Abstract:
A multiple-core processor supporting multiple instruction set architectures provides a power-efficient and flexible platform for virtual machine environments requiring multiple support for multiple instruction set architectures (ISAs). The processor includes multiple cores having disparate native ISAs and that may be selectively enabled for operation, so that power is conserved when support for a particular ISA is not required of the processor. The multiple cores may share a common first level cache and be mutually-exclusively selected for operation, or multiple level-one caches may be provided, one associated with each of the cores and the cores operated as needed, including simultaneous execution of disparate ISAs. A hypervisor controls operation of the cores and locates a core and enables it if necessary when a request to instantiate a virtual machine having a specified ISA is received.

Description:
The Present U.S. patent application is a Continuation of U.S. patent application Ser. No. 11/468,547 filed on Aug. 30, 2006, the disclosure of which is incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to data processing systems, and more particularly, to processors for running multiple virtual machines having disparate instruction set architectures. 
     2. Description of the Related Art 
     Present-day computing systems, and in particular large-scale server systems, often include support for running multiple virtual machines (VMs). The system may be a large-scale on-demand server system that executes hundreds of server instances on a single hardware platform to support customers with varying computing requirements. In the most flexible of these systems, multiple partitions, which may differ in operating system or run-time environment, as well as application mix on those environments, are concurrently present in system memory. Processes executing in each partition are run in an environment that supports their execution on a guest operating system (or run-time environment). The virtual machine provides an environment similar enough to a real hardware platform that the operating system can run with little or no modification. A hypervisor (sometimes referred to as a virtual machine monitor) manages all of the virtual machines or partitions and abstracts system resources so that each partition provides a machine-like environment to each environment instance. 
     However, in order to provide efficient operation, total virtualization of machine code instruction sets is typically not performed. Such total virtualization, generally referred to as processor emulation, cannot reach the efficiency of a machine executing native machine code. Therefore, the above-described systems, in applications in which the VMs must provide environments supporting different native instruction sets, typically include disparate processing units that implement differing instruction set architectures (ISAs). In some instances, disparate processors must be included for critical applications that can only run efficiently in a particular machine code environment. Therefore, even though a particular operating system or run-time environment may be supported across multiple ISAs, a particular application may require that a particular underlying ISA be provided in support of the VM in which that application runs. 
     In particular, custom applications tend to evolve on particular platforms and are frequently coded or ported to run on only one ISA. Those applications must be supported, as well as a mix of any other custom applications, as well as off-the shelf software. The result is increased customization of systems for particular applications, increasing system cost, and a reduction in availability and system efficiency in that not every processing element and resource is necessarily available or usable for any task that might be assigned to the system. For example, when a system must support VMs that require both the power PC (PPC) and x86 ISAs, but the demand for x86 VMs is not continuous and represents a varying fraction of the total system throughput required at any given time, the amount of x86 processing support will either be over-installed or under-available for much of the time. 
     Therefore, it would be desirable to provide an efficient mechanism for supporting multiple VMs requiring disparate ISAs. It would further be desirable to provide such a mechanism that efficiently manages electrical power used by the hardware supporting the multiple ISAs. 
     BRIEF SUMMARY OF THE INVENTION 
     The objective of providing an efficient mechanism for supporting multiple VMs requiring multiple ISAs is provided in a processor, processing system, method and computer program product. 
     The processor includes multiple cores having disparate native ISAs and that may be selectively enabled for operation, so that power is conserved when support for a particular ISA is not required of the processor. The processing system includes one or more such processors and the method of operation is a method of operation of the processing system under control of the computer program product, known as a hypervisor. 
     The hypervisor determines when a particular VM will be instantiated that requires a particular ISA, locates a processor core capable of supporting the ISA, and enables the processor code if the processor core is disabled. The hypervisor then instantiates the VM in memory and starts the VM execution by the processor core. When the VM is terminated, the hypervisor powers down the core if it is no longer needed. 
