Installing flash-attn without compiling it

python/installing-flash-attention.md

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+# Installing flash-attn without compiling it
+
+If you ever run into instructions that tell you to do this:
+```bash
+pip install flash-attn --no-build-isolation
+```
+**Do not try to do this**. It is a trap. For some reason attempting to install this runs a compilation process which can take _multiple hours_. I tried to run this in Google Colab on an A100 machine that I was paying for and burned through $2 worth of "compute units" and an hour and a half of waiting before I gave up.
+
+Thankfully [I learned](https://twitter.com/Sampson4242/status/1849666226299281443) that there's an alternative: the Flash Attention team provide pre-built wheels for their project exclusively through GitHub releases. They're not uploaded to PyPI, possibly because they're 180MB each or maybe because PyPI can't automatically pick the correct torch version?
+
+Whatever the reason, you can find them attached to the most recent release on https://github.com/Dao-AILab/flash-attention/releases
+
+But which one should you use out of the 83 files listed there?
+
+Google Colab has a "ask Gemini" feature so I tried "Give me as many clues as possible as to what flash attention wheel filename would work on this system" and it suggested I look for a `cp310` one (for Python 3.10) on `linux_x86_64` (Colab runs on Linux).
+
+In browsing through the list of 83 options I thought `flash_attn-2.6.3+cu123torch2.4cxx11abiFALSE-cp310-cp310-linux_x86_64.whl` might be the right one (shrug?). So I tried this:
+```
+!wget https://github.com/Dao-AILab/flash-attention/releases/download/v2.6.3/flash_attn-2.6.3+cu123torch2.4cxx11abiFALSE-cp310-cp310-linux_x86_64.whl
+!pip install --no-dependencies --upgrade flash_attn-2.6.3+cu123torch2.4cxx11abiFALSE-cp310-cp310-linux_x86_64.whl
+```
+This _seemed_ to work (and installed in just a couple of seconds):
+```python
+import flash_attn
+flash_attn.__version__
+```
+```
+2.6.3
+```
+But the thing I was trying to run ([deepseek-ai/Janus](https://github.com/deepseek-ai/Janus)) failed with an error:
+
+> `NameError: name '_flash_supports_window_size' is not defined`
+
+At this point I gave up. It's possible I picked the wrong wheel, but there may have been something else wrong.
+