An Early Look At The L1 Terminal Fault "L1TF" Performance Impact On Virtual Machines
Written by Michael Larabel in Software on 15 August 2018. Page 3 of 3. 15 Comments

The Hackbench synthetic kernel scheduler benchmark does show a noticeable impact from having the L1D cache flushing to occur on every VMENTER rather than the default conditional behavior.

The PostgreSQL database server does take a several percent hit with the default L1TF mitigation as well as with the more aggressive L1D flushing. The full mitigation with losing out on SMT/HT does also hurt the performance more if you intend to pursue that route though shouldn't be necessary unless you have untrusted users/VMs.

The synthetic kernel benchmarks via Stress-NG also showed varying degrees of impact from the L1 Terminal Fault.

That's the very cursory look at the L1 Terminal Fault mitigation impact as it pertains to running a single VM on an Intel Core i7 CPU like you might do in a home environment. Similar to Meltdown, most of the performance cost will come in workloads with a high degree of kernel interactivity while the CPU-bound workloads will be minimally affected unless pursuing the full-blown mitigation technique and disabling SMT/HT. Stay tuned for a lot more L1TF Linux benchmarks this week on Phoronix with now spinning up the Xeon test systems.

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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 or contacted via

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