AMD Zen 1 Linux Performance Hit From Retbleed, Accumulated CPU Mitigation Impact

I/O workloads continue to be one of the areas most impacted on Zen CPUs by Retbleed and other relevant mitigations. Going from retbleed=off that is effectively the prior default for Linux until last week to the new current Linux default saw a 13% performance hit now in the PostMark test case. This leaves the Ryzen 7 1700 at around 81% of the performance in this test case as mitigations=off / pre-2018 when these mitigations were yet to be discovered/disclosed.

For the simple test cases stressing operating system primitive operations, there is a clear difference from Retbleed and other mitigations building up on Zen 1.

For Linux networking the Retbleed mitigation impact is quite clear too, similar to the I/O results. With Sockperf disabling SMT yields a nice improvement due to always being backed by a physical CPU core.