Xen users - Nov 2012 - CPU load average above 2 on domU but load average 0 on dom0-XCP 1.6

Hi all,
        I am trying to understand this.I am running *XCP 1.6* on a machine
with 4GB and i5 processor with 3 ubuntu 12.04 64 bit domUs each with one
vcpu.
On one of the domU i am having mongodb taking 100% CPU resulting in load
average of 2.1, 2, 2.But still load average on dom0 is 0, 0, 0.
If the vcpu is over utilized then why there is no impact on dom0,as its
load average  is showing 0.
on the xentop output i can see all other domU are idle but this showing
100% CPU usage.Can any one please explain why this is so?
If there are 4 cores on dom0 and one of the vm takes 100% CPU then
doesn''t
load average  on dom0 should be 1.Can any one please clarify me.

Regards,
kev


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On Wed, 2012-11-28 at 16:17 +0000, kevin parker wrote:
> Hi all,
>         I am trying to understand this.I am running XCP 1.6 on a
> machine with 4GB and i5 processor with 3 ubuntu 12.04 64 bit domUs
> each with one vcpu.
> On one of the domU i am having mongodb taking 100% CPU resulting in
> load average of 2.1, 2, 2.But still load average on dom0 is 0, 0, 0.
> If the vcpu is over utilized then why there is no impact on dom0,as
> its load average  is showing 0.
Unless the domU is requiring services from dom0 (i.e. heavy i/o traffic
to a backend based in dom0) there''s no reason that domU load average
should have any impact on dom0''s (or any other domU) load average.
> on the xentop output i can see all other domU are idle but this
> showing 100% CPU usage.Can any one please explain why this is so?
> If there are 4 cores on dom0 and one of the vm takes 100% CPU then
> doesn''t load average  on dom0 should be 1.Can any one please
clarify
> me. 
vcpus under Xen separate entities isolated, domU vcpus do not somehow
consume dom0 time.

You are perhaps confusing this with the KVM model where guest vcpus are
actually threads in the host OS (which is equivalent to dom0).

Ian.

Hi Ian,
         Please correct me if i am wrong.From my understanding(Eventhough
it seems wrong) All the process in domU polls its cpu which is actually
virtual and process queue in this virtual cpu is processed by the actual
CPU in which hypervisor has direct access to it.In that case if there are
lot of process in the process queue of domU waiting to get cpu of domU,then
wouldnt that affect actual CPU,since it is the actual processor that
process the process queue of  domU.(Even though It seems wrong).

Expecting your kind reply,
Kev

On Fri, Nov 30, 2012 at 3:24 PM, Ian Campbell
<Ian.Campbell@citrix.com>wrote:
> On Wed, 2012-11-28 at 16:17 +0000, kevin parker wrote:
> > Hi all,
> >         I am trying to understand this.I am running XCP 1.6 on a
> > machine with 4GB and i5 processor with 3 ubuntu 12.04 64 bit domUs
> > each with one vcpu.
> > On one of the domU i am having mongodb taking 100% CPU resulting in
> > load average of 2.1, 2, 2.But still load average on dom0 is 0, 0, 0.
> > If the vcpu is over utilized then why there is no impact on dom0,as
> > its load average  is showing 0.
>
> Unless the domU is requiring services from dom0 (i.e. heavy i/o traffic
> to a backend based in dom0) there''s no reason that domU load
average
> should have any impact on dom0''s (or any other domU) load average.
>
> > on the xentop output i can see all other domU are idle but this
> > showing 100% CPU usage.Can any one please explain why this is so?
> > If there are 4 cores on dom0 and one of the vm takes 100% CPU then
> > doesn''t load average  on dom0 should be 1.Can any one please
clarify
> > me.
>
> vcpus under Xen separate entities isolated, domU vcpus do not somehow
> consume dom0 time.
>
> You are perhaps confusing this with the KVM model where guest vcpus are
> actually threads in the host OS (which is equivalent to dom0).
>
> Ian.
>
>
>

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On Thu, 2012-12-06 at 13:06 +0000, kevin parker wrote:
> Hi Ian,
>          Please correct me if i am wrong.From my
> understanding(Eventhough it seems wrong) All the process in domU polls
> its cpu which is actually virtual and process queue in this virtual
> cpu is processed by the actual CPU in which hypervisor has direct
> access to it.In that case if there are lot of process in the process
> queue of domU waiting to get cpu of domU,then wouldnt that affect
> actual CPU,since it is the actual processor that process the process
> queue of  domU.(Even though It seems wrong).
Are you perhaps confusing the load on the physical processors with the
load on the dom0 VCPUs? They are separate things, dom0''s CPUs are VCPUs
just like a domU''s CPUs.

I''m not sure what you mean by a process in domU polling its CPU. domU
(and dom0) VCPUs are scheduled on PCPUS (physical CPUS).

Ian.

Sorry for making things complicated.. yes i was considering load on
physical CPU with load on dom0 VCPU.I thought running top on dom0 reveals
overall cpu usage as in case of normal system.I forgot to consider it as
another Virtual Machine.If this is correct then is there a way to see the
actual cpu utilization.

