An Early Look At The L1 Terminal Fault "L1TF" Performance Impact On Virtual Machines

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.