     The foregoing and other objectives, features, and advantages of the invention will be apparent from the following, more particular, description of the preferred embodiment of the invention, as illustrated in the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
       The novel features believed characteristic of the invention are set forth in the appended claims. The invention itself, however, as well as a preferred mode of use, further objectives, and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying drawings, wherein like reference numerals indicate like components, and: 
         FIG. 1  is a block diagram of a processor in accordance with an embodiment of the present invention. 
         FIG. 2  is a block diagram of a processor in accordance with another embodiment of the present invention. 
         FIG. 3  is a block diagram of a multi-processing system in accordance with an embodiment of the present invention. 
         FIG. 4  is a flowchart depicting a method in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     With reference now to the figures, and in particular with reference to  FIG. 1 , there is depicted a block diagram of a processor  10 A in accordance with an embodiment of the present invention. Processor  10 A includes multiple cores  12 A- 12 C each having disparate ISAs. While the illustrative embodiment depicts three cores having different native ISAs, it is contemplated that any desirable arrangement and number of cores may be included within a processor in accordance with an embodiment of the present, as long as at least one of the processor cores has an ISA differing from that of the other cores. For example, in an 8-core processor, one core may support an ISA that is infrequently required, while the other seven cores implement the most universal ISA. 
     In the illustrated embodiment, core  12 A supports the PowerPC (PPC) instruction set as originally promulgated by the Apple-IBM-Motorola (AIM) Alliance, core  12 B supports x86 instruction sets as originally promulgated by Intel Corporation and implemented by many present-day manufacturers, and core  12 C supports an instruction set optimized for the System Z operating environment, such as the z9 Integrated Information Processor (zIIP) instruction set as promulgated by International Business Machines Corporation. Other types of cores, such as special purpose co-processors and accelerator engines could also be included, but are not illustrated. Each core  12 A- 12 C has an associated L1-level cache  14 A- 14 C, which is then coupled to a common L2-level cache and cache controller  16 . Therefore, with proper address space management by cache controller  16  and the hypervisor, all three cores  12 A- 12 C may be operated simultaneously to support concurrent execution of VMs supporting the disparate ISAs implemented by cores  12 A- 12 C. A power management unit (PMU)  17  controls power to each of cores  12 A- 12 C, so that during intervals of time when one or more of cores  12 A- 12 C is not needed, or when system power, processor  10 A thermal capabilities, or other resource limitations dictate that only a subset of cores  12 A- 12 C can be simultaneously operational, power is removed from the disabled cores. The L1 cache units that are associated with disabled cores may also be disabled. A bus interface unit (BIU) provides for interfacing processor  10 A with other processors and devices, including lower level caches and system memory. A service processor (SP) port  19  provides an interface to a supervisory service processor that performs tasks under direction of the hypervisor and controls PMU  17  to enable, disable, and set the operating environment for cores  12 A- 12 C as cores  12 A- 12 C are brought on-line and off-line. 
     Referring now to  FIG. 2 , a processor  10 B, in accordance with another embodiment of the present invention, is shown. Processor  10 B is similar to processor  10 A of  FIG. 1 , and therefore only differences between them will be described below. In processor  10 B, L1 cache and optional other resources  14  are shared in common between cores  12 A-C, resulting in a reduction of die area required to implement processor  10 B over processor  10 A. However, unlike processor  10 A of  FIG. 1 , in processor  10 A, PMU  17  only enables one core  12 A-C at a time, enabling the sharing of L1 cache and optional other resources  16 , such as floating point hardware, register space and other units that can be controlled by control logic provided from cores  12 A-C, but that can be designed independent of the ISA of any particular core. For example, a core implementing a first ISA requiring 128 64-bit registers may use the same storage units as a second ISA that requires only 64 64-bit registers, with the other 64 registers disabled or unused when the core implementing the second ISA is active. 
