Hi, Linux see twice the amount of CPUs for a host with SMT/hyperthreading enabled. Inspecting the individual cores presented to the operating system using mpstat shows that the guests are running primarily on the “physical cores”, which is expected as the system is SMT aware. The “hyperthreaded cores” are showing guest activity when the host cpu is heavily loaded. Using the traditional tools such as top and vmstat does not take hyperthreading into consideration when calculating the total cpu% usage, again, as expected.
How is the hypervisor host CPU utilization metrics in Ovirt calculated when a hypervisor host has SMT/hyperthreading enabled? Does Ovirt calculate in the same manner as the traditional vmstat/top/etc Linux tools, or does it only count CPU usage on the “physical cores” on the hypervisor? Does it read CPU metrics from the Intel PCM (https://github.com/opcm/pcm <https://github.com/opcm/pcm>) ? Does the “Count Threads as Cores” setting affect how the host hypervisor CPU utilization metrics are calculated? The reason for asking is when using tools for capacity and utilization reporting to attempt to establish cluster growth and to anticipate when and how much hypervisor capacity to add, we need the input utilization data to be a correct representation of what is happening at the hypervisor host. Thanks. Regards, Siggi
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