initiating logical partition and the created partition adjunct, the interfacing including providing the initiating logical partition with a virtual I/O device which replaces the donated physical I/O device, wherein the donated physical I/O device is non-configurable by the initiating logical partition, and the virtual I/O device is configurable by the initiating logical partition.

[0009] Further, additional features and advantages are realized through the techniques of the present invention. Other embodiments and aspects of the invention are described in detail herein and are considered a part of the claimed invention.

[0038] FIG. 1 is a block diagram of a data processing system 100, which in one example, is a symmetric multiprocessing (SMP) server computer system. SMP server computer system 100 includes physical hardware devices that can be mapped to, i.e., temporarily owned by, a user application to execute that application.

[0039] SMP server computer system 100 includes a physical SMP server 102. Physical SMP server 102 includes physical hardware devices such as processor 104, memory 106, and I/O adapters 108. These physical devices are managed by hypervisor 110. Processors 104 are shared processors and each may be a simultaneous multithreading (SMT)-capable processor that is capable of concurrently executing multiple different threads on the processor.

[0040] A virtual server is a proxy for a physical server that has the same capabilities, interfaces, and state. Virtual servers are created and managed by a hypervisor that resides on physical SMP server computer system 100. A virtual server appears to be a physical SMP server to its user: the operating system, middleware, and application software that run upon it. SMP server computer system 100 includes one or more virtual servers such as virtual server 112 and virtual server 112a.

[0041] Each virtual server appears to its software to include its own processor(s), memory, and I/O adapter(s) that are available for the exclusive use of that virtual server. For example, virtual server 112 includes a virtual processor 120, virtual memory 122, and virtual I/O adapters 124. Virtual server 112a includes virtual processors 120a, virtual memory 122a, and virtual I/O adapters 124a.

[0042] Each virtual server supports its own software environment, including an operating system, middleware, and applications. The software environment of each virtual server can be different from the software environment of other virtual servers. For example, the operating systems executed by each virtual server may differ from one another.

[0043] For example, virtual server 112 supports operating system 114, middleware 116, and applications 118. Virtual server 112a supports operating system 114a, middleware 116a, and applications 118a. Operating systems 114 and 114a may be the same or different operating systems.

[0044] A virtual server is a logical description of a server that defines a server environment that acts, to a user, as if it were a physical server, being accessed and providing information in the same way as a physical server. The virtual processors, virtual memory, and virtual I/O adapters that are defined for each virtual server are logical substitutes for physical processors, memory, and I/O adapters.

[0045] Hypervisor 110 manages the mapping between the virtual servers with their virtual processors, virtual memory, and virtual I/O adapters and the physical hardware devices that are selected to implement these virtual devices. For example, when a virtual processor is dispatched, a physical processor, such as one of physical processors 104, is selected by hypervisor 110 to be used to execute and implement that virtual processor. Hypervisor 110 manages the selections of physical devices and their temporary assignment to virtual devices.

[0046] Hypervisor 110 services all of the logical partitions during a dispatch time slice. The dispatch time slice is a particular length of time. During each dispatch time slice, hypervisor 110 will allocate, or assign, the physical processor to each logical partition. When the logical partition has been allocated time on the physical processor, the virtual processors defined by that logical partition will be executed by the physical processor.

[0047] Hypervisor 110 is responsible for dynamically creating, managing, and destroying virtual SMP servers. Whole virtual processors, virtual I/O adapters, and virtual memory blocks can be removed or added by hypervisor 110. Hypervisor 110 is also responsible for dynamic resource allocation, managing time-sharing of physical resources, and altering the physical resource mapped to a processor without involving the operating system. Hypervisor 110 is also able to dedicate physical resources to virtual resources for situations where sharing is not desired. Hypervisor 110 is responsible for managing the addition or removal of physical resources. Hypervisor 110 makes these additions and deletions transparent to the upper level applications.

[0048] FIG. 2 is a more detailed illustration of a computer system that may be used to implement the concepts described herein. Data processing system 200 may be a symmetric multiprocessor (SMP) system including a plurality of shared processors or SMT-capable processors, such as processors 202 and 204 connected to system bus 206. Alternatively, a single processor system may be employed. In the depicted example, processor 204 is a service processor. Each SMT-capable processor is capable of concurrently executing multiple hardware threads on the one processor.

[0049] Also connected to system bus 206 is memory controller/cache 208, which provides an interface to local memory 209. I/O bus bridge 210 is connected to system bus 206 and provides an interface to I/O bus 212. Memory controller/cache 208 and I/O bus bridge 210 may be integrated as depicted.

[0050] Peripheral component interconnect (PCI) bus bridge 214 connected to I/O bus 212 provides an interface to PCI local bus 216. A number of modems may be connected to PCI bus 216. Typical PCI bus implementations will support four PCI expansion slots or add-in connectors. Communications links to network computers 108-112 in FIG. 1 may be provided through modem 218 and network adapter 220 connected to PCI local bus 216 through add-in boards.

[0051] Network adapter 220 includes a physical layer 282 which conditions analog signals to go out to the network, such as for example, an Ethernet network for an R45 connector. A media access controller (MAC) 280 is included within network adapter 220. Media access controller (MAC) 280 is coupled to bus 216 and processes digital network signals. MAC 280 serves as an interface between bus 216 and physical layer 282. MAC 280 performs a number of functions involved in the transmission and reception of data packets. For example, during the transmission of data, MAC 280 assembles the data to be transmitted into a packet with address and error detection fields. Conversely, during the reception of a packet, MAC 280 disassembles the packet and performs address checking and error detection. In addition, MAC 280 typically performs encoding/decoding of digital signals transmitted and performs preamble generation/removal as well as bit transmission/reception.

[0052] Additional PCI bus bridges 222 and 224 provide interfaces for additional PCI buses 226 and 228, from which additional modems or network adapters may be supported. In this manner, data processing system 200 allows connections to multiple network computers. A memory-mapped graphics adapter 230 and hard disk 232 may also be connected to I/O bus 212 as depicted, either directly or indirectly.

[0053] Service processor 204 interrogates system processors, memory components, and I/O bridges to generate and inventory and topology understanding of data processing system 200. Service processor 204 also executes Built-In-Self-Tests (BISTs), Basic Assurance Tests (BATs), and memory tests on all elements found by interrogating a system processor, memory controller, and I/O bridge. Any error information for failures detected during the BISTs, BATs, and memory tests are gathered and reported by service processor 204.

