GPU Work Discarding for Priority Inversion Recovery
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Solution Overview
Problem
Graphics processors face issues with priority inversion where lower-priority work blocks higher-priority work, leading to inefficiencies and long wait times due to the need for lower-priority work to complete before higher-priority work can be executed, especially in distributed GPU systems with multiple replicated portions.
Innovation Solution
Implementing hardware mechanisms to signal priority inversions to software, allowing for the context-switching or discarding of lower-priority work to free execution resources for higher-priority work, using page manager circuitry to allocate and deallocate memory pages, and providing stand-in pages to ensure smooth operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If lower-priority graphics work is allowed to execute before higher-priority work, then resource utilization is improved by keeping execution units busy, but higher-priority work experiences delayed execution and increased wait times
Solution Approach 1:
The system dynamically adjusts the execution schedule of graphics work based on priority levels. When priority inversion is detected, the scheduler dynamically intervenes to discard lower-priority work and reschedule higher-priority work, making the system adaptive rather than static in its resource allocation decisions
Solution Approach 2:
The system discards lower-priority graphics work that is blocking higher-priority work execution. The discarded work is not permanently lost but is recovered through rescheduling once execution resources become available, ensuring that priority requirements are met while maintaining overall system throughput
2Speed
If lower-priority work is discarded to execute higher-priority work immediately, then execution speed of higher-priority work is improved, but system complexity increases due to tracking and managing work discarding
Solution Approach 1:
The system employs self-service mechanisms where the graphics processing unit automatically detects priority inversions and manages the discarding and rescheduling of work items. This automated self-management reduces the need for complex external control mechanisms while maintaining execution speed improvements
Solution Approach 2:
The system uses feedback from priority inversion detection to trigger automatic discarding and rescheduling actions. The feedback loop continuously monitors execution priorities and adjusts scheduling decisions accordingly, simplifying the control mechanism compared to comprehensive manual tracking systems
3Reliability
If lower-priority work is context-switched out instead of discarded, then work preservation is improved, but execution resources remain blocked and higher-priority work still experiences delays
Solution Approach 1:
The system discards lower-priority work items that are blocking higher-priority work execution, with the understanding that discarded work will be recovered and rescheduled later. This approach prioritizes immediate execution of high-priority work over preserving low-priority work in the current execution context
Data Source
AI summary
Techniques are disclosed relating to discarding graphics work, e.g., to free execution resources for higher-priority work. Control circuitry may distribute a first set of graphics work to a set of graphics processor sub-units and initiate a priority inversion signal in response to a determination that a second set of graphics work has a higher priority than the first set of graphics work and is blocked by the first set of graphics work. In response to a discard signal, control circuitry may discard results of the first set of graphics work from the multiple distributed hardware slots, including to: free one or more memory pages written to by the first set of graphics work and provide a stand-in memory page.