Downfall is the latest speculative execution vulnerability discovered in Intel’s x86 CPU architecture. As custom dictates, the chipmaker has released a microcode update and Linux kernel patches to mitigate the flaw. Like most security fixes, these updates degrade performance as they essentially block speculative execution in certain scenarios. Phoronix has compiled some benchmarks showing the impact of the security update on Intel’s Core CPUs:
Downfall primarily affects Skylake, Ice Lake, and Tiger Lake, and we see performance drops as large as 40% after the update. OpenVKL is 10-12% slower following the patch, while the OSPRay ray-tracing benchmark sees a much larger decline.
Ambient Occlusion is a whopping ~40% slower with the new kernel and microcode, while path tracing sees a 20% reduction in real-time performance.
According to Phoronix, AVX/AVX512 workloads without using the VGATHER* instructions aren’t affected and continue to perform as before. However, several AI workloads, most notably ones from Intel’s oneAPI, are notably slower following the mitigation patch.
For most consumers, we recommend skipping out on the mitigation, as side-channel speculative attacks are not really a concern for the average user. The gather_data_sampling=off/mitigations=off route will disable the mitigation.