[0054] Those of ordinary skill in the art will appreciate that the hardware depicted in FIG. 2 may vary. For example, other peripheral devices, such as optical disk drives and the like, also may be used in addition to or in place of the hardware depicted. The depicted example is not meant to imply architectural limitations with respect to the present invention.

[0055] The present invention may be executed within one of the computers or data processing systems depicted in FIG. 1 or 2. As a specific, commercially available example, the data processing system implementing a partition adjunct such as described hereinbelow can be built upon technologies found in IBM's p/i Series product line firmware and systemware, such as described in the “Power Architecture Platform Reference” (PAPR) material at Power.org (http://www.power.org/members/developers/specs/PAPR_Version_—2.2_—09Oct07.pdf), which is incorporated herein by reference.

[0056] Disclosed hereinbelow is the concept of a partition adjunct, which is a partition that is more limited than a full, logical partition. As described below, the partition adjunct runs in a flat, static effective address space and problem state. These restrictions permit the hypervisor to apply a range of hypervisor and processor optimizations that result in a substantial decrease in system overhead associated with a context switch of the state machine from a logical partition to state data of a partition adjunct, that is, compared to a context switch of the state machine between logical partitions. In other respects, a partition adjunct is similar to a full logical partition. For example, a partition adjunct can be assigned resources, either physical or virtual, similar to a full logical partition. Further, a partition adjunct can be an end-point of a virtual input output (VIO) communications mechanism, similar to a full logical partition, such as a virtual input output server (VIOS).

[0057] FIG. 3 illustrates one example of a data processing system 300, comprising a client logical partition (or simply client partition) 310 and a partition adjunct 320, in accordance with an aspect of the present invention. Client partition 310 is a logical partition which comprises one or more customer applications 312, an operating system instance 314 and a virtual I/O facility 316. Client partition 310 runs atop a hypervisor 330, and provides higher-level function than that provided by the hypervisor itself. Hypervisor 330 executes atop the underlying system hardware 340, which is shown to include one or more I/O devices 350.

[0058] Partition adjunct 320 is conceptually a child partition to client partition 310. The partition adjunct is less than a full logical partition, but is run in a manner whereby the hypervisor enforces security and isolation between the partition adjunct and the client partition it runs within. The partition adjunct is provided with reduced functionality compared with a full logical partition, for example, has no access to memory management unit (MMU) configuration or floating-point facilities, and is an environment that only the functionality needed to run the desired service (e.g., I/O driver) is provided. In the illustrated example, partition adjunct 320 includes a virtual I/O interface 322 and a hardware device driver service 324, which allows access to I/O device 350. In operation, client partition 310 accesses I/O device 350 via the partition adjunct 320, as illustrated. By reducing functionality within the partition adjunct environment, the run time overhead of dispatching and maintaining the partition adjunct (compared with another full logical partition) is reduced, and consequently, many of the performance disadvantages of using a separate logical partition as a virtual input output server (VIOS) are avoided.

[0059] As a specific example, the partition adjunct is described herein as running a reduced operating system environment for a device driver service. This service is provided by way of example only. The partition adjunct provides minimal, optimized, infrastructure comprising only (in one example) the structure needed by a device driver. For instance, if a Linux device driver is to run inside of the partition adjunct, then the minimal execution environment includes only the Linux kernel services or equivalent services, that the Linux device driver requires. If an AIX device driver is to run inside of the partition adjunct, then the minimal execution environment includes only the AIX kernel services, or equivalent services, that the AIX device driver requires. Advantageously, the partition adjunct runs in hypervisor/problem-state, directly against hypervisor interfaces. As explained in detail below, dispatching of the partition adjunct does not require a full partition context switch, which simplifies adjunct kernel requirements. This is achieved, in part, by mapping the partition adjunct into the client partition's virtual address page table. Client partition to partition adjunct isolation can be achieved, for example, via hypervisor-managed memory keys. Advantageously, the partition adjunct is not customer viewable. Further, the same partition adjunct service (referred to herein as a global partition adjunct service) may be instantiated within multiple client partitions, as explained below.

[0060] FIGS. 4A-4C depict various partition adjunct usage models which can be implemented in accordance with the concepts disclosed herein for addressing a number of operating system and platform issues. FIG. 4A illustrates one example of a partition adjunct 420 (also referred to in this example as a local partition adjunct), which conceptually, partially resides within an initiating client partition 410 for accessing dedicated resources 440 through a hypervisor 430. For example, a common adapter/driver service may be provided by partition adjunct 420 for a respective dedicated adapter (i.e., resource).

[0061] FIG. 4B illustrates an example of a global partition adjunct, wherein, (for example) a service logical partition such as a virtual input output server partition, donates memory and physical resources for instantiation of the partition adjunct. Such a global partition adjunct 421 is accessible or attachable by multiple client partitions 410, and provides, for example, input output services to a resource 440 via hypervisor 430. As a specific example, the global partition adjunct may comprise a common adapter driver service, and the resource a shared adapter.

[0062] FIG. 4C is an alternate embodiment of a global partition adjunct 422, wherein hypervisor 430 provides resources for the adjunct. In this implementation, the hypervisor employs the partition adjunct for its own use, for example, for protection or isolation services that would otherwise exist in the hypervisor's execution domain.

[0063] Unless otherwise specified, the partition adjunct embodiment described hereinbelow is assumed to be an execution environment that is part of a client partition, yet separated from the client partition by hypervisor isolation and security mechanisms, such as referenced below and described in greater detail in commonly assigned, co-filed application entitled “Hypervisor-Enforced Isolation of Entities Within a Single Logical Partition's Virtual Address Space”, Ser. No. 12/111,041, which issued on Aug. 30, 2011, as U.S. Pat. No. 8,010,763 B2, the entirety of which is hereby incorporated herein by reference. Further details of partition adjunct processing and usage are described in greater detail in commonly assigned, co-filed patent applications entitled: “Partition Adjunct for Data Processing System”, Ser. No. 12/110,923; “Client Partition Scheduling and Prioritization of Service Partition Work”, Ser. No. 12/110,953; and “Multiple Partition Adjunct Instances Interfacing Multiple Logical Partitions to a Self-Virtualizing Input/Output Device”, Ser. No. 12/111,020, the entirety of each of which is also hereby incorporated herein by reference.

