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Re: KVM wrong CPU speed reported



On 12/28/18 9:23 AM, Andrija Panic wrote:
> Hi guys,
> 
> https://github.com/apache/cloudstack/commit/29e389eb872ffa816be99aa66ff20bdec56d3187
> 
> this one gets above gets CPU frequency with "effectively
> "cat sys/devices/system/cpu/cpu0/cpufreq/cpuinfo_max_freq" which gives the
> TurboBoost CPU frequency (in case of Intel CPU) and similar for AMD.
> 
> Problem is that TurboBoost can only boost frequency of a very small number
> of CPU cores for a period of time - not by any means all cores.
> 
> CPU frequency is wrongly reported here as i.e. 3.4 GHz instead of 2.6 GHZ
> (example of Intel(R) Xeon(R) CPU E5-2650 v2 @ 2.60GHz)
> 
> We here thus have effective over-provisioning of 30% by default.
> 
> Can we fix this somehow to actually read the base CPU frequency ?
> i.e. Xen reports correct CPU frequency (base/nominal one)
> 

Probably fixable by reading a different file on the KVM hypervisor. But
I always have the feeling that Ghz are a soft factor. Memory and Storage
are hard limits, but CPUs are different.

We have a over provision of 2x of 3x on many systems as the CPUs are
pretty much idle and the defaults of CS are very conservative.

What does a Ghz really tell us? A Ghz from 5 years ago isn't the same as
one from today.

Wido

> Best,
>