Critical sections of multi-threaded programs, normally protected by locks providing access by only one thread, are speculatively executed concurrently by multiple threads with elision of the lock acquisition and release. Upon a completion of the speculative execution without actual conflict as may be identified using standard cache protocols, the speculative execution is committed, otherwise the speculative execution is squashed. Speculative execution with elision of the lock acquisition, allows a greater degree of parallel execution in multi-threaded programs with aggressive lock usage.

Concurrent Execution of Critical Sections by Eliding Ownership of Locks

Programmable processor and method with wide operations

Processor for executing wide operand operations using a control register and a results register

A system includes multiple program execution entities (e.g., tasks, processes, threads, and the like) and a cache memory having multiple sections. An identifier is assigned to each execution entity. An instruction of one of the execution entities is retrieved and an associated identifier is decoded. Information associated with the instruction is stored in one of the cache sections based on the identifier.

Buffer memory management in a system having multiple execution entities

The apparatus and method described herein are for handling shared memory accesses between multiple processors utilizing lock-free synchronization through transactional-execution. A transaction demarcated in software is speculatively executed. During execution invalidating remote accesses/requests to addresses loaded from and to be written to shared memory are tracked by a transaction buffer. If an invalidating access is encountered, the transaction is re-executed. After a pre-determined number of times re-executing the transaction, the transaction may be re-executed non-speculatively with locks/semaphores.

Transaction based shared data operations in a multiprocessor environment

In a computer system having a plurality of processors with internal caches, a method for handling race conditions arising when multiple processors simultaneously write to a particular cache line. Initially, a determination is made as to whether the cache line is in an exclusive, modified, invalid, or shared state. If the cache line is in either the exclusive or modified state, the cache line is written to and then set to the modified state. If the cache line is in the invalid state, a Bus-Read-Invalidate operation is performed. However, if the cache line is in the shared state and multiple processors initiate Bus-Write-Invalidate operations, the invalidation request belonging to the first processor is allowed to complete. Thereupon, the cache line is sent to the exclusive state, data is updated, and the cache line is set to the modified state. The second processor receives a second cache line, updates this second cache line, and sets the second cache line to the modified state.

Apparatus and method of handling race conditions in mesi-based multiprocessor system with private caches

In a computer system, an apparatus for handling lock conditions wherein a first instruction executed by a first processor processes data that is common to a second processor while the second processor is locked from simultaneously executing a second instruction that also processes this same data. A lock bit is set when the first processor begins execution of the first instruction. Thereupon, the second processor is prevented from executing its instruction until the first processor has completed its processing of the shared data. Hence, the second processor queues its request in a buffer. The lock bit is cleared after the first processor has completed execution of its instruction. The first processor then checks the buffer for any outstanding requests. In response to the second processor's queued request, the first processor transmits a signal to the second processor indicating that the data is now not locked.

Apparatus and method for caching lock conditions in a multi-processor system

A computer system comprising a plurality of caching agents with a cache hierarchy, the caching agents sharing memory across a system bus and issuing memory access requests in accordance with a protocol wherein a line of a cache has a present state comprising one of a plurality of line states. The plurality of line states includes a modified (M) state, wherein a line of a first caching agent in M state has data which is more recent than any other copy in the system; an exclusive (E) state, wherein a line in E state in a first caching agent is the only one of the agents in the system which has a copy of the data in a line of the cache, the first caching agent modifying the data in the cache line independent of other said agents coupled to the system bus; a shared (S) state, wherein a line in S state indicates that more than one of the agents has a copy of the data in the line; and an invalid (I) state indicating that the line does not exist in the cache. A read or a write to a line in I state results in a cache miss. The present invention associates states with lines and defines rules governing state transitions. State transitions depend on both processor generated activities and activities by other bus agents, including other processors. Data consistency is guaranteed in systems having multiple levels of cache and shared memory and/or multiple active agents, such that no agent ever reads stale data and actions are serialized as needed.

Apparatus for maintaining multilevel cache hierarchy coherency in a multiprocessor computer system

The invention provides a cache management system comprising in various embodiment pre-load and pre-own functionality to enhance cache efficiency in shared memory distributed cache multiprocessor computer systems. Some embodiments of the invention comprise an invalidation history table to record the line addresses of cache lines invalidated through dirty or clean invalidation, and which is used such that invalidated cache lines recorded in an invalidation history table are reloaded into cache by monitoring the bus for cache line addresses of cache line recorded in the invalidation history table. In some further embodiments, a write-back bit associated with each L2 cache entry records when either a hit to the same line in another processor is detected or when the same line is invalidated in another processor's cache, and the system broadcasts write-backs from the selected local cache only when the line being written back has a write-back bit that has been set.

Cache line pre-load and pre-own based on cache coherence speculation

A method and apparatus for cache memory replacement line identification have a cache interface which provides a communication interface between a cache memory and a controller for the cache memory. The interface includes an address bus, a data bus, and a status bus. The address bus transfers requested addresses from the controller to the cache memory. The data bus transfers data associated with requested addresses from the controller to the cache memory, and also transfers replacement line addresses from the cache memory to the controller. The status bus transfers status information associated with the requested addresses from the cache memory to the controller which indicate whether the requested addresses are contained in the cache memory. In one embodiment, the data bus also transfers cache line data associated with a requested address from the cache memory to the controller when the requested address hits the cache memory.

Wen-Hann Wang

Papers

Apparatus and method of handling race conditions in mesi-based multiprocessor system with private caches

Apparatus and method for caching lock conditions in a multi-processor system

Apparatus for maintaining multilevel cache hierarchy coherency in a multiprocessor computer system

Cache line pre-load and pre-own based on cache coherence speculation

Method and apparatus for cache memory replacement line identification