[0064] FIG. 5 illustrates one detailed example of a global partition adjunct being employed by multiple client partitions, that is, the embodiment of FIG. 4B. In this example, logical partitions (LPAR A, LPAR B) 510A, 510B are client partitions, and partition 510C is a virtual input output server partition employed by client partitions 510A, 510B in, for example, providing an input/output service. In accordance with the present invention, the input/output service (referred to as the adjunct device driver 520 in this example), is a partition adjunct provided device driver service 520A, 520B for accessing input/output hardware 540 via one or more input/output paths 521 through hypervisor 530. In this example, the partition adjunct facilitates a more direct attachment or more direct path from each client partition to the input/output hardware. As described further below, the partition adjunct is incorporated into the virtual address spaces respectively donated by the client partitions employing the partition adjunct instances.

[0065] In order for a partition adjunct to be a runable program, the hypervisor, along with a client partition that is to use the partition adjunct service, negotiate to establish the partition adjunct environment. Once this negotiation is complete, the client partition will have donated a portion of its virtual address space to the hypervisor for use by the partition adjunct. The hypervisor will use hardware and hypervisor facilities to ensure that the client partition no longer has access to or can modify the donated resources (e.g., the donated virtual address space). The hypervisor instantiates the effective address mappings required to run the partition adjunct using the donated virtual address resources. Subsequently, the hypervisor may switch between dispatching the client partition or the partition adjunct by reprogramming its control of the donated virtual address space. When the client partition runs, it may access all virtual address space assigned to it, except for the donated virtual address range, and when the partition adjunct runs, the hypervisor disables access to all virtual addresses of the client partition, except for the donated virtual address range, that is, the virtual address space to which it is enabled. This toggling of active/inactive virtual address ranges is significantly faster than reprogramming the full memory management and address translation hardware to effect a complete context switch of the current state machine between two full logical partitions, as is necessary to switch, for example, to a virtual input/output server partition. In this manner, the partition adjunct address space is carved out of and separated from the memory management and address translation hardware resources of the client partition. The partition adjunct is thus, from a processor's perspective, part of the client partition, but from the client partition's and hypervisor's perspective, is a distinct entity.

[0066] Advantageously, the partition adjunct concepts presented herein reduce the need to use full logical partitions for providing services to client partitions. This in turn frees up resources and improves performance for customer workloads. Additionally, the partition adjunct disclosed herein encourages the development and deployment of virtual platform services in lieu of development of operating system specific services by reducing the performance penalties associated with virtualized services. This in turn allows for savings and cost development, since services may be implemented only once (i.e., in a partition adjunct), rather than natively among multiple operating systems.

[0067] Various examples of protocol for instantiating and employing a partition adjunct are described below with reference to FIGS. 6-11.

[0068] FIG. 6 is a flowchart of one embodiment of a process for creating a local partition adjunct, for use such as depicted in FIG. 4A. The partition adjunct instantiation or setup protocol 600 begins with inquiry into whether the client partition wants a partition adjunct service 605. If “no”, then the protocol ends 610. Otherwise, the client partition reserves a portion of its virtual address space and memory space for the partition adjunct 615 and invokes the hypervisor to instantiate the partition adjunct with these donated resources 620. The hypervisor creates the new partition adjunct (which is hidden from the administrator), and assigns the donated resources to the partition adjunct 625. Creating the new partition adjunct means that the hypervisor creates a dispatchable program context. The hypervisor sets up hardware protection and enforcement of the donated virtual address space and donated memory, so that the client partition can no longer access that space 630. Further, the hypervisor creates a new dispatchable state for the partition adjunct 635. This new dispatchable state means that the partition adjunct can be dispatched on an individual hardware (SMT) thread of a multithreaded hardware core, while other SMT threads of the processor core continue to run the client partition invoking the partition adjunct. This aspect of the present invention is described further below with reference to FIGS. 19-22.

[0069] Next, the hypervisor loads the partition adjunct program image into the donated adjunct memory 640 and initializes adjunct execution 645. Initializing a partition adjunct execution environment can include the hypervisor initializing effective address space to virtual address translation tables, adjunct protection keys, and special hypervisor problem state privileges. The hypervisor then dispatches the partition adjunct to begin execution at the partition adjunct program entry point 650, and the hypervisor sets up partition adjunct service interface calls for the client partition 655. The hypervisor calls or invokes the client partition per protocols or functions provided by the partition adjunct. The hypervisor then returns to the client partition with status of the partition adjunct instantiation 660.

[0070] FIG. 7 depicts one detailed example of a process for creating a local partition adjunct, in accordance with an aspect of the present invention. In this example, the partition adjunct comprises a device driver service. Input/output instantiation or setup 700 begins with a client partition performing input/output device discovery 705. Processing inquires whether the client partition has its own device driver for a discovered input/output device 710. If “yes”, then the client partition proceeds with normal device driver load and configuration 715, which ends processing 720. If the client partition does not have its own device driver for a discovered I/O device, then processing determines whether a partition adjunct image is available for this I/O device 725. If “no”, then the device cannot be configured 730, and processing ends 720.

[0071] Assuming that a partition adjunct image is available, then the client partition reserves or donates a portion of its virtual address space and memory space for the partition adjunct image 735, and invokes the hypervisor to instantiate the partition adjunct with the donated virtual address space and memory space, as well as the I/O device 740. The hypervisor creates the new partition adjunct and assigns the donated resources to the partition adjunct 745. The hypervisor then sets up appropriate hardware protection and enforcement of the donated virtual address space and memory space, so that the client partition can no longer access the donated space 750. A new dispatchable state for the partition adjunct is created by the hypervisor 755. As noted above, this new dispatchable state can advantageously be dispatched on a single hardware thread of an SMT data processing system, while other hardware threads continue to run the invoking (or requesting) client partition. The hypervisor loads the partition adjunct image into the donated adjunct memory 760, and initializes the partition adjunct execution environment 765. The partition adjunct is then dispatched to begin initialization execution at the partition adjunct image entry point 770. The hypervisor sets up partition adjunct service interface calls for the client partition, which include, for example, a virtual input/output request queuing interface for the subject virtualized device class 775. The hypervisor returns to the client partition with the status of the partition adjunct instantiation, and the new virtual device assigned to the client partition 780, and the client partition proceeds with normal virtual device driver load and configuration 785.

