Advanced Micro Devices Corporation

Globalfoundries Inc.

Gregory William Smaus

John M King

Michael David Achenbach

Mitchell K Alsup

Francesco Spadini

Matthew Andrew Rafacz

Benjamin T Sander

Emil Talpes

Matthew M Crum

Christopher J Burke

Ganesh Venkataramanan

James K Pickett

Kevin Michael Lepak

Brian D McMinn

Gerald David Zuraski, Jr

Philip Enrique Madrid

Debjit Das Sarma

Teik-Chung Tan

Michael A Filippo

Raghuram S Tupuri

Faisal A Syed

Betty Ann McDaniel

Michael E Tuuk

Noah Bamford

Teik Tan

Christopher Svec

Kevin Lepaak

Techniques for selectively executing a lock instruction speculatively or non-speculatively based on lock address prediction and/or temporal lock prediction. including methods an devices for locking an entry in a memory device. In some techniques, a lock instruction executed by a thread for a particular memory entry of a memory device is detected. Whether contention occurred for the particular memory entry during an earlier speculative lock is detected on a condition that the lock instruction comprises a speculative lock instruction. The lock is executed non-speculatively if contention occurred for the particular memory entry during an earlier speculative lock. The lock is executed speculatively if contention did not occur for the particular memory entry during an earlier speculative lock.

Lock address contention predictor

The techniques described herein improve cache traffic performance in the context of contended lock instructions. More specifically, each core maintains a lock address contention table that stores addresses corresponding to contended lock instructions. The lock address contention table also includes a state value that indicates progress through a series of states meant to track whether a load by the core in a spin-loop associated with semaphore acquisition has obtained the semaphore in an exclusive state. Upon detecting that a load in a spin-loop has obtained the semaphore in an exclusive state, the core responds to incoming requests for access to the semaphore with negative acknowledgments. This allows the core to maintain the semaphore cache line in an exclusive state, which allows it to acquire the semaphore faster and to avoid transmitting that cache line to other cores unnecessarily.

Techniques for handling cache coherency traffic for contended semaphores

An arithmetic unit performs store-to-load forwarding based on predicted dependencies between store instructions and load instructions. In some embodiments, the arithmetic unit maintains a table of store instructions that are awaiting movement to a load/store unit of the instruction pipeline. In response to receiving a load instruction that is predicted to be dependent on a store instruction stored at the table, the arithmetic unit causes the data associated with the store instruction to be placed into the physical register targeted by the load instruction. In some embodiments, the arithmetic unit performs the forwarding by mapping the physical register targeted by the load instruction to the physical register where the data associated with the store instruction is located.

Store-to-load forwarding

A system and method for a lightweight fence is described. In particular, micro-operations including a fencing micro-operation are dispatched to a load queue. The fencing micro-operation allows micro-operations younger than the fencing micro-operation to execute, where the micro-operations are related to a type of fencing micro-operation. The fencing micro-operation is executed if the fencing micro-operation is the oldest memory access micro-operation, where the oldest memory access micro-operation is related to the type of fencing micro-operation. The fencing micro-operation determines whether micro-operations younger than the fencing micro-operation have load ordering violations and if load ordering violations are detected, the fencing micro-operation signals the retire queue that instructions younger than the fencing micro-operation should be flushed. The instructions to be flushed should include all micro-operations with load ordering violations.

System and method for a lightweight fencing operation

Techniques for improving execution of a lock instruction are provided herein. A lock instruction and younger instructions are allowed to speculatively retire prior to the store portion of the lock instruction committing its value to memory. These instructions thus do not have to wait for the lock instruction to complete before retiring. In the event that the processor detects a violation of the atomic or fencing properties of the lock instruction prior to committing the value of the lock instruction, the processor rolls back state and executes the lock instruction in a slow mode in which younger instructions are not allowed to retire until the stored value of the lock instruction is committed. Speculative retirement of these instructions results in increased processing speed, as instructions no longer need to wait to retire after execution of a lock instruction.

Speculative retirement of post-lock instructions

The present invention provides a method and apparatus for scheduling based on tags of different types. Some embodiments of the method include broadcasting a first tag to entries in a queue of a scheduler. The first tag is broadcast in response to a first instruction associated with a first entry in the queue being picked for execution. The first tag includes information identifying the first entry and information indicating a type of the first tag. Some embodiments of the method also include marking at least one second entry in the queue is ready to be picked for execution in response to at least one second tag associated with at least one second entry in the queue matching the first tag.

