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Re: KVM wrong CPU speed reported


I agree Wido, it's just that it's wrong - there should be no implicit CPU
over-provisioning by default - and yes, later you can do over-provision by
2-3 as most of us do...
just something that hurts my eyes :)

On Fri, 28 Dec 2018 at 11:39, Wido den Hollander <wido@xxxxxxxxx> wrote:

>
>
> 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,
> >
>


-- 

Andrija Panić