[0072] FIG. 8 is a flowchart of one embodiment of a process for instantiating a global partition adjunct, such as depicted in FIG. 4B. In this example, the partition adjunct instantiation begins from a logical partition which functions as a virtual input output server (VIOS). The adjunct instantiation setup protocol 800 begins with the VIOS reserving or donating part of its memory space and virtual address space for the global partition adjunct 805. The VIOS invokes the hypervisor to instantiate the global partition adjunct with the donated memory and virtual address space, as well as the I/O device to which accelerated, virtualized access is to be provided 810. The hypervisor creates the new global partition adjunct, again hidden from the administrator, and assigns to the partition adjunct the donated memory space and the I/O device 815. The hypervisor sets up the hardware protection and enforcement of the donated virtual address space and memory space, so that the VIOS can no longer access the donated space 820. The hypervisor creates a new dispatchable state for the partition adjunct 825, which can be dispatched on an individual SMT thread, while one or more other SMT threads of a multithreaded hardware processor core continue to run the VIOS partition invoking the partition adjunct 825. The hypervisor loads the global partition adjunct program image into the donated adjunct memory 830, and initializes the adjunct execution environment 835. The hypervisor then dispatches the global partition adjunct to begin initialization execution at the adjunct image entry point 840, and sets up the global partition adjunct service interface call(s) and virtual device instance(s) available for assignment or attachment from client partitions 845, which completes the processing protocol 850.

[0073] FIG. 9 depicts one example of a process for attaching to a global partition adjunct, such as a VIOS partition adjunct created as described above in connection with FIG. 8. This client partition attachment 900 begins with the client partition performing virtual I/O device discovery 905. Processing determines whether the virtual I/O device at issue is capable of global partition adjunct acceleration 910, that is, whether the adjunct service globally exists. If “no”, then the client partition proceeds with normal virtual device configuration 915, for example, using a VIOS, which ends the processing 920. If a virtual I/O device adjunct image is available, then the client partition reserves or donates virtual address space for the adjunct 925, and invokes the hypervisor to attach the global partition adjunct image with the donated virtual address space 930. The hypervisor sets up the hardware protection and enforcement of the donated virtual address space for the client partition 935, and the global partition adjunct is mapped into the client partition page table utilizing the donated virtual address space. The hypervisor creates a virtual I/O mapping for this client partition to the global partition adjunct. Thereafter, processing returns to the client partition to continue with normal virtual device configuration 940, which completes processing 920.

[0074] FIG. 10 illustrates one embodiment of protocol for processing a service request by a partition adjunct submitted from a client partition. Partition adjunct servicing 1000 begins with inquiring whether the client partition needs to invoke the partition adjunct service 1005. If “no”, then processing ends 1010. Otherwise, the client partition invokes a hypervisor call to the partition adjunct service interface for the desired adjunct service call 1015. Processing determines whether the partition adjunct service is available 1020. If “no”, then the service request is failed 1025, and processing ends 1010.

[0075] Assuming that the partition adjunct service is available, then the hypervisor receives the partition adjunct service request 1030, and determines whether to queue the service request or invoke the service request currently 1035. If the service request is to be queued, then the hypervisor queues the service request for the partition adjunct 1040, and returns to inquire whether the client partition needs to invoke a partition adjunct service 1005. If the service request is to be currently invoked, then the hypervisor performs a “light” context switch of the current state machine, and gives control of the processor to the partition adjunct 1050. This light context switch is explained in detail below with reference to FIGS. 12-22. The partition adjunct performs or initiates the requested service, and then returns to the hypervisor 1055. The hypervisor performs a similar light context switch and gives control of the processor back to the client partition initiating the partition adjunct service 1060, which completes the processing 1010.

[0076] FIG. 11 depicts a flowchart of one embodiment of protocol for asynchronously handling service request completion from a partition adjunct. Partition adjunct request completion processing 1100 begins with an inquiry confirming completion of the partition adjunct service request 1105. If request processing is not complete, then processing waits until the partition adjunct service request has been completed, at which point the completion of the service request is queued to the hypervisor 1110. Processing then determines whether the client partition is polling or expecting an interrupt regarding the completion of the service request 1115. If polling is employed, the client partition polls the hypervisor for completion of the service request 1120, otherwise the hypervisor posts an interrupt for the client partition 1125. The hypervisor then performs the light context switch (described below) and invokes the client partition interrupt completion handler 1130. The client partition processes completion of the service request 1135, which completes the processing protocol 1140.

[0077] FIGS. 12-15 illustrate one example of a full logical partition to logical partition context switch within a data processing system. When context switching between two separate full partitions, each logical partition has its own distinct virtual address space assigned to it. When the hypervisor performs a full partition switch on an individual processor, the hypervisor must save and re-store processor context machine state (general purpose registers, floating point registers, special purpose registers, instruction address registers, etc.), as well as invalidate and reinitialize the memory management unit (MMU) hardware. This includes invalidating any address translation caches (e.g., translation lookaside buffer), since a full logical partition context switch also means switching to a different virtual address space, and changing the hardware page table pointers in the processor to point to the new logical partition's in-memory page table. The MMU impacts of a full logical partition context switch are the largest cost in performing a logical partition context switch, as the new logical partition must also re-establish all of its address translations upon reference each time it is dispatched. This is contrasted with the adjunct partition concept disclosed herein (since the adjunct and its client partition share a virtual address space), wherein the MMU hardware does not need to be invalidated or modified, only the subset of processor context/registers that the partition adjunct is allowed to use need to be saved and restored as part of the context switch of the state machine to the partition adjunct.

[0078] As illustrated in FIG. 12, a first logical partition (LPAR 1) 1200 includes a virtual address to real address page table 1205, which comprises the range of virtual addresses assigned to LPAR 1. Similarly, a second logical partition (LPAR 2) 1210 includes a virtual address to real address page table 1215, which comprises the range of virtual addresses assigned to LPAR 2. The virtual address space range employed by LPAR 1 is separate from the virtual address space employed by LPAR 2, and one logical partition cannot access the virtual address space of the other logical partition.

