International Business Machines Corporation

Jeffrey Carl Brownscheidle

Dung Q Nguyen

Sundeep Chadha

Maureen Anne Delaney

Salim Ahmed Shah

Brian William Thompto

Salma Ayub

Tu-An T Nguyen

Joshua W Bowman

Dhivya Jeganathan

Hung Qui Le

Joel Abraham Silberman

Michael Joseph Genden

Mary Douglass Brown

Robert Allen Cordes

James Wilson Bishop

Jafar Nahidi

Brian David Barrick

Kurt Alan Feiste

Brandon R Goddard

Brendan M Wong

Khandker Nabil Adeeb

David S Walder

Eula Faye Abalos Tolentino

Brian D Victor

In an approach for decreasing a rate of logic voltage level transitions in a multiplexor, one of a plurality of inputs to a multiplexor is selected with a first multiplexor select value at a first clock, wherein each input to the multiplexor is identified as one of i) valid and ii) invalid and the first multiplexor select value is latched in a latch until the first multiplexor select value is replaced by a second multiplexor select value. The second multiplexor select value is determined. The second multiplexor select value is applied to the multiplexor at a second clock if and only if the second multiplexor select value is different from the first multiplexor select value and the second multiplexor select value selects a valid input, wherein the second clock follows the first clock. Subsequent to applying the second multiplexor select value, the second multiplexor value is latched in the latch.

Energy efficient source operand issue

Fast issuance and execution of a multi-width instruction across multiple slices in a parallel slice processor core is supported in part through the use of an early notification signal passed between issue logic associated with multiple slices handling that multi-width instruction coupled with an issuance of a different instruction by the originating issue logic for the early notification signal.

Fast multi-width instruction issue in parallel slice processor

Embodiments relate to selection and execution of conditional branch instructions. A computer system is configured with a processing core, including an instruction fetch unit and an instruction sequence unit, operatively coupled to memory. The instruction fetch unit fetches instructions from instruction cache and searches the fetched instruction for any conditional branch instructions. For each conditional branch instruction, an associated confidence level assigned to the instruction is obtained. The instruction sequence unit dispatches conditional branch instructions with their confidence level to a branch issue queue (BRQ). In addition, the instruction sequence unit prioritizes the conditional branch instructions in the BRQ based on the assigned confidence level and age, and selects one of the conditional branch instructions. A branch execution unit is provided as part of the instruction fetch unit to execute the selected conditional branch instruction, followed by dynamically updated any related non-executed instructions in the BRQ.

Prioritization protocols of conditional branch instructions

Operation of a multi-slice processor that includes a plurality of execution slices and an instruction sequencing unit. Operation of such a multi-slice processor includes: receiving, at the instruction sequencing unit, a load instruction indicating load address data and a load data length; determining a previous store instruction in an issue queue such that store address data for the previous store instruction corresponds to the load address data, wherein the previous store instruction corresponds to a store data length; and generating, in dependence upon the store data length matching the load data length, an indication in the issue queue that indicates a dependency between the load instruction and the previous store instruction.

Operation of a multi-slice processor implementing load-hit-store handling

Embodiments herein describe a reservation station (RS) in a processor that merges control data from multiple sources into a merged control data value. Before an instruction issues, the RS gathers and saves control data indicating how the instruction is to be executed. This control data may be saved in control registers. An instruction, however, can update many different types of status control bits in these registers. As such, the RS may store different types of control data for an instruction. Instead of the RS containing multiple registers and data paths for every type of control data, the embodiments herein describe merge logic in the RS that permits control data from different sources to be merged into a single control data value. Once the instruction is issued, the RS passes the merged control data value to an execution unit for processing.

Merging status and control data in a reservation station

Methods and apparatus for transmitting data between execution slices of a multi-slice processor including receiving, by an execution slice, a broadcast message comprising an instruction tag (ITAG) for a producer instruction, a latency, and a source identifier; determining that an issue queue in the execution slice comprises an ITAG for a consumer instruction, wherein the consumer instruction depends on result data from the producer instruction; calculating a cycle countdown using the latency and the source identifier; determining that the cycle countdown has expired; and in response to determining that the cycle countdown has expired, reading the result data from the producer instruction.

Broadcasting messages between execution slices for issued instructions indicating when execution results are ready

Operation of a multi-slice processor that includes a plurality of execution slices. Operation of such a multi-slice processor includes: receiving a first instruction indicating a first target register; receiving a second instruction indicating the first target register as a source operand; responsive to the second instruction indicating the first target register as a source operand, updating a dependent count corresponding to the first instruction; and issuing, in dependence upon the dependent count for the first instruction being greater than a dependent count for another instruction, the first instruction to an execution slice of the plurality of execution slices.

Operation of a multi-slice processor implementing dependency accumulation instruction sequencing

An execution slice circuit for a processor core has multiple parallel instruction execution slices and provides flexible and efficient use of internal resources. The execution slice circuit includes a master execution slice for receiving instructions of a first instruction stream and a slave execution slice for receiving instructions of a second instruction stream and instructions of the first instruction stream that require an execution width greater than a width of the slices. The execution slice circuit also includes a control logic that detects when a first instruction of the first instruction stream has the greater width and controls the slave execution slice to reserve a first issue cycle for issuing the first instruction in parallel across the master execution slice and the slave execution slice.

Linkable issue queue parallel execution slice processing method

Linkable issue queue parallel execution slice for a processor

Techniques are disclosed for back-to-back issue of instructions in a processor. A first instruction is stored in a queue position in an issue queue. The issue queue stores instructions in a corresponding queue position. The first instruction includes a target instruction tag and at least a source instruction tag. The target instruction tag is stored in a table storing a plurality of target instruction tags associated with a corresponding instruction. Each stored target instruction tag specifies a logical register that stores a target operand. Upon determining, based on the source instruction tag associated with the first instruction and the target instruction tag associated with a second instruction, that the first instruction is dependent on the second instruction, a pointer to the first instruction is associated with the second instruction. The pointer is used to wake up the first instruction upon issue of the second instruction.

Techniques to wake-up dependent instructions for back-to-back issue in a microprocessor

Operation of a multi-slice processor that includes execution slices and a dispatch network of the multi-slice processor implementing a hardware level mechanism to overcome a system hang. Such a multi-slice processor includes a plurality of execution slices and a dispatch network of the multi-slice processor implementing a hardware level mechanism to overcome a system hang. Operation of such a multi-slice processor includes, storing, in one or more logical units of a plurality of logical units of an age array, a logical value representing a relative age between instructions; propagating, in response to a current instruction being in a hang state, a hang signal to the plurality of logical units of the age array; in response to the hang signal, generating, from the plurality of logical units, a plurality of logical output values indicating a next instruction ready for execution; and issuing the next instruction for execution.

Operation of a multi-slice processor implementing a mechanism to overcome a system hang

Operation of a multi-slice processor that includes execution slices implementing dynamic switching of instruction issuance order. Such a multi-slice processor includes determining a current issuance order for a plurality of instructions and a change in an operating condition of the multi-slice processor; responsive to determining the change in the operating condition, determining an alternate issuance order for the plurality of instructions; and responsive to determining the alternate issuance order, switching from the current issuance order for the plurality of instructions to the alternate issuance order for the plurality of instructions.

Growing community of inventors

Seattle, WA, United States of America

Jeffrey Carl Brownscheidle