ZFS is thoroughly 64-bit and uses 64-bit math pervasively. That means you have to emulate all those operations with 2 32-bit values, and on the register-starved x86 platform you end up with absolutely horrible performance.
no this difference isn't that great. it doesn't use much less CPU on the same processor using i386 and amd64 kernels - i checked it.
no precise measurements but there are no more than 20% performance difference - comparable to most programs used in i386 and amd64 mode.
so no "horrible performance" on i386, or if you prefer - always horrible performance no matter what CPU mode.
while x86 architecture doesn't have much registers EAX,EBX,ECX,EDX,ESI,EDI,EBP,ESP 8 total (+EIP) it doesn't affect programs that much, as all modern x86 processors perform memory-operand instructions single cycle (or more than one of them).
anyway extra 8 registers and PC-relative addresses are very useful. this roughly 20% performance difference is because of this.
if you mean gain on 64-bit registers when calculating block checksums in ZFS - it's for sure memory-bandwidth and latency limited, not CPU power.
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