[0079] FIG. 13 illustrates one example of a processor machine state including memory management and address translation hardware of a processor core machine 1300. The illustrated hardware includes general purpose registers 1310, floating point registers 1320, vector registers 1330, special purpose registers 1340, a translation lookaside buffer 1350, and a segment lookaside buffer 1360. The translation lookaside buffer is a cache of virtual address to real address translations, while the segment lookaside buffer contains effective to virtual address translations.

[0080] In FIG. 14, LPAR 1 is assumed to be dispatched, i.e., in an active or running state in the processor state machine. As illustrated, this LPAR 1 running machine state comprises state data in general purpose registers 1310, floating point registers 1320, vector registers 1330, special purpose registers 1340, translation lookaside buffer 1350, and segment lookaside buffer 1360. A special purpose register SDR1 1400 points to, and therefore, empowers, the virtual address to real address page table of the logical partition in running state, that is, LPAR 1 1200 in this example. LPAR 2 1210 is in an inactive state.

[0081] FIG. 15 illustrates status of the processor core machine state after LPAR 1 has been switched out and LPAR 2 switched in. As illustrated, the machine state data of LPAR 2 1210 is restored within general purpose registers 1310, floating point registers 1320, vector registers 1330, and special purpose registers 1340. The special purpose register SDR1 1400 in this case is switched to point to the virtual to real address table of LPAR 2 1210, with LPAR 1 1200 being inactive. As a result, the segment lookaside buffer 1360 is restored with LPAR 2 state data, and the translation lookaside buffer 1350 is invalidated. This buffer will fill as LPAR 2 accesses memory addresses.

[0082] In contrast, FIGS. 16-18 illustrate context switching of the current machine state from a logical partition to a partition adjunct, in accordance with an aspect of the present invention. FIG. 16 depicts one embodiment of a data processing system comprising a logical partition 1600 (LPAR 1), which includes a virtual address to real address page table 1620. The data processing system further includes a partition adjunct 1610. In this example, three page table entries 1621 are set aside to map the partition adjunct into the virtual address space of the logical partition. This example assumes that logical partition 1600 is a client partition which initiates the partition adjunct 1610. Thus, as illustrated in FIG. 16, the initiating logical partition has donated virtual address space to the partition adjunct, and the partition adjunct virtual address space resides in the same virtual address range as the initiating logical partition. This is represented by the page table entries being set aside for the partition adjunct being within the virtual address to real address page table 1620 of LPAR 1. As noted above, from the hypervisor's standpoint, in terms of scheduling and isolation, the partition adjunct is a fully separate partition from the initiating logical partition (LPAR 1). Notwithstanding that, the partition adjunct and the logical partition share a virtual address space range as represented.

[0083] FIG. 17 illustrates an example of the processor core machine state with LPAR 1 dispatched in an active, running state. As illustrated, LPAR 1's machine state data acquires general purpose registers 1710, floating point registers 1720, vector registers 1730, and special purpose registers 1740. In addition, the partition's machine state substantially fills the translation lookaside buffer 1750, and fills the segment lookaside buffer 1760. Special purpose register SDR1 1700 points to the virtual address to real address page table 1620 of LPAR 1 1600. In this example, partition adjunct 1610 is in the inactive state. As illustrated, translation lookaside buffer 1750 may still contain one or more entries 1751 for the partition adjunct from a prior time that the adjunct was run. These entries 1751 do not need to be invalidated, since logical partition 1600 is protected from accessing those virtual addresses via hardware protection keys used to isolate sub-portions of the single logical partition address space. For example, page protection mechanisms, such as using a protection key, controlled by a special purpose register, labeled access mask register (AMR) 1770 may be employed. The AMR register 1770 may hold keys that are actively turned on at any given moment. For a page table entry to be referenced, the associated keys must be enabled in the AMR register. When the hypervisor is running LPAR 1, the hypervisor sets the protection key so that LPAR 1 cannot get access to the page table entries 1621, or the entries 1751 of translation lookaside buffer 1750. Further details of this protection and isolation scheme are described in the above-incorporated, co-filed application entitled “Hypervisor-Enforced Isolation of Entities Within a Single Logical Partition's Virtual Address Space”.

[0084] FIG. 18 illustrates the processor core machine state with partition adjunct 1610 dispatched active. In this example, the adjunct service provided by partition adjunct 1610 employs general purpose registers 1710, but not floating point registers 1720 and vector registers 1730, which retain the state information for LPAR 1 1600, presently in the inactive state. Further, only selected special purpose registers 1740 are employed by the partition adjunct, with the remaining special purpose registers being invalidated or containing state information for LPAR 1 1600. The special purpose register SDR1 1700 (in this example) continues to point to the virtual address to real address page table 1620 of LPAR 1 since partition adjunct 1610 is mapped into the donated virtual address spaces 1621 thereof. Various entries 1751 in translation lookaside buffer 1750 are being employed with the partition adjunct dispatched, and the remaining entries retain state information of LPAR 1. A single entry 1761 in segment lookaside buffer 1760 is installed to cover the adjunct's portion of the address space, with the remaining entries retaining the state information for LPAR 1, which is protected from access by LPAR 1. Because of the protection keys employed, for example, by special purpose register AMR 1770, the partition adjunct only has access to the noted registers and table entries. From a hypervisor standpoint, dispatching of the partition adjunct is separate from dispatching of the LPAR 1, however, the processor core machine state information is held for LPAR 1 in various registers and tables not employed by the partition adjunct. The result is that the context switch from LPAR 1 to the partition adjunct is a “light” context switch of the state machine wherein only selected registers and table information is updated with the partition adjunct state information. Similarly, when switching from the partition adjunct back to LPAR 1, only the register information employed by the partition adjunct needs to be updated for translation back to LPAR 1 active state.

[0085] FIGS. 19-22 illustrate one example of context switching the current state machine between a logical partition and a partition adjunct, such as described herein, in a data processing system employing simultaneous hardware multithreading. The example depicted is a two hardware-threaded core. However, those skilled in the art will understand that the concepts described are readily applicable to more than a two hardware-threaded core. By way of example, the POWER5™ and POWER6™ Power Instruction Set Architecture Processors, offered by International Business Machines Corporation, of Armonk, N.Y., employ two hardware-threaded cores.

