[bidlekm]

Motivation

Enable CK Tile configurations on gfx1250 to select the native FP8/BF8 16x16x128 WMMA instruction instead of the default 16x16x64 instruction.

This must remain opt-in because K128 requires a compatible block K tile and may increase register pressure or reduce occupancy. Smaller tiles can perform better in some cases:

FP8 problem	Pipeline	K64 block tile	K128 block tile	K64 advantage
512x512x512	Basic V1	11.803 TFLOP/s	9.401 TFLOP/s	+25.6%
512x512x512	TDM	12.474 TFLOP/s	11.822 TFLOP/s	+5.5%
4096x4096x4096	TDM	1336.35 TFLOP/s	1210.67 TFLOP/s	+10.4%

These results compare block tile sizes rather than only instruction width, demonstrating why configurations should retain explicit control over K128 selection.

Closes #14391

Technical Details

Adds a WiderInstruction template parameter to get_k_warp_tile().

• Defaults to false, preserving existing behavior.
• When enabled for gfx1250 FP8/BF8 with a 16x16 warp tile, selects K128 instead of K64.
• Does not change FP16, FP32, integer, or non-gfx1250 selection.
• Configurations must opt in only when their block K supports the K128 atom.

Example:

get_k_warp_tile<fp8_t, 16, false, true>()

Test Plan

• Compile-time verification that default gfx1250 FP8 still selects K64.
• Compile-time verification that opt-in FP8 and BF8 select K128.
• Compile-time verification that opt-in FP16 remains K32.
• Compile the selector assertions with the gfx1250 toolchain.
• Run clang-format-18.

Benchmark FP8 RCR GEMM with physical 16x16x128 WMMA instructions. Each result is the median of three trials with 20 warmups and 100 measured iterations.

Test Result

All compile-time checks and formatting checks passed.

Shape	Block / warp tile	Reference	K128	Gain	Latency
2304x512x16384	64x64x256 / 16x16x128	464.9	550.3	+18.4%	70.2 us
512x2304x16384	64x64x256 / 16x16x128	452.2	547.0	+21.0%	70.7 us
1024x5120x8192	64x128x128 / 32x32x128	1389.5	1805.6	+29.9%	47.6 us
5120x1024x8192	64x128x128 / 32x32x128	1516.9	1920.9	+26.6%	44.7 us
4096x4096x16384	256x128x128 / 32x32x128	1942.4	2423.9	+24.8%	226.8 us
14336x2048x1024	128x64x128 / 32x32x128	1334.4	1453.7	+8.9%	41.4 us
2048x14336x1024	128x64x128 / 32x32x128	1275.0	1434.4	+12.5%	41.9 us

Submission Checklist

• Look over the contributing guidelines at https://github.com/ROCm/TheRock/blob/main/GOVERNANCE.md#pull-requests.

[Copilot]

🟢 Approval recommended

The narrowly scoped change preserves default behavior and opts into existing K128 backend support, with no blocking issues identified.

No open issues 🎉

What changed in this PR

Adds opt-in wider FP8/BF8 WMMA selection for CK Tile on gfx1250 while preserving existing defaults.

Changes:

• Adds a WiderInstruction template parameter, defaulting to false.
• Selects K128 for eligible FP8/BF8 tiles when enabled, leaving other selection paths unchanged.

File	Description
projects/​composablekernel/​include/​ck_tile/​ops/​gemm/​pipeline/​tile_gemm_shape.hpp	Adds default-disabled K128 selection to get_k_warp_tile().

_{Review effort: Balanced}

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TheRock Submodule Bump Activity

Newest first

• 2026-10-27 — Included in TheRock via ROCm/TheRock#9513.