Unisys Corporation

Donald C Englin

Mitchell A Bauman

Kelvin S Vartti

Donald W Mackenthun

James A Williams

Robert H Andrighetti

Conrad S Shimada

Douglas A Fuller

James L Federici

Mark L Balding

Systems and methods are provided for a data processing system and a cache arrangement. The data processing system includes at least one processor, a first-level cache, a second-level cache, and a memory arrangement. The first-level cache bypasses storing data for a memory request when a do-not-cache attribute is associated with the memory request. The second-level cache stores the data for the memory request. The second-level cache also bypasses updating of least-recently-used indicators of the second-level cache when the do-not-cache attribute is associated with the memory request.

Cache apparatus and method for accesses lacking locality

A cache arrangement of a data processing system provides a cache flush operation initiated by a command from a maintenance processor. The cache arrangement includes a cache memory, a mode register, and a controller. The mode register is settable by the maintenance processor to one of first and second values. The controller selectively writes all of the modified information in the cache memory to the system memory responsive to the command. Also in response to this command, all of the information is invalidated in the cache memory if the mode register is set to the second value. In one embodiment, none of the information except the modified data is invalidated if the mode register is set to the first value. The second value may be utilized to efficiently reassign one or more cache memories to a new partition.

Cache with integrated capability to write out entire cache

A system and method for increasing computing throughput through execution of parallel data error detection/correction and cache hit detection operations. In one path, hit detection occurs independent of and concurrent with error detection and correction operations, and reliance on hit detection in this path is based on the absence of storage errors. A single error correction code (ECC) is used to minimize storage requirements, and data hit comparisons based on the cached address and requested address are performed exclusive of ECC bits to minimize bit comparison requirements.

System and method for increasing cache hit detection performance

The current invention provides a system and method for maintaining memory coherency within a multiprocessor environment that includes multiple requesters such as instruction processors coupled to a shared main memory. Within the system of the current invention, data may be provided from the shared memory to a requester for update purposes before all other read-only copies of this data stored elsewhere within the system have been invalidated. To ensure that this acceleration mechanism does not result in memory incoherency, an instruction is provided for inclusion within the instruction set of the processor. Execution of this instruction causes the executing processor to discontinue execution until all outstanding invalidation activities have completed for any data that has been retrieved and updated by the processor.

System and method for maintaining memory coherency within a multi-processor data processing system

A system and method for pre-fetching data signals is disclosed. According to one aspect of the invention, an Instruction Processor (IP) generates requests to access data signals within the cache. Predetermined ones of the requests are provided to pre-fetch control logic, which determines whether the data signals are available within the cache. If not, the data signals are retrieved from another memory within the data processing system, and are stored to the cache. According to one aspect, the rate at which pre-fetch requests are generated may be programmably selected to match the rate at which the associated requests to access the data signals are provided to the cache. In another embodiment, pre-fetch control logic receives information to generate pre-fetch requests using a dedicated interface coupling the pre-fetch control logic to the IP.

Data pre-fetch system and method for a cache memory

A system and method is provided to selectively flush data from cache memory to a main memory irrespective of the replacement algorithm that is used to manage the cache data. According to one aspect of the invention, novel 'page flush' and 'cache line flush' instructions are provided to flush a page and a cache line of memory data, respectively, from a cache to a main memory. In one embodiment, these instructions are included within the hardware instruction set of an Instruction Processor (IP). According to another aspect of the invention, flush operations are initiated using a background interface that interconnects the IP with its associated cache memory. A primary interface that also interconnects the IP to the cache memory is used to simultaneously issue higher-priority requests so that processor throughput is increased.

Cache flush system and method

A method of and apparatus for improving the efficiency of a data processing system employing a multiple level cache memory system. The efficiencies result from enhancing the response to SNOOP requests. To accomplish this, the system memory bus is provided separate and independent paths to the level two cache and tag memories. Therefore, SNOOP requests are permitted to directly access the tag memories without reference to the cache memory. Secondly, the SNOOP requests are given a higher priority than operations associated with local processor data requests. Though this may slow down the local processor, the remote processors have less wait time for SNOOP operations improving overall system performance.

Method for avoiding delays during snoop requests

Each dual multi-processing system has a number of processors, with each processor having a store in first-level write through cache to a second-level cache. A third-level memory is shared by the dual system with the first-level and second-level caches being globally addressable to all of the third-level memory. Processors can write through to the local second-level cache and have access to the remote second-level cache via the local storage controller. A coherency scheme for the dual system provides each second-level cache with indicators for each cache line showing which ones are valid and which ones have been modified or are different than what is reflected in the corresponding third level memory. The flush apparatus uses these two indicators to transfer all cache lines that are within the remote memory address range and have been modified, back to the remote memory prior to dynamically removing the local cache resources due to either system maintenance or dynamic partitioning.