[0086] As illustrated in FIG. 19, the multithreaded core includes a first hardware thread 1900 and a second hardware thread 1910 which share a translation lookaside buffer 1920. Each hardware thread includes, for example, the general purpose registers, floating point registers, and special purpose registers, as well as the segment lookaside buffer described above in connection with FIGS. 13-18. In FIG. 19, the multithreaded hardware core is illustrated without a logical partition being active. In FIG. 20, a first logical partition (LPAR 1) is assumed to be active, with the LPAR 1 state information occupying the hardware-threaded cores 1900, 1910, as well as the table lookaside buffer 1920.

[0087] In FIG. 21, a context switch of the state machine has occurred between the first logical partition (LPAR 1) and a second logical partition (LPAR 2). As illustrated, this is a full context switch, wherein LPAR 2's machine state occupies first hardware-threaded core 1900, second hardware-threaded core 1910, and table lookaside buffer 1920 of this two hardware-threaded core example.

[0088] FIG. 22 illustrates an example of context switching from LPAR 1 to a partition adjunct initiated by LPAR 1. As illustrated, only a single thread 1910 is updated with partition adjunct's state information, i.e., undergoes a light context switch. Specifically, the general purpose registers and various special purpose registers are employed in this example by the partition adjunct service, with the remaining registers and the segment lookaside buffer retaining machine state information of the logical partition (LPAR 1). Further, the second thread, that is, hardware thread 1900, retains and remains running in the initiating logical partition (i.e., LPAR 1). In this example, the machine state for LPAR 1 is also retained by the table lookaside buffer, with only selected entries 1921 being employed by the partition adjunct. Each hardware thread has its own access mask register that contains a set of keys which control what hardware the partition adjunct (when active on that thread) has access to. Thus, LPAR 1 remains active on one thread, while the partition adjunct is active on a different thread of the multithreaded data processing system.

[0089] In one aspect, the above-described partition adjunct is utilized as a dedicated adjunct providing a logical partition with access to a physical input/output (I/O) device which is non-configurable by the logical partition. Currently, if a logical partition's operating system does not have access to a device driver for an assigned physical I/O adapter, the operating system may not directly use that I/O adapter. Obtaining function from the input/output adapter in such a case requires user intervention to reassign the device to, for example, a virtual input/output server (VIOS) partition, which includes creating the VIOS partition if it does not already exist, and creating virtual input/output channels between the logical partition and the VIOS.

[0090] FIGS. 23A & 23B depict two conventional examples of a dedicated I/O device owned by a logical partition which utilizes a native device driver accessing and using the I/O device. In FIG. 23A, data processing system 2300 comprises an AIX partition 2310, which includes one or more customer applications 2312, an AIX operating system instance 2314, and an AIX hardware device driver 2324. AIX partition 2310 runs above a hypervisor 2330, and provides higher-level function than that provided by the hypervisor. Hypervisor 2330 executes on top of the underlying system hardware 2340, which is shown to include one or more physical I/O device(s) 2350. I/O device(s) 2350 comprises one or more dedicated devices assigned to the particular AIX partition image 2310. In this example, the native AIX hardware device driver 2324 is assumed to allow access to the assigned I/O device(s) 2350.

[0091] FIG. 23B depicts another embodiment of a data processing system 2300′. This data processing system includes a Linux partition 2310′ comprising one or more customer applications 2312′, a Linux operating system 2314′, and a Linux hardware device driver 2324′. Linux partition 2310′ runs on top of a hypervisor 2330′, and provides higher-level function than that provided by the hypervisor itself. Hypervisor 2330′ executes on top of the underlying system hardware 2340′, which is shown to include (one or more) I/O device 2350′. Access to I/O device 2350′ is via the native Linux hardware device driver 2324′.

[0092] In the examples of FIGS. 23A & 23B, it is assumed that the logical partition at issue has the appropriate native device driver for the assigned I/O device(s). This is not always the case. In such cases, a second logical partition, referred to as a virtual I/O server (VIOS) partition, is conventionally employed.

[0093] Device driver development costs may be reduced if device drivers can be shared between operating systems. This is accomplished hereinbelow by deploying device drivers as partition adjunct services, in accordance with an aspect of the present invention. As noted above, partition adjuncts are lightweight execution environments which operate in a separate execution state from the conventional problem and privileged states of the user applications and kernel services, respectively. This new execution state is referred to herein as the hypervisor/problem state, and is illustrated in FIGS. 24A & 24B (wherein AIX and Linux are depicted by way of example only). As explained below, instead of deploying a full VIOS partition, an operating system may instead employ a partition adjunct to support a particular, non-configurable I/O device assigned to that logical partition. In such a case, a partition adjunct is created which employs a non-native operating system's device driver as an interface to the assigned physical I/O device. Note that the native and non-native operating systems may be any two different operating systems.

[0094] FIG. 24A depicts one example of this aspect of the present invention. In this figure, a data processing system 2400 is shown to comprise an AIX partition 2410 and a Linux personality partition adjunct (or Linux personality adjunct) 2420. AIX partition 2410 is a logical partition which includes one or more customer applications 2412, an AIX operating system instance 2414, and a virtual I/O facility 2416. AIX partition 2410 runs above a hypervisor 2430, and provides higher-level function than that provided by the hypervisor. Hypervisor 2430 executes on top of the underlying system hardware 2440, which is shown to include (one or more) I/O device 2450 assigned to AIX partition 2410.

[0095] Linux personality adjunct 2420 is conceptually a dedicated, child partition to AIX partition 2410. As described above, the partition adjunct is less than a full logical partition, but is running in a manner whereby the hypervisor enforces security and isolation between the partition adjunct and the AIX partition it runs with. The partition adjunct is provided with reduced functionality compared with a full logical partition. For example, the partition adjunct has no access to memory management unit (MMU) configuration or floating-point facilities, and is an environment wherein only the functionality needed to run the desired service (e.g., I/O driver) is provided.

