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

[George Dunlap <dunlapg@xxxxxxxxx>]

Are these PV domains, or HVM domains?

If they're HVM domains, by necessity they will be doing QEMU
operations.  When doing qemu operations, they block and dom0 is
scheduled.  This blocking would allow the lower-priority VM space to
run.

Your best bet is to use xentrace + xenalyze to see what's going on
with scheduling.  You can find xenalyze here:
 http://xenbits.xensource.com/ext/xenalyze.hg

 -George

On Tue, Sep 14, 2010 at 7:16 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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