International Business Machines Corporation

Jeffrey Powers Bradford

Timothy Hume Heil

Timothy John Mullins

Harold F Kossman

Jason Nathaniel Dale

Richard James Eickemeyer

Ronald P Hall

David James Shippy

Christopher Michael Abernathy

Kimberly Marie Fernsler

James Allen Rose

Balaram Sinharoy

Gordon Taylor Davis

Clark Debs Jeffries

David Arnold Luick

Lixin Zhang

Srinivasan Ramani

Ken Van Vu

Wael R El-Essawy

Dongming Hwang

Richard William Doing

Chris Abernathy

Douglas Robert Logan

Kartik Sudeep

William E Speght

An apparatus, program product and method initiate, in connection with a context switch operation, a prefetch of data likely to be used by a thread prior to resuming execution of that thread. As a result, once it is known that a context switch will be performed to a particular thread, data may be prefetched on behalf of that thread so that when execution of the thread is resumed, more of the working state for the thread is likely to be cached, or at least in the process of being retrieved into cache memory, thus reducing cache-related performance penalties associated with context switching.

Context switch data prefetching in multithreaded computer

An apparatus initiates, in connection with a context switch operation, a prefetch of data likely to be used by a thread prior to resuming execution of that thread. As a result, once it is known that a context switch will be performed to a particular thread, data may be prefetched on behalf of that thread so that when execution of the thread is resumed, more of the working state for the thread is likely to be cached, or at least in the process of being retrieved into cache memory, thus reducing cache-related performance penalties associated with context switching.

A method, apparatus and computer program product are provided for implementing polymorphic branch history table (BHT) reconfiguration. A BHT includes a plurality of predetermined configurations corresponding predetermined operational modes. A first BHT configuration is provided. Checking is provided to identify improved performance with another BHT configuration. The BHT is reconfigured to provide improved performance based upon the current workload.

Implementing polymorphic branch history table reconfiguration

The present invention provides system and method for a group priority issue schema for a cascaded pipeline. The system includes a cascaded delayed execution pipeline unit having a plurality of execution pipelines that execute instructions in a common issue group in a delayed manner relative to each other. The system further includes circuitry configured to receiving an issue group of instructions, reordering the issue group of instructions using instruction type priority, and executing the reordered issue group of instructions in the cascaded delayed execution pipeline unit. The method, among others, can be broadly summarized by the following steps: receiving an issue group of instructions, reordering the issue group of instructions using instruction type priority, and executing the reordered issue group of instructions in the cascaded delayed execution pipeline unit.

System and method for a group priority issue schema for a cascaded pipeline

Mechanisms for handling data cache misses out-of-order for asynchronous pipelines are provided. The mechanisms associate load tag (LTAG) identifiers with the load instructions and uses them to track the load instruction across multiple pipelines as an index into a load table data structure of a load target buffer. The load table is used to manage cache 'hits' and 'misses' and to aid in the recycling of data from the L2 cache. With cache misses, the LTAG indexed load table permits load data to recycle from the L2 cache in any order. When the load instruction issues and sees its corresponding entry in the load table marked as a &#x201c;miss,&#x201d; the effects of issuance of the load instruction are canceled and the load instruction is stored in the load table for future reissuing to the instruction pipeline when the required data is recycled.

Handling data cache misses out-of-order for asynchronous pipelines

Page size prediction is used to predict a page size for a page of memory being accessed by a memory access instruction such that the predicted page size can be used to access an address translation data structure. By doing so, an address translation data structure may support multiple page sizes in an efficient manner and with little additional circuitry disposed in the critical path for address translation, thereby increasing performance.

Multiple page size address translation incorporating page size prediction

A processor includes an execution unit and instruction sequencing logic that fetches instructions for execution. The instruction sequencing logic includes a branch target address cache having a branch target buffer containing a plurality of entries each associating at least a portion of a branch instruction address with a predicted branch target address. The branch target address cache accesses the branch target buffer using a branch instruction address to obtain a predicted branch target address for use as an instruction fetch address. The branch target address cache also includes a filter buffer that buffers one or more candidate branch target address predictions. The filter buffer associates a respective confidence indication indicative of predictive accuracy with each candidate branch target address prediction. The branch target address cache promotes candidate branch target address predictions from the filter buffer to the branch target buffer based upon their respective confidence indications.

Data processing system, processor and method of data processing having improved branch target address cache

An apparatus, program product and method initiate, in connection with a context switch operation, a prefetch of at least one instruction likely to be executed by a thread prior to resuming execution of that thread. As a result, once it is known that a context switch will be performed to a particular thread, one or more instructions may be prefetched on behalf of that thread so that when execution of the thread is resumed, those instructions are more likely to be cached, or at least in the process of being retrieved into cache memory, thus enabling a thread to begin executing instructions more quickly than if the thread was required to fetch those instructions upon resumption of its execution.

Context switch instruction prefetching in multithreaded computer

Apparatus and method for handling data cache misses out-of-order for asynchronous pipelines

The present invention provides for a computer network method and system that applies 'hysteresis' to an active queue management algorithm. If a queue is at a level below a certain low threshold and a burst of packets arrives at a network node, then the probability of dropping the initial packets in the burst is recalculated, but the packets are not dropped. However, if the queue level crosses beyond a hysteresis threshold, then packets are discarded pursuant to a drop probability. Also, according to the present invention, queue level may be decreased until it becomes less than the hysteresis threshold, with packets dropped per the drop probability until the queue level decreases to at least a low threshold. In one embodiment, an adaptive algorithm is also provided to adjust the transmit probability for each flow together with hysteresis to increase the packet transmit rates to absorb bursty traffic.

Active flow management with hysteresis

A method and apparatus for updating global branch history information are disclosed. A dynamic branch predictor within a data processing system includes a global branch history (GBH) buffer and a branch history table. The GBH buffer contains GBH information of a group of the most recent branch instructions. The branch history table includes multiple entries, each entry is associated with one or more branch instructions. The GBH information from the GBH buffer can be used to index into the branch history table to obtain a branch prediction signal. In response to a fetch group of instructions, a fixed number of GBH bits is shifted into the GBH buffer. The number of GBH bits is the same regardless of the number of branch instructions within the fetch group of instructions. In addition, there is a unique bit pattern associated with the case of no taken branch in the fetch group, regardless of the number of not-taken branches of even if there are any branches in the fetch group.

Growing community of inventors

Rochester, MN, United States of America

Jeffrey Powers Bradford