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Comment by lunixbochs | Hacker News Reader

You can do this in the 99% case on Linux using qemu-user, but I'm not aware of an equivalent for Windows (and booting an entire operating system in an emulator is a poor experience and will be even slower). I imagine this Windows variant works like qemu-user and Rosetta.

QEMU has some bad performance penalties, I think partially related to the generic JIT (TCG), extremely strict floating point, and full host memory isolation. ExaGear is significantly closer to native performance but I think only supports emulating 32-bit x86.

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This is a trade-off with any emulation really. The more hardware accurate your emulation gets, the more you have to keep track of in virtual registers and state, and all that extra tracking adds up in a hurry.

Native virtualization dodges a lot of that performance penalty by using the hardware features directly where possible. But that's only really feasible on systems that have nearly identical hardware; x86 is pretty standardized at this point and virtualizes quite well. ARM is much more varied and harder to virtualize, even on other ARM platforms due to differing feature sets.

It's not that in this case, this is plain binary translation and not cycle accurate emulation. QEMU is super slow on x-to-x translation as well (something like 8x to 80x slowdown). Its translator is inefficient (for the sake of portability, the source native code is first translated to an IR and then the IR is compiled to target native code with limited optimisation) and it emulates all floating point instructions in software.

How does it handle polymorphic code?

And these guys ship an x86 to ARM DBT which they claim has significantly better performance: https://eltechs.com/product/exagear-desktop/. I haven't tried it. QEMU is the slowest DBT system I'm aware of, so it's entirely plausible. Translating from a strongly ordered architecture to a weakly ordered architecture is big challenge, I wonder if they handle threads efficiently.

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