[0096] In the illustrated example, the Linux personality adjunct 2420 includes a virtual I/O interface 2422 and a hardware device driver service 2424, which allows access to I/O device 2450. In this example, the hardware device driver service 2424 is a Linux hardware device driver, which runs within the Linux personality adjunct 2420 spawned by the AIX partition 2410 in response to the AIX partition noting that it had assigned to it an I/O device 2450 which was non-configurable by the AIX partition. The Linux personality adjunct 2420 includes non-native kernel services sufficient to run the Linux hardware device driver for the physical I/O device. These non-native kernel services are less than a corresponding, full operating system, that is, less than a full Linux operating system in this example.

[0097] In operation, AIX partition 2410 accesses I/O device 2450 via the virtual I/O interface 2416, 2422 between the AIX operating system 2414 and the Linux personality adjunct 2420, which includes the Linux hardware device driver 2424. By providing the non-native, Linux personality to the partition adjunct, the Linux hardware device driver is able to be run within the partition adjunct, and thereby provide access to an I/O device 2450 originally assigned to AIX partition 2410, notwithstanding that the I/O device is non-configurable by the AIX partition. The device becomes accessible to the AIX partition through the Linux personality adjunct 2420.

[0098] FIG. 24B depicts another example of the use of a partition adjunct to provide access to a non-configurable I/O device assigned to a logical partition, which in this case is a Linux partition 2410′ of a data processing system 2400′. The partition adjunct for this implementation is an AIX personality adjunct 2420′, which includes sufficient non-native, AIX kernel services within the partition adjunct to run a non-native operating system's device driver, that is, an AIX hardware device driver 2424′ in this example. These non-native kernel services are less than a corresponding, full operating system, that is, less than the full AIX operating system conventionally required to run the AIX hardware device driver. The Linux partition 2410′ is a logical partition which includes one or more customer applications 2412′, a Linux operating system 2414′, and a virtual I/O facility 2416′. Linux partition 2410′ runs above a hypervisor 2430′, and provides higher-level function than that provided by the hypervisor. Hypervisor 2430′ executes on top of the underlying system hardware 2440′, which is shown to include (one or more) I/O device 2450′.

[0099] AIX personality adjunct 2420′ is again conceptually a child partition to client partition 2410′. The partition adjunct is less than a full logical partition, but is run in a manner whereby the hypervisor enforces security and isolation between the partition adjunct and the client partition it runs within, as described above. The partition adjunct is an environment wherein only the functionality needed to run the desired service (e.g., I/O driver) is provided. In this example, it is assumed that the adjunct is dedicated to the spawning logical partition, that is, Linux partition 2410′.

[0100] In the illustrated example, AIX personality adjunct 2420′ includes a virtual I/O interface 2422′ and the AIX hardware device driver 2424′, which allows access to I/O device 2450′. In operation, Linux partition 2410′ accesses I/O device 2450′ via the partition adjunct 2420′, as illustrated.

[0101] As used herein, a personality adjunct is a partition adjunct which has a particular operating system personality, but is less than the full operating system. In the implementation described herein, the personality adjunct is a non-native personality to the native operating system of the logical partition spawning the partition adjunct. For example, AIX partition 2410 of FIG. 24A initiates creation of a Linux personality adjunct, while Linux partition 2410′ of FIG. 24B initiates creation of an AIX personality adjunct. These are provided by way of example only. In an alternate implementation, the personality adjunct may be a native personality to a native operating system of the logical partition spawning the partition adjunct. Further in the non-native personality implementation, the implemented within the partition adjunct may be any non-native operating system to any native operating system of the logical partition. The personality adjunct includes a minimal service set of an operating system device driver runtime environment required by a particular device driver to run inside the adjunct. A device driver conforms to a programming environment that is defined by its host operating system environment. This programming environment typically includes a variety of kernel services for things such as memory allocation, timer services, interrupt handler registration, and invocation in response to interrupts, mapping I/O buffers for DMA (direct memory access), etc. The personality adjunct provides these services and functions in the same way that a real host operating system kernel does, such that the device driver running inside the adjunct does not know the difference between its native host operating environment and the personality adjunct described herein. This enables the unmodified device driver to be run within a lighter weight partition adjunct, in place of a full logical partition.

[0102] By way of specific example, the Linux personality adjunct 2420 of FIG. 24A provides a runtime environment and kernel services which mimic the Linux device driver programming interfaces and execution environment, while the AIX personality adjunct 2420′ of FIG. 24B provides the runtime environment and kernel services which mimic the AIX device driver programming interfaces and execution environment of a full AIX operating system.

[0103] Protocol for creating the partition adjunct is discussed in greater detail below with reference to the exemplary flowchart of FIG. 7. This protocol for establishing a partition adjunct may be initiated by a logical partition that owns a physical input/output (I/O) device which is non-configurable by the logical partition, that is, the logical partition lacks a device driver instance for accessing an assigned physical input/output device.

[0104] Referring to FIG. 7, input/output instantiation (or setup) 700 begins with the logical partition performing input/output device discovery 705. The operating system probes attached I/O buses and/or firmware-provided hardware configuration information looking for I/O devices for which device drivers are needed. For example, the operating system might find a PCI adapter card plugged into a PCI slot, which is identified by a unique vendor and device ID readable from a PCI configuration space. The operating system then determines whether it owns a native device driver for each discovered device. This is essentially the operating system performing a look-up of registered, loadable device drivers 710. If “yes”, then the logical partition proceeds with the normal device driver loading configuration 715, which ends processing 720. If, however, the client partition does not have its own device driver for a discovered I/O device assigned to that partition, then processing determines whether a partition adjunct image is available for this I/O device 725. If “no”, then the device cannot be configured 730, and processing ends.

[0105] Determining whether a partition adjunct device driver image is available for a particular I/O device could be accomplished via look-up of registered partition adjunct images with the operating system, or by querying the platform firmware, or some other partition adjunct image server, to determine whether the partition adjunct device driver image exists and is capable of operating the assigned physical I/O device.

[0106] Assuming that a partition adjunct image is available for the I/O device, then the client partition reserves or donates a portion of its virtual address space and memory space for the partition adjunct image 735, and invokes the hypervisor to instantiate the partition adjunct with the donated virtual address space and memory space, as well as the I/O device 740. The operating system essentially dynamically gives up ownership of the physical I/O device, that it had no device driver for, by relinquishing ownership to the hypervisor. The hypervisor creates the new partition adjunct and assigns the donated resources to the partition adjunct 745. The hypervisor then sets up appropriate hardware protection and enforcement of the donated virtual address space and memory space, so that the client partition can no longer access the donated space 750. A new dispatchable state for the partition adjunct is created by the hypervisor 755.

