# Patent

## Title
Structure for a flexibly configurable multi central processing unit (CPU) supported hypertransport switching

## Abstract

A design structure embodied in a machine readable storage medium for designing, manufacturing, and/or testing a design for addressing deficiencies of the art in respect to hypertransport-based switching for multi-CPU systems and for flexibly configurable multi-CPU supported hypertransport switching is provided. The design structure can include a hypertransport switching data processing system. The system can include a CPU and at least two I/O bridges. Each I/O bridge can provide a communications path for data driven to a corresponding peripheral device from the CPU. Notably, the system can include a flexibly configurable hypertransport switch. The switch can include a first configuration adapting the CPU to both of the I/O bridges, and a second configuration adapting the CPU to a first one of the I/O bridges and a second CPU to a second one of the I/O bridges.

## Background
CROSS-REFERENCE TO RELATED APPLICATION
This application is a continuation-in-part of co-pending U.S. patent application Ser. No. 11/627,514, filed Jan. 26, 2007, which is herein incorporated by reference.


BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is generally related design structures, and more specifically design structures in the field of hypertransport-based switching and more particularly to hypertransport switching multiple central processing units (CPU) in a computing architecture.
2. Description of the Related Art
While CPU performance continues to increase rapidly, the performance of the input/output (I/O) bus architecture has lagged significantly. High-resolution, 3D graphics and streaming video are increasing bandwidth demand between micro CPUs and graphics CPUs. A number of new technologies are responsible for the increasing demand for additional bandwidth. The Scalable Link Interface (SLI) is a method developed for linking two or more graphics cards together via parallel processing in order to increase the processing power available for graphics. In SLI graphics schemes, two identical graphics cards are used to control the screen. Typically, each graphics card controls half the screen. With SLI graphics technology, it is possible to roughly double the amount of graphics complexity that can be handled by a computer system with the addition of the second graphics card.
A common requirement to implement SLI graphics schemes is that data processing systems have more than one CPU for optimal performance. Two separate CPUs typically will generate two separate data streams to the two identical graphics cards and transmit to two separate I/O bridges that are directly connected to each CPU generating its half of the graphics traffic. Unfortunately, when a system has a single CPU, SLI support cannot live up to its full potential. Supporting the minimal single CPU system requires a significant sacrifice in SLI graphics performance since all of the I/O would have to be connected to one single CPU in the absence of a second CPU.
Traditionally, to support a multi-CPU SLI scheme, firmware and supporting architecture must be provided specific to the multi-CPU scheme. Newer versions of processors using hypertransport may need two hypertransports between processors in dual processor socket systems to provide adequate memory performance.
By comparison, different firmware and supporting architecture must be provided to support single-CPU scheme, because the infrastructure of the multi-CPU scheme differs from that of the single CPU scheme. Thus, the presence or absence of a multi-CPU scheme must be known a priori at the time of manufacture in order to provide the proper firmware and supporting architecture. Yet, many end-users prefer to purchase a minimal configuration with an option to upgrade from a single-CPU system to a multi-CPU system on one platform. So much, however, is not possible given the disparate firmware and architecture required to support the multi-CPU scenario.
SUMMARY OF THE INVENTION
Embodiments of the invention address deficiencies of the art in respect to hypertransport-based switching for multi-CPU systems and provide a novel and non-obvious method, system and apparatus for flexibly configurable multi-CPU supported hypertransport switching. In one embodiment of the invention, a hypertransport switching data processing system can be provided. The system can include a CPU and at least two I/O bridges. Each I/O bridge can provide a communications path for data driven to a corresponding peripheral device from the CPU. Notably, the system can include a flexibly configurable hypertransport switch. The switch can include a first configuration adapting the CPU to both of the I/O bridges, and a second configuration adapting the CPU to a first one of the I/O bridges and a second CPU to a second one of the I/O bridges. Finally, the system can include hypertransport balancing logic. The logic can include program code enabled to detecting either a single central processing unit (CPU) configuration or a multi-CPU configuration upon bootstrap. The hypertransport balancing logic can typically be done in firmware but it also can be implemented automatically in hardware.
In one embodiment of the invention, a basic I/O system (BIOS) comprising firmware can be included. The firmware can include program code enabled to set the flexibly configurable hypertransport switch to one of the first configuration and the second configuration. Moreover, the program code can be enabled to set the flexibly configurable hypertransport switch to one of the first configuration and the second configuration based upon detecting either a single CPU coupled to the BIOS or multiple CPUs coupled to the BIOS.
The first configuration can include a switched coupling of the CPU to the second one of the I/O bridges through the hypertransport switch. The second configuration comprises a switched coupling of the second CPU to the second one of the I/O bridges through the hypertransport switch. Alternatively, the second configuration can include a switched coupling of the first CPU to the second CPU through the flexibly configurable hypertransport switch.
There can be any number of additional bridges and CPUs in this scheme. The hypertransport switch described can support a minimal configuration adapting a single CPU to both IO bridges or a larger configuration where one or more additional processors can be added with each of the IO bridges are assigned to separate CPUS. In yet another embodiment of the invention, the peripheral devices can include different graphics cards. Alternatively, the peripheral devices can include different graphics cards of identical type in a scalable link interface (SLI) scheme.
In another embodiment of the invention, a hypertransport switching method can be provided and can include detecting either a single central processing unit (CPU) configuration or a multi-CPU configuration upon bootstrap and responsive to detecting the single CPU configuration, adapting a hypertransport switch for coupling a single CPU to dual input/output (I/O) bridges, each providing a communications path for data driven to a corresponding peripheral device, and otherwise adapting the hypertransport switch for coupling each CPU in the multi-CPU configuration to a corresponding one of the dual I/O bridges.
In another embodiment, a design structure embodied in a machine readable storage medium for at least one of designing, manufacturing, and testing a design can be provided. The design structure can generally include a hypertransport switching data processing system that includes a central processing unit (CPU), at least two input/output (I/O) bridges, each providing a communications path for data driven to a corresponding peripheral device from the CPU, and a flexibly configurable hypertransport switch comprising a first configuration adapting the CPU to both of the I/O bridges, and a second configuration adapting the CPU to a first one of the I/O bridges and a second CPU to a second one of the I/O bridges.
Additional aspects of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The aspects of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.



BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings, which are incorporated in and constitute part of this specification, illustrate embodiments of the invention and together with the description, serve to explain the principles of the invention. The embodiments illustrated herein are presently preferred, it being understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown, wherein:
FIG. 1A is a schematic illustration of a computer architecture configured for flexibly configurable multi-CPU supported hypertransport switching;
FIG. 1B is a schematic illustration of a computer architecture configured for flexibly configurable multi-CPU supported hypertransport switching; and,
FIG. 2 is a flow chart illustrating a process for flexibly configuring a hypertransport switch for multi-CPU support
FIG. 3 is a flow diagram of a design process used in semiconductor design, manufacture, and/or test.



DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Embodiments of the invention provide a method, system and computer program product for flexibly configurable multi-CPU supported hypertransport switching. In accordance with an embodiment of the present invention, a flexibly configurable hypertransport switch can be disposed in a computing architecture. The flexibly configurable hypertransport switch can be configured for adapting a single-CPU to multiple different I/O bridges in a single CPU configuration. Alternatively, the flexibly configurable hypertransport switch can be configured for adapting multiple different CPUs to the multiple different I/O bridges in a multi-CPU configuration.
In this regard, during system boot time, the flexibly configurable hypertransport switch can be reconfigured via BIOS to accommodate either the single CPU configuration or the multi-CPU configuration depending upon the presence of one or more CPUs. In response to detecting a single CPU configuration, hypertransport links can be established between the CPU and multiple I/O bridges. By comparison, in response to detecting a multi-CPU configuration, hypertransport links can be enabled between each CPU in the multi-CPU configuration and multiple I/O bridges for optimizing overall system performance.
In further illustration, FIG. 1A is a schematic illustration of a flexibly configurable hypertransport switching data processing system. As shown in FIG. 1A, the system can include a single CPU 120 coupled to memory module 130. The CPU 120 further can be coupled to a first I/O bridge 140A providing a communications path for data driven to peripheral device 150A, for example a graphics card. The CPU 120 further can be coupled to a second I/O bridge 140B through hypertransport (HT) switch 110. As in the case of the first I/O bridge 140A, the second I/O bridge 140B can provide a communications path for data driven to peripheral device 150B, for example another graphics card in order to support an SLI graphics scheme. The flexibly configured hypertransport switch 110 can be reconfigured via BIOS 100 which is already enabled for setting up additional HT links (HT1, HT3) in the case of an upgrade to a multi-CPU system. The BIOS 100 can implement the HT Balancer 300 to reconfigure the system depending on how many CPUs are present in the current system. The HT balancer 300 can be either system firmware or hardware on the system motherboard.
FIG. 1B is a schematic illustration of a flexibly configurable multi-CPU supported hypertransport switching system. As shown in FIG. 1B, the system can include multiple CPUs, 120A, B, C, D coupled to multiple memory modules 130A, B, C, D. The multiple CPUs 120A, B, C, D can further be coupled to a first I/O bridge 140A providing a communications path for data driven to peripheral device 150A, for example a graphics card. The multiple CPUs 120A, B, C, D can further be coupled to a second I/O bridge 140B through hypertransport (HT) switch 110. As in the case of the first I/O bridge 140A, the second I/O bridge 140B can provide a communications path for data driven to peripheral device 150B, for example another graphics card in order to support an SLI graphics scheme. The flexibly configured hypertransport switch 110 can be reconfigured via BIOS 100 to enable additional HT links (HT1, HT3) for the multi-CPU computer architecture. Thus, BIOS 100 can implement HT Balancer logic 200 to adapt the system to a multi-CPU configuration during boot time.
FIG. 2 is a flow chart illustrating a process for flexibly configurable multi-CPU support hypertransport switching. Beginning in block 210, BIOS can be initiated at system boot time to accommodate either a single CPU configuration or a multi-CPU configuration. In block 220, it can be determined whether or not a multi-processor system is detected. If only one CPU is detected, then block 230A can be implemented to reconfigure the HT switch. Next in block 240A, a single CPU HT link setup can be established by setting up HT links to optimize connections with the I/O Bridges and CPU. If a multi-CPU system is detected, block 230B can be implemented to reconfigure the HT switch to enable new HT connections. Next in block 240B, a multi-CPU HT link setup can be established by setting up new HT links to optimize I/O traffic and CPU interconnections due to a doubling of the memory bandwidth between CPUs. Adding a second HT link between CPUs can lead to improved performance gains in multi-processor configurations.
