Phoronix’s Michael Larabel has shared some benchmarks showing how the mitigations for a new Spectre v2 variant dubbed Spectre-BHI/BHB will affect Intel processors as new as the 12th Gen Core Alder Lake series, and they ain’t pretty. The tests show that chips such as the Core i9-12900K and Core i7-1185G7 can suffer performance degradations as high as 26.7% and 35.6% in areas such as networking and storage based on sockperf, OSBench, and other tests. Disclosed by the VUSec security research group and Intel this week, Spectre-BHI/BHB affects both Intel and Arm CPUs. AMD chips aren’t believed to be affected.
In Light Of Spectre BHI, The Performance Impact For Retpolines On Modern Intel CPUs (Phoronix)
- The VUSec security researchers that discovered BHI are recommending Retpolines be enabled for newer processors even those with hardware mitigations against Spectre V2, but that’s that performance cost?
- Indeed in workloads exposed to return trampolines overhead, there can be quite a noticeable performance hit. This includes various network and I/O benchmarks and does translate to performance penalties in such databases (e.g. KeyDB, RocksDB, SQLite, LevelDB) in particular.
- AMD for their part isn’t believed to be affected by BHI and has still been making use of Retpolines on newer Zen processors. They did discover though their LFENCE/JMP-focused AMD Retpolines implementation to be racy and thus are now moving to use generic Retpolines instead.