How to get the accurate physical CPU utilization in Dom0?

How to get the accurate physical CPU utilization in Dom0?

[Bei Guan]

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Hi,

I run a PV DomU with 1 vcpu on Xen. I pin the vcpu to a physical CPU core,
such as core 3. Then, I run a cpu-bound process in DomU and the vcpu
utilization is 100% (got it with "xentop" in Dom0).
However, when I use "top" in Dom0 to see the physical CPU utilization, the
CPU core 3 utilization is zero or less than 1%. The utilization expected of
CPU core 3 is also 100% like the vcpu. Is it? Why I cannot get the accurate
physical CPU utilization with "top" command in Dom0?

Any advice is appreciated. Thank you for your time.

-- 
Best Regards,
Bei Guan

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Re: How to get the accurate physical CPU utilization in Dom0?

[Roger Pau Monné]

On 27/02/14 16:06, Bei Guan wrote:
> Hi,
> 
> I run a PV DomU with 1 vcpu on Xen. I pin the vcpu to a physical CPU
> core, such as core 3. Then, I run a cpu-bound process in DomU and the
> vcpu utilization is 100% (got it with "xentop" in Dom0).
> However, when I use "top" in Dom0 to see the physical CPU utilization,
> the CPU core 3 utilization is zero or less than 1%. The utilization
> expected of CPU core 3 is also 100% like the vcpu. Is it? Why I cannot
> get the accurate physical CPU utilization with "top" command in Dom0?

top in Dom0 will only show CPU utilization of Dom0 (Xen is not a type 2
hypervisor, so Dom0 is no different than any other DomU in this aspect),
if you want to see CPU utilization of all domains you should use xl top
(xentop).

Roger.

Re: How to get the accurate physical CPU utilization in Dom0?

[Andrew Cooper]

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On 27/02/14 15:06, Bei Guan wrote:
> Hi,
>
> I run a PV DomU with 1 vcpu on Xen. I pin the vcpu to a physical CPU
> core, such as core 3. Then, I run a cpu-bound process in DomU and the
> vcpu utilization is 100% (got it with "xentop" in Dom0).
> However, when I use "top" in Dom0 to see the physical CPU utilization,
> the CPU core 3 utilization is zero or less than 1%. The utilization
> expected of CPU core 3 is also 100% like the vcpu. Is it? Why I cannot
> get the accurate physical CPU utilization with "top" command in Dom0?
>
> Any advice is appreciated. Thank you for your time.

Xen is not KVM; dom0 is just another VM as far as Xen is concerned, so
dom0's cpu3 is not domU's cpu3.

Top in dom0 shows dom0's virtual cpu utilisation.  I am not aware of a
utility like top which gives the physical cpu information, distributed
by physical cpu.

~Andrew

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Re: How to get the accurate physical CPU utilization in Dom0?

[Bei Guan]

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Hi,

Thank you for all your advice. I have another one question.
How does the Xen scheduler map a vcpu to a physical CPU, if the host has
multi-cores? Is there any rules in the map? Or the map is irregular?
Thank you for your time.


2014-02-27 23:40 GMT+08:00 Roger Pau Monné <roger.pau@citrix.com>:

> On 27/02/14 16:06, Bei Guan wrote:
> > Hi,
> >
> > I run a PV DomU with 1 vcpu on Xen. I pin the vcpu to a physical CPU
> > core, such as core 3. Then, I run a cpu-bound process in DomU and the
> > vcpu utilization is 100% (got it with "xentop" in Dom0).
> > However, when I use "top" in Dom0 to see the physical CPU utilization,
> > the CPU core 3 utilization is zero or less than 1%. The utilization
> > expected of CPU core 3 is also 100% like the vcpu. Is it? Why I cannot
> > get the accurate physical CPU utilization with "top" command in Dom0?
>
> top in Dom0 will only show CPU utilization of Dom0 (Xen is not a type 2
> hypervisor, so Dom0 is no different than any other DomU in this aspect),
> if you want to see CPU utilization of all domains you should use xl top
> (xentop).
>
> Roger.
>
>


-- 
Best Regards,
Bei Guan

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