VM CPUs--no turbo boost?

Uncle Lumpy

New Member
Apr 26, 2020
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Relatively new to Proxmox. I have Proxmox VE 6.2.4 installed on an Intel Core I5-8500 with 64GB RAM in the machine. The base clock of the CPU is 3.00GHz but the machine runs a sustained 3.9GHz (all 6 cores) under turbo boost if I have something like Prime95 running on the 6 cores. This is on the host machine. However, every VM I've tried (Debian 10.x, CentOS 7.x, Slackware64-14.2, Windows10) seems to be locked at the base clock rate of 3.00GHz for all cores given to the machine even when running Prime95 on the cores of the respective VM.

Am I missing something? If the cores are running at a sustained 3.9GHz on the Proxmox host machine, why aren't they running at the 3.9GHz on any of the VM cores for the VMs I've tried? I feel like there's a setting I need to adjust but I'm not sure where to start.

I have set the processor type to "host" on all of the VMs. Other processor type options didn't seem to matter, though.

Any help would be appreciated!

Best,
Kel
 

Uncle Lumpy

New Member
Apr 26, 2020
4
0
1
62
Relatively new to Proxmox. I have Proxmox VE 6.2.4 installed on an Intel Core I5-8500 with 64GB RAM in the machine. The base clock of the CPU is 3.00GHz but the machine runs a sustained 3.9GHz (all 6 cores) under turbo boost if I have something like Prime95 running on the 6 cores. This is on the host machine. However, every VM I've tried (Debian 10.x, CentOS 7.x, Slackware64-14.2, Windows10) seems to be locked at the base clock rate of 3.00GHz for all cores given to the machine even when running Prime95 on the cores of the respective VM.

Am I missing something? If the cores are running at a sustained 3.9GHz on the Proxmox host machine, why aren't they running at the 3.9GHz on any of the VM cores for the VMs I've tried? I feel like there's a setting I need to adjust but I'm not sure where to start.

I have set the processor type to "host" on all of the VMs. Other processor type options didn't seem to matter, though.

Any help would be appreciated!

Best,
Kel
Anyone? I can't be the only one who has observed this...

Best,
Kel
 

Uncle Lumpy

New Member
Apr 26, 2020
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AFAIK the cpu speed shown in the guest has no effect on anything. It is just a guide as to what to expect but doesn't track the real CPU clock speed.
Thanks for the response! So even though "watching" /proc/cpuinfo consistently shows a speed of 3GHz in the VM, it might actually be running at ~3.9GHz when being pushed under Prime95? I'll have to see if the Prime95 benchmarking capability can shed some insight into the speed the cores are actually running at in the VM.

Best,
Kel
 

Uncle Lumpy

New Member
Apr 26, 2020
4
0
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62
AFAIK the cpu speed shown in the guest has no effect on anything. It is just a guide as to what to expect but doesn't track the real CPU clock speed.
OK, I'm happy to report the the core speeds in the VM are indeed "turbo boosted" even though only the base core speed is ever reported. If I run a highly optimized, CPU intensive program like Prime95 in both the pve host directly and in a VM, the number of iterations per second reported by Prime95 are nearly identical.

Additionally, with Prime95 running in a VM, the pve host reports a boosted core speed when I use the command "watch grep \'cpu MHz\' /proc/cpuinfo" in the pve host. When I stop Prime95 in the VM, the core speeds drop to "normal" in the pve host.

So even though the VM doesn't show the true core speeds, I'm confident it is indeed taking advantage of the higher core speeds presented by turbo boost mode.

I'm a little embarrassed that I didn't do this rudimentary research before coming onto the forum. I am grateful, though, for the responses I got!

Best,
Kel
 

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