FEX 2609 emulator adds faster JIT and optional JIT disk cache for AArch64 Linux

FEX 2609 is the latest monthly feature release of the open-source emulator that translates x86_64 Linux binaries to AArch64. The update focuses on two JIT-related changes: faster JIT compilation and an optional disk cache for storing compiled code. These changes target the two largest sources of emulation overhead, runtime compilation and repeated compilation of the same code across launches.

The faster JIT performance reduces the CPU time spent generating AArch64 code from x86_64 instructions. This should lower the latency of short-lived processes and improve throughput for workloads that trigger frequent recompilation. The disk cache extends this benefit by persisting compiled code between emulator invocations, allowing subsequent runs to skip recompilation entirely if the cached code remains valid.

Adopting the disk cache requires additional storage and introduces potential consistency issues if the underlying x86_64 binary changes. The cache is optional, so engineers can evaluate its effectiveness without committing to persistent storage overhead. Performance gains will vary; workloads with large, stable codebases are more likely to benefit than those with frequent binary updates or small working sets.

FEX remains a niche tool for running x86_64 software on ARM64 Linux, but its use cases, such as gaming via Steam Proton, are performance-sensitive. The JIT improvements in 2609 do not change the fundamental trade-offs of emulation, but they reduce the cost of those trade-offs. Engineers should benchmark their specific workloads to determine whether the new features justify the added complexity of cache management.