While investigating some HexaPDF test failures, I also played around with the benchmark used by the YJIT team:

https://github.com/Shopify/yjit-bench/tree/main/benchmarks/hexapdf

The performance on JRuby is unusually slow, so I'm guessing something is wrong:

#22: 2017ms
#23: 1975ms
#24: 1969ms
#25: 2056ms

Compared to Ruby 3.4:

#22: 1506ms
#23: 1499ms
#24: 1499ms
#25: 1490ms

And with YJIT:

#22:  762ms
#23:  833ms
#24:  750ms
#25:  833ms

Interestingly, JRuby has a lower RSS than either run of CRuby (679MiB vs 797MiB and 966MiB), so that's good, but we're clearly missing some optimizations that CRuby has added.