The Performance Hit For A Xeon-Backed Ubuntu Linux VM With L1TF / Foreshadow Patches

Written by Michael Larabel in Software on 20 August 2018 at 08:23 AM EDT. Page 5 of 5. 18 Comments.

The Stress-NG Linux kernel benchmarks also show off some of the possible performance implications of this mitigation.

Under sysbench the performance only took a measurable hit with the fully mitigated approach where Hyper Threading is no longer available.

The Apache performance was only slightly impacted by the default mitigation approach but more so under the "always flushing" and full mitigation levels.

In most workloads, the default mitigation for L1 Terminal Fault / Foreshadow yielded up to a few percent performance impact in the default behavior for this mitigation that only should impact the virtual machine performance and not the bare metal system's performance abilities. Obviously when switching to unconditional L1D cache flushing the performance tended to have a more profound performance cost while if opting for the "full" mitigation that disables SMT there is a very sizable performance impact for VMs due to losing out on Hyper Threading. Additional tests are currently running as we continue exploring the performance cost of L1TF/Foreshadow.

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Michael Larabel

Michael Larabel is the principal author of and founded the site in 2004 with a focus on enriching the Linux hardware experience. Michael has written more than 20,000 articles covering the state of Linux hardware support, Linux performance, graphics drivers, and other topics. Michael is also the lead developer of the Phoronix Test Suite, Phoromatic, and automated benchmarking software. He can be followed via Twitter, LinkedIn, or contacted via