Processor Trace Encoder Circular Buffer Flush
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Solution Overview
Problem
Current approaches for tracing control flow changes in processor execution require significant semiconductor area and result in high processing overhead and memory bandwidth usage, impacting performance.
Innovation Solution
A processor with a selectively enabled trace encoder and circular buffer that encodes and stores instruction retirement information in a compressed form, allowing for on-demand flushing to memory, reducing the need for extensive system registers and continuous memory bandwidth usage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If system registers are used for storing control flow change information, then control flow tracing capability is improved, but semiconductor area increases
Solution Approach 1:
The patent creates a copy of control flow information in a trace buffer rather than using full system registers. The trace encoder generates a compressed representation of control flow changes, which is stored in a smaller circular buffer. This copying approach maintains the essential tracing functionality while using significantly less semiconductor area than full system register implementation.
Solution Approach 2:
The patent changes the storage parameter from full register contents to compressed trace data. By encoding only the essential control flow change information (branch targets, conditional branches, etc.) rather than storing complete register states, the system reduces the required buffer size while maintaining accurate control flow tracking capability.
2Measurement precision
If control flow change information is stored in system registers, then control flow tracing is improved, but processing overhead increases
Solution Approach 1:
The trace encoder performs preliminary encoding of control flow information during instruction execution. By pre-processing and compressing the trace data in real-time as instructions execute, the system avoids the need for later heavy processing to retrieve and interpret control flow information, thereby reducing overall processing overhead.
Solution Approach 2:
The patent extracts only the essential control flow change information from the complete instruction execution trace. The trace encoder identifies and extracts only critical control flow events (branches, function calls, returns) while filtering out redundant information. This extraction reduces the amount of data that needs to be stored and processed, thereby reducing processing overhead.
3Measurement precision
If memory bandwidth is used continuously to flush control flow information, then control flow tracing is maintained, but performance is degraded
Solution Approach 1:
The patent implements periodic flushing of the circular buffer to memory rather than continuous flushing. The trace buffer is flushed only when full or when explicitly requested, allowing the processor to execute instructions without constant memory bandwidth constraints. This periodic action maintains tracing continuity while minimizing performance impact during instruction execution.
Solution Approach 2:
The system dynamically adjusts the flushing behavior based on buffer state and system conditions. The trace encoder and circular buffer work together to determine optimal flush timing, balancing the need for trace data availability with the need to maintain high instruction execution throughput. This dynamic approach allows the system to adapt between tracing accuracy and performance based on current operational needs.
Data Source
AI summary
In a general aspect, a processor can include an instruction processing unit configured to execute a plurality of machine-readable instructions of a program in accordance with a control flow of the program and, in response to completing execution of respective instructions of the machine-readable instructions, produce respective instruction retirement information. The processor can also include a selectively enablable trace encoder that is configured, when enabled, to receive the respective instruction retirement information, and encode the instruction retirement information in an instruction trace corresponding with the control flow. The processor can also include a circular buffer that is configured to, when the trace encoder is enabled, receive and store the instruction trace, and, in response to a flush, communicate the stored instruction trace via a memory interface, where the memory interface is selectively enabled in response to the flush request.