Sun Microsystems, Inc.

Denise Chiacchia

Gary R Lauterbach

Herbert Lopez-Aguado

William L Lynch

A central processing unit of a computer includes a single-ported data cache and a dual-ported prefetch cache. The data cache accommodates a first pipeline and the prefetch cache, which is much smaller than the data cache, accommodates both the first pipeline and a second pipeline. If a data cache miss occurs, a row of data corresponding to the specified address is stored in the data cache and the prefetch cache. Thereafter, if a prefetch cache hit occurs, a row of data corresponding to a prefetch address is loaded into the prefetch cache. The prefetch address may, for instance, be generated by adding a fixed increment to the specified address. This operation frequently results in the prefetch cache storing data soon requested by a computer program. When this condition is achieved, the data corresponding to the subsequent address request is rapidly retrieved from cache memory without incurring memory latencies associated with the external cache, the primary memory, and the secondary memory. In this manner, the prefetch cache of the present invention facilitates improved memory latencies. Further, the prefetch cache allows for two data requests to be processed simultaneously without a corresponding two-fold increase in cost of data cache memory.

Microprocessor having a prefetch cache

A central processing unit (CPU) of a computer has a data caching unit which includes a novel dual-ported prefetch cache configured in parallel with a conventional single-ported data cache. If a data cache miss occurs, the requested data is loaded into the data cache and into the prefetch cache. Thereafter, each data request which results in a prefetch cache hit triggers the prefetching of data into the prefetch cache. A data load history tracking circuit maintains a running history of instructions that request data from external memory, and uses the resulting loop heuristics of these instructions to generate a stride. The stride is used to derive a prefetch address which identifies data that is predicted to be soon requested in subsequent instructions. Data corresponding to the prefetch address is then loaded into the prefetch cache. Thus, where a subsequent instruction requests data which has been prefetched into the prefetch cache, latencies associated with external memory may be hidden, thereby increasing the data bandwidth of the CPU.

Apparatus and method for generating a stride used to derive a prefetch

A central processing unit (CPU) of a computer has a data caching unit which includes a novel dual-ported prefetch cache configured in parallel with a conventional single-ported data cache. In response to a data cache miss, the requested data is fetched from external memory and loaded into the data cache and into the prefetch cache. Thereafter, if a prefetch cache hit occurs, the physical address of the corresponding data request is provided to a prefetch engine which, in turn, adds a stride to the physical address to derive a prefetch address. This prefetch address identifies data which is predicted to be soon requested in subsequent instructions of the computer program. Data corresponding to the prefetch address is then retrieved from external memory and loaded into the prefetch cache. This prefetching operation frequently results in the prefetch cache storing data that is requested by subsequently executed instructions in a computer program. When this condition occurs, data is immediately retrieved from the prefetch cache and provided to execution units within the CPU, thereby eliminating latencies associated with external memory.

A central processing unit (CPU) of a computer includes a novel prefetch cache configured in parallel with a conventional data cache. If a data cache miss occurs, the requested data is fetched from external memory and loaded into the data cache and into the prefetch cache. Thereafter, if a prefetch cache hit occurs, a prefetch address is derived, and data corresponding to the prefetch address is prefetched into the prefetch cache. This prefetching operation frequently results in the prefetch cache storing data that is requested by subsequently executed instructions in a computer program, thereby eliminating latencies associated with external memory. A software compiler of the computer ensures the validity of data stored in the prefetch cache. The software compiler alerts the prefetch cache that data stored within the prefetch cache is to be rewritten and, in response thereto, the prefetch cache invalidates the data. In this manner, data may be invalidated without requiring use of conventional cache snooping mechanisms, thereby increasing the speed with which data in cache memory may be invalidated. The ability to more quickly invalidate data in cache memory allows data previously considered 'non-cachable' to be stored, and remain valid, in cache memory.

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Campbell, CA, United States of America

Denise Chiacchia