859acb5ae7
[CK_TILE] Add LLC-aware FMHA head grouping and head-major scheduling on RDNA (#5018) MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit ## Motivation Long-sequence FMHA can become memory-bound when K/V working sets exceed Infinity Cache (LLC), causing repeated DRAM traffic across heads. This PR introduces LLC-aware launch ordering improvements for FMHA forward, and it is currently enabled only on gfx11 and gfx12. The approach is inspired by [`Dao-AILab/flash-attention#2217`](https://github.com/Dao-AILab/flash-attention/pull/2217), adapted to CK’s kernel/runner structure and layout handling. In this context, `bshd` is the layout used in Flash-Attention, while `bhsd` is the default layout used by the CK Tile FMHA example. ## Technical Details This PR adds two complementary strategies: - For `bshd` input layout (`i_perm/o_perm=0`), enable explicit LLC-aware head grouping: - Estimate LLC size (env override, KFD sysfs, or arch default). - Compute group size from K/V bytes per head vs LLC target. - Launch FMHA forward repeatedly per head-group by slicing Q/K/V/O (and related tensors). - For `bhsd` input layout (`i_perm/o_perm=1`), apply implicit launch-order adjustment: - Keep a single kernel launch. - Reinterpret block linearization in `GetTileIndex` to make execution head-major, improving temporal locality of per-head K/V reuse. Additional integration updates: - Propagate `num_head_q_total` and `head_start` through FMHA args/kargs. - Use global head indexing for dropout RNG stream mapping so grouped launches keep deterministic/consistent dropout behavior. - Keep fallback behavior unchanged when grouping is not beneficial or disabled. ## Test Plan - `test_ck_tile_fmha` - `tile_example_fmha_fwd` ## Test Result - `test_ck_tile_fmha`: all tests passed. - `tile_example_fmha_fwd`: tested this on gfx1100, gfx1151, and gfx1201, and all of them show higher performance compared to the baseline. The improvement is consistent, and performance is well maintained even at long sequence lengths. ./build/bin/tile_example_fmha_fwd -prec=bf16 -mode=0 -b=1 -h=24 -d=128 -s={seqlen} -s_k={seqlen} -lse=0 -iperm={0/1} -operm={0/1} - TFLOPs by sequence length target: gfx1100 layout: bhsd SeqLen | Before | After | Speedup -- | -- | -- | -- 1024 | 56.27 | 61.48 | 1.09x 4096 | 67.10 | 72.27 | 1.08x 8192 | 65.99 | 71.64 | 1.09x 12288 | 61.60 | 76.61 | 1.24x 16384 | 58.99 | 75.74 | 1.28x 20480 | 57.32 | 74.42 | 1.30x 24576 | 56.89 | 74.25 | 1.31x 27280 | 18.93 | 24.48 | 1.29x - TFLOPs by sequence length target: gfx1201 layout: bshd SeqLen | Before | After | Speedup -- | -- | -- | -- 1024 | 66.79 | 65.90 | 0.99x 4096 | 85.90 | 86.80 | 1.01x 8192 | 77.06 | 90.29 | 1.17x 12288 | 58.36 | 88.98 | 1.52x 16384 | 52.12 | 88.88 | 1.71x 20480 | 48.11 | 88.42 | 1.84x 24576 | 47.12 | 89.07 | 1.89x 27280 | 49.05 | 50.31 | 1.03x ## Submission Checklist - [x] Look over the contributing guidelines at https://github.com/ROCm/ROCm/blob/develop/CONTRIBUTING.md#pull-requests.
Composable Kernel Tile
concept
ck_tile provides a programming model with templated abstractions to enable users to implement performance-critical kernels for machine learning workloads. introduces following basic concepts to help users building your own operator
- tensor coordinate transformation, this is the core concept of layout/index transform abstraction in both compiler time and run time.
- tile-based programming model, including tile-level api and the concept of distributed tensor.
ck_tile is independently from the old ck, located under /include/ck_tile. You don't need to include anything from old CK, ck_tile has similiar (indeed almost the same) implementations for users to build operators. We will have a transition period to pull everything from old ck into ck_tile, stay tuned.
component
ck_tile is splitted into several componenets including core, host, ops/gemm, ops/fmha... each component you only need to include a single header (e.g #include "ck_tile/core.hpp", #include "ck_tile/ops/fmha.hpp") then you are able to use the function/structure inside (different from old ck)
[core]
ck_tile/core contains all the basic data structure and function to build the kernel, you can only include this header and build your own operators that utilizing all the basic building blocks introduced in ck.
core/container
- array, store runtime variables with fixed length (tensor index, register buffer, etc...)
- tuple, same as std::tuple, hold different type of data, and one of the solution to achieve multiple buffer.
- sequence, compile time integer sequence used to build various internal structures, or to describe tile size
- other convenient structure build on top of above 3
core/numeric
- gpu data type like
fp16_t,bf16_t,fp8_t... and the conversion between each other - constexpr integer similiar to std::integral_constant to be used as compile time integer.
- math functions and numeric utilities
core/algorithm
- coordinate transformation system, used to build tensor transform and compile time indexing. This is the core idea introduced in old
ckto describe how a tensor is build by several basic transform primitives likemerge/unmerge/embedetc... and how we indexing into a ND tensor that finally mapped to 1D memory offset.
core/tensor
- tensor descriptor, to describe how a ND tensor
- distributed tensor, describe the storage of this tensor, and the distribution of how a collection of threads collaborately work for this tensor.
- tile level API, including
load_tile,store_tile,shuffle_tile,slice_tile, etc...
[host]
ck_tile/host contains all the host side utilities to launch a kernel, create the device buffer, and some reference implementations. This can be used to create examples (like that under ck_tile example folder) and simple executable to invoke this kernel, so if you only need ck_tile to build your own device library then it's OK to not include this. Based on this, it is recommended to include the specific header you needed under this folder to avoid including unwanted headers (e.g, only include ck_tile/host/kernel_launch.hpp), unless you are writing a host executable.
[ops/gemm, ops/fmha, ops/reduce...]
our implementation of different device operators.
- warp, warp tile level operator
- block, block tile level operator
- pipeline, pipeline that can achieve a customized tile level mainloop (or epilogue). By switching different pipeline to the kernel template you can have different kind of pipeline optimizations.
- kernel, template interface for users to instantiate a particular kernel
[ops/epilogue]
epilogue part of our kernel. We may extend this epilogue part to let users to build their own cutomized epilogues.
[ref]
reference implementation of cpu or gpu. This folder is supposed to include a specific header on demand.
examples
currently we put all ck_tile related example under /example/ck_tile folder. Please check each example's subfolder.