International Business Machines Corporation

Francis Patrick O'Connell

John Barry Griswell, Jr

Jeffrey A Stuecheli

Yaoqing Gao

David Scott Ray

Michael John Mayfield

Hung Qui Le

Venkat Rajeev Indukuru

Roch Georges Archambault

Edward John Silha

Albert Thomas Williams

William John Starke

Karthick Rajamani

Bradly George Frey

Robert J Blainey

Miles Robert Dooley

Heather Lynn Hanson

Ravi Kumar Arimilli

James Allan Kahle

Steven Wayne White

Lixin Zhang

Lee Evan Eisen

Cathy May

Jason Nathaniel Dale

James Lawrence McInnes

Eric Jason Fluhr

Allan Russell Martin

Joel M Tendler

John David McCalpin

Derek E Williams

Alper Buyuktosunoglu

Pradip Bose

David S Levitan

Robert Brett Tremaine

Richard James Eickemeyer

Peichun Peter Liu

Hazim Shafi

Michael Edward Wazlowski

Wolfram M Sauer

Pascal Vezolle

Alex E Mericas

Richard J Eickemeyer, Jr

Victor Javier Jimenez Perez

A processor system tracks, in at least one counter, a number of cycles in which at least one execution unit of at least one processor core is idle and at least one thread of the at least one processor core is waiting on at least one off-core memory access during run-time of the at least one processor core during an interval comprising multiple cycles. The processor system evaluates an expected performance impact of a frequency change within the at least one processor core based on the current run-time conditions for executing at least one operation tracked in the at least one counter during the interval.

Tracking pipelined activity during off-core memory accesses to evaluate the impact of processor core frequency changes

In an approach for sharing memory bandwidth in one or more processors, a processor receives a first set of monitored usage information for one or more processors executing one or more threads. A processor calculates impact of hardware data prefetching for each thread of the one or more threads, based on the first set of monitored usage information. A processor adjusts prefetch settings for the one or more threads, based on the calculated impact of hardware data prefetching for each thread of the one or more threads.

Intelligent bandwidth shifting mechanism

A technique for data prefetching for a multi-core chip includes determining memory utilization of the multi-core chip. In response to the memory utilization of the multi-core chip exceeding a first level, data prefetching for the multi-core chip is modified from a first data prefetching arrangement to a second data prefetching arrangement to minimize unused prefetched cache lines. In response to the memory utilization of the multi-core chip not exceeding the first level, the first data prefetching arrangement is maintained. The first and second data prefetching arrangements are different.

Data prefetch ramp implemenation based on memory utilization

A processor of an information handling system (IHS) initiates an L3 cache prefetch operation in response to a demand load during instruction processing. The processor selects an L3 cache prefetch at random for tracking as a target prefetched instruction. The processor initiates an L1 cache target prefetch operation and stores the resultant target prefetched instruction in the L1 cache. If a demand load arrives, the processor analyzes the target prefetched instruction for effectiveness and determines the source of the prefetch data. If a demand does not arrive, the processor tests to determine if the particular prefetched instruction timed out in the cache and identifies the ineffectiveness of the prefetch operation. The processor samples multiple prefetch operations at random and generates a history of prefetch effectiveness and other useful prefetch information. The processor stores the prefetch effectiveness information to enable reduction or removal of ineffective prefetch operations.

Ineffective prefetch determination and latency optimization

A data processing system includes a system memory and a cache hierarchy that caches contents of the system memory. According to one method of data processing, a storage modifying operation having a cacheable target real memory address is received. A determination is made whether or not the storage modifying operation has an associated bypass indication. In response to determining that the storage modifying operation has an associated bypass indication, the cache hierarchy is bypassed, and an update indicated by the storage modifying operation is performed in the system memory. In response to determining that the storage modifying operation does not have an associated bypass indication, the update indicated by the storage modifying operation is performed in the cache hierarchy.

Data processing system and method for reducing cache pollution by write stream memory access patterns

A prefetch unit includes a transience register and a length register. The transience register hosts an indication of transient for data stream prefetching. The length register hosts an indication of a stream length for data stream prefetching. The prefetch unit monitors the transience register and the length register. The prefetch unit generates prefetch requests of data streams with a transient property up to the stream length limit when the transience register indicates transient and the length register indicates the stream length limit for data stream prefetching. A cache controller coupled with the prefetch unit implements a cache replacement policy and cache coherence protocols. The cache controller writes data supplied from memory responsive to the prefetch requests into cache with an indication of transient. The cache controller victimizes cache lines with an indication of transient independent of the cache replacement policy.

