What is hardware based speculation in computer architecture?
Hardware-based speculation follows the predicted flow of data values to choose when to execute instructions. This method of executing programs is essentially a data-flow execution: operations execute as soon as their operands are available.
What is dynamic pipeline scheduling?
In a dynamically scheduled pipeline, all instructions pass through the issue stage in order; however they can be stalled or bypass each other in the second stage and thus enter execution out of order. Instructions will also finish out-of-order.
What is dynamic scheduling with speculation?
The dynamic scheduler with speculation maintains four data structures – the reservation station, ROB, a register result data structure that keeps track of the ROB entry that will modify a register and an instruction status data structure. The last one is more for understanding purposes.
How does a reorder buffer help speculation?
The re-order buffer and in-order commit allow us to flush the speculative instructions from the machine when a misprediction is discovered. ROB is another possible source of operands ▪ ROB can provide precise exception in an out-of-order machine ▪ ROB allows us to ignore exceptions on speculative code.
What is static and dynamic scheduling?
Static Scheduling is the mechanism, where we have already controlled the order/way that the threads/processes are executing in our code (Compile time). Dynamic Scheduling is the mechanism where thread scheduling is done by the operating systems based on any scheduling algorithm implemented in OS level.
What is branch prediction and speculative execution?
Branch prediction is done by the processor to try to determine where the execution will continue after a conditional jump, so that it can read the next instruction(s) from memory. Speculative execution goes one step further and determines what the result would be from executing the next instruction(s).
What is speculative data?
Speculation (also known as speculative loading ), is a process implemented in Explicitly Parallel Instruction Computing ( EPIC ) processors and their compiler s to reduce processor-memory exchanging bottlenecks or latency by putting all the data into memory in advance of an actual load instruction.
What is a branch target buffer?
A branch target buffer is a buffer that is index by the branch instruction address with a tag for remaining bits. The info stored can be branch taken history and/or target address so it doesnt have to be recomputed.
What is static scheduling in computer architecture?
In deterministic (static) scheduling, each task in the program has a static assignment to a particular processor, and each time that task is submitted for execution, it is assigned to that processor. A combination of static and dynamic methods is referred to as a hybrid method.
What is the difference between static scheduling and dynamic scheduling in context of real time task scheduling?
Static scheduling makes scheduling decisions at compile time and is off-line. Dynamic scheduling is online and uses schedulabilty test to determine whether a set of tasks can meet their deadlines.
What is the difference between speculation and prediction?
Prediction means that you have evidence to back up your idea. Speculation is a prediction without evidence or very little evidence.
When was speculative execution introduced?
Along with multiple branch prediction (used to predict the instructions most likely to be needed in the near future) and dataflow analysis (used to align instructions for optimal execution, as opposed to executing them in the order they came in), speculative execution delivered a dramatic performance improvement over …
What key architecture features make speculative processing successful?
Branch predictors, which provide accuracies up to 96% (excluding OS code) [8], are the key to effective speculation. The primary disadvantage of speculation is that some processor resources are invariably allocated to useless, wrong-path instructions that must be flushed from the pipeline.
What is speculative memory?
An instruction can remain in the pipeline between being fetched and being executed. Because there can be several unresolved branches in the pipeline, instruction fetches are speculative, meaning there is no guarantee that they are executed.
What is delay slot in pipelining?
The branch delay slot is a side effect of pipelined architectures due to the branch hazard, i.e. the fact that the branch would not be resolved until the instruction has worked its way through the pipeline.
What is branch folding?
Branch folding is a technique where, on the prediction of most branches, the branch instruction is completely removed from the instruction stream presented to the execution pipeline. Branch folding can significantly improve the performance of branches, taking the CPI for branches significantly below 1.
What is dynamic and static scheduling?
In static scheduling, all the memory accesses are scheduled at compile-time, such that there is no memory conflict during the execution. In dynamic scheduling, the untimed memory accesses may affect correctness and performance if the memory arbitration or the memory conflicting accesses are not correctly solved.
What is static vs dynamic scheduling?
Answer: Static Scheduling is the mechanism, where we have already controlled the order/way that the threads/processes are executing in our code (Compile time). Dynamic Scheduling is the mechanism where thread scheduling is done by the operating systems based on any scheduling algorithm implemented in OS level.
What is the difference between static scheduling and dynamic scheduling?
A fundamental distinction is made between static and dynamic scheduling. Static schedules are fixed before execution based on the information available at that time, whereas dynamic schedules are determined during runtime.
What is the difference between preemptive and Nonpreemptive scheduling?
Key Differences Between Preemptive and Non-Preemptive Scheduling: In preemptive scheduling, the CPU is allocated to the processes for a limited time whereas, in Non-preemptive scheduling, the CPU is allocated to the process till it terminates or switches to the waiting state.