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Old 22 June 2019, 10:39   #1
Sim085
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030 vs 040 with fastest possible option ticked

I always thought that with fastest possible option ticked there would not be a bumb in speed between 030 and 040 or even 000 and 040. I always thought you only has to change cpu depending on requirements of application (ex use 040 if application compiled for this).


Yesterday however I installed NetSurf. When I selected 030 (+FPU) it was barely usable. When I selected 040 it was usable. So why is NetSurf faster on 040 when in both cases I have fastest possible option ticked?
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Old 22 June 2019, 12:54   #2
Toni Wilen
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Perhaps you also had some other options selected that would affect speed? (like more compatible)
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Old 22 June 2019, 16:36   #3
quantum8
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Maybe it makes use of opcodes specific to the 040 that help speed things up.
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Old 22 June 2019, 17:07   #4
Toni Wilen
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MOVE16 is the only new user space instruction which can't explain the difference. Another possibility is FPU and program prefers to use single/double FPU instruction variants that are 68040+ (but that would have caused a crash unless program uses separate code path if 68030+FPU is detected)

Check also FPU mode, usually 64-bit host is the most optimal choice between speed and accuracy. 80-bit host mode is more accurate but mainly needed when running some math applications. Softfloat is 100% accurate (and very slow) and only needed in very specific circumstances, for example if you want to run FPU emulation software like 68040/060 missing FPU instructions.
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Old 24 June 2019, 02:32   #5
Sim085
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From what I can see, when moving from 030 to 040, the only thing that changes (automatically) is FPU "CPU Internal" is selected for 040 CPU.

However I only observed a difference with Netsurf (and when loading sites both 030 and 040 look to struggle).
Mostly asked to see if my understanding of fastest possible was correct.

Quote:
Originally Posted by Toni Wilen View Post
Check also FPU mode
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Old 24 June 2019, 20:32   #6
Toni Wilen
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Yeah but speed can change if you don't have "plain" fastest possible CPU mode when switching between different CPUs.

Make sure all following are not set:
- more compatible (both CPU and FPU)
- 24 bit addressing (unlikely to be set)
- Data cache emulation
- Both cycle exact modes (Chipset)

Make sure all following options are set:
- Fastest possible
- Unimplemented CPU emu
- Unimplemented FPU emu
- Immediate blitter (Chipset)

FPU mode = "Host (64-bit)"
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Old 26 June 2019, 21:22   #7
Sim085
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Thanks for this Toni, that did a big change for me!

I had some of the not-to-tick options ticked and some of the to-tick options not ticked. My environment is much faster now.

Many thanks for your advice.

Quote:
Originally Posted by Toni Wilen View Post
Yeah but speed can change if you don't have "plain" fastest possible CPU mode when switching between different CPUs.

Make sure all following are not set:
- more compatible (both CPU and FPU)
- 24 bit addressing (unlikely to be set)
- Data cache emulation
- Both cycle exact modes (Chipset)

Make sure all following options are set:
- Fastest possible
- Unimplemented CPU emu
- Unimplemented FPU emu
- Immediate blitter (Chipset)

FPU mode = "Host (64-bit)"
Sim085 is offline  
 


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