Persistent prefetch data stream settings

The present invention provides a computer implemented method, apparatus, and computer usable program code for compiling instructions to manage a cache system. Loop constructs are analyzed to identify data usage characteristics for cache and prefetching conditions in instructions to form identified prefetch conditions. A set of control instructions are inserted into the instructions based on the data usage characteristics and the identified prefetch conditions to form multiple modified instructions. The set of multiple modified instructions are compiled to generate code for execution to form compiled instructions. The set of control instructions in the compiled instructions form a cache management policy to control movement of data in a memory system during execution of the compiled instructions.

Method and apparatus for software-assisted data cache and prefetch control

A mechanism for minimizing effective memory latency without unnecessary cost through fine-grained software-directed data prefetching using integrated high-level and low-level code analysis and optimizations is provided. The mechanism identifies and classifies streams, identifies data that is most likely to incur a cache miss, exploits effective hardware prefetching to determine the proper number of streams to be prefetched, exploits effective data prefetching on different types of streams in order to eliminate redundant prefetching and avoid cache pollution, and uses high-level transformations with integrated lower level cost analysis in the instruction scheduler to schedule prefetch instructions effectively.

Fine-grained software-directed data prefetching using integrated high-level and low-level code analysis optimizations

A method of prefetching data in a microprocessor includes identifying a data stream associated with a process and determining a depth associated with the data stream based upon prefetch factors including the number of currently concurrent data streams and data consumption rates associated with the concurrent data streams. Data prefetch requests are allocated with the data stream to reflect the determined depth of the data stream. Allocating data prefetch requests may include allocating prefetch requests for a number of cache lines away from the cache line currently being referenced, wherein the number of cache lines is equal to the determined depth. The method may include, responsive to determining the depth associated with a data stream, configuring prefetch hardware to reflect the determined depth for the identified data stream. Prefetch control bits in an instruction executed by the processor control the prefetch hardware configuration.

Data stream prefetching in a microprocessor

A method and logical apparatus for managing processing system resource use for speculative execution reduces the power and performance burden associated with inefficient speculative execution of program instructions. A measure of the efficiency of speculative execution is used to reduce resources allocated to a thread while the speculation efficiency is low. The resource control applied may be the number of instruction fetches allocated to the thread or the number of execution time slices. Alternatively, or in combination, the size of a prefetch instruction storage allocated to the thread may be limited. The control condition may be comparison of the number of correct or incorrect speculations to a threshold, comparison of the number of correct to incorrect speculations, or a more complex evaluator such as the size of a ratio of incorrect to total speculations.

Method and logical apparatus for managing processing system resource use for speculative execution

In a microprocessor having a load/store unit and prefetch hardware, the prefetch hardware includes a prefetch queue containing entries indicative of allocated data streams. A prefetch engine receives an address associated with a store instruction executed by the load/store unit. The prefetch engine determines whether to allocate an entry in the prefetch queue corresponding to the store instruction by comparing entries in the queue to a window of addresses encompassing multiple cache blocks, where the window of addresses is derived from the received address. The prefetch engine compares entries in the prefetch queue to a window ofcontiguous cache blocks. The prefetch engine suppresses allocation of a new entry when any entry in the prefetch queue is within the address window. The prefetch engine further suppresses allocation of a new entry when the data address of the store instruction is equal to an address in a border area of the address window.

Store stream prefetching in a microprocessor

A system and method for improving the page crossing performance of a data prefetcher is presented. A prefetch engine tracks times at which a data stream terminates due to a page boundary. When a certain percentage of data streams terminate at page boundaries, the prefetch engine sets an aggressive profile flag. In turn, when the data prefetch engine receives a real address that corresponds to the beginning/end of a new page, and the aggressive profile flag is set, the prefetch engine uses an aggressive startup profile to generate and schedule prefetches on the assumption that the real address is highly likely to be the continuation of a long data stream. As a result, the system and method minimize latency when crossing real page boundaries when a program is predominately accessing long streams.

System and method for improving the page crossing performance of a data prefetcher

Computer implemented method, system and computer program product for prefetching data in a data processing system. A computer implemented method for prefetching data in a data processing system includes generating attribute information of prior data streams by associating attributes of each prior data stream with a storage access instruction which caused allocation of the data stream, and then recording the generated attribute information. The recorded attribute information is accessed, and a behavior of a new data stream is modified using the accessed recorded attribute information.

System using stream prefetching history to improve data prefetching performance

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Austin, TX, United States of America

Francis Patrick O'Connell