Hybrid tag scheduler to broadcast scheduler entry tags for picked instructions

A method includes selecting for execution in a processor a load instruction having at least one dependent instruction. Responsive to selecting the load instruction, the at least one dependent instruction is selectively awakened based on a status of a store instruction associated with the load instruction to indicate that the at least one dependent instruction is eligible for execution. A processor includes an instruction pipeline having an execution unit to execute instructions, a scheduler, and a controller. The scheduler selects for execution in the execution unit a load instruction having at least one dependent instruction. The controller, responsive to the scheduler selecting the load instruction, selectively awakens the at least one dependent instruction based on a status of a store instruction associated with the load instruction to indicate that the at least one dependent instruction is eligible for execution by the execution unit.

Dependence-based replay suppression

A processor includes a physical register file having physical registers and an execution unit to perform an arithmetic operation to generate a result mapped to a physical register, wherein the processor delays a write of the result to the physical register file until the result is qualified as valid. A method includes mapping the same physical register both to store load data of a load-execute operation and to subsequently store a result of an arithmetic operation of the load-execute operation, and writing the load data into the physical register. The method further includes, in a first clock cycle, executing the arithmetic operation to generate the result, and, in a second clock cycle, providing the result as a source operand for a dependent operation. The method includes, in a third clock cycle, enabling a write of the result to the physical register file responsive to the result qualifying as valid.

Register file management for operations using a single physical register for both source and result

Various embodiments of methods and systems for implementing a microprocessor that includes a trace cache and attempts to transition fetching from instruction cache to trace cache only on label boundaries are disclosed. In one embodiment, a microprocessor may include an instruction cache, a branch prediction unit, and a trace cache. The prefetch unit may fetch instructions from the instruction cache until the branch prediction unit outputs a predicted target address for a branch instruction. When the branch prediction unit outputs a predicted target address, the prefetch unit may check for an entry matching the predicted target address in the trace cache. If a match is found, the prefetch unit may fetch one or more traces from the trace cache in lieu of fetching instructions from the instruction cache.

Transitioning from instruction cache to trace cache on label boundaries

Various embodiments of methods and systems for implementing a set of microcode operations corresponding to a microcoded instruction as a microcode subroutine are disclosed. In one embodiment, a microprocessor includes a dispatch unit configured to dispatch operations and a scheduler coupled to the dispatch unit and configured to schedule dispatched operations for execution. In response to receiving a microcoded instruction, the dispatch unit is configured to dispatch a microcode subroutine call operation that specifies a tag identifying a microcode subroutine.

System and method of implementing microcode operations as subroutines

A technique for reducing stack pointer adjustment operations when stack dependent operations, which correspond to stack dependent instructions, are encountered includes setting a stack pointer to an initial value for a stack. A number of bytes associated with the stack dependent operation is determined. A stack pointer delta is then modified based upon the number of bytes associated with the stack dependent operation. A current location in the stack is determined based on the stack pointer and the stack pointer delta.

Determination of current stack pointer value using architectural and speculative stack pointer delta values

Various embodiments of methods and systems for storing multiple groups of microcode operations and corresponding control sequences per row of microcode ROM are disclosed. In one embodiment, an integrated circuit may include a microcode ROM coupled to a control sequence logic unit. The microcode ROM may store multiple groups of microcode operations per row. For each group of microcode operations stored in a row, a corresponding control sequence may also be stored in the row. Each group of microcode operations may be included in a microcode routine. The groups of microcode operations stored in a row may be included in the same microcode routine, or some of the groups may be included in different microcode routines.

Multiple control sequences per row of microcode ROM

Various embodiments of methods and systems for implementing a microprocessor that fetches a group of instructions into instruction cache in response to a corresponding trace being evicted from the trace cache are disclosed. In some embodiments, a microprocessor may include an instruction cache, a trace cache, and a prefetch unit. In response to a trace being evicted from trace cache, the prefetch unit may fetch a line of instructions into instruction cache.

Growing community of inventors

Austin, TX, United States of America

Gregory William Smaus