What are the physical processors ? (Is it an numa architecture ? if yes, could 
be a memory bandwith problem)

Do you have tried to launch unixbench on the host to compare ?


Maybe can you try to add +x2apic cpu flag ? It should reduce interrupts. (It's 
already in current qemu-server git)


----- Mail original ----- 

De: "Stefan Priebe - Profihost AG" <[email protected]> 
À: [email protected] 
Envoyé: Vendredi 19 Juillet 2013 09:07:27 
Objet: [pve-devel] KVM with same cores as host is as slow as one core 

Hi, 

while benchmarking my kvm machines using unixbench i see the following 
reproducable behaviour. 

Host has 24 cores. 

KVM Machine set to 2 cores: Unixbench Value 2514 
KVM Machine set to 16 cores: Unixbench Value 6714 
KVM Machine set to 24 cores: Unixbench Value 1742 

Also i see a max of 105% CPU Usage of the KVM process when setting the 
cores to 24. 

While i'm seeing more than 1000% setting it to 16 cores. 

Stefan 
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