     Referring now to  FIG. 3 , a processing system in which processors  10 A and/or  10 B may be employed, is depicted. It will be understood that the depicted embodiment is not intended to be limiting, but only exemplary of the type of processing system to which the methods and techniques of the present invention may be applied. The processing system includes a processor group  20  having four processors  22 A-D, at least one of which includes multiple cores  12 A,  12 B supporting disparate native ISAs. Processor group  20  may be connected to other processor groups via a bridge  26  forming a super-scalar processor. Processor group  20  is connected to an L3 cache unit  27 , system local memory  28  and various peripherals  25 , as well as to two service processors  29 A and  29 B. Service processors  29 A-B provide fault supervision, startup assistance and test capability to processor group  20  and may have their own interconnect paths to other processor groups as well as connecting to all of processors  22 A-D. 
     Within processor group  20  are a plurality of processors  22 A-D, each fabricated in a single unit and including a plurality of processor cores  12 A and  12 B that support differing ISAs, and include an internal L1 cache in the illustrated embodiment. Cores  12 A and  12 B are coupled to an L2 cache  16  and an internal memory controller  24 . Cores  12 A and  12 B provide instruction execution and operation on data values for general-purpose processing functions, but support disparate native ISAs simultaneously or mutually-exclusively as described above. Bridge  26 , as well as other bridges within the system, provides communication over wide buses with other processor groups and bus  5  provides connection of processors  22 A-D, bridge  26 , peripherals  25 , L3 cache  27  and system local memory  28 . Other global system memory may be coupled external to bridge  26  for symmetrical access by all processor groups. Service processor  29 A and  29 B are connected to processors  22 A-D via a Joint Test Action Group (JTAG) test port interface that has command and logic extensions providing very facile control of processors  22 A-D, including disabling and enabling cores  12 A and  12 B when operating environment and conditions dictate. 
     Within system local memory  28 , a virtual machine monitor program, or “hypervisor”, provides support for execution of multiple virtual machines (VMs) or “partitions” that each provide an execution environment for an operating system and a number of “guest” programs (applications and services executed by an operating system and running in the associated VM). By referring to metadata that accompanies each VM, the hypervisor is aware of the resource needs and specific ISA requirements for each VM. The hypervisor instantiates VMs by dynamically assigning their virtual resources to the physical resources of the server. The hypervisor manages the mapping of physical memory to virtual memory space within each VM, and therefore prevents conflicts between VMs for physical memory. By virtue of the virtual mapping and control of cache controllers, the hypervisor also prevents conflicts between higher-level caches such as L1 Caches  14 A- 14 C of  FIG. 1  mapping to lines within lower-level L2 cache  16 . Thus, under hypervisor management, support for VMs with differing ISA requirements and with multi-threading context support, a processing system including processors in accordance with embodiments of the present invention can provide multi-ISA support without requiring separate discrete processor modules or dies. 
     Referring now to  FIG. 4 , a method in accordance with an embodiment of the invention is depicted. The hypervisor receives a request to instantiate a VM with support for a particular ISA (step  40 ), for example, when a particular application requiring a particular ISA and operating system is started. The hypervisor attempts to locate a core that is available for support of the ISA (step  42 ), and if the core is not available (decision  44 ), the VM startup fails (step  45 ). Otherwise, if the located core is in power-down mode (decision  46 ), the core is powered up (step  47 ). Next, the VM is instantiated and the operating system and application are loaded (step  49 ). When the application or VM terminates (decision  50 ), if the core is in use by any other VM (decision  52 ), then the hypervisor waits until all VMs/Apps terminate (decision  50 ), otherwise, the core is powered down (step  54 ) until requested again. In the method described above, if the particular hardware implementation requires a significant amount of time to power a core on or off, then the decision to turn off a core can be postponed until some number of idle cycles have passed. In CMOS technologies presently available, times on the order of only a few tens of microseconds are needed to power a core on or off, while the assignment of a virtual processor to run on a core is made for time slices on the order of a millisecond or more. 
     While the invention has been particularly shown and described with reference to the preferred embodiment thereof, it will be understood by those skilled in the art that the foregoing and other changes in form and details may be made therein without departing from the spirit and scope of the invention.