what makes an emu faster than the other ?

[akimikage]

I wanna learn why one emu is faster than the other. Besides the specs of the console it emulates I really have no idea why one emu runs faster than others.

For example : PCSX2 for PS2 , Dolphin for Wii, JPCSP and PPSSPP for PSP. With my current hardware I can run PCSX2 and PPSSPP just fine without any hiccups in speed while I have trouble running Dolphin and JPCSP. I know Wii has the highest specs so it's normal that I may not run it properly but what about JPCSP and PPSSPP ? They emulate the same console but I can hardly run games properly on JPCSP.

[slamandar]

SIMPLE and with no hard develepers word and staff ( no offense ) : JPCSP need java to run so its like an emulator inside an other emulator , you see ? thats way ppsspp is the best psp emulator on multiplatforme ^^

[akimikage]

I see, so that's why. Thanks
Is that the only reason though ?

[Razorback]

Code optimizations and code optimizations.

[VvGHOSTvV]

Better coding = better speed.

[cloud1250000]

It's all about choice. jpcsp didn't choose the good language first, java's too slow to be efficient in this kind of emulation (we are talking about ms and even smaller operation time).... Also, hle vs lle, hle tend to give better result in performance vs lle tend to give more accurate emulation but that's hitting the performance. The jit system is also very important, the more a jit is complete, the better the speedup will be (but then, there's still some cpu operation that's useless to jit).. Emulation hack is also an hard choice for emulator maker, usually they like accurate emulating and they ditch those kind of hack, but pcsx2 didn't have the choice to allow them since the ps2 is retarded and since they want to get good speed on lower specs computer. And then the OPTIMISATION begins... and dolphin and pcsx2 are much likely in those state now, there's always better coding method discovered while you're making an emulator, and your first code doesn't look like the one you just pushed (if you're working on it for years at least). It's all about going all over the old code, reformating and optimizing. Also, the graphic rendering backend can also be an important choice, dirextx is performing well on windows and it's more simple then opengl... while opengl is avalaible on multiple system and allow more advanced rendering stuff. If you can achieve something with two line vs 50 lines, they'll probably use the two line solution (and it should pay in much higher performance)


I think it's all about graphic backend, maturing in coding skill, jit, and dev choice (performance vs accurate, accurate exclude all form of hack)

[TheDax]

About your last bit, Cloud:

There are varying degrees of accuracy. Accurate doesn't necessarily mean no hacks at all; if for example you can get the same effect with a hack that has no bad effects, but increases performance 20%, there's no reason not to do it, unless you're aiming for "pure" code, or perhaps if it makes your code unreadable.

[cloud1250000]

yeah ahah I knew that I shouldn't make that kind of absolute statement -,-

There's one thing that's still mystifying me... how an emulator can read the machine code from a game image -,-

[Squall]

Java does not allow dynrec, therefore it will never be good for emulators.

Another problem are emulators created for "documentation" purposes. Thus, accuracy is more important than speed. Some operations are invalid in real hardware and no game executes these operations. Some faster emulators allow these invalid operations. While it does not break real games, some hacks and homebrews may execute it and consequently they may not work in real hardware and other emulator of the same system.

Byuu (creator of bsnes) had a good explanation about accuracy, but he deleted the articles.

[akimikage]

Oh yeah, I just want to ask. Is it harder to code the emu to run using the GPU rather than the CPU ? I was just wondering why won't the coders assign the processing to the GPU when GPU's are a lot faster on processing data than the CPUs today.

[Squall]

GPU is good for 3D rendering and PPSSPP, Dolphin and PCSX2 use it.
Desmume is slow because it does not use GPU.

If you are talking about GPGPU, it is good for parallel data processing, but it is not good for emulation.

[cloud1250000]

drastic isn't using the gpu at all too

[akimikage]

Another question. hehe
Is virtual overclocking any good on emulation ? PPSSPP is the only emu where I saw this kind of feature. So I'm wondering if it's any beneficial when it comes to speeding up emulation. If so, is it hard to implement ? coz if it's beneficial why won't the others implement it as well ?

[VIRGIN KLM]

NDS does not do frameskipping like PSP or PS2 so overclocking the CPU = game running on a faster speed, downclocking the CPU = slower game speed. FPS and Speed are linked.

[akimikage]

uhh... so is it hard to implement ? why won't the others implement it as well ?