Cpu Design Questions
Branch prediction is a technique used in CPU design to improve the performance of branch instructions, which are instructions that can alter the normal sequential flow of program execution. The concept of branch prediction involves predicting the outcome of a branch instruction before it is actually executed, based on historical information and patterns.
The CPU maintains a branch prediction table, also known as a branch history table or branch target buffer, which stores information about previous branch instructions and their outcomes. When a branch instruction is encountered, the CPU looks up the corresponding entry in the branch prediction table to determine whether the branch is likely to be taken or not taken.
If the prediction is correct, the CPU can continue executing instructions along the predicted path, resulting in improved performance. However, if the prediction is incorrect, a pipeline stall occurs, and the CPU needs to discard the incorrectly fetched instructions and fetch the correct instructions from the target of the branch.
There are different types of branch prediction techniques, such as static prediction, dynamic prediction, and speculative execution. Static prediction assumes that the branch will always be taken or not taken based on the branch instruction itself. Dynamic prediction uses historical information to make predictions, while speculative execution allows the CPU to execute instructions along both the predicted and non-predicted paths simultaneously, discarding the incorrect path later.
Overall, branch prediction plays a crucial role in CPU design by reducing the impact of branch instructions on the overall performance of the processor.