Bitfield Index Representation for Microprocessor Kernel Invocation
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Solution Overview
Problem
Current methods for handling kernel invocation IDs in microprocessor systems, particularly in graphics processors, are inefficient due to the overhead of representing 126-bit indices and cannot effectively handle divergent branching and large numbers of threads.
Innovation Solution
A method that determines the actual number of bits needed to represent each dimension of a kernel's index and packs the index into a bitfield data structure, reducing unnecessary bit provision and enabling more efficient representation and processing of kernel invocation IDs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a full 126-bit kernel invocation ID is used to uniquely identify each kernel invocation, then each invocation can be precisely identified, but the overhead of representing and processing these IDs becomes significant
Solution Approach 1:
The patent segments the 126-bit kernel invocation ID into two parts: a work-group ID (32 bits) and a work-item ID (30 bits). This segmentation allows the system to handle large numbers of kernel invocations by dividing them into manageable work-groups, reducing the overhead while maintaining precise identification capability.
Solution Approach 2:
The patent introduces a hierarchical dimension structure with work-groups as the first dimension and work-items within groups as the second dimension. This dimensional organization transforms the flat 126-bit ID into a structured two-level system, enabling more efficient processing and reduced memory overhead.
2Device complexity
If execution units group kernel invocations into lockstepped groups to amortize indexing cost, then the cost of invocation indexing is reduced, but kernels with divergent branching cannot be used
Solution Approach 1:
The patent makes the execution model dynamic by allowing work-items within a work-group to execute independently rather than in strict lockstep. This dynamic execution approach enables kernels with divergent branching to be used while still maintaining the efficiency benefits of grouped execution, as work-items can diverge and converge naturally within the work-group structure.
3Device complexity
If each execution thread sequentially executes one kernel invocation to maintain simple indexing, then indexing overhead is minimized, but the approach becomes very high cost when the number of execution threads is large
Solution Approach 1:
The patent merges multiple kernel invocation indices into a unified work-group ID structure that can be shared across multiple execution threads. Instead of each thread maintaining its own full 126-bit ID, threads share the work-group ID and only maintain minimal work-item specific information, dramatically reducing per-thread indexing overhead while enabling scalability to large numbers of threads.
Data Source
AI summary
When an OpenCL kernel is to be executed, a bitfield index representation to be used for the indices of the kernel invocations is determined based on the number of bits needed to represent the maximum value that will be needed for each index dimension for the kernel. A bitfield placement data structure 33 describing how the bitfield index representation is partitioned is then prepared together with a maximum value data structure 32 indicating the maximum index dimension values to be used for the kernel. A processor then executes the kernel invocations 36 across the index space indicated by the maximum value data structure 32. A bitfield index representation 35, 37, 38 configured in accordance with the bitfield placement data structure 33 is associated with each kernel invocation to indicate its index.