Geekbench multi falls off a cliff after ~16 cores. E.g. the Epyc 9654 with 96 cores benches lower than the Ryzen 7950X with 16 cores of the same generation.
Base Freq Chip
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2.4GHz EPYC 9654
4.7GHz Ryzen 7950X
Geekbench Single Core - Score
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1,827 EPYC 9654
2,986 Ryzen 7950X
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But why? Wouldn’t total score be approximately corecount*corescore? Of course it’s not exactly that because not all cores run full speed at the same time, but how are the cores weighted that 16 cores are better than 96 cores with half the speed each?
Compare this to a multithreaded benchmark that does scale to all of the cores and you'll find the higher core count CPUs are able to push significantly higher scores despite the single thread difference e.g. https://www.cpubenchmark.net/high_end_cpus.html has them at 62,711 vs 117,317 in the opposite ranking direction. That should feel about right, otherwise AMD would only make the 16 core high frequency CPUs instead of 128 core low frequency monsters.
That's not to say the Geekbench score is bad or useless. It represents a specific type of workload... just not "peak multi core performance". It's more indicative of "mixed workload performance", where the extra 2x cores on the Ultra are more apparently going to be irrelevant.
For some reason the Epyc is radically faster for "Ray Tracer" and "Horizon Detection" but worse for "PDF Renderer" and "Background Blur"
It wouldn't surprise me if PDF renderer and background blur were fast enough tasks that spinning up 96 threads to split rendering across all those cores was a waste of time compared to how fast the actual task was to complete. It was akin to trying to hammer in 50 nails by getting 50 people and handing out 50 hammers and assigning each person one nail, then telling them "okay, start!", then inspecting everyone's work afterwards; at some point, it's faster just to break it into two or three tasks.
I ended up using something else to generate the load I needed, but I can’t remember exactly what. I think it might have been a Monero benchmarking tool?
As a performance metric that does seem like it would be more valuable for lots of use cases, so measuring that seems good.
Maybe they need to add an additional “cpu bound multiprocessing perf”, and make it easier for professional tech reporters to understand complex concepts like benchmark numbers :D (in fairness to the reporters it does sound like the benchmark name legitimately implies that it’s a max parallel throughput benchmark, but if this is your job you should really know what your benchmarks are actually measuring).
Honestly a benchmark I would like to - which is more of a software/kernel/os/scheduling one - is “how responsive is this machine under heavy load”.
A non zero part of wanting that as part of a benchmark is that popular benchmarks often seem to be the only way to get companies to fix “uncommon” issues.