[Xen-devel] Re: Does Xen scheduler preserves 5% of its utilization to every VM?

[walmart <vmwalmart@xxxxxxxxx>]

Hi, all:

I just noticed credit based scheduler have the same behavior. Except
when I set two domains both busy, the utilization for them is both
50%.

Can anyone tell me why a single VCPU can only get 95% of the core,
while two VCPUs can get 100% of it?

I am really confused by this...

Thanks very much!

best!

Sam



On Tue, Sep 14, 2010 at 1:16 AM, walmart <vmwalmart@xxxxxxxxx> wrote:
> Hi, all
>
> I was trying to write a Xen scheduler, it is a fixed priority one and
> would give domain 1 higher priority than domain 2. (which means
> whenever domain 1 is runnable, it got the cpu to run).
>
> I got two domains running. It is on Fedora 13, 64 bit, Xen 4.0.1.
>
> domain 1 and doman 2 both only have one vcpu, and are pinned to the same core.
>
> The strange thing is:
>
> domain 1 is busy, domain 2 is idle, domain 1 got 95% of the cpu;
> domain 1 is idle, domain 2 is busy, domain 2 got 95% of the cpu;
> domain 1 is busy, domain 2 is busy, domain 1 got 95% of the cpu, while
> domain 2 got the remaining 5%.
>
> I checked the schedule() function again and again, still couldn't
> figure out why would this happen.
>
> Could anyone give me some hint?
>
>
> thanks very much!
>
> Best!
>
> Sam
>

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