ROCm: make CK FA2 default instead of Triton (#1924)

As per title.

Triton autotune overhead is prohibitive, as it needs to be done for each
different prompt length.

Dockerfile_amd

@@ -117,8 +117,9 @@ RUN cd pytorch && python tools/amd_build/build_amd.py && python setup.py install
 # Set as recommended: https://github.com/ROCm/triton/wiki/A-script-to-set-program-execution-environment-in-ROCm
 ENV HIP_FORCE_DEV_KERNARG=1
 
-# On MI300, performances for flash with Triton FA is very competitive (actually better than CK)
-ENV ROCM_USE_FLASH_ATTN_V2_TRITON=1
+# On MI250 and MI300, performances for flash with Triton FA are slightly better than CK.
+# However, Triton requires a tunning for each prompt length, which is prohibitive.
+ENV ROCM_USE_FLASH_ATTN_V2_TRITON=0
 
 FROM base AS kernel-builder
 

docs/source/installation_amd.md

@@ -29,7 +29,7 @@ TunableOp is enabled by default, the warmup may take 1-2 minutes. In case you wo
 
 Two implementations of Flash Attention are available for ROCm, the first is [ROCm/flash-attention](https://github.com/ROCm/flash-attention) based on a [Composable Kernel](https://github.com/ROCm/composable_kernel) (CK) implementation, and the second is a [Triton implementation](https://github.com/huggingface/text-generation-inference/blob/main/server/text_generation_server/utils/flash_attn_triton.py).
 
-By default, as its performances have experimentally been better, Triton implementation is used. It can be disabled (using CK implementation instead) by passing `--env ROCM_USE_FLASH_ATTN_V2_TRITON="0"` when launching TGI's docker container.
+By default, the Composable Kernel implementation is used. However, the Triton implementation has slightly lower latency on MI250 and MI300, but requires a warmup which can be prohibitive as it needs to be done again for each new prompt length. If needed, FA Triton impelmentation can be enabled with `--env ROCM_USE_FLASH_ATTN_V2_TRITON="0"` when launching TGI's docker container.
 
 ## Unsupported features