Regards,
kev

On Thu, Dec 6, 2012 at 6:43 PM, Ian Campbell
<Ian.Campbell@citrix.com>wrote:
> On Thu, 2012-12-06 at 13:06 +0000, kevin parker wrote:
> > Hi Ian,
> >          Please correct me if i am wrong.From my
> > understanding(Eventhough it seems wrong) All the process in domU polls
> > its cpu which is actually virtual and process queue in this virtual
> > cpu is processed by the actual CPU in which hypervisor has direct
> > access to it.In that case if there are lot of process in the process
> > queue of domU waiting to get cpu of domU,then wouldnt that affect
> > actual CPU,since it is the actual processor that process the process
> > queue of  domU.(Even though It seems wrong).
>
> Are you perhaps confusing the load on the physical processors with the
> load on the dom0 VCPUs? They are separate things, dom0''s CPUs are
VCPUs
> just like a domU''s CPUs.
>
> I''m not sure what you mean by a process in domU polling its CPU.
domU
> (and dom0) VCPUs are scheduled on PCPUS (physical CPUS).
>
> Ian.
>
>
>

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''xl top'' reveals real-time information about resource
utilization.  ''xl
info'' is also useful for gleaning information about the hardware (vs.
just
Dom0, for instance).

--steve

On Thu, 06 Dec 2012 09:23:32 -0500, kevin parker  
<kevin.parker092@gmail.com> wrote:
>  Sorry for making things complicated.. yes i was considering load on
> physical CPU with load on dom0 VCPU.I thought running top on dom0 reveals
> overall cpu usage as in case of normal system.I forgot to consider it as
> another Virtual Machine.If this is correct then is there a way to see the
> actual cpu utilization.
>
> Regards,
> kev
>
> On Thu, Dec 6, 2012 at 6:43 PM, Ian Campbell  
> <Ian.Campbell@citrix.com>wrote:
>
>> On Thu, 2012-12-06 at 13:06 +0000, kevin parker wrote:
>> > Hi Ian,
>> >          Please correct me if i am wrong.From my
>> > understanding(Eventhough it seems wrong) All the process in domU
polls
>> > its cpu which is actually virtual and process queue in this
virtual
>> > cpu is processed by the actual CPU in which hypervisor has direct
>> > access to it.In that case if there are lot of process in the
process
>> > queue of domU waiting to get cpu of domU,then wouldnt that affect
>> > actual CPU,since it is the actual processor that process the
process
>> > queue of  domU.(Even though It seems wrong).
>>
>> Are you perhaps confusing the load on the physical processors with the
>> load on the dom0 VCPUs? They are separate things, dom0''s CPUs
are VCPUs
>> just like a domU''s CPUs.
>>
>> I''m not sure what you mean by a process in domU polling its
CPU. domU
>> (and dom0) VCPUs are scheduled on PCPUS (physical CPUS).
>>
>> Ian.
>>
>>

''xl top'' (which just execs xentop under the hood) will show
you all of
your VCPUs utilisation, from which you can infer something about PCPU
utilisation. I can''t think of a tool which just gives you PCPU usage
though.

On Thu, 2012-12-06 at 20:26 +0000, Steven Peckins wrote:
> ''xl top'' reveals real-time information about resource
utilization.  ''xl
> info'' is also useful for gleaning information about the hardware
(vs. just
> Dom0, for instance).
> 
> --steve
> 
> On Thu, 06 Dec 2012 09:23:32 -0500, kevin parker  
> <kevin.parker092@gmail.com> wrote:
> 
> >  Sorry for making things complicated.. yes i was considering load on
> > physical CPU with load on dom0 VCPU.I thought running top on dom0
reveals
> > overall cpu usage as in case of normal system.I forgot to consider it
as
> > another Virtual Machine.If this is correct then is there a way to see
the
> > actual cpu utilization.
> >
> > Regards,
> > kev
> >
> > On Thu, Dec 6, 2012 at 6:43 PM, Ian Campbell  
> > <Ian.Campbell@citrix.com>wrote:
> >
> >> On Thu, 2012-12-06 at 13:06 +0000, kevin parker wrote:
> >> > Hi Ian,
> >> >          Please correct me if i am wrong.From my
> >> > understanding(Eventhough it seems wrong) All the process in
domU polls
> >> > its cpu which is actually virtual and process queue in this
virtual
> >> > cpu is processed by the actual CPU in which hypervisor has
direct
> >> > access to it.In that case if there are lot of process in the
process
> >> > queue of domU waiting to get cpu of domU,then wouldnt that
affect
> >> > actual CPU,since it is the actual processor that process the
process
> >> > queue of  domU.(Even though It seems wrong).
> >>
> >> Are you perhaps confusing the load on the physical processors with
the
> >> load on the dom0 VCPUs? They are separate things, dom0''s
CPUs are VCPUs
> >> just like a domU''s CPUs.
> >>
> >> I''m not sure what you mean by a process in domU polling
its CPU. domU
> >> (and dom0) VCPUs are scheduled on PCPUS (physical CPUS).
> >>
> >> Ian.
> >>
> >>
> 
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