Re: [Xen-users] Q: CPU usage in Dom0

[Mark Williamson <mark.williamson@xxxxxxxxxxxx>]

> there's no vm config file form Dom0, right? So how does XEN assign virtual
> CPUs to real CPUs? I see this on a two Dual-Core Opteron machine:
> # xm vcpu-list
> Name                              ID  VCPU  CPU  State  Time(s)  CPU
> Affinity Domain-0                           0     0    1   r--    2927.8 
> any cpu Domain-0                           0     1    2   -b-    2551.1 
> any cpu Domain-0                           0     2    0   -b-    2477.0 
> any cpu Domain-0                           0     3    0   -b-    2231.4 
> any cpu

Well, you have "affinity = any cpu" for all your VCPUs, so they're probably 
running on whatever CPU is free.  Maybe CPU 3 was being used be another 
domain at the time, so the VCPUs had been migrated?

I've not looked into the code here for a while, though, so I could be wrong.

If you run the command again under different workload conditions, you might 
find that the vcpu-list command returns different results...

I think you can vcpu-pin VCPUs to logical processors if you want to do the 
mapping manually (e.g. you want stricter performance partitioning at the 
expense of not using as many available cycles on all CPUs as possible).

Cheers,
Mark

> So VCPU 2 and 3 use the same CPU (0), even though there's another CPU (3).
> Why?
>
> On another machine (same model) things look better:
>
> # xm vcpu-list
> Name                              ID  VCPU  CPU  State  Time(s)  CPU
> Affinity Domain-0                           0     0    0   -b-     142.9 
> any cpu Domain-0                           0     1    2   -b-      90.0 
> any cpu Domain-0                           0     2    1   -b-      81.6 
> any cpu Domain-0                           0     3    3   r--     134.6 
> any cpu
>
> Regards,
> Ulrich
>
>
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-- 
Dave: Just a question. What use is a unicyle with no seat?  And no pedals!
Mark: To answer a question with a question: What use is a skateboard?
Dave: Skateboards have wheels.
Mark: My wheel has a wheel!

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