FIG. 3 shows a block diagram of an exemplary design flow 300 used for example, in semiconductor design, manufacturing, and/or test. Design flow 300 may vary depending on the type of IC being designed. For example, a design flow 300 for building an application specific IC (ASIC) may differ from a design flow 300 for designing a standard component. Design structure 320 is preferably an input to a design process 310 and may come from an IP provider, a core developer, or other design company or may be generated by the operator of the design flow, or from other sources. Design structure 320 comprises the circuits described above and shown in FIGS. 1A-1B in the form of schematics or HDL, a hardware-description language (e.g., Verilog, VHDL, C, etc.). Design structure 320 may be contained on one or more machine readable medium. For example, design structure 320 may be a text file or a graphical representation of a circuit as described above and shown in FIGS. 1A-1B. Design process 310 preferably synthesizes (or translates) the circuit described above and shown in FIGS. 1A-1B into a netlist 380, where netlist 380 is, for example, a list of wires, transistors, logic gates, control circuits, I/O, models, etc. that describes the connections to other elements and circuits in an integrated circuit design and recorded on at least one of machine readable medium. For example, the medium may be a storage medium such as a CD, a compact flash, other flash memory, or a hard-disk drive. The medium may also be a packet of data to be sent via the Internet, or other networking suitable means. The synthesis may be an iterative process in which netlist 380 is resynthesized one or more times depending on design specifications and parameters for the circuit.
Design process 310 may include using a variety of inputs; for example, inputs from library elements 330 which may house a set of commonly used elements, circuits, and devices, including models, layouts, and symbolic representations, for a given manufacturing technology (e.g., different technology nodes, 32 nm, 45 nm, 90 nm, etc.), design specifications 340, characterization data 350, verification data 360, design rules 370, and test data files 385 (which may include test patterns and other testing information). Design process 310 may further include, for example, standard circuit design processes such as timing analysis, verification, design rule checking, place and route operations, etc. One of ordinary skill in the art of integrated circuit design can appreciate the extent of possible electronic design automation tools and applications used in design process 310 without deviating from the scope and spirit of the invention. The design structure of the invention is not limited to any specific design flow.
Design process 310 preferably translates a circuit as described above and shown in FIGS. 1A-1B, along with any additional integrated circuit design or data (if applicable), into a second design structure 390. Design structure 390 resides on a storage medium in a data format used for the exchange of layout data of integrated circuits (e.g. information stored in a GDSII (GDS2), GL1, OASIS, or any other suitable format for storing such design structures). Design structure 390 may comprise information such as, for example, test data files, design content files, manufacturing data, layout parameters, wires, levels of metal, vias, shapes, data for routing through the manufacturing line, and any other data required by a semiconductor manufacturer to produce a circuit as described above and shown in FIGS. 1A-1B. Design structure 390 may then proceed to a stage 395 where, for example, design structure 390: proceeds to tape-out, is released to manufacturing, is released to a mask house, is sent to another design house, is sent back to the customer, etc.
The embodiments of the invention can take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment containing both hardware and software elements. In a preferred embodiment, the invention is implemented in software, which includes but is not limited to firmware, resident software, microcode, and the like. Furthermore, the invention can take the form of a computer program product accessible from a computer-usable or computer-readable medium providing program code for use by or in connection with a computer or any instruction execution system. For the purposes of this description, a computer-usable or computer readable medium can be any apparatus that can contain, store, communicate, propagate, or transport the program for use by or in connection with the instruction execution system, apparatus, or device. 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. Current examples of optical disks include compact disk—read only memory (CD-ROM), compact disk—read/write (CD-R/W) and DVD.
A data processing system suitable for storing and/or executing program code will include at least one processor coupled directly or indirectly to memory elements through a system bus. The memory elements can include local memory employed during actual execution of the program code, bulk storage, and cache memories 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. Input/output or I/O devices (including but not limited to keyboards, displays, pointing devices, 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 modem and Ethernet cards are just a few of the currently available types of network adapters.

