Initial draft

post/2024-10-02-metal-1.4.md

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+title = "Metal.jl 1.4: Metal.rand"
+author = "Christian Guinard"
+abstract = """
+  Metal.jl 1.4 adds higher-quality on-device random number generation from Metal Performance
+  Shaders. Some limitations apply, with fallback to the previously-existing rand
+  implementation in those situations."""
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+{{abstract}}
+
+## Metal.rand and friends
+
+Using functionality provided by the Metal Performance Shaders, improved on-gpu random number
+generation has been implemented. Uniform distributions using `Metal.rand` (and its in-place
+variant `Metal.rand!`) are available for all Metal-supported integer types and Float32.
+However, due to Metal [API](https://developer.apple.com/documentation/metal/mtlblitcommandencoder/1400767-copyfrombuffer?language=objc)
+limitations, 8-bit and 16-bit integers may fall back to the lower-quality GPUArrays.jl random
+numbers if their size in bytes is not a multiple of 4. Normally distributed Float32 values can be
+generated for with `Metal.randn` and `Metal.randn!`. Float16 is not supported by the Metal
+Performance Shaders RNG, and will always fall back to the GPUArrays implementation.
+
+The easiest way to use these is to use the Metal convenience functions `Metal.rand[n][!]`
+as you would the usual functions. However, the regular Random.jl methods can also be used
+by providing the appropriate `RNG` either from `MPS.default_rng()` or `MPS.RNG()` to the
+standard `Random.rand[n][!]` functions.
+
+
+
+## Other improvements since the last blog post
+
+- Since v0.5: `MtlArray` storage mode has been parameterized, allowing one to create a shared storage `MtlArray`
+  by calling `MtlArray{eltype, ndims, Metal.SharedStorage}(...)`.
+- Since v0.3: MPS-accelerated decompositions were added.
+- Various performance improvements
+- *Many* bug fixes.
+
+
+## Future work
+
+Although Metal.jl is now in v1, there is still work to be done to make it as fast and
+feature-complete. In particular:
+
+- since the last blog post, Metal.jl has started using native ObjectiveC FFI for wrapping
+  Metal APIs. However, these wrappers have to be written manually for every piece of
+  Objective-C code. We are looking for help improving Clang.jl and ObjectiveC.jl to enable
+  the automatic generation of these wrappers. See tracking [issue](https://github.com/JuliaInterop/ObjectiveC.jl/issues/41);
+- the MPS wrappers are incomplete, automatic wrapper generation would greatly help with
+  full MPS support;
+- support for atomic operations is missing, which is required to implement a full-featured
+  KernelAbstractions.jl back-end. See tracking [issue](https://github.com/JuliaGPU/Metal.jl/issues/218);
+- full support for BFloat16 values, which has been supported since Metal 3.1 (macOS 14),
+  is not yet in Metal.jl. See tracking [issue](https://github.com/JuliaGPU/Metal.jl/issues/298);
+- some functionality present in CUDA.jl could be ported to Metal.jl to improve usability.
+  See tracking [issue](https://github.com/JuliaGPU/Metal.jl/issues/443);
+- general performance improvements. In particular, improvements to the ObjectiveC.jl type model
+  could greatly reduce the number of allocations currently necessary for every
+  Objective-C/Metal operation. See tracking [issue](https://github.com/JuliaInterop/ObjectiveC.jl/issues/13).