fix: use y-first approach in Compute.calcDispatchSize to minimize wasted workgroups#8538
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mvaligursky merged 1 commit intomainfrom Mar 19, 2026
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…ted workgroups Replace sqrt-based 2D dispatch calculation with y-first approach: y = ceil(count / maxDimension), x = ceil(count / y). This wastes at most y-1 workgroups (typically 0-1) instead of potentially many more with the sqrt approach which doesn't account for the maxDimension limit. Made-with: Cursor
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Pull request overview
Updates Compute.calcDispatchSize to avoid exceeding the per-dimension workgroup limit by switching from a sqrt-based 2D dispatch size calculation to a y-first calculation based on maxDimension.
Changes:
- Replaced sqrt-based
x/ysizing withy = ceil(count / maxDimension),x = ceil(count / y) - Aims to reduce wasted workgroups while staying within the device’s max workgroup dimension
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…ted workgroups (#8538) Replace sqrt-based 2D dispatch calculation with y-first approach: y = ceil(count / maxDimension), x = ceil(count / y). This wastes at most y-1 workgroups (typically 0-1) instead of potentially many more with the sqrt approach which doesn't account for the maxDimension limit. Made-with: Cursor Co-authored-by: Martin Valigursky <mvaligursky@snapchat.com>
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Summary
Compute.calcDispatchSizewith a y-first approach:y = ceil(count / maxDimension),x = ceil(count / y).x = floor(sqrt(count))) balanced dimensions but didn't account formaxDimension, potentially producingx > maxDimensionwhencountis large.y - 1workgroups while guaranteeing both dimensions stay withinmaxDimension.