## Claims

1. A non-transitory computer readable storage medium storing a design structure for at least one of designing, manufacturing, and testing a design, the design structure comprising:
a hypertransport switching data processing system comprising:
a central processing unit (CPU);

at least two input/output (I/O) bridges, each providing a communications path for data driven to a corresponding peripheral device from the CPU;
a flexibly configurable hypertransport switch comprising a first configuration adapting the CPU to both of the I/O bridges, and a second configuration adapting the CPU to a first one of the I/O bridges and a second CPU to a second one of the I/O bridges; and,
a basic I/O system (BIOS) configured to set the flexibly configurable hypertransport switch to one of the first configuration and the second configuration based upon detecting either a single CPU coupled to the BIOS or multiple CPUs coupled to the BIOS.

2. The design structure of claim 1, wherein the BIOS comprises program code enabled to set the flexibly configurable hypertransport switch to one of the first configuration and the second configuration.

3. The design structure of claim 1, wherein the first configuration comprises a switched coupling of the CPU to the second one of the I/O bridges through the hypertransport switch.

4. The design structure of claim 1, wherein the second configuration comprises a switched coupling of the second CPU to the second one of the I/O bridges through the hypertransport switch.

5. The design structure of claim 4, wherein the second configuration further comprises a switched coupling of the first CPU to the second CPU through the flexibly configurable hypertransport switch.

6. The design structure of claim 1, wherein the peripheral devices comprise different graphics cards.

7. The system of claim 6, wherein the peripheral devices comprises different graphics cards of identical type in a scalable link interface (SLI) scheme.

8. The design structure of claim 1, wherein the design structure comprises a netlist, which describes the hypertransport switching data processing system.

9. The design structure of claim 1, wherein the design structure resides on the machine readable storage medium as a data format used for the exchange of layout data of integrated circuits.

10. The design structure of claim 1, wherein BIOS comprises hardware on a system motherboard.