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Posted to dev@cloudstack.apache.org by Andrija Panic <an...@gmail.com> on 2018/12/28 08:23:53 UTC
KVM wrong CPU speed reported
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)
Best,
--
Andrija Panić
Re: KVM wrong CPU speed reported
Posted by Ivan Kudryavtsev <ku...@bw-sw.com>.
Fixing that is not back compatible because SOs can be created aligned to
TurboBoost values. Adding global variable switch can be an option.
пт, 28 дек. 2018 г., 7:38 Andrija Panic andrija.panic@gmail.com:
> 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 <wi...@widodh.nl> 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
>
Re: KVM wrong CPU speed reported
Posted by Andrija Panic <an...@gmail.com>.
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 <wi...@widodh.nl> 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
Re: KVM wrong CPU speed reported
Posted by Wido den Hollander <wi...@widodh.nl>.
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,
>