CPU Load in Performance statistics/Graphs vs. top inconsistent / kvm

henfri · 19. Mai 2023

Hello,

in top, kvm seemingly uses quite a bit of CPU:

Code

Tasks: 452 total,   1 running, 451 sleeping,   0 stopped,   0 zombie
%CPU(s): 11,2 us,  6,3 sy,  0,0 ni, 79,0 id,  3,4 wa,  0,0 hi,  0,1 si,  0,0 st
MiB Spch:   7724,7 total,    268,3 free,   3215,2 used,   4241,2 buff/cache
MiB Swap:  16384,0 total,  14101,2 free,   2282,8 used.   4423,6 avail Spch

    PID USER      PR  NI    VIRT    RES    SHR S  %CPU  %MEM     ZEIT+ BEFEHL
   1609 libvirt+  20   0 5339056 571012   5504 S  32,6   7,2 977:54.85 qemu-system-x86
1707496 henfri    20   0 2952024 159516   7040 S  10,9   2,0 356:19.73 python3

It varies between 30 and 40%.

If I check the CPU load in the guest, it is around 10%. This would mean a virtualization overhead of a factor of 4, which seems a bit much.

However, if I check the performance statistics it looks better:

What can be the reason for this inconsistency?

Can someone tell me the source of the data in this Image?

Greetings,

Hendrik

ryecoaaron · 19. Mai 2023

Zitat von henfri

What can be the reason for this inconsistency?

It depends on your hardware and how the VM is setup. kvm/qemu can do different types of virtualization. If it is doing full virtualization, that has a lot of overhead. Different cpus do different levels of virtualization acceleration as well.

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