Electrical computers and digital processing systems: multicomput – Computer-to-computer data routing – Least weight routing
Reexamination Certificate
1997-10-03
2001-04-24
Courtenay, III, St.-John (Department: 2151)
Electrical computers and digital processing systems: multicomput
Computer-to-computer data routing
Least weight routing
Reexamination Certificate
active
06223208
ABSTRACT:
This invention relates generally to a computer apparatus and a method to enable multithreading capabilities, and more particularly to a computer and method that uses idle register/storage functional units in a processor core to dynamically exchange threads.
BACKGROUND OF THE INVENTION
The fundamental structure of a modern computer includes peripheral devices to communicate information to and from the outside world; such peripheral devices may be keyboards, monitors, tape drives, communication lines coupled to a network, etc. Also included in the basic structure of the computer is the hardware necessary to receive, process, and deliver this information from and to the outside world, including busses, memory units, input/output (I/O) controllers, storage devices, and at least one central processing unit (CPU), etc. The CPU is the brain of the system. It executes the instructions which comprise a computer program and directs the operation of the other system components.
From the standpoint of the computer's hardware, all systems, from the earliest to the most modern, operate in fundamentally the same manner. Processors actually perform very simple operations quickly, such as arithmetic, logical comparisons, and movement of data from one location to another. Programs which direct a computer to perform massive numbers of these simple operations give the illusion that the computer is doing something sophisticated. What is perceived by the user as a new or improved capability of a computer system, however, may actually be the machine performing the same simple operations, but much faster. Therefore, continuing improvements to computer systems require that these systems be made ever faster.
One measurement of the overall speed of a computer system, also called the “throughput”, is measured as the number of operations performed per unit of time. Conceptually, the simplest of all possible improvements to system speed is to increase the clock speeds of the various components, particularly the clock speed of the processor. So that if everything runs twice as fast but otherwise works in exactly the same manner, the system will perform a given task in half the time. Computer processors which were constructed from discrete components years ago performed significantly faster by shrinking the size and reducing the number of components; eventually the entire processor was packaged as an integrated circuit on a single chip. The reduced size made it possible to increase the clock speed of the processor, and accordingly increase system speed.
Despite the enormous improvement in speed obtained from integrated circuitry, the demand for ever faster computer systems still exists. Hardware designers have been able to obtain still further improvements in speed by greater integration, by further reducing the size of the circuits, and by other techniques. Designer, however, think that physical size reductions cannot continue indefinitely and there are limits to continually increasing processor clock speeds. Attention has, therefore, been directed to other approaches for further improvements in overall speed of the computer system.
Without changing the clock speed, it is still possible to improve system speed by using multiple processors. The modest cost of individual processors packaged on integrated circuit chips has made this practical. The use of slave processors considerably improves system speed by off-loading work from the CPU to the slave processor. For instance, slave processors routinely execute repetitive and single special purpose programs, such as input/output device communications and control. It is also possible for multiple CPUs to be placed in a single computer system, typically a host-based system which services multiple users simultaneously. Each of the different CPUs can separately execute a different task on behalf of a different user, thus increasing the overall speed of the system to execute multiple tasks simultaneously.
It is much more difficult, however, to improve the speed at which a single task, such as an application program, executes. Coordinating the execution and delivery of results of various functions among multiple CPUs is a tricky business. For slave I/O processors, this is not so difficult because the functions are pre-defined and limited but for multiple CPUs executing general purpose application programs, it is much more difficult to coordinate functions because, in part, system designers do not know the details of the programs in advance. Most application programs follow a single path or flow of steps performed by the processor. While it is sometimes possible to break up this single path into multiple parallel paths, a universal application for doing so is still being researched. Generally, breaking a lengthy task into smaller tasks for parallel processing is done by a software engineer writing code on a case-by-case basis. This ad hoc approach is especially problematic for executing commercial transactions which are not necessarily repetitive or predictable.
Thus, while multiple processors improve overall system performance, there are still many reasons to improve the speed of the individual CPU. If the CPU clock speed is given, it is possible to further increase the speed of the CPU, i.e., the number of operations executed per second, by increasing the average number of operations executed per clock cycle. Recent advances towards this aim have yielded the superscalar computer which typically executes up to four instructions per processor clock cycle. A Very Long Instruction Word (VLIW) computer may execute sixteen instructions or more per processor cycle.
Various processor hardware design techniques have been used to increase the average number of operations executed per clock cycle. These have involved, for example, the use of pipelines, multiple execution units with look ahead hardware for finding instructions to execute in parallel, etc. Limited improvement is possible using these techniques, but the hardware support required is often massive. Another technique to improve the efficiency of hardware within the CPU is to divide a processing task into segments called threads. This technique is related to breaking a larger task into smaller tasks for independent execution by different processors except here the threads are to be executed by the same processor. When a CPU then, for any of a number of reasons, cannot continue the processing or execution of one of these threads, the CPU switches to and executes another thread.
The CPU is actually an arrangement of integrated circuits, including at least one instruction control unit and an arithmetic and logic unit, that interprets and executes computer instructions. Within the CPU there is a processor core containing specialized functional units, each of which perform primitive operations, such as sequencing instructions, executing operations involving integers, executing operations involving real numbers, transferring values between addressable storage and logical register arrays; those simple operations discussed earlier. Processor cores may have many of these specialized functional units either to achieve higher performance under peak requirements, or because the computer architecture requires more functional units. A single instruction or multiple instructions may dispatch operations to more than one functional unit in a single cycle of the processor's clock. In actuality, however, peak performance is rarely demanded; the duty cycle over time of any one functional unit is less than one hundred percent of the available clock cycles. Hence, there is idle time.
As discussed earlier, those parallel and sequential sets of instructions that can execute separately are called “threads of control” or, simply, “threads.” A processor which has the capability to concurrently maintain more than one path of execution within a computer is called a multithreaded processor. The multithreaded processor usually has at least one backup register which has the data for a second thread while a first thread is executing. Commu
Kiefer Kenneth J.
Luick David A.
Willis John Christopher
Courtenay, III St.-John
International Business Machines - Corporation
Ojanen Karuna
Opie George
LandOfFree
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