Hazards in Pipelined Processing

The three types of hazards are structural hazards, data hazards, and control hazards. Structural hazards occur when a required resource is busy, data hazards arise when an instruction needs to wait for previous data operations, and control hazards relate to decisions based on the outcome of previous instructions.

Structural hazards occur due to conflicts for resource usage, such as when load/store operations require memory access at the same time as instruction fetch. They can be mitigated by using separate instruction and data memories or caches.

Forwarding, also known as bypassing, allows the use of an instruction's result as soon as it is computed instead of waiting for it to be written to a register. This requires additional connections in the datapath to enable quicker data access.

<p>A load-use data hazard occurs when an instruction tries to use data that has not yet been computed due to a previous load instruction. It can't always be resolved by forwarding because the value may not be ready in time for the dependent instruction.</p> Signup and view all the answers

<p>Alignment of memory operands ensures that memory accesses can be completed in a single cycle, optimizing performance. This alignment is crucial for maintaining efficient data processing within the processor.</p> Signup and view all the answers

<p>To illustrate the resource usage of operations over time in a processor.</p> Signup and view all the answers

<p>The WB stage writes the data from memory back to the register file.</p> Signup and view all the answers

<p>In the EX stage for load, the effective memory address is computed, while for store, the address is calculated to store data.</p> Signup and view all the answers

<p>Pipelined control generates control signals based on instructions, and simplification reduces complexity for easier implementation.</p> Signup and view all the answers

<p>Data hazards occur when instructions depend on data from previous instructions, and they can be resolved using forwarding.</p> Signup and view all the answers

<p>Register numbers are passed along the pipeline to identify dependencies and when forwarding should occur.</p> Signup and view all the answers

<p>The ID stage decodes the instruction and reads the necessary register values for load or store operations.</p> Signup and view all the answers

<p>A single-cycle diagram shows the state of the pipeline in one clock cycle, while a multi-cycle diagram emphasizes resource usage over several cycles.</p> Signup and view all the answers

<p>The main types of hazards are data hazards and control hazards.</p> Signup and view all the answers

<p>A Load-Use data hazard occurs when a load instruction is immediately followed by a use of the data loaded, requiring a stall to prevent using incorrect data.</p> Signup and view all the answers

<p>The revised forwarding condition allows for data to be forwarded in the pipeline only when specific EX hazard conditions are not true, thus reducing incorrect data usage.</p> Signup and view all the answers

<p>To stall the pipeline, control values in the ID/EX register are set to 0, preventing updates to the PC and forcing nop operations in EX, MEM, and WB stages.</p> Signup and view all the answers

<p>A branch hazard occurs when the outcome of a branch instruction is not known in time, requiring the flushing of subsequent instructions by setting control values to 0.</p> Signup and view all the answers

<p>Moving hardware to determine the branch outcome to the ID stage reduces branch delay by enabling the pipeline to make decisions about instruction execution sooner.</p> Signup and view all the answers

<p>Stalls reduce performance because they introduce idle cycles in the pipeline, slowing down the overall instruction throughput.</p> Signup and view all the answers

<p>Load-Use hazards are detected by checking the values in the ID stage to see if a load instruction's destination register is used in subsequent instructions.</p> Signup and view all the answers

<p>Forcing control values to 0 prevents further instruction execution and updates, ensuring the current instruction is decoded again properly.</p> Signup and view all the answers

<p>It loads the word from the memory address calculated by adding 50 to the content of register $7 into register $4.</p> Signup and view all the answers

<p>A compiler can arrange code and manage instruction scheduling to avoid hazards and stalls by being aware of the pipeline structure.</p> Signup and view all the answers

<p>It may require a stall cycle in the execution of the following branch instruction.</p> Signup and view all the answers

<p>Two stall cycles are required.</p> Signup and view all the answers

<p>Dynamic branch prediction uses a branch prediction buffer to anticipate the outcome of branches, reducing pipeline stalls.</p> Signup and view all the answers

<p>A branch prediction buffer, or branch history table, stores outcomes of recent branches indexed by their addresses.</p> Signup and view all the answers

<p>A 1-bit predictor can lead to multiple mispredictions in inner loops.</p> Signup and view all the answers

<p>If the prediction is wrong, the pipeline is flushed, and the prediction is flipped.</p> Signup and view all the answers

<p>A stall cycle is a delay inserted into the instruction pipeline to resolve data hazards.</p> Signup and view all the answers

<p>Loop unrolling is the technique of replicating the loop body to expose more parallelism and reduce overhead. This allows for better performance by maximizing instruction throughput.</p> Signup and view all the answers

<p>Register renaming is a method that prevents name dependencies by allowing the CPU to use different physical registers for the same logical register. This reduces hazards and enables more parallel instruction execution.</p> Signup and view all the answers

<p>Dynamic multiple issue allows the CPU to issue multiple instructions simultaneously based on available resources and data dependencies. This flexibility minimizes stalls and maximizes resource utilization.</p> Signup and view all the answers

<p>The reorder buffer holds results of instructions that have executed but not yet committed, ensuring correct execution order while allowing out-of-order processing. It helps manage dependencies until final results are ready.</p> Signup and view all the answers

<p>Load speculation involves predicting the effectiveness of loads to avoid delays caused by cache misses. It enables the CPU to execute loads before confirming earlier operations, enhancing instruction flow.</p> Signup and view all the answers

<p>Dynamic pipeline scheduling allows instructions to execute out of order to reduce stalls while ensuring results are committed in order. This improves throughput and maintains correct program execution.</p> Signup and view all the answers

<p>Loop-carried dependencies can hinder parallel execution by creating delays whenever a subsequent instruction depends on the result of a previous iteration. This can reduce CPU efficiency.</p> Signup and view all the answers

<p>Reducing register usage in loop unrolling is challenging because unrolling increases the number of instructions needing unique registers, which may exceed available register resources. This can lead to performance trade-offs.</p> Signup and view all the answers

<p>Structural hazards occur when hardware resources are insufficient to support all concurrent operations. Dynamic scheduling mitigates these hazards by intelligently issuing instructions based on resource availability.</p> Signup and view all the answers

<p>The reservation station temporarily holds instructions ready to execute while waiting for available operands, allowing for out-of-order execution. This helps optimize instruction throughput.</p> Signup and view all the answers