[hatari-devel] DSP performance

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Just a quick note - perhaps someone can have a look and confirm that the DSP in Hatari is correctly counting cycles w.r.t. the emulation master oscillator?

On closer inspection of my profile results (not using Hatari's profiler but rather using an MFP based profiler and comparing Hatari with HW) I see what looks like a 50% performance benefit on Hatari's side.

i.e. the DSP seems to be clocked at 50MHz or something like that. This sort of explains some of the performance differences I noticed when I picked up Hatari 1.9 and also explains why I didn't run into any timing issues straight away - a faster DSP hides most of the types of issues I would have hit.

Basically what I see is that the CPU timings appear fairly similar to Hatari up to v1.8 - most functions have comparable durations with real HW, perhaps a bit too favourable in places - but the DSP performance has magically gone up by a big margin. One of the DSP-only routines (when serialized for measurment) records 15.5ms on real HW, but only 9.5ms in Hatari.

Anyway I haven't had time to confirm this 100% other than via the profiler I mentioned - it needs to be done in another way to be sure. I'll try to do this with a cycle counter later and see if results tie up. But if anyone has an explanation meantime that would help :D


Ok I quickly ran DSPBENCH on Hatari 1.9 and this confirms a magical 70% speed increase over real HW...

I don't think my own project is affected by this as much as it might have been, because DSP time is often hidden/overlapped - but it does show quite obviously in some cases.


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