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M4 chips: Matrix processing and Power Modes
A matrix multiplication test appears to be run on the AMX matrix co-processor, and behaves differently from in-core tests. And what Power modes really do.
When the M4 first became available in iPads earlier this year, researchers concluded its chip has a new AMX co-processor that can now be programmed using SME matrix extensions supported by the new version of the Arm instruction set in the M4, ARMv9.2-A. Frequencies are controlled by macOS, and this suggests it adopts a standard pattern when running the two in-core tests, and a different one for vDSP_mmul presumably geared to performance of the AMX. Key information vDSP_mmul matrix multiplication from the vDSP sub-library in Accelerate behaves consistently with it being performed in the AMX co-processors in M4 Pro chips.
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