Re: [Xen-users] Need for precisions on SAR measures

[Nicolas80 <dedestri@xxxxxxxxxxx>]

Hi,


Javier Guerra Giraldez wrote:
> 
> - sar doesn't know a bit about virtualization, therefore all its
> measures are relative to the resources available to that VM
> 

A question concerning this point :
If all the measures are relative to the resources available, how can we
explain that : 

On the non virtualized platform, the consumption with a process is :
user      nice    system    iowait   idle
43,54    0        8,56        6,7      41,12

On the virtualized platform without CPU cap by xen (physical CPU accessible
for every domain), the consumption with the same process is :

          user      nice    system    iowait    steal    idle
Dom0   0,01    0        0,97       26,44     1,97    70,61
vm1     21,28  0        8,91       23,48     0,5      45,83    (activity
only on vm1)
vm2     0,01    0        0,1        8,33       0,84    90,81
vm3     0        0        0,01       4,82       0,74    94,34
vm4     0        0        0,01       3,75       0,31    95,92

On the virtualized platform with CPU caped by xen (25% physical CPU
accessible for each domain, except Dom0 which has full access), the
consumption with the same process is :

          user         nice     system     iowait    steal     idle
Dom0   0,02       0         0,58        18,82    1,57      79,01
vm1     14,93     0         2,18        13,43    33,38     36,08   
(activity only on vm1)
vm2     0,01       0         0,02        5,43      0,63      93,9
vm3     0,01       0         0,02        2,64      0,64      96,7
vm4     0,01       0         0,01        4,22      0,14      95,63

So, given these results, caping the CPU for each domain at 25% of the
physical CPU has globaly : 
  - decrased the user, system and iowait consumptions
  - incrased the steal consumption
  - incrased a bit the user + system + iowait + steal sum

If all the measures are relative to the resources available, couldn't we
expect, as fewer CPU ressources are given to vm1, an increase of the CPU
activity measured on vm1 (at least user and system) ?

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