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From dankwiki
From Intel Application Note 485, "Intel Processor Identification and the CPUID Instruction", section 3.1.10:
When EAX is initialized to a value of 9, the CPUID instruction returns DCA information in the EAX, EBX, ECX and EDX registers:
EAX: Value of PLATFORM_DCA_CAP MSR Bits [31:0] (Offset 1F8h)
EBX: Reserved
ECX: Reserved
EDX: Reserved
I've got a list of DCA-enabled NICs.