On the few tests which don't have anything to do with vector units, Power9 does incredibly well. See 7-Zip Compression, Stockfish, Fhourstones, LLVM compiles. Power9 is very, very far ahead of the game here.
When vector units (ie: OpenMP or intrinsics) are involved: such as Parboil, Gimp, x264, Rodinia, etc. etc. the Power9 does very poorly.
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Something else I've noticed: Power9 has a lot of latency behind its units: it is always 2-cycles or 3-cycles of latency (while EPYC or Skylake have many operations with 1-cycle of latency, like add or subtract). Power9 relies upon instruction-level parallelism to get things done.
So there are a few cases like the Rust Mandelbrot benchmark, which surely hits that latency problem, while the Rustlang Prime benchmark shows off the ILP goodness the system offers.
phoronix.com just published some Power9 vs. Xeon vs Epyc benchmarks[1]. It is actually not on par with Xeon/Epyc. also note that the motherboard used by those Power9 has a price tag of $2499, when a dual socket LGA3647 motherboard from a first tier vendor can be purchased at $400 delivered.
[1] https://www.phoronix.com/scan.php?page=article&item=power9-x...