Method and apparatus for parallel store-in second level caching

A method of and apparatus for improving the efficiency of a data processing system employing a multiple level cache memory system. The efficiencies result from managing the process of flushing old data from the second level cache memory. In the present invention, the second level cache memory is a store-in memory. Therefore, when data is to be deleted from the second level cache memory, a determination is made whether the data has been modified by the processor. If the data has been modified, the data must be rewritten to lower level memory. To free the second level cache memory for storage of the newly requested data, the data to be flush is loaded into a flush buffer for storage during the rewriting process.

Method for managing flushes with the cache

An apparatus for and method of queuing memory access requests resulting from level two cache memory misses. The requests are preferably queued separately by processor. To provide the most recent data to the system, write (i.e., input) requests are optimally given preference over read (i.e., output) requests for input/output processors. However, instruction processor program instruction fetches (i.e., read-only requests) are preferably given priority over operand transfers (i.e., read/write requests) to reduce instruction processor latency.

Split control for IP read and write cache misses

Flush apparatus for a dual multi-processing system. Each dual multi-processing system has a number of processors, with each processor having a store in first-level write through cache to a second-level cache. A third-level memory is shared by the dual system with the first-level and second-level caches being globally addressable to all of the third-level memory. Processors can write through to the local second-level cache and have access to the remote second-level cache via the local storage controller. A coherency scheme for the dual system provides each second-level cache with indicators for each cache line showing which ones are valid and which ones have been modified or are different than what is reflected in the corresponding third level memory. The flush apparatus uses these two indicators to transfer all cache lines that are within the remote memory address range and have been modified, back to the remote memory prior to dynamically removing the local cache resources due to either system maintenance or dynamic partitioning. The flush apparatus prevents the loss of system data during such a process due to the inherent nature of a store in second level cache.

Method of and apparatus for store-in second level cache flush

Method and apparatus for maximizing cache memory throughput in a system where a plurality of requesters may contend for access to a same memory simultaneously. The memory utilizes an interleaved addressing scheme wherein each memory segment is associated with a separate queuing structure and the memory is mapped noncontiguously within the same segment so that all segments are accessed equally. Throughput is maximized as the plurality of requesters are queued evenly throughout the system.

Selectable two-way, four-way double cache interleave scheme

An improved conflict detection system for use in maintaining memory coherency in a multiprocessor, shared-cache memory system. The system includes a queue for storing pointers to request addresses that resulted in cache misses. The addresses associated with the queued pointers will generally be presented to a main memory for processing based on a predetermined priority scheme. The system further includes conflict detection logic which uses the queue pointers and the request addresses provided by associated ones of the processors to determine if any two of the queued requests are associated with the same request address. If so, a conflict exists, and the request queue later in time must be re-directed to cache instead of being presented to main memory to maintain cache coherency. The system further includes a mechanism for using pointers to detect conflict situations associated with flush and replacement cache operations. Because the conflict detection system queues pointers to addresses, instead of the addresses themselves, a large amount of silicon area can be saved. In addition, the system performs all conflict detection operations using full address compares to eliminate the detection of false conflicts.

Address conflict detection system employing address indirection for use

A cache architecture for a multiprocessor data processing system. The cache architecture includes multiple first-level caches, two second-level caches, and main storage that is addressable by each of the processors. Each first-level cache is dedicated to a respective one of the processors. Each of the second-level caches is coupled to the other second-level cache, coupled to the main storage, and coupled to predetermined ones of the first-level caches. The range of cacheable addresses for both of the second-level caches encompasses the entire address space of the main storage. Each of the second-level caches may be viewed as dedicated for write access to the set of processors associated with the predetermined set of first-level caches, and shared for read access to the other set of processors. The dedicated and shared nature enhances system efficiency. The cache architecture includes coherency control that filters invalidation traffic between the second-level caches. The filtering of invalidation traffic enhances system efficiency and is accomplished by tracking which second-level cache has the most recent version of the cached data.

Multi-processor data processing system with multiple second level caches

Method and apparatus for reducing address/function transfer pins in a system where cache memories in a system controller are accessed by a number of instruction processors. The reduction of pins is obtained by using two data transfers. The increase in data addressing time, which would otherwise occur using two data transfers, is reduced to nearly the time of the data transfers themselves by responding to the first data transfer while the second data transfer is taking place.

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Shoreview, MN, United States of America

Donald C Englin