Update and document GPU buffer handling #2751
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This updates how we handle GPU buffers. See the new docs page for a simple example. The basic idea, as discussed in ..., is to use host buffers for all metadata objects and device buffers for data. Zarr has two types of buffers: plain buffers (used for a stream of bytes) and ndbuffers (used for bytes that represent ndarrays). To make it easier for users, I've added a new config option `zarr.config.enable_gpu()` that can be used to update those both. If we need additional customizations in the future, we can add them here.
TomAugspurger
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Still looking at this, but there is currently a copy to the host for running Zstd (the cc @madsbk. |
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This should be ready for review now. This fixes the issue with storing metadata in host memory, rather than device memory. It adds a convenience function for setting up everything to use GPUs. Currently, that just sets the buffer prototype. In the future, I think it could also update the default codecs to use GPU codecs. https://gist.github.com/TomAugspurger/ba13bc29b27f587ae4709ac7f30d89c8 has a snippet hacking together an example of what that future might look like, but IIUC @akshaysubr is working on new APIs for compression / codecs, so IMO it makes sense to address that separately. For now, I've left a note that codecs will run on the CPU by default. |
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@dstansby would you be able to confirm that I did the changelog correctly? Happy to add a note to the contributing guide like
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Release notes look good to me 👍 Adding that text in our contributor guide would be awesome (and TIL that you can use |
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Should be good to go. |
| """ | ||
| Configure Zarr to use GPUs where possible. | ||
| """ | ||
| return self.set( |
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I believe this shows it's covered: https://app.codecov.io/github/zarr-developers/zarr-python/blob/TomAugspurger%2Fzarr-python%3Atom%2Ffix%2Fgpu/src%2Fzarr%2Fcore%2Fconfig.py#L66
Maybe the warning comes from the CPU-only coverage run?
This updates how we handle GPU buffers. See the new docs page for a simple example.
The basic idea, as discussed in #2574 is to use host buffers for all metadata objects and device buffers for data.
Zarr has two types of buffers: plain buffers (used for a stream of bytes) and ndbuffers (used for bytes that represent ndarrays). To make it easier for users, I've added a new config option
zarr.config.enable_gpu()that can be used to update those both. If we need additional customizations in the future (like gpu-accelerated codecs), we can add them here.I've opened this as a draft for now. I want to look a bit more at exactly when data is copied between the host and device. Right now, it looks like the default Zarr v3 codec pipeline will automatically transfer bytes to the host in
ZstdCodec._encode_single:zarr-python/src/zarr/codecs/zstd.py
Line 88 in 0c154c3
This PR ensures that you end up with GPU bytes when reading data, but all data I/O and encoding / decoding still happens on the CPU. I think in the future we'll be able to do more work on the GPU while avoiding copies back to the host.
TODO:
docs/user-guide/*.rstchanges/Clsoes #2574