[SPMD] Mesh to support custom device order. #4162
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| ), "PyTorch/XLA SPMD requires PJRT_DEVICE={CPU, TPU}, GPU is currently not supported." | ||
| ) | ||
| @unittest.skipIf(not using_pjrt() or xm.get_xla_supported_devices("GPU"), | ||
| f"Requires PJRT_DEVICE set to `TPU` or `CPU`.") |
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@will-cromar I think PJRT-GPU single core is ready now?
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It's blocked from the our SPMD side, once we support TPU, the transition should be easier to GPU -- maybe sometime next year once we are done with the basic/core SPMD features?
| Args: | ||
| device_ids (Union[np.ndarray, List]): A raveled list of devices (IDs) in a custom order. The list is reshaped | ||
| to an `mesh_shape` array, filling the elements using C-like index order. For example, |
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where is the example lol?
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oh ok it is below, you might want to change the wording here.
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| mesh_shape (Tuple[Union[int, None]]): A int tuple describing the logical topology | ||
| of the device mesh, and each element describes the number of devices in | ||
| the corresponding axis. |
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Looks like mesh_shape can be removed here
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| def test_custom_tile_assignment(self): | ||
| xt = torch.randn(10, 20).to(device=xm.xla_device()) | ||
| mesh_shape = (1, self.n_devices) |
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I see the tests have all devices mapped to a single axis - is there anything stopping us from using e.g. mesh_shape = (2, self.n_devices / 2)?
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No, but for the unit testing a flat mesh is easier to work with since we don't know how many devices we would have (e.g., for CPU, we will have 1).
| def __init__(self, | ||
| device_ids: Union[np.ndarray, List], | ||
| mesh_shape: Tuple[int, ...], | ||
| axis_names: Tuple[str, ...] = None): |
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Just curious - how will axis_names be used long-term? Is it just for annotating the mesh?
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Good question, mesh axis annotation is useful since it makes the annotation logic more readable. We can also build a partitioning rule based on the axis name, instead of int indices.
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This implements
Meshclass from #3871 , to support custom device order in logical XLA device mesh topology.