Re: [Xen-devel] fair scheduling

["Harry Smith" <harry.smith272@xxxxxxxxx>]

Hi Atsushi & Pradeep,

thanks for replying back.
I have 4 VCPUs for each of VM.  But the point I wanted to stress upon is - 
"This happened even in the case where CPU usage by both of vm1,vm2 is
restricted to 100% each. "
I had pinned all 4 VCPUs of each VM to a single phys. CPU. & I have 4 phys. CPUs
means my vm1 was using cpu1, vm2 using cpu2 & domain-0 using cpu0,cpu3

Problem is when there is no load on vm2, webserver performance of vm1 is better.  But when vm2 has some compute-intense load then vm1 webserver performance goes down.
Please note that CPU consumption of vm1 shown by xentop in both cases is 100%,  still webserver performance goes down by around 15-20%.
Even after trying to isolate two VMs, existence of load on one VM is affecting other.

so is it expected behavior ?

thanks,
Harry

On 5/10/07, pradeep singh rautela <rautelap@xxxxxxxxx > wrote:

On 5/10/07, Atsushi SAKAI <sakaia@xxxxxxxxxxxxxx> wrote:

One vcpu can use one pcpu at one time.
It means 100% is maxium for one vcpu domain.
If you want to use cpu resources, you should set more vcpu.

Ok, this explains a lot of things.
As i understand this , more VCPUs means more freedom to hypervisor to migrate them among physical CPUs, depending on the free PCPUs available.

In general

                domU1
               /      |       \
        vcpu1 vcpu2 vcpu3
   
pcpu1 pcpu2 pcpu3 pcpu4 pcpu5 pcpu6

I mean ,domU1 can run on any vcpu , right? now vcpu1, vcpu2, vcpu3 share a one to many reationship between pcpus[1....6]. That is a vcpu can run on any of the pcus available to the Xen hypervisor(unless i explicitly pin it to ).

Is my naive understanding of what you explained is correct?

Thank you
~psr

Thanks
Atsushi SAKAI


"pradeep singh rautela" <rautelap@xxxxxxxxx> wrote:

> Hi Atsushi,
>
> On 5/10/07, Atsushi SAKAI < sakaia@xxxxxxxxxxxxxx> wrote:
> >
> >
> > You should show detail configuration.
> > Your information is too short.
> >
> > Anyway I guess each domain has one vcpu.
> > If so, this is normal behavior.
> > Because one vcpu cannot allocate two or more pcpu at once.
>
>
> Right, but shouldn't Xen hypervisor be capable of migrating the VCPU among
> the available PCPUs on a multiprocessor system, like in this case? And
> criteria should be the load on the PCPU or the idle PCPUs.
> yes/no?
>
> Am i missing something here?
>
> Thanks
> ~psr
>
> Thanks
> > Atsushi SAKAI
> >
> > "Harry Smith" < harry.smith272@xxxxxxxxx> wrote:
> >
> > > hi all,
> > >
> > > I am using xen3.0.3 on dual core hyperthreaded processor (in all 4
> > cores).
> > > There are 2 VMs vm1,vm2 among which vm1 has a webserver running on it.
> > >
> > > While testing the performance of webserver, when I introduce some load
> > on
> > > vm2 which involves some computations the webserver performance goes
> > down.
> > > This happened even in the case where CPU usage by both of vm1,vm2 is
> > > restricted to 100% each.
> > >
> > > Is it expected behavior ?  if yes then how does one can control addition
> > of
> > > new virtual machines as adding every new VM will result in lowering
> > > performance of other VMs.  Through scheduling parameters we can just
> > specify
> > > amount of CPU to be used in relative sense (weight) & upper limit (cap).
> > But
> > > how to tackle this point.
> > >
> > > I am new in this area & wanna set up a lab using virtualization, so want
> > to
> > > find solution for this.
> > >
> > > thanks,
> > > Harry
> > >
> > > we always have a choice...
> >
> >
> >
> > _______________________________________________
> > Xen-devel mailing list
> > Xen-devel@xxxxxxxxxxxxxxxxxxx
> > http://lists.xensource.com/xen-devel
> >
>
>
>
> --
> ---
> pradeep singh rautela
>
> "Genius is 1% inspiration, and 99% perspiration" - not me :)

--
---
pradeep singh rautela

"Genius is 1% inspiration, and 99% perspiration" - not me :)

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