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The point is that if I utilize the CPU on 1 guest, all the other guests see increase in CPU usage. I'm testing with stress-ng, but it's visible with normal workload as well. I really don't know if this is normal behaviour (but I don't think so, atleast i didn't notice stuff like this yet). I'm running the guests on deb9 with the distributed qemu and qemu-kvm packages installed. The host system has 24 cores and there are 32 vcores assigned. All vms have a 30% cfs (cgroup) quota on CPU usage, so the real amount of vcores assigned is 10 (9,6). The CPU usage on the host doesn't go above 15% if we don't do special stuff at that moment (idle state), the steal cpu usage is around 0,3-0,4 in the vms in the same idle state.

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  • Have you more details? The question is too broad as it is. – Rui F Ribeiro Mar 6 at 19:34
  • Well, all guests are running the host CPU model with PCID and NUMA. I've tried without both PCID and NUMA, it didn't help. – Martin Magyarics Mar 6 at 19:42
  • how many cpus you have and how many cpus are the guests using? – Rui F Ribeiro Mar 6 at 19:45
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    sys cpu usage? user cpu usage ? both? steal cpu usage ? – sourcejedi Mar 6 at 19:45
  • The host has 24 cores from a dual socket setup. Some of the guests have 8 vcores, but mostly 4. – Martin Magyarics Mar 6 at 19:46
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Try pinning the CPUs on specific cores, so that they might not interfere:  How to set KVM processors affinities with libvirt.

Other than that you may try to isolate some of the CPUs the guest is running on in order to make sure no user processes are executed on that core.  How to isolate CPUs in Ubuntu 18.04 with isolcpus | Linux kernel.  Also, it would be easier to troubleshoot if we had some more info, for example, /proc/stat of the CPUs, or some htop or top outputs.

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  • Are you “linux_zlatan” (the author / creator / owner of those YouTube videos)? If so, you must say so. – G-Man Says 'Reinstate Monica' Mar 8 at 0:00

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