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Performance considerations related to Intel Meltdown on KVM CPU types


Hello,

Just stumbled upon this
https://twitter.com/berrange/status/950209752486817792

"ensure KVM guest CPU model you choose has the "pcid" feature, otherwise guests will suffer terrible performance from the Meltdown fixes. This means using a named Haswell, Broadwell or Skylake based model or host passthrough"


This means whoever is running with the KVM default CPU (like I do) as opposed to specific ones or host passthrough needs to change this in order to avoid bad performance once the new mitigating kernel is installed.


Bad news is older Xeons do not support this, check if "invpcid" flag shows up in /proc/cpuinfo (you might see "pcid", that one is not enough).





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