International Business Machines Corporation

Motorola Corporation

Sung-Ho Park

Rajesh Bhikhubhai Patel

Belliappa Manavattira Kuttanna

Lee Evan Eisen

Soummya Mallick

Michael Putrino

Romesh Mangho Jessani

Robert Thaddeus Golla

A superscalar processor and method for executing fixed-point instructions within a superscalar processor are disclosed. The superscalar processor has a memory and multiple execution units, including a fixed point execution unit (FXU) and a non-fixed point execution unit (non-FXU). According to the present invention, a set of instructions to be executed are fetched from among a number of instructions stored within memory. A determination is then made if n instructions, the maximum number possible, can be dispatched to the multiple execution units during a first processor cycle if fixed point arithmetic and logical instructions are dispatched only to the FXU. If so, n instructions are dispatched to the multiple execution units for execution. In response to a determination that n instructions cannot be dispatched during the first processor cycle, a determination is made whether a fixed point instruction is available to be dispatched and whether dispatching the fixed point instruction to the non-FXU for execution will result in greater efficiency. In response to a determination that a fixed point instruction is not available to be dispatched or that dispatching the fixed point instruction to the non-FXU will not result in greater efficiency, dispatch of the fixed point instruction is delayed until a second processor cycle. However, in response to a determination that dispatching the fixed point instruction to the non-FXU will result in greater efficiency, the fixed point instruction is dispatched to the non-FXU and executed, thereby improving execution unit utilization.

Method and apparatus for executing fixed-point instructions within idle

A data processing system having enhanced memory performance is provided. The data processing system comprises a processor that issues memory requests, a multilevel storage system including a first level cache, a second level cache, and a main memory connected to the processor in a memory hierarchy, and a memory controller. The memory controller retrieves a cache line from main memory, when a memory request for the cache line is received from the processor at the first level cache that causes a miss in both the first level cache and the second level cache. The memory controller loads the retrieved cache line in both the first level cache and the second level cache if the received memory request is a load request, and loads the retrieved cache line in only the first level cache and not the second level cache if the received memory request is a store request. The resultant reduction in reloads to the second level cache enhances memory performance by allowing immediate execution of subsequent memory requests to the second level cache and producing a higher hit rate as a result of the reduction in castouts from the second level cache.

Cache memory management system having reduced reloads to a second level

A method and apparatus for executing a single beat write (SBW) store instruction during a cache store linefill operation are disclosed. In accordance with the present disclosure, an address associated with the cache memory store linefill operation is first received. This address comprises a tag portion and an index portion. For the cache store linefill operation, the tag portion of this address is sent to a tag latch while the index portion is sent to a burst index latch. During the cache store linefill operation, a second address associated with the single beat write store instruction is received. This second address also comprises a tag portion and an index portion. In response to a determination that a critical word of the cache memory store linefill has been received, the tag portion of the second address is sent to the tag latch and the index portion of the second address is sent to an SBW index latch. By doing so, the single beat write store instruction may be executed before the completion of the cache store linefill operation.

Method and apparatus for executing single beat write store instructions

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Austin, TX, United States of America

Sung-Ho Park