Instruction Dependency Keys for Crash Consistent Memory Ordering
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Solution Overview
Problem
In computing systems with non-volatile main memory (NVMM), ensuring efficient and proper ordering of memory operations becomes increasingly challenging due to the high number of barriers required for crash-consistent applications, which limits flexibility and efficiency in instruction execution.
Innovation Solution
The introduction of explicit dependency keys (EDKs) and complementary parameters within the instruction set architecture (ISA) allows for the definition and enforcement of ordered constraints between instructions, eliminating the need for Data Synchronization Barriers (DSBs) by explicitly linking producer and consumer instructions, enabling precise control over dependency ordering and allowing for out-of-order execution without compromising persistence.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Data Synchronization Barriers (DSBs) are inserted into program code to ensure proper memory operation order, then reliability of persistent state is improved, but device complexity and execution overhead increase
Solution Approach 1:
The patent extracts the ordering information from separate barrier instructions and embeds it directly into the instruction metadata fields. Each instruction now carries its own ordering dependencies (pred_req, succ_req, pred_grant, succ_grant) within its metadata, eliminating the need for external barrier instructions to enforce ordering.
Solution Approach 2:
The patent merges the ordering constraint enforcement mechanism with the instruction execution flow itself. By integrating ordering metadata into each instruction and using these fields to control execution dependencies, the system combines data processing and ordering enforcement into a unified mechanism, reducing the need for separate barrier instructions.
2Reliability
If barriers are inserted to ensure proper ordering of memory operations, then reliability of persistent state is improved, but productivity decreases due to increased execution time
Solution Approach 1:
The patent performs preliminary encoding of ordering requirements directly into instruction metadata during instruction generation. The pred_req and succ_req fields are pre-populated with ordering dependencies, allowing the execution engine to resolve ordering constraints without inserting additional barrier instructions, thus maintaining execution speed while ensuring reliability.
Solution Approach 2:
The patent introduces metadata fields (pred_req, succ_req, pred_grant, succ_grant) as intermediaries that carry ordering information between instructions. These metadata fields act as mediators that enable the execution engine to enforce ordering constraints implicitly without requiring explicit barrier instructions, thereby maintaining productivity while ensuring reliability.
3Adaptability or versatility
If explicit dependency keys are used to link producer and consumer instructions, then instruction execution flexibility is improved, but device complexity increases
Solution Approach 1:
The patent implements dynamic dependency resolution by allowing instructions to have variable ordering requirements specified in their metadata. The pred_req and succ_req fields can be selectively set based on the specific ordering needs of each instruction, enabling flexible adaptation to different execution scenarios without requiring a fixed, complex instruction set architecture.
Solution Approach 2:
The patent applies local quality by allowing each instruction to have its own specific ordering requirements encoded in its metadata fields. Rather than enforcing a uniform ordering policy across all instructions, the system allows each instruction to specify its local ordering dependencies (pred_req, succ_req), enabling fine-grained control over execution ordering without increasing overall system complexity.
Data Source
AI summary
In a particular implementation, a method includes: receiving, at a central processing unit (CPU), first and second instructions of a plurality of instructions obtained from a memory, where the first instruction corresponds to a preceding instruction of a second instruction, and where the second instruction corresponds to a succeeding instruction of the first instruction; determining a dependency of the first and second instructions; sending the first and second instructions to an issue queue of the CPU; executing, at the CPU, the first and second instructions; and completing, at the CPU, the first and second instructions.