Add vectorization sample. #1067
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Currently a draft because I seem to have encountered an AGP bug that makes cross-module dependencies flaky, so I may need to deal with The code itself wouldn't change to accommodate that though. Aside from the todo about checking |
vectorization/README.md
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| making for less concise code than is needed for a constrained vector size like | ||
| we have here, handle windowing of data to fit the hardware vector size for you. | ||
| For problems like the small matrix multiply we do here, it's overkill. For | ||
| portability to a wide variety of (Arm) CPUs, it can reduce the difficulty of |
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this makes it sound more available than it is ... "qualcomm has not shipped SVE" is a pretty huge caveat for real-world use.
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That's fair. I've toned it down, but avoided being specific because I know we won't remember to come fix it as the hardware does roll out. PTAL
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Added a fair amount of content to the readme for explaining FMV (to the best of my knowledge, anyway, and since I learned it all just now it might be wrong). That probably belongs on DAC rather than here, but it can go here for now. |
vectorization/README.md
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| that it is limited by the width of the vector registers for the target hardware. | ||
| To deal with problems that don't fit in the target's vector registers, you would | ||
| need to either alter the algorithm to tile the operations, or use Scalable | ||
| Vector Extensions (AKA [SVE]). |
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does SVE actually help with this problem? (have you considered that negge might be a better reviewer for this stuff? :-) )
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I pointed him at it a few days ago but haven't heard back yet. @negge explicitly now that I know his github username :)
| support big endian, so we can ignore that caveat) is use the `*` operator and | ||
| leave the correct instruction selection up to Clang. | ||
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| In other words, you should probably never use the Neon-specific approach. The |
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(this really seems worth a separate note on the d.a.c neon page...)
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Yes. One thing at a time though :)
Deriving pointer alignment essentially makes this do nothing, since for whatever reason (fighting with Studio maybe?), for new files it's deriving the wrong style.
This adds a new generic vectorization sample to replace hello-neon. Most importantly, it covers non-Neon options for SIMD. One of the useful things it shows, for example, is that there's actually no reason to write SIMD code the way that hello-neon does any more. This also solves a much simpler problem (small matrix multiplication), which makes it easier to see how to deal with the SIMD features rather than figuring out what a FIR filter is. Finally, this sample benchmarks each of the implementations so it's obvious what is and isn't worth doing. I was sort of surprised that auto-vectorization didn't do better, and was pleased to learn that there's no reason at all to write Neon intrinsics. I'll delete hello-neon after this merges and I've fixed up the doc links. android#1011
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This adds a new generic vectorization sample to replace hello-neon. Most importantly, it covers non-Neon options for SIMD. One of the useful things it shows, for example, is that there's actually no reason to write SIMD code the way that hello-neon does any more.
This also solves a much simpler problem (small matrix multiplication), which makes it easier to see how to deal with the SIMD features rather than figuring out what a FIR filter is.
Finally, this sample benchmarks each of the implementations so it's obvious what is and isn't worth doing. I was sort of surprised that auto-vectorization didn't do better, and was pleased to learn that there's no reason at all to write Neon intrinsics.
I'll delete hello-neon after this merges and I've fixed up the doc links.
#1011