[0107] As noted above, this new dispatchable state can advantageously be dispatched on a single hardware thread of an SMT data processing system, while other hardware threads continue to run the invoking (or requesting) client partition. The hypervisor loads the partition adjunct image into the donated adjunct memory 760, and initializes the partition adjunct execution environment 765. The partition adjunct is then dispatched to begin initialization execution at the partition adjunct image entry point 770. The hypervisor sets up partition adjunct service interface calls for the client partition, which include, for example, a virtual input/output request queuing interface for the subject virtualization device class 775. The hypervisor returns to the client partition with the status of the partition adjunct instantiation, and the new virtual I/O device assigned to the client partition 780. In this step, the hypervisor dynamically adds to the client partition a virtual I/O device, for which the client partition's native operating system has a device driver. The client partition then proceeds with normal virtual device driver load and configuration 785 for the virtual I/O device, which ultimately gains access to the physical I/O device that was non-configurable by the client partition.

[0108] To summarize, described hereinabove is a method of establishing access by a logical partition to a physical input/output (I/O) device owned by the logical partition. The method includes: creating a partition adjunct within the data processing system, the partition adjunct being created employing the physical I/O device and virtual address space donated from the logical partition to the partition adjunct, the logical partition including a native operating system, and the partition adjunct comprising a non-native operating system's device driver for the physical I/O device, the physical I/O device being non-configurable by the logical partition; and providing the logical partition with a virtual I/O device interfaced through the partition adjunct's non-native operating system's device driver to the donated physical I/O device. The creating is responsive, in one embodiment, to a logical partition determining that its operating system does not have a native device driver capable of configuring the physical I/O device assigned to it, and to the logical partition noting that a partition adjunct instance is available capable of running a non-native hardware device driver which supports the physical I/O device. In such a case, the hypervisor uses dynamic re-configuration facilities, as described above, to detach the physical input/output device from the logical partition and reassign the device to the partition adjunct being created. In return, the hypervisor creates a virtual device and assigns it to the logical partition. In this manner, the logical partition which started out owning a non-configurable physical input/output device ends up with a configurable, virtual I/O device, through which it can gain access to the physical I/O device via the partition adjunct. It is assumed that the operating systems at issue support such virtual I/O devices, since such facilities are required for operating systems to function in a multi-logical partition system where no physical adapters may have been assigned to the logical partition.

[0109] One or more aspects of the present invention can be included in an article of manufacture (e.g., one or more computer program products) having, for instance, computer usable media. The media has therein, for instance, computer readable program code means or logic (e.g., instructions, code, commands, etc.) to provide and facilitate the capabilities of the present invention. The article of manufacture can be included as a part of a computer system or sold separately.

[0110] One example of an article of manufacture or a computer program product incorporating one or more aspects of the present invention is described with reference to FIG. 25. A computer program product 2500 includes, for instance, one or more computer usable media 2510 to store computer readable program code means or logic 2520 thereon to provide and facilitate one or more aspects of the present invention. The medium can be an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system (or apparatus or device) or a propagation medium. Examples of a computer readable medium include a semiconductor or solid state memory, magnetic tape, a removable computer diskette, a random access memory (RAM), a read-only memory (ROM), a rigid magnetic disk and an optical disk. Examples of optical disks include compact disk-read only memory (CD-ROM), compact disk-read/write (CD-R/W) and DVD.

[0111] A sequence of program instructions or a logical assembly of one or more interrelated modules defined by one or more computer readable program code means or logic direct the performance of one or more aspects of the present invention.

[0112] Although various embodiments are described above, these are only examples.

[0113] Moreover, an environment may include an emulator (e.g., software or other emulation mechanisms), in which a particular architecture or subset thereof is emulated. In such an environment, one or more emulation functions of the emulator can implement one or more aspects of the present invention, even though a computer executing the emulator may have a different architecture than the capabilities being emulated. As one example, in emulation mode, the specific instruction or operation being emulated is decoded, and an appropriate emulation function is built to implement the individual instruction or operation.

[0114] In an emulation environment, a host computer includes, for instance, a memory to store instructions and data; an instruction fetch unit to fetch instructions from memory and to optionally, provide local buffering for the fetched instruction; an instruction decode unit to receive the instruction fetch unit and to determine the type of instructions that have been fetched; and an instruction execution unit to execute the instructions. Execution may include loading data into a register for memory; storing data back to memory from a register; or performing some type of arithmetic or logical operation, as determined by the decode unit. In one example, each unit is implemented in software. For instance, the operations being performed by the units are implemented as one or more subroutines within emulator software.

[0115] Further, a data processing system suitable for storing and/or executing program code is usable that includes at least one processor coupled directly or indirectly to memory elements through a system bus. The memory elements include, for instance, local memory employed during actual execution of the program code, bulk storage, and cache memory which provide temporary storage of at least some program code in order to reduce the number of times code must be retrieved from bulk storage during execution.

[0116] Input/Output or I/O devices (including, but not limited to, keyboards, displays, pointing devices, DASD, tape, CDs, DVDs, thumb drives and other memory media, etc.) can be coupled to the system either directly or through intervening I/O controllers. Network adapters may also be coupled to the system to enable the data processing system to become coupled to other data processing systems or remote printers or storage devices through intervening private or public networks. Modems, cable modems, and Ethernet cards are just a few of the available types of network adapters.

[0117] The capabilities of one or more aspects of the present invention can be implemented in software, firmware, hardware, or some combination thereof. At least one program storage device readable by a machine embodying at least one program of instructions executable by the machine to perform the capabilities of the present invention can be provided.

[0118] The flow diagrams depicted herein are just examples. There may be many variations to these diagrams or the steps (or operations) described therein without departing from the spirit of the invention. For instance, the steps may be performed in a differing order, or steps may be added, deleted, or modified. All of these variations are considered a part of the claimed invention.

[0119] Although embodiments have been depicted and described in detail herein, it will be apparent to those skilled in the relevant art that various modifications, additions, substitutions and the like can be made without departing from the spirit of the invention and these are therefore considered to be within the scope of the invention as defined in the following claims.