RealFeedApp Iret interrupt counts as userspace instruction despite running in kernel
Testing 11 x86_64 CPU implementations revealed that the iret interrupt return instruction is erroneously counted as a user-space instruction despite executing in kernel mode. This causes run-to-run variation in performance counters, complicating deterministic replay and threading libraries.
- Field
- hardware and chips
- What they did
- Researchers investigated 11 x86_64 CPU implementations and discovered that hardware performance counters often overcount and produce different results on repeated runs, even in strictly controlled environments.
- Why it matters
- This knowledge is necessary for developing libraries and systems that require strict determinism, such as reproducible simulations or multi-threading libraries, where predictability is critical.
#x86_64#performance counter#determinism#iret#hardware
