Speculative Writes to Special-Purpose Registers
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Solution Overview
Problem
Existing microprocessor architectures stall subsequent writes and reads to system registers when performing writes to special-purpose registers, such as interrupt mask registers, leading to inefficiencies in processor workloads.
Innovation Solution
Implementing speculative writes to special-purpose registers, allowing younger instructions to proceed while maintaining non-speculative values for control circuitry, enabling speculative execution and later commitment of results.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If writes to special-purpose registers are performed non-speculatively with stalling, then register value accuracy is maintained, but processor throughput deteriorates
Solution Approach 1:
The patent segments the register write operation into speculative and non-speculative portions. The speculative write allows younger instructions to proceed while a separate non-speculative write ensures the correct value is eventually committed to the register file, resolving the contradiction between maintaining accuracy and improving throughput
Solution Approach 2:
The patent performs preliminary speculative writes to system registers before the actual retirement of instructions. This preliminary action allows subsequent instructions to execute without stalling, while the final non-speculative write ensures correctness when the instruction retires
2Stability of the object's composition
If writes to special-purpose registers stall subsequent instructions, then instruction ordering is maintained, but execution efficiency deteriorates
Solution Approach 1:
The patent introduces dynamic handling of instruction execution by allowing younger instructions to execute speculatively out of order while maintaining the ability to commit results in order. The system dynamically adjusts between speculative execution and ordered commitment based on retirement status
Solution Approach 2:
The patent uses an intermediary mechanism where speculative writes to system registers are performed without stalling, and a separate non-speculative write ensures correct ordering. This intermediary approach maintains instruction ordering semantics while enabling efficient out-of-order execution
3Productivity
If speculative writes are performed without stalling, then processor throughput is improved, but register state consistency deteriorates
Solution Approach 1:
The patent performs preliminary speculative writes to system registers to improve throughput, then performs a final non-speculative write to ensure the register state is consistent with the retired instruction before allowing it to take effect in the register file
Data Source
AI summary
Techniques are disclosed relating to speculative writes to special-purpose registers (SPRs). In some embodiments, the disclosed techniques may reduce or avoid system instruction stalls while waiting for SPR writes, which may improve processor performance. In some embodiments, a processor includes a first storage element configured to store a non-speculative value of a special-purpose register and speculative storage circuitry configured to store one or more speculative values of the special-purpose register based on one or more speculatively-performed writes to the special-purpose register. In some embodiments, the processor includes control circuitry configured to: propagate the non-speculative value of the special-purpose register to control other circuitry and provide a youngest speculative value of the special-purpose register in the speculative storage circuitry as a speculative read of the special-purpose register.