Commit Window Move Element for Speculative Trace Diagnostics
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Solution Overview
Problem
Speculative execution in processing circuitry poses challenges for tracing outcomes of instructions, particularly with long-lived speculation events like transactional memory, where traditional commit elements are insufficient, leading to limited diagnostic information and inefficient trace resource usage.
Innovation Solution
The introduction of a commit window move element allows the start of the commit window to be moved relative to the oldest remaining speculative element, enabling the tracing of younger instructions as committed without resolving the oldest speculative element, and a maximum speculation depth is used to control the output of commit elements, optimizing trace bandwidth and resource usage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of information
If traditional commit elements are used for tracing speculative execution, then trace output can be generated, but diagnostic information for long-lived speculation events is insufficient and trace resource usage is inefficient
Solution Approach 1:
The patent segments the commit window into multiple positions that can be independently controlled. Instead of treating the commit window as a single fixed structure, the invention divides it into configurable positions that can be moved relative to the oldest remaining speculative element, allowing selective tracing of different instruction groups within the speculative execution stream.
Solution Approach 2:
The patent introduces dynamic control of the commit window position through the commit window move element. The commit window is no longer static but can be repositioned dynamically based on the tracing needs, allowing the system to adapt the window position to capture relevant diagnostic information for long-lived speculation events while maintaining efficient resource usage.
2Loss of information
If maximum speculation depth is increased to trace long-lived speculation events, then more diagnostic information is available, but trace bandwidth and resource usage increase
Solution Approach 1:
The patent extracts the commit window from its traditional fixed position and separates it from the oldest remaining speculative element. By taking out the commit window and allowing it to move independently, the system can trace long-lived speculation events without requiring an increase in maximum speculation depth, thus maintaining efficient trace bandwidth usage while capturing necessary diagnostic information.
Solution Approach 2:
The patent adds a new dimension of control by introducing the commit window position as an independent variable. Instead of only controlling speculation depth, the system now has two dimensions: the depth of speculation and the position of the commit window within that depth. This additional degree of freedom allows efficient tracing of long-lived events without increasing overall resource requirements.
3Device complexity
If the commit window position is fixed relative to the oldest speculative element, then trace structure is simple, but flexibility in tracing different instruction groups is limited
Solution Approach 1:
The patent prepares the commit window position in advance through the commit window move element, which can reposition the window before tracing operations begin or during execution. This preliminary positioning action allows the system to adapt to different tracing scenarios without complex real-time adjustments, maintaining relatively simple trace structure while achieving high flexibility.
Data Source
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AI summary
A trace module (12) has monitoring circuitry (18) for monitoring processing of instructions by processing circuitry (8), and trace output circuitry (20) for outputting a sequence of elements indicative of outcomes of the processing of instructions by the processing circuitry (8). The trace module supports output of a commit window move element indicating that a commit window, representing a portion of the trace stream comprising at least one speculative element representing at least one speculatively executed instruction, should move while the oldest remaining speculative element of the trace stream remains uncommitted. This can be useful for tracing of transactional memory functionality within program code.