5-Stage Pipeline, Scoreboard, and Tomasulo Approach: Managing Hazards and Improving Performance
a) How does the scoreboard avoid the RAW hazard stalls? How does the scoreboard manage out of order completion?
The scoreboard approach is used to address the RAW hazard stalls and manage out of order completion in the 5-stage pipeline. It avoids RAW hazard stalls by keeping track of dependencies between instructions and ensuring correct execution order. Out of order completion is managed by tracking resource availability.
The scoreboard approach is used to address the RAW hazard stalls and manage out of order completion in the 5-stage pipeline. It keeps track of the dependencies between instructions and ensures that instructions are executed in the correct order, avoiding RAW hazard stalls. The scoreboard achieves this by maintaining a table that tracks the status of each instruction and the availability of resources. When an instruction is fetched, the scoreboard checks if its operands are available. If not, the instruction is stalled until the operands become available. Out of order completion is managed by the scoreboard by tracking the availability of resources.
Drawbacks of the 5-stage pipeline
The 5-stage pipeline, a common implementation in computer architecture, has some drawbacks. One of the main issues is the occurrence of RAW (Read After Write) hazards, which can cause stalls in the IF and ID stages. Additionally, when adding floating-point (FP) execution units, out of order completion can lead to further complications.
The Scoreboard Approach
The scoreboard approach is used to address the RAW hazard stalls and manage out of order completion in the 5-stage pipeline. It keeps track of the dependencies between instructions and ensures that instructions are executed in the correct order, avoiding RAW hazard stalls. The scoreboard achieves this by maintaining a table that tracks the status of each instruction and the availability of resources. When an instruction is fetched, the scoreboard checks if its operands are available. If not, the instruction is stalled until the operands become available. Out of order completion is managed by the scoreboard by tracking the availability of resources. Instructions are executed as soon as their dependencies are satisfied, even if they are not in the original order.