This is the best summary I could come up with:

With yesterday’s disclosure of the Intel Downfall speculative execution vulnerability and the updated CPU microcode and Linux kernel patches I have been very busy testing the performance impact of this mitigation.

Here are some initial numbers and workloads I have found to be impacted as a result of this security mitigation for Skylake to Icelake/Tigerlake client and server processors.

Intel has reported up to 50% performance penalties in extreme cases but from my testing over the past day it thankfully has tended to be less than that but still significant.

But considering Intel Xeon Scalable Ice Lake was still latest-generation at the start of the year prior to the Sapphire Rapids debut, there is a lot of server and client systems out in the wild that are affected.

But besides using the gather instructions, those operations need to be done in hot code-paths for the Downfall mitigation to make a meaningful difference to performance.

But even so in less than one day of benchmarking I’ve found a number of the software packages I commonly use for performance testing to indeed be impacted by this mitigated microcode for Downfall.

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