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Draft of segmented reduce optimization #578
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This reverts commit 84c02eb.
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Experimented with a deterministic version of large segments optimization. Assigned a number of CTAs per each segment. The optimization is quite expensive in terms of the memory and requires about |
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This PR applies a technique similar to one in segmented sort algorithm. Segments are partitioned and various thread groups are applied to various segment categories. While optimizing segmented reduction I introduced warp reduce agent and generalized reduce agent implementation. Below are speedups for small segment sizes, best speedup is about 66x:
Medium size segments experience minor slowdowns, but it can be addressed by further tuning:
Large size segments are not affected by optimization:
In the commits, there's an attempt to fuse small segments reduction with the partitioning stage. This optimization doesn't perform as well. My guess is that it slows down decoupled look-back at the partitioning stage or affects it's occupancy, which leads to overall slowdown.
In order not to break stream capture (if one is used), I incorporated a separate check for that. We might need to check stream capturing mode in our tests later.