GPU Exception Handling for Page Fault Debugging
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Solution Overview
Problem
Current graphics processing units (GPUs) face challenges in debugging unhandled page faults, particularly in longer running kernels with large numbers of threads and memory accesses, as conventional approaches fail to pinpoint the specific thread and instruction causing the fault.
Innovation Solution
Implementing exception handling mechanisms within the GPU to enable detailed debugging of memory access errors, including the ability to identify the specific thread and instruction responsible for unhandled page faults, and providing detailed error information without stalling execution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional debugging approaches are used for unhandled page faults, then execution can proceed without interruption, but the specific thread and instruction causing the fault cannot be pinpointed
Solution Approach 1:
The system performs preliminary actions by capturing and storing exception information (thread ID, instruction pointer, faulting address) at the moment the page fault occurs, before execution continues. This preliminary capture enables precise error location without interrupting the execution flow, resolving the contradiction between debugging efficiency and error location precision.
2Reliability
If execution is stalled to detect errors, then error detection accuracy improves, but processing throughput decreases
Solution Approach 1:
The system implements feedback by continuously monitoring memory access operations and automatically capturing exception information when page faults occur. This feedback mechanism provides accurate error detection without requiring execution stalls, as the monitoring occurs concurrently with normal processing, thus maintaining high throughput while improving reliability.
Solution Approach 2:
An intermediary exception handling mechanism is introduced between the memory access operations and the main execution flow. This intermediary captures fault information without interrupting the primary execution stream, allowing accurate error detection to occur in parallel with normal processing, thereby maintaining processing throughput while improving error detection accuracy.
3Measurement precision
If detailed error information is collected for every memory access, then debugging precision improves, but system complexity increases
Solution Approach 1:
The system applies local quality by collecting detailed exception information only at specific locations where page faults occur, rather than monitoring all memory accesses uniformly. The exception handling logic is localized to the fault detection point, capturing only the necessary information (thread ID, instruction pointer, faulting address) locally at the time of the fault, thus improving debugging precision without proportionally increasing overall system complexity.
Data Source
AI summary
An apparatus to facilitate exception handling for debugging in a graphics environment is disclosed. The apparatus includes load store pipeline hardware circuitry to: in response to a page fault exception being enabled for a memory access request received from a thread of the plurality of threads, allocate a memory dependency token correlated to a scoreboard identifier (SBID) that is included with the memory access request; send, to memory fabric of the graphics processor, the memory access request comprising the memory dependency token; receive, from the memory fabric in response to the memory access request, a memory access response comprising the memory dependency token and indicating occurrence of a page fault error condition and fault details associated with the page fault error condition; and return the SBID associated with the memory access response and fault details of the page fault error condition to a debug register of the thread.