English Amiga Board - View Single Post - PED81C - pseudo-native, no C2P chunky screens for AGA

paraj · 04 December 2023, 16:36

Only expected interrupts. However, I've figured out why it's slow on my machine: ATC-misses! If I disable page address translation and rely just on the TTR's I get 34.72 / 28.57 fps respectively.

I timed a small test program that reads a byte from a (pseudo-)random offset into an array and varied the size:

Up to 256KB there are no differences, and the no-MMU case stays flat at around ~375ns/loop iteration, while with MMU it grows to 867 for at 32MB array.

EDIT: 256KB of course lines up perfectly with 64-entry ATC and page size of 4K, and forgot something actionable: Of course being more cache friendly is likely a big rework, but I think grouping (height,color) rather than having separate arrays would likely be an easy win. Obviously you can't just switch switch off MMU w/o consequences, so don't change something like that in your own code.

04 December 2023, 16:36	#69
paraj Registered User Join Date: Feb 2017 Location: Denmark Posts: 1,115	Only expected interrupts. However, I've figured out why it's slow on my machine: ATC-misses! If I disable page address translation and rely just on the TTR's I get 34.72 / 28.57 fps respectively. I timed a small test program that reads a byte from a (pseudo-)random offset into an array and varied the size: Up to 256KB there are no differences, and the no-MMU case stays flat at around ~375ns/loop iteration, while with MMU it grows to 867 for at 32MB array. EDIT: 256KB of course lines up perfectly with 64-entry ATC and page size of 4K, and forgot something actionable: Of course being more cache friendly is likely a big rework, but I think grouping (height,color) rather than having separate arrays would likely be an easy win. Obviously you can't just switch switch off MMU w/o consequences, so don't change something like that in your own code. Attached Thumbnails Last edited by paraj; 04 December 2023 at 19:40.