JIT on WinUAE

[AMIGASYSTEM]

Ciao Toni, i noticed that when using it JIT the CPU 020/030/040/060 they have the same power/speed, even in some cases 020/030 they are faster 060

[Romanujan]

I can't believe you are surprised...

[AMIGASYSTEM]

In life you can not know everything

give me a technical explanation, thank you

[Dunny]

JIT runs as fast as possible - you know how it works, I'm sure, but if you don't then here's a very, very brief and cut-down explanation:

It analyses code as it runs, and blocks of code (usually between branches) are converted into native x86 code. These blocks are stored so that the next time the virtual CPU encounters them it just runs the block instead of emulating. In a (very) good JIT implementation, you can get very close to native speed if you don't have weird graphics and sound stuff to do.

In theory the 060 and 020 should be identical from a JIT point of view, but perhaps there are things the 060 does that cannot be neatly fit into the JIT methodology, or perhaps it performs more operations (albeit much much faster) than the 020 for things like tracking memory usage, caches etc which when performed even in native code take away time that could be better used running the Amiga code. So the 020 seems faster because it has less to do.

In the real world, the 060 is faster because although it has more to do, it can do it (and the same job the 020 is doing) faster. But JIT levels the playing field and renders the 060 pretty pointless.

I'm sure Toni can offer a better explanation.

[AMIGASYSTEM]

Yes thanks Dunny, more or less I knew this, but doing some software tests I did not notice any difference, see screenshot, executed emulator DGen (that requires so many resources) and i get same speed itself FPS with either 020 that 060

[Toni Wilen]

Fastest possible has always same speed, CPU model won't make any differene as long as code uses same instructions. (=FPU vs no FPU of course make a difference or if code dynamically selects CPU model specific code but note that JIT does not support all 68020+ only instructions which can make 68020+ optimized code _slower_ in JIT mode.)

It is same in all emulators that has "fastest possible" mode.

Real 68060 is faster because thats the whole point of new CPU model!. To have more hardware (cache, scheduling, multiple execution units etc) to execute code faster!

[Dunny]

Originally Posted by AMIGASYSTEM

Yes thanks Dunny, more or less I knew this, but doing some software tests I did not notice any difference, see screenshot, executed emulator DGen (that requires so many resources) and i get same speed itself FPS with either 020 that 060

Hang on, you just said that you get faster speeds when running 020/030, but now you're saying they're the same speed?

[AMIGASYSTEM]

Originally Posted by Dunny

Hang on, you just said that you get faster speeds when running 020/030, but now you're saying they're the same speed?

All depends from what yes run, but roughly they are equivalent

[turrican3]

Originally Posted by AMIGASYSTEM

Yes thanks Dunny, more or less I knew this, but doing some software tests I did not notice any difference, see screenshot, executed emulator DGen (that requires so many resources) and i get same speed itself FPS with either 020 that 060

what's your pc spec ? by the way, the sound is working ?

[AMIGASYSTEM]

I have an old Pentium DualCore E630 2.80Gz 4GB RAM, OS Windows7 32Bit. Regarding the audio if you are referring to DGen he is working on it emufan, you can read HERE

[AMIGASYSTEM]

Ciao Toni, i found that with the program "WhichAmiga" CPU 68040/JIT turns out to be much faster than the CPU 68060/JIT (more than double),
With each test the values are always different.

CPU 68040 From 900 to 1.200 MHz
CPU 68060 From 300 To 450 MHz

[Toni Wilen]

It is most likely program getting confused by weird CPU speeds. Attempting to guess CPU frequency is hopeless attempt in JIT mode.

Don't trust benchmarks in emulation that try to guess something that can't be measured without real CPU specific behavior assumptions.

[AMIGASYSTEM]

Thank you Toni i sensed I wanted confirmation