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The competition is very much bound to a rather narrow ISA which is why CUDA is forward and backwards compatible whilst ROCm isn’t. ROCm will be pointless until

The competition is very much bound to a rather narrow ISA which is why CUDA is forward and backwards compatible whilst ROCm isn’t. ROCm will be pointless until at least forward compatibility will be guaranteed by design.

nimish 3y ago
CUDA is subsequently compiled to the hardware assembly at runtime isn't it? Like precompiled shaders. C++ -> PTX -> Hardware ISA
StillBored 3y ago
How so? One of the ROCm layers is opencl which does runtime target compilation, and there is also the various intermediate language representations. So, presumably much of this is just lack of sufficient resources to assure that all the different combinations are optimally being compiled down on all the independent HW devices. This was always the OpenCL problem too back before everyone just started using CUDA rather than trying to use it. It worked in a lot of places but the higher level code needed to be adjusted for individual devices because each vendor would do a reasonable job maintaining optimal code generation for their target given code optimized for their target, but switching vendors (AMD<->nvidia) would result in needing two different versions of the code tuned for the individual vendors ideas of how code should be tuned for their platform. If that wasn't clear say you wrote and optimized code for vendor A's device X, when vendor A released device Y, things tended to work well, but moving that code to vendor B's devices basically required retuning/rewritting things.
mathisfun123 3y ago
Someone else already said it but it beats repeating: this is wrong > The competition is very much bound to a rather narrow ISA which is why CUDA is forward and backwards compatible whilst ROCm isn’t. PTX isn't an ISA and it goes through another translation step before it hits the real ISA (SASS), which does change internally. Though you are right that PTX as intermediate is part of the reason for CUDA's success in that it makes the code portable across cards.

nimish 3y ago

CUDA is subsequently compiled to the hardware assembly at runtime isn't it? Like precompiled shaders. C++ -> PTX -> Hardware ISA

StillBored 3y ago

How so? One of the ROCm layers is opencl which does runtime target compilation, and there is also the various intermediate language representations. So, presumably much of this is just lack of sufficient resources to assure that all the different combinations are optimally being compiled down on all the independent HW devices. This was always the OpenCL problem too back before everyone just started using CUDA rather than trying to use it. It worked in a lot of places but the higher level code needed to be adjusted for individual devices because each vendor would do a reasonable job maintaining optimal code generation for their target given code optimized for their target, but switching vendors (AMD<->nvidia) would result in needing two different versions of the code tuned for the individual vendors ideas of how code should be tuned for their platform. If that wasn't clear say you wrote and optimized code for vendor A's device X, when vendor A released device Y, things tended to work well, but moving that code to vendor B's devices basically required retuning/rewritting things.

mathisfun123 3y ago

Someone else already said it but it beats repeating: this is wrong > The competition is very much bound to a rather narrow ISA which is why CUDA is forward and backwards compatible whilst ROCm isn’t. PTX isn't an ISA and it goes through another translation step before it hits the real ISA (SASS), which does change internally. Though you are right that PTX as intermediate is part of the reason for CUDA's success in that it makes the code portable across cards.