Hi there,
I had never tried to operate with the CPU-Units option for KVM guests,
but yet read the manuals and the older forum entries.
Today we experienced the following problem:
Host:
16x vCPU Xeon E5520 (2x 4Core Xeon => 8 real cores), 64GB RAM
pveperf
CPU BOGOMIPS: 72529.52
REGEX/SECOND: 821793
HD SIZE: 18.33 GB (/dev/mapper/promo3-root)
BUFFERED READS: 417.91 MB/sec
AVERAGE SEEK TIME: 4.48 ms
FSYNCS/SECOND: 1913.66
vzcpucheck
Current CPU utilization: 3000
Power of the node: 1813240
KVM VM1: 4x CPU / 8 GB RAM / CPUUNITS 1000 / W2008 R2
KVM VM2: 6x CPU / 8 GB RAM / CPUUNITS 1000 / W2008 R2
OpenVZ CT1: 1x CPU / 512MB RAM / CPUUNITS 1000
OpenVZ CT2 : 1x CPU / 512MB RAM / CPUUNITS 1000
Some software on VM1 failed, and pushed up the CPU utilisation to 120%
(!?). Working with VM1 was not possible anymore. We tested this
behaviour for a few times with the same result - as soon as the program
was started the serverload rises in some extreme manner - as we tried
other programs everything was kept fine.
But also VM2 got a very high cpu utilisation, too (at those moments )
and at one situation VM2 went away with a bluescreen. During the time of
high utilisation by VM1 also CT1 and CT2 did show the same behavior on
CPU: normally they stay at about nothing - but in those moments they
rised their cpu utilisation - from 0,01 to 2%.
Is there any possibility to avoid this negative influence on other
guests? Setting kind of a limit?
Since today I thought, if I do not allow the usage of all of the real
cores by only one Guest, I won't ran into such a situation - but
obviously this idea doesn't work.
"man qm" tells according to "-cpulimit": NOTE: This option is
currently ignored.
On "-cpuunits" there is mentiond a maximum of 500.000 - would the
solution be something like:
KVM VM1: cpuunits 250.000
KVM VM2: cpuunits 200.000
OpenVZ CT1: cpuunits 50.000
OpenVZ CT2 cpuunits 50.000
?
Or would it be the right way setting "-cpuunits" to 0 (to disable the
fair-scheduler) and so working with the accounting of cores for each
guest only?
Does anyone have some experiences or strategies with that?
Thank you in advance!
Martin
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