I'm also always amazed at the hardware reqs for emulators. They suggest at least an i5 or i7 and recommend a dedicated gpu! For a gamecube! Released 15 years ago!
As for performance: Using software to implement behavior equivalent to specific hardware is almost inherently inefficient. JIT-style processing of the opcodes helps, but you're still going to use multiple operations on the host CPU for each one that you execute from the guest code. Plus emulation of device synchronization that would've originally been done in hardware and that don't have direct equivalents on the host hardware.
But it works well enough for most games even with an integrated Intel GPU, as long as you don't try to improve on the base game too much (resolution, filtering, etc..)
The emulators that exist today don't have to emulate a single CPU, that would be trivial, but the surrounding hardware.
Here's an example of someone trying to emulate a 6502-based computer (BBC Micro) and the problems they encountered when trying to run Elite, just one game: https://www.youtube.com/watch?v=RiE5pTisEd8
Older games used any optimization they could get, and they'd often exploit quirks in the hardware if it made things work better. Elite flips video modes part-way through the rendering of the screen since it was made in an era of CRTs. Trying to reproduce that effect in a frame-buffer type system is hell.
So most of the emulators out there have to fake a lot of things in order to get software and games to run properly, or at all.
Not really. The emulators for recent systems don't try to emulate the hardware anymore, they emulate the outcome of the system calls and convert them to OpenGL most of the time (HLE).
That's actually necessary for stuff like the PSP. Sony made multiple revisions of the hardware over the course of the PSP life, and therefore relies on such a system anyway to maintain the output identical despite the hardware changes.
You're calling it "emulating the outcome" but that usually means in practice "approximating what the original system does by faking it."
And that's still nowhere near the requirements for cycle-accurate emulation. I'm not sure you can even run a cycle-accurrate N64 emulator on a standard machine.
Yeah, to anyone who has tried to optimize a CPU interpreter before; dynamic recompilers are nothing short of magical.
You'd be quite talented to emulate just a 50 MIPS interpreter core from a sufficiently awkward CPU at 100% speed on modern processors. Let alone all the other parts of the emulator, and synchronization between components.
Of course, dynamic recompilers sacrifice huge amounts of synchronization precision in return for that raw speed. But it's very much a necessary evil -- otherwise we wouldn't have playable modern emulators at all. The developers of dynarecs deserve extra special praise for being willing to give up both idealism and portability when writing them.
If you're saying they hit it at 100% Wii U CPU load at fullspeed, then that's really impressive! :)