IMac 2010 less CPU performance in Mac OS Monterey

[marvin_95l]

Hello,

I have an iMac 2010 27 inch, with an Intel i7 870 and a NVIDIA Quadro K3000M GPU upgrade. I recently updated from Mac OS Big Sur to Mac OS Monterey 12.4 and found that I have less performance than in Big Sur.
I then tested it with Cinebench R20. In Big Sur I got 1034 points and in Monterey it's only 576. Both OS ran with Opencore.

Does anyone have an idea or knows the solution? Half the performance is clearly noticeable in some cases.

Thanks to everyone who wants help me.

 

[pshufd]

I think that Monterey requires the AVX instruction set and register support and that OpenCore emulates AVX if the hardware doesn't support it. I'd guess that Big Sur and earlier used the SSE* instruction sets to do the same work but Apple went to AVX (which uses larger registers and has more parallel operations) and so that has to be emulated now.