The Spectre/Meltdown Performance Impact On Linux 4.20, Decimating Benchmarks With New STIBP Overhead

Next up is a look at the Linux 4.20 impact compared to Linux 4.19 for the dual Intel Xeon Gold 6138 server, which is my highest-end Xeon Scalable server for testing at the moment. That Ubuntu 18.10 server is the Tyan GT24E-B7106 while my EPYC tests continue to be with the Tyan Transport SX TN70A-B8026 and Dell PowerEdge R7425. These results were compared to several EPYC processors for seeing how there is greater competition as a result of the Spectre/Meltdown mitigations. The AMD testing was with their default mitigations throughout.

In the most severe cases where these EPYC and Xeon Gold servers were close to begin with, STIBP in Linux 4.20 in the case of Compile Bench was enough to bump the Intel server behind the tested EPYC processors. The dual Xeon Gold server on Linux 4.19 was 6% faster than the dual EPYC 7601 server but had Spectre/Meltdown not come to light would have been (and last year was) performing 20% faster in this test.

With the new overhead of STIBP on Linux 4.20, it was enough from the Xeon server being positioned between the EPYC 7601 and dual 7601 servers to now running slower than the EPYC 7551 with the Rodinia LavaMD benchmark.

Fortunately, there still are plenty of workloads unaffected by the current Spectre/Meltdown mitigations.